| Under the background of people’s high demand for substances and large energy consumption,the development of microchannels has been promoted.Microchannel heat exchangers are widely used in aerospace,electronic information,biological engineering,military and nuclear energy,microelectronic machinery and other high-tech fields due to their small size and large heat transfer specific surface area,therefore,in-depth research on microchannel heat exchangers,design of microchannels with high comprehensive heat exchange efficiency and reasonable structure has become a hot topic at present.The secondary heat exchange process of the microchannel heat exchanger is carried out along the direction of the height of the solid between the irregular pores,and the secondary heat exchange surface is difficult to determine,and there is no unified calculation method at present.In this paper,a mathematical method for solving the secondary heat exchange surface—the equal-area compensation method is proposed,the unit block model in the microchannel structure is extracted,and the heat exchange area and thickness of the unit block are further obtained,and then the numerical simulation method is used for in-depth research.The minimum heat exchange unit of the arc-section microchannel heat exchanger was established by Solidworks software as the research object,and the thermal-hydraulic properties of the arc-section channels with different aspect ratios were studied by the method of combining numerical simulation and experiment.Especially when the hydraulic diameter,cross-sectional area and arc height are constant,the influence of aspect ratio on the JF factor is studied,and the optimal aspect ratio is selected.A physical model for enhancing heat transfer in microchannels is proposed,that is,regularly adding built-in convex structures in the channel to enhance the turbulent heat transfer effect of microchannels.The numerical simulation and analysis of the flow field of the microchannels were carried out,the enhanced heat transfer corresponding to different arrangements of the raised structures was comparatively studied.Build an experimental platform,design a microchannel heat exchanger with detachable heat exchange sheets to conduct heat exchange performance experiments,measure related physical quantities: the temperature of the cold water inlet and outlet of the microchannel heat exchanger,the temperature of the hot water inlet and outlet,and study the arc section of the microchannel.The effect of heat exchanger on heat transfer performance under different aspect ratios is verified and analyzed with numerical simulation.The research shows that the proposed equal-area compensation method is feasible and can be extended to micro-channel heat exchangers with ordinary holes,so as to obtain a set of reasonable micro-channel low-temperature refrigeration mechanisms for reference.The flow velocity has a great influence on the flow and heat transfer performance of the microchannel.By studying the aspect ratio of the JF factor under different sections,it is found that when the aspect ratio of a specific channel section is used,the overall performance of the microchannel heat exchanger is the best,which can provide information for structural design.A new optimization method,setting a certain bulge height,can effectively improve the comprehensive heat exchange performance in the microchannel heat exchanger,so that the heat exchange efficiency can reach the best ideal state.Compared with uniform,first sparse and then dense arrangement,the arrangement of convex structures is dense first and then sparse can improve the heat transfer without increasing the pressure drop.Through experiments,it is found that the experimental results are basically consistent with the numerical simulation results,and the change trend of the heat transfer coefficient per unit volume is consistent. |
PDF Full Text Request