Multi-scale analysis and optimization of tube shapes for air-to-refrigerant heat exchangers.

Air-to-refrigerant heat exchangers are a key component in heat pumps and refrigeration systems. Literature review shows that significant reduction in material, refrigerant charge and air-side thermal resistance can be obtained by utilizing smaller refrigerant-side hydraulic diameter. While such designs offer some improvement in compactness of the heat exchanger, the air-side resistance is still the dominant resistance. One contributing factor is the shape of the tube itself which is generally limited to a circular or oval profile. This paper describes a comprehensive method for multi-scale analysis and optimization of tube shapes on the air side for novel finless air-to-refrigerant heat exchangers. Bezier curves are employed for tube shape parameterization using a Non-Uniform Rational B-Splines (NURBS) algorithm. Air-side performance is evaluated using CFD in a 2-dimensional periodic computational domain. The method is applied to design a 1.0 kW air-to-water heat exchanger with Parallel Parameterized CFD and Approximation Assisted Optimization techniques. Structural analysis for mechanical stresses and deformation is also carried out. It is shown that the resulting optimum designs can be 50% smaller than compact micro channel heat exchangers with at least 20% better performance.