Boiling Heat Transfer of Carbon Dioxide in Horizontal Tubes

Transfer Coefficient ◽

Mass Flux ◽

Boiling Heat Transfer ◽

Transfer Coefficients ◽

In this study, boiling heat transfer coefficients of carbon dioxide in horizontally located smooth tubes were experimentally investigated. The inner diameter of heat transfer tubes was 1, 2, 4, and 6 mm. Experiments were conducted at evaporating temperature of 5 and 15 °C, heat fluxes from 4.5 to 36 kW/m2, and mass fluxes from 360 to 1440 kg/m2s. The heat transfer coefficients in the pre-dryout region and post-dryout region were investigated, as well as the dryout quality. Due to the small viscosity and surface tension of CO2, the dryout occurs at a small quality from 0.4 to 0.7. The inception quality decreases with the increase of mass flux, and is affected by the heat flux and tube diameter; the effects of heat flux on the heat transfer coefficient are much significant in the pre-dryout region, which is related with the activation of nucleate boiling. On the contrary, the effects of mass flux are relatively low due to the low two-phase density ratio near the critical point. In addition, this tendency becomes more significant when the small tube is tested; In the post-dryout region, mass velocity is the dominating factor on heat transfer coefficient. At small mass flux, the heat transfer coefficient decreases with the increase of quality, while at large mass flux such as 1440kg/m2s, the heat transfer coefficient turns to increasing with the quality. By increasing the evaporating temperature, the pre-dryout heat transfer coefficient increases, while the dryout inception quality and post-dryout heat transfer coefficient are not affected greatly by the evaporating temperature.

ASME 3rd International Conference on Microchannels and Minichannels, Part B cont’d ◽

Evaporative Heat Transfer and Pressure Drop of CO2 in a Microchannel Tube

10.1115/icmm2005-75180 ◽

2005 ◽

Cited By ~ 7

Author(s):

Siyoung Jeong ◽

Eunsang Cho ◽

Hark-koo Kim

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Pressure Drop ◽

Transfer Coefficient ◽

Mass Flux ◽

Transfer Coefficients ◽

Dry Out ◽

Evaporation heat transfer and pressure drop characteristics of carbon dioxide were investigated in a multi-channel micro tube. The aluminum tube has 3 square channels with a hydraulic diameter of 2mm, a wall thickness of 1.5mm, and a length of 5m. The tube was heated directly by electric current. Experiments were conducted at heat fluxes ranging 4–16 kW/m2, mass fluxes from 150 to 750 kg/m2s, evaporative temperature from 0 to 10°C, and qualities from 0 to superheated state. The heat transfer coefficient measured was in the range of 6–15kW/m2K, and the pressure drop was 3–23kPa/m. For the qualities lower than 0.5, the heat transfer coefficient was found to increase with the quality, which is assumed to be the effect of convective boiling. For the qualities higher than 0.6, sudden drop in heat transfer coefficients was sometimes observed due to local dry-out. It was found that dry-out occurred at lower quality if mass flux was smaller. The average heat transfer coefficient was found to increase with increasing heat flux, mass flux, and evaporation temperature, of which the effect of heat flux was the greatest. At given experimental conditions the pressure drop increased almost linearly with increasing quality. The total pressure drop was found to increase with increasing heat flux, mass flux, and evaporation temperature, of which the effect of mass flux was the greatest. From the experimental results simple correlations for heat transfer coefficients and pressure drop were developed.

Study on Flow Boiling Heat Transfer of Carbon Dioxide With PAG-Type Lubricating Oil in Pre-Dryout Region Inside Horizontal Tube

2010 14th International Heat Transfer Conference, Volume 1 ◽

10.1115/ihtc14-23189 ◽

2010 ◽

Cited By ~ 1

Author(s):

Chaobin Dang ◽

Minxia Li ◽

Eiji Hihara

Keyword(s):

Heat Transfer ◽

Carbon Dioxide ◽

Transfer Coefficient ◽

Mass Flux ◽

Boiling Heat Transfer ◽

Flow Boiling ◽

Nucleate Boiling ◽

In this study, the boiling heat transfer coefficients of carbon dioxide with a PAG-type lubricating oil entrained from 0 to 5 wt% in a horizontally placed smooth tube with an inner diameter of 2 mm were experimentally investigated under the following operating conditions: mass fluxes from 170 to 320 kg/m2s, heat fluxes from 4.5 to 36 kW/m2, and a saturation temperature of 15 °C. The results show that for a low oil concentration of approximately 0.5% to 1%, no further deterioration of the heat transfer coefficient was observed at higher oil concentrations in spite of a significant decrement of the heat transfer coefficient compared to that under an oil-free condition. The heat flux still had a positive influence on the heat transfer coefficient in low quality regions. However, no obvious influence was observed in high quality regions, which implies that nucleate boiling dominates in the low quality region whereas it is suppressed in the high quality regions. Unlike the mass flux under an oil-free condition, mass flux has a significant influence on the heat transfer coefficient, with a maximum increase of 50% in the heat transfer. On the basis of our experimental measurements of the flow boiling heat transfer of carbon dioxide under wide experimental conditions, a flow boiling heat transfer model for horizontal tubes has been proposed for a mixture of CO2 and polyalkylene glycol (PAG oil) in the pre-dryout region, with consideration of the thermodynamic properties of the mixture. The surface tension and viscosity of the mixture were particularly taken into account. New factors were introduced into the correlation to reflect the suppressive effects of the mass flux and the oil on both the nucleate boiling. It is shown that the calculated results can depict the influence of the mass flux and the heat flux on both nucleate boiling and convection boiling.

Heat Flux Reduction From Film Cooling and Correlation of Heat Transfer Coefficients From Thermographic Measurements at Engine Like Conditions

Volume 3: Turbo Expo 2002, Parts A and B ◽

10.1115/gt2002-30181 ◽

2002 ◽

Cited By ~ 3

Author(s):

S. Baldauf ◽

M. Scheurlen ◽

A. Schulz ◽

S. Wittig

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Transfer Coefficient ◽

Film Cooling ◽

Transfer Coefficients ◽

Average Heat ◽

New Correlation ◽

Heat transfer coefficients and the resulting heat flux reduction due to film cooling on a flat plate downstream a row of cylindrical holes are investigated. Highly resolved two dimensional heat transfer coefficient distributions were measured by means of infrared thermography and carefully corrected for local internal testplate conduction and radiation effects [1]. These locally acquired data are processed to lateral average heat transfer coefficients for a quantitative assessment. A wide range variation of the flow parameters blowing rate and density ratio as well as the geometrical parameters streamwise ejection angle and hole spacing is examined. The effects of these dominating parameters on the heat transfer augmentation from film cooling are discussed and interpreted with the help of highly resolved surface results of effectiveness and heat transfer coefficients presented earlier [2]. A new method of evaluating the heat flux reduction from film cooling is presented. From a combination of the lateral average of both the adiabatic effectiveness and the heat transfer coefficient, the lateral average heat flux reduction is processed according to the new method. The discussion of the total effect of film cooling by means of the heat flux reduction reveals important characteristics and constraints of discrete hole ejection. The complete heat transfer data of all measurements are used as basis for a new correlation of lateral average heat transfer coefficients. This correlation combines the effects of all the dominating parameters. It yields a prediction of the heat transfer coefficient from the ejection position to far downstream, including effects of extreme blowing angles and hole spacing. The new correlation has a modular structure to allow for future inclusion of additional parameters. Together with the correlation of the adiabatic effectiveness it provides an immediate determination of the streamwise heat flux reduction distribution of cylindrical hole film cooling configurations.

ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 2 ◽

Flow Boiling Heat Transfer Characteristics of a Minichannel Up to Dryout Condition

10.1115/mnhmt2009-18224 ◽

2009 ◽

Cited By ~ 6

Author(s):

Rashid Ali ◽

Bjo¨rn Palm ◽

Mohammad H. Maqbool

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Transfer Coefficient ◽

Mass Flux ◽

Boiling Heat Transfer ◽

Flow Boiling ◽

Working Fluid ◽

In this paper the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.7mm and a uniformly heated length of 220mm. R134a was used as working fluid and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 °C and 32 °C. Mass flux was varied from 50 kg/m2 s to 600 kg/m2 s and heat flux ranged from 2kW/m2 to 156kW/m2. The test section was heated directly using a DC power supply. The direct heating of the channel ensured uniform heating and heating was continued until dry out was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

Flow Boiling Heat Transfer Characteristics of a Minichannel up to Dryout Condition

Journal of Heat Transfer ◽

10.1115/1.4003669 ◽

2011 ◽

Vol 133 (8) ◽

Cited By ~ 21

Author(s):

Rashid Ali ◽

Björn Palm ◽

Mohammad H. Maqbool

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Transfer Coefficient ◽

Mass Flux ◽

Boiling Heat Transfer ◽

Flow Boiling ◽

Working Fluid ◽

In this paper, the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.70 mm and a uniformly heated length of 220 mm. R134a was used as a working fluid, and experiments were performed at two different system pressures corresponding to saturation temperatures of 27°C and 32°C. Mass flux was varied from 50 kg/m2 s to 600 kg/m2 s, and heat flux ranged from 2 kW/m2 to 156 kW/m2. The test section was heated directly using a dc power supply. The direct heating of the channel ensured uniform heating, which was continued until dryout was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux, while mass flux and vapor quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that the dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

Heat Flux Reduction From Film Cooling and Correlation of Heat Transfer Coefficients From Thermographic Measurements at Enginelike Conditions

Journal of Turbomachinery ◽

10.1115/1.1505848 ◽

2002 ◽

Vol 124 (4) ◽

pp. 699-709 ◽

Cited By ~ 21

Author(s):

S. Baldauf ◽

M. Scheurlen ◽

A. Schulz ◽

S. Wittig

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Transfer Coefficient ◽

Film Cooling ◽

Transfer Coefficients ◽

Average Heat ◽

New Correlation ◽

Heat transfer coefficients and the resulting heat flux reduction due to film cooling on a flat plate downstream a row of cylindrical holes are investigated. Highly resolved two-dimensional heat transfer coefficient distributions were measured by means of infrared thermography and carefully corrected for local internal testplate conduction and radiation effects. These locally acquired data are processed to lateral average heat transfer coefficients for a quantitative assessment. A wide range variation of the flow parameters blowing rate and density ratio as well as the geometrical parameters streamwise ejection angle and hole spacing is examined. The effects of these dominating parameters on the heat transfer augmentation from film cooling are discussed and interpreted with the help of highly resolved surface results of effectiveness and heat transfer coefficients presented earlier. A new method of evaluating the heat flux reduction from film cooling is presented. From a combination of the lateral average of both the adiabatic effectiveness and the heat transfer coefficient, the lateral average heat flux reduction is processed according to the new method. The discussion of the total effect of film cooling by means of the heat flux reduction reveals important characteristics and constraints of discrete hole ejection. The complete heat transfer data of all measurements are used as basis for a new correlation of lateral average heat transfer coefficients. This correlation combines the effects of all the dominating parameters. It yields a prediction of the heat transfer coefficient from the ejection position to far downstream, including effects of extreme blowing angles and hole spacing. The new correlation has a modular structure to allow for future inclusion of additional parameters. Together with the correlation of the adiabatic effectiveness it provides an immediate determination of the streamwise heat flux reduction distribution of cylindrical hole film-cooling configurations.

Flow boiling heat transfer coefficient of R-134a/R-290/R-600a mixture in a smooth horizontal tube

Thermal Science ◽

10.2298/tsci0803033b ◽

2008 ◽

Vol 12 (3) ◽

pp. 33-44 ◽

Cited By ~ 2

Author(s):

Raja Balakrishnan ◽

Lal Dhasan ◽

Saravanan Rajagopal

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Transfer Coefficient ◽

Boiling Heat Transfer ◽

Flow Boiling ◽

Transfer Coefficients ◽

R 134A

An investigation on in-tube flow boiling heat transfer of R-134a/R-290/R-600a (91%/4.068%/4.932% by mass) refrigerant mixture has been carried out in a varied heat flux condition using a tube-in-tube counter-flow test section. The boiling heat transfer coefficients at temperatures between -5 and 5?C for mass flow rates varying from 3 to 5 g/s were experimentally arrived. Acetone is used as hot fluid, which flows in the outer tube of diameter 28.57 mm, while the test fluid flows in the inner tube of diameter 9.52 mm. By regulating the acetone flow rate and its entry temperature, different heat flux conditions between 2 and 8 kW/m2 were maintained. The pressure of the refrigerant was maintained at 3.5, 4, and 5 bar. Flow pattern maps constructed for the considered operating conditions indicated that the flow was predominantly stratified and stratified wavy. The heat transfer coefficient was found to vary between 500 and 2200 W/m2K. The effect of nucleate boiling prevailing even at high vapor quality in a low mass and heat flux application is high-lighted. The comparison of experimental results with the familiar correlations showed that the correlations over predict the heat transfer coefficients of this mixture.

Systematic heat transfer measurements in highly viscous binary fluids

Heat and Mass Transfer ◽

10.1007/s00231-021-03087-w ◽

2021 ◽

Author(s):

Ann-Christin Fleer ◽

Markus Richter ◽

Roland Span

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Volatile Component ◽

Test Tube ◽

Heat Fluxes ◽

Transfer Coefficients ◽

Low Viscosity ◽

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

An Experimental Investigation of the Rib Surface-Averaged Heat Transfer Coefficient in a Rib-Roughened Square Passage

Journal of Turbomachinery ◽

10.1115/1.2841122 ◽

1997 ◽

Vol 119 (2) ◽

pp. 381-389 ◽

Cited By ~ 55

Author(s):

M. E. Taslim ◽

C. M. Wadsworth

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Thermal Performance ◽

Blockage Ratio ◽

Transfer Coefficients ◽

Height Ratio ◽

Average Heat ◽

Turbine blade cooling, a common practice in modern aircraft engines, is accomplished, among other methods, by passing the cooling air through an often serpentine passage in the core of the blade. Furthermore, to enhance the heat transfer coefficient, these passages are roughened with rib-shaped turbulence promoters (turbulators). Considerable data are available on the heat transfer coefficient on the passage surface between the ribs. However, the heat transfer coefficients on the surface of the ribs themselves have not been investigated to the same extent. In small aircraft engines with small cooling passages and relatively large ribs, the rib surfaces comprise a large portion of the passage heat transfer area. Therefore, an accurate account of the heat transfer coefficient on the rib surfaces is critical in the overall design of the blade cooling system. The objective of this experimental investigation was to conduct a series of 13 tests to measure the rib surface-averaged heat transfer coefficient, hrib, in a square duct roughened with staggered 90 deg ribs. To investigate the effects that blockage ratio, e/Dh and pitch-to-height ratio, S/e, have on hrib and passage friction factor, three rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested for pitch-to-height ratios of 5, 7, 8.5, and 10. Comparisons were made between the rib average heat transfer coefficient and that on the wall surface between two ribs, hfloor, reported previously. Heat transfer coefficients of the upstream-most rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared. It is concluded that: 1 The rib average heat transfer coefficient is much higher than that for the area between the ribs; 2 similar to the heat transfer coefficient on the surface between the ribs, the average rib heat transfer coefficient increases with the blockage ratio; 3 a pitch-to-height ratios of 8.5 consistently produced the highest rib average heat transfer coefficients amongst all tested; 4 under otherwise identical conditions, ribs in upstream-most position produced lower heat transfer coefficients than the midchannel positions, 5 the upstream-most rib average heat transfer coefficients decreased with the blockage ratio; and 6 thermal performance decreased with increased blockage ratio. While a pitch-to-height ratio of 8.5 and 10 had the highest thermal performance for the smallest rib geometry, thermal performance of high blockage ribs did not change significantly with the pitch-to-height ratio.

Preliminary studies of the loss of heat from leaves under conditions of free and forced convection

Australian Journal of Botany ◽

10.1071/bt9650153 ◽

1965 ◽

Vol 13 (2) ◽

pp. 153 ◽

Cited By ~ 6

Author(s):

GI Pearman

Keyword(s):

Heat Transfer ◽

Wind Tunnel ◽

Transfer Coefficient ◽

Convective Heat Transfer ◽

Transfer Coefficients ◽

Free And Forced Convection ◽

Wind Velocities ◽

An account is given of techniques and methods used in measurement of convective heat transfer from leaves of the succulent Carpobrotus. Heat transfer was studied under still air conditions and in wind (in a specially constructed wind-tunnel) up to velocities of 300 cm sec-1. A correlation was demonstrated between experimentally obtained values of heat transfer coefficients and theoretical values calculated from empirical formulae. At wind velocities of 300 cm sec-1 the heat transfer coefficient for Carpobrotus was increased to seven times its value still air.