Experiment-Calculated Investigation of the Forced Convection of Nanofluids Using Single Fluid Approach

2014 ◽  
Vol 348 ◽  
pp. 123-138 ◽  
Author(s):  
Andrey V. Minakov ◽  
Alexander S. Lobasov ◽  
M.I. Pryazhnikov ◽  
D.V. Guzei
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Experimental Determination ◽  
Forced Convection ◽  
Navier Stokes ◽  
Physical Parameters ◽  
Hydrodynamic Description ◽  
Transfer Equations

An experiment-calculated investigation of forced convection of nanofluids based on Al2O3nanoparticles was carried out. The hydrodynamic description and a model of homogeneous nanofluids were used. The homogeneous nanofluids model assumes that the hydrodynamics and heat transfer can be described by conventional Navier-Stokes and heat transfer equations with the physical parameters corresponding to nanofluids. The results showed that this model very well described the experimental data in some cases. However, in some other cases, there are discrepancies between experiment and theory that can be explained by the real heterogeneity of nanofluids and the errors in the experimental determination of thermal conductivity and viscosity of nanofluids.

Forced Convection Heat Transfer of Nanofluids: A Review

2017 ◽  
Author(s):  
Aditya Kuchibhotla ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Specific Heat ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Convection Heat

Stable homogeneous colloidal suspensions of nanoparticles in a liquid solvents are termed as nanofluids. In this review the results for the forced convection heat transfer of nanofluids are gleaned from the literature reports. This study attempts to evaluate the experimental data in the literature for the efficacy of employing nanofluids as heat transfer fluids (HTF) and for Thermal Energy Storage (TES). The efficacy of nanofluids for improving the performance of compact heat exchangers were also explored. In addition to thermal conductivity and specific heat capacity the rheological behavior of nanofluids also play a significant role for various applications. The material properties of nanofluids are highly sensitive to small variations in synthesis protocols. Hence the scope of this review encompassed various sub-topics including: synthesis protocols for nanofluids, materials characterization, thermo-physical properties (thermal conductivity, viscosity, specific heat capacity), pressure drop and heat transfer coefficients under forced convection conditions. The measured values of heat transfer coefficient of the nanofluids varies with testing configuration i.e. flow regime, boundary condition and geometry. Furthermore, a review of the reported results on the effects of particle concentration, size, temperature is presented in this study. A brief discussion on the pros and cons of various models in the literature is also performed — especially pertaining to the reports on the anomalous enhancement in heat transfer coefficient of nanofluids. Furthermore, the experimental data in the literature indicate that the enhancement observed in heat transfer coefficient is incongruous compared to the level of thermal conductivity enhancement obtained in these studies. Plausible explanations for this incongruous behavior is explored in this review. A brief discussion on the applicability of conventional single phase convection correlations based on Newtonian rheological models for predicting the heat transfer characteristics of the nanofluids is also explored in this review (especially considering that nanofluids often display non-Newtonian rheology). Validity of various correlations reported in the literature that were developed from experiments, is also explored in this review. These comparisons were performed as a function of various parameters, such as, for the same mass flow rate, Reynolds number, mass averaged velocity and pumping power.

Convective Heat Transfer Enhancement With Nanofluids: The Effect of Temperature-Variable Thermal Conductivity

2010 ◽  
Author(s):  
Sezer O¨zerinc¸ ◽  
Almıla G. Yazıcıog˘lu ◽  
Sadık Kakac¸
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Heat Transfer Enhancement ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Thermal Dispersion ◽  
Convection Heat ◽  
Transfer Enhancement ◽  
Experimental Values

A nanofluid is defined as the suspension of nanoparticles in a base liquid. Studies in the last decade have shown that significant amount of thermal conductivity and heat transfer enhancement can be obtained by using nanofluids. In the first part of this study, classical forced convection heat transfer correlations developed for pure fluids are used to predict the experimental values of heat transfer enhancement of nanofluids. It is seen that the experimental values of heat transfer enhancement exceed the enhancement predictions of the classical correlations. On the other hand, a recent correlation based on the thermal dispersion phenomenon created by the random motion of nanoparticles predicts the experimental data well. In the second part of the study, in order to further examine the validity of the thermal dispersion approach, a numerical analysis of forced convection heat transfer of Al2O3/water nanofluid inside a circular tube in the laminar flow regime is performed by utilizing single phase assumption. A thermal dispersion model is applied to the problem and variation of thermal conductivity with temperature and variation of thermal dispersion with local axial velocity are taken into account. The agreement of the numerical results with experimental data might be considered as an indication of the validity of the approach.

scholarly journals Experimental Determination of the Friction Factor in a Tube with Internal Helical Ribs

Energies ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 257 ◽  
Author(s):  
Sławomir Grądziel ◽  
Karol Majewski
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Power Plant ◽  
Experimental Determination ◽  
Friction Factor ◽  
Contact Surface ◽  
Experimental Testing ◽  
New Correlation ◽  
Power Boiler

Due to the extended geometry of internally rifled tubes with helical ribs, the rate of convective heat transfer within them is much higher compared to smooth tubes. Simultaneously, a rise in the contact surface area between the fluid and the solid body increases the friction factor. This paper presents the results of experimental testing performed to determine the friction factor in an internally rifled tube with helical ribs. The tests were carried out on a purpose-built test stand. The tested object was a rifled tube used in the evaporator of a once-through supercritical power boiler operating in a power plant in Poland. The friction factor results obtained from testing are compared to the results of calculations performed by means of correlations known from the literature. Finally, using experimental data, a new correlation is developed that enables the determination of the friction factor in internally rifled tubes with helical ribs.

Heat Transfer Across Opaque Fibers

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Krishpersad Manohar ◽  
Gurmohan S. Kochhar ◽  
David W. Yarbrough
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Fiber Diameter ◽  
Radiation Heat Transfer ◽  
Physical Parameters ◽  
Density Range ◽  
Radiation Heat ◽  
Apparent Thermal Conductivity ◽  
Air Conduction

Predicting the thermal conductivity of loose-fill fibrous thermal insulation is a complex problem, when considering the combined conduction, convection, and radiation heat transfer within a scattering, emitting, and absorbing medium. A piecewise model for predicting the overall apparent thermal conductivity of large diameter opaque fibrous materials was developed by considering the radiation heat transfer, solid conduction and air conduction components separately. The model utilized the physical parameters of emissivity, the density of the solid fiber material, the percentage composition and range of fiber diameter, and the mean fiber diameter to develop specific equations for piecewise contribution from radiation, solid fiber conduction, and air conduction toward the overall effective thermal conductivity. It can be used to predict the overall apparent thermal conductivity for any opaque fibrous specimen of density (ρ), known thickness (t), mean temperature (T), and temperature gradient (ΔΤ). Thermal conductivity measurements were conducted in accordance with ASTM C518 specifications on 52 mm thick, 254 mm square test specimens for coconut and sugarcane fibers. The test apparatus provided results with an accuracy of 1%, repeatability of 0.2%, and reproducibility of 0.5%. The model was applied to and compared with experimental data for coconut and sugarcane fiber specimens and predicted the apparent thermal conductivity within 7% of experimental data over the density range tested. The model also predicted the optimum density range for both coconut and sugarcane fibers.

Free Convection of Nanofluid in Vertical Annuli

2008 ◽  
Author(s):  
Ahmad Falahatpisheh ◽  
Omid Abouali
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Free Convection ◽  
Numerical Study ◽  
Navier Stokes ◽  
Physical Parameters ◽  
Clear Fluid ◽  
Thermal Conductivity Model ◽  
Vertical Annulus ◽  
Vertical Annuli

This paper presents the numerical study of internal free convection in a vertical annulus. To predict the characteristics of nanofluids in heat transfer regime, thermal conductivity, density, and viscosity of clear fluid need to be modified. Numerous models have been disclosed to calculate these properties but recent models for viscosity and thermal conductivity which are in excellent agreement with experiments have been used. These models are thermal conductivity model of Jang and Choi and viscosity correlation of Nguyen et al. for 36nm Al2O3 particles. Inner and outer vertical walls are in constant temperature while horizontal walls are adiabatic. The continuity, Navier-Stokes and energy equation were solved numerically. Effect of nanofluids on buoyancy-driven heat transfer is investigated as a function of geometrical and physical parameters and various particle concentrations for aspect ratio of 0.2<H/L<5, Grashof number of 103<Gr<105 and concentration of 0<φ<0.12. Finally, one correlation is developed to demonstrate the effect of using atom-size particles on Nusselt number.

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