Research Update: CFD Modeling of Offset Strip Plate-fin Exchanger with Vapor and Liquid Services
Compact plate-fin heat exchangers are widely used for electronics, aerospace, and automotive cooling because of the light weight and small size. The majority of open-literature data use air as the test fluid; thus, the application of the ensuing air-based methods to higher Prandtl number, liquid services is dubious. In some applications, liquids are preferred to air as cooling fluids because of better heat transfer properties. In this study, we simulate the heat transfer and pressure drop of an offset fin exchanger with various fluids having a wide range of Prandtl numbers. Boundary layer development in an offset fin array has two aspects: entrance to the fin array (array perspective) and on each fin (fin perspective). Our computational domain is a translational periodic model of a single repeating module from an exchanger for which we have published experimental results. We solved the conjugate heat transfer problem as a function of laminar Reynolds numbers corresponding to the test data. We found excellent agreement with the experimental Colburn j- and f-factor for both polyalphaolefin oil and water at 10 °C. The periodicity of the model eliminates the entrance effects on the array and assures that the boundary layers on the fins are fully developed. Upon successful validation of the approach, we simulated periodic flows at 300 K for other fluids. We found a significant Prandtl number effect on the j-factor itself as well as the dependence on Reynolds number. Additional simulations are planned for higher Reynolds number flows with the goal of correlating the Prandtl number effect over a range of flow regimes from laminar to turbulent.
Research report PFE-03 discusses this topic in more detail.