Analysis of Clumped-Pebble Shape on Thermal Radiation and Conduction in Nuclear Beds by Subcell Radiation Model

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Hao Wu ◽  
Nan Gui ◽  
Xingtuan Yang ◽  
Jiyuan Tu ◽  
Shengyao Jiang
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Thermal Radiation ◽  
Packed Bed ◽  
Radiation Model ◽  
The Core ◽  
Model Combining ◽  
Temperature Ranges ◽  
Pebble Flow ◽  
Good Agreement

Abstract The core of high-temperature gas-cooled reactor is a dense pebble bed of random packing filled with monosized fuel spheres. Subcell radiation model (SCM) is a generic analytical approach to calculate effective thermal conductivity (ETC) of thermal radiation. For the packed bed of monosized spheres operated in various conditions, it is proven that the SCM is still applicable in the particle size ranges of 1.2–60 mm and temperature ranges of 0–1200 °C. Based on the SCM, radiation-to-conduction ratio ξ is presented and radiation becomes an essential part at ξ>0.1 for the accurate evaluation. For the beds of nonoverlapping clumped-sphere particles, the model combining with discrete element method (DEM) and SCM is presented to study the heat transfer behaviors, including effects of particle shape, emissivity distribution and pebble flow with transient heat transfer. For the experimental nuclear pebble beds, the results of SCM are in good agreement with the empirical correlation and accord well with the experimental data under high temperature range.

Modeling Effective Thermal Conductivity of Thermal Radiation for Nuclear Packed Pebble Beds

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Hao Wu ◽  
Nan Gui ◽  
Xingtuan Yang ◽  
Jiyuan Tu ◽  
Shengyao Jiang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Radiation ◽  
Effective Thermal Conductivity ◽  
Transfer Cells ◽  
Transfer Model ◽  
Radiation Model ◽  
Radial Temperature ◽  
Effective Heat ◽  
Good Agreement

In nuclear packed pebble beds, it is a fundamental task to model effective thermal conductivity (ETC) of thermal radiation. Based on the effective heat transfer cells of structured packing, a short-range radiation model (SRM) and a subcell radiation model (SCM) are applied to obtain analytical results of ETC. It is shown that the SRM of present effective heat transfer cells are in good agreement with the numerical simulations of random packing and it is only slightly higher than empirical correlations when temperature exceeds 1200 °C. In order to develop a generic theoretical approach of modeling ETC, the subcell radiation model is presented and in good agreement with Kunii–Smith correlation, especially at very high temperature ranges (over 1500 °C). Based on SCM, one-dimensional (1D) radial heat transfer model is applied in the analysis of the HTTU experiments. The results of ETC and radial temperature distribution are in good agreement with the experimental data.

scholarly journals Evaluation of Alternative Designs for a High Temperature Particle-to-sCO2 Heat Exchanger

2019 ◽  
Vol 141 (2) ◽  
Author(s):  
Clifford K. Ho ◽  
Matthew Carlson ◽  
Kevin J. Albrecht ◽  
Zhiwen Ma ◽  
Sheldon Jeter ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
High Temperature ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Fluidized Bed ◽  
Structural Reliability ◽  
Packed Bed ◽  
Heat Losses ◽  
Transient Operation

This paper presents an evaluation of alternative particle heat-exchanger designs, including moving packed-bed and fluidized-bed designs, for high-temperature heating of a solar-driven supercritical CO2 (sCO2) Brayton power cycle. The design requirements for high pressure (≥20 MPa) and high temperature (≥700 °C) operation associated with sCO2 posed several challenges requiring high-strength materials for piping and/or diffusion bonding for plates. Designs from several vendors for a 100 kW-thermal particle-to-sCO2 heat exchanger were evaluated as part of this project. Cost, heat-transfer coefficient, structural reliability, manufacturability, parasitics and heat losses, scalability, compatibility, erosion and corrosion, transient operation, and inspection ease were considered in the evaluation. An analytic hierarchy process was used to weight and compare the criteria for the different design options. The fluidized-bed design fared the best on heat transfer coefficient, structural reliability, scalability, and inspection ease, while the moving packed-bed designs fared the best on cost, parasitics and heat losses, manufacturability, compatibility, erosion and corrosion, and transient operation. A 100 kWt shell-and-plate design was ultimately selected for construction and integration with Sandia's falling particle receiver system.

Post-Test Investigations of BFBT Critical Power Tests With Trace

2009 ◽  
Author(s):  
Marc Thieme ◽  
Wolfgang Tietsch ◽  
Rafael Macian ◽  
Victor Hugo Sanchez Espinoza
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Critical Power ◽  
The Core ◽  
Fine Mesh ◽  
The Us ◽  
Post Test ◽  
Trace Model ◽  
Good Agreement ◽  
Transfer Models

The validation of heat transfer models of safety analysis codes such as TRACE is very important due to the strong interaction of the thermal hydraulics parameters with the core neutronics. TRACE is the reference system code of the US NRC for LWR. It is being developed and extensively validated within the international CAMP-program. In this paper, the validation of heat transfer models of TRACE related to the prediction of the critical power is presented. The validation is based on a large number of critical power tests performed in the NUPEC BFBT (BWR Full-Size Fine-Mesh Bundle Tests) facility in Japan. These tests were analysed with the TRACE Version 5 RC 2. The comparison of predictions with the experimental data shows good agreement. The developed TRACE model and the comparison of experimental data with code results will be presented and discussed.

An Experimental Investigation of Heat Transfer in Variable Porosity Media

1985 ◽  
Vol 107 (3) ◽  
pp. 642-647 ◽  
Author(s):  
K. Vafai ◽  
R. L. Alkire ◽  
C. L. Tien
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Packed Bed ◽  
Volume Averaging ◽  
Experimental Results ◽  
Variable Porosity ◽  
Local Volume Averaging ◽  
Convection In Porous Media ◽  
Impermeable Boundary ◽  
Good Agreement

This paper presents an experimental investigation on the effects of a solid impermeable boundary and variable porosity on forced convection in porous media. Emphasis is placed on the channeling effects on heat transfer in packed beds. The local volume-averaging technique is used to establish the governing equations and a numerical scheme is developed which incorporates the boundary and variable porosity effects on heat transfer. The experimental results for the heat flux at the boundary are presented as a function of the pertinent variables in a packed bed. The Nusselt number is found to increase almost linearly with an increase in the Reynolds number based on the pore diameter. The experimental results are found to be in good agreement with the theoretical results which account for the variable porosity effects. A comparison between the numerical and the experimental results demonstrates the importance of boundary and variable porosity effects on heat transfer in variable porosity media.

Heat Transfer Coefficient for a Packed Bed of Shredded Materials

2003 ◽  
Author(s):  
Mohammad S. Saidi ◽  
Firooz Rasouli ◽  
Mohammad R. Hajaligol
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Distribution ◽  
Packed Bed ◽  
Spherical Particles ◽  
Channeling Effect ◽  
Nusselt Number Correlation ◽  
Good Agreement

Heat transfer coefficient of packed beds of shredded materials such as biomass fuels at low Peclet numbers is of interest. Due to the dependence of flow distribution on particle shape, the application of the Nusselt number correlation of packed bed of spherical particles overestimates the rate of heat transfer. This discrepancy is even more pronounced due to channeling effect at low Peclet numbers. Here, based on applying a pore submodel and combining the numerical simulation and experimental results of a cylindrical packed bed, a new correlation is derived for apparent Nusselt number of the packed bed of shredded materials. The correlation is approximated by a power law formulation for Pecelt < 25. The Nusselt number calculated from this correlation is in a good agreement with other experimental data.

Investigation of a High-Temperature Packed-Bed Sensible Heat Thermal Energy Storage System With Large-Sized Elements

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Sarada Kuravi ◽  
Jamie Trahan ◽  
Yogi Goswami ◽  
Chand Jotshi ◽  
Elias Stefanakos ◽  
...  
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Energy Storage ◽  
Flow Rate ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Packed Bed ◽  
Inlet Temperature ◽  
Prototype System ◽  
Sensible Heat

A high-temperature, sensible heat thermal energy storage (TES) system is designed for use in a central receiver concentrating solar power plant. Air is used as the heat transfer fluid and solid bricks made out of a high storage density material are used for storage. Experiments were performed using a laboratory-scale TES prototype system, and the results are presented. The air inlet temperature was varied between 300 °C to 600 °C, and the flow rate was varied from 50 cubic feet per minute (CFM) to 90 CFM. It was found that the charging time decreases with increase in mass flow rate. A 1D packed-bed model was used to simulate the thermal performance of the system and was validated with the experimental results. Unsteady 1D energy conservation equations were formulated for combined convection and conduction heat transfer and solved numerically for charging/discharging cycles. Appropriate heat transfer and pressure drop correlations from prior literature were identified. A parametric study was done by varying the bed dimensions, fluid flow rate, particle diameter, and porosity to evaluate the charging/discharging characteristics, overall thermal efficiency, and capacity ratio of the system.

scholarly journals Internal Heat Transfer Coefficient Determination in a Packed Bed From the Transient Response Due to Solid Phase Induction Heating

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
David Geb ◽  
Feng Zhou ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Internal Heat ◽  
Temperature Response ◽  
Packed Bed ◽  
Spherical Particles ◽  
Fluid Temperature ◽  
The Core ◽  
Internal Heat Transfer

Nonintrusive measurements of the internal heat transfer coefficient in the core of a randomly packed bed of uniform spherical particles are made. Under steady, fully-developed flow the spherical particles are subjected to a step-change in volumetric heat generation rate via induction heating. The fluid temperature response is measured. The internal heat transfer coefficient is determined by comparing the results of a numerical simulation based on volume averaging theory (VAT) with the experimental results. The only information needed is the basic material and geometric properties, the flow rate, and the fluid temperature response data. The computational procedure alleviates the need for solid and fluid phase temperature measurements within the porous medium. The internal heat transfer coefficient is determined in the core of a packed bed, and expressed in terms of the Nusselt number, over a Reynolds number range of 20 to 500. The Nusselt number and Reynolds number are based on the VAT scale hydraulic diameter, dh=4ɛ/S. The results compare favorably to those of other researchers and are seen to be independent of particle diameter. The success of this method, in determining the internal heat transfer coefficient in the core of a randomly packed bed of uniform spheres, suggests that it can be used to determine the internal heat transfer coefficient in other porous media.

Split Flow Modified Packed Bed Reactor for Cobalt Oxide Based High-Temperature TCES Systems

2019 ◽  
Author(s):  
Nasser Vahedi ◽  
Alparslan Oztekin
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Pressure Drop ◽  
Energy Density ◽  
Redox Reaction ◽  
Packed Bed ◽  
Packed Bed Reactor ◽  
Flow Ratio ◽  
Packed Bed Reactors ◽  
Split Flow

Abstract The new generation of Concentrated Solar Power (CSP) plants requires high temperature and high energy density storage system with good cyclic stability. The potential solution satisfying such requirements is the thermochemical energy storage (TCES) using gas-solid redox reaction. Design of efficient storage reactor is very critical for applications of such storage systems. Packed bed reactors have a simpler design with no moving components and are more cost-effective compared to other available moving bed design configurations while having high-pressure drop is their main drawback. Any improvement in the pressure drop makes the design more suitable for commercial applications, especially at high temperature operating conditions. Cobalt oxide redox reaction has been considered for this study because of its unique features, especially high enthalpy of reaction (energy density) and high reaction temperature. A rectangular cross-section packed bed reactor with a large aspect ratio is selected as a reference conventional packed bed reactor. The novel split-flow packed bed reactor design configuration is proposed in which a portion of heat transfer fluid is passed through adjacent side channels. The split flow ratio of 1/3 has been considered for the case study. The transient two-dimensional numerical model is developed for solving mass, momentum, and energy equations for both gas and solid phases using suitable reaction kinetics for the reversible reduction and re-oxidation process. Complete storage cycle, including both the charging and discharging mode, has been simulated using finite element method. The split flow design performance is compared with the reference case considering the same size of the reaction bed. It is shown that the conversion time is increased while the pressure drop reduced below half of the pressure loss of the conventional design. Reduced mass flow rate passing through the bed results in considerable improvement in required pressure work with a penalty of storage performance. Further study is needed to optimize the split flow ratio and the surface heat transfer characteristics of the bed. The proposed design configuration could be a breakthrough in packed bed reactors, especially for high-temperature storage applications.

Sign in / Sign up

Export Citation Format

Share Document