Study On Pool Boiling Heat Transfer Of Water Based Self-Wetting Solutions With Multi-Carbon Alcohol

The Internet era is in full swing and the fields of electronic chips and artificial intelligence are developing at a rapid pace.Due to its high-density integration,miniaturization and high power characteristics,the problem of heat dissipation ensues.The use of traditional heat dissipation methods can no longer meet its heat dissipation requirements and there is an urgent need to strengthen boiling heat exchange.Self-wetting solutions can be used as an innovative means of enhancing boiling heat exchange due to their unique Marangoni effect,which allows the boiling evaporation area to be quickly wetted.The self-wetting solution has the advantages of being non-toxic,easy to prepare and inexpensive,so it is important to carry out boiling heat exchange research on it.In this paper,experimental studies have been conducted on the interfacial properties of self-wetting solutions and pool boiling heat transfer performance,with the main findings and conclusions as follows:(1)Basic theory of boiling heat exchange.A theoretical derivation of the bubble growth process based on bubble dynamics is presented,and introduced six classical nucleation boiling models that are currently more widely used.The correlation equations for the boiling heat transfer coefficients of pure and mixed masses are also summarized.It was found that the bubble diameter was proportional to time and that the key factor controlling the growth of the bubble was the micro-liquid layer between the liquid and the bubble.The mechanism by which self-wetting solutions affect boiling heat exchange is further studied in depth.It is concluded that thermal capillary convection and surface tension are key to dissecting the heat transfer mechanism of nucleation of self-wetting solutions.(2)Surface tension studies on self-wetting solutions.Aqueous solutions of n-butanol,n-pentyl alcohol and n-heptanol were prepared in various concentrations,and the surface tension was also measured.It was found that the addition of a high-carbon alcohol solution to pure water resulted in the formation of a very simple non-ionic surfactant solution,leading to a significant reduction in the surface tension of the solution.At lower temperatures,the surface layer adsorption model is not disrupted.As the temperature increases,the alcohol molecules in the surface layer diffuse into the liquid phase and the amount of alcohol adsorbed per unit area of the surface layer decreases,resulting in an increase in the surface tension of the solution.(3)Wettability studies of self-wetting solutions.The heated surfaces were sanded with2000#,500#and 120#sandpaper in two different ways,one unidirectional and one grid type.The roughness of the heated surface after grinding is measured and a three-dimensional picture of the microscopic contours of the heated surface is taken.Contact angles were measured for different concentrations of butanol,pentanol and heptanol aqueous solutions at the heated surface in turn.It was found that the three alcohol solutions showed a consistent pattern,i.e.the contact angle decreased with increasing concentration of alcohol at different coarseness.The Wenzel model was successfully validated at butanol concentrations of<5wt%.However,for butanol concentrations≥5wt%,the contact angle variation patterns at the three coarseness do not fit the Wenzel model,at the same time the contact angles of the three are more similar as the concentration increases.At butanol concentrations of<5wt%,the droplets showed significant anisotropic wetting characteristics in the unidirectional sanding mode.As the concentration of butanol increases,the droplets gradually change from initially round to oval.(4)Study of boiling heat exchange in self-wetting solution.A visualization cell boiling heat exchange experimental system was designed and built to test,and experiments were conducted in the heat flow density interval of 10-80 W/cm~2.The effects of the length of the carbon chain of the self-wetting solution,the subcooling of the solution in the cell,the roughness of the heating surface and the concentration of the self-wetting solution on the boiling heat exchange were investigated separately.The analysis was combined with the bubble behaviors and the boiling heat exchange curve.Results,aqueous butanol solutions are more effective in enhancing pool boiling heat exchange than aqueous pentanol and aqueous heptanol solutions;The subcooling of the solution has a great influence on the boiling heat exchange of the solution,reducing the subcooling of the main solution can significantly enhance the pool boiling heat exchange;There is a pattern of roughness effects on the pool boiling heat exchange,but there are range limitations when it comes to different solutions;After adding different concentrations of aqueous butanol solutions,the bubbles become smaller,the boiling phenomenon is more intense and the heat transfer performance is improved,but there is an optimal concentration interval,i.e.the best heat transfer effect in2wt%and 3wt%aqueous butanol solutions.