【作者】 杨汝仲；

【导师】 邓先和；

【作者基本信息】 华南理工大学 ， 化学工程， 2010， 硕士

【摘要】 本论文采用数值模拟和实验研究相结合的方法以水、50%甘油和85%甘油为传热工质,分别对光滑管和缩放管插入2种不同结构形式旋流片的局部流阻与传热性能进行了数值模拟研究,对不同管内流体介质的温度场和速度场进行了对比分析探讨。结果表明:在水为流动介质高湍流(15000<Re<40000)条件下,缩放管内插旋流片使得管道流体产生了强烈的漩涡流,旋流片产生的自旋流在旋流片下游18倍管径处消失;在有旋流片的一段管道中传热系数Nu和阻力系数都达到最大值,但是由于阻力的增加幅度远大于传热量的提高幅度使得有旋流片的一段管道中综合传热性能很差为0.55,最大值在旋流片下游产生约为1.23。整体综合传热因子小于1,为0.89。所以管内插旋流片在高度湍流条件下综合传热性能不理想的主要原因是:有旋流片的一段产生了太高的形体阻力和旋流片产生的自旋流在下游迅速衰减结束。在50%甘油为流动介质过度流(3000<Re<8000)条件下,缩放管内间隔插入旋流片的局部流阻与传热性能与介质水的情况相似。但是旋流片产生的自旋流在旋流片下游约15倍管径处消失,有旋流片一段管道的综合传热性能得到很大的改善为0.8,综合传热性能评价因子j的峰值为1.38。从总体而言传热综合性能提高1.08。在85%甘油为流动介质层流(400<Re<900)条件下,旋流片也能使得管内流体产生强烈的漩涡流在旋流片下游12倍管径处消失。有旋流片一段管道的综合传热性能为0.95,综合传热性能评价因子的最大值为1.41。所以整体平均上综合传热性能评价因子提高1.18。综上所述,缩放管内插旋流片对液体进行复合强化传热,在Re大于15000的湍流条件下综合传热性能不理想,综合传热性能小于1;在过渡流条件下综合传热性能超过1,但强化的幅度小于10%;在层流的条件下综合传热性能超过1,且强化的幅度大于18%。不同结构旋流片强化传热性能的比较显示出:旋转角为270度的旋流片在提高换热系数的同时带来了更大的形体阻力,其综合传热性能不如旋转角为180度的旋流片。层流条件下,由于管内流体的传热系数的提高幅度大于阻力系数的增加量使得缩放管内插旋流片复合强化传热方式更适用于传热介质在低雷诺数下的流动状态。更多还原

【Abstract】 In this paper, the combining methods of numerical simulation and experimental study were used. Respectively with water, 50% glycerol and 85% glycerol as the heat transfer working fluid, the local flow resistance and heat transfer performance of smooth tube and converging-diverging tube with 2 different twisted-tapes inserted were studied in numerical simulation method. At the same time, both temperature field and velocity field of different pipes fluid mediums were compared and analyzed. The results show that at the condition of high turbulence (15000 <Re <40000) flow with water as working fluid, twisted-tape enables water to produce a strong vortex flow which disappeared at the downstream of the tape by 18-fold in the cyclone diameter. In section of a swirl pipe, the resistance coefficient f and heat transfer coefficient Nu reached maximum. Comprehensive heat transfer performance is poor at 0.55, the maximum produced at the downstream of the twisted-tape which is about 1.23. Therefore, swirl tapes inserted in the pipe at the condition of highly turbulent flow heat transfer performance is not satisfactory mainly due to two reasons. On the one hand, a section of a swirl tape of the body produced too much resistance and on the other hand the swirl flow generated by the twisted-tape decays by the rapid way in the downstream at the end of twisted-tape.Under the condition of 50% glycerol as the flow fluid medium with low turbulent (3000 <Re <8000), the local flow resistance and heat transfer performance of smooth tube and converging-diverging tube with different twisted-tapes inserted are Similar to the situation with the medium fluid water. However, twisted-tape enables medium fluid to produce a strong vortex flow which disappeared at the downstream of the tape by 15-fold in the cyclone diameter. Comprehensive heat transfer performance is greatly improved at 0.8 the maximum produced at the downstream of the twisted-tape which is about 1.38. Overall speaking, comprehensive heat transfer performance is increased 1.08. Under the condition of 85% glycerol as the flow fluid medium with low laminar (400 <Re <900), twisted-tapes can also make fluid in the pipes to produce a strong vortex flow which disappeared at the downstream of the tape by 12-fold in the cyclone diameter. Comprehensive heat transfer performance is at 0.95, the maximum produced at the downstream of the twisted-tape which is about 1.41. So the comprehensive heat transfer performance is increased 1.18.In summary, the use of twisted tapes for the liquid to enhance heat transfer, comprehensive heat transfer performance is at 0.89 which duces poor heat transfer. Integrated under the transitional flow, the result of enhance heat transfer is better, but the enhanced rate less than 10%. Laminar flow conditions in the integrated heat transfer is best, and the enhanced rate of is greater than 18%.mparison performance of enhanced heat transfer capability of different structure twisted-tapes shows that the rotation angle of 270 degrees swirl chip at the same time increases the heat transfer coefficient has brought a greater physical resistance to flow fluid, which Heat transfer performance is not as good as 180-degree rotation angle of swirl tapes. In laminar flow, because the heat transfer coefficient increased in magnitude is greater than the increased in the amount of drag coefficient, the method of compound heat transfer enhancement of a converging-diverging tube with regularly spaced twisted-tapes is more suitable for the heat transfer medium fluid flowing at low Reynolds number condition.更多还原