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Heat transfer augmentation through the use of wire-rod bundles under constant wall heat flux condition
(2013-11-01)
Nanan, K.
;
Pimsarn, M.
;
Jedsadaratanachai, W.
;
Eiamsa-ard, S.
This article reports an experimental investigation on heat transfer, friction factor and thermal performance characteristics of turbulent flow (6000. ≤. Re≤. 20,000) in heat exchanger tubes with wire-rod bundles as flow turbulators. The experiments were carried out at three different pitch ratios (P/D) of 1.0, 1.5 and 2.0 and three wire-rod number per bundle (N) of 4, 6 and 8. The experimental results show that Nusselt number increases with increasing Reynolds number and wire-rod number per bundle, and decreasing pitch ratio (P/D) of the turbulators. As compared to the results of the tube without wire-rod (the plain tube), heat transfer rate and friction factor are respectively increased in ranges of 3.5 to 68.8% and 156 to 353%, depending on the operating conditions. At the same pumping power, the use of wire-rod turbulators results in thermal performance factor up to 1.02 times of those of the plain tube. In addition, the correlations that developed from the present experimental data for Nusselt number, friction factor and thermal performance factor are also presented. © 2013 Elsevier Ltd.
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Heat transfer enhancement in a channel with rib-groove turbulators
(2010-04-01)
Kaewkohkiat, Y.
;
Kongkaitpaiboon, V.
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Eiamsa-Ard, S.
;
Pimsarn, M.
This paper presents the effects of the rib-groove turbulators on the heat transfer and friction characteristics in a rectangular channel. The experiments encompass the Reynolds number range from 1800 to 10,000; pitch ratios (PR=P/e) 6.6-13.3 by using air as the working fluid. The obtained results demonstrate that heat transfer rate in term of Nusselt number (Nu) increases with the increase of Reynolds number, whereas friction factor (f) shows the opposite trend. Both Nusselt number and friction factor increase with decreasing pitch ratio. It is also observed that heat transfer rate and friction factor for the channels with rib-groove turbulators are higher than those for the smooth channel under similar test conditions. In addition, the correlations for heat transfer rate in term of Nusselt number (Nu) and friction factor (f) for channel with rib-groove turbulators are also presented. © 2010 American Institute of Physics.
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Heat transfer enhancement in a rectangular channel with twisted tape inserts
(2009-01-01)
Nuthong, W.
;
Eiamsa-Ard, S.
;
Nanan, K.
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Eiamsa-Ard, P.
;
Thianpong, C.
Experimental investigation of heat transfer and friction factor behaviors in a rectangular channel with multiple twisted tapes (MTTs) is carried out. In each run, five MTTs are simultaneously used as the swirl flow generators in a test section. The lower wall of the channel is subjected to uniform heat flux conditions while the upper wall is insulated. Parametric runs are made for Reynolds numbers ranging from 2700 to 9000, the tapes with twist-length to twist-width ratios (y/w) of 3, 4 and 5 while the aspect ratio of AR = W/H = 10 is fixed throughout. Experiments using smooth channel are also performed for comparison. The experimental results reveal that heat transfer in the channels with MTTs at twist ratios (y/w) of 3, 4 and 5 are respectively increased around 55%, 37% and 22% over those in the smooth channel. In addition, the empirical correlations of the Nusselt number and friction factor in the developed flow region for the channels fitted with MTTs are also derived.
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Turbulent heat transfer through a heat exchanger with porous twisted tape inserts
(2009-01-01)
Eiamsa-Ard, S.
;
Wongcharee, K.
;
Rattanawong, S.
;
Eiamsa-Ard, P.
;
Pimsarn, M.
In this present work, the influences of the porous twisted tape (PT) on the heat transfer and the pressure loss are studied experimentally. The comparative experiments are conducted in the tube fitted with the PT or typical twisted tape (TT) at different twist ratios, y/w = 4.0 and 5.0, in the Reynolds number ranging from 4800 to 16,000 under uniform heat flux conditions. In the experiments, the PT inserts generate swirls that modify the near wall velocity profile resulted in improvement of the heat transfer rate. The experimental results reveal that the heat transfer rates increase with decreasing twist ratio (y/w) for all twisted tapes used in the experiments. The heat transfer rates increase up to 71% with the help of the PT. The increases in average Nusselt numbers of using PT and TT are found to be 48% and 22%, respectively, over those of the corresponding plain tube. However, PT causes a considerable increase in friction factor. The mean increases of friction factors for PT and TT are respectively, about 3.14 and 2.45 times in comparison with that for the plain tube. Mean friction factor and Nusselt number for PT, are respectively 28% and 21% higher than those for TT. In addition, the empirical correlations of the Nusselt number and friction factor are also reported.
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Combustion of rice husk in a fluidized bed combustor with wavy-surfaced chambers
(2009-01-01)
Kaewkohkiat, Y.
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Eiamsa-Ard, S.
;
Wongcharee, K.
;
Thungsotanon, D.
;
Promvonge, P.
The paper deals with an experimental investigation on effects of percent excess airs (EA = 15%, 30%, 45%, 60%, and 75%) on axial/radial temperature distributions, gas emissions and combustion efficiency in a fluidized bed combustor (FBC) with wavy surfaces using rice husk as the fuels. The combustion chamber shape is cylindrical with 200 mm in diameter (D) and 2400 mm in height (H). The top part of the chamber is designed and constructed to be wavy surface walls. In constructing the wavy surface bed at the top chamber, five modules of converging-diverging nozzles are inserted into the bed at which each module has a throat diameter of 100 mm and height of 200 mm. In the experiments, the axial/radial temperature distributions inside the combustor are measured for each percent excess air used while the feeding rate of rice husk is kept constant at 95 kg/hr. From experimental results, the emissions of flue gases are found to be CO = 308 ppm and NO<inf>x</inf> = 298 ppm, at EA = 75%. At all percent excess airs (EA) the axial/radial temperature distributions in the chamber are nearly uniform.
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Enhancement of heat transfer in a circular wavy-surfaced tube with a helical-tape insert
(2007-03-01)
Eiamsa-ard, S.
;
Promvonge, P.
The purpose of the present study is to investigate experimentally the heat transfer and turbulent flow friction characteristics in a circular wavy-surfaced and constant heat-flux tube with a helical-tape insert. In the experiment, heat transfer augmentation is expected from both the turbulence of flow near the tube wall produced by the wavy surface and the swirling flow generated by the helical-tape. The experiments are based on Reynolds number at the tube inlet, ranging from 3000 to 9200. The experimental results obtained are compared with those from plain tubes in the literature. The results show that the heat transfer rate from using the wavy surface and helical tape insert is considerably higher than that from the plain tube. The Nusselt numbers and friction factors are found to be, respectively, 3.0 and 50 times over the plain tube for the tube with wavy- surfaced wall alone and to be 4.2 and about 110 times for the tube with combined wavy-surfaced wall and the helical-tape. The wavy-surfaced tube combined with the helical-tape provides higher heat transfer rate and friction factor than the wavy-surfaced tube alone around 57% and 125%, respectively. In addition, effect of insertion of the helical-tape with/without core-rod is also investigated.

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