MODELING OF PHASE CHANGE WITHIN A WAX ELEMENT THERMOSTAT EMBEDDED IN AN AUTOMOTIVE COOLING SYSTEM

Paper #:
  • 2017-01-0131

Published:
  • 2017-03-28
Abstract:
In an automotive cooling circuit, the wax melting process determines the net and time history of the energy transfer between the engine and its environment. A numerical process that gives insight into the mixing process outside the wax chamber, the wax melting process, and the effect on the poppet valve displacement will be advantageous to both the engine and automotive system design. A fully three dimensional, transient, system level simulation of an inlet controlled automotive cooling circuit is undertaken in this paper. A proprietary CFD algorithm, PumpLinx®, is used to solve this complex problem. A two-phase model is developed in PumpLinx® to simulate the wax melting process. The hysteresis effect of the wax melting process is also considered in the simulation. The coolant circulated using a centrifugal pump, which operates via a constant ratio with respect to the engine speed, is modeled as part of the computational domain. A multiple reference frame approach is utilized in modeling the centrifugal pump. The coolant absorbs engine heat and is subsequently passed through multiple branches, one that contains a radiator, another with a heater core, and a final one that directly takes the coolant back to the thermostat assembly through a bypass valve. For the computational model, the thermostat valve, dynamically responds to the wax melting process. Also, the bypass valve is modeled in the computational simulation as a dynamic response valve based on fluid and spring forces acting on the valve. In order to conserve the mesh size, and save simulation running times, the heater core, engine and radiator, are modeled as simplistic geometries, with the pressure drops across them modeled with porous pressure drop models. The experimentally measured temperatures, converted to total heat source for each volume, are used as boundary conditions in the heater core, radiator and engine, for solving the energy balance equation. For different engine speeds, based on the testing, the wax freezing and melting processes are simulated. The simulation results for the flow rates through the three branches of the circuit, and the temperature drops across the components, compare favorably with the experimental vehicle tests. The viability of this model is further enhanced with the run times of only 12 hours of wall clock time to run 240 secs of cycle time, providing a viable platform for the code coupling with a 1D solver.
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