The Impact of Fin Deformation on Condensation Heat Transfer Coefficients in Internally Grooved Tubes
The Impact of Fin Deformation on Condensation Heat Transfer Coefficients in Internally Grooved Tubes
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DOI：
10.1115/ht2013-17111
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发表时间：
2013-07
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影响因子：
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通讯作者：
S. Mehendale
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文献类型：
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作者：
S. Mehendale
在HVACR设备中，通常使用轴向、十字槽、螺旋和人字形等内部增强型圆管(微翅片)设计来增强蒸发器、冷凝器和热泵的沸腾和冷凝性能。通常，这样的管子通过心轴机械地膨胀成翅片组，以在管子外表面和翅片环之间产生过盈配合，从而将管子和翅片之间的热阻降到最低。然而，在这种膨胀过程中，内部强化物经历了不同程度的变形，这降低了管内的热性能。公开文献中已经报道了大量关于微翅片管内冷凝换热系数的数据。然而，研究人员很少使用膨胀管来获取和报告这样的数据。因此，使用这种原始的管子数据来设计换热器和暖通空调循环系统总是有问题的。此外，暖通空调橡胶行业的铜成本一直在急剧上升，预计这一趋势将在未来几年继续下去。因此，许多设备制造商和供应商都在积极将管材从铜转换为铝。然而，由于铝和铜的材料性质以及其他制造变量(如芯棒尺寸、使用的润滑剂等)之间的显著差异，管膨胀通常比铜翅片变形更大。基于对管膨胀引起的表面积变化的分析，以及对现有最佳管内冷凝换热关联式的评估，本工作提出了一种估算管膨胀对管内冷凝换热影响的方法。这一分析导致了一些有趣和有用的发现，将翅片几何形状和管内冷凝热阻联系在一起。然后，该方法可用于更真实地设计HVACR换热器和系统。版权所有：2013，ASME
In HVACR equipment, internally enhanced round tube (microfin) designs such as axial, cross-grooved, helical, and herringbone are commonly used to enhance the boiling and condensing performance of evaporators, condensers, and heat pumps. Typically, such tubes are mechanically expanded by a mandrel into a fin pack to create an interference fit between the tube outside surface and the fin collar to minimize the thermal contact resistance between tube and fin. However, during this expansion process, the internal enhancements undergo varying amounts of deformation, which degrades the in-tube thermal performance.Extensive data on condensing heat transfer coefficients in microfin tubes have been reported in the open literature. However, researchers have seldom used expanded tubes to acquire and report such data. Hence, it is always questionable to use such pristine tube data for designing heat exchangers and HVACR systems. Furthermore, the HVACR industry has been experiencing steeply rising copper costs, and this trend is expected to continue in coming years. So, many equipment manufacturers and suppliers are actively converting tubes from copper to aluminum. However, because of appreciable differences between the material properties of aluminum and copper, as well as other manufacturing variables, such as mandrel dimensions, lubricant used, etc., tube expansion typically deforms aluminum fins more than copper fins.Based on an analysis of the surface area changes arising from tube expansion, and an assessment of the best extant in-tube condensation heat transfer correlations, this work proposes a method of estimating the impact of tube expansion on in-tube condensation heat transfer. The analysis leads to certain interesting and useful findings correlating fin geometry and in-tube condensation thermal resistance. This method can then be applied to more realistically design HVACR heat exchangers and systems.Copyright © 2013 by ASME