Heat transfer enhancement of wall with a near wall cylinder in a channel at low and middle Reynolds number ranges

Hui Xu,Guannan Xi,Yixi Cai

doi:10.1177/0020294020962127

Abstract

This paper investigated the flow performance around a near-wall cylinder and its effect on heat transfer enhancement in the laminar and early transitional flow region. The numerical model is resolved by finite volume method through FORTRAN code. The results show that the flow field becomes a transitional flow state when Re = 100 due to the insertion of a cylinder. In the transitional flow sate, the heat transfer enhancement is regional, mainly concentrating in the region of –2 ≤ x/D≤ 10, and the region increases with the increase of Re; There are three or four peaks in the distribution of instantaneous local Nusselt number. The first peak is caused by the acceleration of the fluid between the cylinder and the bottom wall. The other peaks are caused by the interaction between the cylinder wake and the bottom wall boundary layer. The vortical structure induced by the periodic instability of the fluid in the transitional flow is the main factor for explaining the local heat transfer enhancement of the cylinder downstream wall. Re has a direct impact on the vortical structure in the flow field. The greater Re, the greater the heat transfer enhancement of the cylinder downstream wall. Under the same blocking ratio of D/H, the greater Re, the smaller the optimal clearance ratio of C/D. The guidelines are suggested for the design on heat dissipation of electronic equipment.

Highlights

With the development of electrical and electronic equipment towards large capacity, high power, miniaturization, on one hand, the rejection heat per unit volume and the heat flux per unit area keep rising, on the other hand, the effective heat dissipation area is reducing continuously
By using the appropriate vortex generation mechanism, the flow state can be changed to the transitional flow state, which is more advantageous for heat transfer, so as to effectively improve the heat transfer performance of such devices
The results showed that blockage ratio, Reynolds number and clearance ratio all have effect on the near-wall heat transfer coefficient (HTC), while the clearance ratio is the main factor

Summary

Introduction

With the development of electrical and electronic equipment towards large capacity, high power, miniaturization, on one hand, the rejection heat per unit volume and the heat flux per unit area keep rising, on the other hand, the effective heat dissipation area is reducing continuously It has important engineering significance on how to enhance the heat dissipation of electrical and electronics equipment, in order to avoid thermal failure by the high temperature, improve equipment reliability and prolong equipment life. The focus of this study is to insert a stationary circular cylinder near the wall as the longitudinal vortex generator, and to investigate the influence of the vortices on heat transfer and flow characteristics

Objectives

Methods

Results

Conclusion