Theoretical investigation into instability of a refrigeration system with an evaporator controlled by a thermostatic expansion valve

A theoretical model is developed and solved to investigate the instability of a refrigeration system with an evaporator controlled by a thermostatic expansion valve. An evaporator time constant is used to account for the delay of the liquid refrigerant distribution along the two phase region. Results show that there is an evaporator critical time constant, below which the system operates in a stable manner. This critical time constant is found to decrease with decreasing the partial load and to increase with increasing the contact thermal resistance and the two-phase region heat transfer coefficient. The bulb size is also found to have a great effect on the stability.