Role of Variable Conductance on Heat and Mass Transport Mechanism Using Generalized Theory

2020 ◽  
Vol 13 (2) ◽  
Author(s):  
Imran Haider Qureshi ◽  
Ahmed Elmoasry ◽  
Jawdat Alebraheem ◽  
M. Nawaz
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Chemical Reaction ◽  
Diffusion Coefficients ◽  
Mass Diffusion ◽  
Memory Effects ◽  
Temperature Dependent ◽  
Newton's Law ◽  
Newton’S Law ◽  
The Impact

Abstract Fourier law of heat conduction, its analog Fick's first law, and Newton's law of viscosity are classical laws that are not capable of exhibiting memory effects. Conservation laws based on these classical laws do not give predictions about memory effects on the transport phenomena. Recently, proposed novel laws are called Cattaneo–Christov heat flux. Models are based on the generalization of classical laws of heat conduction, mass diffusion, and Newton's law of viscosity. This investigation considers this generalized theory to model the impact of relaxation phenomenon on the transport of momentum, heat, and mass in Maxwell fluid (viscoelastic fluid) of temperature-dependent viscosity and thermal conductivity in the presence of temperature-dependent mass diffusion coefficients. It is observed from the simulations that memory effects play a key role in controlling momentum, thermal and concentration boundary layer thicknesses. It is also noted that the rate of diffusion of heat and mass has shown an increasing trend when thermal conductivity and mass diffusion coefficients are increased via rise in temperature of the fluid. The generative chemical reaction on the transport of specie relative to the impact on the transport of specie when it is compared with the impact of destructive chemical reaction on the transport of specie.

A Transient Formulation of Newton's Cooling Law for Spherical Bodies

2000 ◽  
Vol 123 (1) ◽  
pp. 63-64 ◽  
Author(s):  
S. S. Sazhin ◽  
V. A. Gol'dshtein ◽  
M. R. Heikal
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Diesel Engine ◽  
Effective Thermal Conductivity ◽  
Spherical Body ◽  
Fuel Droplet ◽  
Transient Effects ◽  
Newton's Law ◽  
Initial Stage ◽  
Newton’S Law

Newton's law of cooling is shown to underestimate the heat flux between a spherical body (droplet) and a homogeneous gas after this body is suddenly immersed into the gas. This problem is rectified by replacing the gas thermal conductivity by the effective thermal conductivity. The latter reduces to the gas thermal conductivity in the limit of t→∞, but can be substantially higher in the limit of t→0. In the case of fuel droplet heating in a medium duty truck Diesel engine the gas thermal conductivity may need to be increased by more than 100 percent at the initial stage of calculations to account for transient effects during the process of droplet heating.

scholarly journals Exceptional in-plane and interfacial thermal transport in graphene/2D-SiC van der Waals heterostructures

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Md. Sherajul Islam ◽  
Imon Mia ◽  
Shihab Ahammed ◽  
Catherine Stampfl ◽  
Jeongwon Park
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Van Der Waals ◽  
New Physics ◽  
Infinite Length ◽  
Interatomic Potentials ◽  
Van Der Waals Heterostructures ◽  
Functional Efficiency ◽  
Out Of Plane ◽  
The Impact

AbstractGraphene based van der Waals heterostructures (vdWHs) have gained substantial interest recently due to their unique electrical and optical characteristics as well as unprecedented opportunities to explore new physics and revolutionary design of nanodevices. However, the heat conduction performance of these vdWHs holds a crucial role in deciding their functional efficiency. In-plane and out-of-plane thermal conduction phenomena in graphene/2D-SiC vdWHs were studied using reverse non-equilibrium molecular dynamics simulations and the transient pump-probe technique, respectively. At room temperature, we determined an in-plane thermal conductivity of ~ 1452 W/m-K for an infinite length graphene/2D-SiC vdWH, which is superior to any graphene based vdWHs reported yet. The out-of-plane thermal resistance of graphene → 2D-SiC and 2D-SiC → graphene was estimated to be 2.71 × 10−7 km2/W and 2.65 × 10−7 km2/W, respectively, implying the absence of the thermal rectification effect in the heterobilayer. The phonon-mediated both in-plane and out-of-plane heat transfer is clarified for this prospective heterobilayer. This study furthermore explored the impact of various interatomic potentials on the thermal conductivity of the heterobilayer. These findings are useful in explaining the heat conduction at the interfaces in graphene/2D-SiC vdWH and may provide a guideline for efficient design and regulation of their thermal characteristics.

Stagnant lid convection with temperature-dependent thermal conductivity and the thermal evolution of icy worlds

2020 ◽  
Vol 224 (3) ◽  
pp. 1870-1889
Author(s):  
Frédéric Deschamps
Keyword(s):  
Thermal Conductivity ◽  
Thermal Evolution ◽  
Heat Fluxes ◽  
The Body ◽  
Temperature Dependent ◽  
Temperature Dependent Conductivity ◽  
Icy Bodies ◽  
Main Component ◽  
The Impact ◽  
Temperature Dependent Thermal Conductivity

SUMMARY Convection is an efficient process to release heat from planetary interiors, but its efficiency depends on the detailed properties of planetary mantles and materials. A property whose impact has not yet been studied extensively is the temperature dependence of thermal conductivity. Because thermal conductivity controls heat fluxes, its variations with temperature may alter heat transfer. Here, I assess qualitatively and quantitatively the influence of temperature-dependent thermal conductivity on stagnant lid convection. Assuming that thermal conductivity varies as the inverse of temperature $(k \propto 1/T)$, which is the case for ice Ih, the main component of outer shells of solar System large icy bodies, I performed numerical simulations of convection in 3-D-Cartesian geometry with top-to-bottom viscosity and conductivity ratios in the ranges 105 ≤ Δη ≤ 108 and 1 ≤ Rk ≤ 10, respectively. These simulations indicate that with increasing Rk, and for given values of the Rayleigh number and Δη, heat flux is reduced by a factor Rk0.82, while the stagnant lid is thickening. These results have implications for the structures and thermal evolutions of large icy bodies, the impact of temperature-dependent conductivity being more important with decreasing surface temperature, Tsurf. The heat fluxes and thermal evolutions obtained with temperature-dependent conductivity are comparable to those obtained with constant conductivity, provided that the conductivity is fixed to its value at the bottom or in the interior of the ice shell, that is, around 2.0–3.0 W m−1 K−1, depending on the body. By contrast, temperature-dependent conductivity leads to thicker stagnant lids, by about a factor 1.6–1.8 at Pluto (Tsurf = 40 K) and a factor 1.2–1.4 at Europa (Tsurf = 100 K), and smaller interior temperatures. Overall, temperature-dependent thermal conductivity therefore provides more accurate descriptions of the thermal evolutions of icy bodies.

Flow and thermal analysis of Jeffrey nanofluid in a microchannel: Buongiorno's Model

2021 ◽  
pp. 095440892110501
Author(s):  
D.O. Soumya ◽  
B.J. Gireesha ◽  
P. Venkatesh ◽  
Abdulmohsen Alsaiari
Keyword(s):  
Thermal Conductivity ◽  
Brownian Motion ◽  
Thermal Energy ◽  
Energy Concentration ◽  
Physical Parameters ◽  
Temperature Dependent ◽  
Jeffrey Nanofluid ◽  
The Impact ◽  
Temperature Dependent Thermal Conductivity ◽  
Irreversibility Ratio

The present consideration explores the thermal energy and mass transfer process in conducting Jeffrey nanofluid flows through a microchannel. The slip boundary conditions, Brownian motion and temperature-dependent thermal conductivity were considered. The dimensionless governing models have been solved to the best possible investigative solutions using the Runge-Kutta-Fehlberg 4 −5th order numerical procedure. The impact of physical parameters on the momentum, energy, concentration, irreversibility and irreversibility ratio was revealed graphically in detail. It is concluded that the resultant momentum profile is augmented with the relaxation and retardation times parameter all over the flow region. The temperature-dependent thermal conductivity contributes to the resulting thermal energy of the flow system ever-growing to high. The concentration profile was diminutions through growing in the Brownian motion parameter. The irreversibility and irreversibility ratio were obtained mathematically and explained concerning the notable parameters. The magnetic parameter was to diminish the irreversibility rate, but it was augmented by increasing the parameter for the relaxation and retardation times ratio. Effect of thermal radiation, variable thermal conductivity, pressure gradient, buoyancy force and thermophoresis on the Jeffery nanofluid in a microchannel by the Buongiorno model have been inspected for the first time. The effects of this works are innovative and original.

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