Combined Effect of Electric Field and Surface Modification on Pool Boiling of R-123 PDF Download
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Author: Syed Waqas Ahmad
Publisher:
ISBN:
Category :
Languages : en
Pages :
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The effect of surface modification and high intensity electric field (uniform and non - uniform) acting separately or in combination on pool boiling of R-123 is presented in this thesis. The effect of surface modification was investigated on saturated pool boiling of R-123 for five horizontal copper surfaces modified by different treatments, namely: an emery polished surface, a fine sandblasted surface, a rough sandblasted surface, an electron beam (EB) enhanced surface and a sintered surface. Each 40 mm diameter heating surface formed the upper face of an oxygen-free copper block, electrically heated by embedded cartridge heaters. The experiments were performed from the convective heat transfer regime to the critical heat flux, with both increasing and decreasing heat flux, at 1.01 bar, and additionally at 2 bar and 4 bar for the emery polished surface. Significant enhancement of heat transfer with increasing surface modification was demonstrated, particularly for the EB enhanced and sintered surfaces. The emery polished and sandblasted surface results are compared with nucleate boiling correlations and other published data. The effect of uniform and non-uniform electric fields on saturated pool boiling of R-123 at 1.01 bar pressure was also examined. This method of heat transfer enhancement is known as electrohydrodynamic abbreviated as EHD-enhancement. A high voltage potential was applied at the electrode located above the heating surface, which was earthed. The voltage was varied from 0 to 30 kV. The uniform electric field was provided through a 40 mm diameter circular electrode of stainless steel 304 wire mesh having an aperture of 5.1 mm, while the non-uniform electric field was obtained by using a 40 mm diameter circular rod electrode with rods 5 and 8 mm apart. The effect of uniform electric field was investigated using all five modified surfaces, i.e. emery polished, fine sandblasted, rough sandblasted, EB enhanced and sintered surfaces, while non - uniform electric field was tested using the emery polished, fine sandblasted, EB enhanced and sintered surfaces. The effect of pressure on EHD enhancement was also examined using emery polished surface at saturation pressure of 2 and 4 bars while the electric field was fix at 20 kV corresponding to 2 MV/m. Further, the bubble dynamics is presented for the emery polished surface obtained using a high-speed high - resolution camera.
Author: Syed Waqas Ahmad
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The effect of surface modification and high intensity electric field (uniform and non - uniform) acting separately or in combination on pool boiling of R-123 is presented in this thesis. The effect of surface modification was investigated on saturated pool boiling of R-123 for five horizontal copper surfaces modified by different treatments, namely: an emery polished surface, a fine sandblasted surface, a rough sandblasted surface, an electron beam (EB) enhanced surface and a sintered surface. Each 40 mm diameter heating surface formed the upper face of an oxygen-free copper block, electrically heated by embedded cartridge heaters. The experiments were performed from the convective heat transfer regime to the critical heat flux, with both increasing and decreasing heat flux, at 1.01 bar, and additionally at 2 bar and 4 bar for the emery polished surface. Significant enhancement of heat transfer with increasing surface modification was demonstrated, particularly for the EB enhanced and sintered surfaces. The emery polished and sandblasted surface results are compared with nucleate boiling correlations and other published data. The effect of uniform and non-uniform electric fields on saturated pool boiling of R-123 at 1.01 bar pressure was also examined. This method of heat transfer enhancement is known as electrohydrodynamic abbreviated as EHD-enhancement. A high voltage potential was applied at the electrode located above the heating surface, which was earthed. The voltage was varied from 0 to 30 kV. The uniform electric field was provided through a 40 mm diameter circular electrode of stainless steel 304 wire mesh having an aperture of 5.1 mm, while the non-uniform electric field was obtained by using a 40 mm diameter circular rod electrode with rods 5 and 8 mm apart. The effect of uniform electric field was investigated using all five modified surfaces, i.e. emery polished, fine sandblasted, rough sandblasted, EB enhanced and sintered surfaces, while non - uniform electric field was tested using the emery polished, fine sandblasted, EB enhanced and sintered surfaces. The effect of pressure on EHD enhancement was also examined using emery polished surface at saturation pressure of 2 and 4 bars while the electric field was fix at 20 kV corresponding to 2 MV/m. Further, the bubble dynamics is presented for the emery polished surface obtained using a high-speed high - resolution camera.
Author: Victor Sontea
Publisher: Springer Nature
ISBN: 3031427750
Category : Technology & Engineering
Languages : en
Pages : 656
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Book Description
This book reports on advances in fundamental and applied research at the interface between nanotechnology and biomedical engineering. Gathering peer-reviewed contributions to the 6th International Conference on Nanotechnologies and Biomedical Engineering, ICNBME held on September 20-23, 2023, in Chisinau, Republic of Moldova, this first volume of the proceedings focuses on nanotechnologies and nano-biomaterials, and their applications in medicine. With a good balance of theory and practice, the book offers a timely snapshot of multidisciplinary research at the interface between physics, chemistry, biomedicine, materials science, and engineering.
Author: Yonghui Xu
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: S.G. Kandlikar
Publisher: Routledge
ISBN: 135144218X
Category : Science
Languages : en
Pages : 802
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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
Author: Farhan Mody
Publisher:
ISBN:
Category : Dielectrics
Languages : en
Pages : 75
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"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: 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: W.R. Beasant
Publisher:
ISBN:
Category :
Languages : en
Pages : 21
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Author:
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages : 380
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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:
Publisher:
ISBN:
Category : Heat engineering
Languages : en
Pages : 594
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