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1
Tychanicz-Kwiecień, Maria, and Sebastian Grosicki. "Research methods in the study of heat transfer coefficient during flow in minichannels." Journal of Mechanical and Energy Engineering 5, no. 1 (August 13, 2021): 59–68. http://dx.doi.org/10.30464/10.30464/jmee.2021.5.1.59.
Повний текст джерелаАнотація:
The paper presents the specification of research methods commonly encountered in the studies of heat transfer processes in minichannels. In particular the following methods have been emphasized: electrochemical limiting current method as well as the thermal balance method. In thermal balance method the mean heat transfer coefficient is determined by the set of experimental thermal measurements of the investigated heat exchanger. In turn, limiting current method is based on heat and mass transfer analogy. The discussed research methods have been implemented on two specially designed and constructed test facilities with compact minichannel heat exchangers, which have been presented and described in details. In order to validate the designed setup, the preliminary experimental measurements of two minichannel heat exchangers with hydraulic diameter of 2 mm and rectangular cross sections during single-phase liquid flows have been carried out. In further perspective it is planned to extend the experimental studies of minichannel heat exchangers and to compare the results obtained by both methods described.
2
Ingel, L. Kh. "TO THE NONLINEAR DYNAMICS OF TURBULENT THERMALS." XXII workshop of the Council of nonlinear dynamics of the Russian Academy of Sciences 47, no. 1 (April 30, 2019): 61–63. http://dx.doi.org/10.29006/1564-2291.jor-2019.47(1).16.
Повний текст джерелаАнотація:
Often used model of turbulent convection from localized sources of buoyancy and (or) momentum acting for a short time – isolated thermals. In such a model, the perturbation region (thermal) is approximately represented as a “bubble” or a vortex ring of variable volume and mass that rises (or descends depending on the perturbation sign). The volume of thermals is gradually increasing due to the capture of adjacent volumes of the environment (“entrainment”). The dynamics of a thermal is described by a nonlinear system of ordinary differential equations – the equations of balance of mass, momentum and buoyancy. In the present work, the nonlinear integral model of turbulent thermals is generalized to the case of the presence of horizontal components of its motion relative to the medium (for example, the emergence of a thermal in a shear flow). Compared to traditional models, the possibility of the presence in the thermal of volume heat and momentum sources is additionally taken into account. The problem is solved in quadratures. One of the possible applications is the artificial stimulation by local sources of impulse of downward movements in the atmosphere in order to influence convective clouds. The solution depends on nine parameters – stratification, vertical shear of the background current, intensities of the above-mentioned volume sources, initial conditions for the thermal radius, its buoyancy, and the three components of the thermal velocity. Different limiting cases are analyzed. Attention is paid to the nonlinear effect of the interaction of the horizontal and vertical components of the thermal motion, since each of the components affects the intensity of entrainment, i.e. on the growth rate of thermal dimensions and, consequently, on its mobility. Intensification of entrainment due to the interaction of a thermal with a transverse flow can lead to a significant decrease in its mobility. From this, in turn, depends on the degree of horizontal transfer of a thermal by a background current. Some limiting cases were previously analyzed in the author’s cited below. This study was supported by Program 56 of the Fundamental Research of the Presidium of the Russian Academy of Sciences.
3
Pati, Sukumar, and Pranab Kumar Mondal. "Limiting thermal characteristics for flow of non-Newtonian fluids between asymmetrically heated parallel plates: An analytical study." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 233, no. 4 (November 28, 2018): 880–92. http://dx.doi.org/10.1177/0954408918814978.
Повний текст джерелаАнотація:
In this work, an analytical study on the limiting thermal transport characteristics for the flow of a non-Newtonian fluid namely, power law liquid, between asymmetrically heated parallel plates is presented. The transport equations for mass, momentum, and energy are analytically solved to obtain closed-form expressions for the temperature distributions in the flow field and the limiting Nusselt number in terms of relevant parameters. The effects of frictional heating due to viscous dissipation on the heat transfer characteristics are studied. Results are presented in terms of degree of asymmetric heating, Brinkman number, and power law index. The most important finding from the present work is the nontrivial interplay between degree of asymmetric heating and the rheological behavior of the fluid in dictating the thermal transport characteristics of heat.
4
Wang, B. "Hyperbolic Heat Conduction for a Layered Medium of Finite Thickness with an Interface Crack." Applied Mechanics and Materials 271-272 (December 2012): 1312–16. http://dx.doi.org/10.4028/www.scientific.net/amm.271-272.1312.
Повний текст джерелаАнотація:
This paper studies the thermal flow concentration near an interface crack in a layered medium. Solution method for the thermal flow intensity factor is established. Both the Griffith crack and the penny-shaped crack are studied. Limiting cases of the current problem include (1) the solution of crack problem associated with classical Fourier heat conduction, (2) the solution of an interface crack in an infinite layered medium, and (3) the solution of a crack in a homogeneous medium.
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Livescu, Daniel. "Turbulence with Large Thermal and Compositional Density Variations." Annual Review of Fluid Mechanics 52, no. 1 (January 5, 2020): 309–41. http://dx.doi.org/10.1146/annurev-fluid-010719-060114.
Повний текст джерелаАнотація:
Density variations in fluid flows can arise due to acoustic or thermal fluctuations, compositional changes during mixing of fluids with different molar masses, or phase inhomogeneities. In particular, thermal and compositional (with miscible fluids) density variations have many similarities, such as in how the flow interacts with a shock wave. Two limiting cases have been of particular interest: ( a) the single-fluid non-Oberbeck–Boussinesq low–Mach number approximation for flows with temperature variations, which describes vertical convection, and ( b) the incompressible limit of mixing between miscible fluids with different molar masses, which describes the Rayleigh–Taylor instability. The equations describing these cases are remarkably similar, with some differences in the molecular transport terms. In all cases, strong inertial effects lead to significant asymmetries of mixing, turbulence, and the shape of mixing layers. In addition, density variations require special attention in turbulence models to avoid viscous contamination of the large scales.
6
Pert, G. J. "Models of laser-plasma ablation. Part 3. Steady-state theory: deflagration flow." Journal of Plasma Physics 39, no. 2 (April 1988): 241–76. http://dx.doi.org/10.1017/s0022377800013015.
Повний текст джерелаАнотація:
The theory of plasma ablation by laser irradiation from cylindrical and spherical solid targets is considered when thermal conduction is dominant and absorption is local at the critical density. Analytic solutions for both inhibited and uninhibited heat fluxes are developed, but only investigated in detail when flux limiting does not introduce a step discontinuity. In most cases it is found that only a restricted region of flow is steady, and must be terminated by a rarefaction wave. The transition from quasi-planar to strongly divergent flow is shown to depend on a characteristic parameter, which represents the ratio of the thermal conduction length to the target radius.
7
Liu, Jia, Jin Huang, and Jinzhi Hu. "Fuel cell thermal management system based on microbial fuel cell 3-D multi-phase flow numerical model." Thermal Science 25, no. 4 Part B (2021): 3083–91. http://dx.doi.org/10.2298/tsci2104083l.
Повний текст джерелаАнотація:
The paper tests the changes in the pH value of the anolyte and catholyte. The 3-D multi-phase 3-D multi-current conductivity values analyze the electricity generation process and energy utilization of the microbial fuel cell (AMFC) and provide a theory for improving the AMFC following the performance. The test results show that with the operation of AMFC, the pH value of the anolyte and the 3-D multi-flow conductivity show a downward trend, the pH value of the catholyte and the 3-D multi-flow conductivity show an upward trend, and the ratio of the pH value of the catholyte the pH value of the anolyte is about 0.30-0.50 higher, and the average 3-D multi-current conductivity of the anolyte and catholyte does not change much. When AMFC operates stably, the internal ohmic resistance is 29.69 ?, the limiting current is 2.69 mA, the maximum output power is about 0.8 mW, and the corre?sponding internal resistance is about 95.72 ?. The mass transmission of potassium ferricyanide is the limiting factor of limiting current. Numerical analysis of 3-D multi-phase flow found that other microorganisms consume 91.1% of the glucose in AMFC anolyte, and only 8.9% of the glucose is used for power generation. The 88.5% of the energy of the glucose used for power generation is converted into other forms of energy, only 11.5% of the energy is converted into electricity.
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Peng, Xishun, Anjiang Lu, Qiliang Sun, Naitao Xu, Yibo Xie, Jiawen Wu, and Jin Cheng. "Design of H-Shape Chamber in Thermal Bubble Printer." Micromachines 13, no. 2 (January 26, 2022): 194. http://dx.doi.org/10.3390/mi13020194.
Повний текст джерелаАнотація:
The utilization rate of ink liquid in the chamber is critical for the thermal bubble inkjet head. The difficult problem faced by the thermal bubble inkjet printing is how to maximize the use of ink in the chamber and increase the printing frequency. In this paper, by adding a flow restrictor and two narrow channels into the chamber, the H-shape flow-limiting structure is formed. At 1.8 μs, the speed of bubble expansion reaches the maximum, and after passing through the narrow channel, the maximum reverse flow rate of ink decreased by 25%. When the vapor bubble disappeared, the ink fills the nozzle slowly. At 20 μs, after passing through the narrow channel, the maximum flow rate of the ink increases by 39%. The inkjet printing frequency is 40 kHz, and the volume of the ink droplet is about 13.1 pL. The structure improves the frequency of thermal bubble inkjet printing and can maximize the use of liquid in the chamber, providing a reference for cell printing, 3D printing, bioprinting, and other fields.
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Rasheed, Haroon U. R., Saeed Islam, Zeeshan Khan, Sayer O. Alharbi, Hammad Alotaibi, and Ilyas Khan. "Impact of Nanofluid Flow over an Elongated Moving Surface with a Uniform Hydromagnetic Field and Nonlinear Heat Reservoir." Complexity 2021 (May 24, 2021): 1–9. http://dx.doi.org/10.1155/2021/9951162.
Повний текст джерелаАнотація:
The increasing global demand for energy necessitates devoted attention to the formulation and exploration of mechanisms of thermal heat exchangers to explore and save heat energy. Thus, innovative thermal transport fluids require to boost thermal conductivity and heat flow features to upsurge convection heat rate, and nanofluids have been effectively employed as standard heat transfer fluids. With such intention, herein, we formulated and developed the constitutive flow laws by utilizing the Rossland diffusion approximation and Stephen’s law along with the MHD effect. The mathematical formulation is based on boundary layer theory pioneered by Prandtl. Governing nonlinear partial differential flow equations are changed to ODEs via the implementation of the similarity variables. A well-known computational algorithm BVPh2 has been utilized for the solution of the nonlinear system of ODEs. The consequence of innumerable physical parameters on flow field, thermal distribution, and solutal field, such as magnetic field, Lewis number, velocity parameter, Prandtl number, drag force, Nusselt number, and Sherwood number, is plotted via graphs. Finally, numerical consequences are compared with the homotopic solution as a limiting case, and an exceptional agreement is found.
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Annapurna, Sogunuru, Pradapan Vikram, and Suma Varughese. "Thermal Design, Analysis and Packaging of an Airborne Multi-output Power Supply Unit." Defence Science Journal 68, no. 3 (April 16, 2018): 235. http://dx.doi.org/10.14429/dsj.68.12252.
Повний текст джерелаАнотація:
Design of airborne multi-output power supply unit (MOPS) is restricted by space, weight and predefined geometry of air flow path. The unit is cooled by ram air and hence, exposed to the extreme external thermal environment that changes typically from +55°C to -40°C, from ground to cruising altitude within a few minutes. Hence the design should meet the thermal requirements of the electronics inside the packaging adequately, for both the positive and negative extremities of the temperature, so that device limiting temperatures are not exceeded. At the same time, it must accommodate the necessary circuitry. Details of the thermal and mechanical design and performance of the MOPS unit at various altitudes, hot spot location, flow requirements and optimal heat sink design are presented in this paper.
11
Sik Han, Hun, Han-Ok Kang, Juhyeon Yoon, Young In Kim, Youngmin Bae, and Sang Ji Kim. "Performance Analysis and Tube Inlet Orifice Length Evaluation of a Once–Through Steam Generator." E3S Web of Conferences 128 (2019): 03001. http://dx.doi.org/10.1051/e3sconf/201912803001.
Повний текст джерелаАнотація:
A numerical study is conducted for performance analysis and secondary side screw-type tube inlet orifice design of a once–through steam generator (OTSG). Various tube plugging conditions and power levels are considered, and the secondary coolant flow rate is adjusted to maintain a constant thermal power. Comprehensive numerical solutions are acquired to evaluate the OTSG thermal–hydraulic performance and minimum orifice length under various operating conditions. The OTSG performance is analyzed according to the tube plugging condition in terms of the OTSG thermal power, steam outletsuperheat degree, and secondary coolant pressure drop. The results obtained show that a constant thermal power canbe maintained by properly adjusting the secondary coolant flow rate with a variation ofthe steam outlet superheat degree and secondary coolant pressure drop when the OTSG operates at high power level. The required minimum orifice length to suppress the flow oscillation below the allowablelevelis evaluated. The lowest power level results in the highest minimum orifice length, and non-plugging condition provides a limiting case for the orifice length criterion.
12
Genbach, A. A., D. Yu Bondartsev, and A. Y. Shelginsky. "Investigation of nanoscale and microscale structured cooling surfaces of thermal power plants." Safety and Reliability of Power Industry 15, no. 1 (May 6, 2022): 38–44. http://dx.doi.org/10.24223/1999-5555-2022-15-1-38-44.
Повний текст джерелаАнотація:
Studies were conducted of the heat exchange crisis depending on the coolant excess (which determined the underheating and flow rate), the thermal-physical properties of the heating surface, and the ejection of liquid droplets from the porous structure. A model of dynamics of vapor bubbles born on the solid surface in porous structures and the vapor-generating wall (substrate) has been developed. The model is based on cinematography with an SKS-1M speed camera. The removal of high heat flows (up to 2·106 W/m2) is provided through the joint action of capillary and mass forces with the use of intensifiers. Equations are obtained of critical heat flows through the thermohydraulic characteristics of the boiling process in woven porous structures. The research is of practical importance in the limiting state region of the steam-generating surface protected by cooling from overburning. Three mineral media (tuff, granite, marble) of Zaili and Dzungarian Alatau mountains near the city of Almaty (Kazakhstan) were considered. The method of holographic interferometry was used to study porous thermodynamic screens. The stress and deformed state of the samples was studied. Simulation of the acoustic field of the blast wave with th e thermodynamic field created by three thermal sources has shown its high efficiency. The created powerful thermal screen, due to the generation of strain and thermal stress fields, is an obstacle to the propagation of the reflected blast wave, causing the emergence and development of destructive cracks. Nanoscale and microscale structured surfaces in the form of coatings and mesh structures have been developed, which give an integrated effect of industrial meshes with natural mineral media coatings and have synergistic advantages of combining these two developments in an integrated technology of their production, expansion of critical thermal loads and management of the limiting state of porous coatings.
13
Herwig, H., and K. Klemp. "Variable Property Effects of Fully Developed Laminar Flow in Concentric Annuli." Journal of Heat Transfer 110, no. 2 (May 1, 1988): 314–20. http://dx.doi.org/10.1115/1.3250486.
Повний текст джерелаАнотація:
By means of a linear perturbation theory, the influences of density, viscosity, thermal conductivity, and specific heat capacity, all varying with temperature, are taken into account. The wall heat flux is assumed to be constant at the inner and outer wall, with an arbitrary ratio between these two. Even for variable properties the problem can be reduced to solving a set of ordinary differential equations with three parameters: heat flux ratio, diameter ratio, and Prandtl number. Skin friction and heat transfer results are given for specific numbers of the parameters, including the limiting cases of pipe and channel flows.
14
Ziegler, Bartosz, Jędrzej Mosiężny, and Paweł Czyżewski. "Numerical study of heat and mass flow in layered heat storage." MATEC Web of Conferences 240 (2018): 01041. http://dx.doi.org/10.1051/matecconf/201824001041.
Повний текст джерелаАнотація:
An analysis of argon gas flow in exemplary configuration of layered bed thermal energy storage is presented. The analysis incorporates URANS model with conjugate heat transfer between gas and solid storage core. The aim of this analysis was to identify key factors limiting exergy efficiency of this storage type and determine some details about storage transient behaviour. Three full cycles of storage loading and unloading having 17 hours physical time in total are simulated, with calculation of exergetic efficiency for each of the cycles. Conclusions regarding this storage type feasibility for indirect power storage in pumped heat systems are made.
15
Chaudhary, Santosh, and Mohan Choudhary. "Partial slip and thermal radiation effects on hydromagnetic flow over an exponentially stretching surface with suction or blowing." Thermal Science 22, no. 2 (2018): 797–808. http://dx.doi.org/10.2298/tsci160127150c.
Повний текст джерелаАнотація:
This paper is devoted to analyze computational simulation to study the partial slip and thermal radiation effects on the flow of a viscous incompressible electrically conducting fluid through an exponentially stretching surface with suction or blowing in presence of magnetic field. Using suitable similarity variables, the non-linear boundary-layer PDE are converted to ODE and solved numerically by Runge-Kutta fourth order method in association with shooting technique. Effects of suction or blowing parameter, velocity slip parameter, magnetic parameter, thermal slip parameter, thermal radiation parameter, Prandtl number, and Eckert number are demonstrated graphically on velocity and temperature profiles while skin friction coefficient and surface heat transfer rate are presented numerically. Moreover, comparison of numerical results for non-magnetic case is made with previously published work under limiting cases.
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Pert, G. J. "Models of laser-plasma ablation. Part 2. Steady-state theory: self-regulating flow." Journal of Plasma Physics 36, no. 3 (December 1986): 415–46. http://dx.doi.org/10.1017/s0022377800011880.
Повний текст джерелаАнотація:
The theory of plasma ablation by laser irradiation of a solid target is considered when thermal conduction is weak and the absorption is dominated by inverse bremsstrahlung (the self-regulating model). Analytic solutions are identified to treat both steady and time-dependent flows in limiting cases. The intermediate behaviour is explored by numerical modelling. The models are presented for planar, cylindrical and spherical geometries with both tight and weak focused beams. A brief investigation of the applicability of analytic models to the heating of thin foil systems is also presented.
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Zhang, Yang, Peter H. Stone, and Amy Solomon. "The Role of Boundary Layer Processes in Limiting PV Homogenization." Journal of the Atmospheric Sciences 66, no. 6 (June 1, 2009): 1612–32. http://dx.doi.org/10.1175/2008jas2914.1.
Повний текст джерелаАнотація:
Abstract A β-plane multilevel quasigeostrophic channel model with interactive static stability and a simplified parameterization of atmospheric boundary layer physics is used to study the role of different boundary layer processes in eddy equilibration and their relative effect in maintaining the strong boundary layer potential vorticity (PV) gradient. The model results show that vertical thermal diffusion, along with the surface heat exchange, is primarily responsible for limiting PV homogenization by baroclinic eddies in the boundary layer. Under fixed SST boundary conditions, these two processes act as the source of the mean flow baroclinicity in the lower levels and result in stronger eddy heat fluxes. Reducing surface friction alone does not result in efficient elimination of the boundary layer PV gradient, but the equilibrium state temperature gradient is still largely influenced by surface friction and its response to changes in surface friction is not monotonic. In the regime of strong surface friction, with reduced poleward eddy heat flux, a strong temperature gradient is still retained. When the surface friction is sufficiently weak along with the stronger zonal wind, the critical level at the center of the jet drops below the surface. As a result, in the lower levels, the eddy heat flux forcing on the mean flow moves away from the center of the jet and the equilibrium state varies only slightly with the strength of the vertical momentum diffusion in the boundary layer.
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Awais, M., T. Hayat, M. Mustafa, K. Bhattacharyya, and M. Asif Farooq. "Analytic and numeric solutions for stagnation-point flow with melting, thermal-diffusion and diffusion-thermo effects." International Journal of Numerical Methods for Heat & Fluid Flow 24, no. 2 (February 25, 2014): 438–54. http://dx.doi.org/10.1108/hff-10-2011-0220.
Повний текст джерелаАнотація:
Purpose – The aim of this work is to analyze the combined effects of melting, thermal-diffusion and diffusion-thermo on the flow of non-Newtonian fluid. Design/methodology/approach – An efficient approach namely homotopy analysis method is applied to compute the solution of the non-linear problem. Moreover, numerical results using MATLAB function bvp4c are also computed. Findings – Main findings are an increase in the melting process corresponding to increase in the velocity and the boundary layer thickness. However, surface heat and mass transfer decrease by increasing the values of melting parameter M. Originality/value – Combined effects of thermal-diffusion and diffusion-thermo are analyzed and the solutions are computed both numerically and analytically. Some deduced results can be obtained in a limiting sense.
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Adeyeye, Kemi, Kaiming She, and Inês Meireles. "Beyond the flow rate: the importance of thermal range, flow intensity, and distribution for water-efficient showers." Environmental Science and Pollution Research 27, no. 5 (December 30, 2019): 4640–60. http://dx.doi.org/10.1007/s11356-019-07235-y.
Повний текст джерелаАнотація:
AbstractStudies show that user behaviours have not necessarily changed, despite the prevalence of water-efficient products in the market. One reason is because the technical emphasis for delivering the water use efficiency of products has focused on reducing the flow rate. Therefore, this study was undertaken to examine the physical parameters that define the technical efficiency of showerheads against the experiential performance (and therefore the satisfaction with the showerheads). These parameters were measured in a controlled laboratory environment and the findings were triangulated against user feedback from in-home trials. Synergies between the laboratory data and user feedback were found. Notably, it was found that water spray intensity, distribution, and temperature loss all impact the quality of showering experience. These factors also influence shower duration—and thus the volume of water used in the shower. Significantly, these technical metrics affected the overall experiential performance of such products from the users’ perspective. Therefore, the design of water-efficient showerheads, in addition to delivering water discharge savings, should avoid poor spray distribution, intensity, and heat retention. The implications of the findings are that water efficiency labelling and product standards should extend beyond the emphasis on limiting the flow rates—typically to 9 l per min for showerheads. This study shows good merit for including the spray intensity (pressure), distribution, and degree of heat loss, in addition to the discharge rate, as part of the performance and efficiency considerations of showerheads.
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Basir, Md Faisal Md, Mohammed Jashim Uddin, and Ahmad Izani Md Ismail. "Unsteady three-dimensional stagnation point magnetohydrodynamic flow of bionanofluid with variable properties." Proceedings of the Institution of Mechanical Engineers, Part N: Journal of Nanomaterials, Nanoengineering and Nanosystems 232, no. 4 (December 2018): 123–34. http://dx.doi.org/10.1177/2397791418817844.
Повний текст джерелаАнотація:
Unsteady three-dimensional laminar stagnation point forced convective boundary layer magnetohydrodynamic flow of a bionanofluid with variable transport properties is studied theoretically and numerically. Thermal convective and zero mass flux boundary conditions are incorporated in this study. The transport properties are assumed to be a function of nanoparticle volume fraction to get physically realistic results. The dimensional boundary layer equations along with the coupled boundary conditions are transformed via similarity transformations into a system of ordinary differential equations. The transformed equations are solved numerically using the Runge–Kutta–Fehlberg fourth-, fifth-order numerical method. The effect of selected governing parameters, namely, viscosity, thermal conductive, mass diffusivity, microorganism diffusivity, magnetic field and bioconvection Schmidt number, on the dimensionless velocity, temperature, nanoparticle volume fraction, microorganism, skin friction coefficient, heat transfer rate, mass transfer rate and microorganism transfer rate, is illustrated graphically and interpreted in detail. Comparisons with previous works are carried out for some limiting cases and found to be in good agreement.
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Anbarsooz, Morteza, and Hamid Niazmand. "Heat transfer characteristics of slip flow over solid spheres." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 230, no. 19 (August 9, 2016): 3431–41. http://dx.doi.org/10.1177/0954406215612829.
Повний текст джерелаАнотація:
In this study, heat transfer characteristics of slip flow over an isolated impermeable solid sphere are investigated numerically. An isothermal solid sphere is considered at intermediate Reynolds numbers (0 ≤ Re ≤ 50) for Prandtl numbers in the range of 0.7–7.0. The Navier–Stokes and energy equations are solved by a control volume technique in conjunction with the velocity slip and temperature jump boundary conditions. It was found that the size of the thermal wake region according to the Knudsen number depends on the Prandtl number. At lower Prandtl numbers (0.7 ≤ Pr ≤ 2.0), the thermal wake region shrinks as the Knudsen number increases, while at higher Prandtl numbers, it grows as the Knudsen number increases. The maximum temperature jump occurs at the front stagnation point where the local Nusselt is itself maximum, owing to the maximum temperature gradient at this point. The results show that due to the opposing effects of the velocity slip and temperature jump, the average Nusselt number variation with the Knudsen number depends nonlinearly on both the Prandtl and Reynolds numbers. Furthermore, for the limiting case of Re → 0, an analytical solution for the problem is presented which has also served as a validation case.
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Khashi’ie, Najiyah Safwa, Norihan Md Arifin, Roslinda Nazar, Ezad Hafidz Hafidzuddin, Nadihah Wahi, and Ioan Pop. "Mixed Convective Flow and Heat Transfer of a Dual Stratified Micropolar Fluid Induced by a Permeable Stretching/Shrinking Sheet." Entropy 21, no. 12 (November 27, 2019): 1162. http://dx.doi.org/10.3390/e21121162.
Повний текст джерелаАнотація:
The present study accentuates the magnetohydrodynamics (MHD) flow and heat transfer characteristics of a dual stratified micropolar fluid over a permeable stretching/shrinking sheet. Thermal and solutal buoyancy forces are also included to incorporate with the stratification effect. Similarity, transformation is applied to reduce the governing model (partial differential equations) into a set of nonlinear ordinary differential equations (ODEs) due to its complexity. Using bvp4c solver in the MATLAB software, numerical results for some limiting cases are in favorable agreement with the earlier published results. Both assisting and opposing buoyancy flows have dual similarity solutions within specific range of suction and stretching/shrinking parameters, whereas only a distinctive solution is observed for pure forced convective flow. The micropolar fluid shows a disparate pattern of flow, heat and mass transfer characteristics between stretching and shrinking cases. Unlike the shrinking flow, the surface velocity gradient, local Nusselt and Sherwood numbers for stretching flow intensify with the increment of the material parameter. The result from stability analysis reveals that the first solution is the real solution, whereas the second solution is virtual.
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Islam, Saeed, Haroon Ur Rasheed, Kottakkaran Sooppy Nisar, Nawal A. Alshehri, and Mohammed Zakarya. "Numerical Simulation of Heat Mass Transfer Effects on MHD Flow of Williamson Nanofluid by a Stretching Surface with Thermal Conductivity and Variable Thickness." Coatings 11, no. 6 (June 6, 2021): 684. http://dx.doi.org/10.3390/coatings11060684.
Повний текст джерелаАнотація:
The current analysis deals with radiative aspects of magnetohydrodynamic boundary layer flow with heat mass transfer features on electrically conductive Williamson nanofluid by a stretching surface. The impact of variable thickness and thermal conductivity characteristics in view of melting heat flow are examined. The mathematical formulation of Williamson nanofluid flow is based on boundary layer theory pioneered by Prandtl. The boundary layer nanofluid flow idea yields a constitutive flow laws of partial differential equations (PDEs) are made dimensionless and then reduce to ordinary nonlinear differential equations (ODEs) versus transformation technique. A built-in numerical algorithm bvp4c in Mathematica software is employed for nonlinear systems computation. Considerable features of dimensionless parameters are reviewed via graphical description. A comparison with another homotopic approach (HAM) as a limiting case and an excellent agreement perceived.
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Reindl, D. T., W. A. Beckman, and J. W. Mitchell. "Transient Natural Convection in Enclosures With Application to Solar Thermal Storage Tanks." Journal of Solar Energy Engineering 114, no. 3 (August 1, 1992): 175–81. http://dx.doi.org/10.1115/1.2930002.
Повний текст джерелаАнотація:
Many previously studied natural convection enclosure problems in the literature have the bounding walls of the enclosure responsible for driving the flow. A number of relevant applications contain sources within the enclosure which drive the fluid flow and heat transfer. The motivation for this work is found in solar thermal storage tanks with immersed coil heat exchangers. The heat exchangers provide a means to charge and discharge the thermal energy in the tank. The enclosure is cylindrical and well insulated. Initially the interior fluid is isothermal and quiescent. At time zero, a step change in the source temperature begins to influence the flow. The final condition is a quiescent isothermal fluid field at the source temperature. The governing time-dependent Navier-Stokes and energy equations for this configuration are solved by a finite element method. Solutions are obtained for 103≤RaD≤106. Scale analysis is used to obtain time duration estimates of three distinct heat transfer regimes. The transient heat transfer during these regimes are compared with limiting cases. Correlations are presented for the three regimes.
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Mishra, Satya Ranjan, Sushma Baag, Gouranga Charan Dash, and Manas Ranjan Acharya. "Numerical approach to MHD flow of power-law fluid on a stretching sheet with non-uniform heat source." Nonlinear Engineering 9, no. 1 (September 25, 2019): 81–93. http://dx.doi.org/10.1515/nleng-2018-0026.
Повний текст джерелаАнотація:
AbstractIn the present study the flow of power-law fluid, due to a stretching sheet embedded in a saturated porous medium, is considered. This study also accounts for the variable thermal conductivity in the process of heat transfer along with dissipation due to Joule heating. The thermal conductivity is assumed to vary as a linear function of temperature. The similarity transformation is used to convert nonlinear partial differential equations to non linear ordinary equations. The numerical method, Runge-Kutta method with shooting technique has been applied to solve the resulting equations. The power-law fluid exhibits a dual property in the presence of magnetic field. The limiting cases n → 0 and n → ∞ have been discussed. For large n the solution becomes unstable which leads to flow instability(Shown in the graph).
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Hayat, Tasawar, Sabir Ali Shehzad, Muhammad Qasim, and Saleem Obaidat. "Thermal Radiation Effects on the Mixed Convection Stagnation-Point Flow in a Jeffery Fluid." Zeitschrift für Naturforschung A 66, no. 10-11 (November 1, 2011): 606–14. http://dx.doi.org/10.5560/zna.2011-0024.
Повний текст джерелаАнотація:
This study describes the mixed convection stagnation point flow and heat transfer of a Jeffery fluid towards a stretching surface. Mathematical formulation is given in the presence of thermal radiation. The Rosseland approximation is used to describe the radiative heat flux. Similarity transformations are employed to reduce the partial differential equations into the ordinary differential equations which are then solved by a homotopy analysis method (HAM). A comparative study is made with the known numerical solutions in a limiting sense and an excellent agreement is noted. The characteristics of involved parameters on the dimensionless velocity and temperature are also examined. It is noticed that the velocity increases with an increase in Deborah number. Further, the temperature is a decreasing function of mixed convection parameter. We further found that for fixed values of other parameters, the local Nusselt number increases by increasing suction parameter and Deborah number.
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Nazeer, Mubbashar, Farooq Hussain, Fayyaz Ahmad, Sadia Iftikhar, and Gener S. Subia. "Theoretical study of an unsteady ciliary hemodynamic fluid flow subject to the Newton’s boundary conditions." Advances in Mechanical Engineering 13, no. 8 (August 2021): 168781402110404. http://dx.doi.org/10.1177/16878140211040462.
Повний текст джерелаАнотація:
This article addresses the hemodynamic flow of biological fluid through a symmetric channel. Methachronal waves induced by the ciliary motion of motile structures are the main source of Couple stress nanofluid flow. Darcy’s law is incorporated in Navier-Stokes equations to highlight the influence of the porous medium. Thermal transport by the microscopic collision of particles is governed by Fourier’s law while a separate expression is obtained for net diffusion of nanoparticles by using Fick’s law. A closed-form solution is achieved of nonlinear differential equations subject to Newton’s boundary conditions. Moreover, the current findings are compared with previous outcomes for the limiting case and found a complete coherence. Parametric study reveals that nanoflow is resisted by employing Newton’s boundary conditions. Thermal profile enhancement is contributed by the viscous dissipation parameter. Finally, one infers that hemodynamic flow of non-Newtonian fluid is an effective mode of heat and mass transfer especially, in medical sciences for the rapid transport of medicines in drug therapy.
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Khan, Arshad, Ilyas Khan, Farhad Ali, Asma Khalid, and Sharidan Shafie. "Exact Solutions of Heat and Mass Transfer with MHD Flow in a Porous Medium under Time Dependent Shear Stress and Temperature." Abstract and Applied Analysis 2015 (2015): 1–16. http://dx.doi.org/10.1155/2015/975201.
Повний текст джерелаАнотація:
This paper aims to study the influence of thermal radiation on unsteady magnetohyrdodynamic (MHD) natural convection flow of an optically thick fluid over a vertical plate embedded in a porous medium with arbitrary shear stress. Combined phenomenon of heat and mass transfer is considered. Closed-form solutions in general form are obtained by using the Laplace transform technique. They are expressed in terms of exponential and complementary error functions. Velocity is expressed as a sum of thermal and mechanical parts. Corresponding limiting solutions are also reduced from the general solutions. It is found that the obtained solutions satisfy all imposed initial and boundary conditions and reduce to some known solutions from the literature as special cases. Analytical results for the pertinent flow parameters are drawn graphically and discussed in detail. It is found that the velocity profiles of fluid decrease with increasing shear stress. The magnetic parameter develops shear resistance which reduces the fluid motion whereas the inverse permeability parameter increases the fluid flow.
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Denier, James P., and Andrew P. Bassom. "Neutrally stable wave motions in thermally stratified Poiseuille-Couette flow." Journal of the Australian Mathematical Society. Series B. Applied Mathematics 40, no. 1 (July 1998): 123–44. http://dx.doi.org/10.1017/s0334270000012418.
Повний текст джерелаАнотація:
AbstractThe influence of thermal buoyancy on neutral wave modes in Poiseuille-Couette flow is considered. We examine the modifications to the asymptotic structure first described by Mureithi, Denier & Stott [16], who demonstrated that neutral wave modes in a strongly thermally stratified boundary layer are localized at the position where the streamwise velocity attains its maximum value. The present work demonstrates that such a flow structure also holds for Poiseuille-Couette flow but that a new flow structure emerges as the position of maximum velocity approaches the wall (and which occurs as the level of shear, present as a consequence of the Couette component of the flow, is increased). The limiting behaviour of these wave modes is discussed thereby allowing us to identify the parameter regime appropriate to the eventual restabilization of the flow at moderate levels of shear.
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Hayat, Tasawar, and Muhammad Qasim. "Effects of Thermal Radiation on Unsteady Magnetohydrodynamic Flow of a Micropolar Fluid with Heat and Mass Transfer." Zeitschrift für Naturforschung A 65, no. 11 (November 1, 2010): 950–60. http://dx.doi.org/10.1515/zna-2010-1107.
Повний текст джерелаАнотація:
An analysis has been carried out to study the combined effects of heat and mass transfer on the unsteady flow of a micropolar fluid over a stretching sheet. The thermal radiation effects are presented. The arising nonlinear partial differential equations are first reduced to a set of nonlinear ordinary differential equations and then solved by the homotopy analysis method (HAM). Plots for various interesting parameters are presented and discussed. Numerical data for surface shear stress, Nusselt number, and Sherwood number in steady case are also tabulated. Comparison between the present and previous limiting results is given.
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Liu, I.-Chung, and Ahmed M. Megahed. "Homotopy Perturbation Method for Thin Film Flow and Heat Transfer over an Unsteady Stretching Sheet with Internal Heating and Variable Heat Flux." Journal of Applied Mathematics 2012 (2012): 1–12. http://dx.doi.org/10.1155/2012/418527.
Повний текст джерелаАнотація:
We have analyzed the effects of variable heat flux and internal heat generation on the flow and heat transfer in a thin film on a horizontal sheet in the presence of thermal radiation. Similarity transformations are used to transform the governing equations to a set of coupled nonlinear ordinary differential equations. The obtained differential equations are solved approximately by the homotopy perturbation method (HPM). The effects of various parameters governing the flow and heat transfer in this study are discussed and presented graphically. Comparison of numerical results is made with the earlier published results under limiting cases.
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Taguchi, Satoshi, and Kazuo Aoki. "Rarefied gas flow around a sharp edge induced by a temperature field." Journal of Fluid Mechanics 694 (January 17, 2012): 191–224. http://dx.doi.org/10.1017/jfm.2011.536.
Повний текст джерелаАнотація:
AbstractA rarefied gas flow thermally induced around a heated (or cooled) flat plate, contained in a vessel, is considered in two different situations: (i) both sides of the plate are simultaneously and uniformly heated (or cooled); and (ii) only one side of the plate is uniformly heated. The former is known as the thermal edge flow and the latter, typically observed in the Crookes radiometer, may be called the radiometric flow. The steady behaviour of the gas induced in the container is investigated on the basis of the Bhatnagar–Gross–Krook (BGK) model of the Boltzmann equation and the diffuse reflection boundary condition by means of an accurate finite-difference method. The flow features are clarified for a wide range of the Knudsen number, with a particular emphasis placed on the structural similarity between the two flows. The limiting behaviour of the flow as the Knudsen number tends to zero (and thus the system approaches the continuum limit) is investigated for both flows. The detailed structure of the normal stress on the plate as well as the cause of the radiometric force (the force acting on the plate from the hotter to the colder side) is also clarified for the present infinitely thin plate.
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Zhang, Zheyuan, Yonghui Xie, Di Zhang, and Gongnan Xie. "Flow Characteristic and Heat Transfer for Non-Newtonian Nanofluid in Rectangular Microchannels with Teardrop Dimples/Protrusions." Open Physics 15, no. 1 (April 24, 2017): 197–206. http://dx.doi.org/10.1515/phys-2017-0021.
Повний текст джерелаАнотація:
AbstractPorous cavity technology is one of the effective ways to improve local flow structures and thus the overall heat transfer of heat exchanging devices. In the present investigation, the flow characteristics and heat transfer in a microchannel heat sink with teardrop dimples/protrusions are studied with a numerical method. The working substances are Al2O3-water nanofluids, which are defined by power-law shear-thinning model. The relative depth and positive eccentricity of dimples/protrusions arranged in the microchannels are 0.2 and 0.3 respectively. The inlet velocity varies in the range of 1.41 m⋅s−1to 8.69 m⋅s−1and the volume fraction ranges from 0.5% to 3.5%. The effects of the flow and heat transfer characteristics are investigated by analyzing the limiting streamlines structures and temperature distributions. The overall thermal performance is evaluated by parameters of Fanning friction factor, Nusselt number and thermal performance. It is shown that the combination of teardrop dimple/protrusion structure and Al2O3-water nanofluids could effectively strengthen heat transfer with low pressure loss. Moreover, in order to obtain the best overall thermal performance, working substances with volume faction of 3.5% is preferred for the proposed microchannel structure.
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Fatunmbi, Ephesus Olusoji, Samuel Segun Okoya, and Oluwole Daniel Makinde. "Convective Heat Transfer Analysis of Hydromagnetic Micropolar Fluid Flow Past an Inclined Nonlinear Stretching Sheet with Variable Thermo-Physical Properties." Diffusion Foundations 26 (March 2020): 63–77. http://dx.doi.org/10.4028/www.scientific.net/df.26.63.
Повний текст джерелаАнотація:
The current work examines mixed convection boundary layer flow and heat transfer attributes in hydromagnetic micropolar fluid past a heated inclined sheet which stretches nonlinearly along the direction of flow. The impact of variable thermo-physical characteristics of the fluid together with the influence of magnetic field, thermal radiation and viscous dissipation are also checked on the flow field. The modelled governing equations are translated from partial to ordinary differential equations via relevant similarity transformations and the resulting equations are subsequently solved numerically by means of shooting techniques in company with Runge-Kutta integration algorithms. The reactions of the skin friction coefficient, Nusselt number, dimensionless velocity as well as temperature to variations in the emerging controlling parameters are illustrated through different graphs. In the limiting situations, the results obtained exhibit a strong relationship with the existing related works in literature. The facts emanated from this study also reveal that the thickness of the thermal boundary layer grows widely with a rise in the Eckert number and Biot number parameters whereas increasing the material (micropolar) and thermal conductivity parameters have opposite effects on the rate of heat transfer.
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Khan, Zeeshan, Haroon Ur Rasheed, Sahib Noor, Waris Khan, Qayyum Shah, Ilyas Khan, Seifedine Kadry, Yunyoung Nam, and Kottakkaran Sooppy Nisar. "Analytical Solution of UCM Viscoelastic Liquid with Slip Condition and Heat Flux over Stretching Sheet: The Galerkin Approach." Mathematical Problems in Engineering 2020 (February 25, 2020): 1–7. http://dx.doi.org/10.1155/2020/7563693.
Повний текст джерелаАнотація:
This paper provides a substantial amount of study related to coupled fluid flow and heat conduction of an upper-convected-Maxwell viscoelastic liquid over a stretching plane with slip velocity. A new model, presented by Christov, for thermal convection is employed. The partial differential equations are converted to ordinary differential equations by using appropriate transformation variables. The transformed equations are solved analytically by using the Galerkin method. For the sake of soundness, a comparison is done with a numerical method, and good agreement is found. The impacts of various parameters like slip coefficient, elasticity number, the thermal relaxation time of heat flow, and the Prandtl number over the temperature and velocity fields are studied. Furthermore, the Cattaneo–Christov heat flux model is compared with Fourier’s law. Additionally, the present results are also verified by associating with the published work as a limiting case.
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Nandeppanavar, Mahantesh M., Kemparaju M.C., and N. Raveendra. "Double-diffusive free convective flow of Casson fluid due to a moving vertical plate with non-linear thermal radiation." World Journal of Engineering 18, no. 1 (November 16, 2020): 85–93. http://dx.doi.org/10.1108/wje-06-2020-0215.
Повний текст джерелаАнотація:
Purpose This paper aims to report the investigation of over heat and mass transfer of convective Casson fluid flow over a moving vertical plate with nonlinear thermal radiation and convective boundary conditions. Design/methodology/approach The main partial differential equations of the flow, heat and concentration profiles were rehabilitated to nonlinear ordinary differential equations by using an appropriate similarity transformation. The resultant nonlinear ordinary differential equations (ODEs) are solved numerically applying fourth-order Runge–Kutta shooting technique and functions of ODE45 from MATLAB. Findings The effect of convective heat transfer, buoyancy ratio parameter, nonlinear thermal radiation, Prandtl number, Rayleigh number and Schmidt number over velocity, temperature and concentration profiles, equivalent to abundant somatic parameters were graphically scrutinized. Originality/value All the results are very promising and further there is got good agreement of results when compared with earlier published results at limiting conditions.
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Vijaya Lakshmi, R., G. Sarojamma, and Ali J. Chamkha. "Simulation of Thermo Diffusion on Three-Dimensional Flow of a Micropolar Liquid on an Inclined Convective Surface with Nonlinear Stretching Sheet." Journal of Nanofluids 9, no. 3 (September 1, 2020): 133–42. http://dx.doi.org/10.1166/jon.2020.1750.
Повний текст джерелаАнотація:
The present research explores the features of thermal and solutal transport of a 3D micropolar liquid stream on an elongated convectively heated inclined sheet taking Soret effect. Mathematical modelling is designed with the aid of suitable scaling analysis on the governing PDEs conceiving the small magnetic Reynolds number. The resultant set of coupled nonlinear ODEs are derived with MATLAB to obtain computational solutions. Impression of the emerged flow parameters on the three boundary layers is graphically traced and deliberated. The parameters of magnetic field and stretching ratio and power law index diminished frictional drag. Hike in rate of thermal diffusion is prevailed with stronger surface heat convective and Prandtl numbers. Outcomes are collated with the data available in the literature and found to agree very closely as a limiting case.
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Koriko, O. K., I. L. Animasaun, M. Gnaneswara Reddy, and N. Sandeep. "Scrutinization of thermal stratification, nonlinear thermal radiation and quartic autocatalytic chemical reaction effects on the flow of three-dimensional Eyring-Powell alumina-water nanofluid." Multidiscipline Modeling in Materials and Structures 14, no. 2 (June 4, 2018): 261–83. http://dx.doi.org/10.1108/mmms-08-2017-0077.
Повний текст джерелаАнотація:
Purpose The purpose of this paper is to scrutinize the effects of nonlinear thermal radiation and thermal stratification effects on the flow of three-dimensional Eyring-Powell 36 nm alumina-water nanofluid within the thin boundary layer in the presence of quartic autocatalytic kind of chemical reaction effects, and to unravel the effects of a magnetic field parameter, random motion of the tiny nanoparticles and volume fraction on the flow. Design/methodology/approach The chemical reaction between homogeneous (Eyring-Powell 36 nm alumina-water) bulk fluid and heterogeneous (three molecules of the catalyst at the surface) in the flow of magnetohydrodynamic three-dimensional flow is modeled as a quartic autocatalytic kind of chemical reaction. The electromagnetic radiation which occurs within the boundary layer is treated as the nonlinear form due to the fact that Taylor series expansion may not give full details of such effects within the boundary layer. With the aid of appropriate similarity variables, the nonlinear coupled system of partial differential equation which models the flow was reduced to ordinary differential equation boundary value problem. Findings A favorable agreement of the present results is obtained by comparing it for a limiting case with the published results; hence, reliable results are presented. The concentration of homogeneous bulk fluid (Eyring-Powell nanofluid) increases and decreases with ϕ and Pr, respectively. The increase in the value of magnetic field parameter causes vertical and horizontal velocities of the flow within the boundary layer to decrease significantly. The decrease in the vertical and horizontal velocities of Eyring-Powell nanofluid flow within the boundary layer is guaranteed due to an increase in the value of M. Concentration of homogeneous fluid increases, while the concentration of the heterogeneous catalyst at the wall decreases with M. Originality/value Considering the industrial applications of thermal stratification in solar engineering and polymer processing where the behavior of the flow possesses attributes of Eyring-Powell 36 nm alumina-water, this paper presents the solution of the flow problem considering 36 nm alumina nanoparticles, thermophoresis, stratification of thermal energy, Brownian motion and nonlinear thermal radiation. In addition, the aim and objectives of this paper fill such vacuum in the industry.
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Madhu, Macha, N. S. Shashikumar, Bijjanal Jayanna Gireesha, and Naikoti Kishan. "Second Law Analysis of MHD Micropolar Fluid Flow through a Porous Microchannel with Multiple Slip and Convective Boundary Conditions." Defect and Diffusion Forum 409 (May 2021): 123–41. http://dx.doi.org/10.4028/www.scientific.net/ddf.409.123.
Повний текст джерелаАнотація:
The impact of space dependent heat source in the transport of micropolar fluid in the existence of magnetic dipole, Joule heating, viscous heating, thermal radiation, hydrodynamic slips and convective condition effects has been numerically investigated. The dimensioned governing equations are non-dimensionlzed by using dimensionless variables then non-dimensional forms of the corresponding equations are than tackled by the versatile Finite Element Method (FEM). The effects of pertinent physical parameters characterize the flow phenomena are presented through graphs and discussed. It is found that, the impact of thermal based heat source advances the heat transfer characteristics significantly than exponential to space dependent. The thermal performance can be improved through the effects of magnetic dipole, viscous heating, Joule heating and convective condition. Further, the present numerical results are compared with previously published results in the literature as a limiting case of the considered problem and found to be in good agreement with the existing results.
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Hofmeister, Anne M., Everett M. Criss, and Robert E. Criss. "Thermodynamic Relationships for Perfectly Elastic Solids Undergoing Steady-State Heat Flow." Materials 15, no. 7 (April 3, 2022): 2638. http://dx.doi.org/10.3390/ma15072638.
Повний текст джерелаАнотація:
Available data on insulating, semiconducting, and metallic solids verify our new model that incorporates steady-state heat flow into a macroscopic, thermodynamic description of solids, with agreement being best for isotropic examples. Our model is based on: (1) mass and energy conservation; (2) Fourier’s law; (3) Stefan–Boltzmann’s law; and (4) rigidity, which is a large, yet heretofore neglected, energy reservoir with no counterpart in gases. To account for rigidity while neglecting dissipation, we consider the ideal, limiting case of a perfectly frictionless elastic solid (PFES) which does not generate heat from stress. Its equation-of-state is independent of the energetics, as in the historic model. We show that pressure-volume work (PdV) in a PFES arises from internal interatomic forces, which are linked to Young’s modulus (Ξ) and a constant (n) accounting for cation coordination. Steady-state conditions are adiabatic since heat content (Q) is constant. Because average temperature is also constant and the thermal gradient is fixed in space, conditions are simultaneously isothermal: Under these dual restrictions, thermal transport properties do not enter into our analysis. We find that adiabatic and isothermal bulk moduli (B) are equal. Moreover, Q/V depends on temperature only. Distinguishing deformation from volume changes elucidates how solids thermally expand. These findings lead to simple descriptions of the two specific heats in solids: ∂ln(cP)/∂P = −1/B; cP = nΞ times thermal expansivity divided by density; cP = cVnΞ/B. Implications of our validated formulae are briefly covered.
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Novelli, Nick, Justin S. Shultz, Mohamed Aly Etman, Kenton Phillips, Jason O. Vollen, Michael Jensen, and Anna Dyson. "Towards Energy-Positive Buildings through a Quality-Matched Energy Flow Strategy." Sustainability 14, no. 7 (April 4, 2022): 4275. http://dx.doi.org/10.3390/su14074275.
Повний текст джерелаАнотація:
Current strategies for net-zero buildings favor envelopes with minimized aperture ratios and limiting of solar gains through reduced glazing transmittance and emissivity. This load-reduction approach precludes strategies that maximize on-site collection of solar energy, which could increase opportunities for net-zero electricity projects. To better leverage solar resources, a whole-building strategy is proposed, referred to as “Quality-Matched Energy Flows” (or Q-MEF): capturing, transforming, buffering, and transferring irradiance on a building’s envelope—and energy derived from it—into distributed end-uses. A mid-scale commercial building was modeled in three climates with a novel Building-Integrated, Transparent, Concentrating Photovoltaic and Thermal fenestration technology (BITCoPT), thermal storage and circulation at three temperature ranges, adsorption chillers, and auxiliary heat pumps. BITCoPT generated electricity and collected thermal energy at high efficiencies while transmitting diffuse light and mitigating excess gains and illuminance. The balance of systems satisfied cooling and heating demands. Relative to baselines with similar glazing ratios, net electricity use decreased 71% in a continental climate and 100% or more in hot-arid and subtropical-moderate climates. Total EUI decreased 35%, 83%, and 52%, and peak purchased electrical demands decreased up to 6%, 32%, and 20%, respectively (with no provisions for on-site electrical storage). Decreases in utility services costs were also noted. These results suggest that with further development of electrification the Q-MEF strategy could contribute to energy-positive behavior for projects with similar typology and climate profiles.
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Kaleem, S., S. Rentsch, T. Welker, J. Müller, and M. A. Hein. "Thermal analysis, design, and characterization of a reconfigurable switch matrix based on LTCC technology for satellite communications." International Symposium on Microelectronics 2014, no. 1 (October 1, 2014): 000692–97. http://dx.doi.org/10.4071/isom-wp35.
Повний текст джерелаАнотація:
The thermal characteristics of a reconfigurable switch matrix (RSM) module based on low temperature co-fired ceramic (LTCC) technology are presented. Owing to the PIN-diodes based design, a static power of 1.6 W is dissipated on the ceramic package; the double-sided mounting and integrated bias circuitry demands determination of the temperature distribution within the module. A finite-element thermal simulation model was validated by an infrared (IR) thermograph; the steady-state temperature distribution on the surface of the package estimated by the simulation model differs to the IR measurements by < 1%. This temperature distribution is the result of the thermal interaction among components on the multi-die package with different electrical power dissipation. The temperature on the multi-throw switch monolithic microwave integrated circuit (MMIC) is elevated by ~36.7 K relative to the ambient temperature. The peak temperature occurs on the current-limiting resistors in the bias circuitry; the peak temperature is estimated to be ~45 K above the ambient. In a later version of the RSM, the bias current was reduced by 50%, current-limiting resistor was replaced by two parallel resistors, and additional thermal vias and conductive pads were introduced on the ceramic package. The cumulative effect is a temperature distribution on the package with lowered values. Compared to its predecessor, the temperatures at the current-limiting resistor and the MMIC are reduced by ~20 K and ~14 K, respectively. With one heat source active on the ceramic package at a time, the resulting steady-state temperatures on this source and the remaining heat sources provided an estimate of the self- and transfer-thermal resistances, respectively. The reciprocity of the heat flow on the package and the three-dimensional symmetric layout required only ‘4’ thermal simulations to determine the symmetric thermal resistance matrix. The significantly reduced values of the computed matrix for the later version of the RSM module demonstrated lower thermal resistance to the ambient, compared to its predecessor. Lastly, the results of thermal measurements conducted with a vacuum wafer prober are presented, in order to validate RSM functionality for vacuum pressures (≤ 1 mPa) and temperatures between 248 K and 338 K; the control current and the transmission coefficient demonstrated variations of ≤ 0.5% and −0.015 dB/K, respectively.
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Wang, Yan, and Derek O. Northwood. "Life-Limiting Aspects of the Corrosion of Metallic Bipolar Plates for PEM Fuel Cells." Advanced Materials Research 41-42 (April 2008): 469–75. http://dx.doi.org/10.4028/www.scientific.net/amr.41-42.469.
Повний текст джерелаАнотація:
In proton exchange membrane fuel cells (PEMFCs), the bipolar plates supply the reactant gases through the flow channels to the electrodes and serve the purpose of electrochemically connecting one cell to another in the electrochemical cell stack. Requirements of the bipolar plate material are: high values of electronic conductivity; high values of thermal conductivity; high mechanical strength; impermeability to reactant gases; resistance to corrosion; and low cost of automated production. Metallic materials meet many of these requirements but the challenge has been in obtaining the required corrosion resistance. In the paper, six metallic materials were investigated as potential bipolar plate materials. The results showed that the corrosion rates were too high even for the most corrosion resistant metals (SS316L and grade 2 Ti), and that coatings would be required.
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Nandeppanavar, Mahantesh M., M. C. Kemparaju, and S. Shakunthala. "MHD stagnation point slip flow due to a non-linearly moving surface with effect of non-uniform heat source." Nonlinear Engineering 8, no. 1 (January 28, 2019): 270–82. http://dx.doi.org/10.1515/nleng-2017-0109.
Повний текст джерелаАнотація:
Abstract In this paper, we have studied the heat transfer characteristics of stagnation point flow of an MHD flow over a non-linearly moving plate with momentum and thermal slip effects in presence of non-uniform heat source/sink. The governing differential equations are transformed into the ordinary differential equations using suitable similarity transformations. These equations which are BVPs’ and are solved using a numerically by fourth order Runge-Kutta method using MAPLE computing software. The effects of governing parameters are studied on flow, velocity and heat distributions and are discussed in detail. It is observed that the non-uniform heat source parameters enhance the temperature distribution. Our results are agreed well with previously published results for some limiting conditions, which validate our present results are correct.
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Zarichnyak, Yuri P., and Vyacheslav P. Khodunkov. "Analysis of significant measures for thermal conductivity." Izmeritel`naya Tekhnika, no. 3 (2020): 35–42. http://dx.doi.org/10.32446/0368-1025it.2020-3-35-42.
Повний текст джерелаАнотація:
The analysis of a new class of measuring instrument for heat quantities based on the use of multi-valued measures of heat conductivity of solids. For example, measuring thermal conductivity of solids shown the fallacy of the proposed approach and the illegality of the use of the principle of ambiguity to intensive thermal quantities. As a proof of the error of the approach, the relations for the thermal conductivities of the component elements of a heat pump that implements a multi-valued measure of thermal conductivity are given, and the limiting cases are considered. In two ways, it is established that the thermal conductivity of the specified measure does not depend on the value of the supplied heat flow. It is shown that the declared accuracy of the thermal conductivity measurement method does not correspond to the actual achievable accuracy values and the standard for the unit of surface heat flux density GET 172-2016. The estimation of the currently achievable accuracy of measuring the thermal conductivity of solids is given. The directions of further research and possible solutions to the problem are given.
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Hayat, T., M. Waqas, Sabir Ali Shehzad, and A. Alsaedi. "Mixed convection flow of viscoelastic nanofluid by a cylinder with variable thermal conductivity and heat source/sink." International Journal of Numerical Methods for Heat & Fluid Flow 26, no. 1 (January 4, 2016): 214–34. http://dx.doi.org/10.1108/hff-02-2015-0053.
Повний текст джерелаАнотація:
Purpose – The purpose of this paper is to examine the effects of variable thermal conductivity in mixed convection flow of viscoelastic nanofluid due to a stretching cylinder with heat source/sink. Design/methodology/approach – The authors have computed the existence of the solution for Walter’s B and second grade fluids corresponding to Pr=0.5 and Pr=1.5. Skin-friction coefficient, local Nusselt and Sherwood numbers are computed numerically for different values of emerging parameters. Findings – A comparative study with the existing solutions in a limiting sense is made and analyzed. The authors found that the dimensionless velocity filed and momentum boundary layer thickness are increased when the values of viscoelastic parameter increase. The present non-Newtonian fluid flow reduces to the viscous flow in the absence of viscoelastic parameter. The larger values of viscoelastic parameter corresponds to the higher values of local Nusselt and Sherwood numbers. Originality/value – No such analysis exists in the literature yet.
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Mantovani, R., and A. Speranza. "Baroclinic instability of a symmetric, rotating, stratified flow: a study of the nonlinear stabilisation mechanisms in the presence of viscosity." Nonlinear Processes in Geophysics 9, no. 5/6 (December 31, 2002): 487–96. http://dx.doi.org/10.5194/npg-9-487-2002.
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Abstract. This paper presents the analysis of symmetric circulations of a rotating baroclinic flow, forced by a steady thermal wind and dissipated by Laplacian friction. The analysis is performed with numerical time-integration. Symmetric flows, vertically bound by horizontal walls and subject to either periodic or vertical wall lateral boundary conditions, are investigated in the region of parameter-space where unstable small amplitude modes evolve into stable stationary nonlinear solutions. The distribution of solutions in parameter-space is analysed up to the threshold of chaotic behaviour and the physical nature of the nonlinear interaction operating on the finite amplitude unstable modes is investigated. In particular, analysis of time-dependent energy-conversions allows understanding of the physical mechanisms operating from the initial phase of linear instability to the finite amplitude stable state. Vertical shear of the basic flow is shown to play a direct role in injecting energy into symmetric flow since the stage of linear growth. Dissipation proves essential not only in limiting the energy of linearly unstable modes, but also in selecting their dominant space-scales in the finite amplitude stage.
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Majeed, A., A. Zeeshan, Huijin Xu, M. Kashif, and U. Masud. "Heat transfer analysis of magneto-Eyring–Powell fluid over a nonlinear stretching surface with multiple slip effects: Application of Roseland’s heat flux." Canadian Journal of Physics 97, no. 12 (December 2019): 1253–61. http://dx.doi.org/10.1139/cjp-2018-0732.
Повний текст джерелаАнотація:
Non-Newtonian fluid model is intricate, nonlinear, and interesting to study because of the presence of rheological flow parameters and viscoelastic properties, which tend to emerge and make industrial flows considerably more complex to explain accurately. Improvement of industrial applications, such as glass fabrication, is an important consequence of this study. In this manuscript, we have explored the combined impact of the higher order slip with variable transverse magnetic field flow and thermal transport using Roseland’s heat flux of the Eyring–Powell fluid with assumption of boundary layer, on nonlinear stretching sheet, in which fluid is considered electrically conducting. The transformed ordinary differential equations are solved by three-stage Lobatto IIIa collocation finite difference scheme using MATLAB. The impact of pertinent flow parameters on dimensionless velocity and temperature profiles is presented graphically and discussed in detail. Obtained results confirm that excellent agreement is achieved for the limiting case with those from the available literature. It is found that skin friction increases in the presence of slip parameters, whereas the opposite behaviour is noted in the Nusselt number.
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Tarakaramu, Nainaru, P. V. Satya Narayana, and Bhumarapu Venkateswarlu. "Numerical simulation of variable thermal conductivity on 3D flow of nanofluid over a stretching sheet." Nonlinear Engineering 9, no. 1 (May 13, 2020): 233–43. http://dx.doi.org/10.1515/nleng-2020-0011.
Повний текст джерелаАнотація:
AbstractThe present investigation deals with the steady three-dimensional flow and heat transfer of nanofluids due to stretching sheet in the presence of magnetic field and heat source. Three types of water based nanoparticles namely, copper (Cu), aluminium oxide (Al2O3), and titanium dioxide (TiO2) are considered in this study. The temperature dependent variable thermal conductivity and thermal radiation has been introduced in the energy equation. Using suitable similarity transformations the dimensional non-linear expressions are converted into dimensionless system and are then solved numerically by Runge-Kutta-Fehlberg scheme along with well-known shooting technique. The impact of various flow parameters on axial and transverse velocities, temperature, surface frictional coefficients and rate of heat transfer coefficients are visualized both in qualitative and quantitative manners in the vicinity of stretching sheet. The results reviled that the temperature and velocity of the fluid rise with increasing values of variable thermal conductivity parameter. Also, the temperature and normal velocity of the fluid in case of Cu-water nanoparticles is more than that of Al2O3- water nanofluid. On the other hand, the axial velocity of the fluid in case of Al2O3- water nanofluid is more than that of TiO2nanoparticles. In addition, the current outcomes are matched with the previously published consequences and initiate to be a good contract as a limiting sense.
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Afridi, Muhammad Idrees, I. Tlili, Marjan Goodarzi, M. Osman, and Najeeb Alam Khan. "Irreversibility Analysis of Hybrid Nanofluid Flow over a Thin Needle with Effects of Energy Dissipation." Symmetry 11, no. 5 (May 12, 2019): 663. http://dx.doi.org/10.3390/sym11050663.
Повний текст джерелаАнотація:
The flow and heat transfer analysis in the conventional nanofluid A l 2 O 3 − H 2 O and hybrid nanofluid C u − A l 2 O 3 − H 2 O was carried out in the present study. The present work also focused on the comparative analysis of entropy generation in conventional and hybrid nanofluid flow. The flows of both types of nanofluid were assumed to be over a thin needle in the presence of thermal dissipation. The temperature at the surface of the thin needle and the fluid in the free stream region were supposed to be constant. Modified Maxwell Garnet (MMG) and the Brinkman model were utilized for effective thermal conductivity and dynamic viscosity. The numerical solutions of the self-similar equations were obtained by using the Runge-Kutta Fehlberg scheme (RKFS). The Matlab in-built solver bvp4c was also used to solve the nonlinear dimensionless system of differential equations. The present numerical results were compared to the existing limiting outcomes in the literature and were found to be in excellent agreement. The analysis demonstrated that the rate of entropy generation reduced with the decreasing velocity of the thin needle as compared to the free stream velocity. The hybrid nanofluid flow with less velocity was compared to the regular nanofluid under the same circumstances. Furthermore, the enhancement in the temperature profile of the hybrid nanofluid was high as compared to the regular nanofluid. The influences of relevant physical parameters on flow, temperature distribution, and entropy generation are depicted graphically and discussed herein.