Thermal performance enhancement in heat exchangers using active and passive techniques : a detailed review

Abstract

The objective of this article is to study the work carried out in heat transfer augmentation using active and passive techniques. A comprehensive summary of the work is highlighted to showcase the strength of these techniques in terms of enhancement in heat transfer. In this work, research studies done in the area of electrohydrodynamic, magnetic field, corona wind, vortex generators, tape and coil inserts, roughness, and modified duct were reviewed and an attempt has been made to make a common platform on which the performance enhancement has been compared and presented. It was found out that passive methods are comparatively more investigated than active methods due to their safe and sound operation along with no additional requirement of power. Result shows that duct modification is an effective and efficient way for heat transfer enhancement (HTE). Based on the literature studied, more emphasis must be focussed on the usage of HTE methods in combination to get the advantages of both the methods and they should complement each other in the best possible way. On comparing the active and passive way of THE, results with active methods are more appreciable. However, passive techniques gain more momentum due to ease of operation and low cost of equipment. Use of passive augmentation techniques, i.e. vortex generators, artificial roughness, etc., changes flow pattern significantly that helps in the heat transfer augmentation. Although understanding of fluid flow behaviour is very essential and helps in the cause of the heat transfer augmentation that will further help in using compound techniques, altering the duct’s surface using ribs, dimples, roughness, etc., shows the thermal performance enhancement of more than 200% when the results were compared with the plain channel. The modified duct may be combined with any other passive augmentation technique which will further lead to performance enhancement.