Transient numerical investigation of a thermal-driving water pipe cooling system

Abstract

For a simple water cooling system, which consists of a U-shaped round pipe and a reservoir, how to discharge the vapor generated in the heated pipe during the cooling process is an interesting topic, especially when pumps or other driving units are hard to install and maintain in the device. In this paper, a thermal-driving method is proposed. By adding different heat fluxes on different parts of the U-shaped pipe, the fluid density difference between those parts can drive a natural circulation of fluid in the loop, and then the vapor bubbles can be discharged with the flow. Numerical simulations are carried out to study the transient performances of the thermal-driving water pipe cooling system under different heat flux distributions. The aim is to obtain the mechanism and evolution law of fluid movement, phase change and heat dissipation. The numerical results indicate that, when the heat flux is uniformly added on the whole pipe, slugs appear in the vertical pipe and where local heat transfer deterioration occurs. When the heat fluxes are different on the left and right vertical parts of the pipe, an overall circulating flow generates. In this process, small vapor bubbles can be discharged, which avoids the formation of the vapor slugs, and the system works stably at boiling point thereby. In addition, with an increase in the heat flux difference between the two vertical parts of the pipe, the initial time of the overall circulating flow shortens.