CFD Simulation of Reaction and Heat Transfer Near the Wall of a Fixed Bed

2003 ◽  
Vol 1 (1) ◽  
Author(s):  
Anthony G. Dixon ◽  
Michiel Nijemeisland ◽  
Hugh Stitt
Keyword(s):  
Heat Transfer ◽  
Steam Reforming ◽  
Gas Flow ◽  
Cfd Simulation ◽  
Control Volume ◽  
Fixed Bed ◽  
Particle Diameter ◽  
Effect Of Temperature ◽  
Temperature Profiles ◽  
Computational Domain

Modeling of fluid flow, heat transfer and reaction in fixed beds is an essential part of their design. This is especially critical for highly endothermic or exothermic reactions in low tube-to-particle diameter ratio (N) tubes, such as are used in steam reforming and partial oxidation. In the simulations a near-wall section of an entire bed is used to create a simulation geometry that can be handled in the available computational domain. A full bed model was also available for validation of the wall-segment model. In the wall-segment approach a section of the bed is modeled in more detail, allowing for a relatively smaller control volume size and a more detailed view of the flow and heat transfer patterns. A simple model of a steam reforming process is used in the CFD simulation to incorporate the effect of reaction rate on temperature profiles in the bed. Simulations were performed under realistic industrial conditions of high temperature, pressure and gas flow rate, with gas properties corresponding to those of steam reforming. A constant wall heat flux was imposed, and various shapes of particles studied with heat sinks on the surface to simulate the reforming endothermic reaction, which is mainly confined to the surface of the pellet. Results will be presented showing the existence and effect of temperature profiles on the catalyst particles, and the effect on the local heat transfer rates of different gas compositions, corresponding to conditions at different locations along the catalyst tube. Local deactivation of catalyst particles can also lead to wall hot spots, or 'giraffe-necking' which can be well-reproduced by the simulations.

scholarly journals Influence of Macroscopic Wall Structures on the Fluid Flow and Heat Transfer in Fixed Bed Reactors with Small Tube to Particle Diameter Ratio

Processes ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 689
Author(s):  
Thomas Eppinger ◽  
Nico Jurtz ◽  
Matthias Kraume
Keyword(s):  
Heat Transfer ◽  
Fixed Bed ◽  
Particle Diameter ◽  
Diameter Ratio ◽  
Spherical Particles ◽  
Reactor Wall ◽  
Entry Length ◽  
Fixed Bed Reactors ◽  
Wall Structures ◽  
Small Tube

Fixed bed reactors are widely used in the chemical, nuclear and process industry. Due to the solid particle arrangement and its resulting non-homogeneous radial void fraction distribution, the heat transfer of this reactor type is inhibited, especially for fixed bed reactors with a small tube to particle diameter ratio. This work shows that, based on three-dimensional particle-resolved discrete element method (DEM) computational fluid dynamics (CFD) simulations, it is possible to reduce the maldistribution of mono-dispersed spherical particles near the reactor wall by the use of macroscopic wall structures. As a result, the lateral convection is significantly increased leading to a better radial heat transfer. This is investigated for different macroscopic wall structures, different air flow rates (Reynolds number Re = 16 ...16,000) and a variation of tube to particle diameter ratios (2.8, 4.8, 6.8, 8.8). An increase of the radial velocity of up to 40%, a reduction of the thermal entry length of 66% and an overall heat transfer increase of up to 120% are found.

Analysis of a Virtual Prototype First-Stage Rotor Blade Using Integrated Computer-Based Design Tools

2006 ◽  
Author(s):  
Michel Arnal ◽  
Christian Precht ◽  
Thomas Sprunk ◽  
Tobias Danninger ◽  
John Stokes
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Thermal Loading ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Life Assessment ◽  
Element Analysis ◽  
Pressure Losses ◽  
Cooling Channels ◽  
Internally Cooled

The present paper outlines a practical methodology for improved virtual prototyping, using as an example, the recently re-engineered, internally-cooled 1st stage blade of a 40 MW industrial gas turbine. Using the full 3-D CAD model of the blade, a CFD simulation that includes the hot gas flow around the blade, conjugate heat transfer from the fluid to the solid at the blade surface, heat conduction through the solid, and the coolant flow in the plenum is performed. The pressure losses through and heat transfer to the cooling channels inside the airfoil are captured with a 1-D code and the 1-D results are linked to the three-dimensional CFD analysis. The resultant three-dimensional temperature distribution through the blade provides the required thermal loading for the subsequent structural finite element analysis. The results of this analysis include the thermo-mechanical stress distribution, which is the basis for blade life assessment.

Study on Effective Radial Thermal Conductivity of Gas Flow through a Methanol Reactor

2015 ◽  
Vol 13 (1) ◽  
pp. 103-112 ◽  
Author(s):  
Kun Lei ◽  
Hongfang Ma ◽  
Haitao Zhang ◽  
Weiyong Ying ◽  
Dingye Fang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Reynolds Number ◽  
Temperature Distribution ◽  
Large Scale ◽  
Gas Flow ◽  
Fixed Bed ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Particle Reynolds Number

Abstract The heat conduction performance of the methanol synthesis reactor is significant for the development of large-scale methanol production. The present work has measured the temperature distribution in the fixed bed at air volumetric flow rate 2.4–7 m3 · h−1, inlet air temperature 160–200°C and heating tube temperature 210–270°C. The effective radial thermal conductivity and effective wall heat transfer coefficient were derived based on the steady-state measurements and the two-dimensional heat transfer model. A correlation was proposed based on the experimental data, which related well the Nusselt number and the effective radial thermal conductivity to the particle Reynolds number ranging from 59.2 to 175.8. The heat transfer model combined with the correlation was used to calculate the temperature profiles. A comparison with the predicated temperature and the measurements was illustrated and the results showed that the predication agreed very well with the experimental results. All the absolute values of the relative errors were less than 10%, and the model was verified by experiments. Comparing the correlations of both this work with previously published showed that there are considerable discrepancies among them due to different experimental conditions. The influence of the particle Reynolds number on the temperature distribution inside the bed was also discussed and it was shown that improving particle Reynolds number contributed to enhance heat transfer in the fixed bed.

CFD Simulation of a Coolant Flow and a Heat Transfer in a Pebble Bed Reactor

2008 ◽  
Author(s):  
Wang-Kee In ◽  
Won-Jae Lee ◽  
Yassin A. Hassan
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Cfd Simulation ◽  
Reverse Flow ◽  
Temperature Drop ◽  
Coolant Flow ◽  
Normal Operation ◽  
Fuel Temperature ◽  
Pebble Bed Reactor ◽  
Detailed Simulation

This CFD study is to simulate a coolant (gas) flow and heat transfer in a PBR core during a normal operation. This study used a pebble array with direct area contacts among the pebbles which is one of the pebbles arrangements for a detailed simulation of PBR core CFD studies. A CFD model is developed to more adequately represent the pebbles randomly stacked in the PBR core. The CFD predictions showed a large variation of the temperature on the pebble surface as well as in the pebble core. The temperature drop in the outer graphite layer is smaller than that in the pebble-core region. This is because the thermal conductivity of graphite is higher than the fuel (UO2 mixture) conductivity in the pebble core. Higher pebble surface temperature is predicted downstream of the pebble contact due to a reverse flow. Multiple vortices are predicted to occur downstream of the spherical pebbles due to a flow separation. The coolant flow structure and fuel temperature in the PBR core appears to largely depend on the in-core distribution of the pebbles.

Heat Transfer in the Non-reacting Zone of a Cement Rotary Kiln

1996 ◽  
Vol 118 (1) ◽  
pp. 169-172 ◽  
Author(s):  
P. S. Ghoshdastidar ◽  
V. K. Anandan Unni
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Rotary Kiln ◽  
Gas Flow ◽  
Transfer Model ◽  
Temperature Profiles ◽  
Gas Temperature ◽  
Gas Flow Rate ◽  
Steady State Heat ◽  
Steady State Heat Transfer

This paper presents a steady-state heat transfer model for a rotary kiln used for drying and preheating of wet solids with application to the non-reacting zone of a cement rotary kiln. A detailed parametric study indicates that the influence of the controlling parameters such as percent water content (with respect to dry solids), solids flow rate, gas flow rate, kiln inclination angle and the rotational speed of the kiln on the axial solids and gas temperature profiles and the total predicted kiln length is appreciable.

scholarly journals Thermal Lattice Boltzmann Model for Nonisothermal Gas Flow in a Two-Dimensional Microchannel

2020 ◽  
Vol 2020 ◽  
pp. 1-13 ◽  
Author(s):  
Youssef Elguennouni ◽  
Mohamed Hssikou ◽  
Jamal Baliti ◽  
Mohammed Alaoui
Keyword(s):  
Poiseuille Flow ◽  
Lattice Boltzmann ◽  
Gas Flow ◽  
Velocity Slip ◽  
Lattice Boltzmann Model ◽  
Effect Of Temperature ◽  
Temperature Profiles ◽  
Average Value ◽  
First Case ◽  
Thermal Lattice Boltzmann

In this paper, the Thermal Lattice Boltzmann Method (TLBM) is used for the simulation of a gas microflow. A 2D heated microchannel flow driven by a constant inlet velocity profile Uin and nonisothermal walls is investigated numerically. Two cases of micro-Poiseuille flow are considered in the present study. In the first case, the temperature of the walls is kept uniform, equal to zero; therefore, the gas is driven along the channel under the inlet parameters of velocity and temperature. However, in the second one, the gas flow is also induced by the effect of temperature decreasing applied on the walls. For consistent results, velocity slip and temperature jump boundary conditions are used to capture the nonequilibrium effects near the walls. The rarefaction effects described by the Knudsen number, on the velocity and temperature profiles are evaluated. The aim of this study is to prove the efficiency of the TLBM method to simulate Poiseuille flow in case of nonisothermal walls, based on the average value of the Nusselt number and by comparing the results obtained from the TLBM with those obtained using the Finite Difference Method (FDM). The results also show an interesting sensitivity of velocity and temperature profiles with the rarefaction degree and the imposed temperature gradient of the walls.

A Simplified Numerical Approach to Characterize the Thermal Response of a Moving Bed Solar Reactor

2021 ◽  
Author(s):  
Assaad Al Sahlani ◽  
Kelvin Randhir ◽  
Nesrin Ozalp ◽  
James Klausner
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Energy Storage ◽  
Solid Particle ◽  
Gas Flow ◽  
Plug Flow ◽  
Fixed Bed ◽  
Flow Rates ◽  
Proposed Model ◽  
Simulation Results

Abstract Concentrated solar thermochemical storage in the form of a zero-emission fuel is a promising option to produce long-duration energy storage. The production of solar fuel can occur within a cylindrical cavity chemical reactor that captures concentrated solar radiation from a solar field. A heat transfer model of a tubular plug-flow reactor is presented. Experimental data from a fixed bed tubular reactor are used for model comparison. The system consists of an externally heated tube with counter-current flowing gas and moving solid particles as the heated media. The proposed model simulates the dynamic behavior of temperature profiles of the tube wall, gas, and particles under various gas flow rates and residence times. The heat transfer between gas-wall, solid particle-wall, gas-solid particle, are numerically studied. The model is compared with experiments using a 4 kW furnace with a 150 mm heating zone surrounding a horizontal alumina tube (reactor) with 50.8 mm OD and a thickness of 3.175 mm. Solid fixed particles of magnesium manganese oxide (MgMn2O4) with the size of 1 mm are packed within the length of 250 mm at the center of the tube length. Simulation results are assessed with respect to fixed bed experimental data for four different gas flow rates, namely 5, 10, 15, 20 standard liters per minute of air, and furnace temperatures in the range of 200 to 1200 °C. The simulation results showed good agreement with maximum steady state error that is less than 6% of those obtained from the experiments among all runs. The proposed model can be implemented as a low-order physical model for the control of temperature inside plug-flow reactors for thermochemical energy storage (TCES) applications.

The Effect of Temperature Jump on Microscale Heat Transfer: Slip Models and the Moment Methods

2008 ◽  
Author(s):  
Rho-Shin Myong ◽  
Dong-Ho Lee ◽  
Jin-Hee Lee
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Gas Flow ◽  
Computational Models ◽  
Temperature Jump ◽  
Constitutive Relations ◽  
Flow Regimes ◽  
Effect Of Temperature ◽  
Microscale Heat Transfer

The study of non-linear transport in gas flows associated with micro and nanodevices has emerged as an important topic in recent years. In the field of microscale heat transfer, convective heat transfer in slip-flow regimes in simple geometries like channels and tubes is a key problem. Constant-wall-temperature convective heat transfer in microscale tubes and channels has been studied recently using analytical solutions to an extended Graetz problem. In addition, much effort has been put into the development of computational models beyond the theory of linear constitutive relations for the analysis of microscale gas flow and heat transfer, since the Navier-Stokes-Fourier theory is not known to remain valid in the flow regimes of large Knudsen number. The objective of the present paper is to investigate microscale heat transfer where temperature jump is the dominant phenomena. The emphasis will be on the qualitative features of microscale heat transfer, for example, enhancement or reduction of heat transfer in microscale geometries. General features of computational models such as the full kinetic model and fluid dynamics model are also discussed.

Numerical Study of Conduction and Convection Between Immersed Object and Gas Fluidized Bed

Volume 1 ◽  
2004 ◽  
Author(s):  
W. M. Gao ◽  
L. X. Kong ◽  
P. D. Hodgson ◽  
B. Wang
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Solid Phase ◽  
Numerical Study ◽  
Particle Diameter ◽  
Conductive Heat ◽  
Gas Temperature ◽  
Transfer Coefficients ◽  
Immersed Surfaces ◽  
Particle Layer

To analyze the heat transfer mechanism between fluidised beds and surfaces of an immersed object, the heat transfer and gas flow was numerically simulated for different particle systems based on a double particle-layer and porous medium model. It is fund that the conductive heat transfer occurs in the stifling regions between particle and the immersed surface, which have different temperature. The diameter of the circular conduction region, dc, is a function of particle diameter, dp, and can be given by dc/dp = 0.245dp−0.3. In other areas, the heat transfer between the dense gas-solid phase and the immersed object surface is dominated by convection from the moving gas in the tunnel formed by the first-layer particles and the immersed surfaces. The average dimensionless gas velocity, εmfU/Umf, in the tunnel is a constant of about 4.6. The virtual gas temperature at the free stream conditions can be given by the surface temperature of the first-layer particles. The heat transfer coefficient on the conductive region is about 6∼10 times of that on the convection region. The Nusselt numbers for calculating the instantaneous conductive and convective heat-transfer coefficients were theoretically analysed respectively.

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