共查询到16条相似文献,搜索用时 15 毫秒
1.
Hazem A. Attia 《Journal of Mechanical Science and Technology》2006,20(8):1302-1308
The unsteady Hartmann flow of an electrically conducting, viscous, incompressible fluid bounded by two parallel non-conducting
porous plates is studied with heat transfer taking the Hall effect into consideration. An external uniform magnetic field
and a uniform suction and injection are applied perpendicular to the plates while the fluid motion is subjected to an exponential
decaying pressure gradient. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations
are included in the energy equation. The effect of the ion slip and the uniform suction and injection on both the velocity
and temperature distributions is examined.
On leave from: Department of Engineering Mathematics and physics, Fac. of Engineering, El-Fayoum University, El-Fayoum, Egypt. 相似文献
2.
Hazem Ali Attia 《Journal of Mechanical Science and Technology》2006,20(12):2197-2202
The steady hydromagnetic flow due to a rotating disk is studied with heat transfer considering the ion slip. The governing
equations are solved numerically using finite differences. The results show that the inclusion of the ion slip has important
effects on the velocity distribution as well as the heat transfer.
On leave from: Department of Engineering Math. and physics, Fac. of Engineering, El-Fayoum University, El-Fayoum, Egypt. 相似文献
3.
Hazem A. Attia 《Journal of Mechanical Science and Technology》2006,20(4):569-579
In the present study, the unsteady Couette flow with heat transfer of a dusty viscous incompressible electrically conducting
fluid under the influence of an exponential decaying pressure gradient is studied without neglecting the Hall effect. The
parallel plates are assumed to be porous and subjected to a uniform suction from above and injection from below while the
fluid is acted upon by an external uniform magnetic field is applied perpendicular to the plates. The governing equations
are solved numerically using finite differences to yield the velocity and temperature distributions for both the fluid and
dust particles. 相似文献
4.
Eun Soo Jeong 《Journal of Mechanical Science and Technology》1995,9(2):225-239
Effects of axial temperature gradient on heat transfer, momentum transfer and energy conversion mechanisms within a closed
cylinder-piston apparatus are analyzed. Assuming that the gas density change is small, the first-order and steady second-order
solutions of continuity, momentum and energy equations are obtained. The solutions show that there exists a steady circulating
flow and the magnitude of the steady axial velocity increases as the axial temperature gradient increases. There exists not
only an oscillating component of heat flux between the gas and the wall, but also a steady component whose direction depends
on axial temperature gradient. It is shown that heat is pumped from the wall near the piston to the wall near closed-end for
negative axial temperature gradient. Heat transfer relation for both oscillating pressure and oscillating flow conditions
is proposed. 相似文献
5.
Young-Ryoul Back Jae-Heon Lee Byung-Ha Kang Myung-Do Oh 《Journal of Mechanical Science and Technology》1994,8(3):219-230
Characteristics of fluid flow and convective heat transfer of a pulsating flow in a curved tube have been investigated numerically.
The tube wall is assumed to be maintained at a uniform temperature peripherally in a fully developed pulsating flow region.
The temperature and flow distributions over a cross-section of a curved tube with the associated velocity field need to be
studied in detail. This problem is of particular interest in the design of Stirling engine heat exchangers and in understanding
the blood flow in the aorta. The time-dependent, elliptic governing equations are solved, employing finite volume technique.
The periodic steady state results are obtained for various governing dimensionless parameters, such as Womersley number, pulsation
amplitude ration, curvature ratio and Reynolds number. The numerical results indicate that the phase difference between the
pressure gradient and averaged axial velocity increases gradually up to π/2 as Womersley number increases. However, this phase
difference is almost independent of the amplitude ratio of pulsation. It is also found that the secondary flow patterns are
strongly affected by the curvature ratio and Reynolds number. These, in turn, give a strong influence on the convective heat
transfer from the pipe wall to the pulsating flow. The results obtained lead to a better understanding of the underlying physical
process and also provide input that may be used to design the relevant system. The numerical approach is discussed in detail,
and the aspects that must be included for an accurate simulation are discussed. 相似文献
6.
Hazem Ali Attia 《Journal of Mechanical Science and Technology》2007,21(4):672-677
The steady hydromagnetic flow due to a rotating disk is studied with heat transfer considering the ion slip. The governing
equations are solved numerically using finite differences. The results show that the inclusion of the ion slip has important
effects on the velocity distribution as well as the heat transfer. 相似文献
7.
Experimental heat transfer data for single-phase water flow in the annuli with corrugated inner tubes are presented. In the
annuli with parallel flow, ten different annular arrangements are considered. For water (low rate in l,700<Re<13,000 regime,
data for Nusselt numbers are presented. The results show significant effects of both the pitch to trough height ratio (P/e) and the radius ratio (r
*). AsP/e becomes closer to 8 in the range below the radius ratio(r
*) of 0.5. Nusselt numbers increase. However, Nusselt numbers decrease in the range above the radius ratio (r*) of 0.5 because flow reattachment position becomes farther in the narrower clearance. 相似文献
8.
Turbulent heat transfer characteristics in swirling flows downstream of an abrupt pipe expansion with a diameter ratio of
0.5 are predicted by full Reynolds stress model. The uniform heat flux condition is imposed on the downstream wall. The flows
with weak and strong swirls as well as without swirl are computed. The governing differential equations are discretized by
finite volume method. Results show that the Reynolds stress model predicts accurately the maximum local Nusselt number for
the case with strong swirl, but that the effects of swirl are not fully accounted for the case with weak swirl. 相似文献
9.
Soon Hyun Yoon Moon Kyung Kim Dae Hee Lee 《Journal of Mechanical Science and Technology》1997,11(4):476-483
Turbulent flow and heat transfer characteristics of a two-dimensional oblique plate impinging jet (OPIJ) were experimentally
investigated. The local heat transfer coefficients were measured using thermochromic liquid crystals. The jet mean velocity
and turbulent intensity profiles were also measured along the plate. The jet Reynolds number (Re, based on the nozzle width)
ranged from 10, 000 to 35,000, the nozzle-to-plate distance (H/B) from 2 to 16, and the oblique angle (α) from 60 to 90 degree. It has been found that the stagnation point shifted toward
the minor flow region as the oblique angle decreased and the position of the stagnation point nearly coincided with that of
the maximum turbulent intensity. It has also been observed that the local Nusselt numbers in the minor flow region were larger
than those in the major flow region for the same distance along the plate mainly due to the higher levels in turbulent intensity
caused by more active mixing of the jet flow. 相似文献
10.
Soo Whan Ahn ByungChang Lee WonCheol Kim Myung- Whan Bae Yoon Pyo Lee 《Journal of Mechanical Science and Technology》2002,16(9):1175-1182
The commercial viability of heat exchanger is mainly dependent on its long-term fouling characteristic because the fouling
increases the pressure loss and degrades the thermal performance of a heat exchanger. An experimental study was performed
to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with circulating various
solid particles. The present work showed that the higher densities of particles had higher drag force coefficients, and the
increases in heat transfer were in the order of sand, copper, steel, aluminum, and glass below Reynolds number of 5,000. 相似文献
11.
Bum-sik Shin Kwang Min Chun Hang-kyung Lee 《Journal of Mechanical Science and Technology》1997,11(4):468-475
Fuel injection pipe pressures are measured and simulated to study the effect of fuel injection system characteristies on the
heat release in a direct injection diesel engine. The fuel injection simulation is based on a linear model. The governing
equations are solved by the finite difference method. The measured fuel pipe pressures and the simulated fuel pipe pressures
matched well to each other except for the interval when the nozzle is closing. The effects of the fuel pipe length and the
nozzle opening pressure are tested. The longer fuel pipe length causes proportional retardation of the fuel injection time.
The higher nozzle opening pressure results in increase of the maximum fuel pipe pressure and shorter combustion duration. 相似文献
12.
It is important to completely understand heat/mass transfer from a flat plate because it is a basic element of heat/mass transfer.
In the present study, local heat/mass transfer coefficient is obtained for two flow conditions to investigate the effect of
boundary layer using the naphthalene sublimation technique. Obtained local heat/mass transfer coefficient is converted to
dimensionless parameters such as Sherwood number, Stanton number and Colburnj-factor. These also are compared with correlations of laminar and turbulent heat/mass transfer from a flat plate. According
to experimental results, local Sherwood number and local Stanton number are in much better agreement with the correlation
of turbulent region rather than laminar region, which means analogy between heat/mass transfer and momentum transfer is more
suitable for turbulent boundary layer. But average Sherwood number and average Colburnj-factor representing analogy between heat/mass transfer and momentum transfer are consistent with the correlation of laminar
boundary layer as well as turbulent boundary layer. 相似文献
13.
The study focuses on the heat transfer performance of two-phase closed thermosyphons with plain copper tube and tubes having
50, 60, 70, 80, 90 internal grooves. Three different working fluids (distilled water, methanol, ethanol) are used with various
volumetric liquid fill charge ratio from 10 to 40%. Additional experimental parameters such as operating temperature and inclination
angle of zero to 90 degrees are used for the comparison of heat transfer performance of the thermosyphon. Condensation and
boiling heat transfer coefficients, heat flux are obtained using experimental data for each case of specific parameter. The
experimental results are assessed and compared with existing correlations. The results show that working fluids, liquid fill
charge ratio, number of grooves and inclination angle are very important factors for the operation of thermosyphons. The relatively
high rate of heat transfer is achieved when the thermosyphon with internal grooves is used compared to that with plain tube.
The optimum liquid fill charge ratio for the best heat transfer performance lies between 25% and 30%. The range of the optimum
inclination angle for this study is 20°-30° from the horizontal position. 相似文献
14.
Experimental data are presented which describe the effects of a combustor-level high free-stream turbulence on the near-wall
flow structure and heat/mass transfer on the endwall of a linear high-turning turbine rotor cascade. The endwall flow structure
is visualized by employing the partial- and total-coverage oil-film technique, and heat/mass transfer rate is measured by
the naphthalene sublimation method. A turbulence generator is designed to provide a highly-turbulent flow which has free-stream
turbulence intensity and integral length scale of 14.7% and 80mm, respectively, at the cascade entrance. The surface flow
visualizations show that the high free-stream turbulence has little effect on the attachment line, but alters the separation
line noticeably. Under high free-stream turbulence, the incoming near-wall flow upstream of the adjacent separation lines
collides more obliquely with the suction surface. A weaker lift-up force arising from this more oblique collision results
in the narrower suction-side corner vortex area in the high turbulence case. The high free-stream turbulence enhances the
heat/mass transfer in the central area of the turbine passage, but only a slight augmentation is found in the endwall regions
adjacent to the leading and trailing edges. Therefore, the high free-stream turbulence makes the endwall heat load more uniform.
It is also observed that the heat/mass transfers along the locus of the pressure-side leg of the leading-edge horseshoe vortex
and along the suctionside corner are influenced most strongly by the high free-stream turbulence. In this study, the endwall
surface is classified into seven different regions based on the local heat/mass transfer distribution, and the effects of
the high free-stream turbulence on the local heat/mass transfer in each region are discussed in detail. 相似文献
15.
An experimental study was performed to investigate heat transfer characteristics of turbulent swirling flow in an axisymmetric
annuli. The static pressure, the local flow temperature, and the wall temperature with decaying swirl were measured by using
tangential inlet conditions and the friction factor and the local Nusselt number were calculated for Re=30000-70000. The local
Nusselt number was compared with that obtained from the Dittus-Boelter equation with swirl and without swirl. The results
showed that the swirl enhances the heat transfer at the inlet and the outlet of the test tube. 相似文献
16.
A numerical simulation has been performed for the investigation of flow and heat transfer characteristics of a film cooling
system injected through a hole with compound angle orientation. The finite volume method is employed to discretize the governing
equations based on the non-orthogonal coordinate with non-staggered variable arrangement. In order to analyze flow and heat
transfer characteristics, velocity, temperature, aerodynamic loss coefficient, skin friction and vorticity are calculated
with the variation of the skew angle. The maximum longitudinal vorticity and aerodynamics loss depend strongly on the skew
angle. For the symmetric case of β=0 deg, a pair of counter-rotating vortices are formed and the maximum value of the film
cooling effectiveness has appeared in the center plane where the skin friction is the minimum. For the skew angle of β=30
deg and above, only one strong counter-clockwise vortex remains in the downstream region and the maximum value of the film
cooling effectiveness are obtained on the right side of the vortex. The predicted results for the film cooling effectiveness
show good agreements with previous experimental data except the near-hole region. 相似文献