Study On Pool Boiling Heat Transfer Performance Of Surface With Trapezoidal Microchannel

Due to the advantages of high heat transfer coefficient and large latent heat of phase change,pool boiling heat transfer is often used in high heat flux heat transfer process of the chemical industry,thermal engineering,nuclear reaction engineering and large-scale integrated circuit.In order to further enhance the heat transfer performance of pool boiling heat transfer,many scholars have studied the structure characteristics of heat transfer surface.Through the summary of previous studies,this thesis proposes a new type surface with trapezoidal microchannel,using the pool boiling heat transfer in a visual experimental method to study the influence of the different trapezoid parameters on the pool boiling heat transfer performance.The influence of the length and angle of the bottom of the trapezoidal microchannel on the heat transfer performance was obtained and the growth and movement of the bubbles on the heat transfer surface were observed.In the experimental range,the minimum initial boiling surface superheat of the trapezoidal microchannel surface is 1.4 K.The maximum initial boiling surface superheat is 5.2 K.The initial boiling surface superheat of the smooth surface is 5.9 K.The initial boiling temperature of the trapezoidal microchannel surface is lower than that of the smooth surface,and the maximum difference between them is 4.5 K.When the surface superheat is 8.3 K,the maximum heat flux on the trapezoidal microchannel surface is 1.2×10⁶W·m^-2,while the heat flux on the smooth surface is 5.0×10⁴W·m^-2,which is 24.0 times as much as that of the smooth surface.When the surface superheat is 13.2 K,the minimum heat flux on the trapezoidal microchannel surface is 1.3×10⁶W·m^-2,while the heat flux on the smooth surface is 1.7×10⁵W·m^-2,which is 7.6 times as much as that of the smooth surface.When the surface superheat is 10.6 K,the maximum heat flux of the rectangular microchannel surface is 1.3×10⁶W·m^-2.Therefore,the trapezoidal microchannel surface can obtain better pool boiling heat transfer performance.The increase of the bottom length makes the surface area of the trapezoidal microgroove increase,and the heat flux increase,so that the temperature of the liquid working medium in the groove is closer to the wall temperature,and the bubble is easier to produce.The decrease of the bottom angle will enhance the capture effect of the microchannel on gas,which is conducive to the generation of bubbles.Besides,the enhancement of the capillary force in the channel,which is conducive to the backflow of the working medium and the wetting of the heat exchange surface.Therefore,for the trapezoidal microchannel surface,with the increase of the bottom length and the decrease of the bottom angle,the pool boiling heat transfer performance is gradually enhanced.Through visualization experiment,it is observed that with the increase of heat flux,the number of bubbles on the heat transfer surface increases,the detachment diameter increases,and the detachment frequency increases.At both ends of trapezoidal microgroove,bubbles are produced earlier and the bubble detachment diameter is smaller.In the center area of the trapezoidal microchannel surface,bubbles were formed later and the bubble detachment diameter was larger.According to the analysis,the bubble escape resistance at both ends of the microchannel is smaller,and the bubble escape resistance in the center area is relatively larger.In addition,the bubbles generated in the center region produce two phenomena of horizontal fusion and vertical fusion,which is conducive to strengthening the heat transfer performance of the heat transfer surface.