HEAT TRANSFER IN GAS-FILLED POWDERS AT LOW TEMPERATURES

1965 ◽  
Vol 43 (12) ◽  
pp. 2344-2360 ◽  
Author(s):  
D. E. Brodie ◽  
C. F. Mate
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Particle Size ◽  
Low Temperatures ◽  
High Pressures ◽  
Cell Model ◽  
Boundary Resistance ◽  
Kapitza Resistance ◽  
Helium Gas ◽  
A Cell

A cell model is developed for the discussion of heat transfer in uniform gas-filled powders at low temperatures. Calculations from the model are compared with measurements of the (average) thermal conductivity of powdered alumina in helium gas, at helium temperatures, under varying conditions of particle size, gas pressure, temperature, and load supported by the powder. The results at high pressures suggest the presence of a boundary resistance, similar to the Kapitza resistance, at the gas–solid interfaces within the powder.

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.

Thermal Conductivity of Single-Crystal and Sintered RBa2Cu3O7 at low Temperatures

1987 ◽  
Vol 99 ◽  
Author(s):  
J. E. Graebner ◽  
L. F. Schneemeyer ◽  
R. J. Cava ◽  
J. V. Waszczak ◽  
E. A. Rietman
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Single Crystals ◽  
Free Path ◽  
Low Temperatures ◽  
Rayleigh Scattering ◽  
Resonant Scattering ◽  
Sintered Sample ◽  
Mean Free Path ◽  
Strong Scattering

ABSTRACTThe thermal conductivity k of micro-twinned single crystals of YBa2Cu3O7 and HoBa2Cu3O7 and a sintered sample of YBa2Cu3O7 has been measured for temperatures 0.03<T<5K. For the single crystals, k is small and varies as T1.8-1.9 This behavior resembles k for glassy insulators except for the lack of a plateau above IK. It is concluded that the thermal carriers are phonons with their mean free path limited by resonant scattering from tunneling entities, as in glasses. Suggestions for the location of tunneling systems are given. For the sinter, k is still smaller but does not follow a power law T-dependence. It is similar to other sintered ceramics with the same particle size, where the phonon mean free path is dominated by Rayleigh scattering from the particles. This strong scattering from the microstructure presumably masks the scattering from TS within each particle.

scholarly journals Improved Heat Transfer in Guar Gel Composites Reinforced with Randomly Distributed Glass Microspheres

2021 ◽  
Author(s):  
Ruifeng CAO ◽  
Taotao WANG ◽  
Yuxuan ZHANG ◽  
Hui WANG
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Particle Size ◽  
Composite Materials ◽  
Effective Thermal Conductivity ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Glass Microspheres ◽  
Particle Volume ◽  
Number Of Particles

Improved heat transfer in composites consisting of guar gel matrix and randomly distributed glass microspheres is extensively studied to predict the effective thermal conductivity of composites using the finite element method. In the study, the proper and probabilistic three-dimensional random distribution of microspheres in the continuous matrix is automatically generated by a simple and efficient random sequential adsorption algorithm which is developed by considering the correlation of three factors including particle size, number of particles, and particle volume fraction controlling the geometric configuration of random packing. Then the dependences of the effective thermal conductivity of composite materials on some important factors are investigated numerically, including the particle volume fraction, the particle spatial distribution, the number of particles, the nonuniformity of particle size, the particle dispersion morphology and the thermal conductivity contrast between particle and matrix. The related numerical results are compared with theoretical predictions and available experimental results to assess the validity of the numerical model. These results can provide good guidance for the design of advanced microsphere reinforced composite materials.

scholarly journals A predictive model of thermal conductivity of plain woven fabrics

2017 ◽  
Vol 21 (4) ◽  
pp. 1627-1632 ◽  
Author(s):  
Jia-Jia Wu ◽  
Hong Tang ◽  
Yu-Xuan Wu
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Numerical Simulation ◽  
Heat Flux ◽  
Thermal Comfort ◽  
Cell Model ◽  
Woven Fabrics ◽  
Woven Fabric ◽  
Unit Cell Model ◽  
Fabric Structure

This paper proposes an effective method to predict the thermal conductivity of plain woven blended fabric to optimize woven fabric structure, and to evaluate thermal comfort. The unit cell model of fabric is established for numerical simulation of heat transfer through thickness. The thermal conductivity of blended yarns is calculated by a series model. The temperature and heat flux distributions are verified experimentally.

scholarly journals Statistical analysis of thermal conductivity experimentally measured in water-based nanofluids

2021 ◽  
Vol 477 (2250) ◽  
pp. 20210222
Author(s):  
J. Tielke ◽  
M. Maas ◽  
M. Castillo ◽  
K. Rezwan ◽  
M. Avila
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Particle Size ◽  
Particle Concentration ◽  
Statistical Correlation ◽  
Large Scatter ◽  
Water Based ◽  
Homogeneous Media ◽  
Measured Thermal Conductivity ◽  
Specific Particle

Nanofluids are suspensions of nanoparticles in a base heat-transfer liquid. They have been widely investigated to boost heat transfer since they were proposed in the 1990s. We present a statistical correlation analysis of experimentally measured thermal conductivity of water-based nanofluids available in the literature. The influences of particle concentration, particle size, temperature and surfactants are investigated. For specific particle materials (alumina, titania, copper oxide, copper, silica and silicon carbide), separate analyses are performed. The conductivity increases with the concentration in qualitative agreement with Maxwell’s theory of homogeneous media. The conductivity also increases with the temperature (in addition to the improvement due to the increased conductivity of water). Surprisingly, only silica nanofluids exhibit a statistically significant effect of the particle size, whereby smaller particles lead to faster heat transfer. Overall, the large scatter in the experimental data prevents a compelling, unambiguous assessment of these effects. Taken together, the results of our analysis suggest that more comprehensive experimental characterizations of nanofluids are necessary to estimate their practical potential.

scholarly journals Effective thermal conductivity of loose residual coal in goaf: Comparative analysis of experiment and model

2022 ◽  
pp. 014459872110695
Author(s):  
Chunhua Zhang ◽  
Jiahui Shen ◽  
Mei Wan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Particle Size ◽  
Ambient Temperature ◽  
Effective Thermal Conductivity ◽  
Void Fraction ◽  
Coal Particle ◽  
Spontaneous Combustion ◽  
Relative Errors ◽  
Residual Coal

The effective thermal conductivity (ETC) model of loose residual coal in goaf is a method to study the heat transfer law of spontaneous combustion in goaf. In order to study the effect of coal particle size and ambient temperature on heat transfer, coal samples of different sizes were taken from the FuSheng (FS) mine, and the void fraction, the thermal conductivity (TC) of the residual coal under different ambient temperature were tested. Additionally, four types of ETC models of loose residual coal in goaf were obtained and the average relative errors of the TC were analyzed. The results showed that the void fraction, the coal particle size and ambient temperature have different effects on the spontaneous combustion of the residual coal. The effect of coal sample size on the heat transfer is 100 times that of the ambient temperature. The changes in the ETC and average relative error of the different models were consistent. The heat transfer in the spontaneous combustion of residual coal has a direct relationship with the spatial distribution and heat transfer modes of the loose residual coal in the goaf.

The Effect of Additional Polyethylene Glycol (PEG) as Coating Fe3O4 for Magnetic Nanofluid Applications

2021 ◽  
Vol 14 ◽  
Author(s):  
Ganesha Antarnusa ◽  
Yus Rama Denny ◽  
Andri Suherman ◽  
Indri Sari Utami ◽  
Asep Saefullah
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Particle Size ◽  
Polyethylene Glycol ◽  
Fe3o4 Nanoparticles ◽  
Chemical Precipitation ◽  
Heat Transfer Process ◽  
Precipitation Method ◽  
Magnetic Nanofluid ◽  
Peg 6000

Background & Objective: Magnetic nanofluid is a special class of nanofluid that exhibits both magnetic and fluid properties. The main purpose of using magnetic nanofluid as a heat transfer medium comes from the possibility of controlling the flow and the heat transfer process through an external magnetic field. This research aims at identifying the effect of adding polyethylene glycol (PEG) to magnetite (Fe3O4) nanoparticles for magnetic nanofluid applications. Method: The nanofluid were prepared by synthesizing Fe3O4 nanoparticles using the chemical precipitation method, and then dispersed in distilled water using a sonicator. Results: The result of XRD is that nanoparticles had inverse spinel structures and the smallest crystallite size is found in the Fe3O4@PEG-6000 samples. FE-SEM and TEM show that the addition of PEG can reduce the Fe3O4 agglomeration and the smallest particle size is found in the Fe3O4@PEG-6000 samples. The result of FT-IR shows that there is a surface modification of Fe3O4 nanoparticles and PEG polymer. The result of VSM shows the coercivity value is small so that the sample is superparamagnetic material. The addition of PEG increases the thermal conductivity of Fe3O4 nanoparticles. Conclusion: The addition of PEG makes particle size smaller, reduce the agglomeration and increases the thermal conductivity, so that it is potential for magnetic nanofluid applications.

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