摘要
随着能源的日渐紧缺,节能措施变得越来越重要。我国换热设备能源利用率较低,有着很大的节能空间,特别是在翅片管式换热器领域,气体侧的强化换热有着广阔的发展前景。干工况下,理论研究与实验结果都表明:在翅片表面穿孔是一种很好的强化传热措施,具有较好的节能效果。在最窄通道截面风速Umax=1～8m/s的范围内,大直径圆孔翅片最优片型的当量换热系数h比平翅片增加了22.6%～30.4%,压降△P最大增幅不超过8%。在风速u=0.5m/s下结霜工况的实验研究结果表明:与平翅片相比圆孔翅片有效制冷量高出6.02%,表面对流换热系数高出18.84%,霜层形成过程中,传热系数比平翅片平均高出11.53%;圆孔翅片管式换热器的实际制冷换热系数比平翅片高出6.83%,节能6.39%。
圆孔翅片在干工况下强化传热研究只局限于实验,理论分析的深入程度不够。本文利用FLUENT软件的对平翅片、对称圆孔翅片和三对称圆孔翅片管式换热器空气侧的流动和换热进行了数值模拟,分析了不同风速下的速度场、温度场和努谢尔特数分布。模拟结果与已有实验结果吻合较好,平均误差小于10%。模拟结果证实:同等条件下,三对称圆孔翅片平均换热系数比平翅片平均高出25.7%,是其中的最优片型。
前期结霜工况下的实验研究是在一个冰箱中进行的,只有单风速的情况,实验结果不能全面反应圆孔翅片的强化传热性能。本文利用一个标准的风洞实验台,分别对平翅片、对称圆孔翅片和三对称圆孔翅片管式换热器进行了结霜工况下的换热和制冷性能对比性实验。比较分析了三种翅片管式换热器在实验条件下的有效制冷量、平均换热系数和阻力的大小;比较分析了强化翅片的节能效果。结果表明:实验条件下,三对称圆孔翅片的强化传热效果最好。①与平翅片相比较,三对称圆孔翅片的强化传热效果最显著,制冷量最大提高16.87%,平均提高9.1%。②平均当量换热系数与矩形平翅片相比,最大提高了80.15%,最小提高了49.66%,平均提高了64.29%。③COP值最大提高30.16%,最小提高14.95%,平均提高22.93%。
文章最后利用对称圆孔翅片做成的三排变间距蒸发器和非变间距蒸发器进行对比性实验,实验结果表明:①变间距翅片管式蒸发器前三个风速下当量换热系数平均比非变间距翅片管式蒸发器提高12.57%,最大提高18.26%,最小提高9.4%。②在满足制冷量的前提下,变间距翅片管式换热器节省材料21.43%,有显著的节能前景。
With the continual decrease in the world’s energy reserves, it has become more and more urgent for us to take effective energy-saving measures. In china, the energy utilization efficiency of the heat-exchanger equipments is relatively than of the advanced level. So, there are more potential in energy conservation of the heat exchange facilities, especially in the realm of the finned-tube, the enhancement of heat transfer on air-side has a long way to go. Ti has been proved, theoretically and experimentally, that perforating on the fin surface is a good way to enhance the heat transfer in the finned-tube with a perfect of energy conservation under dry condition. At the range of air flow velocity in the narrowest cross section from1 to 8 meter per second, the equivalent coefficient of heat transfer of the optimal holes finned-tube is higher by 22.6~30.4 percent than the plane finned-tube and, while the increase of pressure drop is under 8 percent. When the velocity is 0.5 meter per second, the experiment research show the cooling capacity of the holes finned-tube is higher by 6.02 percent, the heat convection coefficient of the surface is higher by 18.84 percent, and the heat transfer coefficient is higher by 11.53 percent in average during the frosting process than the plane finned-tube. The COP (coefficient of performance) of circle holes fin-tube heat exchanger is higher by 6.83 percent than the plane finned-tube, and saving energy is 6.39 percent.
At present because the enhancement heat transfer researches of holes fins are only used the experiment under dry condition, the air-sides flowing and heat transfer of the plane finned-tube heat exchanger, the symmetrical holes finned-tube heat exchanger and the three symmetrical holes finned-tube heat exchanger in the paper. The distributions of the velocity, the temperature and the Nu(number of Nuselt) are analyzed. The modeling result is high agree with the experiment bates, the average error is less 10% with obtaining the best optimal kind of fin named three symmetrical holes’fin. Its average heat transfer coefficient is higher by 25.7% in average than the plane fin.
Because experiment research is used the refrigerator with only the velocity value under frosting condition, so the experiment result can’t reflect the enhancement heat transfer performance of the circle holes fin. A wind-tunnel system is built for testing the heat transfer and cooling performance of the plane finned-tube heat exchanger, the symmetrical holes finned-tube heat exchanger and the three symmetrical holes finned-tube heat exchanger. The cooling capacity, the average heat transfer coefficient and the resistance of the three kinds of finned-tube heat exchangers are compared and analyzed. The energy conservation effect of the heat enhancement fin is analyzed. The experiment results compared with the plane fins show①the heat enhancement effect of the fin of three symmetrical holes is the best, the max value of cooling capacity is higher by 16.7% and average value is higher by 9.1%.②the max average equivalent heat transfer coefficient is higher by 80.15%, the min value increases by 49.66%, and the average is higher by 64.29%.③the max value of COP is higher by 30.16%, the min value is higher by 14.95% and the average is higher 22.93%.
In the end of the paper the comparative experiments between the variational space and the constant space of evaporator made of fins with perforating symmetrical holes are done. The experiment bates show①the average equivalent heat transfer coefficient of the variational space evaporator is higher 12.57%, the max value is higher by 18.26% and the min value is higher 9.4%.②with meeting the cooling capacity, the variational space finned-tube heat exchanger can saving materials by 21.43%, having the bright future in the energy conservation.
引文
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