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1.
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
2.
Experiments and numerical simulations have been conducted to study the conjugate heat transfer by natural convection and surface
radiation from a planar heat generating element placed centrally between two adiabatic vertical plates. The relevant problem
dependent parameters considered in this study are modified Rayleigh number, channel aspect ratio, stream-wise location of
the heat generating element, and surface emissivities of the heat generating element and the adiabatic side plates. Experiments
are conducted for different values of modified Rayleigh number ranging from 3.2 × 105 to 1.6 × 107 and surface emissivities 0.05, 0.55, 0.75 and 0.85. The interdependence between the heat transfer mechanism and the flow
field under the influence of surface radiation on natural convection is explored and discussed. Experimental correlations
for total and convective Nusselt number, and dimensionless temperature in terms of relevant parameters have been developed.
The mathematical model governing the problem has been numerically solved using a commercial computational fluid dynamics package
FLUENT 6.3 and the numerical predictions substantiate the experimental observations. 相似文献
3.
The work reported in this paper is a systematic experimental and numerical study of friction and heat transfer characteristics
of divergent/convergent square ducts with an inclination angle of 1∘ in the two direction at cross section. The ratio of duct length to average hydraulic diameter is 10. For the comparison purpose,
measurement and simulation are also conducted for a square duct with constant cross section area, which equals to the average
cross section area of the convergent/divergent duct. In the numerical simulation the flow is modeled as being three-dimensional
and fully elliptic by using the body-fitted finite volume method and the kɛ turbulence model. The uniform heat flux boundary condition is specified to simulate the electrical heating used in the experiments.
The heat transfer performance of the divergent/convergent ducts is compared with the duct with uniform cross section under
three constraints (identical mass flow rate, pumping power and pressure drop). The agreement of the experimental and numerical
results is quite good except at the duct inlet. Results show that for the three ducts studied there is a weak secondary flow
at the cross section, and the circumference distribution of the local heat transfer coefficient is not uniform, with an appreciable
reduction in the four corner regions. In addition, the acceleration/deceleration caused by the cross section variation has
a profound effect on the turbulent heat transfer: compared with the duct of constant cross section area, the divergent duct
generally shows enhanced heat transfer behavior, while the convergent duct has an appreciable reduction in heat transfer performance.
Received on 18 September 2000 / Published online: 29 November 2001 相似文献
4.
Hideo Inaba Fujio Komatsu Akihiko Horibe Naoto Haruki Akito Machida 《Heat and Mass Transfer》2008,44(11):1305-1313
This paper describes heat and mass transfer characteristics of organic sorbent coated on heat transfer surface of a fin-tube
heat exchanger. The experiments in which the moist air was passed into the heat exchanger coated with sorption material were
conducted under various conditions of air flow rate (0.5–1.0 m/s) and the temperature of brine (14–20°C) that was the heat
transfer fluid to cool the air flow in the dehumidifying process. It is found that the sorption rate of vapor is affected
by the air flow rate and the brine temperature. Meanwhile, the attempt of clarifying the sorption mechanism is also conducted.
Finally the average mass transfer coefficient of the organic sorbent coated on heat transfer surface of a fin-tube heat exchanger
is non-dimensionalzed as a function of Reynolds number and non-dimensional temperature, and it is found that the effect of
non-dimensional temperature on them is larger than Reynolds number . 相似文献
5.
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
6.
Alvaro Valencia 《Heat and Mass Transfer》1998,33(5-6):465-470
A numerical investigation was conducted into channel flows with a tandem of transverse vortex generators in the form of rectangular
cylinders. The oscillatory behavior of the flow is studied. Data for heat transfer and flow losses are presented for 100≤Re≤400
and cylinder separation distances 1≤S/H≤4. The results are obtained by numerical solution of the full Navier-Stokes equations and the energy equation. Self-sustained
flow oscillations are found for Re>100. Alternate and dynamic shedding of large vortex structures from the cylinders is observed
by visualization of the numerically determined flow field. A heat transfer enhancement up to a factor 1.78 compared to plane
channel flow is observed.
Received on 16 July 1997 相似文献
7.
A numerical study of the steady forced convection heat transfer from an unconfined circular cylinder
Forced convection heat transfer from an unconfined circular cylinder in the steady cross-flow regime has been studied using
a finite volume method (FVM) implemented on a Cartesian grid system in the range as 10 ≤ Re ≤ 45 and 0.7 ≤ Pr ≤ 400. The numerical results are used to develop simple correlations for Nusselt number as a function of the pertinent dimensionless
variables. In addition to average Nusselt number, the effects of Re, Pr and thermal boundary conditions on the temperature field near the cylinder and on the local Nusselt number distributions
have also been presented to provide further physical insights into the nature of the flow. The rate of heat transfer increases
with an increase in the Reynolds and/or Prandtl numbers. The uniform heat flux condition always shows higher value of heat
transfer coefficient than the constant wall temperature at the surface of the cylinder for the same Reynolds and Prandtl numbers.
The maximum difference between the two values is around 15–20%. 相似文献
8.
Enhancement of heat and mass transfer in metal hydride beds with the addition of Al plates 总被引:1,自引:0,他引:1
Z. Guo 《Heat and Mass Transfer》1999,34(6):517-523
A numerical study is made of transient heat and mass transfer in metal hydride beds in the hydriding process with the addition
of internal aluminum plates. The two-dimensional equations governing the hydration kinetics, hydrogen flow and heat transfer
are solved by using the iterative method based on the finite-volume technique. It is found that the heat transfer is enhanced
by the installation of aluminum plates, and the ratio of the gap distance between the aluminum plates (H) and the thickness of the bed (L) emerges to be an important parameter. The reaction process is also strongly influenced by H/L. An optimal value of H/L exists to yield the fastest reaction rate, which is also shown to depend on other relevant parameters, such as the thickness
of hydride bed and the inlet pressure.
Received on 17 July 1998 相似文献
9.
3D numerical simulation on fluid flow and heat transfer characteristics in multistage heat exchanger with slit fins 总被引:1,自引:0,他引:1
In this paper, a numerical investigation is performed for three-stage heat exchangers with plain plate fins and slit fins
respectively, with a three-dimensional laminar conjugated model. The tubes are arranged in a staggered way, and heat conduction
in fins is considered. In order to save the computer resource and speed up the numerical simulation, the numerical modeling
is carried out stage by stage. In order to avoid the large pressure drop penalty in enhancing heat transfer, a slit fin is
presented with the strip arrangement of “front coarse and rear dense” along the flow direction. The numerical simulation shows
that, compared to the plain plate fin heat exchanger, the increase in the heat transfer in the slit fin heat exchanger is
higher than that of the pressure drop, which proves the excellent performance of this slit fin. The fluid flow and heat transfer
performance along the stages is also provided. 相似文献
10.
Zouhaier Mehrez Mourad Bouterra Afif El Cafsi Ali Belghith Patrick Le Quere 《Heat and Mass Transfer》2009,46(1):107-112
A numerical study based on the large eddy simulation methodology was made of heat transfer in locally disturbed turbulent
separated and reattached flow over a backward facing step. The local disturbance was given to the flow by a sinusoidally blowing/suction
of the fluid into a separated shear layer. The Reynolds number was fixed at 33,000 and Richardson number at 0.5. The disturbance
frequency was varied in the range 0 ≤ St ≤ 2, where St is the Strouhal number of disturbance. The obtained results revealed the existence of an optimum perturbation frequency value,
St = 0.25, in terms of the reduced reattachment length. At this frequency the heat transfer is significantly enhanced in the
recirculation zone. The influence of the frequency and the amplitude of disturbance, in the maximum heat transfer positions
and the maximum local Nusselt number, is analysed. 相似文献
11.
This investigation explores the mass/heat transfer from a wall-mounted block in a rectangular fully developed channel flow.
The naphthalene sublimation scheme was used to measure the level of local mass transfer from the block’s surfaces. The heat
transfer coefficient can be obtained by analogy between heat and mass transfer. The effects of the Reynolds number on the
local mass transfer from the block’s surfaces have been widely discussed. Results showed that, owing to the flow complexity
induced by vortices around the block, the block’s surfaces appeared four different spatial Sherwood number distributions,
termed “Wave type”, “U type”, “Slant type”, and “Pit type”. A change in the Reynolds number significantly altered the spatial Sherwood number distributions on the block’s surfaces.
Besides, four correlations between the Reynolds number and the surface-averaged Sherwood number were presented for the front,
top, side, and rear surfaces of the block at a given block’s height, for the purpose of practical applications. 相似文献
12.
The secondary vortex structure of an impingement jet system is enhanced by V-ribs on both the impingement and target plates. Numerical and experimental investigations are conducted to study the flow field and heat transfer resulting from V-rib turbulators in an impingement cooling configuration. Three different cases are tested: V-ribs on both the impingement and target plates (V-rib), V-ribs only on the impingement plate (V-rib-impingement) and V-ribs only on the target plate (V-rib-target). The experiment is carried out on a 9 by 9 inline impingement array test facility. For the transient measurements, narrow band thermochromic liquid crystals (TLC) and thermocouples are applied to obtain the local heat transfer distribution. Pressure taps are used to measure the pressure loss. The numerical simulation is carried out with ANSYS CFX 14, using a steady state Reynolds-Averaged Navier-Stokes (RANS) approach and the Shear Stress Transport (SST) turbulence model. All studies are done for a Reynolds number range of 15,000 to 35,000. There is a good overall agreement between the experimental and numerical results for the cases studied. The detailed flow field from the numerical simulation is used to understand and complement the phenomena observed in the experiment. The evaluation of the flow field confirms that the V-ribs enhance the secondary flow structure in the impingement system and induce a positive heat flux ratio compared to the baseline case. Both experimental and numerical results show a Nusselt number increase for the V-rib-impingement and V-rib configuration, with a highest Nusselt number ratio of 1.16. Notice that the experiment cannot take the rib part into account due to the invalid 1D semi-infinite wall assumption there, while the CFD simulation allows for the consideration of heat transfer on the rib surface and thus complements the heat flux data on the target plate. Depending on the configuration, the CFD simulation shows a heat flux ratio of 1.06–1.34. The pressure loss of the system is comparable to the case with a smooth impingement plate and a smooth target plate. 相似文献
13.
An experimental study was conducted of incompressible, moderate Reynolds number flow of air over heated rectangular blocks
in a two-dimensional, horizontal channel. Holographic interferometry combined with high-speed cinematography was used to visualize
the unsteady temperature fields in self- sustained oscillatory flow. Experiments were conducted in the laminar, transitional
and turbulent flow regimes for Reynolds numbers in the range from Re = 520 to Re = 6600. Interferometric measurements were
obtained in the thermally and fluiddynamically periodically fully developed flow region on the ninth heated block. Flow oscillations
were first observed between Re = 1054 and Re = 1318. The period of oscillations, wavelength and propagation speed of the Tollmien–Schlichting
waves in the main channel were measured at two characteristic flow velocities, Re = 1580 and Re = 2370. For these Reynolds
numbers it was observed that two to three waves span one geometric periodicity length. At Re = 1580 the dominant oscillation
frequency was found to be around 26 Hz and at Re = 2370 the frequency distribution formed a band around 125 Hz. Results regarding
heat transfer and pressure drop are presented as a function of the Reynolds number, in terms of the block-average Nusselt
number and the local Nusselt number as well as the friction factor. Measurements of the local Nusselt number together with
visual observations indicate that the lateral mixing caused by flow instabilities is most pronounced along the upstream vertical
wall of the heated block in the groove region, and it is accompanied by high heat transfer coefficients. At Reynolds numbers
beyond the onset of oscillations the heat transfer in the grooved channel exceeds the performance of the reference geometry,
the asymmetrically heated parallel plate channel.
Received on 26 April 2000 相似文献
14.
Mathematical modeling is performed to simulate forced convection flow of 47 nm- Al2O3/water nanofluids in a microchannel using the lattice Boltzmann method (LBM). Single channel flow and conjugate heat transfer
problem are taken into consideration and the heat transfer rate using a nanofluid is examined. Simulations are conducted at
low Reynolds numbers (2 ≤ Re ≤ 16). The computed average Nusselt number, which is associated with the thermal conductivity of nanofluid, is in the range
of 0.6 £ [`(Nu)] £ 13 0.6 \le \overline{Nu} \le 13 . Results indicate that the average Nusselt number increases with the increase of Reynolds number and particle volume concentration.
The fluid temperature distribution is more uniform with the use of nanofluid than that of pure water. Furthermore, great deviations
of computed Nusselt numbers using different models associated with the physical properties of a nanofluid are revealed. The
results of LBM agree well with the classical CFD method for predictions of flow and heat transfer in a single channel and
a microchannel heat sink concerning the conjugate heat transfer problem, and consequently LBM is robust and promising for
practical applications. 相似文献
15.
The mixed convection flow over a continuous moving vertical slender cylinder under the combined buoyancy effect of thermal
and mass diffusion has been studied. Both uniform wall temperature (concentration) and uniform heat (mass) flux cases are
included in the analysis. The problem is formulated in such a manner that when the ratio λ(= u
w/(u
w + u
∞), where u
w and u
∞ are the wall and free stream velocities, is zero, the problem reduces to the flow over a stationary cylinder, and when λ = 1
it reduces to the flow over a moving cylinder in an ambient fluid. The partial differential equations governing the flow have
been solved numerically using an implicit finite-difference scheme. We have also obtained the solution using a perturbation
technique with Shanks transformation. This transformation has been used to increase the range of the validity of the solution.
For some particular cases closed form solutions are obtained. The surface skin friction, heat transfer and mass transfer increase
with the buoyancy forces. The buoyancy forces cause considerable overshoot in the velocity profiles. The Prandtl number and
the Schmidt number strongly affect the surface heat transfer and the mass transfer, respectively. The surface skin friction
decreases as the relative velocity between the surface and free stream decreases.
Received on 17 May 1999 相似文献
16.
Comparative evaluation of three heat transfer enhancement strategies in a grooved channel 总被引:1,自引:0,他引:1
Results of a comparative evaluation of three heat transfer enhancement strategies for forced convection cooling of a parallel
plate channel populated with heated blocks, representing electronic components mounted on printed circuit boards, are reported.
Heat transfer in the reference geometry, the asymmetrically heated parallel plate channel, is compared with that for the basic
grooved channel, and the same geometry enhanced by cylinders and vanes placed above the downstream edge of each heated block.
In addition to conventional heat transfer and pressure drop measurements, holographic interferometry combined with high-speed
cinematography was used to visualize the unsteady temperature fields in the self-sustained oscillatory flow. The locations
of increased heat transfer within one channel periodicity depend on the enhancement technique applied, and were identified
by analyzing the unsteady temperature distributions visualized by holographic interferometry. This approach allowed gaining
insight into the mechanisms responsible for heat transfer enhancement. Experiments were conducted at moderate flow velocities
in the laminar, transitional and turbulent flow regimes. Reynolds numbers were varied in the range Re = 200–6500, corresponding
to flow velocities from 0.076 to 2.36 m/s. Flow oscillations were first observed between Re = 1050 and 1320 for the basic
grooved channel, and around Re = 350 and 450 for the grooved channels equipped with cylinders and vanes, respectively. At
Reynolds numbers above the onset of oscillations and in the transitional flow regime, heat transfer rates in the investigated
grooved channels exceeded the performance of the reference geometry, the asymmetrically heated parallel plate channel. Heat
transfer in the grooved channels enhanced with cylinders and vanes showed an increase by a factor of 1.2–1.8 and 1.5–3.5,
respectively, when compared to data obtained for the basic grooved channel; however, the accompanying pressure drop penalties
also increased significantly.
Received on 5 April 2001 相似文献
17.
Comparative numerical study of laminar heat transfer characteristics of annular tubes with sinusoidal wavy fins has been conducted
both experimentally and numerically with Re = 299–1,475. The uniform heat flux is imposed on the tube outside wall surface.
Two tube materials (copper and stainless steel) are considered. It is found that the fluid temperature profile is not linear
but convex along the flow direction due to the axial heat conduction in tube wall, and the effects of axial heat conduction
on the heat transfer decreases with an increase in Reynolds number or decrease in tube wall thermal conductivity. The axial
distributions of local Nusselt number could reach periodically fully developed after 3–5 cycles. The convectional data reduction
method based on the traditional method should be improved for tube with high thermal conductivity or low Reynolds numbers,
Otherwise, the heat transfer performance of internally finned tube may be underestimated. 相似文献
18.
The influence of heat transfer on the steady flow of a fourth‐grade fluid between two stationary parallel porous plates is studied. The flow is engendered under the application of a constant pressure gradient. The concept of homotopy analysis method is utilized for the series solution of the governing problem. Numerical solution has been also carried out. In addition, both analytic and numerical solutions are compared. The variations of embedded parameters into the solution are predicted through the graphical representations. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
19.
The flow boiling heat transfer coefficients of R-134a/R-290/R-600a (91%:4.068%:4.932% by mass) refrigerant mixture are experimentally
arrived in two tubes of diameter 9.52 and 12.7 mm. The tests are conducted to target the varied heat flux condition and stratified
flow pattern found in evaporators of refrigerators and deep freezers. The varied heat flux condition is imposed on the refrigerant
using a coaxial counter-current heat exchanger test section. The experiments are performed for mass flow rates of the refrigerant
mixture between 3 and 5 g s−1 and entry temperature between −8.59 and 5.33°C which are bubble temperatures corresponding to a pressure of 3.2 and 5 bar.
The influences of heat flux, mass flow rate, pressure, flow pattern, tube diameter on the heat transfer coefficient are discussed.
The profound effects of nucleate boiling prevailing even at higher vapor qualities in evaporators are highlighted. The heat
transfer coefficient of the refrigerant mixture is also compared with that of R-134a. 相似文献
20.
A numerical study has been performed for the periodically fully-developed flow in two-dimensional channels with streamwise-periodic round disturbances on its two walls. To accurately describe the round disturbance boundary condition, a body fitted grid was used. The flow and heat transfer have been studied in the range of Reynolds number, Re=50–700, and Prandtl number Pr=0.71. The influences of disturbance parameters and Reynolds number on heat transfer and friction have been investigated in detail. Some of the solutions have been examined using both steady and unsteady finite difference schemes; and the same results have been obtained. The results show that different flow patterns can occur with different deployments of the disturbances. With appropriate configuration of the disturbances, the Nusselt number can reach a value four times greater than in a smooth channel at the same condition, with the penalty of a much greater pressure drop. On the other hand, if the disturbances are not deployed properly, augmentation of heat transfer cannot be acquired. © 1998 John Wiley & Sons, Ltd. 相似文献