Laminar flow heat transfer of dilute viscoelastic solutions in flattened tube heat exchangers

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• 作者：Z. Ismail^a ; ^{zubaidahjka@gmail.com} ; R. Karim^b
• 关键词：Aspect ratio ; Flattened exchanger ; Heat transfer ; Polymer ; Viscoelastic liquid
• 刊名：Applied Thermal Engineering
• 出版年：2012
• 期刊代码：8_13594311
• 类别：ce
• 出版时间：June, 2012
• 卷：39
• 期：Complete
• 页码：171-178
• 文件大小：965 K

摘要

Heat transfer studies of non-Newtonian liquids in non-circular exchangers are not many, and much less on viscoelastic liquids in flattened tubes. Heat transfer studies of dilute viscoelastic liquids in flattened tubes with 0.635聽cm and 1.27聽cm original diameters and 50聽cm-76聽cm lengths and aspect ratios ranging from 1.4 to 5.7 were carried out. Five flattened tube heat exchangers with four thermocouples soldered at regular intervals on the outside wall were placed in turn in the experimental circuit to determine the heat transfer coefficients. Hot water was used as the heating medium; and dilute solutions of polyacrylamide in water and in water/glycerol mixtures were used as the viscoelastic solutions. Heat transfer increase as a result of flattening the tubes could be 101%higher while the effect due to secondary flow had a maximum additional increase compared to that for water of 40%for the 250聽ppm solution at an aspect ratio of 1.6. Corresponding values for the 500聽ppm solutions in water and in water/glycerol mixture were about 53%and 55%respectively at an aspect ratio of 1.8. Increased polymer concentration had only a marginal effect on heat transfer performance.