Evaluation of Geometric Parameter Effects on Outer Channel Mean Hydraulic Diameter of Pillow-Plate Heat Exchangers

Abstract: The intricate channel geometry in pillow-plate heat exchangers (PPHEs) remains a challenge in obtaining accurate mean hydraulic diameter (MHD) calculations, particularly in the outer channel (OC) formed between two adjacent inner channels (ICs). The existing method approximates the OC's MHD by a simple correlation using the maximum heights of the IC and OC. This method, derived from hydroforming simulation results, disregards the material and geometric non-linear impacts in simulation and neglects the role of OC structure and configuration, such as welding spot sizes and patterns, on MHD estimation. This work employs a precise hydroforming simulation to determine the OC structure and analyzes effective geometric parameters on the OC MHD. Comparing the MHDs of 3000 simulated OCs to the results of the existing MHD correlation revealed errors, ranging from -23.01% to +6.29%, for the correlation. The analysis of the OCs highlighted the crucial roles of welding spot diameter, curve width between diagonal welding spots, and the diagonal welding spot angle in determining the correct MHD. Capturing the OC structure, these parameters determine the local maximum MHD at 45 degrees and minimum MHD at around 30 and 60 degrees. Evaluating these high-potential structural parameters paves the way for developing novel correlations in future research for the MHD of the OC in PPHEs. Keywords: Mean hydraulic diameter, Pillow-plate heat exchanger, Geometric parameters