Optimization Design and Numerical Simulation of Variable Tube Diameter Heat Exchanger for Split Air Conditioning Indoor Unit

Energy shortage has become one of the most concerning issues in the world today, and improving energy utilization efficiency is a key area of research for experts and scholars worldwide. Small-diameter heat exchangers offer advantages such as reduced material usage, lower refrigerant charge, and compact structure. However, they also face challenges, including increased refrigerant pressure drop and smaller heat transfer area inside the tubes. This paper combines the advantages and disadvantages of both small and large-diameter tubes and proposes a combined-diameter heat exchanger, consisting of large and small diameters, for use in the indoor units of split-type air conditioners. There are relatively few studies in this area. In this paper, A theoretical and numerical computation method is employed to establish a theoretical-numerical calculation model, and its reliability is verified through experiments. Using this model, the optimal combined diameters and flow path design for a combined-diameter heat exchanger using R32 as the working fluid are derived. The results show that the heat transfer performance of all combined diameter configurations improves by 2.79% to 8.26% compared to the baseline design, with the coefficient of performance (COP) increasing from 4.15 to 4.27~4.5. These designs can save copper material, but at the cost of an increase in pressure drop by 66.86% to 131.84%. The scheme IIIH, using R32, is the optimal combined-diameter and flow path configuration that balances both heat transfer performance and economic cost.