Structural Design And Study On Performance Of Flow And Heat Transfer Of Complex Microchannel Heat Exchanger With Reentrant Cavitives

In recent years,with the rapid development of micro-machining technology,microheat exchangers with microchannels have appeared one after another.Micro-scale flow and heat transfer have become the focus of current attention.With the increasing development of large-scale integrated circuits,the heat dissipation of micro-devices with high heat flux is close to 107W/m2,and the microchannel heat exchangers with simple structure can not meet the heat dissipation requirements.Based on the straight microchannel model established in the previous stage,the microchannel with circular reentrant cavitives is designed,and the flow and heat transfer performance are studied by numerical method.Entropy production model of microchannel with circular reentrant cavitives is established based on the second law of thermodynamics.Thermodynamic analysis was carried out using the principle of entropy production and field synergy.Further,the influence of cavity structure parameters such as cavity shape,ellipticity and rib arrangement on the performance of flow,heat transfer,field synergy,entropy production and heat transfer efficiency of microchannel with reentrant cavitives were studied.Through the array process of single microchannel,microchannel array model with complex reentrant cavitives is established,and microchannel heat exchanger with the corresponding complex cavity structure is designed,and further more,numerical simulation analysis is carried out.Also,microchannel heat exchanger with the corresponding complex cavity structure is processed and manufactured.And the experimental platform is designed and built for experimental verification.The main research contents are as follows:1)Heat transfer model of microchannel with reentrant cavitives based on the field synergy principle was established.Based on the principle of field synergy,the intrinsic mechanism of heat transfer enhancement of microchannel with reentrant cavitives is analyzed.The entropy production model of microchannel with reentrant cavitives is established based on the second law of thermodynamics,and the heat transfer enhancement of microchannel with reentrant cavitives is analyzed from the lowest principle of entropy production.At the same time,the thermal energy transfer efficiency of the microchannel heat transfer process is derived from the basic expression of exergy,and the thermodynamic model of the heat transfer enhancement of microchannel with reentrant cavitives is further improved.2)Research on the performance of microchannel with complex reentrant cavitives based on thermodynamic model and field synergy principle.A numerical model of straight microchannel and microchannel with reentrant cavitives were established to analyze the performance of flow,heat transfer,field synergy,entropy production and thermal energy transfer efficiency in the microchannel.The results show that the performance of flow,heat transfer,heat transfer field synergy,entropy production and thermal energy transfer efficiency of microchannel with circular reentrant cavitives are better than those of the straight microchannel,but the flow field synergy is poor than the straight microchannel.3)Combined with thermodynamic model and field synergy principle,the influence of cavity shape,ellipticity and rib arrangement on the performance of flow,heat transfer,field synergy,entropy production and heat transfer efficiency of microchannel with reentrant cavitives were analyzed.The results show that the performance of the microchannel with circular reentrant cavitives is optimal in the structure of different reentrant shapes(rectangular,trapezoidal,and circular).The performance of the microchannels with elliptical reentrant cavitives first improved and then weakened as the ellipticity increases.The microchannel with single-sided rib circular reentrant cavitives has the best flow performance,while the other performance is worse than the microchannel with odd-symmetric rib circular reentrant cavitives and the microchannel with double-symmetric rib circular reentrant cavitives.4)Structural design and numerical simulation of microchannel heat exchangers with complex reentrant cavitives.The flow velocity distribution,performance of the pressure drop and heat transfer of straight microchannel heat exchanger and microchannel heat exchanger with the circular reentrant cavitives are compared and analyzed.The results show that there is a low velocity gyration zone in the microchannel heat exchanger with circular reentrant cavitives.The pressure of both decreases with the increase of the fluid flow distance,and the former produces a larger pressure drop than the latter.The cold water outlet temperature of microchannel heat exchanger with the circular reentrant cavitives is higher than that of the straight microchannel heat exchanger,but the hot water outlet temperature is opposite.Further,the influence of the shape of reentrant cavitives(rectangular,trapezoidal,circular),ellipticity(ellipticity=0.4,ellipticity=0.6,ellipticity=0.8,and ellipticity=1.2)and rib arrangement(single-rib,odd-symmetrical and double-symmetrical)of the structural parameters on the performance of the microchannel heat exchanger were studied.The results show that there are fluid low velocity gyration zones in different shaped reentrant cavitives.The pressure drop and heat transfer performance of microchannel heat exchanger the circular reentrant cavitives are optimal.The pressure drop and heat transfer performance of microchannel heat exchanger with elliptical reentrant cavitives first improved and then weakened with the increase of the ellipticity.The heat transfer performance of microchannel heat exchanger double-symmetric rib circular reentrant cavitives is the best,and the pressure drop performance of microchannel heat exchanger with the single-sided rib circular reentrant cavitives is the best.5)Experimental study on the performance of microchannel heat exchanger with complex reentrant cavitives was investigated.The influence of the cavity,ellipticity and rib arrangement of the shape parameters on the performance of microchannel heat exchanger with complex reentrant cavitives were studied.And the experimental values were compared with the simulated values.The results show that among the different reentrant cavitives,the pressure drop and heat transfer performance of microchannel heat exchanger circular reentrant cavitives are optimal.And the pressure drop and heat transfer performance of microchannel heat exchanger with elliptical reentrant cavitives first improved and then weakened as the ellipticity increases.The microchannel heat exchanger with double-symmetric rib circular reentrant cavitives has the best heat transfer performance.The microchannel heat exchanger with single side rib circular reentrant cavitives has the best pressure drop performance.The simulation and experiment were compared and analyzed.The results show that the simulation is basically consistent with the experiment,which verifies the rationality of the previous numerical simulation.