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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
;
Wongpromma, Pakorn
;
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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Heat transfer characteristics of gas-liquid flow in horizontal rectangular micro-channels
(2014-05-01)
Saisorn, Sira
;
Kuaseng, Piyawat
;
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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An experimental investigation of flow boiling heat transfer of R-134a in horizontal and vertical mini-channels
(2013-04-01)
Saisorn, Sira
;
Kaew-On, Jatuporn
;
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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A critical review of recent investigations on two-phase pressure drop in flow boiling micro-channels
(2012-01-01)
Saisorn, Sira
;
Wongwises, Somchai
Two-phase pressure drop during flow boiling has been studied for several decades. Obviously, the publications available on micro-channels are relatively small compared with those for ordinarily sized channels. Although the use of micro-channels yields several advantages, the pressure drop taking p lace in these extremely small channels is higher than that in the ordinarily sized channels because of the increased wall friction. The knowledge of the two-phase pressure drop characteristics in addition to heat transfer phenomena is essential to the design and evaluation of the micro-systems. In this paper, recent research on the flow boiling pressure drop in micro-scale channels is reviewed. The experimental results as well as the relevant prediction methods based on different researchers are presented.
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A critical review of recent investigations on flow pattern and heat transfer during flow boiling in micro-channels
(2012-01-01)
Saisorn, Sira
;
Wongwises, Somchai
A summary of recent research on flow boiling in micro-channels is provided in this article. This review aims to survey and identify new findings arising in this important area, which may contribute to optimum design and process control of high performance miniature devices comprising extremely small channels. Several criteria for defining a micro-channel are presented at first and the recent works on micro-scale flow boiling are subsequently described into two parts including flow visualization and two-phase heat transfer. The results obtained from a number of previous studies show that the flow behaviours and heat transfer mechanisms in micro-channels deviate significantly from those in ordinarily sized channels. Future research with numerous aspects of flow boiling phenomena necessary to answer the fundamental questions is still required.
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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
;
Kaew-On, Jatuporn
;
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
;
Kaew-On, Jatuporn
;
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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