Begell House Inc.
Heat Transfer Research
HTR
1064-2285
48
17
2017
FRACTIONAL BOUNDARY-LAYER FLOW AND HEAT TRANSFER OF A NANOFLUID OVER AN UNSTEADY MOVING PLATE
1531-1544
Zhi
Cao
School of Mathematics and Physics, University of Science and Technology Beĳing, Beĳing 100083,
China
Jinhu
Zhao
School of Mathematics and Statistics, Fuyang Normal College, Fuyang 236037, Anhui, China
Liancun
Zheng
School of Mathematics and Physics, University of Science and Technology Beĳing, Beĳing 100083,
China
This paper studies the fractional unsteady boundary layer and heat transfer of a two-dimensional nanofluid flow over a moving plate. Time-dependent fractional derivatives are considered in the constitutive relation for the nanofluid. Different nanoparticles and volume fractions are used in the viscoelastic-fluid-based fluid. Finite difference method is employed to solve the fractional boundary governing equations. The influences of involved parameters, namely fractional parameter, relaxation time, unsteadiness parameter, and the volume fraction of nanoparticles, on the velocity and temperature characteristics are discussed in detail. The results show that the relaxation time can adequately describe the long-term memory of flow and heat transfer, as well as the time-dependent fractional parameters. These parameters have a tendency to slow down
the motion and the heat transfer of the nanofluid in the velocity and thermal boundary layer.
LARGE EDDY SIMULATION OF FLUID INJECTION UNDER TRANSCRITICAL CONDITIONS: EFFECTS OF PSEUDOBOILING
1545-1565
Wu
Wei
Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education,
Dalian University of Technology, Dalian City, P.R. China
Maozhao
Xie
Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education,
Dalian University of Technology, Dalian City, P.R. China
Ming
Jia
School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, China
Cryogenic nitrogen injected into a supercritical environment is numerically studied by large eddy simulation to explore
the influence of pseudoboiling on the jet evolution and mixing process. For comparison, the same model is simulated in ideal-gas conditions with the same initial profiles of density and velocity. The results show that the turbulent kinetic energy and vorticity distributions in both cases are nearly the same indicating that the dominant eddies and the production and dissipation of the turbulent kinetic energy are not directly affected by the pseudoboiling phenomenon. Moreover, the axial velocity distributions in the two cases are also similar, revealing that the pseudoboiling has little effect on turbulent transport mechanisms. However, the density distribution is evidently influenced by the pseudoboiling. Because of the existing of pseudoboiling effects, the most thermal energy absorbed from the surroundings is spent to expand the jet volume, rather
than to increase its temperature, so the transcritical fluid is entrained deeply along the axial and radial directions. As a result, before the pseudocritical temperature is reached, the mean profiles of axial and radial density distributions change more slowly in comparison with the ideal-gas condition. Consequently, the mass transport mechanism is considered to be influenced by the pseudoboiling under transcritical conditions.
HEAT AND FLUID FLOW THROUGH A SPACER-FILLED CHANNEL IN A MEMBRANE MODULE
1567-1580
Yazan
Taamneh
Department of Aeronautical Engineering, Jordan Univesity of Science and Technology, Irbid,
Jordan
Flow through commercially available membrane modules is commonly accompanied by different types and orientations of
spacer. Most commonly used spacers change the flow patterns and promote regions of secondary flow. In this study, experimental and computational fluid dynamics (CFD) simulations were performed to gain insight into the effect of a spacer on the commercial direct contact membrane module performance. Fluid flow and heat transfer through an empty and a spacer-filled channel were simulated using a three-dimensional model. Besides predicting the Nusselt number and total drag coefficient, the simulated results present understanding of the role of a spacer in the fluid flow structure. The Nusselt number and the total drag coefficient for the special case of an empty channel were found to be in good agreement with the previous experimental results. The simulated results showed that the spacer enhanced the wall shear stress and increased the Nusselt number by approximately two times over the empty channel.
A COMPUTATIONAL STUDY OF HEAT AND MASS TRANSFER FROM A CIRCULAR CYLINDER IN OSCILLATORY FLOW
1581-1598
Burhan
Cuhadaroglu
Karadeniz Tech. Univ.
Şahin
Yiğit
Department of Mechanical Engineering, Karadeniz Technical University, Trabzon, 61080, Turkey
In the present study, heat and mass transfer in oscillating flow around a wet circular cylinder has been analyzed numerically. The oscillating flow is modeled by defining the vertical velocity component as v(t) = A sin (wt) at the inlet, and, hence, the oncoming flow is controlled by the amplitude and frequency of oscillation. The influence of nondimensional oscillating frequency on heat and mass transfer has been analyzed regarding the Nusselt and Sherwood numbers. The low-Re number k–ε turbulence model equations in conjunction with unsteady Reynolds-averaged Navier–Stokes equations have been
used in the computations. All the numerical simulations have been carried out by the ANSYS-Fluent code using the finite
volume method with nonuniform grid arrangement. Certain values of the dimensionless frequency of the oscillating flow, which is a measure of frequency of the oncoming flow to the vortex shedding frequency, provide a higher heat and mass transfer compared to nonoscillating flow. The position of the separation point on the circular cylinders has a dominant effect on heat and mass transfer as well as unsteady flow structure downstream. In practical applications, such as drying in the food industry, using the oscillating flow technique requires lower energy compared to oscillating solid bodies.
HEAT TRANSFER OF IMPINGING SEAWATER SPRAY AND ICE ACCUMULATION ON MARINE VESSEL SURFACES
1599-1624
Alireza R.
Dehghani-Sanij
Department of Mechanical Engineering, Faculty of Engineering and Applied Science, Memorial
University of Newfoundland, St. John's, NL, A1B 3X5, Canada
G. F.
Naterer
Department of Mechanical Engineering, Faculty of Engineering and Applied Science, Memorial
University of Newfoundland, St. John's, NL, A1B 3X5, Canada
Yuri S.
Muzychka
Department of Mechanical Engineering, Faculty of Engineering and Applied Science, Memorial
University of Newfoundland, St. John's, NL, A1B 3X5, Canada
In this paper, a new predictive model for the ice layer and water film growth, which occurs due to seawater spray impinging on large horizontal surfaces of a supply vessel, is developed using a Stefan-type problem formulation. The icing model includes conduction heat transfer in the ice and brine film layer, assuming the volume and distribution of brine pockets and air bubbles within the ice accumulation are uniform. The model also uses heat and mass balances to predict the freezing fraction, temperature distribution, ice layer, and water film thickness. The results show that the water film salinity and icing intensity change with time during the icing period. Additionally, the water film salinity variations affect the freezing temperature, thermal conductivity, and specific heat capacity of ice formation. As a result, heat conduction within the accumulated
ice changes with time due to the variations of salinity; thus, the conduction heat flux has a significant effect on
the ice thickness growth rate. This new model is a useful tool for forecasting and assessing the potential ice accumulation on marine vessels and structures.