共查询到20条相似文献,搜索用时 31 毫秒
1.
Tong-Bou Chang Wen-Yu Yeh Go-Long Tsai 《Journal of Mechanical Science and Technology》2009,23(12):3399-3406
This study performs a theoretical investigation into the problem of two-dimensional steady filmwise condensation flow on a
horizontal tube with suction effects at the tube surface. An effective suction function is introduced to model the effect
of the wall suction on the thickness of the liquid condensate film. The local condensate film thickness and the local Nusselt
number are then derived using a simple series numerical method. The results show that the Nusselt number varies as a function
of the Jakob number Ja, the Rayleigh number Ra, and the suction parameter Sw. It is found that the wall suction effect has a significant influence on the heat transfer performance. An analytical solution
is derived for the mean Nusselt number for the case in which the wall suction effect is ignored. Finally, a closed-form correlation
is presented for the mean Nusselt number subject to a wall suction effect. 相似文献
2.
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
3.
Shuang-Ying Wu Su-Jun Chen Lan Xiao You-Rong Li 《Journal of Mechanical Science and Technology》2011,25(6):1439-1447
In this study, numerical investigations are conducted for forced convective heat transfer in an annular helicoidal tube under
uniform wall temperature condition for laminar flow including developing region. The numerical computations reveal the developments
and distributions of heat transfer and flow fields in the annular helicoidal tube when the outer tube wall is heated and the
inner tube wall is insulated. The effects of Reynolds number, curvature ratio, and coil pitch on the circumferential average
friction factor and Nusselt number at different axial locations, and the non-dimensional entropy generation number of laminar
convection in an annular helicoidal tube are investigated. In addition, the differences of flow and heat transfer characteristics
between the annular helicoidal tube and circular helicoidal tube are also described. 相似文献
4.
Aminreza Noghrehabadi Mohammad Reza Saffarian Rashid Pourrajab Mohammad Ghalambaz 《Journal of Mechanical Science and Technology》2013,27(3):927-937
The boundary layer heat transfer and entropy generation of a nanofluid over an isothermal linear stretching sheet with heat generation/ absorption have been analyzed. In the nanofluid model, the development of nanoparticles concentration gradient due to slip mechanisms, the effects of Brownian motion and thermophoresis, is taken into account. The dependency of the local Nusselt number and entropy generation number on the non-dimensional parameters is numerically investigated. The results show that the increase of heat generation parameter, Brownian motion parameter, or thermophoresis parameter decreases the entropy generation number in the vicinity of the sheet. 相似文献
5.
为了探究带有方形肋及双倾斜肋片细通道的流动换热及熵产特性,设计了2种带有方形肋及双倾斜肋片的组合细通道(MCDS-L, MCDS-R),然后采用数值模拟的方法分析其流动特性、传热特性和熵产特性,并将其分析结果同2种方形肋细通道(MCS-L, MCS-R)和一种双倾斜肋片细通道(MCD)进行对比。结果表明,在所研究的雷诺数范围内,组合通道的摩擦阻力系数基本一致且均高于其他3组通道(MCS-L, MCS-R, MCD) 。此外,组合通道的努塞尔数均高于其他3组通道,而熵产增大数均低于其他3组通道。其中,MCDS-L通道的努塞尔数最大,熵产增大数最低。表明MCDS-L通道的换热效果最佳,能量的综合利用程度最高。研究成果为微细通道热沉的设计提供参考。 相似文献
6.
Jin Gi Paeng Kyung Hwan Kim Young Hwan Yoon 《Journal of Mechanical Science and Technology》2009,23(2):536-543
The air-side forced convective heat transfer of a plate fin-tube heat exchanger is investigated by experimental measurement
and numerical computation. The heat exchanger consists of a staggered arrangement of refrigerant pipes with a diameter of
10.2 mm and a fin pitch of 3.5 mm. In the experimental study, the forced convective heat transfer was measured at Reynolds
numbers of 1082, 1397, 1486, 1591 and 1649 based on the diameter of the refrigerant piping and on the maximum velocity. The
average Nusselt number for the convective heat transfer coefficient was also computed for the same Reynolds number by using
the commercial software STAR-CD with the standard k - ɛ turbulent model. It was found that the relative errors of the average Nusselt numbers between the experimental and numerical
data were less than 6 percent in a Reynolds number range of 1082∼1649. The errors between the experiment and other correlations
from literature ranged from 7% to 32.4%. However, the literature correlation of Kim et al. is closest to the experimental
data within a relative error of 7%.
This paper was recommended for publication in revised form by Associate Editor Man-Yeong Ha
Jin-Gi Paeng recieved a bachelor’s degree in Aero Mechanical Engineering from Gyeong-sang National University in 2000. He then went on
to recieve his M.S. degrees from Changwon National University in 2004. Currently, he completed the doc-tor’s course and a
doctoral dissertation in 2007 and 2008, respectively. He will take a doctorate in 2008. 相似文献
7.
Entropy analysis of flow and heat transfer caused by a moving plate with thermal radiation 总被引:2,自引:0,他引:2
This study examines the effects of thermal radiation on entropy generation in flow and heat transfer caused by a moving plate. The equations that govern the flow and heat transfer phenomenon are solved numerically. Velocity and temperature profiles are obtained for the parameters involved in the problem. The expressions for the entropy generation number and the Bejan number are obtained based on the profiles. Graphs for velocity, temperature, the entropy generation number, and the Bejan number are plotted and discussed qualitatively. 相似文献
8.
Kwang Hoon Park Kang Mo Yang Keon Woo Lee Hyung Hee Cho Hee Chul Ham Ki Young Hwang 《Journal of Mechanical Science and Technology》2009,23(7):1852-1857
A slot film cooling technique has been used to protect a combustor liner from hot combustion gas. This method has been developed
for gas turbine combustors. A ramjet combustor exposed to high temperature can be protected properly with a multi-slot film
cooling method. An experimental study has been conducted to investigate the change of the first slot angle under recirculation
flow and the influence of wiggle strip within a slot, which affects the film cooling effectiveness. The first slot angle has
been changed to understand the effect of the injection angle on the film cooling effectiveness in a recirculation zone. The
distribution of dimensionless temperature was obtained by a thermocouple rake to investigate the wiggle strip effect, and
the adiabatic film cooling effectiveness on downstream wall was measured by a thermochromic liquid crystal (TLC) method. At
the first slot position, the film cooling effectiveness decreases significantly because of the effects of recirculation flow.
The lip angle of the first slot affects slightly on the film cooling effectiveness. The wiggle strip reinforces the structure
of slot and keeps the uniform open area of slot. However, it induces three dimensional flows and enhances the flow mixing
between the main flow and the injected slot flow. Therefore, the wiggle strip decreases slightly the overall film cooling
effectiveness.
This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008.
Kwanghoon Park received his M.S degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 2007. He is currently working for
an education of an officer as a drillmaster in Army Consolidated Logistics School.
Kang Mo Yang joined the Republic of Korea Army in 2004. He is currently working towards the M.S. degree at the Department of Mechanical
Engineering, Yonsei University.
Keon Woo Lee received his M.S. degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 2008. In 2008, he joined the Doosan
heavy industries & Construction Co, LTD, where he is a member of the IGCC Business Team.
Hyung Hee Cho received his PhD degree in Mechanical Engineering from University of Minnesota, Minneapolis, MN in 1992. In 1995, he joined
the Department of Mechanical Engineering, Yonsei University, Seoul, Korea, where he is currently a full professor in the School
of Mechanical Engineering. His research interests include heat transfer in turbomachineries, rocket/ramjet cooling as well
as nanoscale heat transfer in thin films, and microfabricated thermal sensors.
Hee Cheol Ham received his PhD degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 2001. In 1984, he joined the Agency
for Defense Development, Daejeon, Korea, where he is currently a Principal Researcher.
Ki Young Hwang received his Ph.D. degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 1994. In 1979, he joined the
Agency for Defense Development, Daejon, Korea, where he is currently a principal researcher in the Airbreathing Propulsion
Directorate. 相似文献
9.
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
10.
11.
The combined effect of free and forced convection on the flow of an elasto-viscous liquid between two porous parallel plates with suction and injection at the walls has been studied. The effect of dimensionless numbers such as the elastic number Rc, the cross flow Reynolds number R, the Grashof number G, the Prandtl number Pr, the Brinkman number K and the wall temperature parameter N on the velocity and temperature fields, shear stresses and the rates of heat transfer at the walls have been studied. 相似文献
12.
13.
Qing-Yang Zhao Heeyoon Chung Seok Min Choi Hyung Hee Cho 《Journal of Mechanical Science and Technology》2016,30(2):525-531
The characteristics of fluid flow and heat transfer, which are affected by the guide wall in a jet impinged leading edge channel, have been investigated numerically using three-dimensional Reynolds-averaged Navier–Stokes analysis via the shear stress transport turbulence model and gamma theta transitional turbulence model. A constant wall heat flux condition has been applied to the leading edge surface. The jet-to-surface distance is constant, which is three times that of the jet diameter. The arrangement of the guide wall near the jet hole is set as a variable. Results presented in this study include the Nusselt number contour, velocity vector, streamline with velocity, and local Nusselt number distribution along the central line on the leading edge surface. The average Nusselt number and average pressure loss between jet nozzle and channel exit are calculated to assess the thermal performance. The application of the guide wall is aimed at improving heat transfer uniformity on the leading edge surface. Results indicated that the streamwise guide wall ensures the vertical jet impingement flow intensity and prevents the flow after impingement to reflux into jet flow. Thus, a combined rectangular guide wall benefits the average heat transfer, thermal performance and heat transfer distribution uniformity. 相似文献
14.
Haydar Kucuk 《Journal of Mechanical Science and Technology》2010,24(9):1927-1937
The entropy generation has been numerically investigated in concentric curved annular square ducts under constant wall temperature
boundary condition. The problem has been assumed to be steady, hydrodynamically and thermally fully developed and incompressible
laminar flow with constant physical properties. The solutions of discretized equations for continuity, momentum and energy
have been obtained by using an elliptic Fortran Program based on the SIMPLE algorithm. Solutions have been achieved for i)
Dean numbers ranging from 3.6 to 207.1, ii) Annulus dimension ratios of 5.5, 3.8, 2.9 and 2.36, and iii) Prandtl number of
0.7. In this regard, local entropy generation as well as overall entropy generation in the whole flow field has been analyzed
in detail. Moreover, the effects of Dean number and annulus dimension ratio on entropy generation arising from the friction
and heat transfer have been investigated. Accordingly, it is concluded that the effect of volumetric entropy generation that
is a result of fluid frictional irreversibility can be neglected as compared with volumetric entropy generation due to heat
transfer irreversibility. As Dean number increases, the distribution of volumetric entropy generation coming out from the
heat transfer irreversibility is formed by the temperature field, which is depending on the curvature. 相似文献
15.
Film absorption involves simultaneous heat and mass transfer in the gas-liquid system. While the non-absorbable gas does not
participate directly in the absorption process, its presence does affect the overall heat and mass transfer. An experimental
study was performed to investigate the heat and mass transfer characteristics of LiBr-H2O solution flowing over 6-row horizontal tubes with the water vapor absorption in the presence of non-absorbable gases. The
volumetric concentration of non-absorbable gas. air, was varied from 0.17 to 10.0%. The combined effects of the solution flow
rate and its concentration on the heat and mass transfer coefficients were also examined. The presence of 2% volumetric concentration
of air resulted in a 25% reduction in the Nusselt number and 41% reduction in the Sherwood number. Optimum film Reynolds number
was found to exist at which the heat and mass transfer reach their maximum value independent of air contents. Reduced Nusselt
and Sherwood numbers, defined as the ratio of Nusselt and Sherwood numbers at given non-absorbable gas content to that with
pure water vapor, were correlated to account for the reduction in the heat and mass transfer due to non-absorbable gases in
a falling film absorption process. 相似文献
16.
Young-Deuk Kim Deok-Hong Kang Woo-Seung Kim 《Journal of Mechanical Science and Technology》2009,23(3):631-642
Experimental and numerical studies were performed by considering convective and radiative heat transfer to predict the transient
thermal behavior of a plate in an indirectly fired continuous heat treatment furnace. The temperature profiles in the plate
were determined by solving the transient one-dimensional heat conduction equation in conjunction with appropriate boundary
conditions by using a time marching scheme. The results obtained from the transient analysis were substantiated by comparing
with experimental results. Additionally, parametric investigations were performed to examine how the thermal behavior of the
plate is affected by plate and refractory emissivities, charging temperature and residence time of the plate, gas temperature
of the work and drive sides of the heat treatment furnace, and plate thickness.
This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon
Young-Deuk Kim is a graduate student at Hanyang University in Seoul, Korea. He earned his B.S. in Mechanical Engineering from Korea Maritime
University in 2002 and his M.S. in mechanical engineering from Hanyang university in 2004. His current research areas are
modeling of automotive aftertreatment catalysts, optimal design of thermal systems, and phase change modeling with free surface
flow.
Deok-Hong Kang is a senior researcher at the RIST (Research Institute of Industrial Science and Technology) in Pohang, Korea. He earned
his B.S. and M.S. in mechanical engineering from Hanyang University in 1989 and 1993, respectively, and his Ph.D. in mechanical
engineering from POSTECH in 2004. His current research areas are mathematical modeling for combustion control, furnace optimization
control system, and energy saving engineering in all kinds of furnaces.
Woo-Seung Kim is a professor in mechanical engineering at Hanyang University in Ansan, Korea. He earned his B.S. in Mechanical Engineering
in 1981 from Hanyang University and his M.S. and Ph.D. in mechanical engineering from North Carolina State University in 1986
and 1989, respectively. His current research areas are modeling of automotive aftertreatment systems, inverse heat transfer
problems, optimal design of thermal systems, and phase change heat transfer problems with free surface flow. 相似文献
17.
开展烧结开孔金属泡沫壁在大空间条件下的辐射和自然对流耦合换热试验研究,研究壁面倾角、瑞利数Ra*、泡沫厚度对换热性能的影响。试验所得竖直光铜板的结果与文献结果符合一致,验证了试验方案的有效性。试验结果表明:在一定的加热功率下,随着倾角的增加,纯自然对流努塞尔数和复合努塞尔数先增加后减小,在倾角为60o~80o达到极大值,且辐射换热量占总换热量的33%~44%;竖直放置时,烧结泡沫壁的辐射换热量占总换热量的比值小于光壁,且该值随泡沫厚度增加而增加。与光壁相比,烧结泡沫竖壁复合换热的平均努塞尔数和纯自然对流换热的平均努塞尔数分别提高了1.52~1.98倍和1.16~1.66倍。通过对红外相机拍摄的泡沫表面温度分布进行分析验证了基于泡沫表面平均温度的辐射换热量计算模型的有效性。 相似文献
18.
Effect of variable viscosity on thermal boundary layer over a permeable flat plate with radiation and a convective surface boundary condition 总被引:2,自引:0,他引:2
Oluwole Daniel Makinde 《Journal of Mechanical Science and Technology》2012,26(5):1615-1622
In this paper, the combined effects of radiation, temperature dependent viscosity, suction and injection on thermal boundary layer over a permeable flat plate with a convective heat exchange at the surface are investigated. By taking suitable similarity variables, the governing boundary layer equations are transformed into a boundary value problem of coupled nonlinear ordinary differential equations and solved numerically using the shooting technique with sixth-order Runge-Kutta integration scheme. The solutions for the velocity and temperature distributions together with the skin friction coefficient and Nusselt number depend on six parameters; Prandtl number Pr, Brinkmann number Br, the radiation parameter Ra, the viscosity variation parameter a, suction/injection parameter f w and convection Biot number Bi. Numerical results are presented both in tabular and graphical forms illustrating the effects of these parameters on thermal boundary layer. The thermal boundary layer thickens with a rise in the local temperature as the viscous dissipation, wall injection, and convective heating each intensifies, but decreases with increasing suction and thermal radiation. For fixed Pr, Ra, Br and Bi, both the skin friction coefficient and the Nusselt number increase with a decrease in fluid viscosity and an increase in suction. A comparison with previously published results on special case of the problem shows excellent agreement. 相似文献
19.
The high-precision measure instrument for flow velocity is essential for industrial applications because the high-precision velocity can well reflect the physical characteristic of the flow. A restricted laminar Couette flow with cylindrical baffles, using a synthetic heat conduction liquid, was designed to obtain a steady vortex flow and wider work scope, according to Couette flow and Suspension flow characteristics. The heat transfer mechanism was investigated with a laminar flow model by the Fourier law. The research indicates that the heat transfer enhancement is related to the Temperature Boundary Layer (TBL). The TBL is affected by the Velocity Boundary Layer (VBL). The TBL thickness and Nusselt number (Nu) have a dependent relationship. The Reynolds number (Re) and the gap between the baffle and plate wall (Δh/h) can further affect Nu. The vortex flow generated by Couette flow can significantly enhance the heat transfer performance by a double spiral structure, which can rapidly mix heat fluxes and make the temperature converge to uniform. There is a sensitive and stable relationship between flow velocity and heat transfer. Notably, it is linear when Δh/h or Re is small, which can be used to design a high-precision thermal flow velocity meter. 相似文献