The Experts below are selected from a list of 1038 Experts worldwide ranked by ideXlab platform
Cameron Tropea - One of the best experts on this subject based on the ideXlab platform.
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fast transient spray cooling of a hot thick target
Journal of Fluid Mechanics, 2019Co-Authors: Fabian M. Tenzer, Ilia V. Roisman, Cameron TropeaAbstract:Spray cooling of a hot target is characterized by strong heat flux and fast change of the temperature of the wall interface. The heat flux during spray cooling is determined by the instantaneous substrate temperature, which is illustrated by Boiling curves. The variation of the heat flux is especially notable during different thermodynamic Regimes: film, transitional and Nucleate Boiling. In this study transient Boiling curves are obtained by measurement of the local and instantaneous heat flux produced by sprays of variable mass flux, drop diameter and impact velocity. These spray parameters are accurately characterized using a phase Doppler instrument and a patternator. The hydrodynamic phenomena of spray impact during various thermodynamic Regimes are observed using a high-speed video system. A theoretical model has been developed for heat conduction in the thin expanding thermal boundary layer in the substrate. The theory is able to predict the evolution of the target temperature in time in the film Boiling Regime. Moreover, a remote asymptotic solution for the heat flux during the fully developed Nucleate Boiling Regime is developed. The theoretical predictions agree very well with the experimental data for a wide range of impact parameters.
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Fast transient spray cooling of a hot thick target
Journal of Fluid Mechanics, 2019Co-Authors: Fabian M. Tenzer, Ilia V. Roisman, Cameron TropeaAbstract:Spray cooling a hot target is characterized by strong heat flux density and fast change of the temperature of the wall interface. The heat flux density during spray cooling is determined by the instantaneous substrate temperature, which is illustrated by Boiling curves. The variation of the heat flux density is especially notable during different thermodynamic Regimes: film, transitional and Nucleate Boiling. In this study transient Boiling curves are obtained by measurement of the local and instantaneous heat flux density produced by sprays of variable mass flux, drop diameter and impact velocity. These spray parameters are accurately characterized using a phase Doppler instrument and a patternator. The hydrodynamic phenomena of spray impact during various thermodynamic Regimes are observed using a high-speed video system. A theoretical model has been developed for heat conduction in the thin expanding thermal boundary layer in the substrate. The theory is able to predict the evolution of the target temperature in time in the film Boiling Regime. Moreover, a remote asymptotic solution for a heat flux density during the fully developed Nucleate Boiling Regime is developed. The theoretical predictions agree very well with the experimental data for a wide range of impact parameters.
Iztok Golobic - One of the best experts on this subject based on the ideXlab platform.
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analysis of heater wall temperature distributions during the saturated pool Boiling of water
Experimental Thermal and Fluid Science, 2019Co-Authors: Jure Voglar, Matevž Zupancic, Aljosa Peperko, Patrick Birbarah, Nenad Miljkovic, Iztok GolobicAbstract:Abstract This paper investigates transient temperature fields of thin metal foil heaters recorded with high-speed infra-red thermography during saturated pool Boiling of water at atmospheric pressure. Three different thin heaters were tested: stainless steel (SS316), titanium (Ti) and copper with oxidized superhydrophilic surface (CuO). Experimentally acquired temperature fields were analysed using statistical approach. Samples with lower values of wall-temperature standard deviation and skewness and high values of kurtosis are found to perform better during Nucleate Boiling Regime by providing higher heat transfer coefficient. The same samples had narrower heater-wall temperature distributions with higher peaks. The stainless steel sample exhibited bimodal temperature distributions, which resulted from occurrence of bubbles with relatively large contact diameters and long growth times. In addition to that, it was confirmed that wall temperature distributions are effective tool to distinguish between active nucleation sites and non-active single-phase convection area and also to qualify different bubble evolution cycles.
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analysis of heater wall temperature distributions during the saturated pool Boiling of water
Experimental Thermal and Fluid Science, 2019Co-Authors: Jure Voglar, Matevž Zupancic, Aljosa Peperko, Patrick Birbarah, Nenad Miljkovic, Iztok GolobicAbstract:Abstract This paper investigates transient temperature fields of thin metal foil heaters recorded with high-speed infra-red thermography during saturated pool Boiling of water at atmospheric pressure. Three different thin heaters were tested: stainless steel (SS316), titanium (Ti) and copper with oxidized superhydrophilic surface (CuO). Experimentally acquired temperature fields were analysed using statistical approach. Samples with lower values of wall-temperature standard deviation and skewness and high values of kurtosis are found to perform better during Nucleate Boiling Regime by providing higher heat transfer coefficient. The same samples had narrower heater-wall temperature distributions with higher peaks. The stainless steel sample exhibited bimodal temperature distributions, which resulted from occurrence of bubbles with relatively large contact diameters and long growth times. In addition to that, it was confirmed that wall temperature distributions are effective tool to distinguish between active nucleation sites and non-active single-phase convection area and also to qualify different bubble evolution cycles.
Nenad Miljkovic - One of the best experts on this subject based on the ideXlab platform.
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analysis of heater wall temperature distributions during the saturated pool Boiling of water
Experimental Thermal and Fluid Science, 2019Co-Authors: Jure Voglar, Matevž Zupancic, Aljosa Peperko, Patrick Birbarah, Nenad Miljkovic, Iztok GolobicAbstract:Abstract This paper investigates transient temperature fields of thin metal foil heaters recorded with high-speed infra-red thermography during saturated pool Boiling of water at atmospheric pressure. Three different thin heaters were tested: stainless steel (SS316), titanium (Ti) and copper with oxidized superhydrophilic surface (CuO). Experimentally acquired temperature fields were analysed using statistical approach. Samples with lower values of wall-temperature standard deviation and skewness and high values of kurtosis are found to perform better during Nucleate Boiling Regime by providing higher heat transfer coefficient. The same samples had narrower heater-wall temperature distributions with higher peaks. The stainless steel sample exhibited bimodal temperature distributions, which resulted from occurrence of bubbles with relatively large contact diameters and long growth times. In addition to that, it was confirmed that wall temperature distributions are effective tool to distinguish between active nucleation sites and non-active single-phase convection area and also to qualify different bubble evolution cycles.
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analysis of heater wall temperature distributions during the saturated pool Boiling of water
Experimental Thermal and Fluid Science, 2019Co-Authors: Jure Voglar, Matevž Zupancic, Aljosa Peperko, Patrick Birbarah, Nenad Miljkovic, Iztok GolobicAbstract:Abstract This paper investigates transient temperature fields of thin metal foil heaters recorded with high-speed infra-red thermography during saturated pool Boiling of water at atmospheric pressure. Three different thin heaters were tested: stainless steel (SS316), titanium (Ti) and copper with oxidized superhydrophilic surface (CuO). Experimentally acquired temperature fields were analysed using statistical approach. Samples with lower values of wall-temperature standard deviation and skewness and high values of kurtosis are found to perform better during Nucleate Boiling Regime by providing higher heat transfer coefficient. The same samples had narrower heater-wall temperature distributions with higher peaks. The stainless steel sample exhibited bimodal temperature distributions, which resulted from occurrence of bubbles with relatively large contact diameters and long growth times. In addition to that, it was confirmed that wall temperature distributions are effective tool to distinguish between active nucleation sites and non-active single-phase convection area and also to qualify different bubble evolution cycles.
Amos Ullmann - One of the best experts on this subject based on the ideXlab platform.
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measurements of solid contaminant emission rates from Boiling pools
Chemical Engineering Science, 2000Co-Authors: Abraham Dayan, Sylvia Zalmanovich, Amos UllmannAbstract:Abstract An experimental study was performed to measure release rates of solid particles from Boiling pools. Sensitivity studies were conducted to reveal the dependence of the particle carry-over rate on the pool depth, the Boiling rate and the vertical distance from the pool surface. Experimental data on particle concentrations as a function of size at the pool surface are also provided. The study was conducted in a Nucleate Boiling Regime. Tests were performed with distilled water and solid nickel particles ranging in size from 5 to 40 μm. The test apparatus was made of a cylindrical vessel, 30 cm in diameter and 120 cm in height. Slurry particle concentrations were on the order of milligrams per cubic centimeter of slurry. Heat fluxes on the order of 100 kW/m 2 were attained by electrical bottom heating. Corresponding superficial vapor velocities were on the order of several centimeters per second. The phenomenon of particle emission from the surface of Boiling pools pauses major environmental and industrial problems. Such particles are often undesirable contaminants, especially if toxic or radioactive. Exploration of this subject is of considerable importance to the chemical, nuclear, and power generation industries. The current study provides important data to support safety analyses and development of analytical tools. Surface contamination concentrations and particle emission rates are essential data for environmental contamination evaluations of spills and Boiling, respectively. The study indicates, among other things, that emission rates intensify as pools get shallower. A released particle flux is strongest near the surface; and at a decreasing pace, diminishes to a constant rate as the distance from the surface is increased. Decontamination factors of the Boiling process were found to be in a range of 10 3 –10 4 .
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measurements of solid contaminant emission rates from Boiling pools
Chemical Engineering Science, 2000Co-Authors: Abraham Dayan, Sylvia Zalmanovich, Amos UllmannAbstract:Abstract An experimental study was performed to measure release rates of solid particles from Boiling pools. Sensitivity studies were conducted to reveal the dependence of the particle carry-over rate on the pool depth, the Boiling rate and the vertical distance from the pool surface. Experimental data on particle concentrations as a function of size at the pool surface are also provided. The study was conducted in a Nucleate Boiling Regime. Tests were performed with distilled water and solid nickel particles ranging in size from 5 to 40 μm. The test apparatus was made of a cylindrical vessel, 30 cm in diameter and 120 cm in height. Slurry particle concentrations were on the order of milligrams per cubic centimeter of slurry. Heat fluxes on the order of 100 kW/m 2 were attained by electrical bottom heating. Corresponding superficial vapor velocities were on the order of several centimeters per second. The phenomenon of particle emission from the surface of Boiling pools pauses major environmental and industrial problems. Such particles are often undesirable contaminants, especially if toxic or radioactive. Exploration of this subject is of considerable importance to the chemical, nuclear, and power generation industries. The current study provides important data to support safety analyses and development of analytical tools. Surface contamination concentrations and particle emission rates are essential data for environmental contamination evaluations of spills and Boiling, respectively. The study indicates, among other things, that emission rates intensify as pools get shallower. A released particle flux is strongest near the surface; and at a decreasing pace, diminishes to a constant rate as the distance from the surface is increased. Decontamination factors of the Boiling process were found to be in a range of 10 3 –10 4 .
Catherine Colin - One of the best experts on this subject based on the ideXlab platform.
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Experimental study of steady and transient subcooled flow Boiling
International Journal of Heat and Mass Transfer, 2021Co-Authors: V. Scheiff, Pierre Ruyer, Julien Sebilleau, Frédéric Bergame, Catherine ColinAbstract:This study aims to better characterize the heat transfer and flow structure in the fully developed Nucleate flow Boiling Regime in a semi-annular duct. Experiments with a refrigerant HFE7000 were performed in the range of Reynolds numbers from 13 000 to 40 500, subcoolings close to 15 ◦C, for constant heating power, constant wall temperature and constant heating rates (linear increase of the wall temperature). With constant heating power, the wall heat flux is well predicted by a Chen-type correlation based on a contribution due to the forced convection and a contribution due to Nucleate Boiling, including the effect of the liquid subcooling. A thin layer of bubbles sliding along the wall is observed. The characteristic diameter of the bubbles increases with the heat flux and decreases with the liquid velocity and its subcooling. The bubble diameters can be well predicted versus 3 dimensionless numbers: the Reynolds number of the flow, the Jakob number based on the liquid subcooling and the Boiling number. A drag coefficient of the bubbles sliding on the wall is estimated from the measurements of the bubble relative velocities and is in good agreement with the recent numerical simulation of Shi et al. [1] for a spherical bubble moving close to a wall in a shear flow. In the experiments with a constant set temperature, a non-homogeneity of the surface temperatures is observed as well as high fluctuations of temperatures and heat fluxes. The heat transfer is strongly degraded ( ????-60%) by comparison with heating with a set power. Finally a transient Nucleate Boiling Regime with a constant temperature increase dT/dt is investigated. For dT/dt < 50 K.s−1, the results are similar to those of Auracher and Marquardt and a correlation for the prediction of the wall heat flux versus the wall temperature in the transient Nucleate Boiling Regime is provided.
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Transient flow Boiling in a semi-annular duct: From the Onset of Nucleate Boiling to the Fully Developed Nucleate Boiling
International Journal of Heat and Mass Transfer, 2019Co-Authors: V. Scheiff, Nicolas Baudin, Pierre Ruyer, Julien Sebilleau, Catherine ColinAbstract:This paper presents an investigation of the transient Onset of Nucleate Boiling (ONB) on a vertical heated surface cooled by an upward flow. The duct geometry used (semi-annulus with a heated inner wall) make this study very similar to a fuel rod in a Pressurised Water Reactor (PWR). This test section is then heated with different power steps to show the ONB and observe its propagation along the wall. The fluid used is the refrigerant HFE7000 flowing with flow rates corresponding to Reynolds numbers from 0 to 60,000 and subcoolings Jakob numbers from 8 to 33. Synchronised infra-red (IR) thermal measurements and high-speed camera visualizations provided new data which helped to develop models to characterise the Onset of Nucleate Boiling and the transition to the Fully Developed Nucleate Boiling Regime (FDNB). This very finely characterized local behaviour provides an original insight for the onset of Nucleate Boiling in such sub-cooled convective configuration. It is shown that Boiling is initiated by nucleation at a few specific sites and then propagates in the wake of a large vapor pocket flowing along the wall. Analysis of wall to fluid heat transfer evidences a short heat transfer degradation phase below the first vapor pocket, followed by a very effective cooling in its wake. The wall to fluid heat transfer during this transition toward fully developed Nucleate Boiling appears uncorrelated to the power dissipated within the heating element or to flow conditions.
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Transition between Nucleate and film Boiling in rapid transient heating
Experimental Thermal and Fluid Science, 2017Co-Authors: Shanti Fau, Wladimir Bergez, Catherine ColinAbstract:This article presents an experimental study of rapid transient Boiling Regimes of distilled water at saturation on a thin tungsten wire of 50 lm diameter. The heating rate varied from 0.5 to 5 10^5 K/s. Heat supply was obtained by periodic pulses of constant voltage with a period large enough to avoid response overlap. Rapid video recording (14,000 fps) was associated with electrical measurements. Two transient phenomena were studied: pulse heating and thermal relaxation. During pulse heating, it was observed that, depending on heating rate, three kinds of behavior exist: (i) only Nucleate Boiling appears for small heating rates (10^5 K/s), (ii) transition from Nucleate Boiling to film Boiling by bubble coalescence at intermediate heating rates (2.10^5 K/s), and (iii), at higher heating rates, transition to film Boiling by vapor wave propagation (speed 20 m/s). This last mechanism is interpreted as homogeneous nucleation process and is qualitatively similar to an autowave process. In the relaxation stage, it is observed that film collapse is characterized by two mechanisms: film break up into Nucleate Boiling Regime or continuous vapor receding. This second mechanism is compared to a conduction model of a temperature traveling wave in the wire. The time variation of the vapor film length predicted by the model is in the range of the experimental data.
