Constructal optimization for an organic fluid shell-and-tube heat exchanger based on entransy theory

Abstract

Based on constructal theory and entransy theory, constructal optimization of a shell-and-tube heat exchanger (STHE) for the organic fluid evaporation process is performed using a complex function as an optimization objective. The complex function is composed of the entransy dissipation rate (EDR) caused by heat transfer and the total pumping power. The total heat transfer rate and heat transfer area are taken as constraints in the optimization. The minimum complex function and optimal external diameter of the heat transfer tube can then be obtained. The results show that, compared to the initial design construct, the optimal construct of the STHE reduces the EDR caused by the heat transfer and complex function by 9.54% and 1.56%, respectively, and increases the total pumping power by 22.40%. This illustrates that an overall performance improvement of the STHE can be realized by substantially reducing the fluid flow performance and significantly decreasing the heat transfer irreversibility. The overall performance of the STHE can be further improved by increasing the total heat transfer area and the mass flow rate of the working fluid and decreasing the inlet temperature of the working fluid, as well as choosing an appropriate total number of heat transfer tubes and an optimal mass flow rate of the hot water. The optimal constructs of the STHE derived from the minimizations of the two complex functions, composed of the EDR and total pumping power, heat transfer rate and total pumping power, are obviously different. New guidelines for the optimal structure designs of STHEs are provided by introducing entransy theory into constructal optimizations of organic fluid STHEs.