# The Study of Novel Self-Rewetting Fluid Application to Loop Heat Pipe
###### Abstract  
The purpose of this paper is to develop SRF formulations for LHP performance enhancement. In this paper, the solute of SRF is prepared, and butanol and its isomer, 2-butanol, are selected. In this paper, concentrations of the 2-butanol aqueous solution (10%, 15%, and 20%) plus the butanol 6% aqueous solution were used to measure the surface tension of four different formulations of SRF and water. It was found that the higher the solute concentration became, the stronger the Marangoni effect was, and the more obvious the surface tension change of the 2-butanol 20% aqueous solution was. Water, the butanol 6% aqueous solution and the 2-butanol 20% aqueous solution were filled into LHP respectively, and the heat transfer performance was measured. The 2-Butanol 20% aqueous solution improved LHP performance by about three times compared with water, and the lowest total thermal resistance was only 1/4 that of water. Therefore, the 2-butanol 20% SRF aqueous solution is an ideal formula for improving the LHP heat transfer performance. 2022 20  
and thus wets the surface with a high temperature, which has to delay the occurrence of drying out and enhance the heat transfer efficiency. The working fluid in this research is intended to be a self-rewetting fluid, which has better wettability than the pure material working fluid. The relationship between concentration, temperature and surface tension is shown in Equation (1):  
\[\frac{\partial\sigma}{\partial X}=\sigma_{T}\frac{\partial T}{\partial X}+ \sigma_{C}\frac{\partial C}{\partial X} \tag{1}\]  
where \(\sigma\) is the surface tension, \(T\) is the temperature of the working fluid, and \(C\) is the concentration of the working fluid. Usually, the working fluids of the two-phase heat transfer device, such as pure water, ethanol, acetone, etc., are all pure substances, and their surface tension will gradually decrease with the increase in the operating temperature. In this paper, SRF is applied to the loop heat pipe (LHP), and the related literature is reviewed as follows. In 2001, [PERSON] et al. [4] pointed out that both traditional heat pipes and loop heat pipes are faced with a phenomenon. The surface tension of the working fluid decreases with the increase in temperature, which is unfavorable for the extension or rewetting of the heated surface liquid. Furthermore, they suggested that the best way to solve this problem is to use a working fluid whose surface tension increases with temperature. In 2006, [PERSON] [5] sorted out the research over the years and pointed out that the self-rewetting fluid can push the cooler liquid to the hotter surface through the Marangoni effect because of the reverse surface tension gradient, delay the occurrence of drying, and then improve the heat transfer. The performance is helpful for the heat transfer performance of a non-capillary structure heat pipe, general heat pipe and boiling phenomenon. In 2008, [PERSON] et al. [6] applied the self-rewetting fluid of the 0.1% heptanol aqueous solution to the heat pipe. The experimental results showed that the maximum heat load was more than twice that of water, which not only reduced the thermal resistance, but also delayed the occurrence of dry-out. In 2011, [PERSON] et al. [7] used the butanol aqueous solution as the working fluid (the concentration range included 2%, 5%, and 7%), and carried out the pool boiling heat transfer experiment. The flux increased substantially, and the heat flux did not have a significant effect when the concentration increased to 7%. Figure 1: Identification of self-rewetting fluid [3]. In 2011, [PERSON] et al. [8] sorted out the literature on the theoretical prediction and parameter discussion of loop heat pipes over the years. The paper pointed out the selection and filling amount of the working fluid, the material of the capillary structure, the parameters and geometric dimensions, the temperature and the heat sink temperature.