<p>Pillow plate heat exchanger (PPHE) is a novel heat exchange structure that holds potential for development in the field of phase change heat transfer. The objective of this study is to understand the evaporation flow pattern and heat transfer correlation for R22 in the outflow channel of PPHE. This paper first employs the orthogonal method to design the combination of geometric structural parameters; then utilizes FLUENT simulation to study the evaporation process under different combinations, and finally fits the correlation criteria for evaporation. The simulation contour plots indicate that the evaporation process varies with vapor quality, which is an unstable process involving the transformation between multiple flow patterns. The geometrical structure parameters that have the greatest influence on the evaporation heat transfer coefficient, pressure drop and heat transfer efficiency are outer channel height, followed by the staggered angle, and finally the welding spot diameter. Also the most comprehensively optimal combination of structural parameters is obtained. The mean errors of the fitted <i>Nu</i> and <i>f</i> correlations are 13.15% and 16.10%, respectively. This study provides some theoretical support for the design of PPHE used for evaporating. The obtained results provide certain design references for the application of pillow heat exchangers in the field of reboilers and provide a reliable model for predicting the evaporation heat transfer performance of pillow heat exchangers.</p>