A Novel Correlation for Mean Hydraulic Diameter in Single-Embossed Channels of Pillow-Plate Heat Exchangers

Abstract: The complex structure of single-embossed channels in pillow-plate heat exchangers imposes considerable constraints in accurately estimating the mean hydraulic diameter (MHD). The existing correlation, obtained from finite element simulations of hydroforming, approximates the MHD in double-embossed channels based on the maximum channel height. While this method may be used for single-embossed channels with minor uncertainties, it remains inaccurate as it neglects material and geometry non-linearities in the simulation and disregards other geometric parameter effects, such as welding spot sizes and patterns. This work resolved these issues using a precise hydroforming simulation, capturing the channel structure with appropriate geometric parameters, and presenting a novel MHD correlation for single-embossed channels. By examining relevant dimensionless geometric parameters for 300 channels, a new MHD correlation for single-embossed channels achieved error ranges between -7.12% and +13.54%, with a coefficient of determination, R^2, of 0.9984, in contrast to the current approximation, which had an error range from -16.97% to +51.71%. Additionally, the proposed correlation identified the effects of various geometric parameters and determined the maximum and minimum MHDs based on welding spot patterns. These findings lay a base for enhancing the thermohydraulic performance of single-embossed channels and improving accuracy in pillow-plate heat exchanger research. Keywords: Mean hydraulic diameter, pillow-plate heat exchanger, single-embossed channel