In the coolant circuit the thermostatic valve is one of the most important control units to maintain the system’s desired set point temperature. Due to its mechanical technology usually the thermostat has some delay in its reaction, which should be considered in transient cycle simulation. This example is based on the tutorial example ExEngine. The major modification is that it includes a more detailed model for the thermostat, placed in the subsystem “Thermostat”.
The main idea is that a fluid point mass models the wax element including the metal housing of the thermostat. This point mass is responsible for the hysteresis of the thermostat. The mass of the point mass can be adjusted to fit the current application; moreover, also the heat transfer coefficient from the coolant to the mass can be adjusted, even depending on the flow rate. A corresponding characteristic line is prepared (but contains only a single value in this demo example).
The temperature of the mass (i.e., of the wax element) is then taken into a characteristic line in which the lift opening (between 0 and 100%) of the thermostat is calculated. Based on this lift opening two fluid resistances are calculated that have opposite behavior: If the temperature is still low, then the resistance of the bypass will be low, the resistance of the exit to the radiator branch will be high. If the temperature is high, then it is vice versa.
The example is given for a thermostat working as a branch; the method would work in the same way for a thermostat working as a confluence.Usable from release: KULI 8.0-1.04