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Статті в журналах з теми "Parallel heat flux":
1
Jing, Tingting, Guoqiang He, Fei Qin, Wenqiang Li, Duo Zhang, and Minghao Wang. "Flow Distribution Characteristics of Supercritical Hydrocarbon Fuel in Parallel Channels with Pyrolysis." Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 37, no. 1 (February 2019): 1–6. http://dx.doi.org/10.1051/jnwpu/20193710001.
Анотація:
Due to the asymmetric geometry of flowpath and combustion organization, the heat flux distribution on RBCC's walls are extremely non-uniform. With a validated numerical model considering the changes of thermophysical properties and chemical components, the present study analyzed the effects of heat flux intensity, non-uniformity of heat flux distribution and inlet manifold on the mass flow distribution of parallel regenerative cooling channels. Results show that the intensity of heat flux enlarges the non-uniformity of parallel channels, however, the non-uniformity is reduced when the outlet temperature is above the completely pyrolysis value; and the non-uniformity heat flux distribution increases the mal-distribution of parallel channels dramatically, the difference of mass flow rate reaches to 33.2% when the heat flux difference is only 0.25 MW/m2; increasing the flow area of inlet manifold would improve the flow distribution of parallel channels with decrease of heat transfer efficiency and increases of pressure drop.
2
Zhang, Donghui, Haiyang Xu, Yi Chen, Leiqing Wang, Jian Qu, Mingfa Wu, and Zhiping Zhou. "Boiling Heat Transfer Performance of Parallel Porous Microchannels." Energies 13, no. 11 (June 10, 2020): 2970. http://dx.doi.org/10.3390/en13112970.
Анотація:
Flow boiling in microporous layers has attracted a great deal of attention in the enhanced heat transfer field due to its high heat dissipation potential. In this study, flow boiling experiments were performed on both porous microchannels and a copper-based microchannel, using water as the coolant. As the heat flux was less than 80 W/cm2, the porous microchannels presented significantly higher boiling heat transfer coefficients than the copper-based microchannel. This was closely associated with the promotion of the nucleation site density of the porous coating. With the further increase in heat flux, the heat transfer coefficients of the porous microchannels were close to those of the copper-based sample. The boiling process in the porous microchannel was found to be dominated by the nucleate boiling mechanism from low to moderate heat flux (<80 W/cm2).This switched to the convection boiling mode at high heat flux. The porous samples were able to mitigate flow instability greatly. A visual observation revealed that porous microchannels could suppress the flow fluctuation due to the establishment of a stable nucleate boiling process. Porous microchannels showed no advantage over the copper-based sample in the critical heat flux. The optimal thickness-to-particle-size ratio (δ/d) for the porous microchannel was confirmed to be between 2–5. In this range, the maximum enhanced effect on boiling heat transfer could be achieved.
3
Kuznetsov, Vladimir, Alisher Shamirzaev, and Alexander Mordovskoy. "High heat flux flow boiling of refrigerant R236fa in parallel microchannels." EPJ Web of Conferences 196 (2019): 00062. http://dx.doi.org/10.1051/epjconf/201919600062.
Анотація:
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.
4
Shakier, Raed, Hussam Muhammed, Hussain Khathem, and Haider Abdul-Khathem. "Two-Phase Flow In Mini-Scale Complex Geometry." Al-Kitab Journal for Pure Sciences 1, no. 1 (June 17, 2018): 20–26. http://dx.doi.org/10.32441/kjps.v1i1.88.
Анотація:
Heat-transfer coefficients are reported for one surface, a plain surface, with 50 mm square base area. Parallel channel test piece has one mm by one mm, 25 channelsThe data were produced while boiling R113 at atmospheric pressure. For this surface, the mass flux range was 200 – 600 kg/m2s and the heat flux range was 5 - 80 kW/m2. The results obtained have been compared with standard correlations for tube bundles. The measured heat-transfer coefficients for the parallel micro-channel surface are slightly bigger for any plate channel surface. It is dependent on heat flux and reasonably independent of mass flux and vapor quality. Thus, heat transfer is probably dominated by nucleate boiling. The parallel channel heat transfer coefficients were typically bigger than other plate -channel values.
5
Salman, Yasin K., and Hazim S. Hamad. "LAMINAR NATURAL CONVECTION HEAT TRANSFER BETWEEN DUCTED PARALLEL PLATES." Journal of Engineering 14, no. 03 (September 1, 2008): 2786–803. http://dx.doi.org/10.31026/j.eng.2008.03.18.
Анотація:
Laminar natural convection heat transfer to air flow in a ducted two parallel plates subjected to same constant heat flux has been studied experimentally. In this study a test rig has been designed and constructed to allow studying the effect of plate spacing and plates angle of inclination on the heat transfer process. The study covers three plate spacing 15 mm, 35mm and 60 mm that makes plate aspect ratio (AR) 24, 10.285 and 6, The heat flux implemented in all test runs varies between 55 W/m2– 340 W/m2 that makes the modified Rayleigh number (Ra) varies from 105-108. Experimental results presented as plate temperature distribution, variation of local heat transfer coefficient and the relation between Nu and Ra, reveal for the range of parameters mentioned above, an improvement in heat transfer process as the AR values change from 6 to 24 and the improvement rates is higher for the lower heat flux test (lower Ra). A correlation of the results were made in the form of Nuvr (Gr/AR) in which the effect of duct aspect ratio (AR) has been introduced.
6
Barghouthi, I. A., H. Nilsson, and S. H. Ghithan. "O<sup>+</sup> and H<sup>+</sup> ion heat fluxes at high altitudes and high latitudes." Annales Geophysicae 32, no. 8 (August 26, 2014): 1043–57. http://dx.doi.org/10.5194/angeo-32-1043-2014.
Анотація:
Abstract. Higher order moments, e.g., perpendicular and parallel heat fluxes, are related to non-Maxwellian plasma distributions. Such distributions are common when the plasma environment is not collision dominated. In the polar wind and auroral regions, the ion outflow is collisionless at altitudes above about 1.2 RE geocentric. In these regions wave–particle interaction is the primary acceleration mechanism of outflowing ionospheric origin ions. We present the altitude profiles of actual and "thermalized" heat fluxes for major ion species in the collisionless region by using the Barghouthi model. By comparing the actual and "thermalized" heat fluxes, we can see whether the heat flux corresponds to a small perturbation of an approximately bi-Maxwellian distribution (actual heat flux is small compared to "thermalized" heat flux), or whether it represents a significant deviation (actual heat flux equal or larger than "thermalized" heat flux). The model takes into account ion heating due to wave–particle interactions as well as the effects of gravity, ambipolar electric field, and divergence of geomagnetic field lines. In the discussion of the ion heat fluxes, we find that (1) the role of the ions located in the energetic tail of the ion velocity distribution function is very significant and has to be taken into consideration when modeling the ion heat flux at high altitudes and high latitudes; (2) at times the parallel and perpendicular heat fluxes have different signs at the same altitude. This indicates that the parallel and perpendicular parts of the ion energy are being transported in opposite directions. This behavior is the result of many competing processes; (3) we identify altitude regions where the actual heat flux is small as compared to the "thermalized" heat flux. In such regions we expect transport equation solutions based on perturbations of bi-Maxwellian distributions to be applicable. This is true for large altitude intervals for protons, but only the lowest altitudes for oxygen.
7
Guo, Zeng-Yuan, and Xiao-Bo Wu. "Thermal Drag and Critical Heat Flux for Natural Convection of Air in Vertical Parallel Plates." Journal of Heat Transfer 115, no. 1 (February 1, 1993): 124–29. http://dx.doi.org/10.1115/1.2910637.
Анотація:
Variable property effects on vertical channel natural convection in air are studied systematically. Numerical solutions of the governing equations show that both the mass flow rate and heat transfer in the channel are not only lower than the constant property results, but also show a nonmonotonic variation with increasing wall temperature or wall heat flux. This phenomenon, which seemingly conflicts with the conventional knowledge, has also been identified by experiments. For a vertical channel with a uniform heat flux boundary condition, the wall may experience a sharp rise in temperature up to damage of the channel if the wall heat flux is greater than the critical heat flux. This implies that the crisis phenomenon (or burnout) may occur in channel natural convection in gas as well as in the boiling process.
8
Zhang, Xiao Jing, Bing Qi Liu, Xiao Jie Xu, Xi Wu, and Rui Ming Yuan. "A Study of the Enhancement in Near-Field Radiative Heat Transfer by Surface Polaritons." Applied Mechanics and Materials 448-453 (October 2013): 3211–16. http://dx.doi.org/10.4028/www.scientific.net/amm.448-453.3211.
Анотація:
The influence of surface polaritons on spectral energy flux at different temperatures or distances to the surface of a plate was analyzed. The relations of the net heat flux between two parallel plates with the material type were also discussed. The results demonstrate that the effect of surface polaritons is dominated in the spectral energy flux at 300 K when the distance is decreased to 100 nm. In addition, the intensity of surface polaritons increases with the temperature. The net heat flux between two parallel plates has a nearly linear relation with the temperature and is closely related to the material type. It reaches up to 2.792×107 W/m2 between two SiC plates, approximately 3~6 orders of magnitude larger than that between two different materials. However, the net heat flux between SiC and Al is merely 2329.7 W/m2, even smaller than the result calculated by the classical stefan-boltzman law between two blackbodies.
9
Bergles, A. E., and S. G. Kandlikar. "On the Nature of Critical Heat Flux in Microchannels." Journal of Heat Transfer 127, no. 1 (January 1, 2005): 101–7. http://dx.doi.org/10.1115/1.1839587.
Анотація:
The critical heat flux (CHF) limit is an important consideration in the design of most flow boiling systems. Before the use of microchannels under saturated flow boiling conditions becomes widely accepted in cooling of high-heat-flux devices, such as electronics and laser diodes, it is essential to have a clear understanding of the CHF mechanism. This must be coupled with an extensive database covering a wide range of fluids, channel configurations, and operating conditions. The experiments required to obtain this information pose unique challenges. Among other issues, flow distribution among parallel channels, conjugate effects, and instrumentation need to be considered. An examination of the limited CHF data indicates that CHF in parallel microchannels seems to be the result of either an upstream compressible volume instability or an excursive instability rather than the conventional dryout mechanism. It is expected that the CHF in parallel microchannels would be higher if the flow is stabilized by an orifice at the entrance of each channel. The nature of CHF in microchannels is thus different than anticipated, but recent advances in microelectronic fabrication may make it possible to realize the higher power levels.
10
Fundamenski, W. "Parallel heat flux limits in the tokamak scrape-off layer." Plasma Physics and Controlled Fusion 47, no. 11 (October 6, 2005): R163—R208. http://dx.doi.org/10.1088/0741-3335/47/11/r01.
Дисертації з теми "Parallel heat flux":
1
Kang, Yong Tae. "Experimental investigation of critical heat flux in transient boiling systems with vertical thin rectangular parallel plate channels /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1244826053.
2
Hu, Chih-Chieh. "Mechanistic modeling of evaporating thin liquid film instability on a bwr fuel rod with parallel and cross vapor flow." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28148.
Анотація:
Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Abdel-Khalik, Said; Committee Member: Ammar, Mostafa H.; Committee Member: Ghiaasiaan, S. Mostafa; Committee Member: Hertel, Nolan E.; Committee Member: Liu, Yingjie.
3
Alanazi, Mohammed Awwad. "Non-invasive Method to Measure Energy Flow Rate in a Pipe." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/103179.
Анотація:
Current methods for measuring energy flow rate in a pipe use a variety of invasive sensors, including temperature sensors, turbine flow meters, and vortex shedding devices. These systems are costly to buy and install. A new approach that uses non-invasive sensors that are easy to install and less expensive has been developed. A thermal interrogation method using heat flux and temperature measurements is used. A transient thermal model, lumped capacitance method LCM, before and during activation of an external heater provides estimates of the fluid heat transfer coefficient h and fluid temperature. The major components of the system are a thin-foil thermocouple, a heat flux sensor (PHFS), and a heater. To minimize the thermal contact resistance R" between the thermocouple thickness and the pipe surface, two thermocouples, welded and parallel, were tested together in the same set-up. Values of heat transfer coefficient h, thermal contact resistance R", time constant �[BULLET], and the water temperature �[BULLET][BULLET], were determined by using a parameter estimation code which depends on the minimum root mean square RMS error between the analytical and experimental sensor temperature values. The time for processing data to get the parameter estimation values is from three to four minutes. The experiments were done over a range of flow rates (1.5 gallon/minute to 14.5 gallon/minute). A correlation between the heat transfer coefficient h and the flow rate Q was done for both the parallel and the welded thermocouples. Overall, the parallel thermocouple is better than the welded thermocouple. The parallel thermocouple gives small average thermal contact resistance average R"=0.00001 (m2.�[BULLET][BULLET]/W), and consistence values of water temperature and heat transfer coefficient h, with good repeatability and sensitivity. Consequently, a non-invasive energy flow rate meter or (BTU) meter can be used to estimate the flow rate and the fluid temperature in real life.MS
4
Grosjean, Alex. "Impact of geometry and shaping of the plasma facing components on hot spot generation in tokamak devices." Electronic Thesis or Diss., Aix-Marseille, 2020. http://www.theses.fr/2020AIXM0556.
Анотація:
Cette thèse s’inscrit en support du projet ITER, sur l’étude du comportement thermique de prototypes de CFP dans des tokamaks supraconducteurs : EAST et WEST. Ces prototypes correspondent à un enchaînement de monoblocs de tungstène le long d’un tube de refroidissement, séparés par des interstices (0.5 mm), qui permet d’extraire la chaleur de ces composants. L’introduction de ces interstices entre monoblocs (toroïdaux) ou entre barres de monoblocs (poloïdaux), implique que le bord poloïdal peut être exposé aux lignes de champ avec une incidence quasi-normale. Un échauffement local très important est attendu sur une fine bande latérale de la surface supérieure de chaque monobloc, qui peut être accentué dans le cas où les composants sont désalignés. Nous proposons dans ce travail d’étudier l’impact de deux géométries (arête vive et chanfrein) de ces composants ainsi que de leurs désalignements sur la génération de points chauds locaux, à l’aide de diagnostics embarqués (TC/FBG), et d’une caméra infrarouge très haute résolution (~0.1 mm/pixel), dont l’émissivité varie en fonction de la longueur d’onde, de la température, et de l’état de surface, qui évolue au contact du plasma, lors des différentes campagnes expérimentales. Les sondes de Langmuir permettront de mesurer la température du plasma, et par conséquent d’estimer les rayons de Larmor des ions, qui pourront jouer un rôle important dans la distribution locale du flux de chaleur autour des bords poloïdaux et toroïdaux. Les travaux menés ici, montrent la cohérence entre les calculs prédictifs et les résultats expérimentaux et appuient la décision d'ITER de biseauter les MBs pour protéger leurs bords d'attaqueThis PhD falls within ITER project support, aiming to study the thermal behavior of ITER-like PFC prototypes in two superconducting tokamaks: EAST (Hefei) and WEST (Cadarache). These prototypes correspond to castellated tungsten monoblocks placed along a cooling tube with small gaps (0.5 mm) between them, called plasma-facing units, to extract the heat from the components. The introduction of gaps between monoblocks (toroidal) and plasma-facing units (poloidal), to relieve the thermomechanical stresses in the divertor, implies that poloidal leading edges may be exposed to near-normal incidence angle. A local overheating is expected in a thin lateral band at the top of each monoblocks, which can be enhanced when the neighboring components are misaligned. In this work, we propose to study the impact of two geometries (sharp and chamfered LEs) of these components, as well as their misalignments on local hot spot generation, by means of embedded diagnostics (TC/FBG), and a submillimeter infrared system (~0.1 mm/pixel), whose emissivity varies with wavelength, and the temperature, but above all, the surface state of the component, which evolves under plasma exposure, during the experimental campaigns. The divertor Langmuir probes measure the plasma temperature, and thus estimate the ion Larmor radius that may play a role in the local heat flux distribution around poloidal and toroidal edges. The results presented in this thesis, confirming the modelling predictions by experimental measurements, support the final decision by ITER to include 0.5 mm toroidal beveling of monoblocks on the vertical divertor targets to protect poloidal leading edges from excessive heat flux
5
Huang, Yu-Chi, and 黃佑騏. "The Forced Convection Numerical Simulation using Finite Volume Method in the Entrance Region of a Parallel Plate Channel with Constant Heat Flux." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/40240006240377022501.
Анотація:
碩士國立臺灣海洋大學
機械與機電工程學系
103
In the numerical analysis of engineering world, there are three commonly used numerical schemes, namely, Finite-volume, finite-difference, and finite-element methods. The finite volume method (Finite Volume Method, FVM) is the most common one in the thermal-fluid field. The flow area of interest is divided into many non-overlapping control volumes in the FVM and each grid node is surrounded by a control volume. An integral process is performed for each control volume so that conservation laws (such as mass, momentum, and energy) could be satisfied within each control volume specified. Due to its conservation nature, the FVM approach is applied in the discretization and the solution of the governing equations in this thesis. The FVM with SIMPLE algorithm by Patanker is used in this thesis. Several MATLAB programs are developed to study a steady two dimensional laminar forced convection flow with constant wall heat flux in a parallel plate channel. Staggered grid configuration is used in the numerical solutions. Velocity, pressure,temperature, local Nusselt number, and friction coefficient are solved numerically. Fully developed and developed flow are both studied. Results are compared with those of analytic solutions or empirical correlations available. The numerical results of MATLAB are also compared with those of commercial code Fluent. Firstly, the applicability of staggered grid is examined. The grid size is optimized for different Reynolds numbers up to 1000. The MATLAB program developed is then run for both fully developed and uniform velocity inlet. Hydrodynamical and thermal entry length are obtained and compared with those empirical correlations in the literature. Local friction coefficient and Nusselt number are numerically calculated and compared with those analytic solutions available or Fluent results. The applicability of the MATLAB program developed in this thesis using staggered grid is well justified through above comparisons for solving this type of forced convection problem. Secondly, this thesis also compare the results of the FVM and the Fluent numerical simulation. Except in the computation time, both the FVM and the Fluent numerical simulation could achieve satisfactory results. It is proposed that different thermal boundary conditions (such as variable wall temperature, variable wall heat flux), rectangular or circular pipe, or different algorithms, such as SIMPLEC, could be studied in the future.
Книги з теми "Parallel heat flux":
1
Aktan, Gülçin. Fully developed laminar natural convection in a vertical parallel-plate duct with constant wall heat flux. 1996.
Частини книг з теми "Parallel heat flux":
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Sharath Kumar Reddy, J., and D. Bhargavi. "Thermally Developing Region of a Parallel Plate Channel Partially Filled with a Porous Material with the Effect of Axial Conduction and Viscous Dissipation: Uniform Wall Heat Flux." In Advances in Applied Mechanical Engineering, 27–35. Singapore: Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-15-1201-8_4.
2
Peigin, S., J. Periaux, and S. Timchenko. "Asynchrone parallel genetic algorithm for heat flux optimization problem." In Parallel Computational Fluid Dynamics 1998, 377–84. Elsevier, 1999. http://dx.doi.org/10.1016/b978-044482850-7/50107-8.
3
Kozlov, Vladimir, Vladimir Maz’ya, and Alexander Movchan. "A Boundary Value Problem for the Laplacian in a Multi-Structure." In Asymptotic Analysis of Fields in Multi-Structures, 56–114. Oxford University PressOxford, 1999. http://dx.doi.org/10.1093/oso/9780198514954.003.0002.
Анотація:
Abstract In the present chapter we consider a multi-structure ‖;ε defined as a union of a three-dimensional domain and a number of thin cylinders of normalised thickness ε parallel to each other (see Fig. 2.1). We deal with the asymptotic analysis of a solution u of a mixed boundary value problem for the Laplacian operator in ∂‖;ε.The Dirichlet data are prescribed on the bases of thin cylinders; on the remaining part of the surface ∂Ωε we have the Neumann boundary condition. We note that the solution of this problem describes the temperature field in the multistructure for the case when the heat flux is specified on the boundary surface outside the base regions of the thin cylinder, where the values of the temperature are given.
4
Pallikarakis, Christos N., Dionysios I. Kolaitis, and Maria A. Founti. "Characteristics of surface litter fires: A systematic experimental study." In Advances in Forest Fire Research 2022, 1591–96. Imprensa da Universidade de Coimbra, 2022. http://dx.doi.org/10.14195/978-989-26-2298-9_242.
Анотація:
This work presents the results of laboratory experiments, focused on the characterization of surface wildland fires propagating in a litter fuel bed. A series of fire tests are conducted using an inclinable combustion table, measuring 2 m x 2 m, aiming to identify the effects of several important operational parameters on the characteristics of the developing fire. The parameters studied are the slope angle, the fuel load, the fuel moisture content and the type of ignition. A broad sensor network is installed in the combustion table, including 86 thermocouples, 4 bi-directional velocity probes, 2 Pitot tubes, 3 heat flux sensors, 2 optical cameras and a real-time gas analyser. The obtained measurements are used to determine the time evolution of several characteristic parameters, such as the Rate of Spread and the Heat Release Rate. The construction of a 2D temperature field from the thermocouples that rest on a plane parallel to the propagation axis, illustrates important flame characteristics. It is found that the fire’s Rate of Spread increases with increasing slope angle and fuel load, whereas it decreases with increasing Fuel Moisture Content. The Rate of Spread does not seem to reach a steady state for the fires propagating up-slope. The Heat Release Rate increases with increasing slope and, more intensely, fuel load. As expected, the increase of the Fuel Moisture Content decreases the Heat Release Rate.
5
Carr, Jeremy. "Paranoia and Perception." In Repulsion, 55–70. Liverpool University Press, 2021. http://dx.doi.org/10.3828/liverpool/9781800859326.003.0004.
Анотація:
Reflecting and affecting her fears, the Kensington flat Carol shares with Helen is a palpable expression of dread, realized primarily in Polanski’s illustrative production design. The apartment appears in a perpetual state of flux, with malleable walls, spatial extensions, and a cumulative disarray that parallels Carol’s debilitating breakdown. As Carol moves carefully and woefully from room to room, traversing the hallways with petrified trepidation, external noises signal a peripheral life outside, while inside, ticking clocks, buzzing flies, and harassing phone calls form aural reminders of an animated domestic space, strengthening the abstract ambiance of her torment. Polanski’s camera scans Repulsion’s interiors in a visual establishment of relevant decor, often enlisted alongside tactile, abject textures and revolting objects like bloodstained floors, rotting potatoes, and a decaying rabbit, the head of which finds its way to Carol’s handbag, prompting the public revelation of her private disturbance. While this attention to tangible detail recalls The Tenant (1976), where Polanski’s main character obsesses over clothes and trinkets and such grotesque items as a tooth stuck in a wall, signifying precursors to his mental fissure, this chapter will also consider the Polanski-esque pattern of a few characters in one combustible location.
Тези доповідей конференцій з теми "Parallel heat flux":
1
Kuznetsov, Vladimir V., and Alisher S. Shamirzaev. "HIGH HEAT FLUX FLOW BOILING OF WATER AND DIELECTRIC COOLANT IN PARALLEL MICROCHANNELS." In International Heat Transfer Conference 16. Connecticut: Begellhouse, 2018. http://dx.doi.org/10.1615/ihtc16.bae.022906.
2
Nelson, Douglas J., and Byard D. Wood. "COMBINED HEAT AND MASS TRANSFER NATURAL CONVECTION BETWEEN VERTICAL PARALLEL PLATES WITH UNIFORM FLUX BOUNDARY CONDITIONS." In International Heat Transfer Conference 8. Connecticut: Begellhouse, 1986. http://dx.doi.org/10.1615/ihtc8.3190.
3
Chen, Tailian, and Suresh V. Garimella. "A Study of Critical Heat Flux During Flow Boiling in Microchannel Heat Sinks." In ASME/JSME 2011 8th Thermal Engineering Joint Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajtec2011-44083.
Анотація:
The cooling capacity of two-phase transport in microchannels is limited by the occurrence of critical heat flux (CHF). Due to the nature of the phenomenon, it is challenging to obtain reliable CHF data without causing damage to the device under test. In this work, the critical heat fluxes for flow boiling of FC-77 in a silicon thermal test die containing 60 parallel microchannels were measured at five total flow rates through the microchannels in the range of 20–80 ml/min. CHF is caused by dryout at the wall near the exit of the microchannels, which in turn is attributed to the flow reversal upstream of the microchannels. The bubbles pushed back into the inlet plenum agglomerate; the resulting flow blockage is a likely cause for the occurrence of CHF which is marked by an abrupt increase in wall temperature near the exit and an abrupt decrease in pressure drop across the microchannels. A database of 49 data points obtained from five experiments in four independent studies with water, R-113, and FC-77 as coolants was compiled and analyzed. It is found that the CHF has a strong dependence on the coolant, the flow rate, and the area upon which the flux definition is based. However, at a given flow rate, the critical heat input (total heat transfer rate to the coolant when CHF occurs) depends only on the coolant and has minimal dependence on the details of the microchannel heat sink (channel size, number of channels, substrate material, and base area). The critical heat input for flow boiling in multiple parallel microchannels follows a well-defined trend with the product of mass flow rate and latent heat of vaporization. A power-law correlation is proposed which offers a simple, yet accurate method for predicting the CHF. The thermodynamic exit quality at CHF is also analyzed and discussed to provide insights into the CHF phenomenon in a heat sink containing multiple parallel microchannels.
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Baxi, C. B., O. Gutierrez, R. Schleicher, and C. M. Kendall. "Heat and Mass Transfer in Parallel Flow Mist Cooling." In ASME 2003 Heat Transfer Summer Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/ht2003-47552.
Анотація:
The lasing gain media (LGM) of the solid-state heat capacity laser (SSHCL) need to be cooled in a short time in between laser operations to increase the duty cycle. Parallel flow mist cooling is an attractive option to accomplish this. However, no general correlations exist to predict parallel flow mist cooling heat transfer for various fluids. In order to obtain such a correlation this study was undertaken. Drop size distribution from different nozzles was characterized by laser Doppler anemometer. A parallel flow mist cooling experimental set-up was designed and fabricated. Data from over 300 experiments with air, air-water mist, air-denatured ethanol mist and air-pure ethanol mist was obtained. The parameter ranges were: flow velocity between 5 and 50 m/s, drop diameters between 18 and 75 μm, mist concentrations as high as 0.2 kg/m3, heat fluxes up to 170000 W/m2 and hydraulic diameters between 0.003 and 0.008 m. An enhancement of up to a factor of six relative to the heat flux removed by air was obtained. The experiments indicated that there are four regimes in parallel flow mist cooling. These are: 1) Mass transfer, 2) Forced convection 3), Critical Heat Flux and 4) Film boiling. Two general correlations for parallel flow mist cooling are proposed for the first two of these regimes.
5
Bunderson, Nathan E., and Barton L. Smith. "Quantification of Mixing Performance in Parallel Jets." In ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56852.
Анотація:
Experiments of unvented parallel planar jets having variable slot widths and velocities are presented. A flow visualization study shows that, for sufficiently large spacing, the jets “flap” and that this motion is maximized for a matched exit momentum flux condition. The extent of the jet mixing with the ambient fluid is investigated using two-component hot wire anemometry. It is demonstrated that the flapping increases mixing of the jets with the ambient. In addition, it is shown that the mixing increases with distance between the jets and with jet-width ratio.
6
Bergles, A. E., and S. G. Kandlikar. "On the Nature of Critical Heat Flux in Microchannels." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-42383.
Анотація:
The critical heat flux (CHF) limit is an important consideration in the design of any flow boiling unit. Before the use of microchannels under flow boiling conditions becomes widely accepted in critical applications, such as electronics cooling and laser lenses, it is essential to develop CHF data for microchannels. The experiments required to obtain this information pose unique challenges as the channel dimensions become smaller. The issues of parallel channel instability, experimental control, experimental uncertainty, and conjugate effects need to be carefully addressed. These issues are addressed in the present paper, and guidelines helpful in the design of CHF experiments are outlined.
7
Schygulla, Ulrich, Ju¨rgen J. Brandner, Eugen Anurjew, Edgar Hansjosten, and Klaus Schubert. "Micro Heat Changers and Surface-Micro-Coolers for High Heat Flux." In ASME 2008 6th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2008. http://dx.doi.org/10.1115/icnmm2008-62188.
Анотація:
This publication describes the development of a new microstructure to transfer high heat fluxes. With a simple mathematical model based on heat conduction theory for the heat transfer in a micro channel at laminar flow conditions it was deduced that for the transmission of high heat fluxes only the initial part at the beginning of the micro channels is of importance, i.e. the micro channels should be short. Based on this principle a micro structure was designed with a large number of short micro channels taken in parallel. With this newly developed microstructure a prototype of a micro heat exchanger and a surface micro cooler was manufactured and tested. Using the prototype of the micro heat exchanger, manufactured of plastic, heat fluxes up to 500 W/cm2 were achieved at a pressure loss of 0.16 MPa and a mass flow of the water of 200 kg/h per passage. Due to the use of materials with a higher temperature resistance and higher stability like aluminum or ceramic, higher water throughputs and higher flow velocities could be realized in the micro channels. Thus it was possible to increase the heat flux up to approx. 800 W/cm2 at a pressure loss of approx. 0.35 MPa and a mass flow of 350 kg/h per passage. The important focus of investigation of the surface micro cooler was set on the examination of the surface temperatures for different heat fluxes and different velocities of the water in the micro channels. The experimental results of these surface micro coolers are summarized to characteristic maps. With this characteristic maps it is possible to determine whether a micro surface cooler can be used for a specific application.
8
Bandhauer, Todd M., and Taylor A. Bevis. "High Heat Flux Boiling Heat Transfer for Laser Diode Arrays." In ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2016 Heat Transfer Summer Conference and the ASME 2016 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/icnmm2016-7947.
Анотація:
The principle limit for achieving higher brightness of laser diode arrays is thermal management. State of the art laser diodes generate heat at fluxes in excess of 1 kW cm−2 on a plane parallel to the light emitting edge. As the laser diode bars are packed closer together, it becomes increasingly difficult to remove large amounts of heat in the diminishing space between neighboring diode bars. Thermal management of these diode arrays using conduction and natural convection is practically impossible, and, therefore, some form of forced convective cooling must be utilized. Cooling large arrays of laser diodes using single-phase convection heat transfer has been investigated for more than two decades by multiple investigators. Unfortunately, either large fluid temperature increases or very high flow velocities must be utilized to reject heat to a single phase fluid, and the practical threshold for single phase convective cooling of laser diodes appears to have been reached. In contrast, liquid-vapor phase change heat transport can occur with a negligible increase in temperature and, due to a high enthalpy of vaporization, at comparatively low mass flow rates. However, there have been no prior investigations at the conditions required for high brightness edge emitting laser diode arrays: >1 kW cm−2 and >10 kW cm−3. In the current investigation, flow boiling heat transfer at heat fluxes up to 1.1 kW cm−2 was studied in a microchannel heat sink with plurality of very small channels (45 × 200 microns) using R134a as the phase change fluid. The high aspect ratio channels (4.4:1) were manufactured using MEMS fabrication techniques, which yielded a large heat transfer surface area to volume ratio in the vicinity of the laser diode. To characterize the heat transfer performance, a test facility was constructed that enabled testing over a range of fluid saturation temperatures (15°C to 25°C). Due to the very small geometric features, significant heat spreading was observed, necessitating numerical methods to determine the average heat transfer coefficient from test data. This technique is crucial to accurately calculate the heat transfer coefficients for the current investigation, and it is shown that the analytical approach used by many previous investigations requires assumptions that are inadequate for the very small dimensions and heat fluxes observed in the present study. During the tests, the calculated outlet vapor quality exceeded 0.6 and the base heat flux reached a maximum of 1.1 kW cm−2. The resulting experimental heat transfer coefficients are found to be as large a 58.1 kW m−2 K−1 with an average uncertainty of ±11.1%, which includes uncertainty from all measured and calculated values, required assumptions, and geometric discretization error from meshing.
9
Chung, Shan-Yu, and Chin Pan. "The Enhancement of Boiling Heat Transfer in a Minichannel Heat Sink With Saw-Tooth Structure on Channel Surface." In ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/mnhmt2016-6626.
Анотація:
The dimension of electronic devices becomes smaller and smaller and, thus, it is of crucial importance to enhance the heat dissipation from such tiny devices. The present study investigates the boiling heat transfer in a minichannel heat sink with saw-tooth structure on channel surface. The heat sink is comprised of four minichannels with hydraulic diameter of 0.8 mm and made of copper. The dimensions of the base area of the heat sink are 90 mm (length) × 5 mm (width). The saw-tooth topology on the bottom surface of minichannel was manufactured by wire-cut electrical discharge machining (EDM). The height, tip angle, and pitch of the saw-tooth structure are 0.5 mm, 45°, and 1mm, respectively. This study employed refrigerant HFE-7100, which is of low global warming potential (GWP), as a working fluid to investigate the boiling heat transfer in three kinds of surface structures (i.e., plain, parallel saw-tooth, and counter saw-tooth). The mass flux of the HFE-7100 ranged from 64 to 285 kg/m2s. The experimental results showed that the critical heat flux (CHF), compared to the plain minichannel, is improved by 46.7% and 40.2%, respectively, in the parallel and counter saw-tooth minichannels for a low mass flux of 127 kg/m2s. This result indicated that the CHF is considerably enhanced by the saw-tooth structure with both parallel and counter flow designs for the low mass flux. However, the CHF in the parallel and plain minichannels is nearly the same for a large mass flux of 285 kg/m2s. But for a saw-tooth structure with counter flow design, the CHF increases by 17.1% compared to the plain minichannel. Consequently, the experimental results demonstrated that the CHF can be enhanced by using saw-tooth structure on the channel surface.
10
Kabelac, Stephan, and Sebastian W. Freund. "Local Two-Phase Flow Heat Transfer in Plate Heat Exchangers." In ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference collocated with the ASME 2007 InterPACK Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ht2007-32051.
Анотація:
Experimental results on quasi-local heat transfer coefficients for evaporation and condensation in PHEs related to vapor quality, mass flow rate and heat flux are presented in this paper. The data is obtained from a refrigeration cycle involving a PHE evaporator and a PHE condenser with a secondary fluid loop. The considered refrigerants are ammonia and R-134a. Evaporator and condenser are equipped with multiple thermocouples along the plates, which allow for the deduction of local heat flux and heat transfer coefficients on seven subsections of the plates. The data resolves for the first time the complete evaporation and condensation process along a plate channel and thus may contribute to the understanding of flow distribution and heat transfer mechanisms. The results show an increase of heat transfer coefficients with the vapor quality and the effects of mass flux and heat flux. The results conclude that parallel flow arrangement is advantageous for evaporation while counter flow enhances condensation heat transfer. Plates with low pitch angle chevron corrugations increase the evaporation. Comparisons with the limited available data from literature and various correlations indicate the need for further theoretical development. The data may be suitable for developing correlations of the thermo-hydraulic performance of plate evaporators and condensers as a function of flow, heat flux and plate parameters, which are not established in literature.
Звіти організацій з теми "Parallel heat flux":
1
Kedzierski, Mark A., and Donggyu Kang. Horizontal convective boiling of R1234yf, R134a, and R450A within a micro-fin tube :. Gaithersburg, MD: National Institute of Standards and Technology (U.S.), August 2017. http://dx.doi.org/10.6028/nist.tn.1966.
Анотація:
This report presents local convective boiling heat transfer and Fanning friction factor measurements in a micro-fin tube for R134a and two possible low global warming potential (GWP) refrigerant replacements for R134a: R1234yf and R450A. Test section heating was achieved with water in either counterflow or in parallel flow with the test refrigerant to provide for a range of heat fluxes for each thermodynamic quality. An existing correlation from the literature for single and multi-component mixtures was shown to not satisfactorily predict the convective boiling measurements for flow qualities greater than 40 %. Accordingly, a new correlation was developed specifically for the test fluids of this study so that a fair comparison of the heat transfer performance of the low GWP refrigerants to that of R134a could be made. The new correlation was used to compare the heat transfer coefficient of the three test fluids at the same heat flux, saturated refrigerant temperature, and refrigerant mass flux. The resulting example comparison, for the same operating conditions, showed that the heat transfer coefficient of the multi-component R450A and the single-component R1234yf were, on average, 15 % less and 5 % less, respectively, than that of the single-component R134a. Friction factor measurements were also compared to predictions from an existing correlation. A new correlation for the friction factor was developed to provide a more accurate prediction. The measurements and the new models are important for the evaluation of potential low-GWP refrigerants replacements for R134a.