A Study of Condensation Heat Transfer in a Single Mini-Tube and a Review of Korean Micro- and Mini-Channel Studies

2003 ◽  
Author(s):  
M. H. Kim ◽  
J. S. Shin ◽  
C. Huh ◽  
T. J. Kim ◽  
K. W. Seo
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Flow Characteristics ◽  
Saturation Temperature ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Round Tube ◽  
Two Phase

This paper reviews recent Korean studies of flow characteristics, flow boiling, and flow condensation in micro- and mini-channels. The characteristics of local heat transfer and pressure drops were experimentally investigated using condensing R134a two-phase flow, in a single round tube, with an inner diameter of 0.691 mm. New experimental techniques were developed to measure the condensation heat transfer coefficient. Tests were performed for a mass flux of 100 to 600 kg/m2s, a heat flux of 5 to 20 kW/m2, and a saturation temperature of 40°C. The experimental local condensation heat transfer coefficients and two-phase frictional pressure gradients are shown. Comparisons of experimental data with existing models reveal that the correlations failed to predict the present data. This study contains the unique sub-millimeter-diameter, single round tube, condensation data reported in the literature.

Evaporation of Ammonia in a Smooth Horizontal Tube: Heat Transfer Measurements and Predictions

1999 ◽  
Vol 121 (1) ◽  
pp. 89-101 ◽  
Author(s):  
O. Zu¨rcher ◽  
J. R. Thome ◽  
D. Favrat
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Stainless Steel Tube ◽  
Transfer Coefficients ◽  
Two Phase

Experimental test results for flow boiling of pure ammonia inside horizontal tubes were obtained for a plain stainless steel tube. Tests were run at a nominal saturation temperature of 4°C, nine mass velocities from 20–140 kg/m2 s, vapor qualities from 1–99 percent and heat fluxes from 5–58 kW/m2. Two-phase flow observations showed that the current test data covered the following regimes: fully stratified, stratified-wavy, intermittent, annular, and annular with partial dryout. The Kattan-Thome-Favrat flow boiling model accurately predicted the local heat transfer coefficients measured in all these flow regimes with only two small modifications to their flow map (to extend its application to G < 100 kg/m2 s). Their flow boiling model was also successfully compared to the earlier ammonia flow boiling data of Chaddock and Buzzard (1986). The Gungor-Winterton (1987) correlation instead gave very poor accuracy for ammonia.

Local Heat Transfer Coefficient of Flow Boiling in Microchannels With Artificial Reentrant Cavities

2007 ◽  
Author(s):  
Chih-Jung Kuo ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Bubble Generation ◽  
Parallel Microchannels

Flow boiling in parallel microchannels with structured reentrant cavities was experimental studied. Flow patterns, boiling inceptions and heat transfer coefficients were obtained and studied for G = 83 kg/m2-s to G = 303 kg/m2-s and heat fluxes up to 643 W/cm2. The heat transfer coefficient-mass velocity and quality relations had been analyzed to identify boiling mechanism. Comparisons of the performance of the enhanced and plain-wall microchannels had also been made. The microchannels with reentrant cavities were shown to promote nucleation of bubbles and to support significantly better reproducibility and uniformity of bubble generation.

Flow Boiling in Mini and Microchannels

2004 ◽  
Author(s):  
M. Cortina Di´az ◽  
H. Boye ◽  
I. Hapke ◽  
J. Schmidt ◽  
Y. Staate ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Outer Wall ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Convective Boiling ◽  
Inconel 600

Flow boiling heat transfer characteristics of water and hydrocarbons in mini and microchannels are experimentally studied. Two different test section geometries are employed; a circular channel with a hydraulic diameter of 1500 μm, and rectangular channels with height values of 300–700 μm and a width of 10mm. In both facilities the fluid flows upwards and the test sections, made of the nickel alloy Inconel 600, are directly electrically heated. Thus the evaporation takes place under the defined boundary condition of constant heat flux. Mass fluxes between 25 and 350 kg/(m2s) and heat fluxes from 20 to 350 kW/m2 at an inlet pressure of 0.3 MPa are examined. Infrared thermography is applied to scan the outer wall temperatures. These allow the identification of different boiling regions, boiling mechanisms and the determination of the local heat transfer coefficients. Measurements are carried out in initial, saturated and post-dryout boiling regions. The experimental results in the region of saturated boiling are compared with available correlations and with a physically founded model developed for convective boiling.

Evaporation Heat Transfer and Pressure Drop in Horizontal Tubes With Strip-Type Inserts Using Refrigerant 600a

1999 ◽  
Vol 122 (2) ◽  
pp. 387-391 ◽  
Author(s):  
S.-S. Hsieh ◽  
K.-J. Jang ◽  
Y.-C. Tsai
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Pressure Drops ◽  
Horizontal Tubes ◽  
Evaporation Heat

Results of a study on saturated boiling heat transfer of refrigerant R-600a in horizontal tubes (ID=10.6 mm) with strip-type inserts (longitudinal strip LS with/without perforated holes and cross-strip CS inserts) are reported. Local heat transfer coefficients are measured for a range of heat flux (9.1∼31.2 kW/m2), mass velocity (8.23∼603.3 kg/m2s), and equilibrium mass quality (⩽0.8) and the influences were studied. The data were compared with the performance of the corresponding smooth tubes. Enhancement factors are presented and discussed. Pressure drop measurement was also conducted and it is found that both single-phase and two-phase pressure drops increase with increasing heat flux levels and mass velocities. [S0022-1481(00)00302-9]

Flow Boiling of R134a and R134a/Propane Mixtures at Low Saturation Temperatures Inside a Plain Horizontal Tube

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
A. Rabah ◽  
S. Kabelac
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Azeotropic Point ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Maximum Decrease

Local heat transfer coefficients for flow boiling of pure 1,1,1,2-tetrafluoroethane (R134a) and binary mixtures of propane (R290) and R134a were measured. The experimental setup employed a vapor heated plain horizontal tube (di=10mm, do=12mm, L=500mm). The measurements covered a wide range of saturation temperatures (233≤Ts≤278K), mass fluxes (100≤ṁ≤300kg∕m2s), qualities (0≤ẋ≤1), and concentrations (0≤z̃≤0.65). In the zeotropic region of R134a/R290 mixtures, the measured local heat transfer coefficient was found to show a maximum decrease by a factor of 2 relative to that for pure R134a. At the azeotropic point (65% R290), it was found to increase by a factor of 1.2. The measured local heat transfer coefficients for both R134a and R134a/R290 were compared with a number of correlations.

Measurement of Condensation Heat Transfer Coefficients at Near-Critical Pressures in Refrigerant Blends

2006 ◽  
Vol 129 (8) ◽  
pp. 958-965 ◽  
Author(s):  
Yirong Jiang ◽  
Biswajit Mitra ◽  
Srinivas Garimella ◽  
Ulf C. Andresen
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Condensation Heat Transfer ◽  
Liquid Region ◽  
Transfer Coefficients ◽  
Reduced Pressure ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes

This paper presents the results of an experimental study on condensation heat transfer of refrigerant blends R404A and R410A flowing through horizontal tubes of 9.4 and 6.2mm inner diameter at nominal pressures of 80% and 90% of the critical pressure. Local heat transfer coefficients were measured for the mass flux range 200<G<800kg∕m2‐s in small quality increments over the entire vapor-liquid region. Heat transfer coefficients increased with quality and mass flux, while the effect of reduced pressure was not very significant within this range of pressures. The heat transfer coefficients increased with a decrease in diameter.

An Experimental Investigation on Flow Boiling of Ethylene-Glycol/Water Mixtures

2003 ◽  
Vol 125 (2) ◽  
pp. 317-325 ◽  
Author(s):  
Satish G. Kandlikar ◽  
Murat Bulut
Keyword(s):  
Heat Transfer ◽  
Ethylene Glycol ◽  
Binary Mixtures ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Saturation Temperature ◽  
Local Heat Transfer ◽  
Transfer Coefficients ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Mixtures of ethylene glycol and water are used in cooling the engines in automotive applications. Heat is transferred essentially under subcooled flow boiling conditions as the mixture flows over the hot surfaces, which are at temperatures well above the local saturation temperature of the mixture. Very little information is available in the literature on the subcooled flow boiling characteristics of this mixture. The present work focuses on obtaining experimental heat transfer data for water and its mixtures containing ethylene-glycol (0 to 40 percent mass fraction, limited by the maximum allowable temperature in the present setup) in the subcooled flow boiling region. The experimental setup is designed to obtain local heat transfer coefficients over a small circular aluminum heater surface, 9.5-mm in diameter, placed at the bottom 40-mm wide wall of a rectangular channel 3-mm×40-mm in cross-section. Available models for (a) subcooled flow boiling of pure liquids and (b) saturated flow boiling of binary mixtures are extended to model the subcooled flow boiling of binary mixtures.

scholarly journals Heat Transfer Analysis and Modification of Thermal Probe for Gas-Solid Measurement

2016 ◽  
Vol 2016 ◽  
pp. 1-7
Author(s):  
Hong Zhang ◽  
Xiangying Qi
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Transfer Analysis ◽  
Transfer Coefficients ◽  
Thermal Probe ◽  
Measuring Range ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Thermal Simulations

The presented work aims to measure the gas-solid two-phase mass flow-rate in pneumatic conveyor, and a novel modified thermal probe is applied. A new analysis of the local heat transfer coefficients of thermal probe is presented, while traditional investigations focus on global coefficients. Thermal simulations are performed in Fluent 6.2 and temperature distributions of the probe are presented. The results indicate that the probe has obviously stable and unstable heat transfer areas. Based on understanding of probe characteristics, a modified probe structure is designed, which makes the probe output signal more stable and widens the measuring range. The experiments are carried out in a special designed laboratory scale pneumatic conveyor, and the modified probe shows an unambiguous improvement of the performance compared with the traditional one.

Heat Transfer of Slug Air-Water Flow in a Slightly Upward Inclined Tube

2001 ◽  
Author(s):  
Jae-yong Kim ◽  
Steve Trimble ◽  
Afshin J. Ghajar
Keyword(s):  
Heat Transfer ◽  
Water Flow ◽  
Inclination Angle ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Flux Boundary Condition ◽  
Inclined Tube

Abstract This paper presents a preliminary study on the heat transfer in slug air-water flow in a slightly upward inclined tube, which is a widely appeared pattern in the inclined two-phase flow regime. Local heat transfer coefficients and flow parameters have been measured for slug air-water flow in a pipe [1.097 in (2.79 cm) I.D. and L/D = 100] at slightly upward inclination angles of 2° and 5°. The heat transfer data with slug air-water flow pattern were measured under a uniform wall heat flux boundary condition. The change on the heat transfer with inclination angle compared to the horizontal case is discussed in terms of the change in the overall heat transfer coefficient with respect to the superficial gas and liquid Reynolds numbers. For these data, the superficial Reynolds number ranged from about 3700 to 28000 for the water and from about 540 to 6500 for the air. The results indicate that there is an increase in the heat transfer with only slight increases in the inclination angle. However, the amount of increase is strongly dependent on the magnitudes of superficial liquid and gas Reynolds numbers.

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