Computational Fluid Dynamics Study on Exhaust Heat Recovery of Various Spiral Tube Heat Exchangers

Abstract

With the continuous development of internal combustion engine technology, the thermal efficiency of traditional energy vehicles has been difficult to improve, and the heat loss caused by high-temperature exhaust emissions is an important reason for the low thermal efficiency. To utilize the exhaust heat, the aim is to develop various spiral tube heat exchanger designs, namely, constant curvature heat exchanger with baffle and variable curvature heat exchanger. The design has been evaluated by referring to the performance evaluation coefficient (PEC); furthermore, the convection coefficient h has been taken into consideration as well. The idea is to perform numerical studies via computational fluid dynamics package and evaluate the performance of the spiral tube heat exchanger designs. PEC is the relationship between the heat exchange intensity of the heat exchanger and the flow resistance of the working fluid. The results show that the PEC evaluation index of the heat exchanger is the best when the spiral diameter of the heat exchange tube is 120 mm, and with the increase of the tube diameter and pitch, the overall performance of the heat exchanger decreases. The research on heat transfer enhancement of heat exchangers was carried out, and various spiral tube heat exchangers were designed based on the structure of spiral heat exchange tubes. The variable curvature heat exchanger has better overall performance than the baffle constant curvature heat exchanger. Compared to the single-variable curvature and the double-variable curvature, the maximum PEC difference of them does not exceed 0.01, and the double-variable curvature is more sufficient in volume utilization, and it can save about 13% volume. Considering the use requirements of the actual vehicle waste heat recovery system, the double-variable curvature spiral tube heat exchanger is more suitable for practical engineering applications than the single-variable curvature spiral tube heat exchanger.