The International Journal of Science & Technoledge

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An Experimental Study of Heat Transfer Enhancement in Heat Exchangers


 

This paper presents an experimental study of heat transfer enhancement and friction factor characteristics in turbulent swirl flow generated by a short helical tape placed at the entrance (inner tube) of double pipe heat exchanger. Experiments were conducted for cold water flow rates in inner tube in the range of 3432≤ Re ≤5108 .Experiments were carried out for three helical tapes with different lengths (LH) of 130mm, 270mm, and 370mm. Also, experiments were carried out for two successive helical tapes of length 135 mm at different free space length (Ls). The local and average heat transfer coefficients and pressure drop were measured and compared with the base case of plain tube. The local heat transfer coefficients were found to be increasing to very high values in the region of the helical tape, and then decreasing along the downstream of the helical tape. The thermal performance factor increases with increasing helical tape length at each Reynolds number examined and decreases with increasing Reynolds number in the range of 3432≤ Re ≤5108. The maximum performance factor of ƞ=1.45 was obtained for the length of 370mm at Re=3432. The helical tape of length LH=370 provides the highest average heat transfer rate about 27% over the plain tube but it increased the pressure drop by 2.6 %. To overcome the increasing of pressure drop, different free-spacing ratio (S= Ls/LH) of 1.8, 3.6, and 5.4 between two successive helical tape of length LH=135mm at Re=4083 were examined. It was found that the thermal performance factor of two successive helical tapes of length LH=135mm with free space ratio (S=1.8) is better than the continuous helical tape of length LH=270mm at Re =4083. A performance comparison between a present work and published results of full length helical and twisted tapes inserts has shown superior heat transfer enhancement using short length helical tapes inserted at the cold water tube  as compared to full length twisted tapes in the Reynolds number range of  Re=3432–5108.


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  • An Experimental Study of Heat Transfer Enhancement in Heat Exchangers

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Abstract


This paper presents an experimental study of heat transfer enhancement and friction factor characteristics in turbulent swirl flow generated by a short helical tape placed at the entrance (inner tube) of double pipe heat exchanger. Experiments were conducted for cold water flow rates in inner tube in the range of 3432≤ Re ≤5108 .Experiments were carried out for three helical tapes with different lengths (LH) of 130mm, 270mm, and 370mm. Also, experiments were carried out for two successive helical tapes of length 135 mm at different free space length (Ls). The local and average heat transfer coefficients and pressure drop were measured and compared with the base case of plain tube. The local heat transfer coefficients were found to be increasing to very high values in the region of the helical tape, and then decreasing along the downstream of the helical tape. The thermal performance factor increases with increasing helical tape length at each Reynolds number examined and decreases with increasing Reynolds number in the range of 3432≤ Re ≤5108. The maximum performance factor of ƞ=1.45 was obtained for the length of 370mm at Re=3432. The helical tape of length LH=370 provides the highest average heat transfer rate about 27% over the plain tube but it increased the pressure drop by 2.6 %. To overcome the increasing of pressure drop, different free-spacing ratio (S= Ls/LH) of 1.8, 3.6, and 5.4 between two successive helical tape of length LH=135mm at Re=4083 were examined. It was found that the thermal performance factor of two successive helical tapes of length LH=135mm with free space ratio (S=1.8) is better than the continuous helical tape of length LH=270mm at Re =4083. A performance comparison between a present work and published results of full length helical and twisted tapes inserts has shown superior heat transfer enhancement using short length helical tapes inserted at the cold water tube  as compared to full length twisted tapes in the Reynolds number range of  Re=3432–5108.