| Liquid jet impingement cooling of heated surface is a highly effective cooling method to enhance the boiling heat transfer. The jetting sub-cooled liquid can pass through the vapor bubble on the heated surface to acquire a greater solid-liquid contact angle. By this way, the CHF of sub-cooled liquid jet impingement nuclear boiling can be improved greatly and it is much bigger than that of the CHF of pool boiling. Liquid jet impingement has already been widely used in iron and steel industry, nuclear power process, some microelectronic devices making and thermal control processes.The geometries of a liquid steady jet impinging on a horizontal heated surface can be divided into two modes. One mode is the free film flow named as the mode A, in which a great heated disk or rectangular plate is cooled by a small liquid jet and the ratio of the heated disk area to the nozzle area is much larger than unity. The other mode is the stagnation jet flow named as the mode B, in which the area of the heat transfer surface is the same or smaller than that of the area of jet nozzle.For liquid jet impinging boiling on the heated plate, the critical heat flux (CHF) is a very important parameter that can express heat transfer characteristics. For the steady jet impingement cooling, the CHF is a systematical parameter and it depends on the jet impingement conditions such as the geometries of heated surface, jet impingement liquid, solid-liquid contact angle between jet impingement liquid and heated surface, jet velocity and jet nozzle conditions etc.A systematically steady experimental research about the CHF of saturated or sub-cooled liquid (water, ethanol and R-113) jet impingement cooling on heated copper surface or superhydrophilic surface in mode B was carried out.The following conclusions have been proposed by making use of the jet impingement boiling experiments to saturated water, ethanol and R-113: As to jet impingement boiling of saturated water, ethanol or R-113 on usual copper surface in stagnation zone, the jet nucleate boiling curves extends upward greatly when compared to the pool boiling curve. The CHF has been increased greatly with the increasing jet velocity of saturated water, ethanol and R-113. The jet velocity and jet diameter has great effect on the CHF. As to jet impingement boiling of saturated water, ethanol and R-113 on usual copper surface in stagnation zone, there is a dimensionless correlation exists among the CHF, jet velocity and jet diameter. By making use of combination method of semi-theoretical correlation and jet boiling experimental data of water, ethanol and R-113, an empirical correlation among the CHF, jet velocity and jet diameter has been proposed to saturated water, ethanol and R-113. The correlation can predict the CHF of saturated liquid jet impingement boiling on the usual metal surface and it can be used in a wide range.The following conclusions have been proposed by making use of the jet impingement boiling experiments to sub-cooled water, ethanol and R-113: As to jet impingement boiling of sub-cooled water, ethanol and R-113 on usual copper surface in stagnation zone, the jet nucleate boiling curves extends upward greatly when compared to the pool boiling curve. In the fully developed nucleate boiling zone, the effect of sub-cooling to boiling curve is not great. The CHF is increasing with the increasing sub-cooling of water, ethanol and R-113. As to jet impingement boiling of sub-cooled water, ethanol and R-113 on usual copper surface in stagnation zone, there is a relationship exists among the CHF, jet velocity and jet diameter. The empirical correlations among the CHF, jet velocity and jet diameter have been proposed to sub-cooled water, ethanol and R-113 respectively after the analyzing of experimental data. These correlations can well predict the CHF of sub-cooled water, ethanol and R-113. Besides the experimental research of jet impingement boiling on usual copper surface, a systematically steady experimental research about the CHF of saturated or sub-cooled water jet impingement cooling on heated superhydrophilic surface in stagnation zone was carried out as well. The following conclusions have been proposed after the research: As to the jet impingement boiling of saturated or sub-cooled water on superhydrophilic surface in stagnation zone, the great sub-cooling can increase heat transfer coefficient and delay the boiling incipient point. In the fully developed nucleate boiling zone, the boiling curve is very short. The boiling curve on superhydrophilic surface is very steep and almost vertically. The experimental data show that small contact angle can greatly delay forced convection heat transfer zone and prevent the occurrence of incipient boiling. A correlation has been proposed after the analyzing of experimental data. This correlation can well predict nucleate boiling heat transfer characteristics of water jet impingement on superhydrophilic surface. To the jet impingement boiling on the superhydrophilic surface, there is a relationship exists among the CHF, jet velocity and jet diameter not only to the saturated water, but also to the sub-cooled water. There is a good linear relationship exists between the CHF and sub-cooling of sub-cooled water as well. The contact angle has great effect on the CHF. The CHF on superhydrophilic surface is about 50% higher than that on the usual copper surface not only to the saturated water, but also to the sub-cooled water. A correlation has been proposed after the analyzing of experimental data. This correlation can well predict the CHF of water jet impingement on superhydrophilic surface in stagnation zone.On the basis of above experimental research, a physical mode has been established through theoretical analyze. By making use of combination method of the solving of the control equations in theoretical mode and jet boiling experimental data on traditional metal surface, the CHF numerical value of saturated water jet impingement boiling on different solid-liquid contact angel surface has been got. The relationship between the CHF of saturated water jet impingement boiling in stagnation zone and jet velocity, jet nozzle and solid-liquid contact angle has been studied theoretically.The numerical computation results have been compared with experimental data and semi-empirical semi-theoretical correlation. The numerical computation results agree well with the experimental data of saturated water jet impingement boiling under experimental conditions and semi-empirical semi-theoretical correlation in certain error range.The numerical computation results have been sorted out and the correlation between the CHF and jet velocity, jet nozzle and solid-liquid contact angle of saturated water jet impingement boiling has been proposed. The correlation has been compared with the CHF experimental data of saturated water jet impingement under experimental conditions. The correlation agrees well with the experimental data of saturated water jet impingement boiling under experimental conditions in certain error range.According to the results of numerical computation, the semi-empirical semi-theoretical correlation, which got in the CHF experiment of saturated water jet impingement boiling, has been improved. The effect of solid-liquid contact angle has been added to the correlation. The improved correlation has been compared with the CHF experimental data of saturated water jet impingement under experimental conditions. The correlation agrees well with the experimental data of saturated water jet impingement boiling under experimental conditions in certain error range. |
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