An Experimental Investigation of Gas-Liquid Heat Transfer in Rectangular Micro-Channels

2013 ◽  
Author(s):  
Sira Saisorn ◽  
Somchai Wongwises ◽  
Piyawat Kuaseng ◽  
Chompunut Nuibutr ◽  
Wattana Chanphan
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Camera System ◽  
Micro Channels ◽  
Flow Mechanisms

The investigations of heat transfer and fluid flow characteristics of non-boiling air-water flow in micro-channels are experimentally studied. The gas-liquid mixture from y-shape mixer is forced to flow in the 21 parallel rectangular microchannels with 40 mm long in the flow direction. Each channel has a width and a depth of 0.45 and 0.41 mm, respectively. Flow visualization is feasible by incorporating the stereozoom microscope into the camera system and different flow patterns are recorded. The experiments are performed under low superficial velocities. Two-phase heat transfer gives better results when compared with the single-phase flow. It is found from the experiment that heat transfer enhancement up to 53% is obtained over the single-phase flow. Also, the change in the configuration of the inlet plenum can result in the different two-phase flow mechanisms.

Experimental Study on Heat Transfer of Single-Phase Flow and Boiling Two-Phase Flow in Vertical Narrow Annuli

2002 ◽  
Author(s):  
Suizheng Qiu ◽  
Minoru Takahashi ◽  
Guanghui Su ◽  
Dounan Jia
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Two Phase Flow ◽  
Annular Channel ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Narrow Annuli ◽  
Narrow Gaps

Water single-phase and nucleate boiling heat transfer were experimentally investigated in vertical annuli with narrow gaps. The experimental data about water single-phase flow and boiling two-phase flow heat transfer in narrow annular channel were accumulated by two test sections with the narrow gaps of 1.0mm and 1.5mm. Empirical correlations to predict the heat transfer of the single-phase flow and boiling two-phase flow in the narrow annular channel were obtained, which were arranged in the forms of the Dittus-Boelter for heat transfer coefficients in a single-phase flow and the Jens-Lottes formula for a boiling two-phase flow in normal tubes, respectively. The mechanism of the difference between the normal channel and narrow annular channel were also explored. From experimental results, it was found that the turbulent heat transfer coefficients in narrow gaps are nearly the same to the normal channel in the experimental range, and the transition Reynolds number from a laminar flow to a turbulent flow in narrow annuli was much lower than that in normal channel, whereas the boiling heat transfer in narrow annular gap was greatly enhanced compared with the normal channel.

Mini- and Microchannel Research in Sweden

2003 ◽  
Author(s):  
Bjo¨rn Palm
Keyword(s):  
Heat Exchangers ◽  
Single Phase ◽  
Single Channels ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Compact Heat Exchangers ◽  
Micro Channels ◽  
Parallel Channels ◽  
Institute Of Technology

The purpose of the present paper is to present research and development within the area of mini- and micro channels in Sweden. A review is made of the historical development of highly compact heat exchangers within the country, starting with plate heat exchangers. The main focus is on the research performed at the Royal Institute of Technology, where mini-channel research has been going on since more than ten years. Single-phase flow as well as two-phase flow is treated, both in single channels and in full-size heat exchangers with multiple parallel channels.

Simulation of Two-Phase Flow and Heat Transfer in Mini- and Micro-Channels for Concentrating Photovoltaics Cooling

2011 ◽  
Author(s):  
Devin Pellicone ◽  
Alfonso Ortega ◽  
Marcelo del Valle ◽  
Steven Schon
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Single Phase ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Micro Scale ◽  
Heat Transfer Coefficients ◽  
Flow And Heat Transfer ◽  
Micro Channels

Advances in concentrating photovoltaics technology have generated a need for more effective thermal management techniques. Research in photovoltaics has shown that there is a more than 50% decrease in PV cell efficiency when operating temperatures approach 60°C. It is estimated that a waste heat load in excess of 500 W/cm2 will need to be dissipated at a solar concentration of 10,000 suns. Mini- and micro-scale heat exchangers provide the means for large heat transfer coefficients with single phase flow due to the inverse proportionality of Nusselt number with respect to the hydraulic diameter. For very high heat flux situations, single phase forced convection in micro-channels may not be sufficient and hence convective flow boiling in small scale heat exchangers has gained wider scrutiny due to the much higher achievable heat transfer coefficients due to latent heat of vaporization and convective boiling. The purpose of this investigation is to explore a practical and accurate modeling approach for simulating multiphase flow and heat transfer in mini- and micro-channel heat exchangers. The work is specifically aimed at providing a modeling tool to assist in the design of a mini/micro-scale stacked heat exchanger to operate in the boiling regime. The flow side energy and momentum equations have been implemented using a one-dimensional homogeneous approach, with local heat transfer coefficients and friction factors supplied by literature correlations. The channel flow solver has been implemented in MATLAB™ and embedded within the COMSOL™ FEM solver which is used to model the solid side conduction problem. The COMSOL environment allows for parameterization of design variables leading to a fully customizable model of a two-phase heat exchanger.

Thermofluid Characteristics of Two-Phase Microgap Coolers

2007 ◽  
Author(s):  
Dae W. Kim ◽  
Emil Rahim ◽  
Avram Bar-Cohen ◽  
Bongtae Han
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Pressure Drop ◽  
Single Phase ◽  
Flow Boiling ◽  
Phase Flow ◽  
Dissolved Gas ◽  
Single Phase Flow ◽  
Two Phase ◽  
Phase Water

The thermofluid characteristics of a chip-scale microgap cooler, including single-phase flow of water and FC-72 and flow boiling of FC-72, are explored. Heat transfer and pressure drop results for single phase water are used to validate a detailed numerical model and, together with the convective FC-72 data, establish a baseline for microgap cooler performance. Experimental results for single phase water and FC-72 flowing in 120 μm, 260 μm and 600 μm microgap coolers, 31mm wide by 34mm long, at velocities of 0.1 – 2 m/s are reported. “Pseudo-boiling” driven by dissolved gas and flow boiling of FC-72 are found to provide significant enhancement in heat transfer relative to theoretical single phase values.

Pressure Drop During Two-Phase Flow of R134a and R32 in a Single Minichannel

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Alberto Cavallini ◽  
Davide Del Col ◽  
Marko Matkovic ◽  
Luisa Rossetto
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Single Phase ◽  
Two Phase Flow ◽  
Vapor Flow ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Roughness Effects ◽  
Two Phase ◽  
Adiabatic Flow

Condensation in minichannels is widely used in air-cooled condensers for the automotive and air-conditioning industry, heat pipes, and compact heat exchangers. The knowledge of pressure drops in such small channels is important in order to optimize heat transfer surfaces. Most of the available experimental work refers to measurements obtained within multiport smooth extruded tubes and deal with the average values over the number of parallel channels. In this context, the present authors have set up a new test apparatus for heat transfer and fluid flow studies in single minichannels. This paper presents new experimental frictional pressure gradient data, relative to single-phase flow and adiabatic two-phase flow of R134a and R32 inside a single horizontal minitube, with a 0.96 mm inner diameter and with not-negligible surface roughness. The new all-liquid and all-vapor data are successfully compared against predictions of single-phase flow models. Also the two-phase flow data are compared against a model previously developed by the present authors for adiabatic flow or flow during condensation of halogenated refrigerants inside smooth minichannels. Surface roughness effects on the liquid-vapor flow are discussed. In this respect, the friction factor in the proposed model is modified, in order to take into consideration also effects due to wall roughness.

scholarly journals INVESTIGATION OF SINGLE-PHASE FLOW CHARACTERISTICS IN A STAGGER PIN-FINS COMPLEX GEOMETRY

2021 ◽  
Vol 25 (6) ◽  
pp. 74-81
Author(s):  
R. Shakir ◽  
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Complex Geometry ◽  
Flow Characteristics ◽  
Inlet Temperature ◽  
Phase Flow ◽  
Fluid Temperature ◽  
Single Phase Flow ◽  
Pin Fins ◽  
Micro Pin Fins

The cooling equipment project must use electrical and electronic equipment because of the need to remove the heat generated by this equipment. Investigation; R-113 single-phase flow heat transfer; (50 x 50 mm2) cross-section and (5 mm) height; used in a series of stagger-square micro-pin fins. Inlet temperature of (25 °C); (6) Mass flow rate at this temperature, the recommended range is (0. 0025 -0.01 kg/sec) the inlet and outlet pressures are approximately (1-1.10 bar), and through (25- 225 watts) applied heat. The iterative process is used to obtain the heat flow characteristics, for example; the single-phase heat transfer coefficient is completely laminar flow developing, in this flow, guesses the wall temperature, guess the fluid temperature. The possible mechanism of heat transfer has been discussed

Thermal and Flow Characteristics of Water–Nitrogen Taylor Flow Inside Vertical Circular Tubes

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Jingzhi Zhang ◽  
Wei Li
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Flow Characteristics ◽  
Numerical Data ◽  
Bond Number ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Pressure Drops ◽  
Taylor Flow ◽  
Bubble Rising Velocity

Heat transfer and flow characteristics of Taylor flows in vertical capillaries with tube diameters ranging from 0.5 mm to 2 mm were studied numerically with the volume of fluid (VOF) method. Streamlines, bubble shapes, pressure drops, and heat transfer characteristics of the fully developed gas–liquid Taylor flow were investigated in detail. The numerical data fitted well with experimental results and with the predicted values of empirical correlations. The results indicate that the dimensionless liquid film thickness and bubble rising velocity increase with increasing capillary number. Pressure drops in liquid slug region are higher than the single-phase flow because of the Laplace pressure drop. The flow pattern dependent model and modified flow separation model which takes Bond number and Reynolds number into account can predict the numerical pressure drops well. Compared with the single-phase flow, less time is needed for the Taylor flow to reach a thermal fully developed status. The Nusselt number of Taylor flow is about 1.16–3.5 times of the fully developed single-phase flow with a constant wall heat flux. The recirculation regions in the liquid and gas slugs can enhance the heat transfer coefficient and accelerate the development of the thermal boundary layer.

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