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1.
Heat transfer characteristics to laminar pulsating pipe flow under different conditions of Reynolds number and pulsation
frequency were experimentally investigated. The tube wall of uniform heat flux condition was considered. Reynolds number was
varied from 780 to 1987 while the frequency of pulsation ranged from 1 to 29.5 Hz. The results showed that the relative mean
Nusselt number is strongly affected by pulsation frequency while it is slightly affected by Reynolds number. The results showed
enhancements in the relative mean Nusselt number. In the frequency range of 1–4 Hz, an enhancement up to 30% (at Reynolds
number of 1366 and pulsation frequency of 1.4 Hz) was obtained. In the frequency range of 17–25 Hz, an enhancement up to 9%
(at Reynolds number of 1366 and pulsation frequency of 17.5 Hz) was indicated. The rate of enhancement of the relative mean
Nusselt number decreased as pulsation frequency increased or as Reynolds number increased. A reduction in relative mean Nusselt
number occurred outside these ranges of pulsation frequencies. A reduction in relative mean Nusselt number up to 40% for pulsation
frequency range of 4.1–17 Hz and a reduction up to 20% for pulsation frequency range of 25–29.5 Hz for Reynolds numbers range
of 780–1987 were considered. This reduction is directly proportional to the pulsation frequency. Empirical dimensionless equations
have been developed for the relative mean Nusselt number that related to Reynolds number (750 < Re < 2000) and the dimensionless
frequency (3<Ω<18) with about 10% rms.
Received on 16 May 2000 / Published online: 29 November 2001 相似文献
2.
Using deioned water as a working fluid, the influence of the microscale effects on liquid flow resistance in microtubes with
inner diameters of 19.6 and 44.2 μm, respectively, is experimentally studied. The temperature rise resulted from the microscale
effects, such as viscous dissipation, electric double layer, wall rough on the wall surface, etc., is obtained by an IR camera
with a special magnified lens adopting micro-area thermal image technology and the corresponding pressure drop and the flux
are also measured, so the relationship among friction factor, temperature rise and Reynolds number is obtained. Investigation
shows that experimental data are almost equal to those of Hagen–Poiseuille when Reynolds number is low. With the increase
of Reynolds number, the values of the friction factor depart from that of classical theory due to the microscale effects.
Moreover, the values of the experimental friction factor considering various microscale effects is the maximal 10–15% deviation
from that of friction factor without considering various microscale effects with further increase of Reynolds number. 相似文献
3.
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
4.
Yu. Ya. Trifonov 《Journal of Applied Mechanics and Technical Physics》2007,48(1):91-100
The linear and nonlinear stability of downward viscous film flows on a corrugated surface to freesurface perturbations is
analyzed theoretically. The study is performed with the use of an integral approach in ranges of parameters where the calculated
results and the corresponding solutions of Navier-Stokes equations (downward wavy flow on a smooth wall and waveless flow
along a corrugated surface) are in good agreement. It is demonstrated that, for moderate Reynolds numbers, there is a range
of corrugation parameters (amplitude and period) where all linear perturbations of the free surface decay. For high Reynolds
numbers, the waveless downward flow is unstable. Various nonlinear wavy regimes induced by varying the corrugation amplitude
are determined.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 1, pp. 110–120, January–February, 2007. 相似文献
5.
A. V. Proskurin A. M. Sagalakov 《Journal of Applied Mechanics and Technical Physics》2008,49(3):383-390
The stability of the plane flow of an electrically conducting fluid with respect to small perturbations was studied at large
Reynolds numbers in the presence of a longitudinal magnetic field. The dependence of the critical Reynolds number on the electrical
conductivity is investigated. At large Reynolds numbers, a new branch of instability and a sudden change in the critical Reynolds
numbers is found.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 45–53, May–June, 2008. 相似文献
6.
The full energy dissipation rate and enstrophy are measured simultaneously using a probe consisting of four X-wires in the
intermediate region of a cylinder wake for Taylor microscale Reynolds number in the range of 120–320. Longitudinal and transverse
velocity increments are also obtained temporally using Taylor’s hypothesis. The inertial range scaling exponents indicate
that the full enstrophy field has a stronger intermittency than does the full dissipation field for all the Reynolds numbers
considered. The approximations of the energy dissipation rate and enstrophy based on isotropy are more intermittent than their
corresponding true values. While the scaling exponents of the full energy dissipation rate remain approximately constant for
different Reynolds numbers, those of the enstrophy decrease slightly and consistently with the increase of Reynolds number.
It is conjectured that the scaling of the energy dissipation rate and the enstrophy may be the same when Reynolds number is
extremely high, a trend that is consistent with that suggested by Nelkin (Phys Fluids 11:2202–2204, 1999; Am J Phys 68:310–318, 2000). 相似文献
7.
A. A. Vasil’ev V. N. Rychkov M. E. Topchiyan 《Journal of Applied Mechanics and Technical Physics》2007,48(3):361-367
The laminar-turbulent transition is experimentally studied in boundary-layer flows on cones with a rectangular axisymmetric
step in the base part of the cone and without the step. The experiments are performed in an A-1 two-step piston-driven gas-dynamic
facility with adiabatic compression of the working gas with Mach numbers at the nozzle exit M
∞ = 12–14 and pressures in the settling chamber P0 = 60–600 MPa. These values of parameters allow obtaining Reynolds numbers per meter near the cone surface equal to Re
1e = (53–200) · 106
m
−1. The transition occurs at Reynolds numbers Re
tr
= (2.3–5.7) · 106.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 3, pp. 76–83, May–June, 2007. 相似文献
8.
P. Balakumar 《Theoretical and Computational Fluid Dynamics》1997,9(2):103-119
Two-dimensional nonlinear equilibrium solutions for the plane Poiseuille–Couette flow are computed by directly solving the
full Navier–Stokes equations as a nonlinear eigenvalue problem. The equations are solved using the two-point fourth-order
compact scheme and the Newton–Raphson iteration technique. The linear eigenvalue computations show that the combined Poiseuille–Couette
flow is stable at all Reynolds numbers when the Couette velocity component σ2 exceeds 0.34552. Starting with the neutral solution for the plane Poiseuille flow, the nonlinear neutral surfaces for the
combined Poiseuille–Couette flow were mapped out by gradually increasing the velocity component σ2. It is found that, for small σ2, the neutral surfaces stay in the same family as that for the plane Poiseuille flow, and the nonlinear critical Reynolds
number gradually increases with increasing σ2. When the Couette velocity component is increased further, the neutral curve deviates from that for the Poiseuille flow with
an appearance of a new loop at low wave numbers and at very low energy. By gradually increasing the σ2 values at a constant Reynolds number, the nonlinear critical Reynolds numbers were determined as a function of σ2. The results show that the nonlinear neutral curve is similar in shape to a linear case. The critical Reynolds number increases
slowly up to σ2∼ 0.2 and remains constant until σ2∼ 0.58. Beyond σ2 > 0.59, the critical Reynolds number increases sharply. From the computed results it is concluded that two-dimensional nonlinear
equilibrium solutions do not exist beyond a critical σ2 value of about 0.59.
Received: 26 November 1996 and accepted 12 May 1997 相似文献
9.
The effects of coincidence window and measuring volume size on two-component laser velocimeter measurement of turbulence
in an isothermal liquid flow through a concentric annular channel were studied. Three different coincidence windows (100–500 μs)
and three different measuring volume sizes (diameter, 5–9 wall units; spanwise length, 24–91 wall units) were used in a flow
of Reynolds number 31,500 and data density spanning the high end of intermediate to the low end of high (3–6). While no significant
effects of the coincidence window and measuring volume size were found on the time-mean velocity and turbulence intensities,
the streamwise Reynolds shear stress measured near a wall was found to be markedly affected by both. The smallest feasible
measuring volume along with an appropriate coincidence window provides good measurement of the shear stress.
Received: 8 September 1999/Accepted: 11 July 2000 相似文献
10.
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
11.
12.
In the present case, the conjugate heat transfer involving a turbulent plane offset jet is considered. The bottom wall of
the solid block is maintained at an isothermal temperature higher than the jet inlet temperature. The parameters considered
are the offset ratio (OR), the conductivity ratio (K), the solid slab thickness (S) and the Prandtl number (Pr). The Reynolds number considered is 15,000 because the flow becomes fully turbulent and then it becomes independent of the
Reynolds number. The ranges of parameters considered are: OR = 3, 7 and 11, K = 1–1,000, S = 1–10 and Pr = 0.01–100. High Reynolds number two-equation model (k–ε) has been used for turbulence modeling. Results for the solid–fluid interface temperature, local Nusselt number, local
heat flux, average Nusselt number and average heat transfer have been presented and discussed. 相似文献
13.
C.G. Speziale 《Theoretical and Computational Fluid Dynamics》1999,13(3):161-166
A resent extension of the nonlinear K–ε model is critically discussed from a basic theoretical standpoint. While it was said in the paper that this model was formulated
to incorporate relaxation effects, it will be shown that the model is incapable of describing one of the most basic such turbulent
flows as is obvious but is described for clarity. It will be shown in detail that this generalized nonlinear K–ε model yields erroneous results for the Reynolds stress tensor when the mean strains are set to zero in a turbulent flow
– the return-to-isotropy problem which is one of the most elementary relaxational turbulent flows. It is clear that K–ε type models cannot describe relaxation effects. While their general formalism can describe relaxation effects, the nonlinear
K–ε model – which the paper is centered on – cannot. The deviatoric part of the Reynolds stress tensor is predicted to be zero
when it actually only gradually relaxes to zero. Since this model was formulated by using the extended thermodynamics, it
too will be critically assessed. It will be argued that there is an unsubstantial physical basis for the use of extended thermodynamics
in turbulence. The role of Material Frame-Indifference and the implications for future research in turbulence modeling are
also discussed.
Received 19 February 1998 and accepted 23 October 1998 相似文献
14.
Chun-Lang Yeh 《Heat and Mass Transfer》2008,44(3):275-280
The performances of three linear eddy viscosity models (LEVM) and one algebraic Reynolds stress model (ARSM) for the simulation
of turbulent flow inside and outside pressure-swirl atomizer are evaluated by comparing the interface position with available
experimental data and by comparing the turbulence intensity profiles at the atomizer exit. It is found that the turbulence
models investigated exhibit zonal behaviors, i.e. none of the models investigated performs well throughout the entire flow
field. The turbulence intensity has a significant influence on the global characteristics of the flow field. The turbulence
models with better predictions of the turbulence intensity, such as Gatski-Speziale’s ARSM model, can yield better predictions
of the global characteristics of the flow field, e.g. the reattachment lengths for the backward-facing step flow and the sudden
expansion pipe flow, or the discharge coefficient, film thickness and the liquid sheet outer surface position for the atomizer
flows. The standard k–ε model predicts stronger turbulence intensity as compared to the other models and therefore yields smaller film thickness
and larger liquid sheet outer surface position. In average, the ARSM model gives both quantitatively and qualitatively better
results as compared to the standard k–ε model and the low Reynolds number models. 相似文献
15.
Supersonic flows near flying vehicle elements are calculated in the approximation of the full Navier-Stokes equations for
a viscous compressible heat-conducting gas with different values of free-stream. Mach and Reynolds numbers and angles of attack.
The main laws of the flow near the lifting surface. and in the inlet are obtained.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 2, pp. 98–108, March–April, 2009. 相似文献
16.
Three-dimensional turbulent forced convective heat transfer and flow characteristics, and the non-dimensional entropy generation
number in a helical coiled tube subjected to uniform wall temperature are simulated using the k–ε standard turbulence model. A finite volume method is employed to solve the governing equations. The effects of Reynolds number,
curvature ratio, and coil pitch on the average friction factor and Nusselt number are discussed. The results presented in
this paper cover a Reynolds number range of 2 × 104 to 6 × 104, a pitch range of 0.1–0.2 and a curvature ratio range of 0.1–0.3. The results show that the coil pitch, curvature ratio and
Reynolds number have different effects on the average friction factor and Nusselt number at different cross-sections. In addition,
the flow and heat transfer characteristics in a helical coiled tube with a larger curvature ratio for turbulent flow are different
from that of smaller curvature ratio for laminar and turbulent flow in certain ways. Some new features that are not obtained
in previous researches are revealed. Moreover, the effects of Reynolds number, curvature ratio, and coil pitch on the non-dimensional
entropy generation number of turbulent forced convection in a helical coiled tube are also discussed. 相似文献
17.
Philip Schaefer Markus Gampert Jens Henrik Goebbert Lipo Wang Norbert Peters 《Flow, Turbulence and Combustion》2010,85(2):225-243
Direct Numerical Simulations (DNS) of Kolmogorov flows are performed at three different Reynolds numbers Re
λ
between 110 and 190 by imposing a mean velocity profile in y-direction of the form U(y) = F sin(y) in a periodic box of volume (2π)3. After a few integral times the turbulent flow turns out to be statistically steady. Profiles of mean quantities are then
obtained by averaging over planes at constant y. Based on these profiles two different model equations for the mean dissipation
ε in the context of two-equation RANS (Reynolds Averaged Navier–Stokes) modelling of turbulence are compared to each other.
The high Reynolds number version of the k-ε-model (Jones and Launder, Int J Heat Mass Transfer 15:301–314, 1972), to be called the standard model and a new model by Menter et al. (2006), to be called the Menter–Egorov model, are tested against the DNS results. Both models are solved numerically and it is
found that the standard model does not provide a steady solution for the present case, while the Menter–Egorov model does.
In addition a fairly good quantitative agreement of the model solution and the DNS data is found for the averaged profiles
of the kinetic energy k and the dissipation ε. Furthermore, an analysis based on flow-inherent geometries, called dissipation elements (Wang and Peters, J Fluid Mech 608:113–138,
2008), is used to examine the Menter–Egorov ε model equation. An expression for the evolution of ε is derived by taking appropriate moments of the equation for the evolution of the probability density function (pdf) of the
length of dissipation elements. A term-by-term comparison with the model equation allows a prediction of the constants, which
with increasing Reynolds number approach the empirical values. 相似文献
18.
The flow initiated by a hot gas cloud (thermal) in a stratified atmosphere is calculated on the basis of theκ-ε turbulence model and the transport model for the Reynolds stresses and turbulent fluxes and the results obtained are compared
The nonlocal nature of the turbulent transport in a vortex ring and its effect on certain flow characteristics are explained
In particular, the calculations carried out using the Reynolds stress model show much slower cooling of the temperature-vortex
torus than those based calculated on theκ-ε-model Modification of theκ-ε-model to take the effect of curvature of the streamlines approximately into account makes it only partially possible to reproduce
the results obtained on the basis of the Reynolds stress model
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 12–20, January–February,
1999.
The research was carried out with support from the Russian Foundation for Basic Research (project No. 95-01-00544a). 相似文献
19.
The results of a systematic experimental study of the flow turbulence level effect on the heat transfer and Reynolds analogy
coefficients over a wide range of the relevant parameters (the turbulence intensity and scale and the Reynolds number) are
presented. The notion of the equivalent flow turbulence, which unifies the above-mentioned parameters, is introduced. It is
established that the skin friction and heat transfer coefficients increase with the equivalent turbulence, while the Reynolds
analogy coefficient remains unchanged.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 61–71, January–February,
2000. 相似文献
20.
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