Using patterned surface wettability to enhance air-side heat transfer through frozen water droplet vortex generators – Part II: CFD simulation results

Abstract

• Frozen water droplets can serve as vortex generators (VGs) to increase air-side heat transfer. • Hemispherical domes (i.e. model droplets) were simulated numerically to quantify performance. • Ten different configurations were investigated with the staggered VG pattern performing better than the inline pattern. • Changing the longitudinal spacing between VGs led to better performance. • Heat transfer enhancements from 14.0 to 75.9% were observed with pressure drop penalties from 35.7 to 165.6%. In this study, a novel technique for deploying hemispherical vortex generators (VGs) aimed at heat transfer enhancement via the naturally-occurring processes of condensation and freezing was proposed and investigated. By using patterned surface wettability to collect condensate and encourage coalescence in predetermined locations, it was hypothesized that large frozen droplets could be formed in various configurations which could serve as VGs. This approach was simulated numerically in the present communication (Part II) and examined experimentally in a previous study (Part I). For the CFD simulations, ten different configurations in channel flow emulating a fin density of 5 FPI were investigated. Inlet air velocities of 1.0 and 2.0 m s −1 at 20°C were examined for the flow through the channel where the walls and VGs were set to -9°C to match the experimental conditions used in Part I. The air-side heat transfer coefficient, pressure drop, and temperature changes were then calculated after a converged solution was reached. Compared to a baseline configuration without VGs, heat transfer enhancements ranging from 14.0 to 75.9% were observed, with corresponding pressure drop increases (or penalties) ranging from 35.7 to 165.6%.