Problems involved in the shell-side performance of a longitudinal-flow shell-and-tube heat exchanger with decrease in L/D and its solutions

This paper presents a numerical simulation of the fluid flow and heat transfer in the shell-side of a large-scale shell-and-tube heat exchanger with longitudinal flow through porous-medium and distributed-resistance model. Such characteristics as flow field distribution, shell-side pressure drop, heat transfer performance and overall performance factor of the shell-side were studied with change in L/D and Re. It was shown that when L/D decreased from 6.0 to 1.5 with the same Re, the fluid flow maldistribution became intense, pressure drop increased sharply, and that the overall performance factor η decreased sharply. Particularly, when L/D≤ 2.0, the problems became more and more serious. Through a detailed analysis of the pressure field distribution, it was discovered that >80% of the total pressure drop occurred in the region of the inlet and the outlet, where the fluid flow mainly cross the tube bundle. In order to solve the problems, the use of a novel structure of multi-parallel-channel inlet and outlet (MPC) in the shell-side was proposed. A comprehensive investigation showed that MPC is very effective not only in optimizing the fluid flow distribution of the shell-side and enhancing the global heat transfer performance of a heat exchanger, but also in decreasing shell-side pressure drop. Copyright , Oxford University Press.