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1.
Natural convection heat transfer estimation from a longitudinally finned vertical pipe using CFD 总被引:1,自引:0,他引:1
Hyo Min Jeong Yong Hun Lee Myoung Kuk Ji Kang Youl Bae Han Shik Chung 《Journal of Mechanical Science and Technology》2009,23(6):1517-1527
In this study, CFD analysis of air-heating vaporizers was conducted. A longitudinally finned vertical pipe was used to represent
the air-heating vaporizer in the CFD model. Nitrogen gas was used as the working fluid inside the vertical pipe, and it was
made to flow upward. Ambient air, which was the heat source, was assumed to contain no water vapor. To validate the CFD results,
the convective heat transfer coefficients inside the pipe, hi-c, derived from the CFD results were first compared with the heat transfer coefficients inside the pipe, hi-p, which were derived from the Perkins correlation. Second, the convection heat transfer coefficients outside the pipe, ho-c, derived from the CFD results were compared with the convection heat transfer coefficients, ho-a, which were derived from an analytical solution of the energy equation. Third, the CFD results of both the ambient-air flow
pattern and temperature were observed to determine whether they were their reasonability. It was found that all validations
showed good results. Subsequently, the heat transfer coefficients for natural convection outside the pipe, ho-c, were used to determine the Nusselt number outside the pipe, Nuo.. This was then correlated with the Rayleigh number, Ra. The results show that Ra and Nuo have a proportional relationship in the range of 2.7414×1012 ≤ Ra ≤ 2.8263×1013. Based on this result, a relation for the Nusselt number outside the pipe, Nuo, was proposed.
This paper was recommended for publication in revised form by Associate Editor Man Yeong Ha
Hyomin Jeong is currently a professor of Mechanical and Precision Engineering at Gyeongsang Nation University. He received his ph.D. in
mechanical engineering from the University of Tokyo in 1992 and he joined Arizona State University as a visiting professor
from 2008 to 2009. His research interests are in fluid engineering, CFD, cryogenic system, cascade refrigeration system and
ejector system, mechanical vapor compression
Hanshik Chung is a professor of Mechanical and Precision Engineering at Gyeongsang National University. He obtianed his Ph.D. in Mechanical
Engineering from Donga University. He joined Changwon Master’s College and Tongyeong Fisher National College as an assistant
Professor in 1988 and 1993, respectively. His research fields extend into the thermal engineering, heat transfer, solar heating
& cooling system, LNG vaporizer optimum, solar cell, hydrogen compressor for fuel cell and making fresh water system from
sea water 相似文献
2.
M. M. Khabibullin M. P. Grigor’ev A. P. Ivashkin Yu. G. Kudenko O. V. Mineev A. N. Khotyantsev 《Instruments and Experimental Techniques》2000,43(5):589-596
The CsI(Tl) calorimeter was calibrated in the KEK-E246 experiment withK
μ2-andK
π2-positivekaon decays. The following calorimeter parameters were obtained: an energy resolution (σ) of 4.1% forE=242.5 MeV, a π0 invariant-mass resolution (σ) of 5.6%, and an angular resolution (σ) of 3.1o. 相似文献
3.
Reliability assessment and prediction of a fatigue design criterion for the gas-welded joints 总被引:1,自引:0,他引:1
Gas metal arc welding is a very important and useful technology in the fabrication of railroad cars and commercial vehicle
structures. However, since the fatigue strength of the joints welded by gas metal arc welding is considerably lower than that
of the parent material due to stress concentration and metallurgical changes at the weld, the fatigue-strength assessment
of welded joints is very important for the reliability and durability of railroad cars and the establishment of a criterion
for long-life fatigue design. In this paper, in order to save time and cost for the fatigue design, an accelerated life-prediction
method that is based on the theory of statistical reliability was investigated. Its usefulness was verified by comparing the
(Δσa)R-Nf relationship that was obtained from actual fatigue test results with the (Δσa)R-(Nf)ALP relationship that was derived from accelerated life testing. And the reliability of the predicted life was evaluated. The
reliability of the accelerated life-prediction on the base of actual test data was analyzed to be 80% for the plug-type gas-welded
joints and 95% for the ring-type gas-welded joints. 相似文献
4.
Strain and Stress Fields During Scratch Tests on Amorphous Polymers: Influence of the Local Friction
In this paper, we present results deduced from three-dimensional finite element simulations of scratching, with spherical
indenter geometry at different imposed ratios, a/R in the range of 0.1–0.9. For each simulated ratio a/R, the local friction has been increased from 0 to 1. The paper aims at studying the tangential scratch behaviour of homogeneous
polymeric substrates, considered in first approximation as elastic linear-hardening plastic material. For only elastic–plastic
contacts, without any strain rate or temperature effects, it focuses on studying some characteristic response due to spherical
scratching process as a function of scratching conditions (a/R, μ
loc
) such as the stress and plastic strain fields, including the plastic zone dimension and the definition of an volume average
plastic strain. 相似文献
5.
Based on the Darcy fluid model, by considering the effects of viscous dissipation due to the interaction between solid skeleton
and pore fluid flow and thermal conduction in the direction of the fluid flow, the thermally developing forced convection
of the local thermal equilibrium and the corresponding thermal stresses in a semi-infinite saturated porous plate channel
are investigated in this paper. The expressions of temperature, local Nusselt number and corresponding thermal stresses are
obtained by means of the Fourier series, and the distributions of the same are also shown. Furthermore, influences of the
Péclet number (Pe) and Brinkman number (Br) on temperature, Nusselt number (Nu) and thermal stress are revealed numerically.
__________
Translated from Journal of Lanzhou University (Natural Science Edition), 2006, 42(2): 114–119 [译自: 兰州大学学报(自然科学版)] 相似文献
6.
Dong-Ho Min Kyung-Beom Yoon Hee-Chul Chang Tae-Kuk Kim 《Journal of Mechanical Science and Technology》2008,22(7):1436-1443
The purpose of this research is to study numerically the turbulent gas-particle two-phase flow characteristics using the Eulerian-Eulerian
method. A computer code is developed for the numerical study by using the k-ɛ-k
p
two-phase turbulent model. The developed code is applied for particle-laden flows in which the particle volume fraction is
between 10−5 and 10−2 for the Stokes numbers smaller than unity. The gas and particle velocities and the particle volume fraction obtained by using
this code are in good agreement with those obtained by a commercial code for the gas-particle jet flows within a rectangular
enclosure. The gas-particle jet injected into a vertical rectangular 3D enclosure is numerically modeled to study the effect
of the Stokes number, the particle volume fraction and the particle Reynolds numbers. The numerical results show that the
Stokes number and the particle volume fraction are important parameters in turbulent gas-particle flows. A small Stokes number
(St ≤ 0.07) implies that the particles are nearly at the velocity equilibrium with the gas phase, while a large Stokes number
(St ≥ 0.07) implies that the slip velocity between the gas and particle phase increases and the particle velocity is less affected
by the gas phase. A large particle volume fraction (α
p
≥ 0.0001) implies that the effect of the particles on the gas phase momentum increases, while a small particle volume fraction
(α
p
≤ 0.0001) implies that the particles would have no or small effect on the gas flow field. For fixed Stokes number and particle
volume fraction, an increase of the particle Reynolds number results in a decrease of the slip velocity between the gas and
particle velocities. 相似文献
7.
Deformation by 111-pencil glide has been analyzed by an upper-bound model which combines a least-shear analysis and Piehler's maximum virtual work analysis. The least-shear analysis gives exact solutions if three 111 slip systems are active, while the maximum work analysis provides solutions for the case of four active slip systems. Independent checks are used to determine which solution method is appropriate.Computer calculations using this model have been made to determine; (1) the orientation dependence of the Taylor factor for axisymmetric deformation; (2) the yield loci for textured materials having [100], [110] and [111] sheet metals and rotational symmetry; (3) the isotropic yield locus for randomly oriented materials; and (4) flow stresses along critical loading paths for various assumed textures with rotational symmetry. The latter calculations indicate that anisotropic yield loci of textured bcc metals with rotational symmetry are much better approximated by σxa + σya + R¦σx − σy¦a = (R + 1)Ya where R is the strain ratio and Y is the tensile yield strength with an exponent a = 6 rather than with a = 2 as postulated by Hill. It is not known how well upper-bound calculations like these represent actual yielding behavior. 相似文献
8.
The evaporation heat transfer coefficienthr and frictional pressure drop δpf of refrigerant R-134a flowing in the oblong shell and plate heat exchanger were investigated experimentally in this study.
Four vertical counterflow channels were formed in the oblong shell and plate heat exchanger by four plates of geometry with
a corrugated sinusoid shape of a 45° chevron angle. Upflow of refrigerant R-134a boils in two channels receiving heat from
downflow of hot water in other channels. The effects of the refrigerant mass flux, average heat flux, refrigerant saturation
temperature and vapor quality of R- 134a were explored in detail. Similar to the case of a plate heat exchanger, even at a
very low Reynolds number, the flow in the oblong shell and plate heat exchanger remains turbulent. The results indicate that
the evaporation heat transfer coefficienthr and pressure drop Δpf increase with the vapor quality. A rise in the refrigerant mass flux causes an increase in theh
r
and Δpf. But the effect of the average heat flux does not show significant effect on the hr and Δpf. Finally, at a higher saturation temperature, both theh
r
and Δpf are found to be lower. The empirical correlations are also provided for the measured heat transfer coefficient and pressure
drop in terms of the Nusselt number and friction factor. 相似文献
9.
The current-voltage characteristic, wear resistance, and friction surface roughness of baked model copper-graphite-ShKh15
steel composites are determined. It is shown that the composites containing under 10% and above 50% Cu produce a friction
zone with low conductivity and wear resistance. The composites containing 15–20% Cu produce a friction zone with relatively
high conductivity and wear resistance. The maximum parameters of the roughness (R
a
= 2.98 μm and R
z
= 24.5 μm) appear on the friction surface of the material containing 50% Cu. 相似文献
10.
This paper addresses the fundamental flow distribution question of how to design manifolds of low Reynolds number flow with
both numerical analysis and experiments. The present study introduces new parameters of αc and αd, defined as the ratio of header diameter to header length in combining and dividing manifolds, the parameters which are not
clearly considered in the previous studies of flow distribution in manifolds. The parameters of αc and αd were found to govern the flow distribution independently of each other. varying αc, αd and the Reynolds number respectively, a correlation of optimal flow distribution is obtained for laminar fow in manifolds
as follows; αd·Re
w
m
=K where acu
c≥1/4. The proposed correlation makes predictions possible for wide ranges of αd and Rew. Also, the present numerical results show satisfactory agreements with those of flow visualization. From the flow visualization.
recirculating flow regime was observed at the inlet of each channel, in which hot spots may occur due to small velocities.
The size of recirculating flow regime is strongly dependent on the Reynolds number and is smaller for optimal cases than others. 相似文献
11.
Jin Sung Lee Tae Gyu Kim Tae Sang Park Choong Sik Kim Chan Hoon Park 《Journal of Mechanical Science and Technology》2002,16(7):966-974
An analytic approach has been employed to study condensate film thickness distribution inside cave-shaped cavity of a flat
plate heat pipe. The results indicate that the condensate film thickness largely depends on mass flow rate and local velocity
of condensate. The increasing rate of condensate film for circular region reveals about 50% higher value than that of vertical
region. The physical properties of working fluid affect significantly the condensate film thickness, such as the condensate
film thickness for the case of FC-40 are 5 times larger than that of water. In comparison with condensation on a vertical
wall, the average heat transfer coefficient in the cave-shaped cavity presented 10-15% lower values due to the fact that the
average film thickness formed inside the cave-shaped cavity was larger than that of the vertical wall with an equivalent flow
length. A correlation formula which is based on the condensate film analysis for the cave-shaped cavity to predict average
heat transfer coefficient is presented. Also, the critical minimum fill charge ratio of working fluid based on condensate
film analysis has been predicted, and the minimum fill charge ratios for FC-40 and water are about Ψcrit= 3-7%, Ψcrit=0.5-1.3%, respectively, in the range of heat fluxq” = 5-90kW/2 相似文献
12.
The characteristics of the two-phase flow heat transfer of R-134a in microtubes with inner diameters of 430 μm and 792 μm
were experimentally investigated. The effect of the heat flux on the heat transfer coefficient for microtubes was significant
before the transition quality. The boiling number expressed the interrelation between the heat flux and the mass about the
heat transfer coefficients. The smaller microtube had greater heat transfer coefficients; the average heat transfer coefficient
for the tube A (D
i
= 430 μm) was 47.0% greater than that for the tube B (D
i
= 792 μm) at G = 370 kg/m2·s and q″ = 20 kW·m2. A new correlation for the evaporative heat transfer coefficients in microtubes was developed by considering the following
factors: the laminar flow heat transfer coefficient of liquid-phase flow, the enhancement factor of the convective heat transfer,
and the nucleate boiling correction factor. The correlation developed in present study predicted the experimental heat transfer
coefficients within an absolute average deviation of 8.4%. 相似文献
13.
By depicting the transfer of heat and combustion reaction to take place within thin gas layers close to the propellant surface burning in a steady-state fashion, a mathematical equation has been deduced to describe the burning rate of solid propellant as a function of initial grain temperature and chamber pressure. It has been also assumed that chemical reaction could take place in premixing-diffusing zone but were carried out mainly in the reaction-flame zone. All these phenomena taken place in each zone of combustion have been assumed to be steady-state. In the present investigation, the equation, γ=k·(1/R(T i +C))n. exp (-E a/R(T i +C)(P/z) is being presented and it is compared with experimental data. The proposed model has been tested and evaluated vis-a-vis strand burner data for three different propellants based on CTPB, and it has been found that the deviation of the computed burning rates from the measured rates ranged up to 2%. 相似文献
14.
Two random profile precision roughness calibration specimens with Ra = 0.028 and 0.043 μm are compared with their electroformed replicas. Measurements of surface texture and roughness parameter values show very good agreement. Fluctuations in the Ra values across the replicas track those across the masters to within 1.8 nm. However, the form errors of the replicas, approximately 0.6 μm over a 3.2 × 2.6 mm2 area, are much bigger than those of the masters, and their hardness (HV = 243) is not as good as the master specimens' (HV = 852). 相似文献
15.
Young Don Choi Jong Keun Shin Kun Ho Chun 《Journal of Mechanical Science and Technology》2001,15(3):392-402
The paper reports a multiple source modeling of low-Reynolds-number dissipation rate equation with aids of DNS data. The key features of the model are to satisfy the wall limiting conditions of the individual source terms in the exact dissipation rate equation using the wall damping functions. The wall damping functions are formulated in term of dimensionless dissipation length scalel D +(≡l D (νε)1/4/ν) and the invariants of small and large scale turbulence anisotropy tensors,aij ( = [`(ui uj )] /k - 2dij /3)a_{ij} ( = \overline {u_i u_j } /k - 2\delta _{ij} /3) ande ij (=ε ij /ε-2δ ij /3). The model constants are optimized with aids of DNS data in a plane channel flow. Adopting the dissipation length scale as a parameter of damping function, the applicabilities ofk-ε model are extended to the turbulent flow calculation of complex flow passages. 相似文献
16.
An AZ31 magnesium alloy was tested at constant temperatures ranging from 423 to 473 K (0.46 to 0.51T
m
) under constant stresses. All of the creep curves exhibited two types depending on stress levels. At low stress (σ/G<4×10−3), the creep curve was typical of class A (Alloy type) behavior. However, at high stresses (σ/G>4×10−3), the creep curve was typical of class M (Metal type) behavior. At low stress level, the stress exponent for the steady-state
creep rate was of 3.5 and the true activation energy for creep was 101 kJ/mole which is close to that for solute diffusion.
It indicates that the dominant deformation mechanism was glide-controlled dislocation creep. At low stress level wheren=3.5, the present results are in good agreement with the prediction of Fridel model. 相似文献
17.
The radiation driven response function (R q ) for AP and HMX propellant was obtained and compared with experimental results by using a simple αβγ flame model rather than with detailed chemistry. For an AP propellant, the profile of heat release was assumed by the experimental data. The calculatedR q shows a frequency shift of the peak amplitude to the higher frequency and a decrease in the maximum amplitude as radiation increases. In addition, it was found the increase in the total flux could enhance the mean burning rate[`(r)]b\bar r_b while the phase differences between the radiation and resulting conduction could consequently reduce the fluctuation amplitude Δy b . Fortunately, this is the qualitative duplication of the behavior recently observed in the experiments of RDX propellants. For HMX, the response functionR q has been calculated and showed a quite good agreement with the experimental data. Even though the fairly good agreement ofR q with experimental ones, the unsteady behavior of HMX was not reproduced as the radiation input increased. This is due to lack of the material properties of HMX or the physical understanding of HMX burning at high pressure. 相似文献
18.
The flow structures, drag coefficients (C
d
) and vortex shedding characteristics around a single square cylinder and twin side-by-side square cylinders were experimentally
investigated with various Reynolds numbers (Re) and gap ratios (g*) in a vertical water tunnel. The Reynolds number (Re) and gap ratio (g*) were 178 < Re < 892 and 0 ≤ g* ≤ 2.5, respectively. The flow patterns and vortex shedding frequency were determined using the particle tracking flow visualization
(PTFV). The flow structures, velocity properties, and drag coefficients were calculated using the particle image velocimetry
(PIV). The topological flow patterns of vortex evolution processes were plotted and analyzed based on critical point theory.
Furthermore, the flow structures behind twin side-by-side square cylinders were classified into three modes — single vortex-street mode, gap-flow mode and couple vortex-streets mode. The maximum C
d
occurred in the single vortex-street mode, and the minimum C
d
occurred in the gap-flow mode. The highest Strouhal number (St) occurred in the single vortex-street mode, and the lowest St occurred in the gap-flow mode. 相似文献
19.
The leak-before-break (LBB) behaviors of a structural component under high and low fatigue loads are an important problem in nuclear power plants, liquid nitrogen gas tankers and chemical plants. This paper is an experimental study to evaluate the crack opening behavior after penetration for plate and pipe specimens. Crack opening displacement after penetration under low fatigue load could be satisfactorily determined at the center of the plate thickness regardless of the specimen size. In the case of high fatigue load, it is shown that the crack opening displacement at the center of a penetrated crack can be derived using the gross stress,σ C , and the front surface crack length, a s , together with the back surface crack length, a b . 相似文献
20.
The modified hydrodynamic theory of penetration is extended to take account of the transient, plastic-wave dominated and after-flow phases of penetration. It is also indicated how a more detailed flow field model of the primary phase of penetration leads to the modified Bernoulli equation and a relationship between the dynamic yield strength and the strength factors Rt and Yp. The effect of the decelerative motion on the modified Bernoulli equation is also briefly examined. Finally, the theory is compared with experimental results of previous papers. 相似文献