Flow And Heat Transfer Characteristics Of Micro-channel Heat Exchanger Based On Field Synergy Principle

With the development of miniaturization and highly integrated of electronic equipment,the heat flux increases dramatically,therefore the conventional aircooling technology is limited.The micro-channel heat exchanger has the advantages of small volume,better heat transfer performance and easy packaging,it has important value and application for heat dissipation of large heat flux electronic devices.However,the flow and heat transfer characteristics of micro-channel heat exchanger are not fully understand,therefore need more in-depth study.In this paper,the micro-channel heat exchanger model with different geometric construction is established,and numerical simulation is conducted using pure water as medium to investigate the flow and heat transfer characteristics under different heat flux and flow rate.The effect of inlet and outlet arrangement(I-type,C-type,Z-type),header structure(Rectangular,Trapezoidal,Triangular,Arc),aspect ratio(r=1,2,4,5)and micro-channel arrangement(1#~5#)on flow and heat transfer are analyzed under different flow rate.And the results are analyzed in depth based on the field synergy principle.In addition,the experimental measurement system is set up and the flow and heat transfer characteristics of micro-channel heat exchangers with different structures are studied.Numerical simulation and experimental results show that,(1)For I-type heat exchanger,the flow rate in the middle channel is large,and on two sides gradually decreases;for C-type heat exchanger,the flow rate on the inlet and outlet side is higher and on the other side is lower;for Z-type heat exchanger,the flow rate on two sides is higher and in the middle channel is lower.The I-type heat exchanger has the minimum standard deviation of mass flow rate(SI=0.071).For I-type heat exchanger with different header structure,the analysis results show that the flow rate of the middle channel is higher and the flow rate of the two sides of the channel is lower.Furthermore,the rectangular header structure heat exchanger has the minimum standard deviation for flow rate,the standard deviation for triangular header structure is maximum and the arc header structure and trapezoidal header structure is in the middle.(2)For the same hydraulic diameter,the aspect ratio of channel has a little effect on average temperature of bottom surface,whereas it has a significant effect on heat transfer coefficient,and the convective heat transfer coefficient increasing 23.9%when the aspect ratio changed from 1 to 5.Base on field synergy principle,thesynergy angle between the velocity and temperature field decrease with the increasing of aspect ratio,it suggest that the heat transfer is enhanced.(3)For Z-type,a new heat exchanger(5#)is obtained with the channel stagger arrangement.The result indicate that the distribution uniformity of flow rate is improved,and take into account the pressure drop and mean temperature of heat surface,the heat exchanger with micro-channels stagger arrangement presents better performance.(4)The pressure drop and heat transfer characteristics of three different heat exchangers(1#,3#,5#)are investigated employing experiment method.The results show that the pressure drop between inlet and outlet increases with the increasing of flow rate.Compared with the three heat exchangers with the same flow rate,5#heat exchanger has the smallest pressure drop,whereas the pressure drop of 3# heat exchanger is largest.(5)The result also indicate that the temperature difference between inlet and outlet gradually increase with the increasing of flow rate,and the average temperature of the bottom surface decrease gradually,and the effect of flow rate is inconspicuous until the flow rate greater than 300mL/min.The average heat transfer coefficient increases with the increasing of the flow rate;whereas the impact of heat power is not obvious.Under the same flow rate,the heat transfer coefficient of the 5# heat exchanger is the largest,and 3# heat exchanger is the smallest.Considering the flow and heat transfer characteristics,5#heat exchanger has the lower pressure drop and better heat transfer performance.