Turbulence-resolving simulations of frost buildup in a fin-and-tube heat exchanger*

We present results from frost buildup on shell-and-tube heat exchangers under turbulent flow. This study investigates frost deposition and growth on staggered coil finned tubes within a heat exchanger for bulk Reynolds numbers of 60, 120, and 240. Our turbulence-resolving simulations are dynamically coupled, whereby we employ the immersed boundary method with direct forcing to account for the temporally evolving and spatially varying frost thickness and surface temperature on all surfaces. This is achieved by solving the mass and energy conservation for the frost phase. On the other hand, we solve the continuity, Navier-Stokes, energy, and mass conservation equations for the incompressible air phase. Our results indicate strong spatial variation in frost dynamics. More specifically, we observe the frost deposition to be largest on the fins than on the tubes. The frost is observed to grow at a rate that is two to times faster on the latter compared to the former. Similarly, we observe the frost surface temperature as well as the Nusselt and Sherwood numbers to follow the same trend with larger values on the fins than on the tubes. Finally, to make these simulations computationally feasible, we employ a slow-time acceleration technique to the slow frost phase whereby we accelerate its growth by a factor of 1000.