| The power electronics elements of the next generation would dissipation much high heat flux. Among their thermal management solutions, two-phase jet impingement cooling and spray impingement cooling are two promising methods. Due to the mechanism of generating spray and jet, it is hard to compare those two methods in the consistent conditions. In the first part of this study, electrohydrodynamic atomization (EHDA) method is used to generate spray from the same capillary, from which the jet could be generated either, so that two different impingement cooling methods could be compared in the consistent conditions.;Before the experiment of EHDA impingement cooling, 14 EHDA modes are classified in the testing range with ethanol. Two nondimensional parameters are developed, in order to clearly lay out 11 EHDA modes within the EHDA mode map.;Experiments of EHDA impingement cooling are conducted in various nozzles and conditions. It is found that the EHDA cooling could enhance the heat transfer coefficient in most conditions. As the CHF, EHDA cooling has little benefit. The electric repulse force causes the wide spray angle, which could reduce the CHF by losing certain amount of impingement flux, no matter with single or multi EHDA impingement cooling. In the second part of this study, single and multi micro jet impingement cooling (MJIC) are investigated with three kinds of fluids and three types of microjet nozzles. The experimental results indicate that the existing CHF correlations could not predict experiment data of single MJIC. Based on experimental observation and theoretical analysis, a semi-theoretical CHF mode is proposed that divided the whole surface into two characteristic regimes. The experimental results of water and ethanol are coincided with the prediction by the new CHF correlation based on the model. And the CHF prediction process is discussed and presented with purpose of real application. That CHF correlation over predicts the CHF for HFE7000, possible reasons are discussed in the paper. An interesting and unique trend are found in the CHF test for saturated HFE7000 and subcooled ethanol, our new CHF model shows the potential to explain the unique feature.;Three CHF correlations with the CHF experiments results for the multi MJIC. Monde's V-correlation and the semi-theoretical CHF correlation could not predict very well. The correlation obtained by data regression, works better than the other two. The experimental results show that the heat transfer enhancement by multi MJIC depends on fluids and testing conditions. This approach normally could achieve high CHF at same Re number, but at same flowrate. It might cause negative, neutral and positive effect on water, ethanol and HFE7000, respectively. The heat transfer coefficient could be improved by using multi MJIC with water. However, in case of MJIC with ethanol and HFE7000, multi MJIC shows very little advantages over the single MJIC. |
