Begell House Inc.
Heat Transfer Research
HTR
1064-2285
49
18
2018
EXPERIMENTAL STUDY OF OSCILLATORY FLOW CHARACTERISTICS OF GAS–LIQUID TWO-PHASE FLOW
1761-1771
Hairong
Zhu
School of Mechanical Engineering, Hebei University of Science and Technology, 050018,
Shĳiazhuang, China
Junfa
Duan
School of Mechanical Engineering, North China University of Water Resources and Electric Power,
450045, Zhengzhou, China
Qinggang
Liu
School of Mechanical Engineering, Hebei University of Science and Technology, 050018,
Shĳiazhuang, China
The oscillatory flow characteristics of the gas-liquid two-phase flow are thoroughly studied through visualization experiments. The results show that the oscillatory motion of the gas-liquid two-phase flow obeys specific rules not only in the primary oscillation stage but also in the full oscillation stage. The bubble state and turbulence intensity of the oscillatory two-phase flow are mainly affected by oscillation frequency; otherwise, the flow pattern and movement rule of the oscillatory two-phase flow are mainly affected by the water filling ratio. Both oscillation frequency and water filling ratio have significant effects on the duration and the maximum bubble size in the primary oscillation stage. The effects of oscillation frequency on bubble size and mixing ratio in the full oscillation stage are higher than those of the water filling ratio. The mixing degree of two phases is supreme in the case of low water filling ratio and high oscillation frequency.
ANALYSIS OF MHD FLUID FLOW AND HEAT TRANSFER THROUGH ANNULAR SECTOR DUCTS FILLED WITH DARCY-BRINKMAN POROUS MEDIA
1773-1792
Mazhar
Iqbal
School of Natural Sciences, National University of Sciences and Technology, Islamabad, Pakistan
Farhan
Ahmed
National University of Sciences and Technology, Islamabad, Pakistan
In this study, we consider the fluid flow and heat transfer analysis of electrically conducting MHD Newtonian fluid through an annular sector duct, which is filled with a Darcy-Brinkman porous medium, under the action of an axially applied constant pressure gradient and uniform transverse magnetic field. The finite volume method (FVM) is used to dis-cretize the governing momentum and energy equations. The behavior of velocity and temperature contours, and similarly velocity and temperature profiles against pertinent parameters like the Hartman number Ha and dimensionless permeability factor K are displayed graphically for different channel configurations and explained in a physical manner. Physical quantities of interest such as bulk mean velocity ωm and friction factor fRe are used to explain the fluid flow behavior, whereas the bulk mean temperature τb and average Nusselt number Nu are used to explain the heat transfer analysis. Their values are also computed numerically and compared with the literature in the limiting case.
EXPERIMENTAL INVESTIGATION OF THE THERMAL PERFORMANCE OF MESH WICK HEAT PIPE
1793-1811
Naveen
Gupta
GLA University, Mathura
Arun Kumar
Tiwari
Department of Mechanical Engineering, Institute of Engineering and Technology Lucknow, India
Subrata Kumar
Ghosh
Department of Mechanical Engineering, Indian Institute of Technology (ISM), Dhanbad-826004,
India
In this article, the results obtained from a detailed experimental investigation of the thermal performance of mesh wick heat pipe are presented. The effects of heat input, inclination angle, and the volume of the working fluid on the thermal performance of the heat pipe were investigated. Experimental investigations were carried out over a wide range of heat input (50-150 W), different inclination angles (0°, 15°, 30°, 45°, and 60°), and volumes of the working fluid (20 mL, 25 mL, 30 mL, and 35 mL). The results show that the thermal performance of the heat pipe increases with increase in the heat input until the dryout condition is achieved. The heat pipe achieved the maximum thermal efficiency of 69% at 150 W heat input, 30° inclination angle, and charged with 35 mL of working fluid. The authors highlight the different causes responsible for the enhancement in the thermal performance of the heat pipe.
THERMAL ANALYSIS OF EARTH–AIR HEAT EXCHANGERS UNDER HEATING CONDITIONS AT A CONSTANT SURFACE TEMPERATURE
1813-1823
Refet
Karadag
Harran University, Engineering Faculty, Mechanical Engineering Department, Osmanbey Campuses,
63190, Sanliurfa, Turkey
Husamettin
Bulut
Harran University, Engineering Faculty, Mechanical Engineering Department, Osmanbey Campuses,
63190, Sanliurfa, Turkey
Yunus
Demirtas
Harran University, Engineering Faculty, Mechanical Engineering Department, Osmanbey Campuses,
63190, Sanliurfa, Turkey
Ismail
Hilali
Harran University, Engineering Faculty, Mechanical Engineering Department, Osmanbey Campuses,
63190, Sanliurfa, Turkey
Earth–air heat exchangers (EAHEs) are used for ventilation and air conditioning, taking advantage of the earth energy.
Many experimental, analytical, and numeritical researches of EAHEs have been made so far due to their promising applications. In this study, the thermal performance of an earth–air heat exchanger is investigated numerically and experimentally depending on heating conditions. The computational fluid dynamics simulation soft ware FLUENT is used in the analysis. Numerical solutions are obtained by using computational fluid dynamics (CFD) analysis under constant surface temperature boundary conditions. Computational analysis is conducted for different outside air temperatures, pipe surface temperatures, air velocities (ranging from 0.5 m/s to 5.5 m/s), and different pipe lengths of the EAHE. The numerical results obtained
at different outlet and inlet air temperatures and heat loads are compared with those measured experimentally under
Sanliurfa climatic conditions during winter season. The relation between the Nusselt and Reynolds numbers for the inner surfaces of the EAHE is analyzed by using numerical values, and the results are compared with the equations given in the literature. The maximum and mean deviations between the experimental and numerical results were equal to 30% and 15%, respectively. The results are acceptable, and there is agreement with the literature data, because the average deviation between the results of numerical solutions and equations given in the literature varies from 1.8% to 35% depending on the
length of the heat exchanger and flow Reynolds numbers.
FLUCTUATING LOCAL DISSIPATION SCALES OF TURBULENT RAYLEIGH–BÉNARD CONVECTION USING THE LATTICE BOLTZMANN METHOD
1825-1836
Yikun
Wei
Faculty of Mechanical Engineering and Automatic, Zhejiang Scientific Technical University, Key
Laboratory of Fluid Transmission Technology of Zhejiang, State-Province Joint Engineering
Laboratory of Fluid Transmission System Technology, 310018, Hangzhou, China
Yuxin
Lun
Faculty of Mechanical Engineering and Automatic, Zhejiang Scientific Technical University, Key
Laboratory of Fluid Transmission Technology of Zhejiang, State-Province Joint Engineering
Laboratory of Fluid Transmission System Technology, 310018, Hangzhou, China
Lei
Zhang
Faculty of Mechanical Engineering and Automatic, Zhejiang Scientific Technical University, Key
Laboratory of Fluid Transmission Technology of Zhejiang, State-Province Joint Engineering
Laboratory of Fluid Transmission System Technology, 310018, Hangzhou, China
Yuehong
Qian
School of Mathematical Science, Soochow University, 215006, Jiangsu, China
Fluctuating local dissipation scales for turbulent Rayleigh–Bénard (RB) convection are investigated using the lattice Boltzmann method (LBM) at different Rayleigh numbers (Ra). Special attention is paid to the fluctuating local dissipation scales for turbulent RB convection, the probability density function (PDF) of the local dissipation scale and PDF of the dissipation rates at different Ra. It is observed that a further increase of Ra tears off unstable spokes to form more independent large-scale flow structures generated in the thermal boundary layers and driven by buoyancy. It is validated that the fluctuations of the energy dissipation field can directly be translated into a fluctuating local dissipation scale, which is found to
develop ever finer fluctuations with increasing Ra. It is noted that the scales in the whole cell cover a wider range, both to the large-scale and small-scale end which is centered around the most probable value.
EXPLORATION OF CONVECTIVE HEAT TRANSFER AND FLOW CHARACTERISTICS SYNTHESIS BY Cu–Ag/WATER HYBRID-NANOFLUIDS
1837-1848
Mohsan
Hassan
Department of Mathematics, COMSATS University Islamabad, Lahore Campus, 54000,
Pakistan
Marin
Marin
Department of Mathematics and Computer Science, Transilvania University of Brasov, 500093
Brasov, Romania
Rahmat
Ellahi
Center for Modeling & Computer Simulation, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran-31261, Saudi Arabia; Department of Mathematics and Statistics, FBAS, IIUI, Islamabad, Pakistan
Sultan Z.
Alamri
Department of Mathematics Faculty of Science Taibah University, Madinah Al Munawwarah,
Saudi Arabia
The present study deals with convective heat transfer performance and fluid flow characteristics of Cu–Ag/water hybrid nanofluids. A geometric model of an inverted cone is used. The mathematical model consists of nonlinear governing equations along with associated boundary conditions reduced to a nondimensional form by using appropriate transformation, Boussinesq and boundary-layer approximations. Analytical solutions are obtained for velocity and temperature profiles. The convergence analysis and error of norm 2 are also presented to check the validity of the results. The effects of nanoparticles
volume fraction, hybrid nanoparticles compactness ratio on velocity, temperature, thermophysical properties, convective
heat transfer coefficient, and skin friction coefficient are illustrated in graphical and tabular form. A comparison of hybrid nanofluid with single material nanofluids is also made and it is realized that the hybrid nanofluid has greater thermal conductivity and improved convective heat transfer characteristics as compared to the base fluid and nanofluids. The proposed model can help in designing a way to accelerate and mix liquids in the chemical industry.
NUMERICAL MODELING AND SIMULATION OF NATURAL-CONVECTION BOUNDARY-LAYER FLOW ALONG A VERTICAL WAVY SURFACE IN A DOUBLY STRATIFIED NON-DARCIAN POROUS MEDIUM WITH SORET AND DUFOUR EFFECTS
1849-1865
S.V.S.S.N.V.G. Krishna
Murthy
Department of Applied Mathematics, Defence Institute of Advanced Technology, Deemed
University, Pune – 411025, India
B. V. Rathish
Kumar
Department of Mathematics and Statistics, Indian Institute of Technology Kanpur,
Kanpur-208016, India
Vinay
Kumar
Defence Institute of Advanced Technology (DU), Pune, India 411025
In this paper, we study the natural-convection heat and mass transfer induced by a vertical wavy surface immersed in a
fluid saturated with a doubly stratified non-Darcian porous medium. In particular, we determine the Soret and Dufour effects on the double diffusive convective process. A finite difference scheme based on the Keller box approach has been derived for the proposed mathematical model. The effect of the governing parameters like the wavy wall amplitude (a), buoyancy ratio (B), Lewis number (Le), Soret (Sr) and Dufour (Df) numbers, Grashof number (Gr*), thermal (ST) and mass (SC) stratification values on heat and fluid flow characteristics are analyzed. The obtained results are presented graphically for the local/average Nusselt and Sherwood number plots in all cases. Increasing surface roughness, inertial forces, and thermal/mass stratification levels are seen to reduce the local/average Nusselt and Sherwood number values.
THERMOHYDRAULIC PERFORMANCE OF A CHANNEL EMPLOYING WAVY POROUS SCREENS
1867-1883
L.
Cramer
Mechanical and Aeronautical Engineering Department, University of Pretoria, South Africa
Gazi I.
Mahmood
Mechanical and Aeronautical Engineering Department, University of Pretoria, South Africa
Josua Petrus
Meyer
Department of Mechanical and Aeronautical Engineering, University of Pretoria, Pretoria, Private Bag X20, Hatfield, 0028, South Africa
Porous inserts are commonly employed in the heat exchanger channels to enhance the thermal performance. The present
experimental investigations measure the pressure drop and heat transfer in a rectangular channel that employs a sinusoidally shaped porous screen mesh as inserts. Four screens with different forms of sinusoidal wave are employed: 68% porosity–12-mm period, 48% porosity–12-mm period, 68% porosity–18-mm period, and 48% porosity–18-mm period. The peak-to-peak height of the wave is 5 mm and touches the channel walls along the wave vectors that are parallel to the mean flow. Measurements in the smooth channel are used to normalize the friction factors and Nusselt numbers in the screen channel and provide the enhancements of friction factors f/f0 and Nusselt numbers Nu/Nu0 due to the screens. The Reynolds number Re based on the channel hydraulic diameter varies between 400 and 11,000. The results indicate that the friction factor f, average Nusselt number Nu, Nu/Nu0, and f/f0 in the screen channel depend strongly on Re. The screen porosity and wave period effects are significant on the f and f/f0 only. The thermal performance index, (Nu/Nu0)/(f/f0)(1/3), is also influenced strongly by Re. The present results thus indicate the viability of the wavy porous inserts for heat exchangers.
INDEX VOLUME 49, 2018
1884-1898