Aluminum plate-fin heat exchangers are widely used for cooling applications in industrial, aeronautical and power generation applications, thanks to their low weight, high compactness and efficiency. The cooling capacity is enhanced by employing finned surfaces with complex geometries, that need to be optimized to obtain the best trade-offs between friction losses and heat transfer rates. These extended surfaces often feature offset-strip and wavy geometries, and despite the numerous studies conducted on these fin types, it is still not trivial to carry out accurate predictions about their friction and heat transfer properties, due to the large variety of geometric parameters and working fluids involved.
A numerical method is developed, aimed at the accurate evaluation of the thermal-hydraulic performance of plate-fin heat exchangers. The proposed approach encompasses detailed 3D models for the finned heat transfer surfaces and internal head losses, with a reduced order model for the estimation of head losses and heat transfer rates of the complete heat exchanger. Ultimately the proposed method allows for the obtainment of "digital twins" of actually manufactured heat exchangers.
Detailed CFD models of the internal and external fins are developed, with the aim of assessing friction losses and heat transfer rates for all the geometries considered, and several flow regimes. The results are then employed to construct suitable correlations, for the Darcy friction factor and Nusselt number. These correlations are then used in the reduced order model to obtain the overall heat transfer rates via the ε − NTU method, and overall internal and external head losses by means of the Darcy-Weisbach formula. Finally, numerical results are compared with available experimental data for several heat exchanger configurations, which include different working fluids and flow regimes, showing a remarkable agreement, thus corroborating the validity of the proposed numerical approach.