Analysis of Reverse Currents Parameters and Gas Content in Liquid behind the Roughness Ridge

Resumo

Based on experimental studies, the effect of gas content in the liquid behind the ridges of artificial helical roughness on film thickness and the value of the heat transfer coefficient is shown. The numerical results for the reverse currents velocity distribution and pressure difference along the ridge height and the cavity length, as well as experimental values of gas content in the liquid separation zone, arising from the flow over a regular roughness, are presented. The scale of reverse currents, their location behind the roughness ridge, and gas content depend on the height and shape of the ridge, the irrigation density, and the physical properties of the liquid. It was concluded that the gas bubbles in the liquid form in reverse current zones in the cavities of the artificial roughness due to reduced pressure compared to gas pressure at the interface and, therefore, gas suction from the interface zone. The dependence for calculating gas content via the thickness of the liquid layer in the roughness cavity is proposed.