Bubble behavior and nucleation site density in subcooled flow boiling using a novel method for simulating the microstructure of surface roughness

The wall boiling model in the current research is used to predict the bubble dynamics treatment in flow boiling in a vertical pipe. A random surface roughness is developed for simulating the surface roughness effects in sub-cooled flow boiling as a novel method. This novel method is called direct roughness simulation (DRS). The DRS results are compared to the smooth surface (SS) and surface roughness model (SRM). The SRM is the traditional way of simulating surface roughness. The finite volume methods and Euler-Euler are applied to investigate subcooled flow boiling. The turbulence stresses are simulated by the k- ε model. The surface roughness effect on bubble dynamics for flow boiling is investigated numerically. According to the numerical simulations, nucleation site density is only increased by augmentation of heat flux. In contrast, increasing surface roughness, pressure, mass flux, and subcooled temperature cause a drop in nucleation site density. The bubble detachment waiting time and bubble departure diameter increase with the rise in pressure; however, by increasing other boundary conditions, these two parameters decrease. Results show that the reduction in the nucleation site density at outlet was 28.05% for the DRS and 25.5% for the SRM compared to the SS. The bubble detachment frequency at oulet 2.04% decreases when using the SRM and 6.5% increases when using the DRS. Compared to the SS; the bubble departure diameter at outlet 4.3% increases when using the SRM and 11.8% decreases when using the DRS.