On three forms of momentum equation in transient modeling of residential refrigeration systems

The transient model of thermal components usually consists of three basic governing equations: continuity equation, energy equation, and momentum equation. For different reasons, the momentum equation is used in three different forms: transient, steady-state, and zero pressure drop. In this paper, the three forms of momentum equation are numerically studied and compared at both component level and system level, particularly in the residential applications. It is found that the results with transient and steady-state momentum equation are pretty close at both levels. Therefore, the steady-state momentum equation is recommended in refrigeration system and component transient modeling because of the robustness and the computation speed. To consider only the system-level cases, it is also found that the transient results without pressure drop give very close estimation of control parameters in comparison with the results taking account into the transient or steady-state pressure drop.