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Experimental investigation on flow pattern and void fraction for two-phase gas-liquid upflow in a vertical helically coiled micro-channel
(2025-03-01)
Saisorn, Sira
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Benjawun, Phakkhanan
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Suriyawong, Adirek
;
Wongwises, Somchai
To contribute toward state-of-the-art microfluidic technology, our experiments were conducted to study gas-liquid adiabatic upflow phenomena in a helical micro-channel having a channel diameter of 0.87 mm, a coil diameter of 50 mm, and a helical pitch of 20 mm. The presence of centrifugal acceleration in the micro-scale flow is given as follows. The unique flow pattern having the throat-like gas-core flow generally detected in the straight micro-tube was still present in the curved test section. The void fraction characteristics were not able to match with the homogeneous flow model. The slip ratio data explicitly showed that the annular flow tended to be highly affected by the secondary flow when compared to the throat-annular flow. The prediction based on different approaches indicated that the data aligned well with drift flux model incorporating inertia and channel orientation effects.
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The difference in flow pattern, heat transfer and pressure drop characteristics of mini-channel flow boiling in horizontal and vertical orientations
(2018-04-01)
Saisorn, Sira
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Wongpromma, Pakorn
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Wongwises, Somchai
Flow pattern, heat transfer, and pressure drop data for different flow orientations was presented in this study. The data was obtained based on flow boiling experiments with R-134a flow through a 1 mm diameter channel which was aligned in different orientations, i.e. horizontal flow, vertical upward flow, and vertical downward flow. A constant surface heat flux condition was performed under a saturation pressure of 8 bar, a heat flux range of 1–60 kW/m2, and a mass flux range of 250–820 kg/m2s. The experimental results showed the importance of the change in the flow direction. The shape of the gas slug during horizontal flow did not look the same as in the vertical orientations. Heat transfer coefficient and pressure drop became increased when the refrigerant flowed in the vertical downward direction. The experimental data was also compared with the existing prediction methods.
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Adiabatic two-phase gas-liquid flow behaviors during upward flow in a vertical circular micro-channel
(2015-12-01)
Saisorn, Sira
;
Wongwises, Somchai
A two-phase air-water flow experiment was carried out to obtain flow pattern, void fraction, and pressure drop data from a vertical micro-channel, which was a fused silica tube with a diameter of 0.53. mm and a length of 320. mm. The adiabatic two-phase flow behaviors during vertical upward direction were experimentally investigated, and consequently, a buoyancy effect can be detected in this work. A flow visualization study was performed, leading to observation of slug flow, throat-annular flow, churn flow, annular flow, and annular-rivulet flow. The shape of the interfacial surface in the slug flow pattern was deformed during vertical upward flow, which was different from the bullet-shaped gas slug observed in the horizontal channel. The flow visualization results also indicate that the flow pattern map for vertical upward flow is not completely compatible with that for horizontal flow. Image analysis was performed to determine the void fraction, which increases linearly with increasing volumetric quality. The vertical upward flow gave a lower void fraction than the horizontal flow. The frictional pressure drop can be increased when the churn flow is formed in the channel. In addition, vertical upward flow can result in higher pressure drop when compared with the horizontal channel.
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Heat transfer characteristics of gas-liquid flow in horizontal rectangular micro-channels
(2014-05-01)
Saisorn, Sira
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Kuaseng, Piyawat
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Wongwises, Somchai
An experimental study of heat transfer characteristics of air-water flow in horizontal micro-channels was carried out in this work. The gas-liquid mixture from a y-shaped mixing chamber was forced to pass through a plenum inlet and entered 21 parallel rectangular micro-channels 40. mm long in the direction of flow. Each channel had a width and a depth of 0.45 and 0.41. mm, respectively. The test runs were done at a heat load of 80. W, with superficial Reynolds numbers of gas and liquid ranging between 54-142 and 131-373, respectively. A Stereozoom microscope and camera system were employed to conduct flow visualization. To explore the dependence of a Nusselt number on the flow characteristics, two inlet sections with different designs were used in this work. The experiments revealed that the formation of small gas slugs instead of gas core flow involves an increase in Nusselt numbers. In this work, the gas-liquid flow gave heat transfer enhancement up to 80% over the liquid flow. © 2014 Elsevier Inc.
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Effect of Flow Pattern on Single and Multi-stage High Temperature Proton Exchange Membrane Fuel Cell Stack Performance
(2014-01-01)
Authayanun, Suthida
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Patniboon, Artitaya
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Saebea, Dang
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Patcharavorachot, Yaneeporn
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Arpronwichanop, Amornchai
A high-temperature proton exchange membrane fuel cell (HT-PEMFC) is a promising clean and effective technology for power generation because of its simplified water and heat management as well as high CO tolerance. Therefore, it could be possible to directly use a reformate gas for HT-PEMFC without the need for sophisticated purification processes. Due to the non-uniform of H<inf>2</inf> and CO distributions within fuel cells, the stack design is one of the key factors to enhance the performance and efficiency of HT-PEMFC. In this study, a single HT-PEMFC stack is investigated by considering the CO poisoning effect. The mathematical model of HT-PEMFC based on the electrochemical reaction model coupled with the diffusion model of a gas diffusion layer and electrolyte film layer is used for simulation studies. At high fuel utilization, hydrogen is highly consumed and CO concentration increases, having a significant impact on cell performance. The multi-stack HT-PEMFC is designed to minimize the CO poisoning effect and to maximize its efficiency. The power output that is obtained from each cell stack is presented and the overall power output is compared with single cell stack. Effect of different flow patterns, i.e., co-current and counter-current flow, on the HT-PEMFC stack performance is also presented. © 2014 Elsevier B.V.
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An experimental investigation of flow boiling heat transfer of R-134a in horizontal and vertical mini-channels
(2013-04-01)
Saisorn, Sira
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Kaew-On, Jatuporn
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Wongwises, Somchai
Flow boiling experiments with R-134a flowing in horizontal and vertical mini-channels are performed to obtain flow visualization and heat transfer data. A 1.75mm diameter channel with a length of 600mm is used as test section. Two sets of the horizontal flow and vertical upward flow data are presented based on a mass flux range of 200-1000kg/m2s, a heat flux range of 1-80kW/m2 and a saturation pressure range of 7-13bar. Flow visualization and heat transfer results show heat transfer coefficient depending on flow pattern. The results also indicate that flow regime transition and heat transfer coefficient tend to depend on flow direction under the certain experimental conditions. In addition, the comparisons between the experimental data and the predictions recommended for either macro-scale flow boiling or micro-scale flow boiling are presented in this work. © 2012 Elsevier Inc.
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Two-phase flow of R-134a refrigerant during flow boiling through a horizontal circular mini-channel
(2011-09-01)
Saisorn, Sira
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Kaew-On, Jatuporn
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Wongwises, Somchai
This research focuses on heat transfer to R-134a during flow boiling in a 1.75. mm internal diameter tube. Flow visualisation and heat transfer experiments are conducted to obtain heat transfer coefficients for different flow patterns. The measured data in each flow regime are compared with predictions from a three-zone flow boiling model. The calculations are in fair agreement with the experimental results which correspond in particular to slug flow, throat-annular flow and churn flow regimes under conditions of low heat flux. © 2011 Elsevier Inc.
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Flow pattern and heat transfer characteristics of R-134a refrigerant during flow boiling in a horizontal circular mini-channel
(2010-09-01)
Saisorn, Sira
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Kaew-On, Jatuporn
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Wongwises, Somchai
Flow boiling heat transfer of R-134a refrigerant in a circular mini-channel, 600mm long with a diameter of 1.75mm, is investigated experimentally in this study. The test section is a stainless steel tube placed horizontally. Flow pattern and heat transfer coefficient data are obtained for a mass flux range of 200-1000kg/m2s, a heat flux range of 1-83kW/m2 and saturation pressures of 8, 10, and 13bar. Five different flow patterns including slug flow, throat-annular flow, churn flow, annular flow and annular-rivulet flow are observed and the heat transfer coefficient data for different flow patterns are presented. The heat transfer coefficient increases with increasing heat flux but is mostly independent of mass flux and vapour quality. In addition, it is indicated from the experiments that the higher the saturation pressure, the lower is the heat transfer coefficient. Comparisons of the present data with the existing correlations are also presented. © 2010 Elsevier Ltd.

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