Analysis of Thermal Performances in a Ventilated Room Using LBM-MRT: Effect of a Porous Separation

This article demonstrates the feasibility of porous separation on the performance of displacement ventilation in a rectangular enclosure. A jet of fresh air enters the cavity through an opening at the bottom of the left wall and exits through an opening at the top of the right wall. The porous separation is placed in the center of the cavity and its height varies between 0.2 and 0.8 with three values of thickness, 0.1, 0.2, and 0.3. The heat transfer rate was calculated for different intervals of Darcy (10−6 ≤ Da ≤ 10), Rayleigh (10 ≤ Ra ≤ 106), and Reynolds (50 ≤ Re ≤ 500) numbers. The momentum and the energy equations were solved by the lattice Boltzmann method with multiple relaxation times (LB-MRT). Schemes D2Q9 and D2Q5 were chosen for the velocity and temperature fields, respectively. For porous separation, the generalized Darcy–Brinkman–Forchheimer model was adopted. It is represented by a term added in the standard LB equations. For the dynamic domain, numerical simulations revealed complex flow structures depending on all control parameters. The results showed that the thermal field, mainly in the second compartment, is very dependent on the size and permeability of the porous separation. However, they have no influence on the transfer rate.

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Effects of Important Parameters on the Transition from Forced to Mixed Convection Flow in a Square Cavity

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.406.36 ◽

2021 ◽

Vol 406 ◽

pp. 36-52

Author(s):

Sofiane Boulkroune ◽

Omar Kholai ◽

Brahim Mahfoud

Keyword(s):

Reynolds Number ◽

Prandtl Number ◽

Mixed Convection ◽

Forced Convection ◽

Temperature Fields ◽

Navier Stokes ◽

Convection Flow ◽

Square Cavity ◽

Left Wall ◽

Energy Equations

Combined free and forced convection in a square cavity filled with a viscous fluid characterized by a small Prandtl number is studied numerically. The left wall is moving with a constant velocity v and is maintained at a local cold temperature Tc, while the right wall is fixed and maintained at a local hot temperature Th (Tc <Th). The top and bottom walls of the cavity is assumed to be adiabatic. The governing Navier-Stokes, and energy equations along with appropriate boundary conditions are solved using the finite-volume method. The flow and temperature fields are presented by stream function and isotherms, respectively. The effects of important parameters such as Reynolds number, Prandtl number, and Grashof number on the transition from forced convection to mixed convection are investigated. Results indicate that increasing Reynolds number results to fluid acceleration and, thus, to flow transition. Results also show that Grashof and Prandtl's numbers influenced the conditions for the transition to the mixed convection regime.

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Ciliary Flow of Casson Nanofluid with the Influence of MHD having Carbon Nanotubes

Current Nanoscience ◽

10.2174/1573413716999201015090335 ◽

2020 ◽

Vol 16 ◽

Author(s):

Adel Alblawi ◽

Saba Keyani ◽

S. Nadeem ◽

Alibek Issakhov ◽

Ibrahim M. Alarifi

Keyword(s):

Carbon Nanotubes ◽

Velocity Profile ◽

Pressure Gradient ◽

Volume Fraction ◽

Solid Volume Fraction ◽

Pressure Rise ◽

Shear Stresses ◽

Left Wall ◽

Coupled Equations ◽

The Right

Objective: In this paper, we consider a model that describes the ciliary beating in the form of metachronal waves along with the effects of Magnetohydrodynamic fluid over a curved channel with slip effects. This work aims at evaluating the effect of Magnetohydrodynamic (MHD) on the steady two dimensional (2-D) mixed convection flow induced in carbon nanotubes. The work is done for both the single wall nanotube and multiple wall nanotube. The right wall and the left wall possess a metachronal wave that is travelling along the outer boundary of the channel. Methods: The wavelength is considered as very large for cilia induced MHD flow. The governing linear coupled equations are simplified by considering the approximations of long wavelength and small Reynolds number. Exact solutions are obtained for temperature and velocity profile. The analytical expressions for the pressure gradient and wall shear stresses are obtained. Term for pressure rise is obtained by applying Numerical integration method. Results: Numerical results of velocity profile are mentioned in a table form, for various values of solid volume fraction, curvature, Hartmann number [M] and Casson fluid parameter [ζ]. Final section of this paper is devoted to discussing the graphical results of temperature, pressure gradient, pressure rise, shear stresses and stream functions. Conclusion: Velocity profile near the right wall of the channel decreases when we add nanoparticles into our base fluid, whereas an opposite behaviour is depicted near the left wall due to ciliated tips whereas the temperature is an increasing function of B and ߛ and decreasing function of ߶.

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Significance of Shape Factor in Heat Transfer Performance of Molybdenum-Disulfide Nanofluid in Multiple Flow Situations; A Comparative Fractional Study

Molecules ◽

10.3390/molecules26123711 ◽

2021 ◽

Vol 26 (12) ◽

pp. 3711

Author(s):

Asifa ◽

Talha Anwar ◽

Poom Kumam ◽

Zahir Shah ◽

Kanokwan Sitthithakerngkiet

Keyword(s):

Heat Transfer ◽

Skin Friction ◽

Molybdenum Disulfide ◽

Heat Transfer Rate ◽

Shape Factor ◽

Transfer Rate ◽

Maximum Heat ◽

Left Wall ◽

Maximum Heat Transfer ◽

Mos2 Nanoparticles

In this modern era, nanofluids are considered one of the advanced kinds of heat transferring fluids due to their enhanced thermal features. The present study is conducted to investigate that how the suspension of molybdenum-disulfide (MoS2) nanoparticles boosts the thermal performance of a Casson-type fluid. Sodium alginate (NaAlg) based nanofluid is contained inside a vertical channel of width d and it exhibits a flow due to the movement of the left wall. The walls are nested in a permeable medium, and a uniform magnetic field and radiation flux are also involved in determining flow patterns and thermal behavior of the nanofluid. Depending on velocity boundary conditions, the flow phenomenon is examined for three different situations. To evaluate the influence of shape factor, MoS2 nanoparticles of blade, cylinder, platelet, and brick shapes are considered. The mathematical modeling is performed in the form of non-integer order operators, and a double fractional analysis is carried out by separately solving Caputo-Fabrizio and Atangana-Baleanu operators based fractional models. The system of coupled PDEs is converted to ODEs by operating the Laplace transformation, and Zakian’s algorithm is applied to approximate the Laplace inversion numerically. The solutions of flow and energy equations are presented in terms of graphical illustrations and tables to discuss important physical aspects of the observed problem. Moreover, a detailed inspection on shear stress and Nusselt number is carried out to get a deep insight into skin friction and heat transfer mechanisms. It is analyzed that the suspension of MoS2 nanoparticles leads to ameliorating the heat transfer rate up to 9.5%. To serve the purpose of achieving maximum heat transfer rate and reduced skin friction, the Atangana-Baleanu operator based fractional model is more effective. Furthermore, it is perceived that velocity and energy functions of the nanofluid exhibit significant variations because of the different shapes of nanoparticles.

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Theoretical Effect of Temperature on Threshold in the Hodgkin-Huxley Nerve Model

The Journal of General Physiology ◽

10.1085/jgp.49.5.989 ◽

1966 ◽

Vol 49 (5) ◽

pp. 989-1005 ◽

Cited By ~ 39

Author(s):

Richard Fitzhugh

Keyword(s):

Relaxation Time ◽

Relaxation Times ◽

Giant Axon ◽

Temperature Curve ◽

Effect Of Temperature ◽

Threshold Temperature ◽

Ionic Conductances ◽

And Shifts ◽

The Right ◽

Increasing Temperature

In the squid giant axon, Sjodin and Mullins (1958), using 1 msec duration pulses, found a decrease of threshold with increasing temperature, while Guttman (1962), using 100 msec pulses, found an increase. Both results are qualitatively predicted by the Hodgkin-Huxley model. The threshold vs. temperature curve varies so much with the assumptions made regarding the temperature-dependence of the membrane ionic conductances that quantitative comparison between theory and experiment is not yet possible. For very short pulses, increasing temperature has two effects. (1) At lower temperatures the decrease of relaxation time of Na activation (m) relative to the electrical (RC) relaxation time favors excitation and decreases threshold. (2) For higher temperatures, effect (1) saturates, but the decreasing relaxation times of Na inactivation (h) and K activation (n) factor accommodation and increased threshold. The result is a U-shaped threshold temperature curve. R. Guttman has obtained such U-shaped curves for 50 µsec pulses. Assuming higher ionic conductances decreases the electrical relaxation time and shifts the curve to the right along the temperature axis. Making the conductances increase with temperature flattens the curve. Using very long pulses favors effect (2) over (1) and makes threshold increase monotonically with temperature.

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Theoretical Realizability of Dream-Pipe-Like Oscillating/Pulsating Heat Pipe

Journal of Heat Transfer ◽

10.1115/1.4037748 ◽

2017 ◽

Vol 140 (2) ◽

Author(s):

Masao Furukawa

Keyword(s):

Heat Pipe ◽

Heat Transport ◽

Capillary Tube ◽

Feasibility Studies ◽

Temperature Fields ◽

Pulsating Heat Pipe ◽

Long Distance ◽

Effective Thermal Diffusivity ◽

Energy Equations ◽

Adiabatic Section

The state of the art of thermally self-excited oscillatory heat pipe technology is briefly mentioned to emphasize that there exists no oscillating/pulsating heat pipe (OHP/PHP) suited to long-distance heat transport. Responding to such conditions, this study actively proposes a newly devised conceptually novel type of OHP/PHP. In that heat pipe, the adiabatic section works as it were the dream pipe invented by Kurzweg. This striking quality of the proposed new-style OHP/PHP produces high possibilities of long-distance heat transport. To support such optimistic views, an originally planned mathematical model is introduced for feasibility studies. Hydraulic considerations have first been done to understand what conditions are required for sustaining bubble-train flows in a capillary tube of interest. Theoretical analysis has then been made to solve the momentum and energy equations governing the flow velocity and temperature fields in the adiabatic section. The obtained analytical solutions are arranged to give algebraic expressions of the effective thermal diffusivity, the performance index combined with the tidal displacement, and the required electric power. Computed results of those three are displayed in the figures to demonstrate the realizability of that novel OHP.

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Longer T2relaxation time is a marker of hypothalamic gliosis in mice with diet-induced obesity

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00020.2013 ◽

2013 ◽

Vol 304 (11) ◽

pp. E1245-E1250 ◽

Cited By ~ 23

Author(s):

Donghoon Lee ◽

Joshua P. Thaler ◽

Kathryn E. Berkseth ◽

Susan J. Melhorn ◽

Michael W. Schwartz ◽

...

Keyword(s):

Relaxation Time ◽

High Field ◽

Relaxation Times ◽

Quantitative Mri ◽

Human Studies ◽

Mri Findings ◽

Diet Induced Obesity ◽

Magnetic Resonance Imaging Mri ◽

The Right ◽

Mr Brain

A hallmark of brain injury from infection, vascular, neurodegenerative, and other disorders is the development of gliosis, which can be detected by magnetic resonance imaging (MRI). In rodent models of diet-induced obesity (DIO), high-fat diet (HFD) consumption rapidly induces inflammation and gliosis in energy-regulating regions of the mediobasal hypothalamus (MBH), and recently we reported MRI findings suggestive of MBH gliosis in obese humans. Thus, noninvasive imaging may obviate the need to assess MBH gliosis using histopathological end points, an obvious limitation to human studies. To investigate whether quantitative MRI is a valid tool with which to measure MBH gliosis, we performed analyses, including measurement of T2relaxation time from high-field MR brain imaging of mice fed HFD and chow-fed controls. Mean bilateral T2relaxation time was prolonged significantly in the MBH, but not in the thalamus or cortex, of HFD-fed mice compared with chow-fed controls. Histological analysis confirmed evidence of increased astrocytosis and microglial accumulation in the MBH of HFD-fed mice compared with controls, and T2relaxation times in the right MBH correlated positively with mean intensity of glial fibrillary acidic protein staining (a marker of astrocytes) in HFD-fed animals. Our findings indicate that T2relaxation time obtained from high-field MRI is a useful noninvasive measurement of HFD-induced gliosis in the mouse hypothalamus with potential for translation to human studies.

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On Combined Free and Forced Convection in Channels

Journal of Heat Transfer ◽

10.1115/1.3679915 ◽

1960 ◽

Vol 82 (3) ◽

pp. 233-238 ◽

Cited By ~ 96

Author(s):

L. N. Tao

Keyword(s):

Forced Convection ◽

Rectangular Channel ◽

Complex Function ◽

Vertical Channel ◽

Temperature Fields ◽

Parallel Plates ◽

Free And Forced Convection ◽

Energy Equations ◽

Helmholtz Wave Equation ◽

Transfer Problems

The heat-transfer problems of combined free and forced convection by a fully developed laminar flow in a vertical channel of constant axial wall temperature gradient with or without heat generations are approached by a new method. By introducing a complex function which is directly related to the velocity and temperature fields, the coupled momentum and energy equations are readily combinable to a Helmholtz wave equation in the complex domain. This greatly reduces the complexities of the problems. For illustrations, the cases of flows between parallel plates and in a rectangular channel are treated. It shows that this method is more direct and powerful than those of previous investigations.

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Effect of Heat Source Position in Fluid Flow, Heat Transfer and Entropy Generation in a Naturally Ventilated Room

Mathematics ◽

10.3390/math10020178 ◽

2022 ◽

Vol 10 (2) ◽

pp. 178

Author(s):

Mohammed Alghaseb ◽

Walid Hassen ◽

Abdelhakim Mesloub ◽

Lioua Kolsi

Keyword(s):

Heat Transfer ◽

Rayleigh Number ◽

Heat Source ◽

Numerical Study ◽

Temperature Fields ◽

Left Wall ◽

Heating Efficiency ◽

Discrete Heat Source ◽

Volume Method ◽

The Impact

In this study, a 3D numerical study of free ventilated room equipped with a discrete heat source was performed using the Finite Volume Method (FVM). To ensure good ventilation, two parallel openings were created in the room. A suction opening was located at the bottom of the left wall and another opening was located at the top of the opposite wall; the heat source was placed at various positions in order to compare the heating efficiency. The effects of Rayleigh number (103 ≤ Ra ≤ 106) for six heater positions was studied. The results focus on the impact of these parameters on the particle trajectories, temperature fields and on the heat transfer inside the room. It was found that the position of the heater has a dramatic effect on the behavior and topography of the flow in the room. When the heat source was placed on the wall with the suction opening, two antagonistic behaviors were recorded: an improvement in heat transfer of about 31.6%, compared to the other positions, and a low Rayleigh number against 22% attenuation for high Ra values was noted.

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On the Importance of the Influence of both Velocity and Aspect Ratios on the Occurrence of Bifurcation Phenomena within a Two-Sided Lid-Driven Enclosure

International Letters of Chemistry Physics and Astronomy ◽

10.18052/www.scipress.com/ilcpa.55.160 ◽

2015 ◽

Vol 55 ◽

pp. 160-172

Author(s):

Fayçal Hammami ◽

Nader Ben Cheikh ◽

Brahim Ben Beya

Keyword(s):

Stokes Equations ◽

Numerical Study ◽

Numerical Results ◽

Navier Stokes ◽

Navier Stokes Equations ◽

Left Wall ◽

Driven Cavity ◽

Aspect Ratios ◽

The Stability ◽

The Right

This paper deals with the numerical study of bifurcations in a two-sided lid driven cavity flow. The flow is generated by moving the upper wall to the right while moving the left wall downwards. Numerical simulations are performed by solving the unsteady two dimensional Navier-Stokes equations using the finite volume method and multigrid acceleration. In this problem, the ratio of the height to the width of the cavity are ranged from H/L = 0.25 to 1.5. The code for this cavity is presented using rectangular cavity with the grids 144 × 36, 144 × 72, 144 × 104, 144 × 136, 144 × 176 and 144 × 216. Numerous comparisons with the results available in the literature are given. Very good agreements are found between current numerical results and published numerical results. Various velocity ratios ranged in 0.01≤ α ≤ 0.99 at a fixed aspect ratios (A = 0.5, 0.75, 1.25 and 1.5) were considered. It is observed that the transition to the unsteady regime follows the classical scheme of a Hopf bifurcation. The stability analysis depending on the aspect ratio, velocity ratios α and the Reynolds number when transition phenomenon occurs is considered in this paper.

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