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.

scholarly journals Dual solution of boundary-layer flow driven by variable plate and streaming-free velocity

2020 ◽  
Vol 12 (7) ◽  
pp. 168781402093084
Author(s):  
M Ferdows ◽  
Faris Alzahrani ◽  
Shuyu Sun
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Boundary Layer ◽  
Differential Equations ◽  
Skin Friction ◽  
Numerical Study ◽  
Velocity Ratio ◽  
Dual Solutions ◽  
Physical Parameters ◽  
Branch Solution

This article presents a numerical study to investigate boundary-layer heat transfer fluid associated with a moving flat body in cooperation of variable plate and streaming-free velocity along the boundary surface in the laminar flow. The thermal conductivity is supposed to vary linearly with temperature. Similarity transformations are applied to render the governing partial differential equations for mass, momentum and energy into a system of ordinary differential equations to reveal the possible existence of dual solutions. MATLAB package has been used to solve the boundary value problem numerically. We present the effects of various parameters such as velocity ratio, thermal conductivity and variable viscosity on velocity and temperature distribution. The analysis of the results concerning Skin friction and Nusselt number near the wall is also presented. It is focused on the detection and description of the dual solutions. The study reveals that the undertaken problem admits dual solutions in particular range of values of different physical parameters. It can be seen that for the first branch solution, the fluid velocity decreases near the sheet, but it increases far away from the sheet for velocity ratio parameter, whereas the opposite effect is induced for second branch solution. Skin friction coefficient and rate of heat transfer increase due to increase in thermal conductivity parameter.

scholarly journals Effect of Al2O3/water nanofluid on Conjugate Free Convection in a Baffle Attached Square Enclosure

Mechanika ◽  
2020 ◽  
Vol 26 (2) ◽  
pp. 126-133
Author(s):  
Thansekhar M.Rathinam
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Rayleigh Number ◽  
Free Convection ◽  
Conjugate Heat Transfer ◽  
Volume Fraction ◽  
Numerical Study ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Square Enclosure

A numerical study of conjugate free convection heat transfer of Al2O3/water nanofluid inside a differentially heated square enclosure with a baffle attached to its hot wall has been carried out. A detailed parametric study has been carried out to analyze the effect of Rayleigh number (104 < Ra < 106), length, thickness and position of baffle, conductivity ratio and volume fraction of the nanoparticle (0<<0.2) on heat transfer. The thermal conductivity ratio of the baffle plays a major role on the conjugate heat transfer inside the enclosure. Higher the baffle length better is the effectiveness of the baffle. The average Nusselt number is found to be an increasing function of both thermal conductivity ratio and volume fraction of the nanofluid. The minimum enhancement of conjugate heat transfer is 30% when Al2O3/water nanofluid of 0.1 volume fraction is used for the entire range of Rayleigh number considered.

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.

scholarly journals A Computational Study on the Role of Parameters for Identification of Thyroid Nodules by Infrared Images (and Comparison with Real Data)

Sensors ◽  
2021 ◽  
Vol 21 (13) ◽  
pp. 4459
Author(s):  
José R. González ◽  
Charbel Damião ◽  
Maira Moran ◽  
Cristina A. Pantaleão ◽  
Rubens A. Cruz ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thyroid Nodules ◽  
Numerical Study ◽  
Computational Study ◽  
Internal Heat ◽  
Heat Transfer Process ◽  
The Body ◽  
Physical Parameters ◽  
Infrared Sensors ◽  
Wide Range

According to experts and medical literature, healthy thyroids and thyroids containing benign nodules tend to be less inflamed and less active than those with malignant nodules. It seems to be a consensus that malignant nodules have more blood veins and more blood circulation. This may be related to the maintenance of the nodule’s heat at a higher level compared with neighboring tissues. If the internal heat modifies the skin radiation, then it could be detected by infrared sensors. The goal of this work is the investigation of the factors that allow this detection, and the possible relation with any pattern referent to nodule malignancy. We aim to consider a wide range of factors, so a great number of numerical simulations of the heat transfer in the region under analysis, based on the Finite Element method, are performed to study the influence of each nodule and patient characteristics on the infrared sensor acquisition. To do so, the protocol for infrared thyroid examination used in our university’s hospital is simulated in the numerical study. This protocol presents two phases. In the first one, the body under observation is in steady state. In the second one, it is submitted to thermal stress (transient state). Both are simulated in order to verify if it is possible (by infrared sensors) to identify different behavior referent to malignant nodules. Moreover, when the simulation indicates possible important aspects, patients with and without similar characteristics are examined to confirm such influences. The results show that the tissues between skin and thyroid, as well as the nodule size, have an influence on superficial temperatures. Other thermal parameters of thyroid nodules show little influence on surface infrared emissions, for instance, those related to the vascularization of the nodule. All details of the physical parameters used in the simulations, characteristics of the real nodules and thermal examinations are publicly available, allowing these simulations to be compared with other types of heat transfer solutions and infrared examination protocols. Among the main contributions of this work, we highlight the simulation of the possible range of parameters, and definition of the simulation approach for mapping the used infrared protocol, promoting the investigation of a possible relation between the heat transfer process and the data obtained by infrared acquisitions.

Pin-Fin Heat Sink With Horizontal Base and Blocked Edges

2008 ◽  
Author(s):  
D. Sahray ◽  
H. Shmueli ◽  
N. Segal ◽  
G. Ziskind ◽  
R. Letan
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Contact Resistance ◽  
Cross Section ◽  
Heat Input ◽  
Heat Sink ◽  
Numerical Study ◽  
Heat Sinks ◽  
Transfer Enhancement ◽  
Pin Fin

In the present work, horizontal-base pin fin heat sinks exposed to free convection in air are studied. They are made of aluminum, and there is no contact resistance between the base and the fins. For the same base dimensions the fin height and pitch vary. The fins have a constant square cross-section. The edges of the sink are blocked: the surrounding insulation is flush with the fin tips. The effect of fin height and pitch on the performance of the sink is studied experimentally and numerically. In the experiments, the heat sinks are heated using foil electrical heaters. The heat input is set, and temperatures of the base and fins are measured. In the corresponding numerical study, the sinks and their environment are modeled using the Fluent 6 software. The results show that heat transfer enhancement due to the fins is not monotonic. The differences between sparsely and densely populated sinks are analyzed for various fin heights. Also assessed are effects of the blocked edges as compared to the previously studied cases where the sink edges were exposed to the surroundings.

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.

Free convection heat transfer in vertical annuli

1970 ◽  
Vol 25 (4) ◽  
pp. 605-610 ◽  
Author(s):  
H.R. Nagendra ◽  
M.A. Tirunarayanan ◽  
A. Ramachandran
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Free Convection Heat ◽  
Vertical Annuli

Flow Characteristics in a Three-Dimensional Rectangular Channel With a Pair of Ribs Placed Symmetrically at the Channel Walls

2000 ◽  
Author(s):  
M. Singh ◽  
P. K. Panigrahi ◽  
G. Biswas
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Energy Equations

Abstract A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.

Effective Thermal Conductivity of Submicron Powders: A Numerical Study

2016 ◽  
Vol 846 ◽  
pp. 500-505
Author(s):  
Wei Jing Dai ◽  
Yi Xiang Gan ◽  
Dorian Hanaor
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Effective Thermal Conductivity ◽  
Granular Materials ◽  
Gas Phase ◽  
Numerical Study ◽  
Transfer Model ◽  
Size Of Particles ◽  
Contact Unit

Effective thermal conductivity is an important property of granular materials in engineering applications and industrial processes, including the blending and mixing of powders, sintering of ceramics and refractory metals, and electrochemical interactions in fuel cells and Li-ion batteries. The thermo-mechanical properties of granular materials with macroscopic particle sizes (above 1 mm) have been investigated experimentally and theoretically, but knowledge remains limited for materials consisting of micro/nanosized grains. In this work we study the effective thermal conductivity of micro/nanopowders under varying conditions of mechanical stress and gas pressure via the discrete thermal resistance method. In this proposed method, a unit cell of contact structure is regarded as one thermal resistor. Thermal transport between two contacting particles and through the gas phase (including conduction in the gas phase and heat transfer of solid-gas interfaces) are the main mechanisms. Due to the small size of particles, the gas phase is limited to a small volume and a simplified gas heat transfer model is applied considering the Knudsen number. During loading, changes in the gas volume and the contact area between particles are simulated by the finite element method. The thermal resistance of one contact unit is calculated through the combination of the heat transfer mechanisms. A simplified relationship between effective thermal conductivity and loading pressure can be obtained by integrating the contact units of the compacted powders.

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