Finally re-wrote the Parachor function to be funny SI-compliant.

tests/test_chemical.py

@@ -174,7 +174,7 @@ def test_Chemical_properties_T_dependent():
     assert_allclose(w.Prg, 0.9803087814815961)
 
     assert_allclose(w.solubility_parameter, 47863.51384219548)
-    assert_allclose(w.Parachor, 52.656339998350205)
+    assert_allclose(w.Parachor, 9.363768522707514e-06)
 
 def test_Chemical_properties_T_phase():
     # T-only dependent properties (always or at the moment)
@@ -190,7 +190,7 @@ def test_Chemical_properties_T_phase():
     assert_allclose(w.Z, 0.0007247422467681115)
 
     assert_allclose(w.isobaric_expansion, 0.00027479530461365189, rtol=1E-3)
-    assert_allclose(w.JT, -2.2029508371866032e-07)
+    assert_allclose(w.JT, -2.2029508371866032e-07, rtol=1E-3)
 
     assert_allclose(w.mu, 0.0008537426062537152)
     assert_allclose(w.k, 0.6094991151038377)

tests/test_utils.py

@@ -143,10 +143,11 @@ def test_isentropic_exponent():
     k = isentropic_exponent(33.6, 25.27)
     assert_allclose(k, 1.329639889196676)
 
+
 def test_Parachor():
-    # TODO: replace with a test for a new function
-    P = Parachor(0.02117, 114.22852, 700.03, 5.2609)
-    assert_allclose(P, 352.66655018657565)
+    P = Parachor(100.15888, 800.8088185536124, 4.97865317223119, 0.02672166960656005)
+    assert_allclose(P, 5.088443542210164e-05)
+
 
 def test_phase_select_property():
     assert 150 == phase_select_property(phase='s', s=150, l=10)

thermo/chemical.py

@@ -1619,14 +1619,45 @@ def Prg(self):
 
     @property
     def solubility_parameter(self):
+        r'''Solubility parameter of the chemical at its 
+        current temperature and pressure, in units of Pa^0.5.
+        
+        .. math::
+            \delta = \sqrt{\frac{\Delta H_{vap} - RT}{V_m}}
+        
+        Calculated based on enthalpy of vaporization and molar volume.
+        Normally calculated at STP. For uses of this property, see
+        :obj:`thermo.solubility.solubility_parameter`.
+        
+        Examples
+        --------
+        >>> Chemical('NH3').solubility_parameter
+        24766.329043856073
+        '''
         return solubility_parameter(T=self.T, Hvapm=self.Hvapm, Vml=self.Vml, 
                                     Method=self.solubility_parameter_method, 
                                     CASRN=self.CAS)
 
     @property 
     def Parachor(self):
-        if all((self.sigma, self.MW, self.rhol, self.rhog)):
-            return Parachor(sigma=self.sigma, MW=self.MW, rhol=self.rhol, rhog=self.rhog)
+        r'''Parachor of the chemical at its 
+        current temperature and pressure, in units of N^0.25*m^2.75/mol.
+        
+        .. math::
+            P = \frac{\sigma^{0.25} MW}{\rho_L - \rho_V}
+        
+        Calculated based on surface tension, density of the liquid and gas
+        phase, and molecular weight. For uses of this property, see
+        :obj:`thermo.utils.Parachor`.
+        
+        Examples
+        --------
+        >>> Chemical('octane').Parachor
+        6.291693072841486e-05
+        '''
+        sigma, rhol, rhog = self.sigma, self.rhol, self.rhog
+        if all((sigma, rhol, rhog, self.MW)):
+            return Parachor(sigma=sigma, MW=self.MW, rhol=rhol, rhog=rhog)
         return None
 
     ### Single-phase properties

thermo/thermal_conductivity.py

@@ -998,7 +998,7 @@ def DIPPR9I(ws, ks):
     ----------
     .. [1] Reid, Robert C.; Prausnitz, John M.; Poling, Bruce E. The
        Properties of Gases and Liquids. McGraw-Hill Companies, 1987.
-    .. [2]  Danner, Ronald P, and Design Institute for Physical Property Data.
+    .. [2] Danner, Ronald P, and Design Institute for Physical Property Data.
        Manual for Predicting Chemical Process Design Data. New York, N.Y, 1982.
     '''
     if not none_and_length_check([ks, ws]):  # check same-length inputs

thermo/utils.py

@@ -216,70 +216,66 @@ def int2CAS(i):
     return i[:-3]+'-'+i[-3:-1]+'-'+i[-1]
 
 
+def Parachor(MW, rhol, rhog, sigma):
+    r'''Calculate Parachor for a pure species, using its density in the
+    liquid and gas phases, surface tension, and molecular weight.
 
+    .. math::
+        P = \frac{\sigma^{0.25} MW}{\rho_L - \rho_V}
+    
+    Parameters
+    ----------
+    MW : float
+        Molecular weight, [g/mol]
+    rhol : float
+        Liquid density [kg/m^3]
+    rhog : float
+        Gas density [kg/m^3]
+    sigma : float
+        Surface tension, [N/m]
 
-def Parachor(sigma, MW, rhol, rhog):
-    '''Calculates a Chemical's Parachor according to DIPPR Method.
+    Returns
+    -------
+    P : float
+        Parachor, [N^0.25*m^2.75/mol]
 
-    >>> Parachor(0.02117, 114.22852, 700.03, 5.2609) # Octane; DIPPR: 350.6
-    352.66655018657565
+    Notes
+    -----
+    To convert the output of this function to units of [mN^0.25*m^2.75/kmol], 
+    multiply by 5623.4132519.
+    
+    Values in group contribution tables for Parachor are often listed as 
+    dimensionless, in which they are multiplied by 5623413 and the appropriate
+    units to make them dimensionless.
+    
+    Examples
+    --------
+    Calculating Parachor from a known surface tension for methyl isobutyl 
+    ketone at 293.15 K
+    
+    >>> Parachor(100.15888, 800.8088185536124, 4.97865317223119, 0.02672166960656005)
+    5.088443542210164e-05
+    
+    Converting to the `dimensionless` form:
+    
+    >>> 5623413*5.088443542210164e-05
+    286.14419565030687
+    
+    Compared to 274.9 according to a group contribution method described in
+    [3]_.
+
+    References
+    ----------
+    .. [1] Poling, Bruce E. The Properties of Gases and Liquids. 5th edition.
+       New York: McGraw-Hill Professional, 2000.
+    .. [2] Green, Don, and Robert Perry. Perry's Chemical Engineers' Handbook,
+       8E. McGraw-Hill Professional, 2007.
+    .. [3] Danner, Ronald P, and Design Institute for Physical Property Data.
+       Manual for Predicting Chemical Process Design Data. New York, N.Y, 1982.
     '''
-    rhol, rhog = rhol/1000., rhog/1000.
-    sigma = sigma*1000
-    P = sigma**0.25*MW/(rhol-rhog)
-    return P
-
-
-#def Parachor2(sigma, Vml, Vmg):
-#    r'''Calculate Parachor for a pure species, using its molar volumes in
-#    liquid and vapor form, and surface tension.
-#
-#    .. math::
-#        P = \frac{ \sigma^{0.25} MW}{\rho_L - \rho_V}=\sigma^{0.25} (V_L - V_V)
-#
-#    Parameters
-#    ----------
-#    sigma : float
-#        Surface tension, [N/m]
-#    Vml : float
-#        Liquid molar volume [m^3/mol]
-#    Vmg : float
-#        Gas molar volume [m^3/mol]
-#
-#    Returns
-#    -------
-#    P : float
-#        Parachor, [-]
-#
-#    Notes
-#    -----
-#    Parachor is normally specified in units of [], in which molar volumes must
-#    be converted to mL/mol, and surface tension in mN/m. Pure SI units are:
-#
-#    .. math::
-#        \frac{\text{kg}^{0.25}\cdot\text{meter}^3}
-#        {\text{mole}\cdot \text{second}^{0.5}}
-#
-#    The conversion to pure SI is to multiply by 1.77828e-7.
-#
-#    Examples
-#    --------
-#    Example 12.1 in [1]_.
-#
-#    >>> Parachor(sigma=0.02119, Vml=9.6525097e-05, Vmg=0)
-#    207.09660808998868
-#
-#    References
-#    ----------
-#    .. [1] Poling, Bruce E. The Properties of Gases and Liquids. 5th edition.
-#       New York: McGraw-Hill Professional, 2000.
-#    '''
-#    Vml, Vmg = Vml*1E6, Vmg*1E6
-#    sigma = sigma*1000
-#    P = sigma**0.25/(Vmg-Vml)
-#    return P
-
-#print([Parachor2(sigma=0.02119, Vml=9.6525097e-05, Vmg=0)])
+    rhol, rhog = rhol*1000., rhog*1000. # Convert kg/m^3 to g/m^3
+    return sigma**0.25*MW/(rhol-rhog) # (N/m)**0.25*g/mol/(g/m^3)
+
 
 def property_molar_to_mass(A_molar, MW):  # pragma: no cover
     if A_molar is None: