Variable-dimension optimization study and design of internally finned helically coiled tubes heat exchangers based on numerical simulation and experiment

To improve the heat transfer in the helically coiled tubes, a novel type of internally finned helically coiled tube is proposed. The heat transfer and flow resistance characteristics of internally finned helically coiled tubes are investigated numerically. The empirical correlations to calculate the Nusselt number and friction factor of internally finned helically coiled tubes are summarized. The maximum relative error is not exceeding 18 %. To validate the empirical correlations, a test bench to evaluate the performance of internally finned helically coiled tubes heat exchangers is constructed, with a smooth helically coiled tubes heat exchanger as a comparison. The experimental results indicate that 94 % of the data exhibit a relative error of less than 30 % when compared to the fitting correlations. The heat transfer coefficient of the tube side is increased by approximately 30 %. Based on the validated correlations, a generalized variable-dimension optimization approach is proposed to solve the complex problem of optimizing the design of helically coiled tubes heat exchangers. Taking the area margin, heat transfer area and total cost, the structure of internally finned helically coiled tubes heat exchangers is optimized with different limitation. The optimization results show that the internally finned helically coiled tubes heat exchangers have better performance than smooth helically coiled tubes heat exchangers. A helically coiled tubes heat exchanger has been designed in an engineering project and significant improvements have been achieved in various performance indicators.