| The development trend of electronic devices gradually become miniaturized and integrated, which cause the over concentration of the high heat flux in the device. The adverse thermal environment can seriously degrade the performance and service lives of electronic devices. The advanced cooling technology is needed to solve the thermal problem of the electronic device. Heat pipe technology that utilizes the phase change latent heat of working fluid and transfers the high heat flux from hot side to cold side is expected to solve the thermal problem of electronic devices. In order to increase and strengthen the heat transport performance of heat pipes, finding out a suitable working fluid is one of the most direct and effective ways. Self-rewetting fluids(SRWFs) are believed to improve the thermal performance of heat transfer devices. SRWFs are non-azeotropic solutions satisfied to enjoy a particular surface tension behavior—an increase in the surface tension with increasing temperature. Due to the Marangaoni effect caused by the concentration gradient and the temperature gradient, the fluid spontaneously flows to the hotter region, thus enhancing the heat transfer and preventing the dry out phenomenon of the heated surface. The research progress on heat transfer mechanism of SRWF is still at an initial stage, and most researches focused on the heat transfer enhancement of SRWF. Taking into account the complicated influencing factor of self-wetting fluid heat transfer mechanism, it is necessary to make a further study on the flow and heat transfer mechanism of SRWF.In this paper, the preparation of SRWF is the first part, and the dilute aqueous solutions of long chain carbon alcohols are taken as research objects. It can be found from the research on the thermal physical properties that, the surface tensions of self-rewetting fluids show a non-linear behavior with the increase of temperature. Due to the Marangaoni effect caused by the concentration gradient and the temperature gradient, the fluid spontaneously flows to the hotter region, thus enhancing the heat transfer and preventing the dry out phenomenon of the heated surface. With addition of trace heptanol, the wettability of the solution can be effectively improved, and the value of contact angle is obviously decreased. Through the Young-Laplace equation, compared with the capillary resistance of water, the capillary forces of SRWFs are decreased gradually, the capillary resistance ratio between SRWF and water is only 22%-83%.A series of boiling experiments have been carried out to clarify the basic heat transfer characteristic and heat transfer enhancement mechanism of pool boiling with SRWFs, and dilute heptanol aqueous solution was enployed as SRWF. During the pool boiling tests, a boiling system with a horizontal heated wire was employed. The experimental results show that, the heat transfer enhancement mechanism has been discussed, and the critical heat flux(CHF) of the SRWF was much higher than that of water. The nucleation boiling process on the heated wire was recorded with a high speed video camera. It was found that, the bubble size of the SRWF is much smaller than that of water, and the adjacent bubbles of SRWF were hard to coalesce, which is conducive to the application in small thermal devices. What is more, when the heat flux is up to a certain value, the micro-bubble emission boiling(MEB) appears in the SRWF. It can be concluded that the Marangoni convection induced by surface tension gradient of SRWF is probably one of the key factors causing the formation of MEB.Experimental studies were performed on different heat pipes to find out the strengthening effect. During the experiments, SRWF and pure water were employed as the working fluids. The traditional sintered heat pipes and OHPs with inner diameter of 0.4, 0.8, 1.3 mm and heat transfer length of 100, 150 and 200 mm, consisting of 4 meandering turns, were adopted. The results showed that, the SRWF can spontaneously wet the hotter region due to the unique property that the surface tension increases with increasing temperature. The capillary resistance of the SRWF was much smaller than that of the pure water, and it is beneficial for improving the circulation efficiency of working fluids. Compared with pure water, the SRWF exhibited much better thermal performance, which show as extending the effective operation range and decreasing the thermal resistance of OHPs.Combined with the theoretical analysis, models for predictions of the bubble detachment diameters and the critical heat flux of SRWF are developed. Furthermore, the flow instability of SRWF has been analyzed in detail. It can be concluded that, self-rewetting fluid is a promising working fluid for electronic devices with adverse thermal environment, and the theoretical prediction model can provide an important guidance for cooling technology design. |
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