Experimental Measurements of the Thermal Conductivity of Nanoparticle Packed Beds

2013 ◽  
Author(s):  
Kevin Clarke ◽  
Muftah Elsahati ◽  
Robert F. Richards
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Silica Nanoparticles ◽  
Metallic Nanoparticles ◽  
Silica Nanoparticle ◽  
Packed Bed ◽  
Experimental Measurements ◽  
Packed Beds ◽  
Copper Nanoparticle ◽  
Sem Imaging

Experimental measurements of heat transfer across packed beds of ceramic and metallic nanoparticles are presented. Round disk-shaped cakes of nanoparticles approximately one millimeter thick and 6.75 millimeters diameter are produced by packing either copper or silica nanoparticles into a mold. The thermal conductivity of these packed beds are then determined using a Guard-Heated Calorimeter under steady state conditions. SEM imaging of the packed beds indicates that the copper nanoparticles are neither monosized nor entirely spherical while the silica nanoparticles, are both highly spherical and monosized. However, both packed beds were found to have very similar effective thermal conductivities. The thermal conductivity of the copper nanoparticle packed bed is found to be 0.054 ± 0.006 W/m°C, while the thermal conductivity of silica nanoparticle packed bed is found to be 0.018 ± 0.007 W/m°C. As a result, it is seen that, at least in this limited comparison, particle material and thermal conductivity (metal with high conductivity, or ceramic with low conductivity), as well as the regularity of the nanoparticle itself (size distribution and sphericity) appear to have a small effect on overall packed bed thermal conductivity.

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.

The Effect of Turbulence on Momentum and Heat Transport in Packed Beds with Low Tube to Particle Diameter Ratio

2018 ◽  
Vol 16 (11) ◽  
Author(s):  
F. I. Molina-Herrera ◽  
C. O. Castillo-Araiza ◽  
H. Jiménez-Islas ◽  
F. López-Isunza
Keyword(s):  
Thermal Conductivity ◽  
Heat Transport ◽  
Mass Flux ◽  
Flow Model ◽  
Particle Diameter ◽  
Packed Bed ◽  
Diameter Ratio ◽  
Packed Beds ◽  
Measured Temperature ◽  
Orthogonal Collocation

Abstract This is a theoretical study about the influence of turbulence on momentum and heat transport in a packed-bed with low tube to particle diameter ratio. The hydrodynamics is given here by the time-averaged Navier-Stokes equations including Darcy and Forchheimer terms, plus a κ-ε two-equation model to describe a 2D pseudo-homogeneous medium. For comparison, an equivalent conventional flow model has also been tested. Both models are coupled to a heat transport equation and they are solved using spatial discretization with orthogonal collocation, while the time derivative is discretized by an implicit Euler scheme. We compared the prediction of radial and axial temperature observations from a packed-bed at particle Reynolds numbers (Rep) of 630, 767, and 1000. The conventional flow model uses effective heat transport parameters: wall heat transfer coefficient (hw) and thermal conductivity (keff), whereas the turbulent flow model includes a turbulent thermal conductivity (kt), estimating hw via least-squares with Levenberg-Marquardt method. Although predictions of axial and radial measured temperature profiles with both models show small differences, the calculated radial profiles of the axial velocity component are very different. We demonstrate that the model that includes turbulence compares well with mass flux measurements at the packed-bed inlet, yielding an error of 0.77 % in mass flux balance at Rep = 630. We suggest that this approach can be used efficiently for the hydrodynamics characterization and design and scale-up of packed beds with low tube to particle diameter ratio in several industrial applications.

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.

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.

Experimental and Theoretical Modeling of the Effective Thermal Conductivity of Rough Steel Spheroid Packed Beds

2003 ◽  
Vol 125 (4) ◽  
pp. 693-702 ◽  
Author(s):  
G. Buonanno ◽  
A. Carotenuto ◽  
G. Giovinco ◽  
N. Massarotti
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Solid Mechanics ◽  
Packed Bed ◽  
Elementary Cell ◽  
Upper And Lower Bounds ◽  
Packed Beds ◽  
The Finite Element Method ◽  
Two Phase ◽  
Experimental Apparatus

The upper and lower bounds of the effective thermal conductivity of packed beds of rough spheres are evaluated using the theoretical approach of the elementary cell for two-phase systems. The solid mechanics and thermal problems are solved and the effects of roughness and packed bed structures are also examined. The numerical solution of the thermal conduction problem through the periodic regular arrangement of steel spheroids in air is determined using the Finite Element Method. The numerical results are compared with those obtained from an experimental apparatus designed and built for this purpose.

An Experimental Investigation on Forced Convection Heat Transfer From a Cylinder Embedded in a Packed Bed

1994 ◽  
Vol 116 (1) ◽  
pp. 73-80 ◽  
Author(s):  
K. Nasr ◽  
S. Ramadhyani ◽  
R. Viskanta
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Particle Diameter ◽  
Packed Bed ◽  
Spherical Particles ◽  
Theoretical Equation ◽  
Convection Heat ◽  
Forced Convection Heat Transfer

Forced convection heat transfer from a cylinder embedded in a packed bed of spherical particles was studied experimentally. With air as the working fluid, the effects of particle diameter and particle thermal conductivity were examined for a wide range of thermal conductivities (from 200 W/m K for aluminum to 0.23 W/m K for nylon) and three nominal particle sizes (3 mm, 6 mm, and 13 mm). In the presence of particles, the measured convective heat transfer coefficient was up to seven times higher than that for a bare tube in crossflow. It was found that higher heat transfer coefficients were obtained with smaller particles and higher thermal conductivity packing materials. The experimental data were compared against the predictions of a theory based on Darcy’s law and the boundary layer approximations. While the theoretical equation was moderately successful at predicting the data, improved correlating equations were developed by modifying the form of the theoretical equation to account better for particle diameter and conductivity variations.

The Effect of Element Thermal Conductivity on Turbulent Convective Heat Transfer From Rough Surfaces

2009 ◽  
Author(s):  
Stephen T. McClain ◽  
B. Keith Hodge ◽  
Jeffrey P. Bons
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat Transfer ◽  
Rough Surfaces ◽  
Element Model ◽  
Discrete Element ◽  
Discrete Element Model ◽  
Experimental Measurements ◽  
Fin Efficiency ◽  
Roughness Elements

The discrete-element model for flows over rough surfaces considers the heat transferred from a rough surface to be the sum of the heat convected from the flat surface and the heat convected from the individual roughness elements to the fluid. In previous discrete-element model development, heat transfer experiments were performed using metallic or high-thermal conductivity roughness elements. Many engineering applications, however, exhibit roughness with low thermal conductivities. In the present study, the discrete element model is adapted to consider the effects of finite thermal conductivity of roughness elements on turbulent convective heat transfer. Initially, the boundary-layer equations are solved while the fin equation is simultaneously integrated so that the full conjugate heat transfer problem is solved. However, a simpler approach using a fin-efficiency is also investigated. The results of the conjugate analysis and the simpler fin-efficiency analysis are compared to experimental measurements for turbulent flows over ordered cone surfaces. Possibilities for extending the fin-efficiency method to randomly-rough surfaces and the experimental measurements required are discussed.

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.

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