In order to evaluate the insulation of two-phase immersion cooling in the HV power electronic package,the insulation degradation of the dielectric interface induced by bubbles is investigated.In this paper,a test stra...In order to evaluate the insulation of two-phase immersion cooling in the HV power electronic package,the insulation degradation of the dielectric interface induced by bubbles is investigated.In this paper,a test strategy with 50 Hz unipolar DC and AC combined voltage for partial discharge(PD)at boiling interface of AlN ceramic is proposed.The insulation threshold of an AlN ceramic surface is acquired in several dielectric environments,such as air,FC-72 liquid(FC-72,a Fluorinert^(TM) from 3^(TM)),FC-72 vapor,and boiling state of FC72.This reveals the deterioration of boiling on the insulation of the surface immersed in the dielectric refrigerant.To investigate the mechanism of the PD feature at the boiling interface,the PD patterns of the unrestricted bubble and the accumulated bubble are acquired and contrastively analyzed.Combined with the feature of the back discharge and the bubble behavior,the charged vapor-ceramic interface is relatively stable due to the accumulated vapor layer.This stability of the charged vaporceramic interface is broken if the bubble is unrestricted.Besides,it is discovered that the vapor-liquid interface inside the bubble may be another charged interface,which can also trigger a back discharge.展开更多
To investigate the size effect on the characteristics of boiling heat transfer, boiling behavior of FC-72 in heated vertical miniature circular tubes immersed in a liquid pool was experimentally studied. Two AISI 304 ...To investigate the size effect on the characteristics of boiling heat transfer, boiling behavior of FC-72 in heated vertical miniature circular tubes immersed in a liquid pool was experimentally studied. Two AISI 304 stainless steel tubes with inner diameters of 1.10 mm and 1.55 mm correspondingly, were heated by swirled Ni-Cr wire heaters and sealed in Lucite blocks by silicon adhesive. Both the top and the bottom ends of the circular test sections were open to the liquid pool. The boiling curves and heat transfer coefficients were obtained experimentally. The boiling behaviors at the outlets of the miniature tubes were also visualized with a digital video camera. Experimental results show that the tube geometry has a significant effect on the boiling characteristics. Vapor blocking at the outlet of the smaller circular tube with a diameter of 1.10 mm caused severe boiling hysteresis phenomena. The CHF decreased with reducing in tube size.展开更多
This paper investigates the relative stability between nucleate and film boiling modes of FC-72 and HFE-7100, which have potential to electronic device cooling applications. Equilibrium heat flux, qc, which refers to ...This paper investigates the relative stability between nucleate and film boiling modes of FC-72 and HFE-7100, which have potential to electronic device cooling applications. Equilibrium heat flux, qc, which refers to as an index for measuring the relative stability of boiling, was obtained at a liquid subcooling of 0-20 K. Experimental results reveal that (1) qc increases with liquid subcooling; (2) although the FC-72 exhibits a higher critical heat flux (CHF) than does the HFE-7100, somewhat unexpectedly, the equilibrium heat flux for the latter is greater than the former. Restated, at a prescribed heat flux, the risk to burnout for boiling of FC-72 is higher than that of HFE-7100. The shift in boiling curves interprets the experimental findings.展开更多
基金supported by the National Natural Science Foundation of China-State Grid Corporation Joint Fund for Smart Grid(No.U1766219)。
文摘In order to evaluate the insulation of two-phase immersion cooling in the HV power electronic package,the insulation degradation of the dielectric interface induced by bubbles is investigated.In this paper,a test strategy with 50 Hz unipolar DC and AC combined voltage for partial discharge(PD)at boiling interface of AlN ceramic is proposed.The insulation threshold of an AlN ceramic surface is acquired in several dielectric environments,such as air,FC-72 liquid(FC-72,a Fluorinert^(TM) from 3^(TM)),FC-72 vapor,and boiling state of FC72.This reveals the deterioration of boiling on the insulation of the surface immersed in the dielectric refrigerant.To investigate the mechanism of the PD feature at the boiling interface,the PD patterns of the unrestricted bubble and the accumulated bubble are acquired and contrastively analyzed.Combined with the feature of the back discharge and the bubble behavior,the charged vapor-ceramic interface is relatively stable due to the accumulated vapor layer.This stability of the charged vaporceramic interface is broken if the bubble is unrestricted.Besides,it is discovered that the vapor-liquid interface inside the bubble may be another charged interface,which can also trigger a back discharge.
基金This work was supported by the National Natural Science Foundation of China (No.50176039) and Hong Kong RGC Earmarked Research Grants (No. HKUST6038/02E).
文摘To investigate the size effect on the characteristics of boiling heat transfer, boiling behavior of FC-72 in heated vertical miniature circular tubes immersed in a liquid pool was experimentally studied. Two AISI 304 stainless steel tubes with inner diameters of 1.10 mm and 1.55 mm correspondingly, were heated by swirled Ni-Cr wire heaters and sealed in Lucite blocks by silicon adhesive. Both the top and the bottom ends of the circular test sections were open to the liquid pool. The boiling curves and heat transfer coefficients were obtained experimentally. The boiling behaviors at the outlets of the miniature tubes were also visualized with a digital video camera. Experimental results show that the tube geometry has a significant effect on the boiling characteristics. Vapor blocking at the outlet of the smaller circular tube with a diameter of 1.10 mm caused severe boiling hysteresis phenomena. The CHF decreased with reducing in tube size.
文摘This paper investigates the relative stability between nucleate and film boiling modes of FC-72 and HFE-7100, which have potential to electronic device cooling applications. Equilibrium heat flux, qc, which refers to as an index for measuring the relative stability of boiling, was obtained at a liquid subcooling of 0-20 K. Experimental results reveal that (1) qc increases with liquid subcooling; (2) although the FC-72 exhibits a higher critical heat flux (CHF) than does the HFE-7100, somewhat unexpectedly, the equilibrium heat flux for the latter is greater than the former. Restated, at a prescribed heat flux, the risk to burnout for boiling of FC-72 is higher than that of HFE-7100. The shift in boiling curves interprets the experimental findings.
