Heat Exchanger, Evaporator, Shape Optimization, Experimental Study
Air-conditioning, heating, and refrigeration systems account for a significant fraction of the primary energy consumption in many parts of the world and have a direct impact on our quality of life. Air-to-refrigerant heat exchangers are a key component in these systems. Their airside thermal resistance is dominant and accounts for more than 80% of the overall resistance. Reducing the airside thermal resistance to improve the thermal-hydraulic performance of these heat exchangers, and consequently overall system level COP, has been a topic of research focus for several decades. Generally, secondary surfaces, i.e., fins, are used to enhance the airside performance by drastically increasing surface area. However, fins have disadvantages such as, increased material usage, reduced compactness, and increased viscous resistance. Therefore, it is evident air-to-refrigerant heat exchanger designs have the potential for improved thermal-hydraulic performance by avoiding the use of fins and utilizing different designs. Computational Fluid Dynamics and Multi-Objective Genetic Algorithms were used to design heat exchangers with novel and topology optimized tube shapes. This paper presents an experimental study of a 1-2 kW prototype air-to-refrigerant heat exchanger based on one such optimized tube shape, termed “Copper NURBS Tube Heat Exchanger-1” (CNTHX1). The heat exchanger was manufactured using conventional manufacturing methods. When compared to a state-ofthe-art air-to-refrigerant heat exchanger, the prototype is designed to have a 25% reduction in volume, 20% reduction in face area, and 8% reduction of internal volume with equal to or greater capacity and the same airside pressure drop. This work presents the experimental performance of this prototype under wet and dry evaporator (R410A) conditions in a standardized wind-tunnel. Experimental airside pressure drop and capacity were measured and compared to predicted values. Additionally, the energy balance between the airside and refrigerant-side was within ±5.5% for all test points. The detailed thermal-hydraulic characteristics and the reasons for improvement are discussed.