Short Communication: Comments on the Role of Gas-Phase Axial Thermal Dispersion and Solid-Phase Thermal Conduction for Heat Transfer in a Packed Bed of Solid Particles

2012 ◽  
Vol 51 (16) ◽  
pp. 5826-5829
Author(s):  
Michael G. Beaver ◽  
Shivaji Sircar
Keyword(s):  
Heat Transfer ◽  
Gas Phase ◽  
Thermal Conduction ◽  
Short Communication ◽  
Solid Phase ◽  
Packed Bed ◽  
Solid Particles ◽  
Thermal Dispersion

Heat Transfer in Fixed Bed Elliptic Cylindrical Reactor via Two-Phase Model

2020 ◽  
Vol 400 ◽  
pp. 45-50
Author(s):  
Antonildo Santos Pereira ◽  
Rodrigo Moura da Silva ◽  
Maria Conceição Nóbrega Machado ◽  
Luan Pedro Melo Azerêdo ◽  
Anderson Ferreira Vilela ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Solid Phase ◽  
Homogeneous Model ◽  
Fixed Bed ◽  
Fluid Phase ◽  
Packed Bed ◽  
Two Phase ◽  
Heterogeneous Model ◽  
Fully Implicit ◽  
Cylindrical Reactor

The study of heat transfer in fixed bed tubular reactors of heated or cooled walls has presented great interest by the academy and industry. The adequate and safe design of such equipment requires the use of reliable and realistic mathematical. Unfortunately several studies are restrict to homogeneous model applied to circular and elliptic cylindrical reactors. Then, the objective of this work was to predict heat transfer in packed-bed elliptic cylindrical reactor, by using a proposed heterogeneous model. The mathematical model is composed for one solid phase and another fluid phase, in which the balance equation for each constituent is applied separately. The finite volume method was utilized to solve the partial differential equations using the WUDS scheme for interpolation of the convective and diffusive terms, and the fully implicit formulation. Results of the temperature distribution of the fluid and solid phases along the reactor are presented and analyzed. It was verified that the highest temperature gradients of the phases are located close to the wall and inlet of the reactor.

scholarly journals Enskog kinetic theory for monodisperse gas–solid flows

2012 ◽  
Vol 712 ◽  
pp. 129-168 ◽  
Author(s):  
V. Garzó ◽  
S. Tenneti ◽  
S. Subramaniam ◽  
C. M. Hrenya
Keyword(s):  
Reynolds Number ◽  
Kinetic Theory ◽  
Gas Phase ◽  
Parameter Space ◽  
Shear Viscosity ◽  
Solid Phase ◽  
Constitutive Relations ◽  
Solid Particles ◽  
Analytical Treatment ◽  
Starting Point

AbstractThe Enskog kinetic theory is used as a starting point to model a suspension of solid particles in a viscous gas. Unlike previous efforts for similar suspensions, the gas-phase contribution to the instantaneous particle acceleration appearing in the Enskog equation is modelled using a Langevin equation, which can be applied to a wide parameter space (e.g. high Reynolds number). Attention here is limited to low Reynolds number flow, however, in order to assess the influence of the gas phase on the constitutive relations, which was assumed to be negligible in a previous analytical treatment. The Chapman–Enskog method is used to derive the constitutive relations needed for the conservation of mass, momentum and granular energy. The results indicate that the Langevin model for instantaneous gas–solid force matches the form of the previous analytical treatment, indicating the promise of this method for regions of the parameter space outside of those attainable by analytical methods (e.g. higher Reynolds number). The results also indicate that the effect of the gas phase on the constitutive relations for the solid-phase shear viscosity and Dufour coefficient is non-negligible, particularly in relatively dilute systems. Moreover, unlike their granular (no gas phase) counterparts, the shear viscosity in gas–solid systems is found to be zero in the dilute limit and the Dufour coefficient is found to be non-zero in the elastic limit.

Simulation of Multiphase Heat Transfer in Pebble Bed Modular Reactor

2004 ◽  
Author(s):  
Andrey A. Troshko ◽  
Ajey Y. Walavalkar
Keyword(s):  
Heat Transfer ◽  
Gas Phase ◽  
Packed Bed ◽  
Multiphase Model ◽  
Test Rig ◽  
Pebble Bed ◽  
Model Predictions ◽  
Two Phases ◽  
Drag Law ◽  
Eulerian Multiphase Model

Computational Fluid Dynamics in conjunction with an Eulerian multiphase model of heat transfer in a Pebble Bed Modular Reactor (PBMR) was validated against experimental data obtained in a test rig. The cooling gas and packed fuel pebbles constituted two phases. The velocity of pebble phase was fixed to zero and a drag law accounting for a packed bed condition was used. The density of the gas phase varied with temperature. Volume averaged effective thermal conductivities accounting for radiation and packed spheres geometry were used for both phases. Model predictions compared favorably with the experiment for two gases — helium and nitrogen and two power levels. It was found that accounting for increased affective porosity close to walls results in more realistic velocity field prediction.

scholarly journals Analysis of Heat Transfer in the Structures with Regularly Arranged Gas Cavities

2008 ◽  
Vol 45 (4) ◽  
pp. 14-24 ◽  
Author(s):  
D. Cepīte ◽  
A. Jakovičs
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Conduction ◽  
Building Materials ◽  
Material Structure ◽  
Radiation Heat ◽  
Parallel Orientation ◽  
Transfer Processes ◽  
Radiation Heat Exchange

Analysis of Heat Transfer in the Structures with Regularly Arranged Gas CavitiesIn the work, the effective thermal conductivity (ETC) of anisotropic composite material (well-conducting media with regular cavities of the air) is studied by numerical modelling. The authors examine the influence of orientation and size of the cavities on the ETC of material structure and the role of thermal conduction, convection and radiation in the heat transfer processes. For modelling,Keratermtype material was chosen. It has been proved numerically that the ETC of similar structures is lower in the case when the cavities are oriented perpendicularly to the heat flux direction as compared with parallel orientation. According to the analysis performed, the radiation heat exchange in such cavities dominates over the convective heat transfer in the observed temperature range. In the calculations of ETC in structures of the kind, convection inside the cavities can be omitted. The proposed approach allows optimisation of the arrangement and size of the cavities in similar building materials.

Packed-bed reactor for short time gas phase olefin polymerization: Heat transfer study and reactor optimization

AIChE Journal ◽  
2011 ◽  
Vol 58 (1) ◽  
pp. 256-267 ◽  
Author(s):  
Estevan Tioni ◽  
Roger Spitz ◽  
J. P. Broyer ◽  
Vincent Monteil ◽  
Timothy McKenna
Keyword(s):  
Heat Transfer ◽  
Gas Phase ◽  
Olefin Polymerization ◽  
Packed Bed ◽  
Packed Bed Reactor ◽  
Reactor Optimization ◽  
Short Time ◽  
Transfer Study

Natural Convective Heat Transfer of Water-in-FC72 Nanoemulsion Fluids

2008 ◽  
Author(s):  
Zenghu Han ◽  
Bao Yang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Hydrodynamic Interaction ◽  
Convective Heat Transfer Coefficient ◽  
Relative Viscosity ◽  
Solid Particles ◽  
Water Loading

The use of SOLID-particles has long been a common way of increasing fluid thermal conductivity. In this paper, nanoemulsion fluids—dispersions of LIQUID-nanodroplets—are proposed. As an example, water-in-FC72 nanoemulsion fluids are developed, and their thermophysical properties and impact on natural convective heat transfer are investigated experimentally. A significant increase in thermal conductivity—up to 52% for 12vol% of water nanodroplets (or 7.1 wt%)—is observed in the fluids. The enhancement in conductivity and viscosity of the fluids is found to be nonlinear with water loading, indicating an important role of the hydrodynamic interaction and aggregation of nanodroplets. However, the relative viscosity is found to be about two times the relative conductivity if compared at the same water loading. The presence of water nanodroplets is found to systematically increase the natural convective heat transfer coefficient in these fluids, in contrast to the observation in several conventional nanofluids containing solid nanoparticles.

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