Potential Benefits of Shape Optimized Air-to-Refrigerant Heat Exchangers for New Lower-GWP Refrigerants

Air-to-refrigerant heat exchangers (HXs) are fundamental components in HVAC&R systems, and considerable research has focused on reducing size and weight while improving efficiency.
Recent advancements in Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA), and optimization algorithms have allowed researchers to employ tube shape and topology optimization to design high performance HXs with reduced size, weight, cost, and refrigerant charge compared to current state-of-the-art HXs while maintaining or improving system-level performance, thereby reducing overall environmental impact.

This is especially important given governmental and industrial shifts to lower-GWP flammable and mildly-flammable refrigerants, which have highly-regulated charge amounts. We present a computationally efficient, multi-scale and multi-physics analysis and optimization framework for air-to-refrigerant HXs featuring automated CFD and FEA simulations and approximation-assisted optimization. The framework was utilized to design HXs with shape-optimized tubes that outperform current state-of-the-art HXs for many low-GWP refrigerant applications.

The optimal HXs were shown to deliver similar thermal performance to the baseline HXs while achieving significant (>20 %) reductions in airside pressure drop, core envelope volume, face area, and tube internal volume. The optimization framework was experimentally validated through testing of a conventionally manufactured prototype in a standardized wind tunnel facility. Specifically, predicted heat load and airside pressure drop agreed within ±10 % and ±30 % of measured values for dry evaporator conditions, while for dehumidifying conditions, the predicted sensible and latent heat loads agreed within ±10 % and ±20 % of measured values. Our research demonstrates that systematic optimization can enable highly compact and lighter HXs for many lower-GWP replacement refrigerant applications.