Academic literature on the topic 'Heat transfer limit'
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Journal articles on the topic "Heat transfer limit"
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Li, Xi Bing, Shi Gang Wang, Jian Hua Guo, and Dong Sheng Li. "A Mathematical Modeling Method on Micro Heat Pipe with a Trapezium-Grooved Wick Structure." Applied Mechanics and Materials 29-32 (August 2010): 1686–94. http://dx.doi.org/10.4028/www.scientific.net/amm.29-32.1686.
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With heat flux increasing and cooling space decreasing in the products in microelectronics and chemical engineering, micro heat pipe has become an ideal heat radiator for products with high heat flux. Through analyzing the factors influencing the structure, strength and heat transfer limits of circular micro heat pipe with trapezium-grooved wick structure, the heat transfer models are established in this paper, including the models of viscous limit, sonic limit, entrainment limit, capillary limit, condensing limit, boiling limit, continuous flow limit and frozen startup limit. The study lays a powerful theoretical foundation for the design and manufacture of circular micro heat pipe with a trapezium-grooved wick structure.
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Dobran, Flavio. "Suppression of the Sonic Heat Transfer Limit in High-Temperature Heat Pipes." Journal of Heat Transfer 111, no. 3 (August 1, 1989): 605–10. http://dx.doi.org/10.1115/1.3250725.
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The design of high-performance heat pipes requires optimization of heat transfer surfaces and liquid and vapor flow channels to suppress the heat transfer operating limits. In the paper an analytical model of the vapor flow in high-temperature heat pipes is presented, showing that the axial heat transport capacity limited by the sonic heat transfer limit depends on the working fluid, vapor flow area, manner of liquid evaporation into the vapor core of the evaporator, and lengths of the evaporator and adiabatic regions. Limited comparisons of the model predictions with data of the sonic heat transfer limits are shown to be very reasonable, giving credibility to the proposed analytical approach to determine the effect of various parameters on the axial heat transport capacity. Large axial heat transfer rates can be achieved with large vapor flow cross-sectional areas, small lengths of evaporator and adiabatic regions or a vapor flow area increase in these regions, and liquid evaporation in the evaporator normal to the main flow.
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Martin, Michael J., and Iain D. Boyd. "Stagnation-Point Heat Transfer Near the Continuum Limit." AIAA Journal 47, no. 1 (January 2009): 283–85. http://dx.doi.org/10.2514/1.39789.
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Bertoli, Sávio L., José Alexandre B. Valle, Antônio G. Gerent, and Juliano de Almeida. "Heat transfer at pneumatic particle transport — Limit solutions." Powder Technology 232 (December 2012): 64–77. http://dx.doi.org/10.1016/j.powtec.2012.07.050.
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Kashi, Barak, and Herman D. Haustein. "Microscale sets a fundamental limit to heat transfer." International Communications in Heat and Mass Transfer 104 (May 2019): 1–7. http://dx.doi.org/10.1016/j.icheatmasstransfer.2019.02.003.
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Li, Xi Bing, Chang Long Yang, Gong Di Xu, Wen Yuan, and Shi Gang Wang. "A Mathematical Modeling Method for Capillary Limit of Micro Heat Pipe with Sintered Wick." Solid State Phenomena 175 (June 2011): 335–41. http://dx.doi.org/10.4028/www.scientific.net/ssp.175.335.
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With heat flux increasing and cooling space decreasing in microelectronic and chemical products, micro heat pipe has become an ideal heat dissipation device in high heat-flux products. Through the analysis of its working principle, the factors that affect its heat transfer limits and the patterns in which copper powders are arrayed in circular cavity, this paper first established a mathematical model for the crucial factors in affecting heat transfer limits in a circular micro heat pipe with a sintered wick, i.e. a theoretical model for capillary limit, and then verified its validity through experimental investigations. The study lays a powerful theoretical foundation for designing and manufacturing circular micro heat pipes with sintered wicks.
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OGUSHI, Tetsuro, and Goro YAMANAKA. "Heat transfer performance of axial grooved heat pipes. The capillary pumping limit." Transactions of the Japan Society of Mechanical Engineers Series B 53, no. 486 (1987): 600–607. http://dx.doi.org/10.1299/kikaib.53.600.
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Williams, Richard R., and Daniel K. Harris. "The heat transfer limit of step-graded metal felt heat pipe wicks." International Journal of Heat and Mass Transfer 48, no. 2 (January 2005): 293–305. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2004.08.024.
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Michiyoshi, I., O. Takahashi, and Y. Kikuchi. "Heat transfer and the low limit of film boiling." Experimental Thermal and Fluid Science 2, no. 3 (July 1989): 268–79. http://dx.doi.org/10.1016/0894-1777(89)90016-2.
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Arpacı, V. S., and S. H. Kao. "Thermocapillary Driven Turbulent Heat Transfer." Journal of Heat Transfer 120, no. 1 (February 1, 1998): 214–19. http://dx.doi.org/10.1115/1.2830044.
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A dimensionless number depending on the usual Prandtl and Marangoni numbers, Πs ∼ Ma/(1 + Pr1) = Ma Pr/(1 + Pr), is introduced for thermocapillary driven flows. Three heat transfer models are proposed in terms of Πs. The first model on laminar flow, using some dimensional arguments with a flow scale and the boundary layer concept, leads to Nu ∼ Πs1/4, Nu being the usual Nusselt number. The second model on transition flow, extending Landau’s original idea on the amplitude of disturbances past marginal stability of isothermal flow, leads to Nu − 1 ∼ (ΠS−ΠSc)1/2, ΠSc corresponding to the critical value of Πs for the marginal state. The third model on turbulent flow, introduces a thermal microscale ηθ ∼ (1 + Pr-1)1/4(να2/Ps)1/4 = (1 + Pr)1/4 (α3/Ps)1/4, with ν and α, respectively, being kinematic and thermal diffusivities, and Ps the production rate of thermocapillary energy. The first expression relating ηθ to Prandtl number explicitly includes its limit for Pr → ∞, ηθB ∼ (να2/ε)1/4, which is a Batchelor scale, and the second one explicitly includes its limit for Pr → 0, ηθC ∼ (α3/ε)1/4, which is an Oboukhov-Corrsin scale. In terms of ηθ and an integral scale l, the model leads to Nu ∼ l/ηθ ∼ Πs1/3. Recent experimental literature are interpreted by special cases of the foregoing models corresponding to Pr > 1.
Dissertations / Theses on the topic "Heat transfer limit"
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Kucuk, Sinan. "A Comparative Investigation Of Heat Transfer Capacity Limits Of Heat Pipes." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12609125/index.pdf.
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Heat pipe is a passive two phase device capable of transferring large rates of heat with a minimal temperature drop. It is a sealed tube with a wick structure lined in it and with a working fluid inside the tube. It consists of three parts: an evaporator, a condenser and an adiabatic section. The heat pipes are widely used in electronics cooling and spacecraft applications. Although they can transfer large rate of heat in a short range, they have operating limits, namely: the capillary limit, the viscous limit, the entrainment limit, the sonic limit and the boiling limit. These limits determine the heat transfer capacity of the heat pipe. The properties of the working fluid, the structure of the wick, the orientation of the pipe, the length and the diameter of the tube etc. are the parameters that affect the limits. In this study, an analytical 1-D heat pipe model is formed and a computer code is prepared in order to analyze the effects of the parameters on the heat transfer capacity of a heat pipe. Water, Ammonia and Mercury are investigated as working fluids for different operating temperature ranges. The software is tested for a typical application for each working fluid.
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Gdhaidh, Farouq A. S. "Heat Transfer Characteristics of Natural Convection within an Enclosure Using Liquid Cooling System." Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/7824.
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In this investigation, a single phase fluid is used to study the coupling between natural convection heat transfer within an enclosure and forced convection through computer covering case to cool the electronic chip. Two working fluids are used (water and air) within a rectangular enclosure and the air flow through the computer case is created by an exhaust fan installed at the back of the computer case. The optimum enclosure size configuration that keeps a maximum temperature of the heat source at a safe temperature level (85℃) is determined. The cooling system is tested for varying values of applied power in the range of 15−40𝑊.
The study is based on both numerical models and experimental observations. The numerical work was developed using the commercial software (ANSYS-Icepak) to simulate the flow and temperature fields for the desktop computer and the cooling system. The numerical simulation has the same physical geometry as those used in the experimental investigations. The experimental work was aimed to gather the details for temperature field and use them in the validation of the numerical prediction.
The results showed that, the cavity size variations influence both the heat transfer process and the maximum temperature. Furthermore, the experimental results
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compared favourably with those obtained numerically, where the maximum deviation in terms of the maximum system temperature, is within 3.5%. Moreover, it is seen that using water as the working fluid within the enclosure is capable of keeping the maximum temperature under 77℃ for a heat source of 40𝑊, which is below the recommended electronic chips temperature of not exceeding 85℃. As a result, the noise and vibration level is reduced. In addition, the proposed cooling system saved about 65% of the CPU fan power.
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Gdhaidh, Farouq Ali S. "Heat transfer characteristics of natural convection within an enclosure using liquid cooling system." Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/7824.
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In this investigation, a single phase fluid is used to study the coupling between natural convection heat transfer within an enclosure and forced convection through computer covering case to cool the electronic chip. Two working fluids are used (water and air) within a rectangular enclosure and the air flow through the computer case is created by an exhaust fan installed at the back of the computer case. The optimum enclosure size configuration that keeps a maximum temperature of the heat source at a safe temperature level (85°C) is determined. The cooling system is tested for varying values of applied power in the range of 15-40W. The study is based on both numerical models and experimental observations. The numerical work was developed using the commercial software (ANSYS-Icepak) to simulate the flow and temperature fields for the desktop computer and the cooling system. The numerical simulation has the same physical geometry as those used in the experimental investigations. The experimental work was aimed to gather the details for temperature field and use them in the validation of the numerical prediction. The results showed that, the cavity size variations influence both the heat transfer process and the maximum temperature. Furthermore, the experimental results ii compared favourably with those obtained numerically, where the maximum deviation in terms of the maximum system temperature, is within 3.5%. Moreover, it is seen that using water as the working fluid within the enclosure is capable of keeping the maximum temperature under 77°C for a heat source of 40W, which is below the recommended electronic chips temperature of not exceeding 85°C. As a result, the noise and vibration level is reduced. In addition, the proposed cooling system saved about 65% of the CPU fan power.
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Zhang, Yufang. "Coupled convective heat transfer and radiative energy transfer in turbulent boundary layers." Phd thesis, Ecole Centrale Paris, 2013. http://tel.archives-ouvertes.fr/tel-00969159.
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If radiation plays an important role in many engineering applications, especially in those including combustion systems, influence of radiation on turbulent flows, particularly on the turbulent boundary layers, is still not well known. The objective is here to perform a detailed study of radiation effect on turbulent flows. An optimized emission-based reciprocal (OERM) approach of the Monte-Carlo method is proposed for radiation simulation using the CK model for radiative gas properties. OERM allows the uncertainty of results to be locally controlled while it overcomes the drawback of the original emission-based reciprocity approach by introducing a new frequency distribution function that is based on the maximum temperature of the domain. Direct Numerical Simulation (DNS) has been performed for turbulent channel flows under different pressure, wall temperatures and wall emissivity conditions. Flow field DNS simulations are fully coupled with radiation simulation using the OERM approach. The role of radiation on the mean temperature field and fluctuation field are analyzed in details. Modification of the mean temperature profile leads to changes in wall conductive heat fluxes and new wall laws for temperature when radiation is accounted for. The influence on temperature fluctuations and the turbulent heat flux is investigated through their respective transport equations whose balance is modified by radiation. A new wall-scaling based on the energy balance is proposed to improve collapsing of wall-normal turbulent flux profiles among different channel flows with/without considering radiation transfer. This scaling enables a new turbulent Prandtl number model to be introduced to take into account the effects of radiation. In order to consider the influence of radiation in the near-wall region and predict the modified wall law, a one-dimensional wall model for Large Eddy Simulation (LES) is proposed. The 1D turbulent equilibrium boundary layer equations are solved on an embedded grid in the inner layer. The obtained wall friction stress and wall conductive flux are then fed back to the LES solver. The radiative power term in the energy equation of the 1D wall model is computed from an analytical model. The proposed wall model is validated by a comparison with the former DNS/Monte-Carlo results. Finally, two criteria are proposed and validated. The first one is aimed to predict the importance of wall radiative heat flux while the other one predicts whether a wall model accounting for radiation in the near wall region is necessary. A parametric study is then performed where a k-ǫ model and a turbulent Prandtl number model are applied to simulate the velocity and temperature field of different channel flows under various flow conditions. The obtained criteria values are analyzed and compared.
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Said, Frédérique. "Etude expérimentale de la couche limite marine : structure turbulente et flux de la surface (expérience TOXANE-T)." Toulouse 3, 1988. http://www.theses.fr/1988TOU30022.
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Le travail presente est une etude experimentale des transferts turbulents de chaleur, humidite et quantite de mouvement dans la couche limite marine. La phase experimentale (experience toscane-t) s'est deroulee en mars 1985, au large de la baie d'audierne (finistere). Le principal vecteur utilise pour le travail presente est un avion instrumente pour la physique de l'atmosphere. Ce moyen a permis de determiner une topographie des caracteristiques turbulentes, sur une echelle horizontale de l'ordre de 50km sur 50km, et de calculer les flux par la methode des correlations. Les conditions experimentales rencontrees correspondent a des vents compris enre 3 et 12 metres par seconde et a des conditions d'instabilite caracterisees par des longueurs de monin obukhov negatives comprises entre 50 et 300 metres. La structure turbulente de la couche limite marine est presentee dans le cadre de la theorie de similitude. Les resultats obtenus sont en accord avec les donnees acquises en couche limite dynamique, marine ou continentale. Ils sont egalement compares aux caracteristiques turbulentes des couches limites convectives. La finalisation de cette etude est resumee au moyen d'une parametrisation des flux de surface. Celle-ci est utilisable dans les modeles de grande echelle et consiste a calculer les coefficients aerodynamiques. Dans les conditions experimentales de l'etude les valeurs obtenues sont les suivantes: 1. 8 10**(-3) pour la quantite de mouvement (cd::(10)); 1. 5 10**(-3) pour la chaleur sensible (ct::(10)); et 1. 5 10**(-3) pour la chaleur latente (cq::(10)); ces coefficients sont independants de l'echelle d'integration spatiale a laquelle ils ont ete determines (de 5 km sur 5 km a 50 km sur 50 km).
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Stefanini, Luciano Martinez. "Efeitos da camada limite térmica na formação de gelo em aerofólios de uso aeronáutico." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3150/tde-17082009-165521/.
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O modelo de avaliação da camada limite dinâmica e térmica foi implementado, no presente trabalho, em um código numérico para o cálculo do coeficiente de transferência de calor convectivo sobre aerofólios de uso aeronáutico com formação de gelo. Foram considerados, no modelo da camada limite turbulenta, os efeitos da rugosidade equivalente do grão de areia ks, e transição entre o regime laminar e turbulento foi avaliada por dois modelos, um abrupto e um suave. Para a transição suave foi utilizada uma função intermitência proposta por (ABU-GHANNAM; SHAW, 1980). O código desenvolvido neste trabalho foi acoplado aos módulos do código ONERA com o objetivo de simular as formas de gelo em aerofólios para diversas condições de escoamento do ar com conteúdo de água. As formas de gelo obtidas foram comparadas com dados experimentais de Shine Bond (1994) e com resultados de simulações dos códigos LEWICE, TRAJICE e ONERA (KIND, 2001). Os resultados das simulações do presente trabalho apresentaram boa semelhança com os resultados dos outros códigos. A simulação da previsão de formas de gelo do tipo Glaze, do presente trabalho e dos outros códigos, resultou em formas de gelo de espessura e volume menores que as formas experimentais. Foi verificado que uma previsão adequada do coeficiente de transferência de calor convectivo afeta a simulação das formas deste tipo de gelo. Um caso de Kind (2001) foi utilizado para avaliar os efeitos dos parâmetros da camada limite dinâmica e térmica na formação de gelo em aerofólios. Verificou-se que a posição do início da transição do regime laminar para o turbulento, o comprimento d a transição e o valor da rugosidade afetam a forma, a espessura e o volume do gelo, e que estes parâmetros podem ser utilizados para ajustes dos modelos de camada limite para melhores previsões de formas de gelo do tipo Glaze.The model to evaluate the momentum and thermal boundary layer was implemented, in the present work, in a numerical module to calculate the convective heat transfer coecient over aeronautical airfoils with ice accretion. It was considered, in the turbulent boundary layer model, the eects of the equivalent sand grain roughness ks , and the laminar to turbulent transition was evaluated with two models, the abrupt and the smooth one. The smooth transition model used an intermittency function proposed by (ABU-GHANNAM; SHAW, 1980). The module developed in this work was integrated with the modules of the code ONERA in order to simulate the airfoil icing shapes for several air stream with water droplets condition. The ice shapes obtained was compared with experimental data of Shin e Bond (1994) and with simulation results for the codes LEWICE, TRAJICE e ONERA (KIND, 2001). The results of the simulations for the present work showed a good similarity with the other codes results. The Glaze icing shapes simulation, in the present work and in the other codes, resulted in icing shapes with thickness and volumes lesser than the experimental shapes. It was noted that a reasonable prediction of the convective heat transfer coecient aects the simulation of this type of ice shape. One case of Kind (2001) was used to evaluate the eects of the momentum and thermal boundary layer for the icing accreations in the airfoil. It was noted the onset position, the lenght of the laminar-turbulent transition, and the sand grain roughness value aects the icing shape, thickness and volume and this parameters might be used to adjust the boundary layer models in order to get better predictions of Glaze icing shapes.
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Lambrinos, Grégoire. "Sublimation des milieux disperses congeles soumis a des temperatures negatives." Paris 6, 1988. http://www.theses.fr/1988PA066637.
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Thiagalingam, Ilango. "Modélisation des transferts thermiques convectifs en régime turbulent à l'interface milieu poreux / paroi dans les lits catalytiques." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066126/document.
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Le travail réalisé porte sur la modélisation à l'échelle macroscopique des transferts thermiques dans les lits catalytiques et au voisinage de la paroi. L'objectif principal de ce travail est de comprendre et de modéliser les mécanismes physiques responsables des transferts thermiques dans cette région. La physique proche paroi est capturée à l'échelle macroscopique de façon univoque à l'aide du concept de changement d'échelle et la notion de prise de moyenne volumique est étendue aux types de systèmes que nous considérons. Le coefficient de transfert à la paroi du modèle à deux coefficients λr - hw est premièrement décortiqué afin de mettre en lumière les mécanismes physiques contenus dans cette notion ainsi que le poids de leur contribution respective. Un modèle, basé sur la dynamique de l'écoulement et décrivant le transport de la chaleur dans la direction radiale, est ensuite dérivé à l'échelle macroscopique. Il met notamment en évidence une zone proche paroi particulière, dominée par l'effet de canalisation, qui amortit les transferts diffusifs dans la direction normale à la paroi. On montre ainsi que les transferts thermiques pilotés essentiellement par des mécanismes de dispersion mécanique sont limités dans cette région par des effets de résistance thermique de type convective. Finalement, une loi de paroi décrivant une couche limite perturbée par la matrice solide est utilisée pour faire le raccord à la paroi, ce qui a permis de prédire avec satisfaction la température à la paroiThis work deals with the modeling of near wall heat transfers in catalytic packed beds at the macroscopic scale. The main aims of the present work are the understanding and the modeling of physical mechanisms responsible for the heat transfers in the vicinity of the wall at the observation scale. Volume averaging concept is first extended to systems we consider. Thus, relevant physical mechanisms occurring in the near wall zone are unequivocally up-scaled from pore to bed scale. Then, the detailed analysis of the wall heat transfer coefficient, used in the popular two coefficient model λr - hw, brings to light each physical mechanism and its respective weighted contribution lumped in it. A model, based on the flow dynamic and describing the radial heat transfer, is finally derived at the reactor scale. It highlights that a channel effect occurs in the near wall zone, damping transfers by diffusion in the wall normal direction. It is hence showed that heat transfers mainly driven by mechanical dispersion are facing a convective thermal resistance near the wall. A wall law is also derived to model boundary layer/porous medium interactions, which ultimately connect the porous media model to the wall. Wall temperature is thus recovered with satisfaction
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Gadiraju, Siddhartha. "Study of Lean Blowout Limits and Effects of Near Blowout Oscillations on Flow Field and Heat Transfer on Gas Turbine Combustor." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/82480.
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Modern gas turbine combustors implement lean premixed (LPM) combustion system to reduce the formation of NOx pollutants. LPM technology has advanced to have the ability to produce extremely low level of NOx emissions. The current focus of research on LPM is focused on reducing the NOx emission to much smaller scales, which is mandated because of the stricter regulations and environmental concerns. However, LPM combustors are susceptible to lean blowout (LBO), and other corresponding instabilities as the combustor is operated lean. Therefore, it is essential to understand the LBO limits and dynamics of flow in lean operating conditions. One of the other primary parameters for the improved combustion chamber designs is an accurate characterization of the heat loads on the liner walls in the wide range of operating conditions. Currently, there are very limited studies on the flame side heat transfer in reacting conditions. Current gas turbine combustion technology primarily focuses on burning natural gas as the gas fuel option for industrial systems. However, interest in utilizing additional options due to environmental regulations as well as concerns about energy security have motivated interest in using fuel gases that have blends of Methane, Propane, H2, CO, CO2, and N2. For example, fuel blends of 35%/60% to 55%/35% of CH4/CO2 are typically seen in Landfill gases. Syngas fuels are typically composed primarily of H2, CO, and N2. Gases from anaerobic digestion of sewage, used commonly in wastewater treatment plants, usually have 65–75% CH4 with the balance being N2.
The objective of this study is to understand the LBO limits and the effects of the instabilities that arise (called near blowout oscillations) as the combustor is operated lean. Near blowout oscillations arise as the equivalence ratio is reduced. These oscillations are characterized by continuous blowout and re-ignition events happening at low frequencies. The low-frequency oscillations have very high-pressure amplitude and can potentially damage the liner wall. The impact of the near blowout oscillations on the flow field and heat transfer on the liner walls are studied. To accomplish this, the experiments were conducted at Advanced Propulsion and Power laboratory located at Virginia Tech. A lean premixed, swirl stabilized fuel nozzle designed with central pilot hub was used for the study. Additionally, this work also studies the lean blowout limits with fuel blends of CH4-C3H8, CH4-CO2, and CH4-N2 and also their effect on the stability limits as the pilot fuel percentage was changed.
Flow field during near blowout oscillations was studied using planar particle image velocimetry (PIV) and flame shapes and locations during these oscillations was studied by using high-speed imaging of the flame. A statistical tool called proper orthogonal decomposition (POD) was utilized to post-process the PIV data and high-speed imaging data. Heat transfer on the liner walls was studied using a transient IR thermography methodology. The heat transfer on the liner wall during the near blowout instabilities was resolved. LBO limits and near blowout oscillations were characterized by studying the pressure measurements in the primary combustor region.
Fluctuating heat loads on the liner walls with the same frequency as that of near blowout instabilities was observed. The magnitude of fluctuation was found to be very high. Phase sorted POD reconstructed flame images demonstrated the location of the flame during near blowout oscillations. Thus, blowout and re-ignition events are resolved from the high-speed flame images. POD reconstructed flow field from the PIV data demonstrated the statistically significant flow structures during near blowout oscillations. A hypothesis for the mechanism of near blowout oscillations was explained based on the measurements and observations made.
Lean Blowout limits (LBO) changed when the percentage of pilot and air flow rates was changed. As the pilot percentage increased, LBO limits improved. Results on the study of fuel mixtures demonstrate that the addition of propane, nitrogen and carbon dioxide has minimal effect on when the flame becomes unstable in lean operating conditions. However, on the other hand, the addition of diluent gas showed a potential blowout at higher operating conditions. It was also observed that Wobbe index might not be a good representation for fuels to study the fuel interchangeability in lean operating conditions.Ph. D.
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Sharma, Sushank. "Transition laminaire turbulent dans les couches limites supersoniques : différents scénarios et contrôle possible Control of oblique-type breakdown in a supersonic boundary layer employing streaks Turbulent flow topology in supersonic boundary layer with wall heat transfer Laminar-to-turbulent transition in supersonic boundary layer : : Effects of initial perturbation and wall heat transfer Effect of thermo-mechanical non-equilibrium on the onset of transition in supersonic boundary layers." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMIR16.
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Les simulations numériques directes (DNS) des couches limites supersoniques adiabatiques et isothermes (chauffées et refroidies) sont effectuées. Deux différents scénarios de transition, à savoir la décomposition de type oblique et la transition de type 'by-pass', sont présentés en détail. Pour le scénario de transition de type oblique, les résultats montrent que les modes contrôles avec un nombre d'onde quatre à cinq fois supérieur au nombre fondamental se révèlent être bénéfiques pour contrôler la transition. Dans la première région après le forçage du mode de contrôle, la distorsion de flux moyenne (MFD) bénéfique générée en induisant le mode de contrôle est uniquement responsable de l'entrave à la croissance du mode fondamental. Globalement, le MFD et la partie tridimensionnelle du contrôle contribuent également à contrôler la rupture oblique. Les effets de paramètres physiques tels que la température de paroi, l'intensité de la perturbation et le 'baseflow' sont étudiés pour la transition de 'By-pass'. Les résultats concernant le scénario de by-pass révèlent que l'augmentation de l'intensité de la perturbation déplace le début de la transition en amont et augmente également la longueur de la région de transition. De plus, en dessous de 1 % des niveaux de perturbation, le refroidissement de la paroi stabilise le flux, tandis que l'inverse se produit à des valeurs plus élevées. L'existence d'un non-équilibre thermomécanique avance le début de la transition pour les cas chauffés alors que la paroi refroidie se comporte dans le sens opposé. Les analyses de la couche limite turbulente montrent que les facteurs thermiques influencent la topologie et l'inclinaison des structures tourbillonnaires. De plus, en ce qui concerne le flux de chaleur, un processus de transfert différent est dominant dans la région proche paroi pour la paroi refroidieDirect numerical simulations (DNS) of both adiabatic and isothermal (heated and cooled) supersonic boundary layers are performed. Two different transition scenarios, namely the Oblique-type breakdown and the By-pass transition are presented in detail. For the oblique-type transition scenario, the results show that the control modes with four to five times the fundamental wavenumber are beneficial for controlling the transition. In the first region, after the control-mode forcing, the beneficial mean-flow distortion (MFD) generated by inducing the control mode is solely responsible for hampering the growth of the fundamental-mode. Globally, the MFD and the three-dimensional part of the control contribute equally towards controlling the oblique breakdown. Effects of physical parameters like wall-temperature, perturbation intensity and baseflow are investigated for the By-pass transition. The results regarding the by-pass scenario reveal that increasing the perturbation intensity moves the transition onset upstream and also increases the length of the transition region. Additionally, below 1% perturbation levels, wall-cooling stabilizes the flow while inverse happens at higher values. The existence of the thermo-mechanical non-equilibrium advances the onset of transition for the heated cases while the cooled wall behaves in the opposite sense. The analyses of the turbulent boundary layer show that the thermal factors influence the topology and inclination of the vortical structures. Moreover, regarding the heat flux, different transfer process is dominant in the near-wall region for the cooled wall
Books on the topic "Heat transfer limit"
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Bensoussan, Alain. Asymptotic analysis for periodic structures. Providence, R.I: American Mathematical Society, 2011.
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Rez, Peter. Buildings. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198802297.003.0003.
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Most of the energy used by buildings goes into heating and cooling. For small buildings, such as houses, heat transfer by conduction through the sides is as much as, if not greater than, the heat transfer from air exchanges with the outside. For large buildings, such as offices and factories, the greater volume-to-surface ratio means that air exchanges are more significant. Lights, people and equipment can make significant contributions. Since the energy used depends on the difference in temperature between the inside and the outside, local climate is the most important factor that determines energy use. If heating is required, it is usually more efficient to use a heat pump than to directly burn a fossil fuel. Using diffuse daylight is always more energy efficient than lighting up a room with artificial lights, although this will set a limit on the size of buildings.
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Parlange, Marc B., and Jan W. Hopmans. Vadose Zone Hydrology. Oxford University Press, 1999. http://dx.doi.org/10.1093/oso/9780195109900.001.0001.
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The vadose zone is the region between ground level and the upper limits of soil fully saturated with water. Hydrology in the zone is complex: nonlinear physical, chemical, and biological interactions all affect the transfer of heat, mass, and momentum between the atmosphere and the water table. This book takes an interdisciplinary approach to vadose zone hydrology, bringing together insights from soil science, hydrology, biology, chemistry, physics, and instrumentation design. The chapters present state-of-the-art research, focusing on new frontiers in theory, experiment, and management of soils. The collection addresses the full range of processes, from the pore-scale to field and landscape scales.
Book chapters on the topic "Heat transfer limit"
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Frederking, T. H. K. "Heat Transfer Related to Superconducting Magnet Stability: He II - He I Dynamic Limits." In Advances in Cryogenic Engineering, 149–53. Boston, MA: Springer US, 1990. http://dx.doi.org/10.1007/978-1-4613-0639-9_18.
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Hennes, Christian, J. Lehmann, P. Kožuch, and T. Koch. "Assessment of factors influencing the wall heat transfer with regard to increasing efficiency and compliance with future CO2 limits for commercial vehicles." In Proceedings, 235–52. Wiesbaden: Springer Fachmedien Wiesbaden, 2019. http://dx.doi.org/10.1007/978-3-658-26528-1_14.
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Milanezi de Andrade, Rafhael, André Palmiro Storch, Lucas de Amorim Paulo, Antônio Bento Filho, Claysson Bruno Santos Vimieiro, and Marcos Pinotti. "Transient Thermal Analysis of a Magnetorheological Knee for Prostheses and Exoskeletons during Over-Ground Walking." In Heat Transfer - Design, Experimentation and Applications [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.95372.
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Proper knee movement is essential for accomplishing the mobility daily tasks such as walking, get up from a chair and going up and down stairs. Although the technological advances in active knee actuators for prostheses and exoskeletons to help impaired people in the last decade, they still present several usage limitations such as overweight or limited mechanical power and torque. To address such limitations, we developed the Active Magnetorheological Knee (AMRK) that comprises a Motor Unit (MU), which is a motor-reducer (EC motor and Harmonic Drive) and a MR clutch, that works in parallel to a magnetorheological (MR) brake. Magnetorheological fluids, employed in the MR clutch and brake, are smart materials that have their rheological properties controlled by an induced magnetic field and have been used for different purposes. With this configuration the actuator can work as a motor, clutch or brake and can perform similar movements than a healthy knee. However, the stability, control, and life of magnetorheological fluids critically depend on the working temperature. By reaching a certain temperature limit, the fluid additives quickly deteriorate, leading to irreversible changes of the MR fluid. In this study, we perform a transient thermal analysis of the AMRK, when it is used for walking over-ground, to access possible fluid degradation and user’s discomfort due overheating. The resulting shear stress in the MR clutch and brake generates heat, increasing the fluid temperature during the operation. However, to avoid overheating, we proposed a mode of operation for over-ground walking aiming to minimize the heat generation on the MR clutch and brake. Other heat sources inside the actuator are the coils, which generate the magnetic fields for the MR fluid, bearings, EC motor and harmonic drive. Results show that the MR fluid of the brake can reach up to 31°C after a 6.0 km walk, so the AMRK can be used for the proposed function without risks of fluid degradation or discomfort for the user.
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Oladokun, Olagoke, Bemgba Bevan Nyakuma, and Arshad Ahmad. "Fundamental Theories and Kinetic Models for the Pyrolysis of Lignocellulosic Biomass Wastes." In Handbook of Research on Resource Management for Pollution and Waste Treatment, 123–51. IGI Global, 2020. http://dx.doi.org/10.4018/978-1-7998-0369-0.ch007.
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Biomass agricultural waste has a great potential for meeting part of the world energy need and is completely environmentally friendly. One conversion method is thermochemical processes and specifically, pyrolysis. Pyrolysis converts the lignocellulose waste to fuel and essential chemicals into three products: biogas, bio-oil, and biochar. However, performance issues limit the potential of lignocellulose pyrolysis such as design and operation of pyrolysis reactor for effective heat transfer from the heat source to the biomass feedstock. Therefore, this study presents the necessary tools for pyrolysis scientists and engineers in determining the optimal operation and design of lignocellulose agricultural waste pyrolysis. The tools consist of mathematical equations that govern the lignocellulose kinetics (model and model-free) and pyrolysis reactor macro and micro models. A practical model for hydrogen production from pyrolysis bio oil solidifies the viability of biomass as an energy source.
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"1Chapter 2 Optically Thin and Thick Limits for Radiative Transfer in Participating Media." In Thermal Radiation Heat Transfer, 611–48. CRC Press, 2010. http://dx.doi.org/10.1201/9781439894552-19.
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Beris, Antony N., and Brian J. Edwards. "Non-Conventional Transport Phenomena." In Thermodynamics of Flowing Systems: with Internal Microstructure. Oxford University Press, 1994. http://dx.doi.org/10.1093/oso/9780195076943.003.0015.
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In this chapter, we wish to exploit the availability of the bracket formalism in the description of complex, non-conventional transport phenomena. In the first section, §10.1, we analyze relaxational phenomena in heat and mass transfer. The next section, §10.2, includes the description of phase transitions in inhomogeneous media. The last section, §10.3, contains a first effort to describe inertial effects in viscoelasticity. These problems have rarely been considered in the past, and when they have it has always been from a phenomenological perspective. We explore the availability of the bracket formalism here to provide a more systematic basis for these systems than has heretofore been available, and hence we characterize the models in this chapter as semi-phenomenological. The basic approach that we use is to first establish an appropriate internal variable for the system in consideration, and then to divine an appropriate Hamil-tonian which does, in some limits, produce available phenomenological models. (The latter step indicates why we characterize the models deve-loped in this chapter as “semi-phenomenological.”) As we shall see, describing the models on this more fundamental basis clears up a number of inconsistencies, as well as extending their range of validity without unduly sacrificing their simplicity. In most engineering applications of heat and mass transfer, the simple linear constitutive relations of (6.4-12) are adequate in order to describe the respective transport processes. A couple of very simple examples are the heat flux, when the affinity is the temperature gradient (giving Fourier's law of heat conduction), and the mass diffusion flux, when the affinity is the chemical potential (giving Pick's law of mass diffusion). The importance of such relationships in engineering practice cannot be overestimated. The validity of the linearized equations is generally established by steady-state experiments, so the question that naturally arises is whether or not the same constitutive relationship will hold for transient phenomena. This question cannot be answered as long as only steady-state experiments are performed. From physical considerations alone, it is obvious that the linearized constitutive relationships cannot be complete, in and of themselves.
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Kobayashi, Shiro, Soo-Ik Oh, and Taylan Altan. "Analysis and Technology in Metal Forming." In Metal Forming and the Finite-Element Method. Oxford University Press, 1989. http://dx.doi.org/10.1093/oso/9780195044027.003.0006.
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The design, control, and optimization of forming processes require (1) analytical knowledge regarding metal flow, stresses, and heat transfer, as well as (2) technological information related to lubrication, heating and cooling techniques, material handling, die design and manufacture, and forming equipment. The purpose of using analysis in metal forming is to investigate the mechanics of plastic deformation processes, with the following major objectives. • Establishing the kinematic relationships (shape, velocities, strain-rates, and strains) between the undeformed part (billet, blank, or preform) and the deformed part (product); i.e., predicting metal flow during the forming operation. This objective includes the prediction of temperatures and heat transfer, since these variables greatly influence local metal-flow conditions. • Establishing the limits of formability or producibility; i.e., determining whether it is possible to perform the forming operation without causing any surface or internal defects (cracks or folds) in the deforming material. • Predicting the stresses, the forces, and the energy necessary to carry out the forming operation. This information is necessary for tool design and for selecting the appropriate equipment, with adequate force and energy capabilities, to perform the forming operation. Thus, the mechanics of deformation provides the means for determining how the metal flows, how the desired geometry can be obtained by plastic deformation, and what the expected mechanical properties of the produced part are. For understanding the variables of a metal-forming process, it is best to consider the process as a system, as illustrated in Fig. 2.1 in Chap. 2. The interaction of most significant variables in metal forming are shown, in a simplified manner, in Fig. 3.1. It is seen that for a given billet or blank material and part geometry, the speed of deformation influences strain-rate and flow stress. Deformation speed, part geometry, and die temperature influence the temperature distribution in the formed part. Finally, flow stress, friction, and part geometry determine metal flow, forming load, and forming energy. In steady-state flow (kinematically), the velocity field remains unchanged, as is the case in the extrusion process; in nonsteadystate flow, the velocity field changes continuously with time, as is the case in upset forging.
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Nur Parin, Fatma. "Retrospective, Perspective and Prospective of B-Complex Vitamins: Encapsulation of Vitamins and Release from Vitamin-Loaded Polymers." In B-Complex Vitamins - Sources, Intakes and Novel Applications [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.99284.
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Vitamins are regarded as vital nutrients because, when combined, they performed hundreds of functions in the body. They strengthen bones, heal wounds, and boost your immune system. In addition, they transform food into energy and heal cellular damage. In this regard, B-complex vitamins, such as thiamine, riboflavin, and niacin are soluble vitamins that serve as coenzymes in energy metabolism enzymatic activities which building blocks of a healthy body. However, B-complex vitamins are sensitive to light, pH conditions, and temperature. Consequently, they must be encapsulated before they may be used in pharmaceuticals. Recently, it is mainly focused on reducing drug degradation or loss, increase drug bioavailability, limit adverse effects, and improve drug accumulation in the targeted location. To maintain optimum bioavailability during a defined term of therapy, the fraction of drug dosage released from a controlled release product must be significant enough to adjust for the quantity of active drug metabolized and/or eliminated from the body over the same period. Drug release systems also aim to increase the effectiveness of the drug and treat the damaged area. In this chapter, it is aimed to study the production of the vitamin-loaded polymer systems in various forms, such as micro/nanoparticles, micelle, hydrogel, liposome, and nanofiber, as well as release studies in pharmaceutical and biomedical applications.
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Kobayashi, Shiro, Soo-Ik Oh, and Taylan Altan. "Metal-Forming Processes." In Metal Forming and the Finite-Element Method. Oxford University Press, 1989. http://dx.doi.org/10.1093/oso/9780195044027.003.0005.
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In metal forming, an initially simple part—a billet or sheet blank, for example—is plastically deformed between tools (or dies) to obtain the desired final configuration. Thus, a simple part geometry is transformed into a complex one, in a process whereby the tools “store” the desired geometry and impart pressure on the deforming material through the tool-material interface. The physical phenomena constituting a forming operation are difficult to express with quantitative relationships. The metal flow, the friction at the tool-material interface, the heat generation and transfer during plastic flow, and the relationships between microstructure/properties and process conditions are difficult to predict and analyze. Often, in producing discrete parts, several forming operations (preforming) are required to transform the initial “simple” geometry into a “complex” geometry, without causing material failure or degrading material properties. Consequently, the most significant objective of any method of analysis is to assist the forming engineer in the design of forming and/or preforming sequences. For a given operation (preforming or finish-forming), such design essentially consists of (1) establishing the kinematic relationships (shape, velocities, strain-rates, strains) between the deformed and undeformed part, i.e., predicting metal flow; (2) establishing the limits of formability or producibility, i.e., determining whether it is possible to form the part without surface or internal defects; and (3) predicting the forces and stresses necessary to execute the forming operation so that tooling and equipment can be designed or selected. For the understanding and quantitative design and optimization of metal-forming operations it is useful (a) to consider a metal forming process as a system and (b) to classify these processes in a systematic way. A metal-forming system comprises all the input variables relating the billet or blank (geometry and material), the tooling (geometry and material), the conditions at the tool-material interface, the mechanics of plastic deformation, the equipment used, the characteristics of the final product, and finally the plant environment in which the process is being conducted. Such a system is illustrated in Fig. 2.1, using impression die forging as an example.
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İsmail Tosun, Yıldırım. "Adsorption of Heavy Metals by Microwave Activated Shale/Asphaltite Char/Zeolite Granule Composts from Hazardous Sludges and Industrial Waste Slurries." In Clay Science and Technology [Working Title]. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.94404.
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There is a great concern about surface water pollution with high level mercury, lead (Pb) over 10 mg/l, 30 mg/l to the fishing lakes and streams in Şırnak Province even contaminating fresh water fishing and poisonening of human by merury and lead in thr region. The chromium over 50 mg/l from industrial seepages was disposed to lakes and streams in our country. There is a great green concern prompting land in order to control acidic mine waters so that the research study controlled and avoided hazardous metal limits of residual stream contaminants of heavy metals by sorption local clay and zeolite compost. The contamination rate changes to those based on seepage concentrations and wetness. The stream amendments, such as shale char carbonized from Şırnak asphaltite containing 52–60% shale activated by acid washing under microwave radiation as geo material composted for waste water treatment should control contaminated effluents concentration. The field studies to evaluate the stability of heavy metal concentrations and salts were scarce. The initial objective of this study was to determine the effects of seepage flow to surface and groundwater from the industrial discharge. In this study, important investigations have been made on composite granules production with Şırnak shale char and zeolite feed in order to activated in microwave oven 2 M HCl dissolution. The compost sorbent for high level heavy metal sorption in laboratory water packed bed column adsorption compost system. However, the results of filled packed bed zeolite yield high metal transfer to compost. Due to the complex chemistry of shale pores, and high porosity, heat conduction improved in the microwave sorption depended on granule size decreased. The other heavy metal sorption distribution was changed in the activation dependent on the microwave heating power.
Conference papers on the topic "Heat transfer limit"
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Lesin, S., A. Baron, H. Branover, and Jose C. Merchuk. "DIRECT CONTACT BOILING AT THE SUPERHEAT LIMIT." In International Heat Transfer Conference 10. Connecticut: Begellhouse, 1994. http://dx.doi.org/10.1615/ihtc10.580.
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Ku, Jentung, Laura Ottenstein, Paul Rogers, and Kwok Cheung. "Investigation of Capillary Limit in a Loop Heat Pipe." In International Heat Transfer Conference 12. Connecticut: Begellhouse, 2002. http://dx.doi.org/10.1615/ihtc12.2770.
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Flik, Markus I., and Kunio Hijikata. "APPROXIMATE THERMAL PACKAGING LIMIT FOR HYBRID SUPERCONDUCTOR-SEMICONDUCTOR ELECTRONIC CIRCUITS." In International Heat Transfer Conference 9. Connecticut: Begellhouse, 1990. http://dx.doi.org/10.1615/ihtc9.500.
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Kadoguchi, K., T. Fukano, and Y. Emi. "OPERATING LIMIT OF A CLOSED TWO-PHASE THERMOSYPHON WITH A BINARY MIXTURE." In International Heat Transfer Conference 10. Connecticut: Begellhouse, 1994. http://dx.doi.org/10.1615/ihtc10.1270.
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Ji, Yulong, Chao Chang, Gen Li, and Hongbin Ma. "An Investigation on Operating Limit of an Oscillating Heat Pipe." In The 15th International Heat Transfer Conference. Connecticut: Begellhouse, 2014. http://dx.doi.org/10.1615/ihtc15.hpp.009442.
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Pratt, David M., Won Soon Chang, and Kevin P. Hallinan. "EFFECTS OF THERMO CAPILLARY STRESSES ON THE CAPILLARY LIMIT OF CAPILLARY-DRIVEN HEAT TRANSFER DEVICES." In International Heat Transfer Conference 11. Connecticut: Begellhouse, 1998. http://dx.doi.org/10.1615/ihtc11.110.
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Yuksel, Anil, Michael Cullinan, and Jayathi Murthy. "Thermal Energy Transport Below the Diffraction Limit in Close-Packed Metal Nanoparticles." In ASME 2017 Heat Transfer Summer Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/ht2017-4968.
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Fabrication of micro and nanoscale electronic components has become increasingly demanding due to device and interconnect scaling combined with advanced packaging and assembly for electronic, aerospace and medical applications. Recent advances in additive manufacturing have made it possible to fabricate microscale, 3D interconnect structures but heat transfer during the fabrication process is one of the most important phenomena influencing the reliable manufacturing of these interconnect structures. In this study, optical absorption and scattering by three-dimensional (3D) nanoparticle packings are investigated to gain insight into micro/nano heat transport within the nanoparticles. Because drying of colloidal solutions creates different configurations of nanoparticles, the plasmonic coupling in three different copper nanoparticle packing configurations were investigated: simple cubic (SC), face-centered cubic (FCC) and hexagonal close packing (HCP). Single-scatter albedo (ω) was analyzed as a function of nanoparticle size, packing density, and configuration to assess effect for thermo-optical properties and plasmonic coupling of the Cu nanoparticles within the nanoparticle packings. This analysis provides insight into plasmonically enhanced absorption in copper nanoparticle particles and its consequences for laser heating of nanoparticle assemblies.
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Ju, Yiguang. "Theoretical Analysis of Flame Propagation in Meso and Microscale Channels." In ASME 2003 Heat Transfer Summer Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/ht2003-47516.
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Extinction and flame propagation in a meso and microscale channels are investigated analytically. Emphasis was paid to the coupling of wall heat loss, wall preheating, external heat loss and chemical reaction. The results showed that, wall thermal properties, channel width and flow velocity have dramatic effects on the flame propagation and lead to multiple flame regimes and extinction limits. With the decrease of channel width, flame reaches its first quenching limit, the so called critical quenching distance. However, with a further decrease of channel width, the results show that there exists a slow burning flame. With the increase of wall heat loss the speed of the slow burning flame slightly decreases and eventually reaches its second burning limit. With the change of the flow velocity, the results show that sub-limit flame can only exist at flow velocity larger than a critical value. At moderate flow velocity, flame speed increases with the increase of flow speed. At very large flow velocity, flame will be blown off. The above results are confirmed from the recent experimental data.
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Ju, Yiguang, Kenichi Takita, Masuya Goro, Fengshan Liu, and Hongsheng Guo. "ANALYSES OF EXTINCTION AND FLAMMABILITY LIMIT OF STRETCHED PREMIXED FLAMES USING THE STATISTICAL NARROW-BAND MODEL." In International Heat Transfer Conference 11. Connecticut: Begellhouse, 1998. http://dx.doi.org/10.1615/ihtc11.4280.
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Feng, Qijing, and Klaus Johannsen. "THE HIGH-TEMPERATURE LIMIT OF THE TRANSITION BOILING REGIME FOR WATER IN VERTICAL UPFLOW AT MEDIUM PRESSURE." In International Heat Transfer Conference 9. Connecticut: Begellhouse, 1990. http://dx.doi.org/10.1615/ihtc9.4300.
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