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.

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.

A Parameter for Selection of Nano-Dispersoids in Nanofluids for Thermal Applications

2012 ◽  
Vol 736 ◽  
pp. 223-228
Author(s):  
M.M. Ghosh ◽  
S. Ghosh ◽  
S.K. Pabi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Elastic Modulus ◽  
Heat Source ◽  
Ethylene Glycol ◽  
Preliminary Identification ◽  
Water Based ◽  
Selection Of ◽  
Poissons Ratio

A model reported by the present investigators has earlier shown that the extent of heat pick up by a nanoparticle during its collision with the heat source in a given nanofluid would depend on the thermal conductivity (kp, unit W/m.K), density (ρ, unit kg/m3), elastic modulus (E, unit GPa) and Poissons ratio (μ) of the nanoparticle and heat source. Considering the expression for collision period and thermal conductivity of nanoparticle, a factor χ =kp(ρ/E)0.4 is proposed here and examined for the preliminary identification of the potential of a dispersoid in enhancing the thermal conductivity of a nanofluid. The χ-factor for Ag, Cu, CuO, Al2O3 and SiO2 are 2960, 2247, 116, 14.1 and 5.5, respectively. The higher χ-factor of CuO compared to that of Al2O3 can explain why water and ethylene glycol (EG) based CuO-nanofluid is reported to show higher enhancement in the thermal conductivity, when compared to similar Al2O3-nanofluid. The χ for SiO2 is much smaller than that for Ag, which also corroborates well with the marginal enhancement in thermal conductivity of water based nanofluid containing SiO2 nanoparticles. Therefore, a high value of χ of the nanodispersoid can serve as a parameter for the design of nanofluids for heat transfer applications.

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 Synthesis and thermal conductivity of functionalized biocarbon-Fe3O4 nanocomposite-based green nanofluid for heat transfer applications

2021 ◽  
Vol 321 ◽  
pp. 01003
Author(s):  
Divya Barai ◽  
Sohan Parbat ◽  
Bharat Bhanvase
Keyword(s):  
Heat Transfer ◽  
Electron Microscopy ◽  
Thermal Conductivity ◽  
Nanocomposite Particles ◽  
X Ray ◽  
Conductivity Enhancement ◽  
Water Based ◽  
One Step ◽  
Ultrasound Assisted ◽  
Scanning Electron

Bio-based graphitic carbon was synthesized in this work by one-step carbonization of bamboo waste at low temperature. This bio-based carbon was then functionalized in order to decorated it with Fe3O4 nanoparticles. The functionalized biocarbon-Fe3O4 (f-biocarbon-Fe3O4) nanocomposite was synthesized using ultrasound-assisted coprecipitation method which was then confirmed by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffractometry. Water-based nanofluid was prepared using the synthesized f-biocarbon-Fe3O4 nanocomposite particles. Thermal conductivity of this nanofluid was analyzed at different concentrations and temperatures. A thermal conductivity enhancement of almost 80% was recorded at 35°C for nanofluid containing 0.1 vol.% of f-biocarbon-Fe3O4 nanocomposite particles compared to water. Also, empirical model is developed for prediction of thermal conductivity as a function of concentration and temperature of bamboo waste-derived f-biocarbon-Fe3O4 nanocomposite-based green nanofluid.

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.

Intertube Falling-Film Heat Transfer Behavior of Multiwall Carbon Nanotube Suspensions (MWCNT Nanofluids)

2011 ◽  
Author(s):  
Binglu Ruan ◽  
Anthony M. Jacobi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Ethylene Glycol ◽  
Multiwall Carbon Nanotube ◽  
Falling Film ◽  
Water Based ◽  
Film Heat Transfer ◽  
The Heat Transfer Coefficient ◽  
Multiwall Carbon

The thermal conductivity and viscosity of water-based and ethylene-glycol-based multiwall carbon nanotube (MWCNT) suspensions are measured for MWCNT volume concentrations up to 0.24%. The thermal conductivity is found to increase up to 8.6% and 9.3% for water-based and ethylene-glycol-based nanofluids, respectively. The viscosity of the nanofluids increases compared to that of their base fluids, with larger increases for the ethylene-glycol-based nanofluids. Intertube falling-film heat transfer characteristics of these nanofluids are measured and compared to data for the base fluids. The heat transfer coefficient of the water-based nanofluids decreases at low MWCNT concentrations but increases as the concentration increases. The heat transfer coefficient of the ethylene-glycol-based nanofluids decreases with an increase in MWCNT concentration, with a maximum deviation of 30%.

Sign in / Sign up

Export Citation Format

Share Document