# The Study of Novel Self-Rewetting Fluid Application to Loop Heat Pipe
###### Abstract
Ambient temperature, the design of evaporator and compensation chamber, the inclination of system operation, and the presence of non-condensable gas will all affect the performance of the loop heat pipe. Among them, the capillary structure parameters have the most important influence on the performance of the loop heat pipe. In 2014, [PERSON] et al. [9] used the SRF fluid in micro oscillating heat pipes (MOHPs), and the SRF fluid of heptanol 0.1% aqueous solution and deionized water were used as working fluids to carry out the heat transfer experiments. The result shows that SRF has smaller surface tension than deionized water, which is beneficial to improve the efficiency and improve the heat transfer performance. In 2015, [PERSON] [10] first reported that SRF fluid was applied to LHP with a Ni wick to measure the surface tension of SRF (including butanol, pentanol and hexanol aqueous solutions) with different concentrations of alcohol aqueous solutions. The Marangoni effect becomes more vigorous, but above the saturation concentrations, the effect does not increase any further. Therefore, the optimal concentration of SRF is the saturation concentration, and the surface tension measurement results show that the critical heat load is increased by 1.6 times, and the total thermal resistance is reduced by about 60% compared with the heat transfer performance of the water working fluid. In 2017, [PERSON] et al. [11] first reported the application of SRF to LHP of the PTFE wick. The PTFE wick has a low thermal conductivity and can overcome heat leakage during LHP operation. However, PTFE is a hydrophobic material and cannot use pure water, the traditional working fluid. The butanol aqueous solution of SRF successfully passed the PTFE wick. After the LHP performance test, it was found that the butanol 6% aqueous solution PTFE system reduced the total thermal resistance by half, and the heat flux increased by more than 50% compared with the water-nickel system. In 2017, [PERSON] et al. [12] applied the SRF of aqueous solutions of different alcohols (butanol, pentanol, hexanol, and heptanol) to thermosyphon, and also pointed out that the optimal concentration of SRF for different alcohol aqueous solutions is its saturation concentration. In 2018, [PERSON] et al. [13] used two SRFs, ethanol 5% and butanol 5% plus water, for the study of pool boiling. It was found that the critical heat flux (CHF) increase in the butanol 5% aqueous solution was 1.91 times higher than that of water due to the Marangoni effect caused by the surface tension gradient. It was pointed out that the Marangoni effect should be the key factor to enhance the heat transfer of pool boiling. In 2019, [PERSON] et al. [14] soaked the wick itself with the SRF butanol 3% aqueous solution and pure water, respectively, and conducted evaporation visualization experiments. It was found that with the increase in applied power, the vapor film formed by the wick when the working medium was pure water also changed. However, the shape of the vapor film formed by SRF decreases with the increase in the applied power, which more effectively solves the obstacle of the vapor film. In 2021, [PERSON] et al. [15] applied the mixed fluid of the butanol 3% aqueous solution and gold nanofluid to the capillary heat pipe (CHP), pointing out that the butanol aqueous solution using SRF can reduce the evaporator temperature. Using visualization to observe the internal phase change, it was found that SRF can improve the vapor film barrier and effectively improve the heat transfer performance. Summarizing the above literature, it is pointed out that the more obvious the Marangoni effect of SRF, the better its performance in the evaporative heat transfer operation. It is also found in the literature that the increase in the solute concentration of SRF [10,11] will increase the Marangoni effect and improve the LHP heat. Therefore, the purpose of this study is to develop an ideal SRF formulation for the improvement of heat transfer performance of LHP.