From ac59ebef5b902d6ff7d34d61be3cce1335e3b13b Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Thu, 27 Aug 2020 18:11:06 -0500
Subject: [PATCH 01/14] [thermo] Add convenience class for liquid-water-IAPWS95

---
 data/liquidvapor.yaml                    | 12 ++++++++++++
 interfaces/cython/cantera/liquidvapor.py | 13 +++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/data/liquidvapor.yaml b/data/liquidvapor.yaml
index 123a234cf89..084cec491a0 100644
--- a/data/liquidvapor.yaml
+++ b/data/liquidvapor.yaml
@@ -25,6 +25,18 @@ phases:
     T: 300.0
     P: 1.01325e+05
   pure-fluid-name: water
+- name: liquid-water
+  elements: [O, H]
+  species: [H2O]
+  thermo: liquid-water-IAPWS95
+  transport: water
+  state:
+    T: 300.0
+    P: 1.01325e+05
+  note: |-
+    Phase definition based on "The IAPWS Formulation 1995 for the
+    Thermodynamic Properties of Ordinary Water Substance for General and
+    Scientific Use," J. Phys. Chem. Ref. Dat, 31, 387, 2002.
 - name: nitrogen
   thermo: pure-fluid
   elements: [N]
diff --git a/interfaces/cython/cantera/liquidvapor.py b/interfaces/cython/cantera/liquidvapor.py
index fbb1e40c9a3..ac57fb6a2c0 100644
--- a/interfaces/cython/cantera/liquidvapor.py
+++ b/interfaces/cython/cantera/liquidvapor.py
@@ -15,6 +15,19 @@ class WaterWithTransport(PureFluid, _cantera.Transport):
     return WaterWithTransport('liquidvapor.yaml', 'water', transport_model='Water')
 
 
+def LiquidWater():
+    """
+    Create a `PureFluid` object using the IAPWS Formulation 1995 for
+    thermodynamic properties and the `WaterTransport` class for viscosity
+    and thermal conductivity.
+    """
+    class WaterWithTransport(PureFluid, _cantera.Transport):
+        __slots__ = ()
+
+    return WaterWithTransport('liquidvapor.yaml', 'liquid-water',
+                              transport_model='Water')
+
+
 def Nitrogen():
     """Create a `PureFluid` object using the equation of state for nitrogen."""
     return PureFluid('liquidvapor.yaml', 'nitrogen')

From e6968361dfe11151ca193feb29ec55adb278fc30 Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Thu, 27 Aug 2020 20:52:52 -0500
Subject: [PATCH 02/14] [thermo] Update docstrings for PureFluid convenience
 wrapper classes

- Docstrings are updated to include information already available
  in MATLAB (or C++ base classes)
---
 data/liquidvapor.yaml                    |  13 +-
 interfaces/cython/cantera/liquidvapor.py | 152 +++++++++++++++++++++--
 2 files changed, 153 insertions(+), 12 deletions(-)

diff --git a/data/liquidvapor.yaml b/data/liquidvapor.yaml
index 084cec491a0..fe2269a1123 100644
--- a/data/liquidvapor.yaml
+++ b/data/liquidvapor.yaml
@@ -29,13 +29,12 @@ phases:
   elements: [O, H]
   species: [H2O]
   thermo: liquid-water-IAPWS95
-  transport: water
   state:
     T: 300.0
     P: 1.01325e+05
-  note: |-
-    Phase definition based on "The IAPWS Formulation 1995 for the
-    Thermodynamic Properties of Ordinary Water Substance for General and
+  note: >-
+    Phase definition based on W. Wagner, A. Pruss, "The IAPWS Formulation 1995
+    for the Thermodynamic Properties of Ordinary Water Substance for General and
     Scientific Use," J. Phys. Chem. Ref. Dat, 31, 387, 2002.
 - name: nitrogen
   thermo: pure-fluid
@@ -104,6 +103,12 @@ phases:
     T: 300.0
     P: 1.01325e+05
   pure-fluid-name: HFC-134a
+  note: >-
+    Phase definition based on R. Tillner-Roth and H. D. Baehr, "An International
+    Standard Formulation for The Thermodynamic Properties of
+    1,1,1,2-Tetrafluoroethane (HFC-134a) for Temperatures From 170 K to 455 K
+    and Pressures up to 70 MPa". J. Phys. Chem. Ref. Data, Vol. 23, No. 5, 1994.
+    pp. 657--729.
 - name: hfc134a
   thermo: pure-fluid
   elements: [C, F, H]
diff --git a/interfaces/cython/cantera/liquidvapor.py b/interfaces/cython/cantera/liquidvapor.py
index ac57fb6a2c0..e60b7a1d096 100644
--- a/interfaces/cython/cantera/liquidvapor.py
+++ b/interfaces/cython/cantera/liquidvapor.py
@@ -8,11 +8,30 @@ def Water():
     """
     Create a `PureFluid` object using the equation of state for water and the
     `WaterTransport` class for viscosity and thermal conductivity.
+
+    The object returned by this method implements an accurate equation of
+    state for water that can be used in the liquid, vapor, saturated
+    liquid/vapor, and supercritical regions of the phase diagram. The
+    equation of state is taken from
+
+    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+    computational equations for forty substances.* Stanford: Stanford
+    University, 1979. Print.
+
+    whereas formulas for transport are taken from
+
+    J. V. Sengers, J. T. R. Watson, *Improved International Formulations for
+    the Viscosity and Thermal Conductivity of Water Substance,* J. Phys. Chem.
+    Ref. Data, 15, 1291, 1986.
+
+    For more details, see classes Cantera::PureFluid, tpx::water and
+    Cantera::WaterTransport in the Cantera C++ source code documentation.
     """
     class WaterWithTransport(PureFluid, _cantera.Transport):
         __slots__ = ()
 
-    return WaterWithTransport('liquidvapor.yaml', 'water', transport_model='Water')
+    return WaterWithTransport('liquidvapor.yaml', 'water',
+                              transport_model='Water')
 
 
 def LiquidWater():
@@ -20,6 +39,23 @@ def LiquidWater():
     Create a `PureFluid` object using the IAPWS Formulation 1995 for
     thermodynamic properties and the `WaterTransport` class for viscosity
     and thermal conductivity.
+
+    The object returned by this method implements an accurate equation of
+    state for water that can be used in the liquid and supercritical regions
+    of the phase diagram. The equation of state is taken from
+
+    W. Wagner, A. Pruss, *The IAPWS Formulation 1995 for the Thermodynamic
+    Properties of Ordinary Water Substance for General and Scientific Use,*
+    J. Phys. Chem. Ref. Dat, 31, 387, 2002.
+
+    whereas formulas for transport are taken from
+
+    J. V. Sengers, J. T. R. Watson, *Improved International Formulations for
+    the Viscosity and Thermal Conductivity of Water Substance,* J. Phys. Chem.
+    Ref. Data, 15, 1291, 1986.
+
+    For more details, see classes Cantera::PureFluid, Cantera::WaterSSTP and
+    Cantera::WaterTransport in the Cantera C++ source code documentation.
     """
     class WaterWithTransport(PureFluid, _cantera.Transport):
         __slots__ = ()
@@ -29,35 +65,135 @@ class WaterWithTransport(PureFluid, _cantera.Transport):
 
 
 def Nitrogen():
-    """Create a `PureFluid` object using the equation of state for nitrogen."""
+    """
+    Create a `PureFluid` object using the equation of state for nitrogen.
+
+    The object returned by this method implements an accurate equation of
+    state for nitrogen that can be used in the liquid, vapor, saturated
+    liquid/vapor, and supercritical regions of the phase diagram. The
+    equation of state is taken from
+
+    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+    computational equations for forty substances* Stanford: Stanford
+    University, 1979. Print.
+
+    For more details, see classes Cantera::PureFluid and tpx::nitrogen in the
+    Cantera C++ source code documentation.
+    """
     return PureFluid('liquidvapor.yaml', 'nitrogen')
 
 
 def Methane():
-    """Create a `PureFluid` object using the equation of state for methane."""
+    """
+    Create a `PureFluid` object using the equation of state for methane.
+
+    The object returned by this method implements an accurate equation of
+    state for methane that can be used in the liquid, vapor, saturated
+    liquid/vapor, and supercritical regions of the phase diagram.  The
+    equation of state is taken from
+
+    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+    computational equations for forty substances* Stanford: Stanford
+    University, 1979. Print.
+
+    For more details, see classes Cantera::PureFluid and tpx::methane in the
+    Cantera C++ source code documentation.
+    """
     return PureFluid('liquidvapor.yaml', 'methane')
 
 
 def Hydrogen():
-    """Create a `PureFluid` object using the equation of state for hydrogen."""
+    """
+    Create a `PureFluid` object using the equation of state for hydrogen.
+
+    The object returned by this method implements an accurate equation of
+    state for hydrogen that can be used in the liquid, vapor, saturated
+    liquid/vapor, and supercritical regions of the phase diagram. The
+    equation of state is taken from
+
+    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+    computational equations for forty substances* Stanford: Stanford
+    University, 1979. Print.
+
+    For more details, see classes Cantera::PureFluid and tpx::hydrogen in the
+    Cantera C++ source code documentation.
+    """
     return PureFluid('liquidvapor.yaml', 'hydrogen')
 
 
 def Oxygen():
-    """Create a `PureFluid` object using the equation of state for oxygen."""
+    """
+    Create a `PureFluid` object using the equation of state for oxygen.
+
+    The object returned by this method implements an accurate equation of
+    state for oxygen that can be used in the liquid, vapor, saturated
+    liquid/vapor, and supercritical regions of the phase diagram.  The
+    equation of state is taken from
+
+    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+    computational equations for forty substances* Stanford: Stanford
+    University, 1979. Print.
+
+    For more details, see classes Cantera::PureFluid and tpx::oxygen in the
+    Cantera C++ source code documentation.
+    """
     return PureFluid('liquidvapor.yaml', 'oxygen')
 
 
 def Hfc134a():
-    """Create a `PureFluid` object using the equation of state for HFC-134a."""
+    """
+    Create a `PureFluid` object using the equation of state for HFC-134a.
+
+    The object returned by this method implements an accurate equation of
+    state for refrigerant HFC134a (R134a) that can be used in the liquid,
+    vapor, saturated liquid/vapor, and supercritical regions of the phase
+    diagram. Implements the equation of state given in:
+
+    R. Tillner-Roth and H. D. Baehr. *An International Standard Formulation for
+    The Thermodynamic Properties of 1,1,1,2-Tetrafluoroethane (HFC-134a) for
+    Temperatures From 170 K to 455 K and Pressures up to 70 MPa.* J. Phys.
+    Chem. Ref. Data, Vol. 23, No. 5, 1994. pp. 657--729.
+    http://dx.doi.org/10.1063/1.555958
+
+    For more details, see classes Cantera::PureFluid and tpx::HFC134a in the
+    Cantera C++ source code documentation.
+    """
     return PureFluid('liquidvapor.yaml', 'HFC-134a')
 
 
 def CarbonDioxide():
-    """Create a `PureFluid` object using the equation of state for carbon dioxide."""
+    """
+    Create a `PureFluid` object using the equation of state for carbon dioxide.
+
+    The object returned by this method implements an accurate equation of
+    state for carbon dioxide that can be used in the liquid, vapor, saturated
+    liquid/vapor, and supercritical regions of the phase diagram. The
+    equation of state is taken from
+
+    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+    computational equations for forty substances.* Stanford: Stanford
+    University, 1979. Print.
+
+    For more details, see classes Cantera::PureFluid and tpx::CarbonDioxide in
+    the Cantera C++ source code documentation.
+    """
     return PureFluid('liquidvapor.yaml', 'carbon-dioxide')
 
 
 def Heptane():
-    """Create a `PureFluid` object using the equation of state for heptane."""
+    """
+    Create a `PureFluid` object using the equation of state for heptane.
+
+    The object returned by this method implements an accurate equation of
+    state for n-heptane that can be used in the liquid, vapor, saturated
+    liquid/vapor, and supercritical regions of the phase diagram. The
+    equation of state is taken from
+
+    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+    computational equations for forty substances.* Stanford: Stanford
+    University, 1979. Print.
+
+    For more details, see classes Cantera::PureFluid and tpx::Heptane in the
+    Cantera C++ source code documentation.
+    """
     return PureFluid('liquidvapor.yaml', 'heptane')

From d08e0b1d3a021a7e48a7645d7774e8d85fc4ad1e Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Thu, 27 Aug 2020 21:47:24 -0500
Subject: [PATCH 03/14] Minor formatting changes

---
 interfaces/matlab/toolbox/HFC134a.m | 4 ++--
 src/tpx/HFC134a.h                   | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/interfaces/matlab/toolbox/HFC134a.m b/interfaces/matlab/toolbox/HFC134a.m
index 3ebb902d309..61aa00d3cba 100644
--- a/interfaces/matlab/toolbox/HFC134a.m
+++ b/interfaces/matlab/toolbox/HFC134a.m
@@ -2,10 +2,10 @@
 % HFC134A  Return an object representing refrigerant HFC134a.
 % h = HFC134a()
 % The object returned by this method implements an accurate equation of
-% state for refrigerant HFC134a (R134a)  that can be used in the liquid,
+% state for refrigerant HFC134a (R134a) that can be used in the liquid,
 % vapor, saturated liquid/vapor, and supercritical regions of the phase
 % diagram. Implements the equation of state given in:
-% R. Tillner-Roth and H.D. Baehr. "An International Standard Formulation for
+% R. Tillner-Roth and H. D. Baehr. "An International Standard Formulation for
 % The Thermodynamic Properties of 1,1,1,2-Tetrafluoroethane (HFC-134a) for
 % Temperatures From 170 K to 455 K and Pressures up to 70 MPa". J. Phys.
 % Chem. Ref. Data, Vol. 23, No. 5, 1994. pp. 657--729.
diff --git a/src/tpx/HFC134a.h b/src/tpx/HFC134a.h
index 498facb4d95..0351279ec51 100644
--- a/src/tpx/HFC134a.h
+++ b/src/tpx/HFC134a.h
@@ -13,7 +13,7 @@ namespace tpx
 //! Equation of state for HFC-134a.
 //!
 //! Implements the equation of state given in:
-//! R. Tillner-Roth and H.D. Baehr. "An International Standard Formulation for
+//! R. Tillner-Roth and H. D. Baehr. "An International Standard Formulation for
 //! The Thermodynamic Properties of 1,1,1,2-Tetrafluoroethane (HFC-134a) for
 //! Temperatures From 170 K to 455 K and Pressures up to 70 MPa". J. Phys.
 //! Chem. Ref. Data, Vol. 23, No. 5, 1994. pp. 657--729.

From b929c029ea4aae1ec57bb9df74ff7a3542e9ed20 Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Thu, 27 Aug 2020 22:10:57 -0500
Subject: [PATCH 04/14] [thermo] Improve documentation of WaterSSTP helper
 classes

Co-authored by: Shekhar Shukla <47356149+24sharkS@users.noreply.github.com>
---
 include/cantera/thermo/WaterProps.h         | 3 +++
 include/cantera/thermo/WaterPropsIAPWS.h    | 3 +++
 include/cantera/thermo/WaterPropsIAPWSphi.h | 3 +++
 3 files changed, 9 insertions(+)

diff --git a/include/cantera/thermo/WaterProps.h b/include/cantera/thermo/WaterProps.h
index ec0520b2bee..fbaced025af 100644
--- a/include/cantera/thermo/WaterProps.h
+++ b/include/cantera/thermo/WaterProps.h
@@ -83,6 +83,9 @@ class PDSS_Water;
 //! The WaterProps class is used to house several approximation routines for
 //! properties of water.
 /*!
+ * This is a helper class for WaterSSTP and is not instantiable on its own
+ * (see \ref thermoprops and class \link Cantera::WaterSSTP WaterSSTP\endlink).
+ *
  * The class is also a wrapper around the WaterPropsIAPWS class which provides
  * the calculations for the equation of state properties for water.
  *
diff --git a/include/cantera/thermo/WaterPropsIAPWS.h b/include/cantera/thermo/WaterPropsIAPWS.h
index 85f14b9e5c4..a3db0af8994 100644
--- a/include/cantera/thermo/WaterPropsIAPWS.h
+++ b/include/cantera/thermo/WaterPropsIAPWS.h
@@ -37,6 +37,9 @@ namespace Cantera
 
 //! Class for calculating the equation of state of water.
 /*!
+ * This is a helper class for WaterSSTP and is not instantiable on its own
+ * (see \ref thermoprops and class \link Cantera::WaterSSTP WaterSSTP\endlink).
+ *
  * The reference is W. Wagner, A. Pruss, "The IAPWS Formulation 1995 for the
  * Thermodynamic Properties of Ordinary Water Substance for General and
  * Scientific Use," J. Phys. Chem. Ref. Dat, 31, 387, 2002.
diff --git a/include/cantera/thermo/WaterPropsIAPWSphi.h b/include/cantera/thermo/WaterPropsIAPWSphi.h
index fc274b1c347..db143d3d8cb 100644
--- a/include/cantera/thermo/WaterPropsIAPWSphi.h
+++ b/include/cantera/thermo/WaterPropsIAPWSphi.h
@@ -20,6 +20,9 @@ namespace Cantera
 
 //! Low level class for the real description of water.
 /*!
+ * This is a helper class for WaterSSTP and is not instantiable on its own
+ * (see \ref thermoprops and class \link Cantera::WaterSSTP WaterSSTP\endlink).
+ *
  * The reference is W. Wagner, A. Pruss, "The IAPWS Formulation 1995 for the
  * Thermodynamic Properties of Ordinary Water Substance for General and
  * Scientific Use," J. Phys. Chem. Ref. Dat, 31, 387, 2002.

From 7a8407b3a4e481161846acda19030701c8c1adb0 Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Fri, 28 Aug 2020 11:29:24 -0500
Subject: [PATCH 05/14] [thermo] Ensure that WaterSSTP satisfies model
 assumptions

---
 src/thermo/ThermoPhase.cpp | 11 +++++++++--
 src/thermo/WaterSSTP.cpp   | 32 +++++++++++++++++++++++++-------
 2 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/src/thermo/ThermoPhase.cpp b/src/thermo/ThermoPhase.cpp
index 294cd0dc297..33aed0ad12e 100644
--- a/src/thermo/ThermoPhase.cpp
+++ b/src/thermo/ThermoPhase.cpp
@@ -135,8 +135,15 @@ void ThermoPhase::setState_TPY(doublereal t, doublereal p, const std::string& y)
 
 void ThermoPhase::setState_TP(doublereal t, doublereal p)
 {
-    setTemperature(t);
-    setPressure(p);
+    double tsave = temperature();
+    double dsave = density();
+    try {
+        setTemperature(t);
+        setPressure(p);
+    } catch (CanteraError&) {
+        setState_TR(tsave, dsave);
+        throw;
+    }
 }
 
 void ThermoPhase::setState_RPX(doublereal rho, doublereal p, const doublereal* x)
diff --git a/src/thermo/WaterSSTP.cpp b/src/thermo/WaterSSTP.cpp
index a381c01aa87..28993d8e085 100644
--- a/src/thermo/WaterSSTP.cpp
+++ b/src/thermo/WaterSSTP.cpp
@@ -266,15 +266,27 @@ doublereal WaterSSTP::pressure() const
 void WaterSSTP::setPressure(doublereal p)
 {
     double T = temperature();
-    double dens = density();
-    int waterState = WATER_GAS;
-    double rc = m_sub.Rhocrit();
-    if (dens > rc) {
-        waterState = WATER_LIQUID;
+    double dens = 1.;
+    double pp = m_sub.psat(T);
+    int waterState = WATER_SUPERCRIT;
+    if (T < m_sub.Tcrit()) {
+        if (p >= pp) {
+            waterState = WATER_LIQUID;
+            dens = 1000.;
+        } else {
+            throw CanteraError("WaterSSTP::setPressure",
+                               "Pressure p = {} lies below the saturation "
+                               "pressure\n(P_sat = {}), which violates model "
+                               "assumptions.", p, pp);
+        }
     }
-    doublereal dd = m_sub.density(T, p, waterState, dens);
+
+    double dd = m_sub.density(T, p, waterState, dens);
     if (dd <= 0.0) {
-        throw CanteraError("WaterSSTP::setPressure", "error");
+        throw CanteraError("WaterSSTP::setPressure",
+                           "error: T = {}, p = {}, psat = {}\n"
+                           "density_guess = {}, density_fail = {}",
+                           T, p, pp, dens, dd);
     }
     setDensity(dd);
 }
@@ -323,6 +335,12 @@ doublereal WaterSSTP::critDensity() const
 
 void WaterSSTP::setTemperature(const doublereal temp)
 {
+    if (temp < 273.16) {
+        throw CanteraError("WaterSSTP::setTemperature",
+                           "Temperature T = {} lies below the triple point "
+                           "temperature,\nwhich violates model assumptions.",
+                           temp);
+    }
     Phase::setTemperature(temp);
     m_sub.setState_TR(temp, density());
 }

From 721e6e01f3e0472ddc67177a8ee3d1102ce5b9ab Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Fri, 28 Aug 2020 11:29:50 -0500
Subject: [PATCH 06/14] [thermo] Ensure that WaterPropsIAPWS::density works for
 critical point

---
 src/thermo/WaterPropsIAPWS.cpp | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/thermo/WaterPropsIAPWS.cpp b/src/thermo/WaterPropsIAPWS.cpp
index 59aacaa68e1..3f373cef0d2 100644
--- a/src/thermo/WaterPropsIAPWS.cpp
+++ b/src/thermo/WaterPropsIAPWS.cpp
@@ -78,6 +78,15 @@ doublereal WaterPropsIAPWS::pressure() const
 doublereal WaterPropsIAPWS::density(doublereal temperature, doublereal pressure,
                                     int phase, doublereal rhoguess)
 {
+    if (fabs(pressure - P_c) / P_c < 1.e-8 &&
+        fabs(temperature - T_c) / T_c < 1.e-8) {
+        // Catch critical point, as no solution is found otherwise
+        setState_TR(temperature, Rho_c);
+        return Rho_c;
+    } else if (fabs(rhoguess - Rho_c) / Rho_c < 1.e-8) {
+        // Starting a search with the critical density would fail
+        rhoguess *= .9;
+    }
     doublereal deltaGuess = 0.0;
     if (rhoguess == -1.0) {
         if (phase != -1) {
@@ -109,7 +118,7 @@ doublereal WaterPropsIAPWS::density(doublereal temperature, doublereal pressure,
     setState_TR(temperature, rhoguess);
     doublereal delta_retn = m_phi.dfind(p_red, tau, deltaGuess);
     doublereal density_retn;
-    if (delta_retn >0.0) {
+    if (delta_retn > 0.0) {
         delta = delta_retn;
 
         // Dimensionalize the density before returning

From 25dfb2b10a579599e1c43b284f47e3a6ea145dad Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Fri, 28 Aug 2020 12:57:32 -0500
Subject: [PATCH 07/14] [thermo] Implement allowGasPhase override for WaterSSTP

---
 include/cantera/thermo/WaterSSTP.h                   | 3 +++
 src/thermo/WaterSSTP.cpp                             | 4 ++--
 test_problems/cathermo/testWaterTP/testWaterSSTP.cpp | 2 ++
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/cantera/thermo/WaterSSTP.h b/include/cantera/thermo/WaterSSTP.h
index 215304cbfb9..66f4feda72a 100644
--- a/include/cantera/thermo/WaterSSTP.h
+++ b/include/cantera/thermo/WaterSSTP.h
@@ -238,6 +238,9 @@ class WaterSSTP : public SingleSpeciesTP
         return m_waterProps.get();
     }
 
+    //! Switch that enables calculations in the gas phase
+    void allowGasPhase(bool flag) { m_allowGasPhase = flag; }
+
 protected:
     /**
      * @internal This internal routine must be overridden because it is not
diff --git a/src/thermo/WaterSSTP.cpp b/src/thermo/WaterSSTP.cpp
index 28993d8e085..8d37e28d3c4 100644
--- a/src/thermo/WaterSSTP.cpp
+++ b/src/thermo/WaterSSTP.cpp
@@ -266,14 +266,14 @@ doublereal WaterSSTP::pressure() const
 void WaterSSTP::setPressure(doublereal p)
 {
     double T = temperature();
-    double dens = 1.;
+    double dens = density();
     double pp = m_sub.psat(T);
     int waterState = WATER_SUPERCRIT;
     if (T < m_sub.Tcrit()) {
         if (p >= pp) {
             waterState = WATER_LIQUID;
             dens = 1000.;
-        } else {
+        } else if (!m_allowGasPhase) {
             throw CanteraError("WaterSSTP::setPressure",
                                "Pressure p = {} lies below the saturation "
                                "pressure\n(P_sat = {}), which violates model "
diff --git a/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp b/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp
index 2e1a433a293..f885e170202 100644
--- a/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp
+++ b/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp
@@ -1,4 +1,5 @@
 #include "cantera/thermo/ThermoFactory.h"
+#include "cantera/thermo/WaterSSTP.h"
 #include <iostream>
 
 using namespace std;
@@ -21,6 +22,7 @@ int main()
     double pres;
     try {
         ThermoPhase* w = newPhase("liquid-water.xml");
+        (dynamic_cast<WaterSSTP*>(w))->allowGasPhase(true);
 
         /*
          * Print out the triple point conditions

From ffef9e30427cbc71f1f152b7ff5a54f33b5676da Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Fri, 28 Aug 2020 11:52:04 -0500
Subject: [PATCH 08/14] [unittests] Add/update tests for LiquidWater object

---
 .../cython/cantera/test/test_composite.py     |  3 +++
 .../cython/cantera/test/test_convert.py       |  8 +++---
 .../cython/cantera/test/test_purefluid.py     | 25 +++++++++++++++++++
 3 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/interfaces/cython/cantera/test/test_composite.py b/interfaces/cython/cantera/test/test_composite.py
index b63687f2735..06e1742d73f 100644
--- a/interfaces/cython/cantera/test/test_composite.py
+++ b/interfaces/cython/cantera/test/test_composite.py
@@ -87,6 +87,9 @@ def check(a, b):
             try:
                 sol = ct.Solution(self.yml_file, ph_name)
                 a = ct.SolutionArray(sol, 10)
+                if ph['thermo'] == 'liquid-water-IAPWS95':
+                    # ensure that phase remains liquid
+                    a.TP = sol.T, sol.critical_pressure
 
                 # assign some state
                 T = 373.15 + 100*np.random.rand(10)
diff --git a/interfaces/cython/cantera/test/test_convert.py b/interfaces/cython/cantera/test/test_convert.py
index 88b508e173f..228891d2afa 100644
--- a/interfaces/cython/cantera/test/test_convert.py
+++ b/interfaces/cython/cantera/test/test_convert.py
@@ -841,10 +841,10 @@ def checkConversion(self, basename, cls=ct.Solution, ctmlphases=(),
 
         return ctmlPhase, yamlPhase
 
-    def checkThermo(self, ctmlPhase, yamlPhase, temperatures, tol=1e-7):
+    def checkThermo(self, ctmlPhase, yamlPhase, temperatures, pressure=ct.one_atm, tol=1e-7):
         for T in temperatures:
-            ctmlPhase.TP = T, ct.one_atm
-            yamlPhase.TP = T, ct.one_atm
+            ctmlPhase.TP = T, pressure
+            yamlPhase.TP = T, pressure
             cp_ctml = ctmlPhase.partial_molar_cp
             cp_yaml = yamlPhase.partial_molar_cp
             h_ctml = ctmlPhase.partial_molar_enthalpies
@@ -1134,7 +1134,7 @@ def test_water_IAPWS95_thermo(self):
             Path(self.test_work_dir).joinpath("liquid-water.yaml"),
         )
         ctmlWater, yamlWater = self.checkConversion("liquid-water")
-        self.checkThermo(ctmlWater, yamlWater, [300, 500, 1300, 2000])
+        self.checkThermo(ctmlWater, yamlWater, [300, 500, 1300, 2000], pressure=22064000.0)
         self.assertEqual(ctmlWater.transport_model, yamlWater.transport_model)
         dens = ctmlWater.density
         for T in [298, 1001, 2400]:
diff --git a/interfaces/cython/cantera/test/test_purefluid.py b/interfaces/cython/cantera/test/test_purefluid.py
index 8cbe2c9aa60..271efe62bcc 100644
--- a/interfaces/cython/cantera/test/test_purefluid.py
+++ b/interfaces/cython/cantera/test/test_purefluid.py
@@ -357,6 +357,31 @@ def test_phase_of_matter(self):
         co2 = ct.CarbonDioxide()
         self.assertEqual(co2.phase_of_matter, "gas")
 
+    def test_liquidwater(self):
+        w = ct.LiquidWater()
+        self.assertNear(w.critical_density, 322.)
+        self.assertNear(w.critical_temperature, 647.096)
+        self.assertNear(w.critical_pressure, 22064000.0)
+
+        # test internal TP setters (setters update temperature at constant
+        # density before updating pressure)
+        w.TP = 300, ct.one_atm
+        dens = w.density
+        w.TP = 2000, ct.one_atm # supercricial
+        w.TP = 300, ct.one_atm # state goes from supercritical -> gas -> liquid
+        self.assertNear(w.density, dens)
+
+        # test setters for critical conditions
+        w.TP = w.critical_temperature, w.critical_pressure
+        self.assertNear(w.density, 322.)
+        w.TP = 2000, ct.one_atm # uses current density as initial guess
+        w.TP = 273.16, ct.one_atm # uses fixed density as initial guess
+        self.assertNear(w.density, 999.84376)
+        with self.assertRaisesRegex(ct.CanteraError, "violates model assumptions"):
+            w.TP = 273.1599999, ct.one_atm
+        with self.assertRaisesRegex(ct.CanteraError, "violates model assumptions"):
+            w.TP = 500, ct.one_atm
+
 
 # To minimize errors when transcribing tabulated data, the input units here are:
 # T: K, P: MPa, rho: kg/m3, v: m3/kg, (u,h): kJ/kg, s: kJ/kg-K

From b54ba6ea1f48501bb8bcfd3fa540de20fda190dc Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Fri, 28 Aug 2020 15:49:59 -0500
Subject: [PATCH 09/14] [thermo] Implement phaseOfMatter for WaterSSTP class

---
 include/cantera/thermo/WaterSSTP.h               | 8 +++++---
 interfaces/cython/cantera/test/test_purefluid.py | 7 ++++++-
 src/thermo/WaterSSTP.cpp                         | 7 +++++++
 3 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/include/cantera/thermo/WaterSSTP.h b/include/cantera/thermo/WaterSSTP.h
index 66f4feda72a..156081581e8 100644
--- a/include/cantera/thermo/WaterSSTP.h
+++ b/include/cantera/thermo/WaterSSTP.h
@@ -20,7 +20,7 @@ namespace Cantera
 class WaterPropsIAPWS;
 class WaterProps;
 //! Class for single-component water. This is designed to cover just the liquid
-//! part of water.
+//! and supercritical phases of water.
 /*!
  * The reference is W. Wagner, A. Pruss, "The IAPWS Formulation 1995 for the
  * Thermodynamic Properties of Ordinary Water Substance for General and
@@ -143,6 +143,8 @@ class WaterSSTP : public SingleSpeciesTP
         return "Water";
     }
 
+    virtual std::string phaseOfMatter() const;
+
     //! @name  Molar Thermodynamic Properties of the Solution
     //! @{
 
@@ -281,8 +283,8 @@ class WaterSSTP : public SingleSpeciesTP
     bool m_ready;
 
     /**
-     *  Since this phase represents a liquid phase, it's an error to
-     *  return a gas-phase answer. However, if the below is true, then
+     *  Since this phase represents a liquid (or supercritical) phase, it is an
+     *  error to return a gas-phase answer. However, if the below is true, then
      *  a gas-phase answer is allowed. This is used to check the thermodynamic
      *  consistency with ideal-gas thermo functions for example.
      */
diff --git a/interfaces/cython/cantera/test/test_purefluid.py b/interfaces/cython/cantera/test/test_purefluid.py
index 271efe62bcc..2dc44a6173a 100644
--- a/interfaces/cython/cantera/test/test_purefluid.py
+++ b/interfaces/cython/cantera/test/test_purefluid.py
@@ -367,9 +367,11 @@ def test_liquidwater(self):
         # density before updating pressure)
         w.TP = 300, ct.one_atm
         dens = w.density
-        w.TP = 2000, ct.one_atm # supercricial
+        w.TP = 2000, ct.one_atm # supercritical
+        self.assertEqual(w.phase_of_matter, "supercritical")
         w.TP = 300, ct.one_atm # state goes from supercritical -> gas -> liquid
         self.assertNear(w.density, dens)
+        self.assertEqual(w.phase_of_matter, "liquid")
 
         # test setters for critical conditions
         w.TP = w.critical_temperature, w.critical_pressure
@@ -377,6 +379,9 @@ def test_liquidwater(self):
         w.TP = 2000, ct.one_atm # uses current density as initial guess
         w.TP = 273.16, ct.one_atm # uses fixed density as initial guess
         self.assertNear(w.density, 999.84376)
+        self.assertEqual(w.phase_of_matter, "liquid")
+        w.TP = w.T, w.P_sat
+        self.assertEqual(w.phase_of_matter, "liquid")
         with self.assertRaisesRegex(ct.CanteraError, "violates model assumptions"):
             w.TP = 273.1599999, ct.one_atm
         with self.assertRaisesRegex(ct.CanteraError, "violates model assumptions"):
diff --git a/src/thermo/WaterSSTP.cpp b/src/thermo/WaterSSTP.cpp
index 8d37e28d3c4..abbea3d8e3f 100644
--- a/src/thermo/WaterSSTP.cpp
+++ b/src/thermo/WaterSSTP.cpp
@@ -44,6 +44,13 @@ WaterSSTP::WaterSSTP(XML_Node& phaseRoot, const std::string& id) :
     importPhase(phaseRoot, this);
 }
 
+std::string WaterSSTP::phaseOfMatter() const {
+    const vector<std::string> phases = {
+        "gas", "liquid", "supercritical", "unstable-liquid", "unstable-gas"
+    };
+    return phases[m_sub.phaseState()];
+}
+
 void WaterSSTP::initThermo()
 {
     SingleSpeciesTP::initThermo();

From 3f1a3d1715a5bcabc31b20a0edae94683e755cfd Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Fri, 28 Aug 2020 20:36:03 -0500
Subject: [PATCH 10/14] [thermo] Add IAPWS as alternative backend to existing
 Water wrapper

While the current 'liquid-water-IAPWS95' thermo model only implements liquid
(and supercritical) states, the underlying IAPWS formulation can be extended
beyond in future revisions.

- avoid 'liquid' as part of the nomenclature
- YAML phase name is updated to `water-iapws95`
- Instead of creating a new wrapper, `iapws95` is added as an alternative
  backend to the existing `Water` class
---
 data/liquidvapor.yaml                         |   2 +-
 interfaces/cython/cantera/liquidvapor.py      | 116 ++++++++----------
 .../cython/cantera/test/test_purefluid.py     |  17 ++-
 src/thermo/WaterSSTP.cpp                      |  14 +--
 .../cathermo/testWaterTP/testWaterSSTP.cpp    |   2 +-
 5 files changed, 70 insertions(+), 81 deletions(-)

diff --git a/data/liquidvapor.yaml b/data/liquidvapor.yaml
index fe2269a1123..2c45fd14024 100644
--- a/data/liquidvapor.yaml
+++ b/data/liquidvapor.yaml
@@ -25,7 +25,7 @@ phases:
     T: 300.0
     P: 1.01325e+05
   pure-fluid-name: water
-- name: liquid-water
+- name: water-iapws95
   elements: [O, H]
   species: [H2O]
   thermo: liquid-water-IAPWS95
diff --git a/interfaces/cython/cantera/liquidvapor.py b/interfaces/cython/cantera/liquidvapor.py
index e60b7a1d096..078bd7a89c9 100644
--- a/interfaces/cython/cantera/liquidvapor.py
+++ b/interfaces/cython/cantera/liquidvapor.py
@@ -4,64 +4,48 @@
 from . import PureFluid, _cantera
 
 
-def Water():
+def Water(backend='default'):
     """
     Create a `PureFluid` object using the equation of state for water and the
     `WaterTransport` class for viscosity and thermal conductivity.
 
-    The object returned by this method implements an accurate equation of
-    state for water that can be used in the liquid, vapor, saturated
-    liquid/vapor, and supercritical regions of the phase diagram. The
-    equation of state is taken from
-
-    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
-    computational equations for forty substances.* Stanford: Stanford
-    University, 1979. Print.
-
-    whereas formulas for transport are taken from
-
-    J. V. Sengers, J. T. R. Watson, *Improved International Formulations for
-    the Viscosity and Thermal Conductivity of Water Substance,* J. Phys. Chem.
-    Ref. Data, 15, 1291, 1986.
-
-    For more details, see classes Cantera::PureFluid, tpx::water and
-    Cantera::WaterTransport in the Cantera C++ source code documentation.
-    """
-    class WaterWithTransport(PureFluid, _cantera.Transport):
-        __slots__ = ()
+    The object returned by this method implements an accurate equation of state
+    for water, where implementations are selected using the *backend* switch.
 
-    return WaterWithTransport('liquidvapor.yaml', 'water',
-                              transport_model='Water')
+    For the ``default`` backend, the equation of state is taken from
 
+        W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+        computational equations for forty substances.* Stanford: Stanford
+        University, 1979. Print.
 
-def LiquidWater():
-    """
-    Create a `PureFluid` object using the IAPWS Formulation 1995 for
-    thermodynamic properties and the `WaterTransport` class for viscosity
-    and thermal conductivity.
+    which can be used in the liquid, vapor, saturated liquid/vapor, and
+    supercritical regions of the phase diagram.
 
-    The object returned by this method implements an accurate equation of
-    state for water that can be used in the liquid and supercritical regions
-    of the phase diagram. The equation of state is taken from
-
-    W. Wagner, A. Pruss, *The IAPWS Formulation 1995 for the Thermodynamic
-    Properties of Ordinary Water Substance for General and Scientific Use,*
-    J. Phys. Chem. Ref. Dat, 31, 387, 2002.
+    The ``iapws95`` backend implements an IAPWS (International Association for
+    the Properties of Water and Steam) formulation for thermodynamic properties
+    taken from
 
-    whereas formulas for transport are taken from
+        J. V. Sengers, J. T. R. Watson, *Improved International Formulations for
+        the Viscosity and Thermal Conductivity of Water Substance,* J. Phys.
+        Chem. Ref. Data, 15, 1291, 1986.
 
-    J. V. Sengers, J. T. R. Watson, *Improved International Formulations for
-    the Viscosity and Thermal Conductivity of Water Substance,* J. Phys. Chem.
-    Ref. Data, 15, 1291, 1986.
+    which currently only implements liquid and supercritical regions.
 
-    For more details, see classes Cantera::PureFluid, Cantera::WaterSSTP and
-    Cantera::WaterTransport in the Cantera C++ source code documentation.
+    For more details, see classes Cantera::PureFluid, tpx::water,
+    Cantera::WaterSSTP and Cantera::WaterTransport in the Cantera C++ source
+    code documentation.
     """
     class WaterWithTransport(PureFluid, _cantera.Transport):
         __slots__ = ()
 
-    return WaterWithTransport('liquidvapor.yaml', 'liquid-water',
-                              transport_model='Water')
+    if backend == 'default':
+        return WaterWithTransport('liquidvapor.yaml', 'water',
+                                  transport_model='Water')
+    if backend == 'iapws95':
+        return WaterWithTransport('liquidvapor.yaml', 'water-iapws95',
+                                  transport_model='Water')
+
+    raise KeyError("Unknown backend '{}'".format(backend))
 
 
 def Nitrogen():
@@ -73,9 +57,9 @@ def Nitrogen():
     liquid/vapor, and supercritical regions of the phase diagram. The
     equation of state is taken from
 
-    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
-    computational equations for forty substances* Stanford: Stanford
-    University, 1979. Print.
+        W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+        computational equations for forty substances* Stanford: Stanford
+        University, 1979. Print.
 
     For more details, see classes Cantera::PureFluid and tpx::nitrogen in the
     Cantera C++ source code documentation.
@@ -92,9 +76,9 @@ def Methane():
     liquid/vapor, and supercritical regions of the phase diagram.  The
     equation of state is taken from
 
-    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
-    computational equations for forty substances* Stanford: Stanford
-    University, 1979. Print.
+        W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+        computational equations for forty substances* Stanford: Stanford
+        University, 1979. Print.
 
     For more details, see classes Cantera::PureFluid and tpx::methane in the
     Cantera C++ source code documentation.
@@ -111,9 +95,9 @@ def Hydrogen():
     liquid/vapor, and supercritical regions of the phase diagram. The
     equation of state is taken from
 
-    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
-    computational equations for forty substances* Stanford: Stanford
-    University, 1979. Print.
+        W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+        computational equations for forty substances* Stanford: Stanford
+        University, 1979. Print.
 
     For more details, see classes Cantera::PureFluid and tpx::hydrogen in the
     Cantera C++ source code documentation.
@@ -130,9 +114,9 @@ def Oxygen():
     liquid/vapor, and supercritical regions of the phase diagram.  The
     equation of state is taken from
 
-    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
-    computational equations for forty substances* Stanford: Stanford
-    University, 1979. Print.
+        W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+        computational equations for forty substances* Stanford: Stanford
+        University, 1979. Print.
 
     For more details, see classes Cantera::PureFluid and tpx::oxygen in the
     Cantera C++ source code documentation.
@@ -149,11 +133,11 @@ def Hfc134a():
     vapor, saturated liquid/vapor, and supercritical regions of the phase
     diagram. Implements the equation of state given in:
 
-    R. Tillner-Roth and H. D. Baehr. *An International Standard Formulation for
-    The Thermodynamic Properties of 1,1,1,2-Tetrafluoroethane (HFC-134a) for
-    Temperatures From 170 K to 455 K and Pressures up to 70 MPa.* J. Phys.
-    Chem. Ref. Data, Vol. 23, No. 5, 1994. pp. 657--729.
-    http://dx.doi.org/10.1063/1.555958
+        R. Tillner-Roth, H. D. Baehr. *An International Standard Formulation for
+        The Thermodynamic Properties of 1,1,1,2-Tetrafluoroethane (HFC-134a) for
+        Temperatures From 170 K to 455 K and Pressures up to 70 MPa.* J. Phys.
+        Chem. Ref. Data, Vol. 23, No. 5, 1994. pp. 657--729.
+        http://dx.doi.org/10.1063/1.555958
 
     For more details, see classes Cantera::PureFluid and tpx::HFC134a in the
     Cantera C++ source code documentation.
@@ -170,9 +154,9 @@ def CarbonDioxide():
     liquid/vapor, and supercritical regions of the phase diagram. The
     equation of state is taken from
 
-    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
-    computational equations for forty substances.* Stanford: Stanford
-    University, 1979. Print.
+        W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+        computational equations for forty substances.* Stanford: Stanford
+        University, 1979. Print.
 
     For more details, see classes Cantera::PureFluid and tpx::CarbonDioxide in
     the Cantera C++ source code documentation.
@@ -189,9 +173,9 @@ def Heptane():
     liquid/vapor, and supercritical regions of the phase diagram. The
     equation of state is taken from
 
-    W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
-    computational equations for forty substances.* Stanford: Stanford
-    University, 1979. Print.
+        W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
+        computational equations for forty substances.* Stanford: Stanford
+        University, 1979. Print.
 
     For more details, see classes Cantera::PureFluid and tpx::Heptane in the
     Cantera C++ source code documentation.
diff --git a/interfaces/cython/cantera/test/test_purefluid.py b/interfaces/cython/cantera/test/test_purefluid.py
index 2dc44a6173a..2b5ff884a9c 100644
--- a/interfaces/cython/cantera/test/test_purefluid.py
+++ b/interfaces/cython/cantera/test/test_purefluid.py
@@ -357,8 +357,17 @@ def test_phase_of_matter(self):
         co2 = ct.CarbonDioxide()
         self.assertEqual(co2.phase_of_matter, "gas")
 
-    def test_liquidwater(self):
-        w = ct.LiquidWater()
+    def test_water_backends(self):
+        w = ct.Water(backend='default')
+        self.assertEqual(w.thermo_model, 'PureFluid')
+        w = ct.Water(backend='iapws95')
+        self.assertEqual(w.thermo_model, 'Water')
+        with self.assertRaisesRegex(KeyError, 'Unknown backend'):
+            ct.Water('foobar')
+
+
+    def test_water_iapws(self):
+        w = ct.Water(backend='iapws95')
         self.assertNear(w.critical_density, 322.)
         self.assertNear(w.critical_temperature, 647.096)
         self.assertNear(w.critical_pressure, 22064000.0)
@@ -382,9 +391,9 @@ def test_liquidwater(self):
         self.assertEqual(w.phase_of_matter, "liquid")
         w.TP = w.T, w.P_sat
         self.assertEqual(w.phase_of_matter, "liquid")
-        with self.assertRaisesRegex(ct.CanteraError, "violates model assumptions"):
+        with self.assertRaisesRegex(ct.CanteraError, "Not implemented"):
             w.TP = 273.1599999, ct.one_atm
-        with self.assertRaisesRegex(ct.CanteraError, "violates model assumptions"):
+        with self.assertRaisesRegex(ct.CanteraError, "Not implemented"):
             w.TP = 500, ct.one_atm
 
 
diff --git a/src/thermo/WaterSSTP.cpp b/src/thermo/WaterSSTP.cpp
index abbea3d8e3f..b252746a2f4 100644
--- a/src/thermo/WaterSSTP.cpp
+++ b/src/thermo/WaterSSTP.cpp
@@ -282,18 +282,14 @@ void WaterSSTP::setPressure(doublereal p)
             dens = 1000.;
         } else if (!m_allowGasPhase) {
             throw CanteraError("WaterSSTP::setPressure",
-                               "Pressure p = {} lies below the saturation "
-                               "pressure\n(P_sat = {}), which violates model "
-                               "assumptions.", p, pp);
+                               "Not implemented: pressure p = {} lies below\n"
+                               "the saturation pressure (P_sat = {}).", p, pp);
         }
     }
 
     double dd = m_sub.density(T, p, waterState, dens);
     if (dd <= 0.0) {
-        throw CanteraError("WaterSSTP::setPressure",
-                           "error: T = {}, p = {}, psat = {}\n"
-                           "density_guess = {}, density_fail = {}",
-                           T, p, pp, dens, dd);
+        throw CanteraError("WaterSSTP::setPressure", "Error");
     }
     setDensity(dd);
 }
@@ -344,8 +340,8 @@ void WaterSSTP::setTemperature(const doublereal temp)
 {
     if (temp < 273.16) {
         throw CanteraError("WaterSSTP::setTemperature",
-                           "Temperature T = {} lies below the triple point "
-                           "temperature,\nwhich violates model assumptions.",
+                           "Not implemented: temperature T = {} lies below\n"
+                           "the triple point temperature (T_triple = 273.16).",
                            temp);
     }
     Phase::setTemperature(temp);
diff --git a/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp b/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp
index f885e170202..13a9530225b 100644
--- a/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp
+++ b/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp
@@ -21,7 +21,7 @@ int main()
 #endif
     double pres;
     try {
-        ThermoPhase* w = newPhase("liquid-water.xml");
+        ThermoPhase* w = newPhase("liquidvapor.yaml", "water-iapws95");
         (dynamic_cast<WaterSSTP*>(w))->allowGasPhase(true);
 
         /*

From fbc2657bd5b2b52290e5704f8ec0a6c7ce5d12c0 Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Sun, 30 Aug 2020 09:02:17 -0500
Subject: [PATCH 11/14] [thermo] Clarify WaterSSTP::type

---
 include/cantera/thermo/WaterSSTP.h               | 2 +-
 interfaces/cython/cantera/test/test_purefluid.py | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/include/cantera/thermo/WaterSSTP.h b/include/cantera/thermo/WaterSSTP.h
index 156081581e8..fb949391cf3 100644
--- a/include/cantera/thermo/WaterSSTP.h
+++ b/include/cantera/thermo/WaterSSTP.h
@@ -140,7 +140,7 @@ class WaterSSTP : public SingleSpeciesTP
     explicit WaterSSTP(XML_Node& phaseRef, const std::string& id = "");
 
     virtual std::string type() const {
-        return "Water";
+        return "WaterSSTP";
     }
 
     virtual std::string phaseOfMatter() const;
diff --git a/interfaces/cython/cantera/test/test_purefluid.py b/interfaces/cython/cantera/test/test_purefluid.py
index 2b5ff884a9c..57198ea7832 100644
--- a/interfaces/cython/cantera/test/test_purefluid.py
+++ b/interfaces/cython/cantera/test/test_purefluid.py
@@ -361,11 +361,10 @@ def test_water_backends(self):
         w = ct.Water(backend='default')
         self.assertEqual(w.thermo_model, 'PureFluid')
         w = ct.Water(backend='iapws95')
-        self.assertEqual(w.thermo_model, 'Water')
+        self.assertEqual(w.thermo_model, 'WaterSSTP')
         with self.assertRaisesRegex(KeyError, 'Unknown backend'):
             ct.Water('foobar')
 
-
     def test_water_iapws(self):
         w = ct.Water(backend='iapws95')
         self.assertNear(w.critical_density, 322.)

From 7abfaa110a63b18347627f8936d1602c73237a00 Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Tue, 1 Sep 2020 22:03:16 -0500
Subject: [PATCH 12/14] [thermo] Finalize liquid-water-IAPWS95 updates

---
 data/liquidvapor.yaml                         | 13 +++---
 include/cantera/thermo/WaterProps.h           |  6 ++-
 include/cantera/thermo/WaterPropsIAPWS.h      |  6 ++-
 include/cantera/thermo/WaterPropsIAPWSphi.h   |  6 ++-
 include/cantera/thermo/WaterSSTP.h            |  8 +++-
 interfaces/cython/cantera/liquidvapor.py      | 40 +++++++++++--------
 .../cython/cantera/test/test_purefluid.py     | 12 +++---
 src/thermo/WaterSSTP.cpp                      |  9 ++---
 .../cathermo/testWaterTP/testWaterSSTP.cpp    |  2 +-
 9 files changed, 60 insertions(+), 42 deletions(-)

diff --git a/data/liquidvapor.yaml b/data/liquidvapor.yaml
index 2c45fd14024..f06363dd3fb 100644
--- a/data/liquidvapor.yaml
+++ b/data/liquidvapor.yaml
@@ -25,7 +25,7 @@ phases:
     T: 300.0
     P: 1.01325e+05
   pure-fluid-name: water
-- name: water-iapws95
+- name: liquid-water-IAPWS95
   elements: [O, H]
   species: [H2O]
   thermo: liquid-water-IAPWS95
@@ -33,9 +33,10 @@ phases:
     T: 300.0
     P: 1.01325e+05
   note: >-
-    Phase definition based on W. Wagner, A. Pruss, "The IAPWS Formulation 1995
-    for the Thermodynamic Properties of Ordinary Water Substance for General and
-    Scientific Use," J. Phys. Chem. Ref. Dat, 31, 387, 2002.
+    Equation of state is based on W. Wagner, A. Pruss, "The IAPWS Formulation
+    1995 for the Thermodynamic Properties of Ordinary Water Substance for
+    General and Scientific Use," J. Phys. Chem. Ref. Dat, 31, 387, 2002.
+    Important: Only liquid and supercritical states are currently implemented
 - name: nitrogen
   thermo: pure-fluid
   elements: [N]
@@ -104,8 +105,8 @@ phases:
     P: 1.01325e+05
   pure-fluid-name: HFC-134a
   note: >-
-    Phase definition based on R. Tillner-Roth and H. D. Baehr, "An International
-    Standard Formulation for The Thermodynamic Properties of
+    Equation of state is based on R. Tillner-Roth and H. D. Baehr, "An
+    International Standard Formulation for The Thermodynamic Properties of
     1,1,1,2-Tetrafluoroethane (HFC-134a) for Temperatures From 170 K to 455 K
     and Pressures up to 70 MPa". J. Phys. Chem. Ref. Data, Vol. 23, No. 5, 1994.
     pp. 657--729.
diff --git a/include/cantera/thermo/WaterProps.h b/include/cantera/thermo/WaterProps.h
index fbaced025af..74fd66d7209 100644
--- a/include/cantera/thermo/WaterProps.h
+++ b/include/cantera/thermo/WaterProps.h
@@ -83,8 +83,10 @@ class PDSS_Water;
 //! The WaterProps class is used to house several approximation routines for
 //! properties of water.
 /*!
- * This is a helper class for WaterSSTP and is not instantiable on its own
- * (see \ref thermoprops and class \link Cantera::WaterSSTP WaterSSTP\endlink).
+ * This is a helper class for WaterSSTP and PDSS_Water and does not constitute
+ * a complete implementation of a thermo phase by itself (see \ref thermoprops
+ * and classes \link Cantera::WaterSSTP WaterSSTP\endlink and
+ * \link Cantera::PDSS_Water PDSS_Water\endlink).
  *
  * The class is also a wrapper around the WaterPropsIAPWS class which provides
  * the calculations for the equation of state properties for water.
diff --git a/include/cantera/thermo/WaterPropsIAPWS.h b/include/cantera/thermo/WaterPropsIAPWS.h
index a3db0af8994..b0d5a26b103 100644
--- a/include/cantera/thermo/WaterPropsIAPWS.h
+++ b/include/cantera/thermo/WaterPropsIAPWS.h
@@ -37,8 +37,10 @@ namespace Cantera
 
 //! Class for calculating the equation of state of water.
 /*!
- * This is a helper class for WaterSSTP and is not instantiable on its own
- * (see \ref thermoprops and class \link Cantera::WaterSSTP WaterSSTP\endlink).
+ * This is a helper class for WaterSSTP and PDSS_Water and does not constitute
+ * a complete implementation of a thermo phase by itself (see \ref thermoprops
+ * and classes \link Cantera::WaterSSTP WaterSSTP\endlink and
+ * \link Cantera::PDSS_Water PDSS_Water\endlink).
  *
  * The reference is W. Wagner, A. Pruss, "The IAPWS Formulation 1995 for the
  * Thermodynamic Properties of Ordinary Water Substance for General and
diff --git a/include/cantera/thermo/WaterPropsIAPWSphi.h b/include/cantera/thermo/WaterPropsIAPWSphi.h
index db143d3d8cb..e0faa94133f 100644
--- a/include/cantera/thermo/WaterPropsIAPWSphi.h
+++ b/include/cantera/thermo/WaterPropsIAPWSphi.h
@@ -20,8 +20,10 @@ namespace Cantera
 
 //! Low level class for the real description of water.
 /*!
- * This is a helper class for WaterSSTP and is not instantiable on its own
- * (see \ref thermoprops and class \link Cantera::WaterSSTP WaterSSTP\endlink).
+ * This is a helper class for WaterSSTP and PDSS_Water and does not constitute
+ * a complete implementation of a thermo phase by itself (see \ref thermoprops
+ * and classes \link Cantera::WaterSSTP WaterSSTP\endlink and
+ * \link Cantera::PDSS_Water PDSS_Water\endlink).
  *
  * The reference is W. Wagner, A. Pruss, "The IAPWS Formulation 1995 for the
  * Thermodynamic Properties of Ordinary Water Substance for General and
diff --git a/include/cantera/thermo/WaterSSTP.h b/include/cantera/thermo/WaterSSTP.h
index fb949391cf3..410a43b8342 100644
--- a/include/cantera/thermo/WaterSSTP.h
+++ b/include/cantera/thermo/WaterSSTP.h
@@ -140,7 +140,7 @@ class WaterSSTP : public SingleSpeciesTP
     explicit WaterSSTP(XML_Node& phaseRef, const std::string& id = "");
 
     virtual std::string type() const {
-        return "WaterSSTP";
+        return "liquid-water-IAPWS95";
     }
 
     virtual std::string phaseOfMatter() const;
@@ -241,6 +241,12 @@ class WaterSSTP : public SingleSpeciesTP
     }
 
     //! Switch that enables calculations in the gas phase
+    /**
+     *  Since this phase represents a liquid (or supercritical) phase, it is an
+     *  error to return a gas-phase answer. The sole intended use for this
+     *  member function is to check the thermodynamic consistency of the
+     *  underlying WaterProps class with ideal-gas thermo functions.
+     */
     void allowGasPhase(bool flag) { m_allowGasPhase = flag; }
 
 protected:
diff --git a/interfaces/cython/cantera/liquidvapor.py b/interfaces/cython/cantera/liquidvapor.py
index 078bd7a89c9..8bf6a17d834 100644
--- a/interfaces/cython/cantera/liquidvapor.py
+++ b/interfaces/cython/cantera/liquidvapor.py
@@ -4,7 +4,7 @@
 from . import PureFluid, _cantera
 
 
-def Water(backend='default'):
+def Water(backend='Reynolds'):
     """
     Create a `PureFluid` object using the equation of state for water and the
     `WaterTransport` class for viscosity and thermal conductivity.
@@ -12,7 +12,7 @@ def Water(backend='default'):
     The object returned by this method implements an accurate equation of state
     for water, where implementations are selected using the *backend* switch.
 
-    For the ``default`` backend, the equation of state is taken from
+    For the ``Reynolds`` backend, the equation of state is taken from
 
         W. C. Reynolds, *Thermodynamic Properties in SI: graphs, tables, and
         computational equations for forty substances.* Stanford: Stanford
@@ -21,28 +21,34 @@ def Water(backend='default'):
     which can be used in the liquid, vapor, saturated liquid/vapor, and
     supercritical regions of the phase diagram.
 
-    The ``iapws95`` backend implements an IAPWS (International Association for
+    The ``IAPWS95`` backend implements an IAPWS (International Association for
     the Properties of Water and Steam) formulation for thermodynamic properties
     taken from
 
+        W. Wagner, A. Pruss, *The IAPWS Formulation 1995 for the Thermodynamic
+        Properties of Ordinary Water Substance for General and Scientific Use,*
+        J. Phys. Chem. Ref. Dat, 31, 387, 2002.
+
+    which currently only implements liquid and supercritical regions.
+
+    In both cases, formulas for transport are taken from
+
         J. V. Sengers, J. T. R. Watson, *Improved International Formulations for
         the Viscosity and Thermal Conductivity of Water Substance,* J. Phys.
         Chem. Ref. Data, 15, 1291, 1986.
 
-    which currently only implements liquid and supercritical regions.
-
-    For more details, see classes Cantera::PureFluid, tpx::water,
-    Cantera::WaterSSTP and Cantera::WaterTransport in the Cantera C++ source
+    For more details, see classes :ct:PureFluid, tpx::water,
+    :ct:WaterSSTP and :ct:WaterTransport in the Cantera C++ source
     code documentation.
     """
     class WaterWithTransport(PureFluid, _cantera.Transport):
         __slots__ = ()
 
-    if backend == 'default':
+    if backend == 'Reynolds':
         return WaterWithTransport('liquidvapor.yaml', 'water',
                                   transport_model='Water')
-    if backend == 'iapws95':
-        return WaterWithTransport('liquidvapor.yaml', 'water-iapws95',
+    if backend == 'IAPWS95':
+        return WaterWithTransport('liquidvapor.yaml', 'liquid-water-IAPWS95',
                                   transport_model='Water')
 
     raise KeyError("Unknown backend '{}'".format(backend))
@@ -61,7 +67,7 @@ def Nitrogen():
         computational equations for forty substances* Stanford: Stanford
         University, 1979. Print.
 
-    For more details, see classes Cantera::PureFluid and tpx::nitrogen in the
+    For more details, see classes :ct:PureFluid and tpx::nitrogen in the
     Cantera C++ source code documentation.
     """
     return PureFluid('liquidvapor.yaml', 'nitrogen')
@@ -80,7 +86,7 @@ def Methane():
         computational equations for forty substances* Stanford: Stanford
         University, 1979. Print.
 
-    For more details, see classes Cantera::PureFluid and tpx::methane in the
+    For more details, see classes :ct:PureFluid and tpx::methane in the
     Cantera C++ source code documentation.
     """
     return PureFluid('liquidvapor.yaml', 'methane')
@@ -99,7 +105,7 @@ def Hydrogen():
         computational equations for forty substances* Stanford: Stanford
         University, 1979. Print.
 
-    For more details, see classes Cantera::PureFluid and tpx::hydrogen in the
+    For more details, see classes :ct:PureFluid and tpx::hydrogen in the
     Cantera C++ source code documentation.
     """
     return PureFluid('liquidvapor.yaml', 'hydrogen')
@@ -118,7 +124,7 @@ def Oxygen():
         computational equations for forty substances* Stanford: Stanford
         University, 1979. Print.
 
-    For more details, see classes Cantera::PureFluid and tpx::oxygen in the
+    For more details, see classes :ct:PureFluid and tpx::oxygen in the
     Cantera C++ source code documentation.
     """
     return PureFluid('liquidvapor.yaml', 'oxygen')
@@ -139,7 +145,7 @@ def Hfc134a():
         Chem. Ref. Data, Vol. 23, No. 5, 1994. pp. 657--729.
         http://dx.doi.org/10.1063/1.555958
 
-    For more details, see classes Cantera::PureFluid and tpx::HFC134a in the
+    For more details, see classes :ct:PureFluid and tpx::HFC134a in the
     Cantera C++ source code documentation.
     """
     return PureFluid('liquidvapor.yaml', 'HFC-134a')
@@ -158,7 +164,7 @@ def CarbonDioxide():
         computational equations for forty substances.* Stanford: Stanford
         University, 1979. Print.
 
-    For more details, see classes Cantera::PureFluid and tpx::CarbonDioxide in
+    For more details, see classes :ct:PureFluid and tpx::CarbonDioxide in
     the Cantera C++ source code documentation.
     """
     return PureFluid('liquidvapor.yaml', 'carbon-dioxide')
@@ -177,7 +183,7 @@ def Heptane():
         computational equations for forty substances.* Stanford: Stanford
         University, 1979. Print.
 
-    For more details, see classes Cantera::PureFluid and tpx::Heptane in the
+    For more details, see classes :ct:PureFluid and tpx::Heptane in the
     Cantera C++ source code documentation.
     """
     return PureFluid('liquidvapor.yaml', 'heptane')
diff --git a/interfaces/cython/cantera/test/test_purefluid.py b/interfaces/cython/cantera/test/test_purefluid.py
index 57198ea7832..8913204f76a 100644
--- a/interfaces/cython/cantera/test/test_purefluid.py
+++ b/interfaces/cython/cantera/test/test_purefluid.py
@@ -358,15 +358,15 @@ def test_phase_of_matter(self):
         self.assertEqual(co2.phase_of_matter, "gas")
 
     def test_water_backends(self):
-        w = ct.Water(backend='default')
+        w = ct.Water(backend='Reynolds')
         self.assertEqual(w.thermo_model, 'PureFluid')
-        w = ct.Water(backend='iapws95')
-        self.assertEqual(w.thermo_model, 'WaterSSTP')
+        w = ct.Water(backend='IAPWS95')
+        self.assertEqual(w.thermo_model, 'liquid-water-IAPWS95')
         with self.assertRaisesRegex(KeyError, 'Unknown backend'):
             ct.Water('foobar')
 
     def test_water_iapws(self):
-        w = ct.Water(backend='iapws95')
+        w = ct.Water(backend='IAPWS95')
         self.assertNear(w.critical_density, 322.)
         self.assertNear(w.critical_temperature, 647.096)
         self.assertNear(w.critical_pressure, 22064000.0)
@@ -390,9 +390,9 @@ def test_water_iapws(self):
         self.assertEqual(w.phase_of_matter, "liquid")
         w.TP = w.T, w.P_sat
         self.assertEqual(w.phase_of_matter, "liquid")
-        with self.assertRaisesRegex(ct.CanteraError, "Not implemented"):
+        with self.assertRaisesRegex(ct.CanteraError, "assumes liquid phase"):
             w.TP = 273.1599999, ct.one_atm
-        with self.assertRaisesRegex(ct.CanteraError, "Not implemented"):
+        with self.assertRaisesRegex(ct.CanteraError, "assumes liquid phase"):
             w.TP = 500, ct.one_atm
 
 
diff --git a/src/thermo/WaterSSTP.cpp b/src/thermo/WaterSSTP.cpp
index b252746a2f4..85926fcfd38 100644
--- a/src/thermo/WaterSSTP.cpp
+++ b/src/thermo/WaterSSTP.cpp
@@ -282,8 +282,8 @@ void WaterSSTP::setPressure(doublereal p)
             dens = 1000.;
         } else if (!m_allowGasPhase) {
             throw CanteraError("WaterSSTP::setPressure",
-                               "Not implemented: pressure p = {} lies below\n"
-                               "the saturation pressure (P_sat = {}).", p, pp);
+                "Model assumes liquid phase; pressure p = {} lies below\n"
+                "the saturation pressure (P_sat = {}).", p, pp);
         }
     }
 
@@ -340,9 +340,8 @@ void WaterSSTP::setTemperature(const doublereal temp)
 {
     if (temp < 273.16) {
         throw CanteraError("WaterSSTP::setTemperature",
-                           "Not implemented: temperature T = {} lies below\n"
-                           "the triple point temperature (T_triple = 273.16).",
-                           temp);
+            "Model assumes liquid phase; temperature T = {} lies below\n"
+            "the triple point temperature (T_triple = 273.16).", temp);
     }
     Phase::setTemperature(temp);
     m_sub.setState_TR(temp, density());
diff --git a/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp b/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp
index 13a9530225b..26c9683bec4 100644
--- a/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp
+++ b/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp
@@ -21,7 +21,7 @@ int main()
 #endif
     double pres;
     try {
-        ThermoPhase* w = newPhase("liquidvapor.yaml", "water-iapws95");
+        ThermoPhase* w = newPhase("liquidvapor.yaml", "liquid-water-IAPWS95");
         (dynamic_cast<WaterSSTP*>(w))->allowGasPhase(true);
 
         /*

From 4b3bf78ca07b109d52cbad577003ec8e3da53f5b Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Sun, 6 Sep 2020 14:01:12 -0500
Subject: [PATCH 13/14] [thermo] Avoid spurious WaterPropsIAPWS::density
 failures

Some initial guesses fail (see GitHUb issue #577, or starting with an initial
density guess equl to the critical density); running an alternative initial
guess prevents spurious failures (fix is a band-aid).
---
 src/thermo/WaterPropsIAPWS.cpp | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/thermo/WaterPropsIAPWS.cpp b/src/thermo/WaterPropsIAPWS.cpp
index 3f373cef0d2..9eee1dfc33d 100644
--- a/src/thermo/WaterPropsIAPWS.cpp
+++ b/src/thermo/WaterPropsIAPWS.cpp
@@ -83,9 +83,6 @@ doublereal WaterPropsIAPWS::density(doublereal temperature, doublereal pressure,
         // Catch critical point, as no solution is found otherwise
         setState_TR(temperature, Rho_c);
         return Rho_c;
-    } else if (fabs(rhoguess - Rho_c) / Rho_c < 1.e-8) {
-        // Starting a search with the critical density would fail
-        rhoguess *= .9;
     }
     doublereal deltaGuess = 0.0;
     if (rhoguess == -1.0) {
@@ -117,6 +114,11 @@ doublereal WaterPropsIAPWS::density(doublereal temperature, doublereal pressure,
     deltaGuess = rhoguess / Rho_c;
     setState_TR(temperature, rhoguess);
     doublereal delta_retn = m_phi.dfind(p_red, tau, deltaGuess);
+    if (delta_retn <= 0) {
+        // No solution found for first initial guess; perturb initial guess once
+        // to avoid spurious failures (band-aid fix)
+        delta_retn = m_phi.dfind(p_red, tau, 0.9 * deltaGuess);
+    }
     doublereal density_retn;
     if (delta_retn > 0.0) {
         delta = delta_retn;

From 62f9d7d1a631126592d5045e8e57126739eee8c1 Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Fri, 29 Jan 2021 10:24:09 -0600
Subject: [PATCH 14/14] Mark _allowGasPhase override as not intended for
 general use

---
 include/cantera/thermo/WaterSSTP.h                   | 2 +-
 test_problems/cathermo/testWaterTP/testWaterSSTP.cpp | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/cantera/thermo/WaterSSTP.h b/include/cantera/thermo/WaterSSTP.h
index 410a43b8342..e6850d5a9a7 100644
--- a/include/cantera/thermo/WaterSSTP.h
+++ b/include/cantera/thermo/WaterSSTP.h
@@ -247,7 +247,7 @@ class WaterSSTP : public SingleSpeciesTP
      *  member function is to check the thermodynamic consistency of the
      *  underlying WaterProps class with ideal-gas thermo functions.
      */
-    void allowGasPhase(bool flag) { m_allowGasPhase = flag; }
+    void _allowGasPhase(bool flag) { m_allowGasPhase = flag; }
 
 protected:
     /**
diff --git a/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp b/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp
index 26c9683bec4..54066c47ee4 100644
--- a/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp
+++ b/test_problems/cathermo/testWaterTP/testWaterSSTP.cpp
@@ -22,7 +22,7 @@ int main()
     double pres;
     try {
         ThermoPhase* w = newPhase("liquidvapor.yaml", "liquid-water-IAPWS95");
-        (dynamic_cast<WaterSSTP*>(w))->allowGasPhase(true);
+        (dynamic_cast<WaterSSTP*>(w))->_allowGasPhase(true);
 
         /*
          * Print out the triple point conditions