A Review of Airside Heat Transfer Augmentation with Vortex Generators on Heat Transfer Surface

Lei Chai,Savvas Tassou

doi:10.3390/en11102737

Abstract

Heat exchanger performance can be improved via the introduction of vortex generators to the airside surface, based on the mechanism that the generated longitudinal vortices can disrupt the boundary layer growth, increase the turbulence intensity and produce secondary fluid flows over the heat transfer surfaces. The key objective of this paper is to provide a critical overview of published works relevant to such heat transfer surfaces. Different types of vortex generator are presented, and key experimental techniques and numerical methodologies are summarized. Flow phenomena associated with vortex generators embedded, attached, punched or mounted on heat transfer surfaces are investigated, and the thermohydraulic performance (heat transfer and pressure drop) of four different heat exchangers (flat plate, finned circular-tube, finned flat-tube and finned oval-tube) with various vortex-generator geometries, is discussed for different operating conditions. Furthermore, the thermohydraulic performance of heat transfer surfaces with recently proposed vortex generators is outlined and suggestions on using vortex generators for airside heat transfer augmentation are presented. In general, the airside heat transfer surface performance can be substantially enhanced by vortex generators, but their impact can also be significantly influenced by many parameters, such as Reynolds number, tube geometry (shape, diameter, pitch, inline/staggered configuration), fin type (plane/wavy/composite, with or without punched holes), and vortex-generator geometry (shape, length, height, pitch, attack angle, aspect ratio, and configuration). The finned flat-tube and finned oval-tube heat exchangers with recently proposed vortex generators usually show better thermohydraulic performance than finned circular tube heat exchangers. Current heat exchanger optimization approaches are usually based on the thermohydraulic performance alone. However, to ensure quick returns on investment, heat exchangers with complex geometries and surface vortex generators, should be optimized using cost-based objective functions that consider the thermohydraulic performance alongside capital cost, running cost of the system as well as safety and compliance with relevant international standards for different applications.

Highlights

Heat exchangers are used for heat transfer between two or more fluids with temperature difference, which are widely used in many diverse industries and applications, including the process and chemical industries, transportation, air conditioning and refrigeration [1]
The thermohydraulic performance of heat exchangers is dependent on the geometry of vortex generators (VGs) and operation conditions, but strongly determined by the type of heat transfer surface that controls the flow passage of the mainstream, so we provide more detailed information and comments regarding the thermohydraulic performance mentioned in Tables 1 and 2 based on the different types of heat transfer surface, e.g., flat plates, finned circular-tube heat exchangers, finned flat-tube heat exchangers, finned oval-tube heat exchangers, etc
The airside thermohydraulic performance of heat transfer surfaces associated with VGs has

Summary

Introduction

Heat exchangers are used for heat transfer between two or more fluids with temperature difference, which are widely used in many diverse industries and applications, including the process and chemical industries, transportation, air conditioning and refrigeration [1]. High-efficiency heat exchangers can reduce the fluid inventory, cost of materials and energy consumption, leading to increased efficiency and return on investment, and lower environmental impacts. For the typical applications of an air-cooled heat exchanger, due to the inherently lower thermal conductivity of gas, and the lower heat transfer coefficient, than that of liquid. To improve performance to meet the demands for high efficiency and low cost, the most common way is to use heat transfer surfaces those are periodically interrupted along the streamwise direction [3,4]. Some typical examples are heat transfer surfaces mounted with louvred fin, offset fin, offset strip fin, rectangular plate-fin, and vortex generators (VGs) such as fins, ribs and wings

Objectives

Methods

Findings

Conclusion