Wavy Fin Profile Optimization Using NURBS for Air-To-Refrigerant Tube-Fin Heat Exchangers with Small Diameter Tubes

摘要

The major limitation of any air-to-refrigerant Heat eXchanger (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 either have 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 the longitudinal direction as well. The tools used in this work include automated CFD simulations, metamodeling and Multi-Objective Genetic Algorithm (MOGA). The analysis comprises optimizing a conventional Herringbone wavy fin and uses it as a baseline. While maintaining tube diameter, tube pitches, and number of rows, fin spacing and thickness we perform an optimization on the fin profile using NURBS and compare the potential thermal-hydraulic performance improvements.