Experimental Study on the Heat and Mass Transfer of Teflon-Coated Tubes for the Latent Heat Recovery |
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Authors: | JANGHO LEE TAE-JOO KIM MOO HWAN KIM |
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Affiliation: | Department of Mechanical Engineering , Pohang University of Science and Technology , Pohang, Korea |
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Abstract: | Abstract The heat and mass transfer on stainless steel and Teflon-coated tube surfaces in a steam-air mixture flow were experimentally studied to obtain design data for a heat exchanger to be used in the latent heat recovery from flue gases. The test section consisted of three horizontal tubes with a pitch of 67 mm. The diameter of the tubes was 25.4 mm, and the tube wall thickness was 1.2 mm. The steam-air mixture flowed vertically from top to bottom. The Teflon coating degraded the overall heat transfer coefficient by 19%, as compared to the bare stainless steel tube. The degradation of the overall heat transfer coefficient of the Teflon-coated tube comes from the additional heat transfer resistance due to Teflon coating. Its magnitude on heat transfer resistance is comparable to the in-tube heat transfer resistance. Nusselt and Sherwood numbers of Teflon-coated surfaces have a different trend compared to bare stainless steel surface in the higher Reynolds number of our test. The higher contact angle of the condensate on the Teflon-coated surface, about 25°, is the reason for the kind of trend observed. |
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