| With the wide application of new energy technologies(such as trough solar thermal technology)and the system of deep utilization of waste heat,lowheat flow and lowflow heat exchange have drawn more and more attention.Moreover,with the continuous application of boiling heat trans fer phenomenon,the horizontal arrangement of heat transfer pipes is applied in more andmore o ccasions.In the solar collector system of low heat flux density,when the heat pipes are arranged horizontally,there is a gas-liquid stratification phenomenon.In the circumferential direction,due to the existence of gas-liquid stratification,there is a large temperature difference between the top and bottom regions of the evaporating section,In the axial direction,due to the change of the flow pattern,a large temperature difference occurs in the axial direction,the axial temperature uniformity is poor.There is a lot of room for improvement for both the circumferential direction and the average axial temperature in the evaporation section.In this paper,based on the horizontal arrangement of experimental system of natural circulation flow boiling and evaporimeter homogenization temperature control in evaporation section,different wettability surfaces were prepared by chemical surface etching,and the circumferential and axial soaking temperature were controlled by different wettability combinations With improvement.The temperature uniformity in the evaporating section was controlled by semi-superheated and semi-superposed hydrophilic surface of the evaporating section.The axial uniform temperature in the evaporating section was controlled by the superhydrophilic surface of the evaporating section and the compound surface(three kinds)of the evaporating section.Based on the target of controlling the temperature uniformity in the evaporating section,the temperature uniformity in the evaporating section improved obviously after half-tube modification.Under the conditions of 1000W power,the maximum temperature difference in the evaporating section decreased from 10.4 ℃ to 4.29 ℃,and the temperature uniformity difference in the circumferential direction From 5.4 ℃ to 3.19 ℃.Under different power conditions,the half-tube modification of evaporation section has the same significant improvement on the temperature uniformity in the evaporating section,and the optimal solution for the circumferential regulation of different power evaporating sections is obtained.Based on the heat transfer characteristics of the evaporation section has also been significantly improved.Based on the target of controlling axial temperature uniformity in the evaporating section,a modified method of partial superhydrophilic and compound surfaces(three kinds)was adopted.Using partial superhydrophilic modification of the surface,the maximum axial temperature difference in the evaporating section was reduced by one half compared with the original surface under different power conditions.The axial mean square deviation of the evaporating section was less than 2 ℃ under the power of 1500W,and the temperature uniformitywas improved The effect is more obvious;on the basis of improving the axial temperature uniformity,the heat transfer coefficient of the evaporation section also has a higher magnification.Adopting the three kinds of compound surface modification evaporation section axial temperature uniformity has a more significant improvement.Under the condition of 1000W power,the maximum axial temperature difference in the evaporating section reached to 1 ℃ and the mean square deviation in the evaporating section was less than 1 ℃.Under different power conditions,the axial temperature uniformity in the evaporating section improved obviously.Under the five power conditions,The maximum axial temperature difference is less than 1.5 ℃,and the maximum axial mean square error of evaporating section is less than 1 ℃ under the five power conditions.And the optimal solution of axial temperature uniformity control under different power conditions is obtained.On the basis of improving the axial temperature uniformity in the evaporating section,the heat transfer characteristics of the evaporating section are also obviously improved. |
