Critical Heat Flux on Subcooled Boiling (Effect of Concentration of Non-Condensible Gas)

实验研究了不凝气体对过冷沸腾临界热流密度的影响。不凝性气体的浓度用专门设计的气体收集器测量，其中测试液体被加热到蒸汽饱和温度以排出溶解的气体。2000年的研究旨在建立水中不凝性气体浓度的测量技术，研究表明：（1）加热液体以排空溶解气体的热通量必须足够高，以在加热器上产生蒸汽，并且液体的旋流有效地减少收集时间-最少5分钟。(2)由于收集的气体中含有水蒸气，因此需要使用气体释放时测量的气体温度减去水蒸气分压。以空气或二氧化碳为溶解气体，纯净水为测试流体，研究了溶解气体浓度对传热的影响， ...更多信息 2001年研究了临界热通量和气泡行为。沸腾表面是水平安装的直径为0.5 mm的铂丝，并用直流电加热。以约5 mm/s的速度供应过冷度和不凝气体浓度受控的试验液体。液体的过冷度固定在30 K，气体的浓度从0.2 dm^3/m^3到饱和。结果总结如下。(1)当气体浓度较大时，在低热流密度下换热得到增强，而在高热流密度下换热减弱。临界热流密度与浓度无关，几乎相同。(2)临界热流密度随气体浓度的增大而减小。(3)在相同浓度下，溶解CO2的水的临界热流密度比溶解空气的高约1 MW/m^2。(4)溶解二氧化碳的水的临界热通量较高的原因是，在气泡的冷凝侧，排空的气体更容易溶解到水中。它减少了翻斗效应对气泡收缩的影响。少

The objective is to investigate experimentally the effect of non-condensible gas on critical heat flux on subcooled boiling. The concentration of non-condensible gas was measured with a specially designed gas collector in which the test liquid was heated up to vapor saturation temperature to evacuate dissolved gas. The research in 2000 aimed at the establishment of the measurement technique of the concentration of non-condensible gas in water, which revealed the following :(1) Heat flux of heating liquid to evacuate dissolved gas must be high enough to generate vapor on the heater, and the swirl of liquid is effective to minimize the period of collecting - 5 minutes minimum.(2) Since the collected gas contains vapor, the subtraction of the partial pressure of vapor is necessary using the temperature of the gas, measured when the gas is released.Using air or carbon dioxide as dissolved gas, purified water as test fluid, the effects of the concentration of dissolved gas on heat transfer, … More critical heat flux and bubble behavior were studied in 2001. The boiling surface is 0.5 mm in diameter platinum wire horizontally mounted, and heated with direct current. Test liquid, the subcooling and the concentration of non-condensible gas of which were controlled, was supplied at about 5 mm/s. The subcooling of liquid is fixed at 30 K, and the concentration of gas was from 0.2 dm^3/m^3 to that of saturation. The results are summarized as followed.(1) When the concentration of gas is large, heat transfer is enhanced at low heat flux but reduced at high heat flux. Critical heat flux is attained nearly the same superheating independent of the concentration.(2) Critical heat flux decreases very much as the concentration of gas becomes large.(3) Critical heat flux in water dissolving carbon dioxide is about 1 MW/m^2 higher that that dissolving air comparing at the same concentration.(4) The reason why the critical heat flux in water dissolving carbon dioxide is higher is that the evacuated gas is easier to dissolve to the water at the condensation side of the bubbles. It reduces the dumper effect on shrinkage of bubbles on condensation. Less