Constructal design of a shell-and-tube heat exchanger for organic fluid evaporation process

Abstract

A shell-and-tube heat exchanger for organic fluid evaporation process is investigated in this paper. A complex function considering the heat transfer and fluid flow performances of the shell-and-tube heat exchanger is introduced as the optimization objective. For the fixed total heat transfer area of the heat transfer tubes, structure optimizations of the shell-and-tube heat exchanger are conducted based on constructal theory. The results show that the complex function has its minimum with an optimal external diameter of the heat transfer tube. Compared the performances of the shell-and-tube heat exchanger with initial design, the total heat transfer rate, total pumping power and complex function after optimization are decreased by 7.59%, 70.65% and 11.50%, respectively. It illustrates that the complex function sacrifices a certain heat transfer performance and greatly improves the fluid flow performance, which results in an evident reduction of the complex function. Among the discussed seven working fluids, the R152a has the smallest complex function, and the R236fa has the biggest complex function. The complex function has its double minimum with an optimal mass flow rate of the hot water or an optimal total tube number. These illustrate that the overall performance of the shell-and-tube heat exchanger can be further improved by choosing appropriate working fluid, mass flow rate of the hot water and total tube number.