Begell House Inc.
Heat Transfer Research
HTR
1064-2285
50
15
2019
A COMPUTATIONAL STUDY FOCUSED ON REVEALING THE RELATION BETWEEN CONVECTIVE AND RADIATIVE HEAT TRANSFER FROM A RADIANT HEATED WALL
1437-1455
10.1615/HeatTransRes.2019018679
Ozgen
Acikgoz
Heat and Thermodynamics Division, Department of Mechanical Engineering, Yildiz Technical University, Yildiz,
Istanbul 34349, Turkey
asymmetric thermal radiation
radiant heating
heat transfer
radiation
heat flux
Asymmetric thermal radiation is a major reason deteriorating thermal comfort in living environments being caused by wide windows, cold surfaces arising from uninsulated walls or ceilings, and the walls exposed to solar radiation. This leads different parts of a human body to face surfaces having different temperatures, and thus discrete simultaneous radiation gains or losses, which brings discomfort. In the present investigation, to simulate this thermal discomfort condition, realistic thermal boundary conditions, emissivity values, and floor dimensions are selected and applied to an enclosure. The characteristics pertaining to a heated wall, such as the proportion of radiative to convective heat transfer coefficient alongside radiative and total heat flux are examined. To achieve this purpose, a computational fluid dynamics approach for convective data, and a theoretical calculation method for the solution of radiation heat transfer within the chamber are utilized. It is revealed that as the distance between the heated wall and the opposite wall (forming a heat sink that generates an asymmetric thermal radiation) increases from 3 m to 4 m, and to 6 m, the radiative heat transfer coefficient decreases and thus the range of the ratio hr/hc also narrows from 1.10-1.70 to 1.10-1.55 due to the dwindling effects of radiation. Furthermore, three novel correlations comprising the effect of asymmetric radiation in the chamber have been derived for the ratio hr/hc radiative heat flux qr, and the total heat flux qt the deviation ranges of which remain within ± 15%, ± 10%, and ± 15%, respectively.
BOILING HEAT TRANSFER PERFORMANCE OF A BRASS BEADS-PACKED POROUS LAYER SUBJECTED TO SUBMERGED JET IMPINGEMENT
1457-1476
10.1615/HeatTransRes.2019027922
Yunsong
Zhang
Merchant Marine College, Shanghai Maritime University, Shanghai, 201306, P.R. China
Wei
Chen
Merchant Marine College, Shanghai Maritime University, Shanghai 201306, China
submerged jet impingement
nucleate boiling
beads-packed porous layer
heat transfer coefficient
critical heat flux
vapor bubbles dynamics
Submerged impingement boiling has been extensively applied in industrial cooling owing to its high heat transfer coefficient (HTC). A particles-packed porous layer with enlarged heat transfer area and special internal porous structure can improve the fluid disturbance and produce adequate bubble nucleation sites. An experimental investigation on submerged jet impinging boiling of a brass beads-packed porous layer was conducted. The effects of jet flow rate, fluid inlet subcooling, beads diameter, layer number as well as various double layer combination models on heat transfer performance were analyzed. The impact on the onset of nucleate boiling (ONB) and critical heat flux (CHF) was also explored. The results show that better cooling property can be obtained for a higher jet flow rate, a higher fluid inlet subcooling, and a smaller single layer bead diameter, while the optimal layer number and double layer combination model exist for best heat transfer. Besides, a high-speed camera was utilized to capture the actual scene of submerged jet impingement boiling for visualization study of the dynamics evolution of vapor bubbles which would be highly linked to the heat transfer process.
EXPERIMENTAL AND NUMERICAL INVESTIGATION OF HEAT TRANSFER ENHANCEMENT IN A PLATE HEAT EXCHANGER USING A FLY ASH NANOFLUID
1477-1494
10.1615/HeatTransRes.2019029136
Halil Ibrahim
Variyenli
Gazi University, Technology Faculty, Energy Systems Engineering, Teknikokullar, 06500 Ankara,
Turkey
plate heat exchanger
nanofluid
fly ash
experimental
numerical
overall heat transfer coefficient
High-efficiency plate heat exchangers are widely used in many industries. Nanofluids can be used as working fluids in heat exchangers to improve the heat transfer rate. In this study, the effects of using a fly ash nanofluid in a plate heat exchanger were analyzed experimentally and numerically. ANSYS FLUENT software was used to simulate heat transfer characteristics in a plate heat exchanger. Fly ash nanoparticles with average sizes of 14 nm were used for making the nanofluid. The prepared nanofluid had nanoparticles of content 2% (wt./wt.). The experiments were carried out in various working conditions with changes in fluid mass flow rate and temperature. The obtained experimental results showed that using the fly ash nanofluid enhanced the overall heat transfer coefficient between 6-20%. Moreover, theoretical and experimental results are in good agreement with each other.
CHEMICALLY REACTIVE HYDROMAGNETIC FLOW OVER A STRETCHABLE OSCILLATORY ROTATING DISK WITH THERMAL RADIATION AND HEAT SOURCE/SINK: A NUMERICAL STUDY
1495-1512
10.1615/HeatTransRes.2019025546
Amar
Rauf
Department of Mathematics, The Islamia University of Bahawalpur, Bahawalpur, 63100, Pakistan; Department of Mathematics, COMSATS University Islamabad, Sahiwal 57000, Pakistan
Zaheer
Abbas
Department of Mathematics, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan
Sabir A.
Shehzad
Department of Mathematics, COMSATS University Islamabad, Sahiwal 57000, Pakistan
viscous fluid
oscillatory flow
MHD
rotating disk
chemical reaction
A numerical exploration of unsteady oscillatory three-dimensional magnetohydrodynamic (MHD) flow of a viscous liquid over rotating oscillatory disk is presented. The disk stretches in the radial direction with time-based sinusoidal oscillations. Adaptation of thermal radiation with the heat source/sink is made in the energy equation while the mass equation incorporates the impacts of a chemical reaction parameter. The normalized system of partial differential equations is obtained by implementing similarity transformations. Such system of equations is solved then by the finite difference scheme and successive overrelaxation (SOR) method. The analysis is presented to study the effects of dimensionless parameters appearing in the governing equations. The results are presented in the forms of graphs and tables. It is scrutinized that the increase in the magnetic parameter falls off the flow amplitude. The fluid temperature increased with the passage of time for enhancement in radiation parameter. The increase in the Sherwood number is observed for enhanced unsteady parameter and Schmidt number.
SIMULATION OF NATURAL CONVECTION OF AN Al2O3/WATER NANOFLUID IN A COMPLEX WAVY-WALL CAVITY USING THE LATTICE BOLTZMANN METHOD
1513-1530
10.1615/HeatTransRes.2018018737
Alireza
Shahriari
Department of Mechanical Engineering, University of Zabol, Zabol, Iran; Department of Mechanical Engineering, Birjand University, Birjand, Iran
Ebrahim Jahanshahi
Javaran
Department of Energy, Institute of Science and High Technology and Environmental Sciences,
Graduate University of Advanced Technology, Kerman, Iran
Mohammad
Rahnama
Department of Mechanical Engineering, Shahid Bahonar University of Kerman, Kerman, Iran
nanofluid
lattice Boltzmann method
natural convection
Nusselt number
cavity
In this paper, two-dimensional natural convection of an Al2O3/water nanofluid is presented using the lattice Boltz-mann method. Natural convection occurs in a cavity with two complex-wavy vertical walls, as hot and cold surfaces while the top and bottom ones are insulated. The effect of pertinent parameters such as the volume fraction of nanoparticles, Rayleigh numbers, and complex-wavy-wall geometry parameters on flow and heat transfer fields are investigated in detail. Results show an increase in the Nusselt number with volume fraction for Rayleigh numbers in the range 103 < Re < 106. Moreover, the effect of wavy-surface geometry parameters such as the wavelength and amplitude ratio, on heat transfer is studied, and an optimum value for heat transfer rate is obtained.
ISOFLUX NUSSELT NUMBER EXPRESSION FOR COMBINED POISEUILLE AND COUETTE FLOW CAPTURING ASYMMETRY AND SLIP
1531-1538
10.1615/HeatTransRes.2018024625
Daniel
Kane
Tufts University, 200 College Ave., Medford, MA 02138
Marc
Hodes
Tufts University, 200 College Ave., Medford, MA 02138
Nusselt number
microchannel cooling
superhydrophobic
We analytically consider steady, fully-developed, laminar thermal transport between isoflux, parallel plates. Hydrodynamic slip length, thermal slip length, and heat flux are prescribed at each plate. A combined Poiseuille and Couette flow is driven by an imposed pressure gradient and a moving plate. A Nusselt number expression is presented as a
function of dimensionless forms of the aforementioned flow and thermal parameters. The limiting cases of Poiseuille
flow with and without slip and Couette flow without slip agree with existing expressions. The expressions for combined Poiseuille and Couette flow with and without slip and Couette flow with slip are new.