Study On Heat Transfer Enhancement Characteristics Of Rough Microchannels Based On Field Synergy Principle And Entransy Dissipation Theory

In recent years,how to improve the efficiency of energy utilization has been paid close attention to by the contemporary society,so how to improve the efficiency of heat exchangers in the field of flow and heat transfer has become a research hotspot.Compared with conventional heat exchangers,microchannel heat exchangers have the advantages of small size and strong heat transfer capacity,so further improving the heat transfer capacity of microchannel heat exchangers has become an inevitable requirement for social development.In order to study the flow and heat transfer characteristics of rough microchannels,water is used as the fluid medium,and CFD software is used to simulate the flow and heat transfer of rough microchannels in laminar flow state.The influence of geometrical shape of rough elements on the flow and heat transfer of rough microchannels is analyzed.Based on field synergy and entransy dissipation theory,the theoretical analysis of heat transfer enhancement and flow drag reduction is carried out to explore the heat transfer enhancement of rough microchannels.The characteristics of flow and drag reduction provide theoretical basis for industrial application of microchannel heat exchangers.The numerical results show that:?1?For numerical simulation of two-dimensional periodic microchannels and entrance microchannels,microchannels Nu increases with the increase of relative roughness,while f increases with the increase of relative roughness.The PEC of the 2-D periodic microchannels and 2-D entrance microchannels with relative roughness of 5%in the simulated laminar flow range is the highest.The average heat transfer synergy angle?of the two microchannels decreases with the increase of relative roughness,and the average pressure drop synergy angle?increases with the increase of relative roughness,and the total entransy dissipation value E_vh increases with the increase of relative roughness.?2?Due to the influence of rough element shape,the square roughness element microchannels are the largest in the 2-D periodic microchannels and the 2-D entrance microchannels.PEC is used to evaluate the maximum PEC of the 2-D periodic microchannel stack roughness element microchannels,while the PEC of the square roughness element microchannels is the largest in the two-dimensional entrance microchannels;the average heat transfer of the square roughness element in both microchannels is the largest.The synergistic angle theta is the smallest,but the average pressure drop synergistic angle beta of square rough element microchannels is the largest,and the total entransy dissipation value E_vh is also the largest.?3?In the numerical simulation of the regular rough element in the two-dimensional entrance section,the influence of the distance between the rough elements is analyzed.When the spacing of rough elements is 1:1,the PEC is the largest;Comparing square roughness element with random roughness element,Nu and f in random roughness element microchannel are larger than square roughness element.It is estimated by PEC that the PEC of random roughness element microchannel is larger than square roughness element;the average heat transfer synergy angle?in random roughness element microchannel is smaller than square roughness element,but the average pressure drop synergy angle?in random roughness element microchannel is smaller than square roughness element.The total entransy dissipation value of E_vh in random rough element microchannels is larger than that in square rough element microchannels.?4?The numerical simulation of the random rough element microchannel in the three-dimensional entrance section is studied from the X and Z directions.The effect of random rough element on the thermodynamics of three-dimensional entrance microchannels is studied.The mechanism of heat transfer enhancement is analyzed based on field synergy and entransy dissipation principle,which lays a foundation for further study of heat transfer enhancement characteristics of three-dimensional microchannels.