Simulation Studies Of Enhanced Heat Transfer Characteristics Of Secondary Flow In Spiral Tube

The spiral wound heat exchanger is widely used in industrial production and is an important equipment for heat exchange.As the basic heat transfer element of the spiral wound heat exchanger,the enhanced heat transfer performance of the spiral tube is very important to the energy saving and consumption reduction of the industrial process.Secondary flow is a common flow state in spiral tube,and secondary flow enhancement heat transfer technology has been preliminarily studied and applied.In order to make better use of the secondary flow to strengthen the convection heat transfer in the spiral tube,two new parameters which can describe the intensity of the secondary flow in the spiral tube are first proposed,and then the relationship between the secondary flow type,the secondary flow strength and the convection heat transfer strength in the spiral tube is analyzed.flow pattern regulation method;finally,a new type of spiral longitudinal groove tube is proposed,and a stable high strength secondary flow is obtained in the tube,which realizes the further strengthening of the convection heat transfer process in the tube.The main contents,results and conclusions of this paper are as follows:(1)Numerical simulation was carried out to study the change rule of secondary flow pattern in spiral tube.The results show that the secondary flow pattern in the spiral tube presents a symmetric double vortex structure.In a certain range,the vortex increases with the Reynolds number and decreases with the pitch.However,when Reynolds number or pitch increase to a certain extent,the double-vortex structure of secondary flow presents instability.The Angle between the two vortex centers and the vertical direction increases with the increase of the pitch.(2)In order to define the secondary flow intensity in a spiral tube more accurately,the heat transfer law of enhanced secondary flow in a spiral tube was explored.The secondary flow strength parameters Ds number and the secondary flow strength Angle are presented respectively for ordinary and complex spiral tubes.The greater the Ds number and,the greater the secondary flow intensity.The secondary flow pattern,secondary flow intensity and convective heat transfer intensity in aspiral tube were numerically simulated.The results show that,within the range of structural parameters and technological parameters of spiral pipe studied in this paper,when the Ds number is within the range of about 1327 to 4016,that is,when the secondary flow intensity Angle in the tube is within the range of 0.5°to 1.5°,the spiral pipe has better heat transfer performance.In this case,the comprehensive evaluation factor of convective heat transfer of spiral pipe is within the range of 1.15 to 1.25.(3)In order to further improve the heat transfer effect of secondary flow in a spiral pipe,a new type of spiral longitudinal pipe is proposed,and its heat transfer performance is verified by numerical simulation.The results show that the heat transfer performance of spiral longitudinal tube is the best,and the heat transfer enhancement effect for high Prandtl number fluid is better than that for low Prandtl number fluid.In addition,the structural parameters of the spiral slotted pipe were optimized,including the depth of the spiral groove,the spiral Angle of the spiral groove and the number of the spiral slotted heads.The results show that the helix Angle has great influence on the comprehensive evaluation factor,while the groove depth and head number have little influence on the comprehensive evaluation factor.The optimal parameter scheme is as follows: the groove depth is 0.5mm,the spiral groove Angle is 82°,and the number of spiral groove heads is 1.In this case,the comprehensive evaluation factor of the spiral longitudinal groove tube is 1.173 compared with the ordinary spiral tube.