Numerical Simulation On Refrigerant Flow Distribution In Parallel-flow Evaporator And Fin-Side Performance Optimization

The compactness, porosity and efficiency make parallel flow heat exchanger appeared timely as a new type heat exchanger. In this paper, a parallel flow evaporator model was established, and the performances of refrigerant-side flow and air-side heat transfer of parallel flow heat exchanger were numerically investigated.We set the single flat tube as a porous zone considering the varying properties and evaporation phase change process. And the numerical simulation was made on the two-phase flow distribution in the parallel flow evaporator condenser tube. The effects of the relevant structural parameters and operating conditions on the uniformity of the fluid distribution were comparatively analyzed. The simulation results show that the side-in manifold flow distribution was better than the case of end-in. And the inlet tube at the center position of the manifold reaches the optimum uniformity of flow distribution. With the increase of combined depths between flat tube and manifold, the total distribution uniformity of flow first decreases and then increases. The optimal flow distribution uniformity occurs at the combined depth W=0.5. Varing by the inlet mass flow rate and inlet quality, each flat tube of flow distribution uniformity showed the same trend. With the inlet flow increases, the non-uniformity increased sharply with the biggest difference of58.73%. With the increase of the entrance quality, the total flow distribution uniformity was in the increasing trend, but the impact of the entrance quality is relatively much smaller than that of inlet mass flow rate.The model for louver-vortex generator composite fins of the parallel flow evaporator is then developed in the present study. Flow and heat transfer characteristics of the composite fins are simulated numerically in the Re range of200-1200. The results show that with increase of Re, the increases of pressure drop and heat transfer coefficient of full louver fins are the largest, while those fins with composite length ratio (ξ) of1:3are the smallest. Referring to the comprehensive heat transfer performance R=(j/jo)/(f/fo)1/3, it is suggested that within the Re range of200-600, the fins with ξ=1:3are the best, R value of which is13.68%higher than that of full louver fins (the worst among all kinds of fins); For Re=800, the comprehensive heat transfer performances of four fins differ little; For Re=1000-1200, R increases slowly for full louver fins, better than other fins, the largest upgrade of3.11%.The results for the performance of parallel flow evaporator optimization provide evidence and reference for engineering application.