Pillow Plate Heat Exchanger, Multi-Objective Optimization, Computational Fluid Dynamics
Optimization is a powerful mathematical methodology that can be employed to miniaturize and improve the performance of plate heat exchangers in order to achieve higher levels of energy efficiency. Achieving these goals means less material used, and less charge, and thus a lower impact on the environment Plate heat exchangers (PHXs) are favored by the HVAC&R industry since they combine between the advantages of compactness, and desirable thermal-hydraulic characteristics due to their small approach temperature. However, the challenge with plate heat exchangers lies within the costly new designs. Pillow plate heat exchanger (PPHX) is a promising type of PHXs which also possesses desirable thermal-hydraulic characteristics due to their complex 3D wavy structure which creates a fully developed turbulent flow enhancing heat transfer. Furthermore, PPHXs are manufactured in a simpler more economical way compared to conventional PHXs. In this study, hundreds of new designs for PPHXs are investigated in order to maximize the thermal-hydraulic performance. The geometrical characteristics for the PPHXs are varied including pillow height, spot welds pitch ratio, and spot diameter. The PPHX pillow surface is created using CFD simulations ensuring structural stability while resembling the manufacturing process. The computational domain is then obtained from the deformed surface, meshed, and simulated. The whole CFD simulation process with its different components is automated using a Python script. The Latin Hypercube Sampling (LHS) is used to sample points from the design space, and the meta-modeling is calculated using the Kriging method. The optimization problem has four design variables which are the spot weld ratio, the spot weld diameter, the pillow height, and the inlet velocity. The objective is to maximize the heat transfer coefficient and minimize the pressure drop per unit length. The potential enhancement is found to be up to 3 times improvement in heat transfer coefficient and up to 98% reduction in pressure drop as compared to a selected PPHX baseline design. Sensitivity analysis is conducted on the optimal designs to provide insights into factors affecting their performance. The sensitivity study shows that the spot weld diameter is a significant parameter where further improvements can be applied. A comparison of optimal PPHX designs with Chevron PHXs shows that the optimal designs possess a higher heat transfer coefficient at similar values of pressure drop, as high as 3 times at low pressure drop values, and about 23% higher at moderate pressure drop values. It also show that optimum PPHXs designs have lower pressure drop at similar values of heat transfer coefficient, as low as 30%.