Modeling the Performance Characteristics of Aluminum Fin-Tube Heat Exchangers for Residential Space Cooling

Energy consumption for space cooling is projected to more than double to ~6200 TWh by the year 2050 as the adoption of air conditioning technologies increases drastically globally. Condenser-type heat exchangers (HXs), particularly air-coupled condensers, are vital components in such thermodynamic systems where heat is rejected to the outdoor environment. A major drawback of air-coupled HXs is the large surface area and volume required due to the insulative properties of air as a heat transfer fluid, which necessitates the use of finned tubes. Aluminum alloys are commonly used as fin stock owing to their high thermal conductivity and corrosion resistance, while serving as sacrificial anodes to extend the lifespan of HVAC systems. Another benefit of aluminum is its recyclability, which offsets the greenhouse gas emissions and costs associated with bauxite refining. Additionally, the composition, temper, coating, gauge, and joining method can significantly impact properties. This research evaluates the impact of introducing novel aluminum alloys (with higher recycled content) on the thermohydraulic performance of condenser heat exchangers.

A steady-state model is developed using empirical correlations to represent air-coupled condenser HXs. The heat duty and pressure drop are evaluated for a finned tube bank in superheated vapor, film condensing, and subcooled liquid flow regimes for different refrigerants (e.g., R32, R1234yf, Ammonia), all in crossflow with air. Parametric analyses are conducted on the fin thickness, pitch, thermal conductivity, and geometry for a range of typical operating conditions and a selection of condenser designs. Thermophysical properties of the aluminum alloys are characterized using laser flash analysis (LFA) and differential scanning calorimetry (DSC) to highlight differences between conventional and novel materials, and the resulting effects on HX performance. Overall, this study outlines key considerations for the adoption of more sustainable aluminum alloys in space cooling technologies.