Nucleate Pool Boiling of High Dielectric Fluids from Enhanced Surfaces PDF Download
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Author: Victor Joseph Lepere
Publisher:
ISBN:
Category : Mechanical engineering
Languages : en
Pages :
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Author: Victor Joseph Lepere
Publisher:
ISBN:
Category : Mechanical engineering
Languages : en
Pages :
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Author: Victor Joseph Lepere (Jr)
Publisher:
ISBN:
Category :
Languages : en
Pages : 97
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Experimental results of the heat transfer performance of three enhanced surfaces, a Union Carbide, Linde High Flux, a Hitachi Thermoexcel-E, a Wieland Gewa-T, and a plain copper surface in the nucleate pool boiling regime in R-113 and FC-72 are presented. Prior to obtaining the data, each of the surfaces was subjected to one of three initial conditions, and the effect of past history on boiling incipience was observed. The data showed that all the surfaces behaved in a similar manner prior to the onset of boiling. Temperature overshoots were most pronounced for the initial condition in which the surfaces were submerged in the liquid pool overnight. All of the enhanced surfaces exhibited a two to tenfold increase in the heat transfer coefficient when compared to the plain surface. The High Flux surface was most effective over a broad range of heat fluxes. The Hitachi surface showed a similar gain in heat transfer coefficient to that of the High Flux surface below 10 kW/sq m, while the Gewa-T surface was not as effective as the other surfaces at low heat fluxes. At high fluxes, the Gewa-T surface performed in a comparable if not better manner. (Author).
Author:
Publisher: Springer
ISBN: 9783319266947
Category : Science
Languages : en
Pages : 0
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Book Description
This Handbook provides researchers, faculty, design engineers in industrial R&D, and practicing engineers in the field concise treatments of advanced and more-recently established topics in thermal science and engineering, with an important emphasis on micro- and nanosystems, not covered in earlier references on applied thermal science, heat transfer or relevant aspects of mechanical/chemical engineering. Major sections address new developments in heat transfer, transport phenomena, single- and multiphase flows with energy transfer, thermal-bioengineering, thermal radiation, combined mode heat transfer, coupled heat and mass transfer, and energy systems. Energy transport at the macro-scale and micro/nano-scales is also included. The internationally recognized team of authors adopt a consistent and systematic approach and writing style, including ample cross reference among topics, offering readers a user-friendly knowledgebase greater than the sum of its parts, perfect for frequent consultation. The Handbook of Thermal Science and Engineering is ideal for academic and professional readers in the traditional and emerging areas of mechanical engineering, chemical engineering, aerospace engineering, bioengineering, electronics fabrication, energy, and manufacturing concerned with the influence thermal phenomena.
Author: N. Zuber
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 216
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Author: Javed Arshad
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 188
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Author: Camil-Daniel Ghiu
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages :
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Book Description
A study of pool boiling of a dielectric liquid (PF 5060) from single-layered enhanced structures was conducted. The parameters investigated were the heat flux, the width of the microchannels and the microchannel pitch. The boiling performance of the enhanced structures increases with increase in channel width and decrease in channel pitch. Simple single line curve fits are provided as a practical way of predicting the data over the entire nucleate boiling regime. The influence of confinement on the thermal performance of the enhanced structures was also assessed. The main parameter investigated was the top space (0 mm 3{13 mm). High-speed visualization was used as a tool . For the total confinement (= 0 mm), the heat transfer performance of the enhanced structures was found to depend weakly on the channel width. For>0 mm, the enhancement observed for plain surfaces in the low heat fluxes regime is not present for the present enhanced structure. The maximum heat flux for a prescribed 85 °C surface temperature limit increased with the increase of the top spacing, similar to the plain surfaces case. Two characteristic regimes of pool boiling have been identified and described: isolated flattened bubbles regime and coalesced bubbles regime. A semi-analytical predictive model applicable to pool boiling under confinement is developed. The model requires a limited number of empirical constants and is capable of predicting the experimental heat flux within 30%.
Author: Smreeti Dahariya
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Boiling has received considerable attention in the technology advancement of electronics cooling for high-performance computing applications. Two-phase cooling has an advantage over a single-phase cooling in the high heat removal rate with a small thermal gradient due to the latent heat of vaporization. Many surface modifications have been done in the past including surface roughness, mixed wettability and, porous wick copper play a crucial role in the liquid-vapor phase change heat transfer. However, the mechanisms of high-pressure pool-boiling heat transfer enhancement due to surface modifications has not been well studied or understood. The properties of water, such as the latent heat of vaporization, surface tension, the difference in specific volume of liquid and vapor, decrease at high-pressure. High-pressure pool-boiling heat transfer enhancement is studied fundamentally on various engineered surfaces. The boiling tests are performed at a maximum pressure of 90 psig (620.5 kPa) and then compared to results at 0 psig (0 kPa). The results indicate that the pressure influences the boiling performance through changes in bubble dynamics. The bubble departure diameter, bubble departure frequency, and the active nucleation sites change with pressure. The pool-boiling heat transfer enhancement of a Teflon© coated surface is also experimentally tested, using water as the working fluid. The boiling results are compared with a plain surface at two different pressures, 30 and 45 psig. The maximum heat transfer enhancement is found at the low heat fluxes. At high heat fluxes, a negligible effect is observed in HTC. The primary reasons for the HTC enhancement at low heat fluxes are active nucleation sites at low wall superheat and bubble departure size. The Teflon© coated surface promotes nucleation because of the lower surface energy requirement. The boiling results are also obtained for wick surfaces. The wick surfaces are fabricated using a sintering process. The boiling results are compared with a plain surface. The reasons for enhancements in the pool-boiling performance are primarily due to increased bubble generation, higher bubble release frequency, reduced thermal-hydraulic length modulation, and enhanced thermal conductivity due to the sintered wick layer. The analysis suggests that the Rayleigh-critical wavelength decreases by 4.67 % of varying pressure, which may cause the bubble pinning between the gaps of sintered particles and avoids the bubble coalescence. Changes in the pitch distance indicate that a liquid-vapor phase separation happens at the solid/liquid interface, which impacts the heat-transfer performance significantly. Similarly, the role of the high-pressure over the wicking layer is further analyzed and studied. It is found that the critical flow length, [lambda]u reduces by three times with 200 [mu]m particles. The results suggest that the porous wick layer provides a capillary-assist to liquid flow effect, and delays the surface dry out. The surface modification and the pressure amplify the boiling heat transfer performance. All these reasons may contribute to the CHF, and HTC enhancement in the wicking layer at high-pressure.
Author: Farhan Mody
Publisher:
ISBN:
Category : Dielectrics
Languages : en
Pages : 75
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Book Description
"The miniaturization trend of transistors and increase in packing density of electronic devices has resulted in high heat flux generation, which has created a need for efficient heat removal systems. The present research is an experimental study of pool boiling using plain copper chip and microchannel chip with boiling surface of 34.5mm x 32mm. Three dielectric fluids, Perfluoro-2-methylpentane (PP1), perfluoro-methyl-cyclopentane (PP1C), and fluorocarbon (FC-87) were used in a closed loop pool boiling system to determine their performance at atmospheric pressure. The pool boiling results have been compared with literature for a boiling surface of 10 mm x 10 mm to study the effect of heater size. To improve the performance of the pool boiling system, we desire high critical heat flux and low surface temperatures. In the current study, we introduced two external structures fitted on the test surfaces for regulating the flow of vapor through specific structures and generating independent liquid-vapor pathways without any deposition and/or chemical surface modifications of the test surface. Firstly, an array of hollow conical structures (HCS) called volcano manifold are printed using additive manufacturing technique. A critical heat flux (CHF) of 28.1 W/cm2, 38.3 W/cm2 and 32.5 W/cm2 was achieved for volcano manifold with plain copper chip using PP1, PP1C and FC87 respectively giving 19%, 33% and 6.5% enhancement in CHF respectively as compared to a plain chip without volcano manifold. Secondly, dual taper manifold having taper angle of 15° is printed using a stereolithography (SLA) additive manufacturing technique. Plain chip with dual taper manifold gave the CHF of 25.6 W/cm2, 31.7 W/cm2 and 32.3 W/cm2 for PP1, PP1C and FC-87, respectively. These results indicate a deterioration in CHF caused by vapor constriction. In addition, the heater size effect was studied by comparing the pool boiling performance of a plain copper boiling surface of 34.5 mm x 32 mm (Large heater) with 10 mm x 10 mm (Small heater) from published literature for all three refrigerants. It was noted that 31%, 66% and 104% increment in maximum heat transfer coefficient was obtained for PP1, PP1C and FC-87 respectively with larger heater over smaller heater at CHF. The geometrical parameters of the enhancement structures were based on published results for water. The results show that the external surface modification techniques require further geometrical parameter optimization as the current designs based on water performance caused vapor constriction effects that caused performance deterioration for dielectric fluids."--Abstract.
Author:
Publisher: Academic Press
ISBN: 0080575846
Category : Technology & Engineering
Languages : en
Pages : 467
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Book Description
Advances in Heat Transfer
Author: S.G. Kandlikar
Publisher: Routledge
ISBN: 1351442198
Category : Science
Languages : en
Pages : 786
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Book Description
Provides a comprehensive coverage of the basic phenomena. It contains twenty-five chapters which cover different aspects of boiling and condensation. First the specific topic or phenomenon is described, followed by a brief survey of previous work, a phenomenological model based on current understanding, and finally a set of recommended design equa
