scholarly journals Measurement of Thermal Conductivity along the Radial Direction in a Vertical Cylindrical Packed Bed

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
Swaren Bedarkar ◽  
Nurni Neelakantan Viswanathan ◽  
Nidambur Bharatha Ballal
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Crucial Role ◽  
Iron Ore ◽  
Radial Direction ◽  
Thermal Response ◽  
Packed Bed ◽  
Lumped Parameter ◽  
Scientists And Engineers

Heat transfer in packed beds and their thermal response have been of great interest for scientists and engineers for the last several years, since they play a crucial role in determining design and operation of reactors. Heat transfer of a packed bed is characterised through lumped parameter, namely, effective thermal conductivity. In the present studies, experiments were performed to investigate the thermal conductivity of a packed bed in radial direction. The packed bed was formed using iron ore particles. To determine the effective thermal conductivity a new transient methodology is proposed. The results obtained were compared with the models proposed by ZBS and Kunii and Smith.

scholarly journals Investigation of Effective Thermal Conductivity for Ordered and Randomly Packed Bed with Thermal Resistance Network Method

Energies ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1666 ◽  
Author(s):  
Jian Yang ◽  
Yingxue Hu ◽  
Qiuwang Wang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Effective Thermal Conductivity ◽  
Packed Bed ◽  
Random Packing ◽  
Packing Factor ◽  
Resistance Network ◽  
Network Method ◽  
Thermal Conductivities

In the present paper, the effective thermal conductivities of Li4SiO4-packed beds with both ordered and random packing structures were investigated using thermal resistance network methods based on both an Ohm’s law model and a Kirchhoff’s law model. The calculation results were also validated and compared with the numerical and experimental results. Firstly, it is proved that the thermal resistance network method based on the Kirchhoff’s law model proposed in the present study is reliable and accurate for prediction of effective thermal conductivities in a Li4SiO4-packed bed, while the results calculated with the Ohm’s law model underestimate both ordered and random packings. Therefore, when establishing a thermal resistance network, the thermal resistances should be connected along the main heat transfer direction and other heat transfer directions as well in the packing unit. Otherwise, both the total heat flux and effective thermal conductivity in the packing unit will be underestimated. Secondly, it is found that the effect of the packing factor is remarkable. The effective thermal conductivity of a packed bed would increase as the packing factor increases. Compared with random packing at similar packing factor, the effective thermal conductivity of packed bed would be further improved with an ordered packing method.

Effects of Fin Configuration on Heat Transfer Rate in Packed Bed Reactors for Improvement of Their Thermal Characteristics

2010 ◽  
Author(s):  
Koichi Nakaso ◽  
Takuro Aoki ◽  
Jun Fukai
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Thermal Response ◽  
Packed Bed ◽  
Packed Bed Reactors ◽  
Apparent Thermal Conductivity ◽  
Spiral Type ◽  
Thermal Conductivities

Packed bed reactors are utilized for catalysts, chemical heat pumps, etc. Because the effective thermal conductivities of the packed beds of particles are generally low (≈10−1 W/mK), this matter often results in low performance and degradation of catalyst. Many heat transfer tubes with fins and/or much filler with high thermal conductivities are inserted in the packed bed reactors to improve heat transfer rate. In return to this, the volume of reactive particles packed into the reactors, or stored energy, decreases. In this study, the effect of fin configurations on the heat transfer rate in the reactors is numerically investigated. Three configurations of fins are studied. (1) “Sheet type” is a longitudinal fin attached on the heat transfer tubes. It is placed to connect between heat transfer tubes. (2) “Straight type” is several longitudinal fins in the half length of the tube pitch attached on the tube with radial structure. (3) “Spiral type” is many narrow rectangular fins attached on the tube with spiral structure. To discuss the effect of fin configuration on the heat transfer generally, the heat conduction equation in the packed bed around the tube is converted to the dimensionless form. The transient temperature responses in the packed bed and fins at a uniform temperature are calculated when the temperature of the tube surface is stepwise changes. In another analytical system, a homogeneous body around the tube is assumed. To evaluate the thermal performance of the fin, apparent thermal conductivity is defined as the thermal conductivity which gives the same thermal response as that calculated in the heterogeneous system. As a result, the spiral type rather than the straight and sheet types effectively increases apparent thermal conductivity. The apparent thermal conductivity of the spiral type is two-three times larger than the straight type, and ten times as large as the sheet type. This result indicates dispersion of fins in packed bed is essential to improve the thermal response in the reactors.

Experimental Analysis of Heat Transfer inside Packed Beds of Soybean Seeds

2012 ◽  
Vol 727-728 ◽  
pp. 1818-1823
Author(s):  
G.F.M.V. Souza ◽  
R. Béttega ◽  
R.F. Miranda ◽  
O.S.H. Mendoza ◽  
M.A.S. Barrozo
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Fluid Dynamic ◽  
Fixed Bed ◽  
Packed Bed ◽  
Soybean Seeds ◽  
Packed Beds ◽  
Flow Conditions ◽  
Separation Systems

Several applications in chemical industry use randomly packed bed of particles, such as particulate separation systems, chemical reactors or fixed bed drying. Fluid dynamic behavior, heat and mass transfer, in addition to structural properties of the bed are fundamental issues to design of these processes. Several studies about heat transfer in packed beds aiming drying application have been performed in order to contribute with the process. Seeds drying temperature is especially important for the seeds quality indices and must be carefully controlled in drying process. In this paper temperature profiles experimentally obtained in a packed bed composed by soybean seeds are presented and discussed. Axial profiles of temperature were applied for obtaining effective thermal conductivity following previous studies from literature. The results indicate that thermal homogeneity can be achieved inside the bed for controlled air flow conditions. Axial effective thermal conductivity presented results in agreement with previous studies from literature.

Figure of Merit-Based Optimization Approach of Phase Change Material-based Composites for Portable Electronics Using Simplified Model

2021 ◽  
Author(s):  
Ayushman Singh ◽  
Srikanth Rangarajan ◽  
Leila Choobineh ◽  
Bahgat Sammakia
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Phase Change ◽  
Effective Thermal Conductivity ◽  
Phase Change Material ◽  
Figure Of Merit ◽  
Volume Fraction ◽  
Simplified Model ◽  
Transient Temperature ◽  
Change Material

Abstract This work presents an approach to optimally designing a composite with thermal conductivity enhancers (TCEs) infiltrated with phase change material (PCM) based on figure of merit (FOM) for thermal management of portable electronic devices. The FOM defines the balance between effective thermal conductivity and energy storage capacity. In present study, TCEs are in the form of a honeycomb structure. TCEs are often used in conjunction with PCM to enhance the conductivity of the composite medium. Under constrained composite volume, the higher volume fraction of TCEs improves the effective thermal conductivity of the composite, while it reduces the amount of latent heat storage simultaneously. The present work arrives at the optimal design of composite for electronic cooling by maximizing the FOM to resolve the stated trade-off. In this study, the total volume of the composite and the interfacial heat transfer area between the PCM and TCE are constrained for all design points. A benchmarked two-dimensional direct CFD model was employed to investigate the thermal performance of the PCM and TCE composite. Furthermore, assuming conduction-dominated heat transfer in the composite, a simplified effective numerical model that solves the single energy equation with the effective properties of the PCM and TCE has been developed. The effective thermal conductivity of the composite is obtained by minimizing the error between the transient temperature gradient of direct and simplified model by iteratively varying the effective thermal conductivity. The FOM is maximized to find the optimal volume fraction for the present design.

scholarly journals The effect of particle shape on the packed bed effective thermal conductivity based on DEM with polyhedral particles on the GPU

2020 ◽  
Vol 219 ◽  
pp. 115584 ◽  
Author(s):  
Nicolin Govender ◽  
Paul W. Cleary ◽  
Mehran Kiani-Oshtorjani ◽  
Daniel N. Wilke ◽  
Chuan-Yu Wu ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Particle Shape ◽  
Packed Bed ◽  
Polyhedral Particles

scholarly journals Effective thermal conductivity of the hair coat of Holstein cows in a tropical environment

2009 ◽  
Vol 38 (11) ◽  
pp. 2218-2223 ◽  
Author(s):  
Alex Sandro Campos Maia ◽  
Roberto Gomes da Silva ◽  
João Batista Freire de Souza Junior ◽  
Rosiane Batista da Silva ◽  
Hérica Girlane Tertulino Domingos
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Free Convection ◽  
Effective Thermal Conductivity ◽  
Tropical Environment ◽  
Holstein Cows ◽  
Hair Coat ◽  
Black And White ◽  
Low K

The objective of the present study was to assess the effective thermal conductivity of the hair coat (k ef, mW.m-1.K-1) of Holstein cows in a tropical environment, as related to conduction and radiation in the absence of free convection. The average k ef was 49.72 mW.m-1.K-1, about twice the conductivity of the air (26 mW.m-1.K-1) and much less than that of the hair fibres (260 mW.m-1.K-1). The low k ef values were attributed mainly to the small cross area of individual hairs, ρef/ρf (17.2% and 21.3% for black and white hairs, respectively). White coats were denser, with longer hairs and significantly higher k ef (53.15 mW.m-1.K-1) than that of the black hairs (49.25 mW.m-1.K-1). The heritability coefficient of the effective thermal conductivity was calculated as h²=0.18 the possibility was discussed of selecting cattle for increased heat transfer through the hair coat.

scholarly journals High-Fidelity Calculation of Effective Thermal Response of Composite Media With Heat Generation Source

2020 ◽  
Author(s):  
Kevin Irick ◽  
Nima Fathi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Behavior ◽  
Nuclear Fuel ◽  
Heat Generation ◽  
Thermal Response ◽  
Thermal Conditions ◽  
Unit Cell ◽  
High Fidelity ◽  
Conductive Heat

Abstract The complexity of conductive heat transfer in a structure increases with heterogeneity (e.g., multi-component solid-phase systems with a source of internal thermal heat generation). Any discontinuity of material property — especially thermal conductivity — would warrant a thorough analysis to evaluate the thermal behavior of the system of interest. Heterogeneous thermal conditions are crucial to heat transfer in nuclear fuel assemblies, because the thermal behavior within the assemblies is governed significantly by the heterogeneous thermal conditions at both the system and component levels. A variety of materials have been used as nuclear fuels, the most conventional of which is uranium dioxide, UO2. UO2 has satisfactory chemical and irradiation tolerances in thermal reactors, whereas the low thermal conductivity of porous UO2 can prove challenging. Therefore, the feasibility of enhancing the thermal conductivity of oxide fuels by adding a high-conductivity secondary solid component is still an important ongoing topic of investigation. Undoubtedly, long-term, stable development of clean nuclear energy would depend on research and development of innovative reactor designs and fuel systems. Having a better understanding of the thermal response of the unit cell of a composite that represents a fuel matrix cell would help to develop the next generation of nuclear fuel and understand potential performance enhancements. The aim of this article is to provide an assessment of a high-fidelity computational model response of heterogeneous materials with heat generation in circular fillers. Two-dimensional, steady-state systems were defined with a circular, heat-generating filler centered in a unit-cell domain. A Fortran-based finite element method (FEM) code was used to solve the heat equation on an unstructured triangular mesh of the systems. This paper presents a study on the effects of a heat-generating filler material’s relative size and thermal conductivity on effective thermal conductance, Geff, within a heterogenous material. Code verification using the method of manufactured solution (MMS) was employed, showing a second-order accurate numerical implementation. Solution verification was performed using a global deviation grid convergence index (GCI) method to assess solution convergence and estimate solution numerical uncertainty, Unum. Trend results are presented, showing variable response in Geff to filler size and thermal conductivity.

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