Simulation Study On Heat Transfer Characteristics Of Variable Diameter Heat Conduction Tubing In Molten Salt Heat Storage Device

Serpentine heat exchange tube as a mature heat exchange tube section is widely used in a variety of heat exchange processes,its production is simple,mature technology,easy to clean,suitable for many occasions,so the study of the snake tube heat transfer has practical significance.It is of great theoretical significance to improve the energy utilization rate to strengthen the heat transfer efficiency by studying the method of intensifying heat transfer.In order to solve the problem of low heat transfer efficiency of ordinary serpentine tubes,this paper proposes to change the straight tube segment into alternating scaling tube on the basis of ordinary serpentine tubes,and use CFD software to carry out numerical simulation calculation on the heat transfer process of ordinary serpentine tubes and the modified serpentine tubes,and compare and analyze the change of heat transfer characteristics and resistance characteristics of the modified serpentine tubes.By means of numerical simulation,the heat transfer of the modified serpentine tube and ordinary serpentine tube is studied.It is found that the modified serpentine tube will strengthen the disturbance to the fluid in the tube,so as to achieve the effect of enhancing the heat transfer.Through the analysis of the results of numerical simulation,found that after the modification of 6 kinds of coil of Nu number average Nu number is larger than normal coil,and variable diameter coil in uniform fluid temperature distribution in the central area,long and contraction of 20 mm,expansion is the 10 mm long,groove deep 2mm diameter changes of the snake-like tube fluid low temperature high,and the heat transfer effect is best.But as the depth of the groove increases,so does the resistance.Therefore,the increasing depth of the groove will increase the flow resistance of the fluid while strengthening the heat transfer between the fluid in the tube and the wall of the tube.As far as the comprehensive heat transfer characteristics are concerned,the best reduced-diameter serpent tube with the shrinkage section length of 20 mm,expansion section length of 10 mm and groove depth of 1mm is obtained.By studying the influence of the curvature radius of the expansion section on the heat transfer characteristic of the variable diameter serpent tube,it is found that the comprehensive evaluation performance index of the heat transfer tube decreases with the decrease of the curvature radius of the expansion section.In terms of the research range,when the curvature radius of the expansion section is 15.4mm,the comprehensive heat transfer characteristic is the best.Molten salt heat storage device model is set up,using ordinary coil and best variable diameter coil heat exchanger with molten salt,through the analysis on heat transfer characteristics of the two kinds of heat storage device and the pressure drop,it is found that the heat transfer coefficient of the heat storage device using the best variable diameter serpentine tube is larger,but its resistance coefficient is relatively large,and the EEC value of the heat storage device using the best variable diameter serpentine tube is greater than 1,indicating The heat exchange effect of the modified best serpentine tube and molten salt is better than that of the ordinary serpentine tube.