Conference Year

2016

Keywords

Airside heat transfer, airside friction, optimization, wavy fin, NURBS

Abstract

The major limitation of any air-to-refrigerant HX is the air side thermal resistance which can account for 90%, or more, of the overall thermal resistance. For this reason the secondary heat transfer surfaces (fins) play a major role in these HX’s by providing additional surface area. Many researchers extensively investigate how to improve the performance of fins. The most common passive heat transfer augmentation method applied to fins uses surface discontinuity; providing an efficient disruption-reattachment mechanism of the boundary layer. Such approach is leveraged by louvers, slits and even vortex generators. In some applications, however, these concepts are not adequate especially when there is high fouling or frosting, which is the case of many HVAC&R systems including heat pumps for cold climates. In such cases a continuous fin surface is required, which can usually be plain or wavy. The latter provides larger surface area and can induce turbulent flows improving the heat transfer. Normally the wavy fins are either a smooth sinusoidal or Herringbone profile, longitudinal to the airflow direction. In this paper we propose a novel wavy fin design method using Non-Uniform Rational B-Splines (NURBS) on both longitudinal and transverse directions. In this method the fin surface is subdivided in to 1 x n identical cells with periodic boundaries. The horizontal and vertical edges independently describe a NURBS curve on separate planes with the third spatial direction. The tools used in this work include automated CFD simulations, metamodeling and Multi-Objective Genetic Algorithm (MOGA). The analysis comprises of optimizing all wavy fin types, both the conventional ones and the novel designs presented in this paper, and compare their performance and compactness while fixing hydraulic diameter and Reynolds numbers. In conclusion, design recommendations for made for the use of the proposed novel fins.Â

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