Abstract:

Current heat exchanger simulation models typically divide the condenser into three regimes (desuperheating, twophase and subcooled) and assume that condensation does not start until the bulk refrigerant flow reaches a state of saturated vapor. However, plenty of experiments have verified that condensation can occur much earlier than that when the tube wall surface temperature drops below the dew point of refrigerant even though the bulk flow is still superheated. This phenomenon is called wet-wall desuperheating (also referred to as wet-desuperheating, or condensation from desuperheated vapor in some publications). Wet-wall desuperheating is rarely modelled in the extant heat exchanger simulations due to lack of understanding in its physical process. However, neglecting this important phenomenon may lead to substantial performance prediction errors. This paper proposes a new fin-and-tube condenser heat exchanger model to bridge the research gap. In the proposed model, the heat exchanger is divided into four regimes: dry-wall desuperheating, wet-wall desuperheating, two-phase condensation and subcooled. The existence of dry-wall desuperheating and the onset point of wet-wall desuperheating are determined by rigorous algorithms. Boundaries between different flow regimes are captured to eliminate numerical discontinuities. A tubeby-tube analysis is adopted to allow for the simulation of complex tube circuitries. Simulation studies are performed to demonstrate the capabilities of the proposed model. The results show that wet-wall desuperheating always exists in the condenser with refrigerant vapor entering at the inlet, and neglecting the phenomenon can lead to significant prediction errors for heat exchanger performance.