Refrigerant Migration Modeling During Shut-down And Start-up Cycling Transients

Refrigerant mass migration and redistribution have been regarded as factors influencing the performance of air conditioning and refrigeration systems. This paper presents a dynamic model of an R134a automotive A/C system that is able to capture the shut-down and start-up cycling dynamics including the refrigerant mass migration transients. Building upon recent work (Li and Alleyne, 2010), the heat exchangers are developed using a switched moving-boundary modeling framework, which maintains constant model structures but accommodates different model representations. Thermosys, a Matlab/Simulink toolbox, is introduced to simulate system transient behaviors. Model validations against experimental data show that the developed dynamic model can well predict the migration performance of the refrigerant mass across the components during shut-down transients, and the resulting refrigerant redistribution transients at start-up operations. The qualitative accuracy of the validation results demonstrates the potential of this dynamic modeling approach for control design and diagnosis in improving system start-up performance.