# The Study of Novel Self-Rewetting Fluid Application to Loop Heat Pipe
## 3 Results and Discussion  
### Surface Tension Measurement Results  
The surface tension of SRF (2-butanol and butanol 6% aqueous solution) was measured, and the surface tension of SRF decreased with the increase in temperature. Until the temperature reaches a specific temperature (40-50 \({}^{\circ}\)C), the surface tension of SRF increases with temperature, which is characteristic of SRF fluids. For 2-butanol 20%, the surface tension begins its reversal at about 40 \({}^{\circ}\)C; the surface tension value is about 19 mN/m; and the surface tension value is 48.5 mN/m when the temperature is 70 \({}^{\circ}\)C. In the temperature range of 40-70 \({}^{\circ}\)C, the surface tension measurement is about 20.5 mN/m for the 2-butanol 15% aqueous solution, and the surface tension measurement is about 42 mN/m at a temperature of about 70 \({}^{\circ}\)C. In the temperature range of 40-70 \({}^{\circ}\)C, the difference in surface tension is about 22.5 mN/m. The surface tension measurement is about 20.5 mN/m for the 2-butanol 15% aqueous solution, and the surface tension measurement is about 42 mN/m at a temperature of about 70 \({}^{\circ}\)C, or the 2-butanol 10% aqueous solution, the surface tension measurement is about 21.5 mN/m at a turning temperature of about 40 \({}^{\circ}\)C, and the surface tension measurement is about 37 mN/m at a temperature of about 70 \({}^{\circ}\)C. In the temperature range of 40-70 \({}^{\circ}\)C, the surface tension difference is about 16 mN/m. It can be seen that the higher the solute concentration of 2-butanol SRF, the larger the surface tension inverse gradient. In particular, the 2-butanol 20% inverse gradient is the most obvious, and in Ref. [11], it is stated that the higher the concentration of butanol, the more vigorous the Marangoni effect; the more vigorous Marangoni effect also raises the critical heat load.  
In Figure 6, it can be observed that the higher the saturation concentration of SRF, such as the 2-butanol 20% aqueous solution, the lower the initial 20 \({}^{\circ}\)C surface tension value. It helps to evaporate the surface tension inverse gradient between 40 and 70 \({}^{\circ}\)C, and the size is also positively correlated with the SRF formulation concentration size. In the literature, [PERSON] [3] stated that the larger the inverse gradient of SRF, the more pronounced the Marangoni effect.  
In this paper, the surface tension was measured according to the saturation concentration of Butanol 6%, and the results showed that the surface tension value was about 31 mN/m at the turning temperature of the Marangoni effect of 50 \({}^{\circ}\)C, and about 46 mN/m at the temperature of 70 \({}^{\circ}\)C. In the temperature range of 50-70 \({}^{\circ}\)C, the surface tension difference was about 15 mN/m. Additionally, 15 mN/m is also the characteristic value of the Marangoni effect, and the larger the value, the more vigorous the Marangoni effect.  
The results of Figure 6 show that the higher the concentration of the SRF formulation, the more obvious the Marangoni effect, but this is limited by the saturation concentration of the solute. Therefore, the SRF of each solute saturation concentration working fluid was selected, including the 2-butanol 20% aqueous solution, butanol 6% aqueous solution and non-SRF water, and we further conducted the heat transfer performance test of the LHP transfer performance test.