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1
Liu, L. H., i S. X. Chu. "On the Entropy Generation Formula of Radiation Heat Transfer Processes". Journal of Heat Transfer 128, nr 5 (21.10.2005): 504–6. http://dx.doi.org/10.1115/1.2190695.
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Because thermal radiation is a long-range phenomenon, the local radiative heat flux is dependent on the temperature distribution of the entire enclosure under consideration and is not determined by the local temperature gradient. In the community of heat transfer, traditionally, the conduction-type formula of entropy generation rate is used to calculate the entropy generation rate of radiation heat transfer. In the present study, three counterexamples are considered. The discrete ordinates method is employed to solve the radiative transfer equation and then solve the radiative entropy generation rate. The results show that the traditional formulas of entropy generation rate for heat transfer generally cannot be used to calculate the local entropy generation rate of radiation heat transfer. Only in optically extremely thick situations, the traditional formula of entropy generation rate for heat transfer can be approximately used to calculate the local entropy generation rate of radiation heat transfer.
2
Zhang, Chong, Zhongnong Zhang i Chun Lou. "Thermodynamic Irreversibility Analysis of Thermal Radiation in Coal-Fired Furnace: Effect of Coal Ash Deposits". Materials 16, nr 2 (13.01.2023): 799. http://dx.doi.org/10.3390/ma16020799.
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In this paper, a three-dimensional (3-D) high-temperature furnace filled with a gas-solid medium was investigated, and the radiative transfer equation and the radiative entropy transfer equation in the chamber were applied in order to analyze the effect of coal deposits on thermal radiation. The heat flux on the walls of the furnace and the entropy generation rate were determined due to the irreversibility of the radiative heat transfer process in the furnace. Furthermore, the effect of ash deposits on the wall surface on the irreversibility of the radiation heat transfer process was investigated. The numerical results show that when burning bituminous and sub-bituminous coal, ash deposits in the furnace led to a 48.2% and 63.2% decrease in wall radiative heat flux and a 9.1% and 12.4% decrease in the radiative entropy rate, respectively. The ash deposits also led to an increase in the entropy generation number and a decrease in the thermodynamic efficiency of the radiative heat transfer process in the furnace.
3
Saleem, M., M. A. Hossain, Suvash C. Saha i Y. T. Gu. "Heat Transfer Analysis of Viscous Incompressible Fluid by Combined Natural Convection and Radiation in an Open Cavity". Mathematical Problems in Engineering 2014 (2014): 1–14. http://dx.doi.org/10.1155/2014/412480.
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The effect of radiation on natural convection of Newtonian fluid contained in an open cavity is investigated in this study. The governing partial differential equations are solved numerically using the Alternate Direct Implicit method together with the Successive Overrelaxation method. The study is focused on studying the flow pattern and the convective and radiative heat transfer rates are studied for different values of radiation parameters, namely, the optical thickness of the fluid, scattering albedo, and the Planck number. It was found that, in the optically thin limit, an increase in the optical thickness of the fluid raises the temperature and radiation heat transfer of the fluid. However, a further increase in the optical thickness decreases the radiative heat transfer rate due to increase in the energy level of the fluid, which ultimately reduces the total heat transfer rate within the fluid.
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Budaev, Bair V., i David B. Bogy. "The role of EM wave polarization on radiative heat transfer across a nanoscale gap". Journal of Applied Physics 132, nr 5 (7.08.2022): 054903. http://dx.doi.org/10.1063/5.0094382.
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This work presents a novel study of radiative heat transfer between closely separated plates based on an extension of Planck’s spectrum of thermal radiations to systems with a steady heat flux. This extension together with electromagnetic wave theory is chosen specifically to avoid the commonly used so-called fluctuation dissipation theory, which is also limited to equilibrium systems. The spectrum of thermal radiation with a heat flux is described by the introduction of an analog of a chemical potential, which creates a bias toward the direction of heat transfer. This is the first comprehensive study of radiative heat transfer based on the generalization of Planck’s spectrum for systems with a heat flux, which eliminates contradictions arising when a heat flux is described in terms of the laws limited to equilibrium systems. The total heat flux is split into fluxes carried by waves with different frequencies, directions of propagation, and polarizations. This simplifies the analysis because due to the stochastic independence, the energy fluxes of such waves are additive, and this also reveals that the heat carrying capacity of radiation with the parallel polarization is significantly higher than that of the perpendicularly polarized radiation. This suggests that the rate of radiative heat transfer may be noticeably increased by the control of the polarization of thermal radiation.
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Bayazitoglu, Y., i P. V. R. Suryanarayana. "Transient Radiative Heat Transfer From a Sphere Surrounded by a Participating Medium". Journal of Heat Transfer 111, nr 3 (1.08.1989): 713–18. http://dx.doi.org/10.1115/1.3250741.
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Transient radiative cooling of a solid or liquid sphere in space, surrounded by a radiatively participating vapor cloud, is considered. A quasi-steady assumption is applied to the radiation transfer in the medium, with the unsteadiness being retained at the inner spherical boundary. The problem is solved by applying the third-order (P3) spherical harmonics approximation to the radiative transfer equation for the participating cloud, and a finite difference scheme for transient conduction in the sphere. In general, the presence of a participating medium decreases the cooling rate of the sphere, and cooling curves are presented to show this effect. Effective emissivity of the surface in the presence of a surrounding medium is evaluated, and an approximate explicit equation is given.
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Nguyen, Phuc-Danh, Huu-Tri Nguyen, Pascale Domingo, Luc Vervisch, Gabriel Mosca, Moncef Gazdallah, Paul Lybaert i Véronique Feldheim. "Flameless combustion of low calorific value gases, experiments, and simulations with advanced radiative heat transfer modeling". Physics of Fluids 34, nr 4 (kwiecień 2022): 045123. http://dx.doi.org/10.1063/5.0087077.
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Thermal radiation is the dominant mode of heat transfer in many combustion systems, and in typical flameless furnaces, it can represent up to 80% of the total heat transfer. Accurate modeling of radiative heat transfer is, thus, crucial in the design of these large-scale combustion systems. Thermal radiation impacts the thermochemistry, thereby the energy efficiency and the temperature sensitive species prediction, such as NOx and soot. The requirement to accurately describe the spectral dependence of gaseous radiative properties of combustion products interacts with the modeling of finite rate chemistry effects and conjugates heat transfer and turbulence. Additionally, because of the multiple injection of fuels and/or oxidizers of various compositions, case-specific radiative properties' expressions are required. Along these lines, a comprehensive modeling to couple radiation and combustion in reacting flows is attempted and applied to the simulation of flameless combustion. Radiation is modeled using the spectral line-based weighted-sum-of-gray-gases approach to calculate gaseous radiative properties of combustion products using the correlation of the line-by-line spectra of H2O and CO2. The emissivity weights and absorption coefficients were optimized for a range of optical thicknesses and temperatures encountered in the considered furnace. Efforts were also made on the development of a reliable and detailed experimental dataset for validation. Measurements are performed in a low calorific value syngas furnace operating under flameless combustion. This test rig features a thermal charge which can extract about 60% of combustion heat release via 80% of radiative heat transfer, making it of special interest for modeling validation. The comparison between the simulation and the experiment demonstrated a fair prediction of heat transfer, energy balance, temperature, and chemical species fields.
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Hu, Xuanyu, Bastian Gundlach, Ingo von Borstel, Jürgen Blum i Xian Shi. "Effect of radiative heat transfer in porous comet nuclei: case study of 67P/Churyumov-Gerasimenko". Astronomy & Astrophysics 630 (20.09.2019): A5. http://dx.doi.org/10.1051/0004-6361/201834631.
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Context. Radiative heat transfer occurs in a porous medium, such as regolith on planetary bodies. Radiation enhances the efficiency of heat transport through the subsurface, effecting a strong temperature dependence of thermal conductivity. However, this effect has been omitted in many studies of comet 67P/Churyumov-Gerasimenko (67P). Aims. We concisely review the method for characterizing radiative heat transfer and present a generic treatment in thermal modeling. In particular, we study the impact of radiative heat transfer on 67P subject to both diurnal and seasonal variations of insolation. Methods. We adapted a numerical model based on the Crank–Nicolson scheme to estimate the subsurface temperatures and water production rate of 67P, where conductivity may vary with depth. Results. Radiative heat transfer is efficient during the day near the surface but it dicreases at night, which means that more energy is deposited underneath the diurnal thermal skin. The effect increases with pore size and accordingly, with the size of the constituent aggregates of the nucleus. It also intensifies with decreasing heliocentric distance. Close to perihelion, within 2 au, for example, radiation may raise the temperature by more than 20 K at a depth of 5 cm, compared with a purely conductive nucleus. If the nucleus is desiccated and composed of centimeter-sized aggregates, the subsurface at 0.5 m may be warmed to above 180 K. Conclusions. Radiative heat transfer is not negligible if the nucleus of 67P consists of aggregates that measure millimeters or larger. To distinguish its role and ascertain the pore size of the subsurface, measurements of temperatures from a depth of ~1 cm down to several decimeters are most diagnostic. The water production rate of the nucleus, on the other hand, does not provide a useful constraint.
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Tong, T. W., i S. B. Sathe. "Heat Transfer Characteristics of Porous Radiant Burners". Journal of Heat Transfer 113, nr 2 (1.05.1991): 423–28. http://dx.doi.org/10.1115/1.2910578.
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This paper reports a numerical study of the heat transfer characteristics of porous radiant burners, which have significant advantages over conventional burners. The heat transfer characteristics are investigated using a one-dimensional conduction, convection, and radiation model. The combustion phenomenon is modeled as spatially dependent heat generation. Nonlocal thermal equilibrium between the gas and solid phases is accounted for by using separate energy equations for the two phases. The solid matrix is assumed to emit, absorb, and scatter radiant energy. The spherical harmonics approximation is used to solve the radiative transfer equation. The coupled energy equations and the radiative transfer equations are solved using a numerical iterative procedure. The effects of the various factors on the performance of porous radiant burners are determined. It is revealed that for a given rate of heat generation, large optical thicknesses and high heat transfer coefficients between the solid and gas phases are desirable for maximizing radiant output. Also, low solid thermal conductivities, scattering albedos and flow velocities, and high inlet environment reflectivities produced high radiant output.
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Fernandez Arroiabe, Peru, Jon Iturralde Iñarga, Mercedes Gómez de Arteche Botas, Susana López Pérez, Eduardo Ubieta Astigarraga, Iñigo Unamuno, Manex Martinez-Agirre i M. Mounir Bou-Ali. "Design of a radiative heat recuperator for steel processes". MATEC Web of Conferences 330 (2020): 01034. http://dx.doi.org/10.1051/matecconf/202033001034.
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In recent years, there has been an increasing interest in the recovery of the waste heat of steel and glass processes. This work proposes a numerical study of a waste heat exchanger system for steel production processes. The radiative energy is transferred to a commercial oil, which can be used to produce electricity. The behavior of the recuperator is analysed using a 3D numerical model, considering the constrains of a real production plant. The influence of the radiation properties of the materials on the temperature and heat transfer rate are also examined. The results show that the absorptivity of the tubes influences significantly the absorbed waste heat. Furthermore, heterogeneous mass flow distribution should be applied to optimize the total heat transfer rate.
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Vyas, Prashant Dineshbhai, Harish C. Thakur i Veera P. Darji. "Nonlinear analysis of convective-radiative longitudinal fin of various profiles". International Journal of Numerical Methods for Heat & Fluid Flow 30, nr 6 (29.05.2019): 3065–82. http://dx.doi.org/10.1108/hff-08-2018-0444.
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Purpose This paper aims to study nonlinear heat transfer through a longitudinal fin of three different profiles. Design/methodology/approach A truly meshfree method is used to undertake a nonlinear analysis to predict temperature distribution and heat-transfer rate. Findings A longitudinal fin of three different profiles, such as rectangular, triangular and concave parabolic, are analyzed. Temperature variation, along with the fin length and rate of heat transfer in steady state, under convective and convective-radiative environments has been demonstrated and explained. Moving least square (MLS) approximants are used to approximate the unknown function of temperature T(x) with Th(x). Essential boundary conditions are imposed using the penalty method. An iterative predictor–corrector scheme is used to handle nonlinearity. Research limitations/implications Modelling fin in a convective-radiative environment removes the assumption of no radiation condition. It also allows to vary convective heat-transfer coefficient and predict the closer values to the real problems for the corresponding fin surfaces. Originality/value The meshless local Petrov–Galerkin method can solve nonlinear fin problems and predict an accurate solution.
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Esfahani, Javad, i Ali Abdolabadi. "Effect of char layer on transient thermal oxidative degradation of polyethylene". Thermal Science 11, nr 2 (2007): 23–36. http://dx.doi.org/10.2298/tsci0702023e.
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A transient one dimensional model has been presented to simulate degradation and gasification of polyethylene, in early stage of fire growth. In the present model effect of oxygen on degradation and rate of polymer gasification while the sample is subjected to an external radiative heat source is numerically investigated. This model includes different mechanism, which affect the degradation process, such as in depth thermal oxidative decomposition, in depth absorption of radiation, heat transfer, volatiles advection in solid phase and convective heat transfer on surface. Also effects of radiative parameters, due to formation of char layer such as surface reflectivity and absorptivity on thermal degradation of polyethylene are investigated. The results for 40 kW/m2 heat source are reported and yielded realistic results, comparing to the published experimental data. The results show that an increase in oxygen concentration leads to considerable increase in gasification rate and also leads to sharp increase of surface temperature. .
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Ben-Mansour, Rached, Mohamed A. Habib i Pervez Ahmed. "The Effect of Radiation on Oxy-Fuel Combustion Characteristics in Microchannels". Applied Mechanics and Materials 302 (luty 2013): 49–54. http://dx.doi.org/10.4028/www.scientific.net/amm.302.49.
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The importance of thermal radiation in heat transfer mechanism in many micro combustion systems has been well identified in the past few years. There is currently lack of quantitative understanding on the radiation heat transfer in relatively small scale laminar diffusion flames in microchannels. In the present study a two dimensional model is considered to investigate the effects of radiation on oxy-fuel combustion characteristics in microchannels. The discrete-ordinates radiation model is used for the study. It is observed that excluding radiation model results in the over-prediction of combustion temperatures in the micro-reactor. It has also been observed that the overall reaction rate and its peak value increase when accounting for radiative heat transfer, despite the decrease in temperature caused by radiation. Therefore, it is important to incorporate a radiation heat transfer model in combustion micro-systems in order to predict their characteristics accurately.
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Wang, Tianxiang, Yinan Qiu, Gang Lei, Jinjin Zhang, Yonghua Huang i Guang Yang. "Transient characteristics of coupled thermal radiation and natural convection in a three-dimensional cylindrical cavity containing a heated plate". Thermal Science, nr 00 (2022): 135. http://dx.doi.org/10.2298/tsci220523135w.
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In this study, a numerical study of transient combined natural convection and surface radiation in a cylindrical cavity with a heated plate placed inside is carried out using the open-source platform OpenFOAM. The effects of the Rayleigh number (105 ? Ra ? 107), inclination angle (0? ? ? ? 90?), and surface emissivity (0 ? ? ? 1) on the velocity components, temperature field, and Nusselt number are investigated in detail. Results show that the Rayleigh number has a greater effect on the radiative heat transfer than on natural convection. Radiative heat transfer increases monotonously with the increase of surface emissivity, and its contribution could be over 50% of the total heat transfer rate. The inclination angle of the plate affects the flow structure, but the difference in total Nusselt number is less than 10% for various inclination angles. Results in this study provide insights into the transient characteristics of coupled thermal radiation and natural convection in a three-dimensional cavity and will guide the optimal design of related devices.
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Collins, M., S. J. Harrison, D. Naylor i P. H. Oosthuizen. "Heat Transfer From an Isothermal Vertical Surface With Adjacent Heated Horizontal Louvers: Numerical Analysis". Journal of Heat Transfer 124, nr 6 (1.12.2002): 1072–77. http://dx.doi.org/10.1115/1.1481357.
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The present study examines the influence of heated, horizontal, and rotatable louvers on the convective and radiative heat transfer from a heated or cooled vertical isothermal surface. The system represents an irradiated Venetian blind adjacent to the indoor surface of a window. Detailed heat transfer results were obtained using a steady, laminar, two-dimensional, conjugate conduction/convection/radiation finite element model for two window temperatures (warm and cool compared to ambient) and irradiation levels, two louver to surface spacings, and three louver angles. The effect of the heated louvers on the heat transfer rate from the surface has been demonstrated.
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Zhao, J. M., i L. H. Liu. "Spectral Element Approach for Coupled Radiative and Conductive Heat Transfer in Semitransparent Medium". Journal of Heat Transfer 129, nr 10 (5.02.2007): 1417–24. http://dx.doi.org/10.1115/1.2755061.
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A spectral element method is presented to solve coupled radiative and conductive heat transfer problems in multidimensional semitransparent medium. The solution of radiative energy source is based on a second order radiative transfer equation. Both the second order radiative transfer equation and the heat diffusion equation are discretized by spectral element approach. Four various test problems are taken as examples to verify the performance of the spectral element method. The h-and the p-convergence characteristics of the spectral element method are studied. The convergence rate of p refinement for different values of Planck number follows the exponential law and is superior to that of h refinement. The spectral element method has good property to tolerate skewed meshes. The predicted dimensionless temperature distributions determined by the spectral element method agree well with the results in references. The presented method is very effective to solve coupled radiative and conductive heat transfer in semitransparent medium with complex configurations and demands little on the quality of mesh.
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Singh, Khilap, i Manoj Kumar. "Influence of Chemical Reaction on Heat and Mass Transfer Flow of a Micropolar Fluid over a Permeable Channel with Radiation and Heat Generation". Journal of Thermodynamics 2016 (7.12.2016): 1–10. http://dx.doi.org/10.1155/2016/8307980.
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The effects of chemical reaction on heat and mass transfer flow of a micropolar fluid in a permeable channel with heat generation and thermal radiation is studied. The Rosseland approximations are used to describe the radiative heat flux in the energy equation. The model contains nonlinear coupled partial differential equations which have been transformed into ordinary differential equation by using the similarity variables. The relevant nonlinear equations have been solved by Runge-Kutta-Fehlberg fourth fifth-order method with shooting technique. The physical significance of interesting parameters on the flow and heat transfer characteristics as well as the local skin friction coefficient, wall couple stress, and the heat transfer rate are thoroughly examined.
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Mungekar, Hemant P., i Arvind Atreya. "Flame Radiation and Soot Emission From Partially Premixed Methane Counterflow Flames". Journal of Heat Transfer 128, nr 4 (23.10.2005): 361–67. http://dx.doi.org/10.1115/1.2165204.
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Motivated by heat transfer and environmental concerns, a study of flame radiation and soot particulate emission is reported for partial premixing in low strain-rate (<20s−1) methane counterflow flames. Temperature, OH concentration, and soot volume fraction distributions were measured along the stagnation streamline for progressive addition of oxygen to methane. These measurements along with an optically thin model for soot and gas radiation were used to study the effect of partial premixing on flame radiation and soot emission. It was found that with progressive partial premixing, the peak soot loading and the thickness of the soot zone first decreased and then increased, and while the gas radiation was enhanced, the gas radiative fraction (gas radiation per unit chemical energy release) showed a systematic decrease. The net radiative fraction (soot+gas), however, first decreased and then increased. A configuration with the soot zone spatially entrapped between the premixed and non-premixed reaction zones was experimentally found. This flame configuration has the potential to enhance radiative heat transfer while simultaneously reducing soot and NOx emissions.
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Palesskiy, F. S. "Numerical Study of Combustion Regimes and Heat Radiation of Cylindrical Porous Burner". Key Engineering Materials 685 (luty 2016): 94–98. http://dx.doi.org/10.4028/www.scientific.net/kem.685.94.
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Temperature and radiative characteristics of different regimes of premixed gas combustion in porous cylindrical burner are investigated numerically. Two-temperature thermal diffusion model with radiative heat transfer and external radiative heat losses described in the framework of Eddington model is applied. It is found that two different combustion regimes can be realized under the same mixture equivalence ratio and flow rate depends on ignition conditions. It is shown that total radiative heat flux from the external surface of the burner and burner’s radiative efficiency strongly depend on the combustion regime.
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Sultana Jahan, M. Ferdows, Md. Shamshuddin i Khairy Zaimi. "Radiative Mixed Convection Flow Over a Moving Needle Saturated with Non-Isothermal Hybrid Nanofluid". Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 88, nr 1 (11.10.2021): 81–93. http://dx.doi.org/10.37934/arfmts.88.1.8193.
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A steady incompressible boundary layer flow and heat transfer past on a moving thin needle saturated with hybrid nanofluid are investigated with the effects of solar radiation and viscous dissipation. The simulation is also influenced by the effects of thermophoresis and Brownian motion. We consider (Al2O3-Cu-water) as a hybrid nanofluid, where water is the base fluid and alumina and copper are the hybrid nanoparticles. By utilizing the technique of similarity transformations, we transformed the dimensional partial differential equations into dimensionless ordinary differential equations. Using the MAPLE software scheme, the transformed equations have been solved numerically. The graphical representation of different parameters including Mixed convection, Power-law exponent, Buoyancy ratio parameter, Eckert number are illustrated on velocity, temperature, the concentration of nanoparticles profiles and explained in detail. Skin friction coefficient, heat transfer rate, and mass transfer rate are also obtained numerically. With the presence of hybrid nanoparticles, the heat transfer rate is higher in all cases. In the temperature profile, we observed a reduction with the increasing values of the mixed convection parameter. It also revealed that greater values of volume fraction of nanoparticle (Cu) reduce the mass transfer rate but accelerates the heat transfer rate.
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Supramono, Dijan, Adithya Fernando Sitorus i Mohammad Nasikin. "Synergistic Effect on the Non-Oxygenated Fraction of Bio-Oil in Thermal Co-Pyrolysis of Biomass and Polypropylene at Low Heating Rate". Processes 8, nr 1 (2.01.2020): 57. http://dx.doi.org/10.3390/pr8010057.
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Biomass pyrolysis and polypropylene (PP) pyrolysis in a stirred tank reactor exhibited different heat transfer phenomena whereby heat transfer in biomass pyrolysis was driven predominantly by heat radiation and PP pyrolysis by heat convection. Therefore, co-pyrolysis could exhibit be expected to display various heat transfer phenomena depending on the feed composition. The objective of the present work was to determine how heat transfer, which was affected by feed composition, affected the yield and composition of the non-polar fraction. Analysis of heat transfer phenomena was based on the existence of two regimes in the previous research in which in regime 1 (the range of PP composition in the feeds is 0–40%), mass ejection from biomass particles occurred without biomass particle swelling, while in regime 2 (the range of PP composition in the feeds is 40–100%), mass ejection was preceded by biomass particle swelling. The co-pyrolysis was carried out in a stirred tank reactor with heating rate of 5 °C/min until 500 °C and using N2 gas as carrier gas. Temperature measurement was applied to pyrolysis fluid at the lower part of the reactor and small biomass spheres of 6 mm diameter to simulate heat transfer to biomass particles. The results indicate that in regime 1 convective and radiative heat transfers sparingly occurred and synergistic effect on the yield of non-oxygenated phase increased with increasing convective heat transfer at increasing %PP in feed. On the other hand, in regime 2, convective heat transfer was predominant with decreasing synergistic effect at increasing %PP in feed. The optimum PP composition in feed to reach maximum synergistic effect was 50%. Non-oxygenated phase portion in the reactor leading to the wax formation acted as donor of methyl and hydrogen radicals in the removal of oxygen to improve synergistic effect. Non-oxygenated fraction of bio-oil contained mostly methyl comprising about 53% by mole fraction, while commercial diesel contained mostly methylene comprising about 59% by mole fraction
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Mustafa, M., Junaid Ahmad Khan, T. Hayat i A. Alsaedi. "Numerical Solutions for Radiative Heat Transfer in Ferrofluid Flow due to a Rotating Disk: Tiwari and Das Model". International Journal of Nonlinear Sciences and Numerical Simulation 19, nr 1 (23.02.2018): 1–10. http://dx.doi.org/10.1515/ijnsns-2015-0196.
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AbstractIn this paper, we explore the von-Kármán infinite disk problem for the situation where ferrofluid resides in the space above the rotating disk. Furthermore, flow field is influenced by axial magnetic field. In this study, we treat water as the base fluid which consists of homogeneous suspensions of ${\rm{F}}{{\rm{e}}_{\rm{3}}}{{\rm{O}}_{\rm{4}}}$ ferromagnetic particles. The main motivation here is to resolve heat transfer problem in the existence of non-linear radiative heat transfer. With the aid of von-Kármán relations, the equations of fluid motion and heat transfer are changed into a set of self-similar differential equations. These equations are dealt by an implicit finite-difference method with high precision. The results reveal that wall heat transfer rate can be improved by increasing solid volume fraction of ferromagnetic particles. Drag coefficient at the disk and heat transfer rate are increased as the strength of Lorentz force is enhanced. Viscous dissipation effect has an important part in improving heart transfer process which is vital in some applications. The results demonstrate that cooling capability of magnetite–water nanofluid is much superior to the conventional coolants. An excellent correlation of present results with the previous published articles is found in the all the cases.
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Watanabe, Hirofumi, Shiori Iizuka, Takaya Kato, Masae Kanda i Satarou Yamaguchi. "Heat leak variation with the surface temperature of a cryogenic pipe of the superconducting power transmission". Journal of Physics: Conference Series 2323, nr 1 (1.08.2022): 012036. http://dx.doi.org/10.1088/1742-6596/2323/1/012036.
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Abstract The measurements of the heat leak variation with the surface temperature of a cryogenic pipe of the superconducting power transmission were performed in the range of 23.7 °C–36.4 °C. The cryogenic pipe which was an object of the present study was that used in the project of the superconducting DC power transmission conducted in Ishikari, Japan (Ishikari project). This cryogenic pipe has two inner pipes in one outer pipe, with a radiation shield used to conceal the inner pipe installing the cable from the outer pipe, which is at room temperature, to reduce heat leakage. A test pipe with the length of 12 m was used for the measurements. The liquid nitrogen was filled in the test pipe and the evaporated nitrogen gas rate was measured to obtain the heat leak. The heat leak to the inner pipe installing the cable was almost constant at around 0.04 W/m, whereas the heat leak to the other inner pipe used to return liquid nitrogen for circulation was around 1.3 W/m at surface temperatures ranging from 23.7 °C to 36.4 °C. The latter, with previous measurements, was well fitted by a function considering radiative heat transfer and conductive heat transfer. Portions of the radiative heat transfer and the conductive heat transfer were separated with this function. This information can be used to improve the cryogenic pipe in the future.
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Din, Zia Ud, Amir Ali, Sharif Ullah, Gul Zaman, Kamal Shah i Nabil Mlaiki. "Investigation of Heat Transfer from Convective and Radiative Stretching/Shrinking Rectangular Fins". Mathematical Problems in Engineering 2022 (15.04.2022): 1–10. http://dx.doi.org/10.1155/2022/1026698.
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We study the efficiency of shrinking/stretching radiative fins to improve heat transfer rate. To evaluate the competence of suggested fins, the influence of shrinking/stretching, thermogeometric parameters, surface temperature, convection conduction, radiation conduction, and Peclet number is investigated. The problem is solved numerically using a shooting method. To validate the numerical solution, the results are compared with the solution of a differential transform method. Temperature distribution increases with a rise in convection and radiation conduction parameters when Peclet number, stretching/shrinking, ambience, and surface temperatures are raised. The temperature of the fin’s tip increases as ambient temperature, Peclet number, and surface temperature increase, and decreases for enhanced radiation and convection conduction parameters. Radiation and convection cause the efficiency of the fin to increase for shrinking and decrease for stretching, which shows an important role in heat transfer analysis in mechanical engineering. The formulated model is also studied analytically, and the result is compared to numerical solution, which shows qualitatively good agreement.
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Waini, Iskandar, Najiyah Safwa Khashi’ie, Nurul Amira Zainal, Khairum Bin Hamzah, Abdul Rahman Mohd Kasim, Anuar Ishak i Ioan Pop. "Magnetic Dipole Effects on Radiative Flow of Hybrid Nanofluid Past a Shrinking Sheet". Symmetry 15, nr 7 (27.06.2023): 1318. http://dx.doi.org/10.3390/sym15071318.
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The boundary layer flows exhibit symmetrical characteristics. In such cases, the flow patterns and variables are symmetrical with respect to a particular axis or plane. This symmetry simplifies the analysis and enables the use of symmetry-based boundary conditions or simplifications in mathematical models. Therefore, by using these concepts, the governing equations of the radiative flow of a hybrid nanofluid past a stretched and shrunken surface with the effect of a magnetic dipole are examined in this paper. Here, we consider copper (Cu) and alumina (Al2O3) as hybrid nanoparticles and use water as a base fluid. The heat transfer rate is enhanced in the presence of hybrid nanoparticles. It is observed that the heat transfer rate is increased by 10.92% for the nanofluid, while it has a 15.13% increment for the hybrid nanofluid compared to the base fluid. Also, the results reveal that the non-uniqueness of the solutions exists for a certain suction and shrinking strength. Additionally, the ferrohydrodynamic interaction has the tendency to reduce the skin friction and the heat transfer coefficients for both solution branches. For the upper branch solutions, the heat transfer rate increased over a stretching sheet but decreased for the shrinking sheet in the presence of the radiation. It is confirmed by the temporal stability analysis that one of the solutions is stable and acceptable as time evolves.
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Gibbins, Goodwin, i Joanna D. Haigh. "Entropy Production Rates of the Climate". Journal of the Atmospheric Sciences 77, nr 10 (1.10.2020): 3551–66. http://dx.doi.org/10.1175/jas-d-19-0294.1.
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AbstractThere is ongoing interest in the global entropy production rate as a climate diagnostic and predictor, but progress has been limited by ambiguities in its definition; different conceptual boundaries of the climate system give rise to different internal production rates. Three viable options are described, estimated, and investigated here, two—the material and the total radiative (here “planetary”) entropy production rates—that are well established and a third that has only recently been considered but appears very promising. This new option is labeled the “transfer” entropy production rate and includes all irreversible processes that transfer heat within the climate, radiative, and material, but not those involved in the exchange of radiation with space. Estimates in three model climates put the material rate in the range 27–48 mW m−2 K−1, the transfer rate at 67–76 mW m−2 K−1, and the planetary rate at 1279–1312 mW m−2 K−1. The climate relevance of each rate is probed by calculating their responses to climate changes in a simple radiative–convective model. An increased greenhouse effect causes a significant increase in the material and transfer entropy production rates but has no direct impact on the planetary rate. When the same surface temperature increase is forced by changing the albedo instead, the material and transfer entropy production rates increase less dramatically and the planetary rate also registers an increase. This is pertinent to solar radiation management as it demonstrates the difficulty of reversing greenhouse gas–mediated climate changes by albedo alterations. It is argued that the transfer perspective has particular significance in the climate system and warrants increased prominence.
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Kairi, Rishi. "Free convection around a slender paraboloid of non-Newtonian fluid in a porous medium". Thermal Science 23, nr 5 Part B (2019): 3067–74. http://dx.doi.org/10.2298/tsci170809005k.
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This paper emphasizes the radiative heat transfer of non-Newtonian fluid on free convection around a slender paraboloid in a non-Darcy porous medium. The Ostwald-de Waele power-law representation is employed to express the non-Newto?nian behavior of fluid. Similarity analysis is applied to transform the set of non-dimensional PDE into set of ODE and then the resulting system of equations are solved by 4th order Runge-Kutta scheme with Shooting technique. The control of pertinent parameters on velocity, temperature and non-dimensional heat transfer rates are analyzed through graphical representation and explored in detail. It is evident that as the radius of the slender body increases the heat transfer coefficient decreases but the role of radiation on heat transfer rate getting reduced for all feasible values of the power-law index parameter.
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Bianchi, Daniele, Giuseppe Leccese, Francesco Nasuti, Marcello Onofri i Carmine Carmicino. "Modeling of High Density Polyethylene Regression Rate in the Simulation of Hybrid Rocket Flowfields". Aerospace 6, nr 8 (9.08.2019): 88. http://dx.doi.org/10.3390/aerospace6080088.
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Numerical analysis of hybrid rocket internal ballistics is carried out with a Reynolds-averaged Navier–Stokes solver integrated with a customized gas–surface interaction wall boundary condition and coupled with a radiation code based on the discrete transfer method. The fuel grain wall boundary condition is based on species, mass, and energy conservation equations coupled with thermal radiation exchange and finite-rate kinetics for fuel pyrolysis modeling. Fuel pyrolysis is governed by the convective and radiative heat flux reaching the surface and by the energy required for the propellant grain to heat up and pyrolyze. Attention is focused here on a set of static firings performed with a lab-scale GOX/HDPE motor working at relatively low oxidizer mass fluxes. A sensitivity analysis was carried out on the literature pyrolysis models for HDPE, to evaluate the possible role of the uncertainty of such models on the actual prediction of the regression rate. A reasonable agreement between the measured and computed averaged regression rate and chamber pressure was obtained, with a noticeable improvement with respect to solutions without including radiative energy exchange.
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Lebelo, Ramoshweu Solomon, i Kholeka Constance Moloi. "Transient Heat Analysis in a Two-Step Radiative Combustible Slab". Key Engineering Materials 872 (styczeń 2021): 15–19. http://dx.doi.org/10.4028/www.scientific.net/kem.872.15.
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In this article, analysis of heat transfer in a stockpile of reactive materials modelled in a rectangular slab is carried out. A two-step exothermic chemical reaction is assumed and the heat loss to the surrounding environment is by radiation. The ordinary differential equation (ODE) governing the problem is tackled numerically by Runge-Kutta Fehlberg (RKF45) method coupled with Shooting technique. The heat transfer analysis is simplified by investigation some kinetic parameters’ effects on the temperature of the combusting system. It was found out that some kinetic parameters raise the levels of the temperature by encouraging the exothermic chemical reaction, whereas some, reduce the levels of the temperature to slow down the heat transfer rate. The results are depicted graphically and discussed accordingly.
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Lebelo, Ramoshweu Solomon, i Kholeka Constance Moloi. "Transient Heat Analysis in a Two-Step Radiative Combustible Slab". Key Engineering Materials 872 (styczeń 2021): 15–19. http://dx.doi.org/10.4028/www.scientific.net/kem.872.15.
Pełny tekst źródłaStreszczenie:
In this article, analysis of heat transfer in a stockpile of reactive materials modelled in a rectangular slab is carried out. A two-step exothermic chemical reaction is assumed and the heat loss to the surrounding environment is by radiation. The ordinary differential equation (ODE) governing the problem is tackled numerically by Runge-Kutta Fehlberg (RKF45) method coupled with Shooting technique. The heat transfer analysis is simplified by investigation some kinetic parameters’ effects on the temperature of the combusting system. It was found out that some kinetic parameters raise the levels of the temperature by encouraging the exothermic chemical reaction, whereas some, reduce the levels of the temperature to slow down the heat transfer rate. The results are depicted graphically and discussed accordingly.
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hamid, Aamir, Abdul Hafeez i Masood Khan. "Characteristics of combined heat and mass transfer on mixed convection flow of Sisko fluid model: A numerical study". Modern Physics Letters B 34, nr 24 (6.06.2020): 2050255. http://dx.doi.org/10.1142/s0217984920502553.
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In this paper, the combined heat and mass transfer of mixed convection, non-similar Sisko fluid flow in the presence of a magnetic field is studied. The combined effects of thermal radiation and heat generation/absorption are examined for Sisko fluid flow via local non-similar method. For the radiative heat transfer, Rosseland approximation model is used. The governing partial differential equations of the present problem are transformed into a system of nonlinear ordinary differential equations by employing the Sparrow–Quack–Boerner local non-similarity method (LNM). The obtained equations are then numerically investigated by utilizing the bvp4c function in MATLAB. The impact of different supervising parameters on the velocity, temperature, skin friction and rate of heat transfer is performed graphically. It is observed that the velocity is more for a higher rate of the buoyancy force parameter while it is less for opposing buoyancy fluid. The thermal boundary layer thickness for the shear thickening fluids is smaller than the shear thinning fluids.
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Nelson, D. J., i B. D. Wood. "Evaporation Rate Model for a Natural Convection Glazed Collector/Regenerator". Journal of Solar Energy Engineering 112, nr 1 (1.02.1990): 51–57. http://dx.doi.org/10.1115/1.2930759.
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In the present work, a numerical method has been applied to model the water evaporation rate of a glazed collector/regenerator component of an open-cycle absorption refrigeration system. This two-dimensional model calculates local heat and mass-transfer coefficients as part of the solution. The air flow in the glazed channel is driven by the combined buoyancy of both heat and mass transfer (water evaporation). Since the heat and mass-transfer coefficients each depend on both of the driving potentials determined by local conditions in the falling film, a solution of the conjugate problem is required. The resulting nonuniform air-film interface conditions cause the local heat and mass transfer to differ significantly from the uniform boundary condition case. The glazed collector/regenerator is much less sensitive to the ambient temperature and humidity than the unglazed collector. The addition of a glazing over the collector/regenerator provides a significant performance improvement and enhances solution regeneration in a windy humid climate. The glazed collector/regenerator water evaporation rate is higher relative to the unglazed case because the reduction in convective and radiative heat losses increases the absorbent temperature and vapor pressure sufficiently to overcome the concomitant reduction in the mass-transfer coefficient.
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Alshehri, Nawal A., Awatef Abidi, Muhammad Riaz Khan, Yanala Dharmendar Reddy, Saim Rasheed, Elham Alali i Ahmed M. Galal. "Unsteady Convective MHD Flow and Heat Transfer of a Viscous Nanofluid across a Porous Stretching/Shrinking Surface: Existence of Multiple Solutions". Crystals 11, nr 11 (8.11.2021): 1359. http://dx.doi.org/10.3390/cryst11111359.
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The suspension of tiny solid particles inside the energy transport liquids could enhance their thermal conductivity as well as provide an efficient and inventive approach to significantly improve their properties of heat transport. Therefore, our aim is to explore the radiative two-dimensional unsteady flow of a viscous nanofluid about an aligned magnetic field that includes the joint effect of suction, velocity slip, and heat source across a porous convective stretching/shrinking surface. Initially, using non-dimensional variables, the nonlinear governing partial differential equations (PDEs) were transformed into ordinary differential equations (ODEs) which were subsequently solved with the help of bvp4c built-in package in MATLAB. The results declare that escalating the values of the unsteadiness parameter escalates the friction drag whereas it reduces with the escalation of the slip parameter. Furthermore, the heat transfer rate escalates with the escalation of radiation and concentration parameter, and the escalation of the heat source parameter causes to reduce the heat transfer rate. Finally, it is found that the rate of heat transfer and friction drag continuously improve and decline against the rising rates of stretching, respectively.
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Su, Yun, Jiazhen He i Jun Li. "An improved model to analyze radiative heat transfer in flame-resistant fabrics exposed to low-level radiation". Textile Research Journal 87, nr 16 (9.08.2016): 1953–67. http://dx.doi.org/10.1177/0040517516660892.
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An improved heat transfer model, based on the two-flux model, in a multilayer flame-resistant fabric system with an air gap was proposed. The developed model considered the thermal radiation by absorbing, transmitting, emitting and reflecting in porous fabrics. The predicted results of the new model were compared with the previous Beer’s law model and the experimental results, and were found to be in good agreement with the experimental ones. The aim of this study is to investigate the mechanism of radiant heat transfer in the multilayer fabric system and the effects of the optical properties of flame-resistant fabric on heat transfer in the fabric system. The numerical results demonstrated that the self-emission in multilayer fabric system increases not only the rate of thermal energy transferred to human skin during thermal exposure, but also the rate of thermal energy transmitting to the ambience during cooling. The fabric’s optical properties have a complex influence on the transmitted and stored energy in multilayer protective clothing. The finding obtained in this study can provide references for the improvement of the thermal protective performance of flame-resistant fabrics.
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Imran Khan, M., T. Hayat, M. Ijaz Khan i T. Yasmeen. "Thermal properties and time-dependent flow behavior of a viscous fluid". Bulgarian Chemical Communications 51, nr 2 (2019): 180–84. http://dx.doi.org/10.34049/bcc.51.2.4618.
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Our goal in this attempt is to model a nonlinear stretchable flow of a radiative viscous liquid with magnetohydrodynamics. Flow caused is due to a unsteady stretching surface with variable thickness. Consideration of thermal radiation effect characterizes the heat transfer process. Induced electric and magnetic fields are not accounted for. Appropriate transformations gave nonlinear systems. Modern methodology, i.e., НAM, is implemented for the computational process. Velocity and temperature are plotted for influential variables which are important in this problem. Moreover, surface drag force and heat transfer rate are computed and discussed. Velocity field is noted to decay the function of the larger Hartman number whereas opposite situation for temperature is examined via larger radiation parameter.
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SARMA, D., N. AHMED i H. DEKA. "MHD FREE CONVECTION AND MASS TRANSFER FLOW PAST AN ACCELERATED VERTICAL PLATE WITH CHEMICAL REACTION IN PRESENCE OF RADIATION". Latin American Applied Research - An international journal 44, nr 1 (31.01.2014): 1–8. http://dx.doi.org/10.52292/j.laar.2014.412.
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This paper deals with the study of the thermal radiation and chemical reaction effects on an unsteady MHD free convective mass transfer flow past an accelerated infinite vertical plate embedded in a porous medium. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The dimensionless governing equations of motion are solved by using Laplace transform technique in closed form. Expressions for the velocity, temperature and concentration are obtained. The resulting velocity and temperature profiles as well as the skin-friction, rate of heat and mass transfer are shown graphically for different values of the physical parameters viz., Grashof number, Prandtl number, Schmidt number, Chemical reaction parameter, Radiation parameter, Magnetic parameter and Porosity parameter.
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Zaimuddin, Izzatun Nazurah, i Fazlina Aman. "Nanoparticle Shapes (Sphere, Cylinder and Laminar) Impact with Dusty Carbon Nanotubes-Fluid in Magnetohydrodynamics Radiative Flow". Journal of Nanofluids 11, nr 3 (1.06.2022): 434–52. http://dx.doi.org/10.1166/jon.2022.1850.
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The idea of dust particles embedded on the MHD radiative flow of single walled carbon nanotubes-fluid (SWCNTs) and multi walled carbon nanotubes-fluid (MWCNTs) with different nanoparticle shapes along water, ethylene glycol and engine oil as based fluids has been investigated. Based on the typical shapes (sphere, cylinder and laminar), the rate of heat transfer is analysed in between fluid phase and dust phase for the velocity and temperature profiles for the first time. The partial differential equations (PDEs) are reformed into ordinary differential equations (ODEs) using similarity transformation and are solved numerically using Runge-Kutta Fehlberg method with shooting technique. With several parameters involved such as volume fraction of dust particle/nanoparticle, magnetic strength, thermal radiation and various nanoparticle shapes, it is found that the involvement of dust particle in carbon nanotubes-fluid (CNTs-fluid) has greater dynamic on heat transfer than a normal fluid. Moreover, the shape differences of nanoparticle resulting in different rate of the heat transfer. The impact of different shapes of nanoparticle are compared using fixed parameter values.
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Mjankwi, Musa Antidius, Verdiana Grace Masanja, Eunice W. Mureithi i Makungu Ng’oga James. "Unsteady MHD Flow of Nanofluid with Variable Properties over a Stretching Sheet in the Presence of Thermal Radiation and Chemical Reaction". International Journal of Mathematics and Mathematical Sciences 2019 (2.05.2019): 1–14. http://dx.doi.org/10.1155/2019/7392459.
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The unsteady magnetohydrodynamics (MHD) flow of nanofluid with variable fluid properties over an inclined stretching sheet in the presence of thermal radiation and chemical reaction is studied taking into account the effect of variable fluid properties in thermal conductivity and diffusion coefficient. The governing partial differential equations are transformed into ordinary differential equations by using similarity transformation. The numerical solutions of the problem are obtained by using the fourth order Runge-Kutta method in line with the shooting technique. It is found that the increase in both thermal conductivity and radiative heat flux decreases the heat transfer rate but increases the skin friction and mass transfer rates. It is further observed that the increase in porosity parameter and magnetic field reduces the skin friction, heat, and mass transfer rates.
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Khan, Muhammad Ijaz, Sohail Ahmad Khan, Tasawar Hayat, Muhammad Faisal Javed i Ahmed Alsaedi. "Entropy generation in radiative flow of Ree-Eyring fluid due to due rotating disks". International Journal of Numerical Methods for Heat & Fluid Flow 29, nr 6 (3.06.2019): 2057–79. http://dx.doi.org/10.1108/hff-11-2018-0642.
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Purpose This study aims to examine the flow characteristics of Ree–Eyring fluid between two rotating disks. The characteristics of heat transfer are discussed in presence of viscous dissipation, heat source/sink and nonlinear radiative heat flux. Design/methodology/approach Nonlinear flow expressions lead to ordinary ones through adequate similarity transformations. The ordinary differential system has been tackled through optimal homotopic method. The impact of different flow variables on the velocity field, entropy generation rate and temperature fields is graphically discussed. The surface drag force and heat transfer rate are numerically examined via various pertinent parameters. Findings By minimization of values of stretching parameter and Brinkman number, the entropy generation rate can be controlled. The entropy generation rate enhances for higher values of magnetic parameter, while the Bejan number is decreased via magnetic parameter. Originality/value No such work is yet published in the literature.
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Singh, Phool, Tomer Singh, Sandeep Kumar i Deepa Sinha. "Effect of radiation and porosity parameter on magnetohydrodynamic flow due to stretching sheet in porous media". Thermal Science 15, nr 2 (2011): 517–26. http://dx.doi.org/10.2298/tsci1102517s.
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An analysis is made for the steady two-dimensional flow of a viscous incompressible electrically conducting fluid in the vicinity of a stagnation point on a stretching sheet. Fluid is considered in a porous medium under the influence of (i)transverse magnetic field, (ii)volumetric rate of heat generation/absorption in the presence of radiation effect. Rosseland approximation is used to model the radiative heat transfer. The governing boundary layer equations are transformed to ordinary differential equations by taking suitable similarity variables. In the present reported work the effect of porosity parameter, radiation parameter, magnetic field parameter and the Prandtl number on flow and heat transfer characteristics have been discussed. Variation of above discussed parameters with the ratio of free stream velocity parameter to stretching sheet parameter have been graphically represented.
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Ma, Jing, Yasong Sun i Sida Li. "Element Differential Method for Non-Fourier Heat Conduction in the Convective-Radiative Fin with Mixed Boundary Conditions". Coatings 12, nr 12 (30.11.2022): 1862. http://dx.doi.org/10.3390/coatings12121862.
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Fin is an efficient and straightforward way to enhance heat transfer rate. When the heat source varies dramatically in a very short time, non-Fourier heat conduction should be considered. In the paper, taking advantage of numerical stability and no integral and easy-to-implement features of an element differential method, a numerical model is developed to evaluate the fin efficiency of the convective-radiative fin within non-Fourier heat conduction. In this fin, heat is generated by an internal heat source and dissipated by convection and radiation. Both periodic and adiabatic boundary conditions are considered. The accuracy and efficiency of the element differential method is validated by several numerical examples with analytical solutions. The results indicate that the element differential method has high precision and flexibility to solve non-Fourier heat conduction in convective-radiative fin. Besides, the effects of Vernotte number, dimensionless periodicity, thermal conductivity coefficient, and emissivity coefficient on dimensionless fin tip temperature, instantaneous fin efficiency, and average fin efficiency are comprehensively analyzed.
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Sulochana, C., i S. R. Aparna. "Unsteady magnetohydrodynamic radiative liquid thin film flow of hybrid nanofluid with thermophoresis and Brownian motion". Multidiscipline Modeling in Materials and Structures 16, nr 4 (17.12.2019): 811–34. http://dx.doi.org/10.1108/mmms-08-2019-0160.
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Purpose The purpose of this paper is to analyze heat and mass transport mechanism of unsteady MHD thin film flow of aluminium–copper/water hybrid nanofluid influenced by thermophoresis, Brownian motion and radiation. Design/methodology/approach The authors initially altered the time dependent set of mathematical equations into dimensionless form of equations by using apposite transmutations. These equations are further solved numerically by deploying Runge–Kutta method along with shooting technique. Findings Plots and tables for skin friction coefficient, Nusselt number, Sherwood number along with velocity, temperature and concentration profiles against pertinent non-dimensional parameters are revealed. The study imparts that aluminium–copper hybrid nanoparticles facilitate higher heat transfer rate compared to mono nanoparticles. It is noteworthy to disclose that an uplift in thermophoresis and Brownian parameter depreciates heat transfer rate, while concentration profiles boost with an increase in thermophoretic parameter. Research limitations/implications The current study targets to investigate heat transfer characteristics of an unsteady thin film radiative flow of water-based aluminium and copper hybrid nanofluid. The high thermal and electrical conductivities, low density and corrosion resistant features of aluminium and copper with their wide range of industrial applications like power generation, telecommunication, automobile manufacturing, mordants in leather tanning, etc., have prompted us to instil these particles in the present study. Practical implications The present study has many practical implications in the industrial and manufacturing processes working on the phenomena like heat transfer, magnetohydrodynamics, thermal radiation, nanofluids, hybrid nanofluids with special reference to aluminium and copper particles. Originality/value To the best extent of the authors’ belief so far no attempt is made to inspect the flow, thermal and mass transfer of water-based hybridized aluminium and copper nanoparticles with Brownian motion and thermophoresis.
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Rahman, M. M., i T. Sultana. "Radiative Heat Transfer Flow of Micropolar Fluid with Variable Heat Flux in a Porous Medium". Nonlinear Analysis: Modelling and Control 13, nr 1 (25.01.2008): 71–87. http://dx.doi.org/10.15388/na.2008.13.1.14590.
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A two-dimensional steady convective flow of a micropolar fluid past a vertical porous flat plate in the presence of radiation with variable heat flux has been analyzed numerically. Using Darcy-Forchheimer model the corresponding momentum, microrotation and energy equations have been solved numerically. The local similarity solutions for the flow, microrotation and heat transfer characteristics are illustrated graphically for various material parameters. The effects of the pertinent parameters on the local skin friction coefficient, plate couple stress and the heat transfer are also calculated. It was shown that large Darcy parameter leads to decrease the velocity while it increases the angular velocity as well as temperature of the micropolar fluids. The rate of heat transfer in weakly concentrated micropolar fluids is higher than strongly concentrated micropolar fluids.
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Đorđević, Milan, Velimir Stefanović, Mića Vukić i Marko Mančić. "EXPERIMENTAL INVESTIGATION OF THE CONVECTIVE HEAT TRANSFER IN A SPIRALLY COILED CORRUGATED TUBE WITH RADIANT HEATING". Facta Universitatis, Series: Mechanical Engineering 15, nr 3 (9.12.2017): 495. http://dx.doi.org/10.22190/fume171001027d.
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The Archimedean spiral coil made of a transversely corrugated tube was exposed to radiant heating in order to represent a heat absorber of the parabolic dish solar concentrator. The main advantage of the considered innovative design solution is a coupling effect of the two passive methods for heat transfer enhancement - coiling of the flow channel and changes in surface roughness. The curvature ratio of the spiral coil varies from 0.029 to 0.234, while water and a mixture of propylene glycol and water are used as heat transfer fluids. The unique focus of this study is on specific boundary conditions since the heat flux upon the tube external surfaces varies not only in the circumferential direction, but in the axial direction as well. Instrumentation of the laboratory model of the heat absorber mounted in the radiation field includes measurement of inlet fluid flow rate, pressure drop, inlet and outlet fluid temperature and 35 type K thermocouples welded to the coil surface. A thermal analysis of the experimentally obtained data implies taking into consideration the externally applied radiation field, convective and radiative heat losses, conduction through the tube wall and convection to the internal fluid. The experimental results have shown significant enhancement of the heat transfer rate compared to spirally coiled smooth tubes, up to 240% in the turbulent flow regime.
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Solomon, P. R., M. A. Serio, J. E. Cosgrove, D. S. Pines, Y. Zhao, R. C. Buggeln i S. J. Shamroth. "A Coal-Fired Heat Exchanger for an Externally Fired Gas Turbine". Journal of Engineering for Gas Turbines and Power 118, nr 1 (1.01.1996): 22–31. http://dx.doi.org/10.1115/1.2816545.
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Significant improvements in efficiency for electricity generation from coal can be achieved by cycles that employ a high-temperature, highly recuperative gas turbine topping cycle. The principal difficulty of employing a gas turbine in a coal-fired power generation system is the possible erosion and corrosion of the high-temperature rotating gas turbine components caused by the coal’s inorganic and organically bound constituents (ash, sulfur, and alkali metals). One route to overcome this problem is the development of an externally fired gas turbine system employing a coal fired heat exchanger. The solution discussed in this paper is the design of a Radiatively Enhanced, Aerodynamically Cleaned Heat-Exchanger (REACH-Exchanger). The REACH-Exchanger is fired by radiative and convective heat transfer from a moderately clean fuel stream and radiative heat transfer from the flame of a much larger uncleaned fuel stream, which supplies most of the heat. The approach is to utilize the best ceramic technology available for high-temperature parts of the REACH-Exchanger and to shield the high-temperature surfaces from interaction with coal minerals by employing clean combustion gases that sweep the tube surface exposed to the coal flame. This paper presents a combined experimental/computational study to assess the viability of the REACH-Exchanger concept. Experimental results indicated that the REACH-Exchanger can be effectively fired using radiation from the coal flame. Both computation and experiments indicate that the ceramic heat exchanger can be aerodynamically protected by a tertiary stream with an acceptably low flow rate.
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Mushtaq, Ammar, M. Mustafa, T. Hayat i A. Alsaedi. "Boundary layer flow over a moving plate in a flowing fluid considering non-linear radiations". International Journal of Numerical Methods for Heat & Fluid Flow 26, nr 5 (6.06.2016): 1617–30. http://dx.doi.org/10.1108/hff-12-2014-0365.
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Purpose – The purpose of this paper is to consider a laminar two-dimensional incompressible flow of an electrically conducting fluid over a moving flat plate with a parallel free stream. Design/methodology/approach – The governing equations are first reduced into self-similar forms and then solved for the numerical solutions by shooting method. Findings – The results are compared with the available studies is some special cases and found in excellent agreement. It is noticed that an increase in the magnetic field strength leads to a decrease in the momentum boundary layer thickness and enhancement in the rate of heat transfer from the plate. It is also observed that temperature and heat transfer from the plate increase when radiation effect is strengthened. Originality/value – A recently proposed idea of nonlinear radiative heat transfer with Joule heating and viscous dissipation effects is analyzed.
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Qasim, Muhammad, Tasawar Hayat i Saleem Obaidat. "Radiation Effect on the Mixed Convection Flow of a Viscoelastic Fluid Along an Inclined Stretching Sheet". Zeitschrift für Naturforschung A 67, nr 3-4 (1.04.2012): 195–202. http://dx.doi.org/10.5560/zna.2012-0006.
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This study concentrates on the heat transfer analysis of the steady flow of viscoelastic fluid along an inclined stretching surface. Analysis has been carried out in the presence of thermal radiation and the Rosseland approximation is used to describe the radiative heat flux in the energy equation. The equations of continuity, momentum and energy are reduced into the system of governing differential equations and solved by homotopy analysis method (HAM). The velocity and temperature are illustrated through graphs. Exact and homotopy solutions are compared in a limiting sense. It is noticed that viscoelastic parameter decreases the velocity and boundary layer thickness. It is also observed that increasing values of viscoelastic parameter reduces the thickness of momentum boundary layer and increase the heat transfer rate. However, it is found that increasing the radiation parameter has the effect of decreasing the local Nusselt number
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Fayyadh, Mohammed M., Kohilavani Naganthran, Md Faisal Md Basir, Ishak Hashim i Rozaini Roslan. "Radiative MHD Sutterby Nanofluid Flow Past a Moving Sheet: Scaling Group Analysis". Mathematics 8, nr 9 (26.08.2020): 1430. http://dx.doi.org/10.3390/math8091430.
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The present theoretical work endeavors to solve the Sutterby nanofluid flow and heat transfer problem over a permeable moving sheet, together with the presence of thermal radiation and magnetohydrodynamics (MHD). The fluid flow and heat transfer features near the stagnation region are considered. A new form of similarity transformations is introduced through scaling group analysis to simplify the governing boundary layer equations, which then eases the computational process in the MATLAB bvp4c function. The variation in the values of the governing parameters yields two different numerical solutions. One of the solutions is stable and physically reliable, while the other solution is unstable and is associated with flow separation. An increased effect of the thermal radiation improves the rate of convective heat transfer past the permeable shrinking sheet.
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Leonardi, S. A., R. Viskanta i J. P. Gore. "Analytical and Experimental Study of Combustion and Heat Transfer in Submerged Flame Metal Fiber Burners/Heaters". Journal of Heat Transfer 125, nr 1 (29.01.2003): 118–25. http://dx.doi.org/10.1115/1.1527910.
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A theoretical model has been developed to predict the thermal performance of inert, direct-fired, woven-metal fiber-matrix porous radiant burner. The local chemical heat release was modeled by a detailed mechanism, and convection heat transfer between the gas and the solid phases in the burner was described by an empirical heat transfer coefficient. The solid matrix was modeled as a gray medium, and the discrete ordinates method was used to solve the radiative transfer equation to calculate the local radiation source/sink in the energy equation for the solid phase. The fully coupled nature of the calculations without external specification of flame location represents a key advance over past efforts towards modeling of porous radiant burners, because for a given mass flow rate the actual heat loss from the flame determines its position and is not a free parameter. The calculated results for the burner surface temperature, the gas exhaust temperature and the radiation efficiency for a single layer Fecralloy burner were compared with experimental data from this laboratory and reasonable agreement was obtained for a range of operating conditions.
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Abu-Hamdeh, Nidal H., Abdulmalik A. Aljinaidi, Mohamed A. Eltaher, Khalid H. Almitani, Khaled A. Alnefaie, Abdullah M. Abusorrah i Mohammad Reza Safaei. "Implicit Finite Difference Simulation of Prandtl-Eyring Nanofluid over a Flat Plate with Variable Thermal Conductivity: A Tiwari and Das Model". Mathematics 9, nr 24 (7.12.2021): 3153. http://dx.doi.org/10.3390/math9243153.
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The current article presents the entropy formation and heat transfer of the steady Prandtl-Eyring nanofluids (P-ENF). Heat transfer and flow of P-ENF are analyzed when nanofluid is passed to the hot and slippery surface. The study also investigates the effects of radiative heat flux, variable thermal conductivity, the material’s porosity, and the morphologies of nano-solid particles. Flow equations are defined utilizing partial differential equations (PDEs). Necessary transformations are employed to convert the formulae into ordinary differential equations. The implicit finite difference method (I-FDM) is used to find approximate solutions to ordinary differential equations. Two types of nano-solid particles, aluminium oxide (Al2O3) and copper (Cu), are examined using engine oil (EO) as working fluid. Graphical plots are used to depict the crucial outcomes regarding drag force, entropy measurement, temperature, Nusselt number, and flow. According to the study, there is a solid and aggressive increase in the heat transfer rate of P-ENF Cu-EO than Al2O3-EO. An increment in the size of nanoparticles resulted in enhancing the entropy of the model. The Prandtl-Eyring parameter and modified radiative flow show the same impact on the radiative field.
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Sanchez, Florian, Susan Liscouët-Hanke i Tanmay Bhise. "Influence of Ventilation Flow Rate and Gap Distance on the Radiative Heat Transfer in Aircraft Avionics Bays". Aerospace 9, nr 12 (8.12.2022): 806. http://dx.doi.org/10.3390/aerospace9120806.
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The feasibility of the future more-electric, hybrid-electric, and all-electric aircraft configurations will depend on a good understanding of thermal aspects early in the design. However, thermal analysis of aircraft equipment bays is typically performed at later design stages to validate if the design meets the minimal certification requirements rather than to optimize the cooling strategy. The presented work aims to provide new insight into thermal aspects in typical aircraft equipment bays. In particular, system thermal interactions, such as radiation, play a more significant role in tightly packaged bays, such as avionics bays. This paper investigates the influence of radiation on the overall system heat dissipation in two representative avionics bays. Using Computational Fluid Dynamics (CFD) simulation, combined with an analytical approach, the authors analyze the impact of several parameters, such as varying mass flow rates and distances between adjacent systems, on their thermal interaction. The results suggest that the radiative effects must be considered when the gap distance between the systems is larger than 0.1 m, the flow rate between two systems is not strong enough to have high convective heat exchanges, when the systems of interest are hidden by other systems from the ventilation sources, and when the system’s internal heat dissipation is significant. Overall, this paper’s results will contribute enhance conceptual design methods, such as the previously developed Thermal Risk Analysis, and help optimize thermal management strategies for future aircraft.