The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Sidy Ndao - One of the best experts on this subject based on the ideXlab platform.
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enhanced pool boiling Heat transfer and Critical Heat Flux on femtosecond laser processed stainless steel surfaces
International Journal of Heat and Mass Transfer, 2015Co-Authors: Corey Kruse, Troy Anderson, Chris Wilson, Craig Zuhlke, George Gogos, Dennis R Alexander, Sidy NdaoAbstract:Abstract In this paper, we present an experimental investigation of pool boiling Heat transfer on multiscale (micro/nano) functionalized metallic surfaces. Heat transfer enhancement in metallic surfaces is very important for large scale high Heat Flux applications like in the nuclear power industry. The multiscale structures were fabricated via a femtosecond laser surface process (FLSP) technique, which forms self-organized mound-like microstructures covered by layers of nanoparticles. Using a pool boiling experimental setup with deionized water as the working fluid, both the Heat transfer coefficients and Critical Heat Flux were investigated. A polished reference sample was found to have a Critical Heat Flux of 91 W/cm 2 at 40 °C of superHeat and a maximum Heat transfer coefficient of 23,000 W/m 2 K. The processed samples were found to have a maximum Critical Heat Flux of 142 W/cm 2 at 29 °C and a maximum Heat transfer coefficient of 67,400 W/m 2 K. It was found that the enhancement of the Critical Heat Flux was directly related to the wetting and wicking ability of the surface which acts to replenish the evaporating liquid and delay Critical Heat Flux. The Heat transfer coefficients were also found to increase when the surface area ratio was increased as well as the microstructure peak-to-valley height. Enhanced nucleate boiling is the main Heat transfer mechanism, and is attributed to an increase in surface area and nucleation site density.
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Enhanced pool-boiling Heat transfer and Critical Heat Flux using femtosecond laser surface processing
Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), 2014Co-Authors: Corey M. Kruse, Troy Anderson, Chris Wilson, Craig Zuhlke, Dennis Alexander, George Gogos, Sidy NdaoAbstract:In this paper, we present the experimental investigation of pool boiling Heat transfer on multiscale (micro/nano) functionalized metallic surfaces. The multiscale structures were fabricated via a femtosecond laser surface process (FLSP) technique which forms mound-like microstructures covered by layers of nanoparticles. Using a pool boiling experimental setup with deionized water as the working fluid, both the Heat transfer coefficient and Critical Heat Flux were investigated. The polished reference sample was found to have a Critical Heat Flux of 91 W/cm2 at 40 °C of superHeat and a maximum Heat transfer coefficient of 23,000 W/m2-K. The processed sample was found to have a Critical Heat Flux of 122 W/cm2 at 18 °C superHeat and a maximum Heat transfer coefficient of 67,400 W/m2-K. Flow visualization revealed nucleate boiling to be the main two-phase Heat transfer mechanism. The overall Heat transfer performance of the metallic multiscale structured surface has been attributed to both augmented Heat transfer surface area and enhanced nucleate boiling regime. On the other hand, increase in the Critical Heat Flux can be attributed to the superhydrophilic nature of the laser processed surface and the presence of nanoparticle layers.
John R. Thome - One of the best experts on this subject based on the ideXlab platform.
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Critical Heat Flux of R134a and R245fa Inside Small-Diameter Tubes
Heat Transfer Engineering, 2020Co-Authors: Cristiano Bigonha Tibiriça, Sylwia Szczukiewicz, Gherhardt Ribatski, John R. ThomeAbstract:This article presents new experimental Critical Heat Flux results under saturated flow boiling conditions for a macro-/microscale tube. The data were obtained in a horizontal 2.20-mm inside diameter stainless-steel tube with Heating lengths of 361 and 154 mm, R134a and R245fa as working fluids, mass velocities ranging from 100 to 1500 kg/m2-s, Critical Heat Flux from 25 to 300 kW/m2, exit saturation temperatures of 25, 31, and 35°C, and Critical vapor qualities ranging from 0.55 to 1. The experimental results show that Critical Heat Flux (CHF) increases with increasing mass velocity and inlet subcooling but decreases with increasing saturation temperature and Heated length. The data also indicated a higher CHF for R245fa when compared with R134a at similar conditions. The experimental data were compared against four CHF predictive methods and the results of the comparisons are reported.
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Prediction of Critical Heat Flux in Microchannels
Microfluidics Based Microsystems, 2010Co-Authors: John R. Thome, L. ConsoliniAbstract:An overview of the state-of-the-art of predicting Critical Heat Flux during saturated flow boiling in microchannels is presented. First, a selection of experimental results is described for single channels and for multi-channels in parallel, including non-circular channel shapes. Next, the various empirical methods for predicting CHF are presented and discussed. Then, the theoretically based model of Revellin and Thome for microchannels, including prediction of CHF under hot spots, is described and discussed. Finally, some overall comments on the status of CHF modeling and experi-mentation are provided.
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saturated Critical Heat Flux in a multi microchannel Heat sink fed by a split flow system
Experimental Thermal and Fluid Science, 2010Co-Authors: A W Mauro, John R. Thome, D Toto, Giuseppe Peter VanoliAbstract:An extensive experimental campaign has been carried out for the measurement of saturated Critical Heat Flux in a multi-microchannel copper Heat sink. The Heat sink was formed by 29 parallel channels that were 199 mu m wide and 756 mu m deep. In order to increase the Critical Heat Flux and reduce the two-phase pressure drop, a split flow system was implemented with one central inlet at the middle of the channels and two outlets at either end. The base Critical Heat Flux was measured using three HFC Refrigerants (R134a, R236fa and R245fa) for mass Fluxes ranging from 250 to 1500 kg/m(2) s, inlet subcoolings from -25 to -5 K and saturation temperatures from 20 to 50 degrees C. The parametric effects of mass velocity, saturation temperature and inlet subcooling were investigated. The analysis showed that significantly higher CHF was obtainable with the split flow system (one inlet-two outlets) compared to the single inlet-single outlet system, providing also a much lower pressure drop. Notably several existing predictive methods matched the experimental data quite well and quantitatively predicted the benefit of higher CHF of the split flow. (C) 2009 Elsevier Inc. All rights reserved.
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investigation of saturated Critical Heat Flux in a single uniformly Heated microchannel
Experimental Thermal and Fluid Science, 2006Co-Authors: Leszek Wojtan, Remi Revellin, John R. ThomeAbstract:Abstract A series of tests have been performed to determine the saturated Critical Heat Flux (CHF) in 0.5 and 0.8 mm internal diameter microchannel tubes as a function of refrigerant mass velocity, Heated length, saturation temperature and inlet liquid subcooling. The tested refrigerants were R-134a and R-245fa and the Heated length of microchannel was varied between 20 and 70 mm. The results show a strong dependence of CHF on mass velocity, Heated length and microchannel diameter but no influence of liquid subcooling (2–15 °C) was observed. The experimental results have been compared to the well-known CHF single-channel correlation of Y. Katto and H. Ohno [An improved version of the generalized correlation of Critical Heat Flux for the forced convective boiling in uniformly Heated vertical tubes, Int. J. Heat and Mass Transfer 27 (9) (1984) 1641–1648] and the multichannel correlation of W. Qu and I. Mudawar [Measurement and correlation of Critical Heat Flux in two-phase microchannel Heat sinks, Int. J. Heat and Mass Transfer 47 (2004) 2045–2059]. The comparison shows that the correlation of Katto–Ohno predicts microchannel data with a mean absolute error of 32.8% with only 41.2% of the data falling within a ±15% error band. The correlation of Qu and Mudawar shows the same trends as the CHF data but significantly overpredicts them. Based on the present experimental data, a new microscale version of the Katto–Ohno correlation for the prediction of CHF during saturated boiling in microchannels has been proposed.
Nam-jin Kim - One of the best experts on this subject based on the ideXlab platform.
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Effects of spray-deposited oxidized multi-wall carbon nanotubes and graphene on pool-boiling Critical Heat Flux enhancement
Journal of Industrial and Engineering Chemistry, 2015Co-Authors: Sung-seek Park, Myung Taek Hyun, Yong-han Jeon, Yong-hwan Kim, Nam-jin KimAbstract:This paper examines the differences in Critical Heat Flux (CHF) based on multi-wall carbon nanotubes and graphene have been found as new Heat-transfer materials which are carbon allotropes with different shapes. The analysis of experimental data and results of calculations in pool-boiling Critical Heat Flux experiments by spray-depositing oxidized multi-wall carbon nanotubes and graphene onto Heat-transfer samples have been done to improve the economic efficiency and safety of the Heat-transfer apparatus. The results show that the contact angle of the Heat-transfer surface linearly decreased with spray deposition time, which resulted in an increased Critical Heat Flux. The oxidized multi-wall carbon nanotubes and graphene showed maximum pool-boiling Heat-transfer coefficients at 19.8° and 21.7°, respectively, while the pool-boiling Heat-transfer coefficients decreased at angles of 9.9° or less and 12.5° or less, respectively. Also, the following new correction formula has been derived and compared with a current model by introducing a correction factor to Kandlikar's prediction model.
Ali Akbar Alemrajabi - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of pool boiling Heat transfer and Critical Heat Flux of nanostructured surfaces
International Journal of Heat and Mass Transfer, 2013Co-Authors: Davood Saeidi, Ali Akbar AlemrajabiAbstract:Abstract The present study aims to investigate the effect of pool boiling on nanostructured surfaces. For this purpose, nanocoating was performed on aluminum surface specimens by anodizing and their boiling Heat transfer characteristics were compared with those of bare surface of aluminum. Also, the Critical Heat Flux and boiling Heat transfer coefficients were evaluated experimentally. Chromic acid and sulfuric acid solutions were utilized as the electrolytes. Prior to anodizing, sandblasting and etching were applied as mechanical and chemical treatments of the surfaces. The coating was performed over three different durations. The maximum Critical Heat Flux was observed to occur in samples which had been weakly etched and anodized for 30 min in the sulfuric acid solution. Critical Heat Flux increased by 8% compared with that of the untreated aluminum alloy surface. Also, boiling Heat transfer coefficient increased by 159% in weakly etched samples. In order to investigate surface characteristics, contact angle and atomic force microscope (AFM) images were used. The surface roughness and real area were measured in six samples. The AFM images indicated that surface roughness increased with anodizing time. The change in roughness was more pronounced in surfaces treated in the chromic acid solution compared with those treated in the sulfuric acid solution.
W J Minkowycz - One of the best experts on this subject based on the ideXlab platform.
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nanofluids and Critical Heat Flux experimental and analytical study
Applied Thermal Engineering, 2009Co-Authors: Mihajlo Golubovic, H.d. Madhawa Hettiarachchi, William M. Worek, W J MinkowyczAbstract:In recent years, nanofluids have been attracting significant attention in the Heat transfer research community. These fluids are obtained by suspending nanoparticles having sizes between 1 and 100 nm in regular fluids. It was found by several researchers that the thermal conductivity of these fluids can be significantly increased when compared to the same fluids without nanoparticles. Also, it was found that pool boiling Critical Heat Flux increases in nanofluids. In this paper, our objective is to evaluate the impact of different nanoparticle characteristics including particle concentration, size and type on Critical Heat Flux experimentally at saturated conditions. As a result, this work will document our experimental findings about pool boiling Critical Heat Flux in different nanofluids. In addition, we will identify reasons behind the increase in the Critical Heat Flux and present possible approaches for analytical modeling of Critical Heat Flux in nanofluids at saturated conditions.