Browsing by Author "Tseng, Chih-Yung"

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A new correlation and the review of two-phase flow pressure change across sudden expansion in small channels
(2010-09-01)
Wang, Chi-Chuan
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Tseng, Chih-Yung
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Chen, Ing Youn
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機械工程學系
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Department of Mechanical Engineering
In this study, the authors first present a short overview on the single-phase flow across sudden expansion, followed by a thorough review of the relevant literature for two-phase flow across sudden expansion, and examination of the applicability of the existing correlations. Also, 282 data available from five publications are collected. It is found that none of the existing correlations can accurately predict the entire database. Most of the correlations highly over predict the data with a mini test section which has a Bond number being less than 0.1 in which the effect of surface tension dominates. Also, some of the correlations significantly under predict the data for very large test sections. Among the models/correlations being examined, the homogeneous model shows a poor predictive ability than the others, but it is handy for the engineering aspect. Hence by taking account the influences of Bond number, Weber number, Froude number, liquid Reynolds number, gas quality and area ratio into the original homogeneous model, a modified homogeneous model is proposed that considerably improves the predictive ability over existing correlations with a mean deviation of 23% and a standard deviation of 29% to all the data with wider ranges of operating parameters for application. (C) 2010 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
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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
"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.
A novel double pipe pulsating heat pipe design to tackle inverted heat source arrangement
(2016-08-05)
Tseng, Chih-Yung
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Yang, Kai-Shing
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Chien, Kuo-Hsiang
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Wu, Shih-Kuo
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Wang, Chi-Chuan
Traditional pulsating heat pipe with fewer turns is functional only when the heat source is placed at the bottom while the heat sink is on top. This study proposes a novel design having alternative double-pipe tube diameter with some extra open connections of these double-pipes. By introducing extra un-balanced pressure force, capillary force and gravity force, the PHP can be easily starting up even for an opposite heat source/sink arrangement while the conventional single tube design fails to start up with this opposite arrangement. The thermal resistance of double pipe PHP can be lowered to 0.0729 W/K with an effective thermal conductivity of 12,603 W/m.K when the heat source is placed on top. Yet the thermal resistance for the proposed double pipe design is only half of the single tube design. (C) 2016 Elsevier Ltd. All rights reserved.
A Novel Thermal Module with 3-D Configuration Pulsating Heat Pipe for High-Flux Applications
(2018-12-01)
Tseng, Chih-Yung
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Wu, Ho-Meng
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Wong, Shwin-Chung
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Yang, Kai-Shing
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Wang, Chi-Chuan
A pulsating heat pipe (PHP) contains a wickless design with aligned serpentine tube configuration whose simple structure offers a comparatively easy manufacturing capability. The bends with large curvature are often used for serpentine PHPs. This eventually results in a decline in effective contact surface area between evaporator/condenser and PHP circuitry, thereby impairing the benefit of the wickless design of a PHP. A novel thermal module featuring a 3-D configuration pulsating heat pipe, an evaporator, and a fin-and-tube condenser is proposed to tackle the high-flux application. Methanol is used as the working fluid with a filling ratio of around 60%. Test results indicate the thermal resistance of the proposed module varies from 0.148 K/W to 0.0595 K/W when the supplied power changes from 100 to 1000 W. The proposed thermal module can handle a supplied power up to 1 kW and the corresponding power or heat flux is much higher than any existing literatures.
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.
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.
Investigation of the evacuation pressure on the performance of pulsating heat pipe
(2017-07-01)
Sun, Chien-Hung
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Tseng, Chih-Yung
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Yang, Kai-Shing
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Wu, Shih-Kuo
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Wang, Chi-Chuan
This study examines the influence of evacuation pressure on the startup and overall performance of pulsating heat pipes (PHP). The outer diameter of the copper tube is 3 mm and 2 mm (double tube design) having a wall thickness of 0.3 mm and 0.2 mm, respectively. The working fluids in this study include water and HFE-7000 with filling ratios around 50%, and the evacuation pressure ranging from 0.01 Torr to atmosphere pressure. For an evacuation pressure of 0.01 Torr at a supplied power of 80 W, the thermal resistance of the PHP filling with water is 0.928 K/W while it is 1.161 K/W for HFE-7000. However, the trend is reversed and the thermal resistance for HFE-7000 is lower than water when the evacuation pressure is increased over 100 Torr. The corresponding effective thermal conductivity of waterfilling PHP reaches 51,448 W/m K in comparison with 12,692 W/m K for HFE-7000. However, the effective thermal conductivity for waterfilling PHP drops appreciably with rising evacuation pressure, and the PHP is not functional at the atmosphere pressure. Conversely, although the effective thermal conductivity for HFE-7000 PHP still drops with the rise of evacuation pressure, the HFE-7000 PHP is still in operation even without any evacuation. The gigantic difference in the startup and performance of PHP is related to the solubility of noncondensable gas amid water and HFE-7000.
Investigation of the performance of pulsating heat pipe subject to uniform/alternating tube diameters
(2014-04-01)
Tseng, Chih-Yung
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Yang, Kai-Shing
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Chien, Kuo-Hsiang
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Jeng, Ming-Shan
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Wang, Chi-Chuan
The present study examines the performance of closed-loop pulsating heat pipes (CLPHPs) with an ID of 2.4 mm. The effect of uniform and alternating tube diameter on the performance is investigated. The working fluids include distilled water, methanol and HFE-7100. Tests are performed with both horizontal and vertical arrangement. For the horizontal arrangement, when compared to uniform design, the alternating channel design can be started at a rather low heat input with a much smaller thermal resistance. Normally the thermal resistance is decreased with the rise of heat input, and reveals a minimum value at a certain heat input followed by shows a marginal rise when the heat input is increased further. Both uniform and alternating design reveals the similar trend. For the vertical arrangement, the thermal resistance is much lower than that in horizontal arrangement. Different from that in horizontal arrangement, the thermal resistance shows a continuous decline against heat input for all the working fluids. For a low input power, CLPHP with HFE-7100 shows the least thermal resistance. By contrast, CLPHP with distilled water shows the smallest thermal resistance when the input power is increased over 60 W. (C) 2014 Elsevier Inc. All rights reserved.
Non-Uniform Three-Dimensional Pulsating Heat Pipe for Anti-Gravity High-Flux Applications
(2020-06-01)
Tseng, Chih-Yung
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Yang, Kai-Shing
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Wang, Chi-Chuan
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交大名義發表
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National Chiao Tung University
This study proposes a novel high-flux pulsating heat pipe that can lift the major constraint of the conventional pulsating heat pipe (PHP) which is unable to function properly upon anti-gravity operations. The proposed PHP introduces additional unbalance force via uneven tube diameter/geometry in the adiabatic sections to tailor the problem in anti-gravity operation. The design contains a three-dimensional configuration circuitry with compact arrangement tubes on the evaporator and condenser. Through this design, the non-uniform three-dimensional pulsating heat pipe (3D-PHP) manipulates the uneven inner diameters of the adiabatic sections to form uneven vapor/liquid distributions in the adiabatic sections to yield a unitary flow pattern that is able to withstand a much higher input power. The present PHP uses methanol as working fluid, with 38% volumetric filling ratio, and has a high-flux of 22.9 W/cm(2)and a low the thermal resistance ratio (Ranti-gravity/Rgravity-assisted) of 1.05 when the input power is 800 W. Both the heat flux and thermal resistance ratio for the proposed design are far better than the existing literature.
Performance and two-phase flow pattern for micro flat heat pipes
(2014-10-01)
Yang, Kai-Shing
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Lin, Chen-Chuan
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Shyu, Jin-Cherng
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Tseng, Chih-Yung
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Wang, Chi-Chuan
In this study, thermal performance and flow visualization of a double layer flat micro vapor chamber are reported. Two micro vapor chambers having pin fin and pin fin array support structure are fabricated and tested. The micro vapor chambers are composed of silicon and glass wafers having an overall size of 35 x 40 x 1.525 mm. Test results show that both the pin fin and pin fin array vapor chambers show an appreciably lower thermal resistance as compared to the solid silicon counterpart, the thermal resistance of the pin fin vapor chamber is about 52-60% of the solid silicon whereas the corresponding thermal resistance of pin fin array is only 17-20% of the solid silicon. The thermal resistance of the pin fin vapor chamber is moderately increased subject to the increase of supplied power whereas opposite trend is encountered for the pin fin array. The phenomenon is associated with the influence of dry-out phenomenon. It is found that the pin fin array vapor chamber is still in function even for an upside-down arrangement. The thermal resistance, however, is reduced with the rise of tilt angle, and the vertical arrangement gives the lowest thermal resistance. However, the thermal resistance is considerably increased if the heat source is placed upwards, and the corresponding thermal resistance for an upside-down heat source can be threefold higher than that of the vertical arrangement. (C) 2014 Elsevier Ltd. All rights reserved.