Add Valve block with Cv pressure-drop flow equation

Author: milanofthe

src/pathsim_chem/process/valve.py

@@ -0,0 +1,58 @@
+#########################################################################################
+##
+##                              Pressure-Drop Valve Block
+##
+#########################################################################################
+
+# IMPORTS ===============================================================================
+
+import numpy as np
+
+from pathsim.blocks.function import Function
+
+# BLOCKS ================================================================================
+
+class Valve(Function):
+    """Algebraic pressure-drop valve with standard flow equation.
+
+    Models an isenthalpic valve (no temperature change for liquids)
+    with flow proportional to the square root of the pressure drop.
+
+    Mathematical Formulation
+    -------------------------
+    .. math::
+
+        F = C_v \\sqrt{|P_{in} - P_{out}|} \\cdot \\mathrm{sign}(P_{in} - P_{out})
+
+    .. math::
+
+        T_{out} = T_{in}
+
+    Parameters
+    ----------
+    Cv : float
+        Valve flow coefficient. Must be positive.
+    """
+
+    input_port_labels = {
+        "P_in":  0,
+        "P_out": 1,
+        "T_in":  2,
+    }
+
+    output_port_labels = {
+        "F":     0,
+        "T_out": 1,
+    }
+
+    def __init__(self, Cv=1.0):
+        if Cv <= 0:
+            raise ValueError(f"'Cv' must be positive but is {Cv}")
+
+        self.Cv = Cv
+        super().__init__(func=self._eval)
+
+    def _eval(self, P_in, P_out, T_in):
+        dP = P_in - P_out
+        F = self.Cv * np.sqrt(np.abs(dP)) * np.sign(dP)
+        return (F, T_in)

tests/process/test_valve.py

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+########################################################################################
+##
+##                                  TESTS FOR
+##                             'process.valve.py'
+##
+########################################################################################
+
+# IMPORTS ==============================================================================
+
+import unittest
+import numpy as np
+
+from pathsim_chem.process import Valve
+
+
+# TESTS ================================================================================
+
+class TestValve(unittest.TestCase):
+    """Test the pressure-drop valve block."""
+
+    def test_init_default(self):
+        """Test default Cv."""
+        V = Valve()
+        self.assertEqual(V.Cv, 1.0)
+
+    def test_init_custom(self):
+        """Test custom Cv."""
+        V = Valve(Cv=5.0)
+        self.assertEqual(V.Cv, 5.0)
+
+    def test_init_validation(self):
+        """Test input validation."""
+        with self.assertRaises(ValueError):
+            Valve(Cv=0)
+        with self.assertRaises(ValueError):
+            Valve(Cv=-1)
+
+    def test_port_labels(self):
+        """Test port label definitions."""
+        self.assertEqual(Valve.input_port_labels["P_in"], 0)
+        self.assertEqual(Valve.input_port_labels["P_out"], 1)
+        self.assertEqual(Valve.input_port_labels["T_in"], 2)
+        self.assertEqual(Valve.output_port_labels["F"], 0)
+        self.assertEqual(Valve.output_port_labels["T_out"], 1)
+
+    def test_forward_flow(self):
+        """Flow should be positive when P_in > P_out."""
+        V = Valve(Cv=2.0)
+        V.inputs[0] = 200000.0  # P_in
+        V.inputs[1] = 100000.0  # P_out
+        V.inputs[2] = 350.0     # T_in
+
+        V.update(None)
+
+        F = V.outputs[0]
+        self.assertGreater(F, 0)
+        expected = 2.0 * np.sqrt(100000.0)
+        self.assertAlmostEqual(F, expected, places=4)
+
+    def test_reverse_flow(self):
+        """Flow should be negative when P_in < P_out."""
+        V = Valve(Cv=2.0)
+        V.inputs[0] = 100000.0  # P_in
+        V.inputs[1] = 200000.0  # P_out
+        V.inputs[2] = 350.0
+
+        V.update(None)
+
+        F = V.outputs[0]
+        self.assertLess(F, 0)
+
+    def test_zero_dp(self):
+        """No flow when pressures are equal."""
+        V = Valve(Cv=2.0)
+        V.inputs[0] = 101325.0
+        V.inputs[1] = 101325.0
+        V.inputs[2] = 350.0
+
+        V.update(None)
+
+        self.assertAlmostEqual(V.outputs[0], 0.0)
+
+    def test_temperature_passthrough(self):
+        """Temperature should pass through unchanged (isenthalpic)."""
+        V = Valve()
+        V.inputs[0] = 200000.0
+        V.inputs[1] = 100000.0
+        V.inputs[2] = 375.0
+
+        V.update(None)
+
+        self.assertAlmostEqual(V.outputs[1], 375.0)
+
+
+# RUN TESTS LOCALLY ====================================================================
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)