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## Engine Cooling System

This example shows how to model a basic engine cooling system using custom thermal liquid blocks. A fixed-displacement pump drives water through the cooling circuit. Heat from the engine is absorbed by the water coolant and dissipated through the radiator. The system temperature is regulated by the thermostat, which diverts flow to the radiator only when the temperature is above a threshold.

The custom thermal liquid blocks include the Fixed-Displacement Pump, the Fluid Jacket, the Radiator, and the Thermostat. Click on the source code link on the block dialog to inspect the code and see how existing Thermal Liquid Library blocks can be modified to suit a specific application.

The Fluid Jacket and the Radiator are modifications of the Pipe (TL) block. These components represent an internal volume of liquid to model the effects of dynamic compressibility and thermal capacity using the mass and energy conservation equations. Default priorities for the pressure and temperature are set to high to provide initial conditions for the liquid state.

The Fixed-Displacement Pump is a modification of the Mass Flow Rate Source (TL) block. The Thermostat is a modification of the Local Restriction (TL) block. Both components are assumed to contain negligible volume of liquid. Therefore, they are assumed quasi-steady.

All four components inherit from foundation.thermal_liquid.two_port_dynamic or foundation.thermal_liquid.two_port_steady base classes, which implements common equations to calculate the energy flow rate based on a smoothed upwind method. This method allows energy to be convected downstream, enabling the proper propagation of information throughout the thermal liquid network.

### Simulation Results from Simscape Logging

These plots show the effect of opening the thermostat in the engine cooling system. The temperature of the piston climbs steadily until the thermostat opens. At that point, the flow of coolant through the radiator climbs sharply and the flow of coolant through the bypass hose decreases. Because coolant passing through the radiator releases heat to the atmosphere, the piston temperature rises more slowly.

This plot shows the density of the coolant at different locations in the cooling system over time. The density of the coolant varies throughout the network based on the local temperature and pressure.

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