Abstract
The aim of this work is to numerically analyse fluid flow and heat transfer characteristics in a crossflow air-to-water fin-and-tube heat exchanger (FTHEX) by implementing two configurations of delta-winglet type vortex generators at the air side: delta-winglet upstream (DWU) and delta-winglet downstream (DWD). The vortex generators are mounted on a fin surface and deployed in a “common flow up” orientation. The effects of attack angles of 15°, 30° and 45° on air-side heat transfer and pressure drop were examined. Since the implementation of the full-size model would involve large numerical resources, the computational domain is simplified by considering a small segment in the direction of water flow. The fully developed temperature and velocity boundary conditions were set at the water inlets. To validate the defined mathematical model and numerical procedure, measurements have been performed on a plain FTHEX. The air side Reynolds number, based on hydraulic diameter, was in the range of 176 ≤ ReDh ≤ 400 and water side Reynolds number, based on inner tube diameter, was constant Redi = 17,065. The results have shown that the highest increase in the Colburn factor j (by 11–27%) and reduction in the air-side thermal resistance fraction (from 78.2–76.9% for ReDh = 176 to 76–72.4% for ReDh = 400) is achieved by using the DWD configuration with attack angle 45°. In addition, the overall heat transfer coefficient is improved by up to 15.7%. The DWD configuration with the attack angle 30° provides the greatest improvement in the heat transfer to pressure loss ratio, 5.2–15.4% over the range of ReDhstudied.
Highlights
Compact fin-and-tube heat exchangers (FTHEX) have widespread use in commercial, domestic and industrial applications, such as heating and air conditioning systems, power plants, manufacturing processes, electronic cooling equipment and aerospace industries, etc
Based on the review mentioned above, this paper investigates the influence of two delta-winglet types of vortex generators (VGs): upstream and downstream, on the heat transfer and pressure drop characteristics in the crossflow air-to-water fin-and-tube heat exchanger, implementing a conjugate 3D numerical model with fluid flow and heat transfer on both air and water sides
In order to investigate the effects of the attack angle on the air-side thermal and hydraulic performances of FTHEX with delta-winglets, three different angle values were considered: 15◦, 30◦, and 45◦
Summary
Compact fin-and-tube heat exchangers (FTHEX) have widespread use in commercial, domestic and industrial applications, such as heating and air conditioning systems, power plants, manufacturing processes, electronic cooling equipment and aerospace industries, etc. The FTHEXs are classified as gas-to-liquid heat exchangers, in which one fluid is a gas (more commonly, air) and the other is a low-pressure liquid (more commonly, water). The attention has been focused on enhancing the gas-side thermal performance through the development of passive and active techniques [1]. Interrupted fins, in the form of wavy, louvered or slotted fins, improve heat transfer by disrupting primary flow with a significant pressure drop penalty. Apart from interrupting the primary flow, fins with VGs provide better heat transfer in the recirculating zones downstream of the tubes and significantly reduce the pressure drop compared to interrupted fins [2,3]
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