Flow Boiling of Coolant (HFE-7000) Inside Structured and Plain Wall Microchannels

2009 ◽  
Vol 131 (12) ◽  
Author(s):  
C.-J. Kuo ◽  
Y. Peles
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Side Walls ◽  
Parallel Microchannels ◽  
The Heat Transfer Coefficient

Flow boiling was experimentally studied using coolant HFE-7000 for two types of parallel microchannels: a plain-wall microchannel and a microchannel with structured reentrant cavities on the side walls. Flow morphologies, boiling inceptions, heat transfer coefficients, and critical heat fluxes were obtained and studied for mass fluxes ranging from G=164 kg/m2 s to G=3025 kg/m2 s and mass qualities (energy definition) ranging from x=−0.25 to x=1. Comparisons of the performance of the enhanced and plain-wall microchannels were carried out. It was found that reentrant cavities were effective in reducing the superheat at the onset of nucleate boiling and increasing the heat transfer coefficient. However, they did not seem to increase the critical heat flux.

Flow Boiling of R134a in Circular Microtubes—Part I: Study of Heat Transfer Characteristics

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Saptarshi Basu ◽  
Sidy Ndao ◽  
Gregory J. Michna ◽  
Yoav Peles ◽  
Michael K. Jensen
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Heat Fluxes ◽  
Average Error ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Two Phase Heat Transfer

An experimental study of two-phase heat transfer coefficients was carried out using R134a in uniformly heated horizontal circular microtubes with diameters from 0.50 mm to 1.60 mm over a range of mass fluxes, heat fluxes, saturation pressures, and vapor qualities. Heat transfer coefficients increased with increasing heat flux and saturation pressure but were independent of mass flux. The effects of vapor quality on heat transfer coefficients were less pronounced and varied depending on the quality. The data were compared with seven flow boiling correlations. None of the correlations predicted the experimental data very well, although they generally predicted the correct trends within limits of experimental error. A correlation was developed, which predicted the heat transfer coefficients with a mean average error of 29%. 80% of the data points were within the ±30% error limit.

Flow Morphology and Heat Transfer During Subcooled Flow Nucleate Boiling of HFE-7000 in Microchannels

2008 ◽  
Author(s):  
Chih-Jung Kuo ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Subcooled Flow Boiling ◽  
Heat Transfer Coefficients ◽  
Subcooled Flow ◽  
Hydraulic Conditions ◽  
Parallel Microchannels ◽  
Bubble Agitation

Flow boiling was experimentally studied in parallel microchannels using coolant HFE-7000. Subcooled nucleate boiling was achieved under various thermal-hydraulic conditions for mass velocities ranging from G = 164 kg/m2·s to G = 3025 kg/m2·s. Local surface temperatures were measured and flow visualizations were conducted to obtain flow morphologies, boiling curves, and heat transfer coefficients during boiling process. It was found that heat transfer was significantly enhanced during subcooled flow boiling by bubble agitation of the liquid.

scholarly journals Experimental Study of Nucleate Boiling of Flammable, Environmentally Friendly Refrigerants

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 160 ◽  
Author(s):  
Bartosz Gil ◽  
Beata Fijałkowska
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
New Correlation ◽  
Boiling Process ◽  
The Heat Transfer Coefficient

This paper investigates the nucleate boiling process of dimethyl ether and selected hydrocarbons. The main goal of this study is to measure the heat transfer coefficients of RE170, R600a, and R601, and to compare them with R134a. The experiments were carried out for heat fluxes up to 70 kW/m2. Experimental results have shown a typical trend that the heat transfer coefficient of flammable refrigerants increases as the heat flux increases. Among the tested fluids, the highest values of heat transfer coefficient were obtained for RE170. Available correlations describing this coefficient showed a deviation of up to 93%, as compared to the data obtained. The new correlation was developed by regression analysis taking into account dimensionless variables affecting the boiling process.

scholarly journals COMPARATIVE ANALYSES OF THE THERMAL PERFORMANCE OF REFRIGERANTS R134A, R245fa, R407C AND R600a DURING FLOW BOILING IN A MICROCHANNELS HEAT SINK

2018 ◽  
Vol 17 (2) ◽  
pp. 57
Author(s):  
H. L. S. L. Leão ◽  
D. B. Marchetto ◽  
G. Ribatski
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

A comparative study of the performance of of refrigerants R134a, R407C, R245fa and R600a during flow boiling was performed for a 123x494 µm2 heat sink composed of 50 parallel rectangular microchannels. Heat transfer experimental results for heat fluxes up to 310 kW/m2, mass velocities from 300 to 800 kg/(m2 s), liquid subcoolings of 5 and 10 °C and saturation temperature close to 30 ºC were obtained. Global heat transfer coefficients (footprint) up to 10 kW/(m2 °C) were found. The liquid superheating necessary for the onset of nucleate boiling (ONB) was also characterized, and the fluids R245fa and R407C presented the highest and lowest, respectively, superheating to trigger the boiling process. Moreover, for a fixed averaged vapor quality, the average effective heat transfer coefficient increases with increasing mass velocity and liquid subcooling. The refrigerants R600a and R407C presented the highest and the lowest heat transfer coefficients, respectively. Five heat transfer predictive methods from literature provided accurate predictions of the data for R134a, R245fa and R600a, capturing most of the data trends. No one method provided accurate predictions of the heat transfer coefficient data of R407C.

Flow Boiling Heat Transfer of R134a in a Microchannel Heat Sink

2012 ◽  
Author(s):  
Francisco J. do Nascimento ◽  
Hugo L. S. L. Leão ◽  
Gherhardt Ribatski
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Mass Velocity ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Spreader ◽  
Heat Transfer Coefficients ◽  
The Difference

In the present study, the thermal performance of a micro heat spreader based on flow boiling mechanism was evaluated. The heat spreader under study has a foot print area of 15 × 15 mm2 and is composed by 50 channels with width of 100 μm and depth of 500 μm. Experiments were performed for R134a, heat fluxes up to 310 kW/m2 (based on the foot print area), mass velocities from 400 to 1500 kg/m2s, saturation temperatures of approximately 25°C and liquid subcoolings of 5 and 15°C. Heat-sink averaged heat transfer coefficients based on the effective heat transfer area up to 9 kW/m2K were obtained. From the analyses of the experimental results, for a fixed heat-spreader averaged wall superheating, it was found that the dissipated heat flux increases with decreasing the mass velocity and liquid subcooling. Moreover, the trend with varying mass velocity of the difference between the heat spreader averaged superheating for the onset of nucleate boiling (ONB) and the respective value under boiling conditions is not clear, however it seems that its value increases with increasing the liquid subcooling. The wall superheating excess necessary for the onset of nucleate boiling becomes negligible for mass velocities higher than 1000 kg/m2s.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

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.

The Effects of Nucleate Boiling Versus Film Boiling on Heat Transfer in Power Boiler Tubes

1962 ◽  
Vol 84 (4) ◽  
pp. 365-371 ◽  
Author(s):  
H. S. Swenson ◽  
J. R. Carver ◽  
G. Szoeke
Keyword(s):  
Heat Transfer ◽  
Nucleate Boiling ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Inside Surface ◽  
Film Boiling ◽  
Stainless Steel Tube ◽  
Transfer Coefficients ◽  
Steam Quality ◽  
Heat Transfer Coefficients

In large, subcritical pressure, once-through power boilers heat is transferred to steam and water mixtures ranging in steam quality from zero per cent at the bottom of the furnace to 100 per cent at the top. In order to provide design information for this type of boiler, heat-transfer coefficients for forced convection film boiling were determined for water at 3000 psia flowing upward in a vertical stainless-steel tube, AISI Type 304, having an inside diameter of 0.408 inches and a heated length of 6 feet. Heat fluxes ranged between 90,000 and 180,000 Btu/hr-sq ft and were obtained by electrical resistance heating of the tube. The operation of the experimental equipment was controlled so that nucleate boiling, transition boiling, and stable film boiling occurred simultaneously in different zones of the tube. The film boiling data were correlated with a modified form of the equation Nu = a a(Re)m(Pr)n using steam properties evaluated at inside surface temperature. Results of a second series of heat-transfer tests with tubes having a helical rib on the inside surface showed that nucleate boiling could be maintained to much higher steam qualities with that type of tube than with a smooth-bore tube.

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.

Oil Effects on In-Tube Evaporation of CO2 by Altering Flow Regime and Properties

2013 ◽  
Author(s):  
Pega Hrnjak ◽  
Seongho Kim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Circulation Rate ◽  
Convective Boiling ◽  
Mass Fluxes

Flow boiling heat transfer characteristics of CO2 with and without oil were investigated experimentally in horizontal smooth and enhanced tubes with an inner diameter of 11.2 mm. The visualization of flow pattern provides a detailed attributes of the nucleate and the convective boiling heat transfer. In order to investigate the effect of the miscible oil on the heat transfer of CO2, POE (polyolester) RENSIO C85E oil is added to give an oil circulation rate (OCR) between 0.5% and 2%. Results are compared with those of pure CO2. The experimental conditions include evaporation temperatures of −15 °C, mass fluxes from 40 to 200 kg/m2 s, heat fluxes from 0.5 to 10 kW/m2, and vapor qualities from 0.1 to 0.8. Oil generally deteriorates the heat transfer coefficient of pure CO2. The reduction in heat transfer coefficient is most apparent at low vapor qualities, 0.1 to 0.4, and at low mass fluxes, 100 and 200 kg/m2. It is caused by the suppression of nucleate boiling due to increased surface tension. At conditions where the convective boiling contribution is dominant, vapor qualities above 0.5, oil increases heat transfer coefficients. Through visualization, it is shown that the wetted area on the perimeter of inner tube is enhanced due to formation of foaming in the smooth tube. However, such enhancement of heat transfer due to forming is negligible in the enhanced tube, because the enhanced factor due to micro-finned structures is dominant.

Subcooled Water Flow Boiling Heat Transfer in a Short SUS304-Tube With Twisted-Tape Insert

2010 ◽  
Author(s):  
Koichi Hata ◽  
Suguru Masuzaki
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Test Tube ◽  
Heat Fluxes ◽  
Effective Length ◽  
Twisted Tape ◽  
Subcooled Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

The subcooled boiling heat transfer (HT) and the steady-state critical heat fluxes (CHFs) in a short SUS304-tube with twisted-tape insert are systematically measured for mass velocities (G = 4016 to 13850 kg/m2s), inlet liquid temperatures (Tin = 285.82 to 363.96 K), outlet pressures (Pout = 764.76 to 889.02 kPa) and exponentially increasing heat input (Q = Q0exp(t/τ), τ = 8.5 s) by the experimental water loop comprised of a multistage canned-type circulation pump controlled by an inverter. The SUS304 test tube of inner diameter (d = 6 mm), heated length (L = 59.5 mm), effective length (Leff = 49.1 mm), L/d (= 9.92), Leff/d (= 8.18) and wall thickness (δ = 0.5 mm) with average surface roughness (Ra = 3.18 μm) is used in this work. The SUS304 twisted tape with twist ratio, y [= H/d = (pitch of 180° rotation)/d], of 3.39 is used. The relation between inner surface temperature and heat flux for the SUS304-tube with the twisted-tape insert are clarified from non-boiling to CHF. The subcooled boiling heat transfer for SUS304-tube with the twisted-tape insert is compared with our empty SUS304-tube data and the values calculated by our and other workers’ correlations for the subcooled boiling heat transfer. The influences of the twisted-tape insert and the swirl velocity on the subcooled boiling heat transfer and the CHFs are investigated into details and the widely and precisely predictable correlations of the subcooled boiling heat transfer and the CHFs for turbulent flow of water in the SUS304-tube with twisted-tape insert are given based on the experimental data. The correlations can describe the subcooled boiling heat transfer coefficients and the CHFs obtained in this work within −25 to +15% difference.

Sign in / Sign up

Export Citation Format

Share Document