摘要
对于冷风机蒸发器、无霜冰箱蒸发器等“空气—制冷剂”型制冷换热器,由于管内制冷剂相变换热,表面传热系数远高于管外空气强迫对流换热表面传热系数,因此多采用矩形平翅片来作为扩展表面,目的是增加空气侧换热面积,有效地降低传热总热阻,提高传热系数和传热量。平翅片具有结构简单、紧凑、利于除霜、容易加工等优点。但其对流换热效果差,翅片效率低,由其组合而成的翅片管式制冷换热器体积大,耗材耗电。因此,对平翅片的表面结构进行深入研究,采用换热和流阻性能优异且在积霜状况下仍能维持较好换热特征的高效翅片,对更新及改造该类换热器具有重要意义。
在翅片表面换热薄弱的部位开孔可使流动边界层分段发展并增加气流扰动,达到强化传热的效果。圆孔翅片和三对称大直径圆孔翅片(以下简称SK型翅片)就是以此为原理发展起来的。计算机模拟和实验研究均表明:实验条件下,与平翅片及圆孔翅片相比,三对称圆孔翅片的强化传热效果最好。①与平翅片相比较,SK型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平均当量表面传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%。
前期实验证实,SK型翅片具有最优的强化传热效果。然而,所有实验均在实验台上完成,并未将该新型翅片运用在现有“空气—制冷剂”型制冷换热器上进行测试。为进一步说明SK型翅片优越的强化传热效果,将科学研究成果转化为生产力。本文分别制作了平翅片冷风机及SK型翅片冷风机各一台,并将已有的按冷库标准建造的人工气候室进行改造,对两台冷风机的节能性能进行对比性工业样机试验。试验结果证实:在制冷剂充入量相等、迎面风速u=3.75m/s时,SK型样机的制冷量比平翅片样机的制冷量平均提高了7.7%~10%;耗电量平均降低了12.1%~10.4%;压缩机能效比平均提高了22.5%以上。研究结果同时证实:对于工作于潮湿环境下的速冷式冷风机,其除霜周期不宜太长,否则将导致运行能耗大幅度上升。
For the cooling fan evaporator, frost-free refrigerator evaporator "air - refrigerant" type refrigeration heat exchanger,As the tube refrigerant phase change heat, the surface heat transfer coefficient is much higher than the air outside tube surface heat transfer coefficient of forced convection heat transfer,Therefore, multi-level rectangular fin as the extension surface, the aim is increasing the air-side heat transfer area, effectively reducing the overall heat transfer thermal resistance, improve heat transfer coefficient and heat transfer. Flat fin with a simple and compact structure, which will help defrost, easy processing advantages and so on . However, the convective heat transfer effects of poor fin efficiency is low, by a combination of fin-tube refrigerating heat exchanger bulky power supplies. Therefore, the surface structure of the flat fin-depth study, using high performance heat transfer and flow resistance and frost conditions in the plot better able to maintain efficient heat transfer characteristics of fin, to update and transformation of such heat exchanger with a significance.
The fin heat transfer surface area with weak openings allow air flow and increase the sub-boundary layer disturbances to achieve enhanced heat transfer effect. Hole, and three symmetric fin fin large diameter hole (hereinafter referred to as SK-fin) is this as a principle to develop. Computer simulation and experimental studies show that:in the experimental conditions, the three symmetric hole enhanced heat transfer fins the best results than the flat fin and fin hole.①compared with the flat fin, SK-type fin is the most significant effect of enhancing heat transfer, refrigeration largest increase 16.87%, an average increase of 9.1%.②the average equivalent heat transfer coefficient compared with the rectangular flat fin, the largest increase 80.15 percent, the smallest increase of 49.66%, with an average increase of 64.29%.③COP values increase 30.16 percent the largest, the smallest increase 14.95 percent, an average increase of 22.93%.
Preliminary experiments confirmed that, SK-type fin has the best heat transfer effects. However, all experiments were completed in the experimental stage, the new type of fin is not used in the existing "air - cooling agent" type refrigeration heat exchangers to be tested. To further illustrate the superiority of SK-type finned heat transfer enhancement effect ,the scientific research achievements into productive forces. In this paper, a flat fin air cooler, and SK-Fin Cooler is produced each one, and according to existing standards for the construction of cold storage to transform the artificial climate chamber for two energy-saving air cooler compare the performance of industrial prototype test .Experimental results show that: when charged into the head-wind speed u = 3.75m / s in the same amount of refrigerant, SK-type prototype prototype refrigeration cooling fins is increased by an average of 7.7% -10% than flat; power consumption reduced by an average 12.1% -10.4%; compressor energy efficiency increased by an average of 22.5% or more. The results also confirmed that:for the speed cooling fan working in wet environments, its defrost cycle should not be too long, otherwise, substantial increase of energy consumption would come into being.
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