Browsing by Author "Wongwises, Somchai"

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Airside performance of fin-and-tube heat exchangers in dehumidifying conditions - Data with larger diameter
(2010-03-01)
Liu, Young-Chang
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Wongwises, Somchai
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Chang, Wen-Jeng
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Wang, Chi-Chuan
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機械工程學系
This study presents the airside performance of the fin-and-tube heat exchangers having plain fin geometry with a larger diameter tube (D(c) = 15.88 mm) under dehumidifying condition. A total of nine samples of heat exchangers subject to change of the number of tube row and fin pitch are made and tested. It is found that the effect of fin pitch on the sensible j factor is, in general, diminished with the rise of tube row. However, there is a unique characteristic of fin pitch at a shallow tube row, the heat transfer performance is first increased at a wider pitch but a further increase of fin pitch lead to a falloff of heat transfer performance due to interactions amid flow development and bypass flow. The influence of tube row on the airside performance is rather small for both heat transfer and frictional characteristics at a fin pitch of 2.1 mm and when the Reynolds number is less than 4000. A slight deviation of this effect is encountered when fin pitch is increased to 2.54 mm or 3.1 mm due to condensate adhered phenomena. (C) 2009 Elsevier Ltd. All rights reserved.
Effect of elliptical winglet on the air-side performance of fin-and-tube heat exchanger
(2018-08-01)
Chimres, Nares
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Wang, Chi-Chuan
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Wongwises, Somchai
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機械工程學系
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Department of Mechanical Engineering
This study numerically examines the elliptical winglets (EW) on the overall performance of fin-and-tube heat exchanger. The major geometrical parameters characterizing the EW has been investigated thoroughly, including the winglet location, attack angle and the trailing angle of the elliptical winglets with two different winglet lengths which are 1.0 mm and 1.5 mm. The numerical results indicate that the elliptical winglets with the 30 degrees attack angle, 0 mm horizontal distance, 6 mm vertical distance and 120 degrees trailing angle of both winglet lengths shows the highest performance. The heat transfer coefficients and pressure drops obtained by both winglet sizes are larger than that of the plain fin by about 13% and 35%, respectively. In term of the performance efficiency index, the 1.5 mm winglet length indicates about 1.8-2.9% improvement relative to plain fin geometry and the efficiency index of 1.0 mm winglet length is comparable with that of the plain fin. (C) 2018 Elsevier Ltd. All rights reserved.
Effect of fin pitches on the air-side performance of crimped spiral fin-and-tube heat exchangers with a multipass parallel and counter cross-flow configuration
(2011-04-01)
Pongsoi, Parinya
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Pikulkajorn, Santi
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Wang, Chi-Chuan
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Wongwises, Somchai
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機械工程學系
This study investigates the effect of fin pitches and fin materials on the air-side performance of crimped fin-and-tube heat exchangers in the range of high Reynolds numbers (4000-13000). The test samples are made from copper and aluminium with different fin pitches (f(p) = 3.2, 4.2 and 6.2 mm). It is found that the proposed simple average effectiveness equation from the pure counter and parallel circuitry arrangement can well represent the effectiveness-NTU relationship for the current z-shape arrangement. The experimental results reveal that the fin pitch casts insignificant effect on the heat transfer characteristics (Colburn j factor). However, a detectable rise of the friction factor is seen when the fin pitch is increased to f(p) = 6.2 mm. On the other hand, the effect of fin material on the airside performance is negligible. (C) 2010 Elsevier Ltd. All rights reserved.
Effect of number of tube rows on the air-side performance of crimped spiral fin-and-tube heat exchanger with a multipass parallel and counter cross-flow configuration
(2012-01-31)
Pongsoi, Parinya
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Pikulkajorn, Santi
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Wang, Chi-Chuan
;
Wongwises, Somchai
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機械工程學系
The air-side performance of crimped spiral fin and tube heat exchangers at high Reynolds number (3000-13,000) is investigated in this study. The test heat exchangers have a new type of multipass parallel and counter cross-flow water flow arrangement which is a combination of parallel cross-flow and counter cross-flow. The test samples are made from copper and aluminium with different number of tube rows (N-row = 2, 3, 4 and 5). The effects of number of tube rows and fin material on the heat transfer and friction characteristics are studied. The results show that no significant effect for either number of tube rows or fin materials on the heat transfer performance is found at high Reynolds number. In addition, the correlation of the air-side performances of this type of the heat exchangers at high Reynolds number is developed for industrial applications. (c) 2011 Elsevier Ltd. All rights reserved.
Optimal design of the semi-dimple vortex generator in the fin and tube heat exchanger
(2018-05-01)
Chimres, Nares
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Wang, Chi-Chuan
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Wongwises, Somchai
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機械工程學系
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Department of Mechanical Engineering
The fin and tube heat exchanger with a semi-dimple pair is numerically studied in terms of the air side's thermal performance. The investigated parameters consist of the diameter, attack angle and the placed location of the semi-dimple. The results show that the 30 attack angle, 5.5 mm vertical distance and 7.5 mm horizontal distance can perform the highest j/f ratio or "goodness parameter" of every semi-dimple's diameter. Additionally, the thermal performance of the fin with a semi-dimple pair is also compared with that of the fin with existing semi-dimples and the plain fin within the Reynolds number ranging from 813 to 4019. Obviously, the existing semi-dimple exhibits the highest heat transfer coefficient and pressure drop. However, the semi-dimples' pair demonstrates a goodness factor of 33-37% greater than the existing semi-dimples and 15-20% greater than the plain fin, approximately. (C) 2017 Published by Elsevier Ltd.
The New Mathematical Models for Plain Fin-and-Tube Heat Exchangers With Dehumidification
(2015-03-01)
Pirompugd, Worachest
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Wang, Chi-Chuan
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Wongwises, Somchai
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機械工程學系
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Department of Mechanical Engineering
For evaluating performance of fin-and-tube heat exchangers under dehumidifying conditions, the recent lumped approach models are based on the enthalpy potential or equivalent dry bulb temperature. This study proposes a new lumped approach model based on the dry bulb temperature difference. The concept of dry bulb temperature was first presented by McQuiston for derivation of fin efficiency under dehumidifying conditions in 1975. This concept is simpler than the concepts of enthalpy potential and equivalent dry bulb temperature. Nevertheless, it cannot be found that this concept is applied to the fin-and-tube heat exchangers. Moreover, this study also presents the finite circular fin method (FCFM) based on the dry bulb temperature and equivalent dry bulb temperature. The FCFM was first presented in our published literature but it was based on the enthalpy potential. The FCFM is done by dividing the fin-and-tube heat exchanger into many small segments. Then, the segments are divided into three cases: fully dry condition, fully wet condition, and partially wet condition. From the results, the new lumped approach model based on dry bulb temperature gives a good result. It is the simplest method for evaluating heat transfer performance of fin-and-tube heat exchangers under fully wet conditions. For the FCFM, the heat and mass transfer characteristics obtained by dry bulb temperature and equivalent dry bulb temperature are nearly the same as those obtained by the enthalpy potential. However, the heat and mass transfer characteristics by the FCFM based on equivalent dry bulb temperature are higher than those obtained by the FCFM based on dry bulb temperature. This is because of the effect of the nonconstant term in the two methods. The correlations applicable for both fully wet and partially wet conditions for the FCFMs based on equivalent dry bulb temperature and dry bulb temperature are proposed to describe the heat and mass transfer characteristics for the present plain fin configuration.
Two-Phase Flow Across Small Sudden Expansions and Contractions
(2010)
Chen, Ing Young
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Wongwises, Somchai
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Yang, Bing-Chwen
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Wang, Chi-Chuan
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機械工程學系
Two-phase flow approaching singularities such as abrupt expansions and sudden contractions is widely encountered in typical industrial and heat exchanging devices. There have been some studies concerning this subject but they mostly are applicable for larger channels. In this study, the first attempt is made to review the existing efforts concerning two-phase flow across sudden expansions/contractions and to examine the applicability of the existing correlations with respect to the recent data in small channels. The second part of this study presents some newly measured pressure drops and observed flow patterns pertaining to some special flow phenomena by expansion/contraction. For an abrupt expansion, it is found that the existing correlations all fail to provide a reasonably predictive capability against the newly collected data. Furthermore, a unique flow pattern called "liquid jet-like flow pattern" occurs at a very low quality region of total mass flux of 100 kg.m(-2).s(-1), and it raises a setback phenomenon of pressure drop. By contrast, an appreciable increase of pressure difference is seen when the liquid jet-like flow pattern is completely gone. A similar conclusion is drawn for the data of contractions. For the correlations/predictive models, the homogeneous model gives satisfactory prediction for conventional macro-channels but fails to do so when the channels become smaller. This is especially pronounced for a small-diameter tube with a Bond number being less than 1, in which the effect of surface tension dominates.