Optimization Design And Numerical Analysis Of Steam Heat Exchanger For Setting Machine

Heat exchanger is wide applied in machinery, power, transportation, air conditioning, refrigeration, low temperature, heat recovery, alternative fuels and manufacturing areas. Compared to traditional industrial heat exchanger, steam heat exchanger for heat setting machine needs higher steam flow. The average steam consumption of a heat exchanger is about 0.5-1.2 ton per hour. So optimize the design of heat setting machine and improve the heat transfer efficiency, will obviously raise the energy efficiency of the heat exchanger. For this target, in this paper we will devide the steam heat exchanger for heat setting machine into two parts:tube side heat transfer and shell side heat transfer, then analyze the flow process and heat transfer process of both parts through numerical simulation.In the part of tube side heat transfer, we insert mandrel into horizontal heat transfer tube to optimize its structure, and through numerical simulation, we analyze changes of heat pipe's heat transfer property under different ratios of mandrel diameter and tube diameter, then find out the optimum ratio. Through simulation analysis, we know that inserting mandrel into horizontal heat transfer tube could improve the velocity gradient of mixture fluid in tube, and it will also improve the effect of condensation heat transfer. With mandrel in a horizontal tube, the heat exchange efficiency of horizontal tube increases with the increase of the diameter ratio. When the diameter ratio is between 0.517 and 0.571, the heat exchange efficiency of horizontal tube achieves its maximum value. When the diameter ratio is above 0.571, the heat exchange efficiency will decrease. With the increase of the diameter ratio, the cooperative performance of the horizontal pipe is improved, especially when the diameter ratio is above 0.517.In the part of shell side heat transfer, we will analyze the structure parameters of the screwed pipe by using numerical simulation, and then find out the optimum structure parameter of the fin. The analysis results will be compared and verified according to the field synergy theory. According to the results of simulation, the spacing of fins has the biggest influence on screwed pipe's heat exchange coefficient, and the next is the height of fins, the thickness of fins has the lowest influence. Decrease the spacing of fins, increase the height of fins or decrease the thickness of fins in a certain range at the same time, will increase the heat exchange coefficient of the screwed pipe. And with the decrease of fin spacing, the increase of fin height and the decrease of fin thickness, the average pressure drop of the screwed pipe will increase, that mean the increasing trend of heat exchange coefficient will slow down, or even disappear.At the same time, we also research the tube spacing and tube bundle arrangement of the heat exchange tube, investigate the influence of these two factors put on the heat exchanger, and explore the optimum value of heat transfer enhancement in horizontal tube under different tube bundle arrangements. After comparing the numerical simulation results of inline arrangement and staggered arrangement, we find that under staggered arrangement the fluid flow in the continuous expanding and shrinking channel, and its flow intensity is greater than inline arrangement. So it's more difficult to form stagnation zone in the downstream region of pipes and fins, and the heat transfer effect of staggered arrangement is obviously better than inline arrangement. The computational results show that the average Nu of staggered arrangement is 25.3% higher than inline arrangement. This result shows that under the same pipe spacing, the heat exchange effect of inline arrangement is worse than staggered arrangement, but its reduce of external pipe flow resistance is smaller. In the parameters range of the simulation study in this paper, horizontal spacing has its best position for the heat transfer capability of the heat pipe heat exchanger. In this paper, the heat pipe model we select to do bundle arrangement has these parameters:the pipe diameter is 20 mm, the fin height is 6mm and the fin thickness is 1.3 mm. When it is inline arranged, the best horizontal spacing is 110mm, when it is staggered arranged, the best horizontal spacing is 50mm.