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1.
Numerical studies were conducted to investigate the natural convection heat transfer around a uniformly heated thin plate
with arbitrary inclination in an infinite space. The numerical approach was based on the finite volume technique with a nonstaggered
grid arrangement. For handling the pressure–velocity coupling the SIMPLE-algorithm was used. QUICK scheme and first order
upwind scheme were employed for discretization of the momentum and energy convective terms respectively. Plate width and heating
rate were used to vary the modified Rayleigh number over the range of 4.8×106 to 1.87×108. Local and average heat transfer characteristics were compared with regarding to the inclination angle. The empirical expressions
for local and average Nusselt number were correlated. It has been found that for inclination angle less than 10∘, the flow and heat transfer characteristics are complicated and the average Nusselt number can not be correlated by one equation
while for inclination angle larger than 10∘, the average Nusselt number can be correlated into an elegant correlation.
Received on 18 April 2001 / Published online: 29 November 2001 相似文献
2.
The flow and heat transfer in an inclined and horizontal rectangular duct with a heated plate longitudinally mounted in the
middle of cross section was experimentally investigated. The heated plate and rectangular duct were both made of highly conductive
materials, and the heated plate was subjected to a uniform heat flux. The heat transfer processes through the test section
were under various operating conditions: Pr ≈ 0.7, inclination angle ϕ = −60° to +60°, Reynolds number Re = 334–1,911, Grashof number Gr = 5.26 × 102–5.78 × 106. The experimental results showed that the average Nusselt number in the entrance region was 1.6–2 times as large as that
in the fully developed region. The average Nusselt numbers and pressure drops increased with the Reynolds number. The average
Nusselt numbers and pressure drops decreased with an increase in the inclination angle from −60° to +60° when the Reynolds
number was less than 1,500. But when the Reynolds number increased to over about 1,800, the heat transfer coefficients and
pressure drops were independent of inclination angles. 相似文献
3.
Two-dimensional numerical studies of flow and temperature fields for turbulent natural convection and surface radiation in
inclined differentially heated enclosures are performed. Investigations are carried out over a wide range of Rayleigh numbers
from 108 to 1012, with the angle of inclination varying between 0° and 90°. Turbulence is modeled with a novel variant of the k–ε closure model. The predicted results are validated against experimental and numerical results reported in literature. The
effect of the inclination of the enclosure on pure turbulent natural convection and the latter’s interaction with surface
radiation are brought out. Profiles of turbulent kinetic energy and effective viscosity are studied to observe the net effect
on the intensity of turbulence caused by the interaction of natural convection and surface radiation. The variations of local
Nusselt number and average Nusselt number are presented for various inclination angles. Marked change in the convective Nusselt
number is found with the orientation of enclosure. Also analyzed is the influence of change in emissivity on the flow and
heat transfer. A correlation relevant to practical applications in the form of average Nusselt number, as a function of Rayleigh
number, Ra, radiation convection parameter, N
RC and inclination angle of the enclosure, φ is proposed. 相似文献
4.
S. A. Nada 《Heat and Mass Transfer》2008,44(8):929-936
In the present study, an experimental investigation of heat transfer and fluid flow characteristics of buoyancy-driven flow
in horizontal and inclined annuli bounded by concentric tubes has been carried out. The annulus inner surface is maintained
at high temperature by applying heat flux to the inner tube while the annulus outer surface is maintained at low temperature
by circulating cooling water at high mass flow rate around the outer tube. The experiments were carried out at a wide range
of Rayleigh number (5 × 104 < Ra < 5 × 105) for different annulus gap widths (L/D
o = 0.23, 0.3, and 0.37) and different inclination of the annulus (α = 0°, 30° and 60°). The results showed that: (1) increasing
the annulus gap width strongly increases the heat transfer rate, (2) the heat transfer rate slightly decreases with increasing
the inclination of the annulus from the horizontal, and (3) increasing Ra increases the heat transfer rate for any L/D
o and at any inclination. Correlations of the heat transfer enhancement due to buoyancy driven flow in an annulus has been
developed in terms of Ra, L/D
o and α. The prediction of the correlation has been compared with the present and previous data and fair agreement was found. 相似文献
5.
Natural convective heat transfer from an isothermal narrow flat plate embedded in a plane adiabatic surface and inclined at
moderate positive and negative angles to the vertical has been numerically and experimentally studied. The solution has the
Rayleigh number, the dimensionless plate width, the angle of inclination, and the Prandtl number as parameters. Attention
was restricted to a Prandtl number of 0.7. The numerical results have been obtained for Rayleigh numbers between 103 and 107 for dimensionless plate widths of between 0.3 and 1.2 and for angles of inclination between +45° and −45°. In the experimental
study, results have been obtained for Rayleigh numbers between 4 × 102 and 105 for dimensionless plate widths of 0.4 and 2.5 and for angles of inclination between +45° and −45° to the vertical. Empirical
equations for the heat transfer rate have been derived. 相似文献
6.
Free convection heat transfer along an isothermal vertical wavy surface was studied experimentally and numerically. A Mach-Zehnder
Interferometer was used in the experiment to determine the local heat transfer coefficients. Experiments were done for three
different amplitude–wavelength ratios of α = 0.05, 0.1, 0.2 and the Rayleigh numbers ranging from Ra
l
= 2.9 × 105 to 5.8 × 105. A finite-volume based code was developed to verify the experimental study and obtain the results for all the amplitude–wavelength
ratios between α = 0 to 0.2. It is found that the numerical results agree well with the experimental data. Results indicate
that the frequency of the local heat transfer rate is the same as that of the wavy surface. The average heat transfer coefficient
decreases as the amplitude–wavelength ratio increases and there is a significant difference between the average heat transfer
coefficients of the surface with α = 0.2 and those surfaces with α = 0.05 and 0.1. The experimental data are correlated
with a single equation which gives the local Nusselt number along the wavy surface as a function of the amplitude–wavelength
ratio and the Rayleigh number. 相似文献
7.
The results of a numerical study of the effect of cold-water density inversion (Prandtl number Pr=11.59) on the flow and heat
transfer in a horizontal plane-parallel channel with isothermal top and bottom walls are presented. The calculations were
performed for the Grashof number Gr=3·104, the Reynolds number Re=10, and the channel segment length-to-height ratiol/d=40. The wall temperature was so varied that the temperature difference between the top and bottom walls remained constant.
Surgut. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 72–78, January–February,
2000. 相似文献
8.
Gurkan YesilozOrhan Aydin 《Experimental Thermal and Fluid Science》2011,35(6):1169-1176
Natural convective flow and heat transfer in an inclined quadrantal cavity is studied experimentally and numerically. The particle tracing method is used to visualize the fluid motion in the enclosure. Numerical solutions are obtained via a commercial CFD package, Fluent. The working fluid is distilled water. The effects of the inclination angle, ? and the Rayleigh number, Ra on fluid flow and heat transfer are investigated for the range of angle of inclination between 0° ? ? ? 360°, and Ra from 105 to 107. It is disclosed that heat transfer changes dramatically according to the inclination angle which affects convection currents inside, i.e. flow physics inside. A fairly good agreement is observed between the experimental and numerical results. 相似文献
9.
Experiments of flow boiling heat transfer and two-phase flow frictional pressure drop in a spirally internally ribbed tube
(φ22×5.5 mm) and a smooth tube (φ19×2 mm) were conducted, respectively, under the condition of 6×105 Pa (absolute atmosphere pressure). The available heated length of the test sections was 2500 mm. The mass fluxes were selected,
respectively, at 410, 610 and 810 kg/m2 s. The maximum heat flux was controlled according to exit quality, which was no more than 0.3 in each test run. The experimental
results in the spirally internally ribbed tube were compared with that in the smooth tube. It shows that flow boiling heat
transfer coefficients in the spirally internally ribbed tube are 1.4–2 times that in the smooth tube, and the flow boiling
heat transfer under the condition of smaller temperature differences can be achieved in the spirally internally ribbed tube.
Also, the two-phase flow frictional pressure drop in the spirally internally ribbed tube increases a factor of 1.6–2 as compared
with that in the smooth tube. The effects of mass flux and pressure on the flow boiling heat transfer were presented. The
effect of diameters on flow boiling heat transfer in smooth tubes was analyzed. Based on the fits of the experimental data,
correlations of flow boiling heat transfer coefficient and two-phase flow frictional factor were proposed, respectively. The
mechanisms of enhanced flow boiling heat transfer in the spirally internally ribbed tube were analyzed.
Received on 1 December 1999 相似文献
10.
Experimental investigation of mixed convection heat transfer in a horizontal and inclined rectangular channel 总被引:2,自引:0,他引:2
Mixed convection heat transfer in rectangular channels has been investigated experimentally under various operating conditions.
The lower surface of the channel is subjected to a uniform heat flux, sidewalls are insulated and adiabatic, and the upper
surface is exposed to the surrounding fluid. Experiments were conducted for Pr=0.7, aspect ratios AR=5 and 10, inclination
angles 0° ≤ θ ≤ 30°, Reynolds numbers 50 ≤ Re ≤ 1000, and modified Grashof numbers Gr*=7.0 × 105 to 4.0 × 107. From the parametric study, local Nusselt number distributions were obtained and effects of channel inclination, surface
heat flux and Reynolds number on the onset of instability were investigated. Results related to the buoyancy affected secondary
flow and the onset of instability have been discussed. Some of the results obtained from the experimental measurements are
also compared with the literature, and a good agreement was observed. The onset of instability was found to move upstream
for increasing Grashof number and increasing aspect ratio. On the other hand, onset of instability was delayed for increasing
Reynolds number and increasing inclination angle.
Received on 19 March 2001 / Published online: 29 November 2001 相似文献
11.
T. Aihara K. Yamamoto K. Narusawa T. Haraguchi M. Ukaku A. Lasek F. Feuillebois 《Heat and Mass Transfer》1997,33(1-2):109-120
Heat transfer characteristics of a turbulent, dilute air-solids suspension flow in thermally developing/developed regions
were experimentally studied, using a uniformly heated, horizontal 54.5 mm-ID pipe and 43-μm-diameter glass beads. The local
heat transfer was measured at 27 locations from the inlet to 120-dia downstream of the heated section over a range of Reynolds
numbers 3×104−1.2×105 and solids loading ratio 0–3, and the fully developed profiles of air velocity/temperature and particle mass flux were measured
at a location 140-dia downstream of the heated section using specially designed probes, inserted into the suspension flow.
The effects of the Reynolds number, solids loading ratio, and azimuthal/longitudinal locations on the heat transfer characteristics
and their interactions are discussed through comparison of the present results with the data obtained by other investigators.
Received on 14 October 1996 相似文献
12.
Natural convection heat transfer in an inclined fin attached square enclosure is studied both experimentally and numerically.
Bottom wall of enclosure has higher temperature than that of top wall while vertical walls are adiabatic. Inclined fin has
also adiabatic boundary conditions. Numerical solutions have been done by writing a computer code in Fortran platform and
results are compared with Fluent commercial code and experimental method. Governing parameters are Rayleigh numbers (8.105 ≤ Ra ≤ 4 × 106) and inclination angle (30° ≤ and ≤ 120°). The temperature measurements are done by using thermocouples distributed uniformly
at the wall of the enclosure. Remarkably good agreement is obtained between the predicted results and experimental data. A
correlation is also developed including all effective parameters on heat transfer and fluid flow. It was observed that heat
transfer can be controlled by attaching an inclined fin onto wall. 相似文献
13.
A detailed numerical study is carried out to investigate fluid flow and heat transfer characteristics in a channel with heated
V corrugated upper and lower plates. The parameters studied include the Reynolds number (Re = 2,000–5,500), angles of V corrugated plates (θ = 20°, 40°, 60°), and constant heat fluxs (q″ = 580, 830, 1,090 W/m2). Numerical results have been validated using the experimented data reported by Naphon, and a good agreement has been found.
The angles of V corrugated plates (θ) and the Reynolds number are demonstrated to significantly affect the fluid flow and the heat transfer rate. Increasing the
angles of V corrugated plates can make the heat transfer performance become better. The increasing Reynolds number leads to
a more complex fluid flow and heat transfer rate. The numerical calculations with a non-equilibrium wall function have a better
accuracy than with a standard wall function for solving high Reynolds numbers or complex flow problems. 相似文献
14.
In this study, steady-state forced convection heat transfer and pressure drop characteristics in a horizontal rectangular cross-sectioned duct, baffles mounted on the bottom surface with different inclination angles were investigated experimentally in the Reynolds number range from 1 × 103 to 1 × 104. The study was performed under turbulent flow conditions. Effects of different baffle inclination angles on flow and heat transfer were studied. Results are also presented in terms of thermal enhancement factor. It is observed that increasing in baffle inclination angle enhances the heat transfer and causes an increase in pressure drop in the duct. 相似文献
15.
An experimental investigation was carried out to study the enhancement of the heat transfer from a heated flat plate fitted
with rectangular blocks of 1 × 2 × 2 cm3 dimensions in a channel flow as a function of Reynolds number (Reh), spacing (S
y
) of blocks in the flow direction, and the block orientation angle (α) with respect to the main flow direction. The experiments were performed in a channel of 18 cm width and 10 cm height, with
air as the working fluid. For fixed S
x
=3.81 cm, which is the space between the blocks in transverse to the flow direction, the experimental ranges of the parameters
were S
y
=3.33–4.33 cm, α=0–45°, Reh=7625–31550 based on the hydraulic diameter and the average velocity at the beginning of the test section in the channel.
Correlations for Nusselt number were developed, and the ratios of heat transfer with blocks to those with no blocks were given.
The results indicated that the heat transfer could be enhanced or reduced depending on the spacing between blocks, and the
block orientation angle. The maximum heat transfer rate was obtained at the orientation angle of 45°.
Received on 13 December 2000 / Published online: 29 November 2001 相似文献
16.
The mixed convection in a vertical plane-parallel channel with two heat sources of finite dimensions located at the wall is
analyzed on the basis of a two-dimensional numerical simulation. The effect of the distance between the heat sources on the
flow pattern and the temperature field is studied. Calculations are performed on the Grashof and Reynolds number ranges from
0–105 and 0–10, respectively, at a Prandtl number of 0.7. The mathematical model is based on the time-dependent Navier-Stokes equations
in the Boussinesq approximation. The problem is solved by the finite element method. 相似文献
17.
Heat transfer coefficients were measured on a horizontal platinum wire and converted to data on horizontal copper tubes. The
measurements spanned a large region of pressures p* = p/pcrit = 0.05–0.50 and heat fluxes of q = 103–1.5 × 105 W/m2. The preparation of the test equipment is described. The effects of pressure and concentration on the heat transfer coefficients
are shown. The mixture behaves very much like an azeotropic mixture; concentration has only a small effect, the heat transfer
coefficients can be obtained from the heat transfer coefficients of the pure components according to their molar fractions.
The conversion steps from wire- to tube-data are presented. A comparison of wire-data with correlations given in literature
is shown. It renders good agreement. 相似文献
18.
H. M. Badr 《Heat and Mass Transfer》1998,34(2-3):229-236
The paper deals with the problem of two-dimensional laminar forced convection heat transfer from a straight isothermal tube
of elliptic cross-section placed in a uniform stream. The study is based on numerical solutions of the conservation equations
of mass, momentum, and energy which covers the entire flow domain including the wake region. The parameters influencing the
heat transfer process are essentially the Reynolds number, Re, the tube geometry represented by its minor to major axis ratio,
Ar, and the angle of inclination, λ. The study focuses on the effect of Re, Ar, and λ on the heat transfer process in the
range of Re from 20 to 500. The study reveals that the rate of heat transfer reaches its maximum when λ=0∘ while the minimum occurs when λ=90∘. The results also show that smaller axis ratio gives higher heat transfer rate when λ=0∘. The local Nusselt number and surface vorticity distributions are plotted for a number of cases and the effect of vortex
shedding on the overall rate of heat transfer is briefly discussed.
Received on 20 September, 1997 相似文献
19.
G. Juncu 《Heat and Mass Transfer》1998,34(2-3):203-208
The reverse of the transfer direction in the unsteady conjugate heat transfer between a spherical particle and a surrounding
fluid flow has been analysed. The aspect this work is focused on is the influence of the continuous phase convection on the
occurrence and development of this phenomenon. The energy equations are solved by the ADI finite difference method. The range
of the Pe numbers investigated is between 0 and 10. The ratios of the thermal conductivity and volume heat capacity between
the particle and its ambient flow belong to the interval 0.01–100. It was found that, in creeping flow, the thermal wake occurs
at Pe=0.690·10−3. Increasing the Pe number up to 1 the dimension of thermal wake increases. For Pe>1, the increase in Pe decreases thermal
wake.
Received on 13 January 1998 相似文献
20.
A. N. Golovanov 《Journal of Applied Mechanics and Technical Physics》2006,47(5):637-642
A gas-dynamic flow in an axisymmetric convective jet is studied experimentally. It is demonstrated that the jet flow with
Grashof numbers Gr = (0.4–2.0) · 106 is self-similar. Acoustic oscillations directed perpendicular to the axis of symmetry transform the profiles of the gas-flow
parameters; two temperature maximums located outside the axis can appear. The results obtained indicate that flow instability
is generated in high-gradient regions.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 5, pp. 27–33, September–October, 2006. 相似文献