The effect of different variables and using of the internal adiabatic wall in the construction and performance of thermosiphon heat pipes: Experimental investigation

Abstract

Heat pipes are a practical and powerful tool for recovering thermal energy and conserving energy sources. Thermosiphon is one of the most widely used devices that can transfer large amounts of heat at high rates between hot and cold sources without the use of external energy. The amount of vacuum in the pipe, the percentage of fluid filling, the type of operating fluid, the pipe’s length and the quantity of heat flux are the factors affecting the efficiency and effectiveness of the thermosiphon heat pipe. In this paper, the effects of different variables in the construction of heat pipes such as working fluid, pipe length, the use of mesh screen wick structure and the use of internal adiabatic wall on the thermosiphon heat pipes performance are investigated. The results show that using of an internal adiabatic wall eliminates and reduces limitations such as boiling, evaporator drying, thermosiphon flooding and vapor pressure and significantly improves the heat pipe’s performance. So that, the effective thermal conductivity (K) is increased up to 350% using the internal adiabatic wall. However, in some nanofluids, such as water/multi-walled carbon nanotubes (MWCNT), with increasing the nanofluid’s mass fraction, the startup speed in heat pipes with internal adiabatic wall is reduced by up to 20%.