Research On Enhanced Heat Transfer Performance Of Bionic Structure Microchanne

In recent years,with the continuous improvement of microfabrication technology,the integration of devices in many engineering fields has become more and more advanced,and the consequent heat dissipation problem has become more and more severe,and the micro cooling system represented by the micro channel heat exchanger has received wide attention in the international academic community.Especially in the field of microelectronics,the heat dissipation of micro devices with high heat flow density has been increasing,and the traditional rectangular microchannel heat exchanger has been unable to meet the cooling demand.In order to enhance the integrated performance of fluid flow and heat transfer inside the microchannel,bionic ideas are introduced to guide the structural design and optimization of microchannel heat exchangers.Combining numerical simulation and theoretical methods,the thermodynamic model and structural optimization model of the bionic structure microchannel are constructed to explore the integrated heat transfer performance of the bionic structure microchannel in single-phase and boiling processes,reveal the enhanced heat transfer mechanism of the microstructure,and aim to design a compact micro heat exchanger with excellent heat dissipation effect.The main contents of the paper are as follows:（1）By simplifying the structure of shark epidermal shield scales,four new shark bionic rib microchannels were designed,namely,equal-length parallel-arranged ribs,equal-length staggered-arranged ribs,non-equal-length parallel-arranged ribs and non-equal-length staggered-arranged ribs with rib height H of 0.01-0.1 mm,which were arranged at the bottom of the microchannels to enhance the flow and heat transfer performance.The effect of rib arrangement and rib height on the flow and heat transfer performance was investigated by means of performance evaluation diagrams and entropy yield principle.It was found that the microchannels with staggered and unequal bionic ribs had the best overall heat transfer performance,and the entropy generation increase N_s,a reached the lowest value of 0.43 at the optimum rib height of 0.06 mm and Re=770,indicating the highest energy utilization.（2）By combining fish scales with shark epidermal shield scale microstructure,a novel fish scale structured microchannel with splitting slits was designed,and the effects of the number of fish scales and arrangement on the flow and heat transfer performance were investigated.The results show that under the parallel arrangement condition,the comprehensive heat transfer performance of the fish scale microchannel with splitting slits is the best when the number of fish scales is 32;at Re=1180 and the number of fish scales is 32,the comprehensive heat transfer performance of the microchannel with triangular arrangement is the best,and the enhanced heat transfer factor is 2.08,because the arrangement of the microstructure increases the secondary flow diffusion area,reduces the pressure drop and increases the effective heat transfer area.（3）The microstructure of microchannels can also effectively enhance the flow boiling heat transfer.By comparing the vapor bubble behavior and flow boiling characteristics in the bionic structure microchannels and rectangular microchannels,the mechanism of microstructures such as concave cavities and bionic ribs to suppress the flow instability and enhance the boiling heat transfer is revealed.In the flow boiling process,the local drying phenomenon leads to boiling instability,and the microstructure suppresses the local drying phenomenon,which makes the wall temperature and inlet pressure of the bionic structure microchannel more stable;comparing the two microchannels,the nucleation point of vapor bubbles inside the bionic structure microchannel is significantly increased,and the cavity structure can limit the excessive growth of vapor bubbles and avoid local drying,so the bottom temperature of the channel is lower and the heat transfer performance is better.At the flow rate G=498 kg/（m²·s）and heat flow density q_w=600k W/m²,the boiling heat transfer coefficient of the bionic structure microchannel is about 1.45 times that of the rectangular microchannel.