Prevent mixture calculations with starting value of 0 K

src/tespy/components/heat_exchangers/base.py

@@ -381,10 +381,10 @@ def calculate_td_log(self):
         o2 = self.outl[1]
 
         # temperature value manipulation for convergence stability
-        T_i1 = i1.calc_T(T0=i1.T.val_SI)
-        T_i2 = i2.calc_T(T0=i2.T.val_SI)
-        T_o1 = o1.calc_T(T0=o1.T.val_SI)
-        T_o2 = o2.calc_T(T0=o2.T.val_SI)
+        T_i1 = i1.calc_T()
+        T_i2 = i2.calc_T()
+        T_o1 = o1.calc_T()
+        T_o2 = o2.calc_T()
 
         if T_i1 <= T_o2:
             T_i1 = T_o2 + 0.01
@@ -581,8 +581,8 @@ def ttd_u_func(self):
         """
         i = self.inl[0]
         o = self.outl[1]
-        T_i1 = i.calc_T(T0=i.T.val_SI)
-        T_o2 = o.calc_T(T0=o.T.val_SI)
+        T_i1 = i.calc_T()
+        T_o2 = o.calc_T()
         return self.ttd_u.val - T_i1 + T_o2
 
     def ttd_u_func_doc(self, label):
@@ -636,8 +636,8 @@ def ttd_l_func(self):
         """
         i = self.inl[1]
         o = self.outl[0]
-        T_i2 = i.calc_T(T0=i.T.val_SI)
-        T_o1 = o.calc_T(T0=o.T.val_SI)
+        T_i2 = i.calc_T()
+        T_o1 = o.calc_T()
         return self.ttd_l.val - T_o1 + T_i2
 
     def ttd_l_func_doc(self, label):

src/tespy/components/heat_exchangers/condenser.py

@@ -327,9 +327,9 @@ def calculate_td_log(self):
         o2 = self.outl[1]
 
         T_i1 = i1.calc_T_sat()
-        T_i2 = i2.calc_T(T0=i2.T.val_SI)
-        T_o1 = o1.calc_T(T0=o1.T.val_SI)
-        T_o2 = o2.calc_T(T0=o2.T.val_SI)
+        T_i2 = i2.calc_T()
+        T_o1 = o1.calc_T()
+        T_o2 = o2.calc_T()
 
         if T_i1 <= T_o2 and not i1.T.is_set:
             T_i1 = T_o2 + 0.5
@@ -452,7 +452,7 @@ def ttd_u_func(self):
         i = self.inl[0]
         o = self.outl[1]
         T_i1 = i.calc_T_sat()
-        T_o2 = o.calc_T(T0=self.outl[1].T.val_SI)
+        T_o2 = o.calc_T()
         return self.ttd_u.val - T_i1 + T_o2
 
     def ttd_u_func_doc(self, label):

src/tespy/components/heat_exchangers/parabolic_trough.py

@@ -274,7 +274,7 @@ def energy_group_func(self):
         i = self.inl[0]
         o = self.outl[0]
 
-        T_m = 0.5 * (i.calc_T(T0=i.T.val_SI) + o.calc_T(T0=o.T.val_SI))
+        T_m = 0.5 * (i.calc_T() + o.calc_T())
 
         iam = (
             1 - self.iam_1.val * abs(self.aoi.val)

src/tespy/components/heat_exchangers/simple.py

@@ -535,8 +535,8 @@ def kA_group_func(self):
         i = self.inl[0]
         o = self.outl[0]
 
-        ttd_1 = i.calc_T(T0=i.T.val_SI) - self.Tamb.val_SI
-        ttd_2 = o.calc_T(T0=o.T.val_SI) - self.Tamb.val_SI
+        ttd_1 = i.calc_T() - self.Tamb.val_SI
+        ttd_2 = o.calc_T() - self.Tamb.val_SI
 
         # For numerical stability: If temperature differences have
         # different sign use mean difference to avoid negative logarithm.
@@ -651,8 +651,8 @@ def kA_char_group_func(self):
         # For numerical stability: If temperature differences have
         # different sign use mean difference to avoid negative logarithm.
 
-        ttd_1 = i.calc_T(T0=i.T.val_SI) - self.Tamb.val_SI
-        ttd_2 = o.calc_T(T0=o.T.val_SI) - self.Tamb.val_SI
+        ttd_1 = i.calc_T() - self.Tamb.val_SI
+        ttd_2 = o.calc_T() - self.Tamb.val_SI
 
         if (ttd_1 / ttd_2) < 0:
             td_log = (ttd_2 + ttd_1) / 2

src/tespy/components/heat_exchangers/solar_collector.py

@@ -231,7 +231,7 @@ def energy_group_func(self):
         i = self.inl[0]
         o = self.outl[0]
 
-        T_m = 0.5 * (i.calc_T(T0=i.T.val_SI) + o.calc_T(T0=o.T.val_SI))
+        T_m = 0.5 * (i.calc_T() + o.calc_T())
 
         return (
             i.m.val_SI * (o.h.val_SI - i.h.val_SI)

src/tespy/components/nodes/separator.py

@@ -299,9 +299,9 @@ def energy_balance_func(self):
                 \forall j \in \text{outlets}
         """
         residual = []
-        T_in = self.inl[0].calc_T(T0=300)
+        T_in = self.inl[0].calc_T()
         for o in self.outl:
-            residual += [T_in - o.calc_T(T0=300)]
+            residual += [T_in - o.calc_T()]
         return residual
 
     def energy_balance_func_doc(self, label):

src/tespy/components/turbomachinery/compressor.py

@@ -374,7 +374,7 @@ def char_map_pr_func(self):
         i = self.inl[0]
         o = self.outl[0]
 
-        x = np.sqrt(i.T.design / i.calc_T(T0=i.T.val_SI))
+        x = np.sqrt(i.T.design / i.calc_T())
         y = (i.m.val_SI * i.p.design) / (i.m.design * i.p.val_SI * x)
 
         yarr, zarr = self.char_map_pr.char_func.evaluate_x(x)
@@ -477,7 +477,7 @@ def char_map_eta_s_func(self):
         i = self.inl[0]
         o = self.outl[0]
 
-        x = np.sqrt(i.T.design / i.calc_T(T0=i.T.val_SI))
+        x = np.sqrt(i.T.design / i.calc_T())
         y = (i.m.val_SI * i.p.design) / (i.m.design * i.p.val_SI * x)
 
         yarr, zarr = self.char_map_eta_s.char_func.evaluate_x(x)

src/tespy/connections/connection.py

@@ -737,6 +737,8 @@ def primary_ref_deriv(self, k, **kwargs):
             self.jacobian[k, ref.obj.get_attr(variable).J_col] = -ref.factor
 
     def calc_T(self, T0=None):
+        if T0 is None:
+            T0 = self.T.val_SI
         return T_mix_ph(self.p.val_SI, self.h.val_SI, self.fluid_data, self.mixing_rule, T0=T0)
 
     def T_func(self, k, **kwargs):

src/tespy/tools/data_containers.py

@@ -12,8 +12,6 @@
 
 SPDX-License-Identifier: MIT
 """
-import collections
-
 import numpy as np
 
 from tespy.tools import logger

src/tespy/tools/fluid_properties/helpers.py

@@ -67,7 +67,7 @@ def get_molar_fractions(fluid_data):
 def inverse_temperature_mixture(p=None, target_value=None, fluid_data=None, T0=None, f=None):
     # calculate the fluid properties for fluid mixtures
     valmin, valmax = get_mixture_temperature_range(fluid_data)
-    if T0 is None:
+    if T0 is None or T0 == 0 or np.isnan(T0):
         T0 = (valmin + valmax) / 2.0
 
     function_kwargs = {