Semnan University Press Journal of Heat and Mass Transfer Research 2345-508X 13 3 2026 09 01 Design and Performance Evaluation of a Multi-Stepped Absorber Plate Fin in a Flat Plate Solar Collector 273 284 9828 10.22075/jhmtr.2025.36908.1682 EN Gulshan Baharuddin Ahmed Durgapur Institute of Advanced Technology and Management Durgapur, West Bengal 713212, India Md Naim Hossain Department of Mechanical Engineering, Jalpaiguri Government Engineering College West Bengal 735102, India Arijit Kundu Department of Mechanical Engineering, Jalpaiguri Government Engineering College West Bengal 735102, India Ashwani Kumar Department of Mechanical Engineering, Technical Education Department Uttar Pradesh Kanpur 202480 India & Department of Mechanical Engineering, Graphic Era Deemed to be University Dehradun 248002 India Journal Article 2025 02 15 This research investigates the thermal performance and optimization of a new absorber plate fin design with a double step change in thickness (rectangular profile with double step changes in local thickness, RPDSLT). It compares the thermal performance of RPDSLT to fins with simpler geometries (rectangular, trapezoidal, and rectangular with a single step change) across a wide range of geometrical parameters. The main objective of researchers in this field is to determine the maximum fin efficiency with minimal fin material usage. Therefore, the focus is on understanding the impact of the additional step change in RPDSLT on heat transfer efficiency and examining whether the fin efficiency is enhanced or not. The study aims to identify the optimal values of the geometrical parameters (plate fin thickness ratios and dimensionless step lengths) that maximize efficiency. The absorber plate fin thickness plays a crucial role in solar collector efficiency. The research explores how the double step change in RPDSLT thickness affects collector efficiency compared to simpler fin designs. Detailed schematics of each fin profile and a solar collector demonstration are presented. The result show that the RPDSLT fin exhibits a maximum fin efficiency roughly 5% greater than the rectangular profile with step changes in local thickness (RPSLT) fin when their geometries is optimized. Compared to rectangular and trapezoidal fins, the RPDSLT offers a smaller efficiency improvement of 1-2%. Nevertheless, the superior thermal performance of the RPDSLT design could make it a preferred choice for flat plate solar collectors despite its more intricate fabrication. The study indicates that optimal efficiency is achieved with the minimum tested step-length ratios of 0.1 and the maximum tested thickness ratios of 0.9. Therefore, for efficient material utilization in the plate fin, it is recommended to use minimal step-length ratios and maximal thickness ratios. https://jhmtr.semnan.ac.ir/article_9828_55664a5dc5ed2f36206b1c73678efa75.pdf