Moving Boundary Heat Exchanger Model and Validation Procedure

Abstract

Abstract A moving-boundary model for condenser and evaporator heat exchangers in vapour compression cycles is presented. The model is formulated as system of differential and algebraic equations suitable for an implementation in the mod- eling language Modelica. The main idea of moving boundary models is to in- troduce separate control volumes for two-phase and single phase fluid flow. The boundaries of these control volumes or zones change dynamically. The model consists of a maximum of three zones: superheating, subcooling and condens- ing/evaporating. During simulation the number of zones dynamically changes by switching between different equations. Occurring discontinuities are formulated in a way that allows the simulation tool to handle them numerically stable. The models are well-suited for control design purposes as well as for model based con- trol. Additionally, a validation procedure is presented. The zone lengths, which are differential states of the model, are measured directly by infrared thermogra- phy. This method allows a direct comparison of simulated and measured values of all state variables.