An improved moving-boundary heat exchanger model using the variable time step method

Moving-boundary heat exchanger model is a fast low order model. In this paper, an improved moving-boundary heat exchanger model is developed to provide a stable fast model for the research on control strategy of refrigeration system. In this model, the treatment of each iterative time step is added. Before the calculation of the state variables of the next step, the maximum time step of the next iterative is determined by the change state variable values in per unit time of the current iterate. Then, the time step of the next iterative is determined by the maximum time step and the setting time step. Meanwhile, in order to meet the need of the research on control strategy, the independent variable is employed with temperature variable instead of pressure and enthalpy variable in the calculation of refrigerant state parameters. The simulation results shows that the present model can well predict the transient behaviours of heat exchangers using any setting value of time step, and the computing speed of the present model is faster than the speed of original model.