scholarly journals Thermal study of fluid flow inside an annular pipe filled with porous media under local thermal non-equilibrium condition

2019 ◽  
Vol 13 (2) ◽  
pp. 4880-4897
Author(s):  
Abdelkrim Bouaffane ◽  
Kamel Talbi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Biot Number ◽  
Convection Heat Transfer ◽  
Radius Ratio ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Convection Heat ◽  
Local Difference ◽  
Annular Pipe

The present work involves the thermal numerical simulation of fluid flow inside an annular pipe completely filled porous material. The mathematical model of the energy transport is based on the Local Thermal Non-Equilibrium (LTNE) between the fluid and the solid phases. The governing equations are discretized by the finite volume method. SIMPLE algorithm has been used to solve the set of algebraic discretized coupled equations. This work is divided in two parts. In the first part, the effect of the pertinent dimensionless parameters which govern the study such as Biot number (Bi), solid-fluid thermal conductivity ratio (Rc) and radius ratio (Rr) on the LTNE intensity are analyzed by calculating: the local difference of temperature (LDT), the maximum of the local difference of temperature (LDTmax) and the average of LDT. The results show that the increase of Biot number and the solid-fluid thermal conductivity ratio, and the decrease of radius ratio reduce the LTNE intensity. The intensity of the LTNE in the developing region is greater than that of the fully developed region. In the second part, the convection heat transfer enhancement is studied, the results illustrate that the increase of Biot number and the solid-fluid thermal conductivity ratio, and the decrease of radius ratio represent good factors to ameliorate the rate of the convection heat transfer between the fluid and the inner wall.

Conjugate Nusselt Numbers for Simultaneously Developing Flow Through Rectangular Ducts

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Georgios Karamanis ◽  
Marc Hodes
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Extended Surface ◽  
Side Walls ◽  
Extended Surfaces ◽  
Prandtl Numbers

We consider conjugate forced-convection heat transfer in a rectangular duct. Heat is exchanged through the isothermal base of the duct, i.e., the area comprised of the wetted portion of its base and the roots of its two side walls, which are extended surfaces within which conduction is three-dimensional. The opposite side of the duct is covered by an adiabatic shroud, and the external faces of the side walls are adiabatic. The flow is steady, laminar, and simultaneously developing, and the fluid and extended surfaces have constant thermophysical properties. Prescribed are the width of the wetted portion of the base, the length of the duct, and the thickness of the extended surfaces, all three of them nondimensionalized by the hydraulic diameter of the duct, and, additionally, the Reynolds number of the flow, the Prandtl number of the fluid, and the fluid-to-extended surface thermal conductivity ratio. Our conjugate Nusselt number results provide the local one along the extended surfaces, the local transversely averaged one over the isothermal base of the duct, the average of the latter in the streamwise direction as a function of distance from the inlet of the domain, and the average one over the whole area of the isothermal base. The results show that for prescribed thermal conductivity ratio and Reynolds and Prandtl numbers, there exists an optimal combination of the dimensionless width of the wetted portion of the base, duct length, and extended surface thickness that maximize the heat transfer per unit area from the isothermal base.

scholarly journals Effect of an inserted porous layer on heat and fluid flow in a vertical channel with mixed convection

2015 ◽  
Vol 19 (3) ◽  
pp. 1005-1016 ◽  
Author(s):  
Hasan Celik ◽  
Moghtada Mobedi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Pressure Drop ◽  
Mixed Convection ◽  
Porous Layer ◽  
Convection Heat Transfer ◽  
Vertical Channel ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Transfer Condition

Temperature and velocity fields in a vertical channel partially filled with porous medium under mixed convection heat transfer condition are obtained. The heat transfer equation and equation of motion for clear and porous layer regions are written and solved analytically. The nondimensionalization of the governing equations yields two Grashof numbers as Grc and Grd for clear and porous sections where Grd=Da.Grc. The dimensionless governing parameters for the problem are Grc (or Grd), Da, thermal conductivity ratio (i.e., K) and thickness of porous layer. The temperature and velocity profiles for different values of Grc, Da, K and thickness of porous layer are plotted and their changes with the governing parameters are discussed. Moreover, the variation of pressure drop with the governing parameters is investigated. The decrease of porous layer thickness or thermal conductivity ratio increases the possibility of the downward flows. Thermal conductivity ratio plays important role on pressure drop, particularly for the channels with high values of Grc/Re.

Conjugate Natural Convection in Porous Medium With a Thick Square-Wave Partition

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Jayesh Subhash Chordiya ◽  
Ram Vinoy Sharma
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Convection Heat Transfer ◽  
Thermal Conductivity Ratio ◽  
Convection Heat ◽  
Square Wave ◽  
Porous Enclosure

Abstract Natural convection within a differentially heated porous enclosure is substantially affected by the presence of partition, fins, or baffles within it. However, not much is known about the effect of partition shape and size. Thus, a solid thick partition in a square-wave shape embedded within a differentially heated porous enclosure has been investigated in this numerical analysis. Through this study, it is sought to contemplate the reduction in the convection heat transfer rate that could be achieved across a differentially heated porous enclosure. The influence of partition thickness, partition amplitude, thermal conductivity ratio, and partition position has been studied. Darcy’s flow model has been solved using the successive accelerated replacement scheme by the finite difference method. One of the findings of this study suggests that lower thermal conductivity of partition, lower partition amplitude, and higher thickness results in a greater reduction in the convection heat transfer rate.

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.

Experimental and Numerical Investigation on Natural Convection Heat Transfer of TiO2–Water Nanofluids in a Square Enclosure

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Yanwei Hu ◽  
Yurong He ◽  
Shufu Wang ◽  
Qizhi Wang ◽  
H. Inaki Schlaberg
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Numerical Investigation ◽  
Convection Heat Transfer ◽  
Distribution Functions ◽  
Lattice Boltzmann Model ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Square Enclosure

An experimental and numerical investigation on natural convection heat transfer of TiO2–water nanofluids in a square enclosure was carried out for the present work. TiO2–water nanofluids with different nanoparticle mass fractions were prepared for the experiment and physical properties of the nanofluids including thermal conductivity and viscosity were measured. Results show that both thermal conductivity and viscosity increase when increasing the mass fraction of TiO2 nanoparticles. In addition, the thermal conductivity of nanofluids increases, while the viscosity of nanofluids decreases with increasing the temperature. Nusselt numbers under different Rayleigh numbers were obtained from experimental data. Experimental results show that natural convection heat transfer of nanofluids is no better than water and even worse when the Rayleigh number is low. Numerical studies are carried out by a Lattice Boltzmann model (LBM) coupling the density and the temperature distribution functions to simulate the convection heat transfer in the enclosure. The experimental and numerical results are compared with each other finding a good match in this investigation, and the results indicate that natural convection heat transfer of TiO2–water nanofluids is more sensitive to viscosity than to thermal conductivity.

Effects of a centered conducting body on natural convection of non-Newtonian fluid in a square enclosure with time-periodic temperature distribution

2020 ◽  
Author(s):  
Peixin Ye ◽  
Dinggen Li ◽  
Zihao Yu ◽  
Haifeng Zhang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Transient Heat Transfer ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Transfer Ratio ◽  
Periodic Temperature ◽  
Power Law Index ◽  
Time Periodic

In this paper, a modified lattice Boltzmann model that incorporates the effect of heat capacity is adopted to study the effects of a centered conducting body on natural convection of non-Newtonian fluid in a square cavity with time-periodic temperature distribution. The effects of power-law index, Rayleigh number, heat capacity ratio, thermal conductivity ratio, body size, temperature pulsating period and the temperature pulsating amplitude on fluid flow and heat transfer are analyzed in detail. The results showed that the increase of Rayleigh number and thermal conductivity ratio as well as the decrease of power-law index can strengthen both transient and global heat transfer, while the increase of heat capacitance of fluid to the solid wall can only enhance the transient heat transfer, and has little effect on the overall heat transfer. Further, the increase of body size will reduce both the transient heat transfer ratio and the overall heat transfer ratio. In addition, the decrease of temperature pulsating period can enhance the transient heat transfer, but it will slightly weaken the overall heat transfer. Finally, the results show that both the transient and the overall heat transfer ratio are increased with the increase of temperature pulsating amplitude.

Change of Thermal Conductivity and Cooling Performance for Water Based Al2O3-Surfactant Nanofluid with Time Lapse

2018 ◽  
Vol 26 (01) ◽  
pp. 1850009 ◽  
Author(s):  
Man Bae Kim ◽  
Hong Gen Park ◽  
Chang Yong Park
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Cooling System ◽  
Pure Water ◽  
Sodium Dodecyl ◽  
Convection Heat Transfer ◽  
Sodium Dodecyl Benzene Sulfonate ◽  
Time Lapse ◽  
Convection Heat ◽  
Conductivity Enhancement

An experimental research was performed to study the effect of time lapse on the change of water-Al2O3 nanofluid thermal conductivity and its convection heat transfer. The size of Al2O3 nanoparticle size was 20[Formula: see text]nm and 70[Formula: see text]nm, and initial volumetric concentration range was from 0.5% to 3%. A surfactant was added to the nanofluid and the change of thermal conductivity and convection heat transfer was also measured. The surfactant was Sodium Dodecyl Benzene Sulfonate (SDBS) and its mass fractions in the nanofluid were from 0.5% to 3.0%. Thermal conductivity of water and nanofluid was measured by the transient hot wire method. The accuracy of the measurement method was confirmed by the measurement error with 0.92% for distilled water at 20[Formula: see text]C. The thermal conductivity of the nanofluid without SDBS increased up to 11.3% and the enhancement decreased with time lapse. The reduction of thermal conductivity enhancement with the time lapse could be retarded by the addition of SDBS and its effect became higher with the increase of its mass fraction. The convection heat transfer characteristics of the nanofluid was measured in a small cooling system. Compared with pure water, nanofluid convection heat transfer could be enhanced but higher pressure drop also occurred. Compared with the convection heat transfer enhancement for the nanofluid without SDBS, the addition of SDBS decreased the enhancement at the initial stage of the experiment, but it could retard the reduction of convection heat transfer with time lapse.

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.

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.

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