Browsing by Author "Liaw, Jane-Sunn"

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A Criterion of Heat Transfer Deterioration for Supercritical Organic Fluids Flowing Upward and Its Heat Transfer Correlation
(2020-02-01)
Li, Yung-Ming
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Liaw, Jane-Sunn
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Wang, Chi-Chuan
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機械工程學系
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Department of Mechanical Engineering
The main objective of this study was to develop the supercritical heat transfer correlation applicable for organic fluids when flowing upward in smooth tubes based on the available experimental data. The organic fluids contain R-22, R-134a, R-245fa and Ethanol and the associated heat transfer characteristics were compared with non-organic fluids like water and carbon-dioxide (CO2). It was found that the limit heat flux may result in heat transfer deterioration (HTD) of organic fluid and the corresponding values are much smaller than water or CO2. A new criterion to predict the HTD was developed and this criterion yields the best predictive ability against database. It was found that HTD occurs can be well described by the acceleration parameter evaluated at the wall condition rather than at bulk condition. For estimation of the supercritical heat transfer coefficient (HTC) for organic fluid, the present study proposes a new correlation with a physically based correction factor, which gives satisfactory predictions against the HTC of supercritical organic fluid. The new correlation can offer the smallest average deviation of 0.007 and standard deviation of 0.181 among the existing correlations.
"A novel ""partial bypass"" concept to augment the performance of air-cooled heat exchangers"
(2012-09-01)
Wang, Chi-Chuan
;
Chen, Kuan-Yu
;
Liaw, Jane-Sunn
;
Tseng, Chih-Yung
;
機械工程學系
"This study proposes a novel ""partial bypass"" concept which facilitates the heat transfer augmentation without the pumping power penalty. The basic idea is to introduce bypass cold stream which bypasses the front part of the heat exchanger and mixes with the hot stream across the front part of the heat exchanger, and the mixed stream flows through the rear part of the heat exchanger. Through this concept, heat transfer performance at the front part is slightly reduced but the rear part is substantially increased. The concept can be implemented with either maintaining the same total flowrate, heat transfer rate but accompanies with a much lower pressure drop or it can be applied with the same pumping power but accompanies with a much higher heat transfer rate. It is found that the ""partial bypass"" concept is especially fruitful for a heat exchanger with a comparatively large number of transfer unit (NTU). The concept is especially helpful in the design of a deep tube bank operated at lower frontal velocity. For validating the proposed concept, the calculation is also compared with the experimental measurements, and good agreement amid the calculations and measurements are reported. (C) 2012 Elsevier Ltd. All rights reserved."
A novel "partial bypass" concept to augment the performance of air-cooled heat exchangers
(2012-09-01)
Wang, Chi-Chuan
;
Chen, Kuan-Yu
;
Liaw, Jane-Sunn
;
Tseng, Chih-Yung
;
機械工程學系
This study proposes a novel "partial bypass" concept which facilitates the heat transfer augmentation without the pumping power penalty. The basic idea is to introduce bypass cold stream which bypasses the front part of the heat exchanger and mixes with the hot stream across the front part of the heat exchanger, and the mixed stream flows through the rear part of the heat exchanger. Through this concept, heat transfer performance at the front part is slightly reduced but the rear part is substantially increased. The concept can be implemented with either maintaining the same total flowrate, heat transfer rate but accompanies with a much lower pressure drop or it can be applied with the same pumping power but accompanies with a much higher heat transfer rate. It is found that the "partial bypass" concept is especially fruitful for a heat exchanger with a comparatively large number of transfer unit (NTU). The concept is especially helpful in the design of a deep tube bank operated at lower frontal velocity. For validating the proposed concept, the calculation is also compared with the experimental measurements, and good agreement amid the calculations and measurements are reported. (C) 2012 Elsevier Ltd. All rights reserved.
Air-side performance of herringbone wavy fin-and-tube heat exchangers under dehumidifying condition - Data with larger diameter tube
(2012-05-01)
Wang, Chi-Chuan
;
Liaw, Jane-Sunn
;
機械工程學系
;
Department of Mechanical Engineering
This study examines the airside performance of the herringbone wavy fin-and-tube heat exchangers in dehumidifying condition having a larger diameter tube (D-c = 16.59 mm) with the tube row ranging from 2 to 12. Test results are compared to that of dry conditions and plain fin geometry. Upon the influence of surface condition (dry or wet) on the heat transfer performance, the heat transfer performance in dehumidifying condition normally exceeds that in dry condition, and is more pronounced with the rise of tube row or reduction of fin pitch. By contrast, it is found that the heat transfer coefficient for plain fin geometry in dehumidifying condition is slightly lower than that in dry condition. The pressure drops in wet condition is much higher than that in dry condition. However, the difference in pressure drop amid dry and dehumidifying condition for wavy fin configuration is less profound as that of plain fin geometry. (C) 2012 Elsevier Ltd. All rights reserved.
Airside Performance of H-Type Finned Tube Banks with Surface Modifications
(2019-02-02)
Bhale, Pradhyumn
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Kaushik, Mrinal
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Liaw, Jane-Sunn
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Wang, Chi-Chuan
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機械工程學系
The present study numerically investigates some novel modifications to augment the performance of the H-type finned tube banks, which are widely used in waste heat recovery in industries. The imposed modifications upon the original H-type finned tube banks include the following: (1) Design 1 contains some triangular cuts at the edge of the original rectangular fin; (2) Design 2 modifies the original rectangular geometry into a trapezoid shape; (3) Design 3 renders the original rectangular cross-section fin thickness into trapezoid cross-section; and (4) Design 4 changes the original rectangular shape into a circular shape. Based on the simulations, it is found that Design 1 shows barely any improvements in the heat transfer performance and surface area reduction. Design 2 can provide some weight saving and surface area reduction at a slightly inferior heat transfer performance. Design 3 can offer up to 14% improvements in the overall heat transfer performance without any pumping power penalty. Yet, Design 4 provides the maximum weight saving as compared to the original reference case. With 3-9% lesser surface area than the reference case, Design 4 still offers marginally higher heat transfer performance.
Airside performance of herringbone wavy fin-and-tube heat exchangers - data with larger diameter tube
(2011-02-01)
Wang, Chi-Chuan
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Liaw, Jane-Sunn
;
Yang, Bing-Chwen
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機械工程學系
;
Department of Mechanical Engineering
This study examines the airside performance of the wavy fin-and-tube heat exchangers having a larger diameter tube (D(c) = 16.59 mm) with the tube row ranging from 1 to 16. It is found that the effect of tube row on the heat transfer performance is quite significant, and the heat transfer performance deteriorates with the rise of tube row. The performance drop is especially pronounced at the low Reynolds number region. Actually more than 85% drop of heat transfer performance is seen for F(p) similar to 1.7 mm as the row number is increased from 1 to 16. Upon the influence of tube row on the frictional performance, an unexpected row dependence of the friction factor is encountered. The effect of fin pitch on the airside performance is comparatively small for N = 1 or N = 2. However, a notable drop of heat transfer performance is seen when the number of tube row is increased, and normally higher heat transfer and frictional performance is associated with that of the larger fin pitch. (C) 2010 Elsevier Ltd. All rights reserved.
An experimental study of the air-side performance of fin-and-tube heat exchangers having plain, louver, and semi-dimple vortex generator configuration
(2015-01-01)
Wang, Chi-Chuan
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Chen, Kuan-Yu
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Liaw, Jane-Sunn
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Tseng, Chih-Yung
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機械工程學系
In this study, a comparative study of the airside performance of fin-and-tube heat exchangers having plain, louver, and semi-dimple vortex generator (VG) are made. A total of eighteen samples are made and tested with the corresponding fin pitch (F-p) being 1.6 mm and 2.0 mm and the number of tube row (N) are 1, 2 and 4, respectively. Test results indicate that the heat transfer coefficient for N = 1 for louver fin geometry with a smaller fin pitch of 1.6 mm is higher than that of semi-dimple VG and plain fin geometry. For N = 1 with a larger fin pitch of 2.0 mm, the semi-dimple VG is marginally higher than that of louver fin geometry when the frontal velocity is lower than 2 m s(-1). However, the trend is reversed where the heat transfer coefficient for louver fin outperforms that of semi-dimple VG when the velocity is increased further. For the airside performance for N = 2 or N = 4, the heat transfer coefficients for louver fin geometry is about 2-15% higher than those of semi-dimple geometry. The difference is increased with the rising velocity and the results prevail for both fin pitches. However, the difference is smaller at a larger fin pitch due to the comparatively effectively swirled motion of the semi-dimple VG. The effect of the number of tube row on the heat transfer coefficients is negligible for louver fin geometry and is also rather small for semi-dimple VG. For the plain fin geometry, the effect of tube row is also small when N > 1. The heat transfer performance for N = 1 is different from N = 2 or N = 4 due to its inline configuration. (C) 2014 Elsevier Ltd. All rights reserved.
Compound Heat Transfer Enhancement of Wavy Fin-and-Tube Heat Exchangers through Boundary Layer Restarting and Swirled Flow
(2018-08-01)
Sadeghianjahromi, Ali
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Kheradmand, Saeid
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Nemati, Hossain
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Liaw, Jane-Sunn
;
Wang, Chi-Chuan
This study performs a 3D turbulent flow numerical simulation to improve heat transfer characteristics of wavy fin-and-tube heat exchangers. A compound design encompassing louver, flat, and vortex generator onto wavy fins can significantly enhance the heat transfer performance of wavy fin-and-tube heat exchangers. Replacement of wavy fins around tubes with flat fins is not effective as far as the reduction of thermal resistance is concerned, although an appreciable pressure drop reduction can be achieved. Adding two louvers with a width of 8 mm to the flat portion can reduce thermal resistance up to 6% in comparison with the reference wavy fin. Increasing the louver number and width can further decrease the thermal resistance. Also, it is found that the optimum louver angle is equal to the wavy angle for offering the lowest thermal resistance. Therefore, compound geometry with three louvers, a width of 12 mm, and the louver angle being equal to wavy angle with waffle height to be the same as fin pitch of the reference wavy fin has the most reduction in thermal resistance of 16% for a pumping power of 0.001 W. Adding punching longitudinal vortex generators on this compound geometry can further decrease thermal resistance up to 18%.
Effect of partial bypass on the heat transfer performance of dehumidifying coils
(2014-11-01)
Wang, Chi-Chuan
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Cheng, Yu-Cheng
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Liaw, Jane-Sunn
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Tseng, Chih-Yung
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機械工程學系
This study extends a so called "partial bypass" concept to dehumidifying fin-and-tube heat exchangers. Tests are performed for a 2-row and 4-row fin-and-tube heat exchangers having plain fin configuration. The inlet dry bulb temperature is fixed at 25 degrees C while the inlet relative humidities are 50% and 80%, respectively. Test results showed that for a 2-row coil under RH = 50%, the corresponding heat transfer augmentation ratio (Q(R)) and pressure penalty ratio (P-R) decrease with the rise of bypass ratio (BR). At a smaller frontal velocity, the regime of appropriate bypass ratio where Q(R) > 1 and P-R < 1 is more apparent. The effect of partial bypass decreases as the velocity increases. As the velocity gets close to 2 m s(-1), it shows that the performance at high bypass ratio becomes more efficient. At the same time, when bypass ratio becomes lager, the tendency of the decreasing of Delta P is more drastic than the decreasing of Q. Nevertheless, not for all the cases that the performances get better as the bypass ratio increases. For V-fr = 4 m s(-1), the experiment results show that the overall effect is less efficient\' than at V-fr = 2 m s(-1). The major reason is caused by the flow pattern. The rise of bypass airflow is quite large which may act as an air curtain to distort the main airflow, and result in higher pressure drop. This implies that the design of the bypass design is quite imperative in the practice of real applications. For a 4-row heat exchanger, the experiment data of QR and PR for the 4-row coil performs better than a 2-row coil. (C) 2014 Elsevier Ltd. All rights reserved.