Effect of Velocity on Heat Transfer to Boiling Freon-113

1980 ◽  
Vol 102 (1) ◽  
pp. 26-31 ◽  
Author(s):  
Salim Yilmaz ◽  
J. W. Westwater
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Atmospheric Pressure ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Forced Flow ◽  
Film Boiling ◽  
Square Root ◽  
Peak Heat Flux

Measurements were made of the heat transfer to Freon-113 at near atmospheric pressure, boiling outside a 6.5 mm dia horizontal steam-heated copper tube. Tests included pool boiling and also forced flow vertically upward at uelocities of 2.4, 4.0 and 6.8 m/s. The metal-to-liquid ΔT ranged from 13 to 125° C, resulting in nucleate, transition, and film boiling. The boiling curves for different velocities did not intersect or overlap, contrary to some prior investigators. The peak heat flux was proportional to the square root of velocity, agreeing with the Vliet-Leppert correlation, but disagreeing with the Lienhard-Eichhorn prediction of an exponent of 0.33. The forced-flow nucleate boiling data were well correlated by Rohsenow’s equation, except at high heat fluxes. Heat fluxes in film boiling were proportional to velocity to the exponent 0.56, close to the 0.50 value given by Bromley, LeRoy, and Robbers. Transition boiling was very sensitive to velocity; at a ΔT of 55° C the heat flux was 900 percent higher for a velocity of 2.4 m/s than for zero velocity.

Dynamics of Pool Boiling on Plain and Nanotube Coated Silicon Surfaces

2010 ◽  
Author(s):  
Vijaykumar Sathyamurthi ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Chaotic Dynamics ◽  
Pool Boiling ◽  
Deterministic Chaos ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Film Boiling ◽  
Test Fluid

Saturated pool boiling experiments are conducted over silicon substrates with and without Multi-walled Carbon Nanotubes (MWCNT) with PF-5060 as the test fluid. Micro-fabricated thin film thermocouples located on the substrate acquire surface temperature fluctuation data at 1 kHz frequency. The high frequency surface temperature data is analyzed for the presence of chaotic dynamics. The shareware code, TISEAN© is used in analysis of the temperature time-series. Results show the presence of low-dimensional deterministic chaos, near Critical Heat Flux (CHF) and in some parts of the Fully Developed Nucleate Boiling (FDNB) regime. Some evidence of chaotic dynamics is also obtained for the film boiling regimes. Singular value decomposition is employed to generate pseudo-phase plots of the attractor. In contrast to previous studies involving multiple nucleation sites, the pseudo-phase plots show the presence of multi-fractal structure at high heat fluxes and in the film boiling regime. An estimate of invariant quantities such as correlation dimensions and Lyapunov exponents reveals the change in attractor geometry with heat flux levels. No significant impact of surface texturing is visible in terms of the invariant quantities.

A Variable Heat Flux Model of Heat Transfer in Grinding With Boiling

1996 ◽  
Vol 118 (2) ◽  
pp. 463-470 ◽  
Author(s):  
T.-C. Jen ◽  
A. S. Lavine
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Temperature Distribution ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Film Boiling ◽  
Grinding Fluid ◽  
Flux Model ◽  
Background Temperature ◽  
Heat Flux Model

In grinding processes, the grinding fluid is used to suppress the temperature rise in the grinding zone. Under some circumstances, the grinding fluid may undergo film boiling in the grinding zone, causing the workpiece temperature to rise significantly. The onsets of nucleate boiling and film boiling in the grinding zone are investigated in the present study. A model of heat transfer in grinding was previously developed (Jen and Lavine, 1995), which predicts the temperature and heat fluxes in the grinding zone. With some modification, this model is used here to predict the occurrence of film boiling of the grinding fluid. The dependence of the workpiece background temperature on the various grinding parameters is explored. The workpiece background temperature distribution along the grinding zone, and comparisons with experimental results, are presented.

Measurement of Condensation Curves for Dropwise Condensation of Steam at Atmospheric Pressure

1983 ◽  
Vol 105 (3) ◽  
pp. 633-638 ◽  
Author(s):  
I. Tanasawa ◽  
Y. Utaka
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Atmospheric Pressure ◽  
Heat Fluxes ◽  
Dropwise Condensation ◽  
Maximum Heat ◽  
Transfer Block ◽  
Peak Heat Flux ◽  
The One ◽  
The Heat Transfer Coefficient

Condensation curves for dropwise condensation of steam at atmospheric pressure were measured for the range of surface subcooling between 0.5 and 180 K using a heat transfer block having a concave spherical condensing surface. The heat transfer coefficient remained constant with the increase of surface subcooling up to about 10 K, and then it decreased. The maximum heat fluxes were found to be between 9.3 and 12.2 MW/m2. Dropwise condensation could be observed at a surface subcooling larger than the one corresponding to the peak heat flux, but shortly the mode of condensation shifted to pseudo-film or on-ice condensation.

scholarly journals High heat flux flow boiling of refrigerant R236fa in parallel microchannels

2019 ◽  
Vol 196 ◽  
pp. 00062
Author(s):  
Vladimir Kuznetsov ◽  
Alisher Shamirzaev ◽  
Alexander Mordovskoy
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Flux Flow ◽  
Microchannel Heat Exchanger ◽  
Parallel Microchannels

This paper presents the results of an experimental study of the heat transfer during flow boiling of refrigerant R236fa in a horizontal microchannel heat sink. The experiments were performed using closed loop that re-circulates coolant. Microchannel heat exchanger that contains two microchannels with 2x0.4 mm cross-section was used as the test section. The dependence of average heat flux on wall superheat and critical heat flux were measured in the range of mass fluxes from 600 to 1600 kg/m2s and in the range of heat fluxes from 5 to 120 W/cm2. For heat flux greater than 60 W/cm2, nucleate boiling suppression has significant effect on the flow boiling heat transfer, and this leads to decrease of the heat transfer coefficient with heat flux grows.

Concerning the Effect of Surface Material on Nucleate Boiling Heat Transfer of R-113

2011 ◽  
Author(s):  
R. Hosseini ◽  
A. Gholaminejad ◽  
Mahdi Nabil ◽  
Mohammad Hossein Samadinia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Surface Material ◽  
Effect Of Surface

This paper presents results of an experimental investigation carried out to determine the effects of surface material on nucleate pool boiling heat transfer of refrigerant R113. Experiments were performed on horizontal circular plates of brass, copper and aluminum. The heat transfer coefficient was evaluated by measuring wall superheat and effective heat flux removed by boiling. The experiments were carried out in the heat flux range of 8 to 200kW/m2. The obtained results have shown significant effect of surface material, with copper providing the highest heat transfer coefficient among the samples, and aluminum the least. There was negligible difference at low heat fluxes, but copper showed 23% better performance at high heat fluxes than aluminum and 18% better than brass.

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.

Study on Subcooled-Forced Flow Boiling Heat Transfer and Critical Heat Flux of Solid-Water Two-Phase Mixture

1999 ◽  
Author(s):  
Yasuo Koizumi ◽  
Hiroyasu Ohtake ◽  
Manabu Mochizuki
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Liquid Layer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Forced Flow ◽  
Superheated Liquid ◽  
Flow Boiling Heat Transfer

Abstract The effect of solid particle introduction on subcooled-forced flow boiling heat transfer and a critical heat flux was examined experimentally. In the experiment, glass beads of 0.6 mm diameter were mixed in subcooled water. Experiments were conducted in a range of the subcooling of 40 K, a velocity of 0.17–6.7 m/s, a volumetric particle ratio of 0–17%. When particles were introduced, the growth of a superheated liquid layer near a heat trasnsfer surface seemed to be suppressed and the onset of nucleate boiling was delayed. The particles promoted the condensation of bubbles on the heat transfer surface, which shifted the initiation of a net vapor generation to a high heat flux region. Boiling heat trasnfer was augmented by the particle introduction. The suppression of the growth of the superheated liquid layer and the promotion of bubble condensation and dissipation by the particles seemed to contribute that heat transfer augmentation. The wall superheat at the critical heat flux was elevated by the particle introduction and the critical heat flux itself was also enhanced. However, the degree of the critical heat flux improvement was not drastic.

Study on onset of nucleate boiling with screw tube for fusion reactor application

2021 ◽  
Author(s):  
Ji Hwan Lim ◽  
Minkyu Park
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
High Heat ◽  
Transfer Mechanism ◽  
High Heat Flux ◽  
Heat Transfer Mechanism ◽  
System Parameters ◽  
Smooth Tubes

Abstract The onset of nucleate boiling (ONB) is the point at which the heat transfer mechanism in fluids changes and is one of the thermo-hydraulic factors that must be considered when establishing a cooling system operation strategy. Because the high heat flux of several MW/m2, which is loaded within a tokamak, is applied under a one-side heating condition, it is necessary to determine a correlative relation that can predict ONB under special heating conditions. In this study, the ONB of a one-side-heated screw tube was experimentally analyzed via a subcooled flow boiling experiment. The helical nut structure of the screw tube flow path wall allows for improved heat transfer performance relative to smooth tubes, providing a screw tube with a 53.98% higher ONB than a smooth tube. The effects of the system parameters on the ONB heat flux were analyzed based on the changes in the heat transfer mechanism, with the results indicating that the flow rate and degree of subcooling are proportional to the ONB heat flux because increasing these factors improves the forced convection heat transfer and increases the condensation rate, respectively. However, it was observed that the liquid surface tension and latent heat decrease as the pressure increases, leading to a decrease in the ONB heat flux. An evaluation of the predictive performance of existing ONB correlations revealed that most have high error rates because they were developed based on ONB experiments on micro-channels or smooth tubes and not under one-side high heat load conditions. To address this, we used dimensional analysis based on Python code to develop new ONB correlations that reflect the influence of system parameters.

Heat Transfer Enhancement in Compact Phase Change Microchannel Heat Exchangers for High Flux Laser Diodes

2018 ◽  
Author(s):  
Jensen Hoke ◽  
Todd Bandhauer ◽  
Jack Kotovsky ◽  
Julie Hamilton ◽  
Paul Fontejon
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Flow Boiling ◽  
Laser Diodes ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Maximum Heat ◽  
Average Maximum

Liquid-vapor phase change heat transfer in microchannels offers a number of significant advantages for thermal management of high heat flux laser diodes, including reduced flow rates and near constant temperature heat rejection. Modern laser diode bars can produce waste heat loads >1 kW cm−2, and prior studies show that microchannel flow boiling heat transfer at these heat fluxes is possible in very compact heat exchanger geometries. This paper describes further performance improvements through area enhancement of microchannels using a pyramid etching scheme that increases heat transfer area by ∼40% over straight walled channels, which works to promote heat spreading and suppress dry-out phenomenon when exposed to high heat fluxes. The device is constructed from a reactive ion etched silicon wafer bonded to borosilicate to allow flow visualization. The silicon layer is etched to contain an inlet and outlet manifold and a plurality of 40μm wide, 200μm deep, 2mm long channels separated by 40μm wide fins. 15μm wide 150μm long restrictions are placed at the inlet of each channel to promote uniform flow rate in each channel as well as flow stability in each channel. In the area enhanced parts either a 3μm or 6μm sawtooth pattern was etched vertically into the walls, which were also scalloped along the flow path with the a 3μm periodicity. The experimental results showed that the 6μm area-enhanced device increased the average maximum heat flux at the heater to 1.26 kW cm2 using R134a, which compares favorably to a maximum of 0.95 kw cm2 dissipated by the plain walled test section. The 3μm area enhanced test sections, which dissipated a maximum of 1.02 kW cm2 showed only a modest increase in performance over the plain walled test sections. Both area enhancement schemes delayed the onset of critical heat flux to higher heat inputs.

Analytical Model Quantifying the Net Coolant Flow Rate to a Microstructured Copper Surface validated with Two-Phase PIV Measurements

2021 ◽  
Author(s):  
Matt Harrison ◽  
Joshua Gess
Keyword(s):  
Heat Transfer ◽  
Analytical Model ◽  
Flow Rate ◽  
Circular Disk ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Coolant Flow ◽  
Coolant Flow Rate ◽  
Two Phase

Abstract Using Particle Image Velocimetry (PIV), the amount of fluid required to sustain nucleate boiling was quantified to a microstructured copper circular disk. Having prepared the disk with preferential nucleation sites, an analytical model of the net coolant flow rate requirements to a single site has been produced and validated against experimental data. The model assumes that there are three primary phenomena contributing to the coolant flow rate requirements at the boiling surface; radial growth of vapor throughout incipience to departure, bubble rise, and natural convection around the periphery. The total mass flowrate is the sum of these contributing portions. The model accurately predicts the quenching fluid flow rate at low and high heat fluxes with 4% and 30% error of the measured value respectively. For the microstructured surface examined in this study, coolant flow rate requirements ranged from 0.1 to 0.16 kg/sec for a range of heat fluxes from 5.5 to 11.0 W/cm2. Under subcooled conditions, the coolant flow rate requirements plummeted to a nearly negligible value due to domination of transient conduction as the primary heat transfer mechanism at the liquid/vapor/surface interface. PIV and the validated analytical model could be used as a test standard where the amount of coolant the surface needs in relation to its heat transfer coefficient or thermal resistance is a benchmark for the efficacy of a standard surface or boiling enhancement coating/surface structure.

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