TDEM simulation and analysis of thermal conduction through packed granular beds

2016 ◽  
Vol 94 (9) ◽  
pp. 826-833 ◽  
Author(s):  
Nan Gui ◽  
Xingtuan Yang ◽  
Jiyuan Tu ◽  
Shengyao Jiang
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Thermal Diffusivity ◽  
Thermal Conduction ◽  
Packed Bed ◽  
Particle Collision ◽  
Granular Bed ◽  
Granular Assembly ◽  
And Diffusion ◽  
Granular Properties

The work deals with evaluation and simulation of the thermal discrete element method (TDEM) for particle–particle collision and thermal conduction in a packed bed. The effects of different granular properties, such as particle size, stiffness factor or compression degree, thermal diffusivity, void fraction or concentrations, and packing states, on the thermal conduction and insulation characteristics of granular assembly are discussed. The thermal conductivity and diffusion still play dominant roles in the overall thermal conduction and insulation of the granular bed. However, it is also indicated that increasing compression degree, reducing particle size and void concentration will increase the thermal conduction throughout the granular materials, and vice versa.

Binary Particle Mixtures as a Heat Transfer Media in Shell-and-Plate Moving Packed Bed Heat Exchangers

2021 ◽  
Author(s):  
Chase Ellsworth Christen
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Particle Size ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Packed Bed ◽  
Particle Sizes ◽  
Overall Heat Transfer Coefficient ◽  
Solid Media

Solid particles are being considered in several high temperature thermal energy storage systems and as heat transfer media in concentrated solar power (CSP) plants. The downside of such an approach is the low overall heat transfer coefficients in shell-and-plate moving packed bed heat exchangers caused by the inherently low packed bed thermal conductivity values of the low-cost solid media. Choosing the right particle size distribution of currently available solid media can make a substantial difference in packed bed thermal conductivity, and thus, a substantial difference in the overall heat transfer coefficient of shell-and-plate moving packed bed heat exchangers. Current research exclusively focuses on continuous unimodal distributions of alumina particles. The drawback of this approach is that larger particle sizes require wider particle channels to meet flowability requirements. As a result, only small particle sizes with low packed bed thermal conductivities have been considered for the use in the falling-particle Gen3 CSP concepts. Here, binary particle mixtures, which are defined in this thesis as a mixture of two continuous unimodal particle distributions leading to a continuous bimodal particle distribution, are considered to increase packed bed thermal conductivity, decrease packed bed porosity, and improve moving packed bed heat exchanger performance. This is the first study related to CSP solid particle heat transfer that has considered the packed bed thermal conductivity and moving packed bed heat exchanger performance of bimodal particle size distributions at room and elevated temperatures. Considering binary particle mixtures that meet particle sifting segregation criteria, the overall heat transfer coefficient of shell-and-plate moving packed bed heat exchangers can be increased by 23% when compared to a monodisperse particle system. This work demonstrates that binary particle mixtures should be seriously considered to improve shell-and-plate moving packed bed heat exchangers.

On: “An analytical study of a two-layer transient thermal conduction problem as applied to soil temperature surveys” by T. H. Larson and A. T. Hsui (February 1992 GEOPHYSICS, p. 306–312)

Geophysics ◽  
1992 ◽  
Vol 57 (12) ◽  
pp. 1644-1645
Author(s):  
Virgil J. Lunardini
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Thermal Conduction ◽  
Thermal Response ◽  
Periodic Surface ◽  
Ground Temperatures ◽  
Ground Conditions ◽  
Thermal Properties Of Materials ◽  
Properties Of Materials ◽  
Transient Thermal

This paper presents a solution to the two‐layer conduction problem, a problem which has already been solved exactly and published (Lachenbruch, 1959; Lunardini, 1981). In fact the three‐layer solution is also available, (Lachenbruch, 1959). Unfortunately the Larson and Hsui paper uses an incorrect boundary condition for the energy flow continuity between the layers; this refers to the last equation after equation (3), or equation (A-20) of their paper. The temperature gradient must be multiplied by the thermal conductivity, not the thermal diffusivity as the paper has done. The results obtained in the paper are only valid if the heat capacities ρc of the two layers are equal. However, few soils have the same heat capacity, as can be seen from the thermal properties of materials often encountered in geotechnical situations, given in Table 1. Thus, a second parameter is required for interpreting ground temperatures: the ratio of the thermal conductivities of the two layers. The interpretation given to the effects of only the thermal diffusivity ratios is then open to question. Calculations of the same ground conditions as used by Larsen and Hsui, with the same diffusivity ratios but with realistic thermal conductivity ratios, give significantly different temperature predictions. Of course, the general conclusions of the paper on the profound effect of layering on the thermal response of soils to periodic surface temperatures are still true.

scholarly journals Optimization of Variables Influencing the Thermal Conductivity and Fracture Strength of Reinforced PMMA by Using the Taguchi Method

2020 ◽  
Vol 57 (3) ◽  
pp. 137-146
Author(s):  
Esra Kul ◽  
Faruk Yesildal ◽  
Emre Mandev ◽  
Cafer Celik
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Thermal Diffusivity ◽  
Flexural Strength ◽  
Design Method ◽  
In Vitro Study ◽  
Fracture Load ◽  
Denture Base ◽  
Base Resin

How the particle size and volumetric ratio of silicon carbide (SiC) powder additions will strengthen polymethyl methacrylate (PMMA) is unclear. The purpose of this in vitro study was to optimize the reinforcement parameters of PMMA with SiC powder by using the Taguchi experimental design method. Particle size, volumetric rate, silane coupling rate, and mixing type were determined as parameters that would affect the reinforcement of PMMA with SiC powder. Using the Taguchi L9 orthogonal array, test specimens with different parameter combinations were fabricated and tested. The fracture load (in newtons) of each specimen group was recorded with the 3-point bend test. The thermal conductivity values of 60x50-mm and 3-mm-thick rectangular specimens were measured by using the Linseis THB100 thermal conductivity unit. The thermal diffusivity values were then calculated. Thermal analysis indicated improvement in the thermal conductivity of PMMA after reinforcement with SiC. The maximum thermal diffusivity was obtained with 15% SiC powder by volume. Thermal conductivity and flexural strength increased with an increase in particle size. The maximum flexural strength value was obtained with 5% SiC powder by volume. Increasing the particle size of the filler SiC powder resulted in increased thermal conductivity and flexural strength. Increasing the SiC filler powder by volume increased the thermal conductivity of PMMA but reduced its flexural strength. This study helped determine the optimum conditions for the use of SiC powder. Knowledge of the importance of these variables will help in more effective modification of denture base resin with SiC powder to improve heat transfer without adversely affecting strength.

Thermal Conductivity of Fly Ash Cenospheres for Variable Particle Size Ranges

2016 ◽  
Vol 4 (2) ◽  
pp. 19
Author(s):  
MENEZES CRAIG ◽  
RATHOD AJIT P ◽  
WASEWAR KAILAS L. ◽  
◽  
◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Fly Ash ◽  
Fly Ash Cenospheres
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