Experimental Investigation On Heat Transfer Performance Of Heat Pipes With Self-Rewetting Fluids

One of the characteristic properties of self-rewetting fluid is that its surface tension increases with temperature going higher after some critical value.Appling the sort of fluid to heat pipe systems could induce a simultaneous liquid flow from the cold part of heat pipe system to the hot part,known as Marangoni flow,which can enhance the heat transfer of heat pipes by promoting cold liquid returning.In this paper,the heat transfer performance of self-rewetting fluids in the gravity heat pipes(GHPs)and the loop heat pipes(LHPs)is studied by experiments.This paper conducts a comparative investigation(with water as comparison object)of the effects of self-rewetting fluid on heat transfer in heat pipe systems by operating GHPs in different orientations(including horizontal,small-angled and vertical ones)and those with different n-heptanol and n-pentanol concentration aqueous solutions as working medium.In addition,the effects of self-rewetting fluid in LHPs are studied by comparing with water LHP in terms of start-up tests and stable operation tests under variable heat loads.The main study and the conclusions of the paper are as follows:(1)A review on working principles of self-rewetting fluid,GHPs and LHPs as well as their recent research development,and a statement of the shortage and prospects of self-rewetting fluid as working fluid in heat pipes.(2)The design,fabrication and tests of self-rewetting fluid-based GHPs and LHP systems as well as data processing principles and uncertainty evaluation.(3)The effects of self-rewetting fluid on heat transfer in GHPs are experimentally studied under horizontal,small-angled and vertical orientations.The results show that 1)whatever the orientation,GHPs with n-heptanol and n-pentanol aqueous solution as working fluid have lower evaporation section temperature and thermal resistance but higher heat transfer coefficient than those of water GHP;2)in horizontal oriented experiment,applying n-heptanol and n-pentanol aqueous solution can increase the heat transfer limit of GHP and enhance the heat transfer ability,especially for that of evaporation section.Compared with n-pentanol aqueous solution,the heat transfer enhancement caused by n-heptanol aqueous solution is more obvious.(4)The start-up tests and stable operation experiments under variable heat loads are carried out.Results show that self-rewetting fluid-based LHPs start up faster than its water counterpart under the same heat load and have lower evaporator temperature and systematic thermal resistance when operating stably,which represent the advantage of self-rewetting fluid on heat transfer in LHPs.