| With the rapid development of electronic information technology,the miniaturization and integration of electronic equipment is getting higher and higher,resulting in a sharp increase in heat flux density per unit area,ordinary cooling methods have been unable to meet the heat dissipation needs,microneedle rib heat exchanger two-phase boiling cooling technology based on the principle of phase change of working fluid,compared with other cooling methods,compact structure,high space utilization,the same heat load under the mass flow of smaller heat dissipation technology cooling efficiency is higher,has become a hot spot in the field of heat dissipation.At present,many research works on micro-scale flow and heat transfer are based on macro-scale experience,and due to the complexity of the needle-rib spacing and arrangement of microneedle rib heat exchangers on the heat transfer mechanism of two-phase flow at microscale,the applicability of macro-scale empirical formulas at microscale has yet to be verified.Moreover,the naming of the twophase flow pattern of the working fluid in the microneedle rib heat exchanger is not uniform,and the influence of the bubble behavior of the working fluid on the heat transfer capacity is more complicated,in order to make up for the shortcomings of the two-phase flow boiling heat transfer research of the microneedle rib heat exchanger at this stage,the main research content of this paper is as follows;1)Aiming at the two-phase flow heat transfer process of microneedle rib heat exchanger,by analyzing the mass transfer model of the multi-phase flow model,the twophase flow heat transfer model of the microneedle rib heat exchanger was constructed,focusing on the analysis of the bubble growth law and flow pattern evolution process in the microneedle rib heat exchanger.2)Based on the two-phase flow test platform of the microneedle rib heat exchanger,with deionized water as the working fluid,the mass flow rate of the channel inlet is set to be 88.92 hkg /,134.28 hkg /,171.72 hkg /,220.68 hkg /,the inlet water temperature is23℃、25℃、 27 ℃,29℃ and the heating power is 1481 W,1657W,1851 W,1983W,respectively,to 0.25 mm,0.5mm,0.75 mm,1.00 mm The heat transfer performance of the microneedle rib heat exchanger with 4 spacing cross-arranged microneedle rib heat exchangers was analyzed.The results show that;(1)For linear arrangement of microneedle rib heat exchangers,in general,the heat transfer coefficient per unit area will increase with the increase of inlet mass flow,bottom heating power and working fluid inlet temperature.However,when the flow rate is small,LA-0.25 flow pattern appears compared to LA-0.50 more dense bubbles,resulting in local evaporation drying,affecting the heat transfer effect,LA-0.50 unit area heat transfer coefficient is greater than LA-0.25,with the increase of mass flow,LA-0.25 unit area heat transfer coefficient eventually exceeds LA-0.50 unit area heat transfer coefficient,in the needle rib spacing unchanged,linear arrangement microneedle rib heat exchanger will become larger with the heating power and limited increase,under the same heating power,linear arrangement microneedle rib heat exchanger its unit area heat transfer coefficient with the increase of needle rib spacing and decrease 。 The heat transfer coefficient per unit area of linear arrangement microneedle rib heat exchanger increases with the increase of working fluid inlet temperature,and the heat transfer coefficient per unit area of LA-0.25 is optimal in the same arrangement microneedle rib heat exchanger at the same working fluid inlet temperature.(2)For cross-arranged microneedle ribbed heat exchangers,the heat transfer coefficient per unit area increases with the increase of the flow rate.And with the gradual increase of mass flow,the relationship between the heat transfer coefficient and the microneedle rib spacing of the cross-arranged microneedle rib heat exchanger changes,with the increase of the bottom heating power,the heat transfer coefficient per unit area of the cross-arranged microneedle rib heat exchanger will become limited and larger,under the same heating power,the heat transfer coefficient per unit area of the linear arrangement of the microneedle rib heat exchanger decreases with the increase of the needle rib spacing.Under the condition of the same heating power,the decrease of needle rib spacing has a significant effect on the heat transfer coefficient per unit area of cross-arranged microneedle rib heat exchanger.When the needle rib spacing of the microneedle rib heat exchanger remains unchanged,the heat transfer coefficient per unit area of the crossarranged microneedle rib heat exchanger increases with the increase of the working fluid inlet temperature,and the influence of the spacing on the heat transfer capacity is also very significant when the same working fluid inlet temperature is also very significant.(3)Under the same spacing,under low mass flow,the difference between CA-0.25 and LA-0.25,CA-0.50 and LA-0.50 per unit area heat transfer coefficient is not obvious,when the inlet flow rate gradually becomes larger,the heat transfer coefficient per unit area of the cross-arranged microneedle rib heat exchanger is significantly greater than that of the linear arrangement of the microneedle rib heat exchanger.Under the condition of the same heating power,the heat transfer coefficient per unit area of the cross-arranged microneedle rib heat exchanger is greater than that of the linear arrangement of the microneedle rib heat exchanger,and with the increase of the spacing,the impact of different arrangement on the heat transfer coefficient per unit area will gradually become greater under the same heating power.When the inlet temperature of the working fluid is the same,the heat transfer coefficient per unit area of the linear arrangement microneedle rib heat exchanger and the cross-arranged microneedle rib heat exchanger shows the same law as when the heating power is the same. |
PDF Full Text Request