The aim of this study is to optimize the design of a screw heat exchanger (SHX) in terms of varying coil aspect ratio (CAR) as a liquid-suction heat exchanger (LSHE) in a vapor compression refrigeration system through Computational Fluid Dynamics (CFD) simulation. The novelty of this study is that it focuses on the fluid-to-fluid heat transfer of SHX to measure its heat transfer effectiveness as compared to many research studies that focus only on helical duct heat exchanger under constant wall temperature and constant heat flux. Optimization of the SHX was done through conjugate heat transfer in a CFD model. High confidence on the computational package was determined as the results of the package on heat transfer between water flows through a shell-and-coil heat exchanger match well with available experimental data of the same setup in related literature.
The performance of SHX with square coil section (SHXSCS) was compared to that of the SHX with circular coil section (SHXCCS). The optimum SHXSCS was then compared to a commercially available LSHE in the form of tube-in-tube heat exchanger (TTHE) which is the most commonly used LSHE in vapor compression refrigeration systems.
The SHXSCS has nominal degrees of superheat of 22.17 °C and nominal degrees of subcool of 17.63 °C. The ratio of the heat of superheating to that of subcooling is seen to increase with increasing CAR and NTU. The RE of SHXSCS is larger by an average of 3.87%, 18.25% and 26.46% compared to those of the SHXCCS, TTHE and the standard vapor compression cycle (VCC), respectively. The COP of the SHXSCS is 2.55%, 10.74% and 5.94% higher than those of the SHXCCS, TTHE and the standard VCC, respectively. The SHXSCS is more capable than SHXCCS in splitting the heat due to the less complicated square cross sections of flows and even less interface materials for heat transfer. Moreover, the SHXSCS is more effective in splitting the heat from subcooling into moderated superheating and largely to the surounding compared to the TTHE mainly due to longer length of interaction of the flows.