improves compressor initialization (#1350)

* improves compressor initialization

* pylint

* minor modifications

* pylint

* renaming state_args

* pylint

* minor modification

---------

Co-authored-by: Keith Beattie <ksbeattie@lbl.gov>

watertap/unit_models/mvc/components/compressor.py

@@ -18,6 +18,7 @@
     units as pyunits,
 )
 from pyomo.common.config import ConfigBlock, ConfigValue, In
+from copy import copy
 
 # Import IDAES cores
 from idaes.core import (
@@ -300,19 +301,44 @@ def initialize_build(
                 else:
                     state_args[k] = state_dict[k].value
 
+        state_args_out_isentropic = copy(state_args)
+        state_args_out_isentropic["pressure"] = (
+            state_args["pressure"] * self.pressure_ratio.value * pyunits.Pa
+        )
+        state_args_out_isentropic["temperature"] = (
+            state_args["temperature"]
+            * self.pressure_ratio.value ** (1 - 1 / 1.3)
+            * pyunits.K
+        )
+
         self.properties_isentropic_out.initialize(
             outlvl=outlvl,
             optarg=optarg,
             solver=solver,
-            state_args=state_args,
+            state_args=state_args_out_isentropic,
         )
         init_log.info_high("Initialization Step 2 Complete.")
 
+        state_args_out_actual = copy(state_args_out_isentropic)
+        # assume a constant vapor specific heat for initialization:
+        state_args_out_actual["temperature"] = (
+            state_args_out_isentropic["temperature"]
+            - state_args["temperature"] * pyunits.K
+        ) / self.efficiency.value + state_args["temperature"] * pyunits.K
+
+        self.control_volume.properties_out.initialize(
+            outlvl=outlvl,
+            optarg=optarg,
+            solver=solver,
+            state_args=state_args_out_actual,
+        )
+        init_log.info_high("Initialization Step 3 Complete.")
+
         # ---------------------------------------------------------------------
         # Solve unit
         with idaeslog.solver_log(solve_log, idaeslog.DEBUG) as slc:
             res = opt.solve(self, tee=slc.tee)
-        init_log.info_high("Initialization Step 3 {}.".format(idaeslog.condition(res)))
+        init_log.info_high("Initialization Step 4 {}.".format(idaeslog.condition(res)))
 
         # ---------------------------------------------------------------------
         # Release Inlet state

watertap/unit_models/mvc/tests/test_mvc.py

@@ -25,7 +25,6 @@
 import idaes.core.util.scaling as iscale
 import idaes.logger as idaeslog
 from idaes.core.util.initialization import propagate_state
-from idaes.core.util.exceptions import InitializationError
 
 # Import components
 from watertap.unit_models.mvc.components import Evaporator
@@ -106,8 +105,7 @@ def specify(m):
     m.fs.evaporator.area.fix(400)  # m^2
 
     # Compressor
-    m.fs.compressor.pressure_ratio = 2
-    m.fs.compressor.control_volume.work.fix(5.8521e05)
+    m.fs.compressor.pressure_ratio.fix(2)
     m.fs.compressor.efficiency.fix(0.8)
 
 
@@ -123,10 +121,8 @@ def initialize(m, solver=None):
 
     # initialize compressor
     propagate_state(m.fs.s01)
-    try:
-        m.fs.compressor.initialize(outlvl=idaeslog.DEBUG)
-    except InitializationError:
-        pass
+
+    m.fs.compressor.initialize(outlvl=idaeslog.DEBUG)
 
     # initialize condenser
     propagate_state(m.fs.s02)
@@ -150,27 +146,32 @@ def test_mvc():
 
     results = solver.solve(m, tee=True)
     assert_optimal_termination(results)
+    brine_blk = m.fs.evaporator.properties_brine[0]
 
     m.fs.compressor.report()
     m.fs.condenser.report()
     m.fs.evaporator.display()
-    brine_blk = m.fs.evaporator.properties_brine[0]
+
     # evaporator values
     assert brine_blk.pressure.value == pytest.approx(1.9849e4, rel=1e-3)
-    assert m.fs.evaporator.lmtd.value == pytest.approx(30.50, rel=1e-3)
-    assert m.fs.evaporator.heat_transfer.value == pytest.approx(1.220e7, rel=1e-3)
+    assert m.fs.evaporator.lmtd.value == pytest.approx(26.1769036038, rel=1e-3)
+    assert m.fs.evaporator.heat_transfer.value == pytest.approx(
+        10470761.441558, rel=1e-3
+    )
 
     # compressor values
     compressed_blk = m.fs.compressor.control_volume.properties_out[0]
+
     assert m.fs.compressor.control_volume.work[0].value == pytest.approx(
-        5.8521e5, rel=1e-3
+        500376.0409289, rel=1e-3
     )
-    assert compressed_blk.pressure.value == pytest.approx(3.9656e4, rel=1e-3)
+
+    assert compressed_blk.pressure.value == pytest.approx(39723.543091, rel=1e-3)
     assert compressed_blk.temperature.value == pytest.approx(407.70, rel=1e-3)
 
     # condenser values
     condensed_blk = m.fs.condenser.control_volume.properties_out[0]
     assert m.fs.condenser.control_volume.heat[0].value == pytest.approx(
-        -1.220e7, rel=1e-3
+        -10470761.441558, rel=1e-3
     )
-    assert condensed_blk.temperature.value == pytest.approx(342.20, rel=1e-3)
+    assert condensed_blk.temperature.value == pytest.approx(339.13470452, rel=1e-3)