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1.
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
2.
Numerical analysis was performed for the two-dimensional turbulent natural convection in an inclined enclosure. The enclosure
has two walls which one is heated and the other cooled, and has the other two walls of the linear temperature distributions.
The inclined angle is equal to zero when the wall of linear temperature was horizontal and increases counter-clockwise. The
mean continuity, mean momentum and mean energy equations have been obtained by using the conventional time-averaging procesure.
The turbulent model has been applied ak-ε two equation model of turbulence similar to the one proposed by the Launder and Spalding. Numerical results were studied
for a series of inclined angle, ranging from 0° to 60° and for a Grashof number range of 6×106∼108. The average heat transfer rate on hot wall is shown maximum value at 30° regardless of Grashof number taken here. When Gr≥5×107 and θ≥45°, the flow region of whole enclosure became a significant turbulence.
This paper was presented at the International Symposium on the Refined Flow Modeling and Turbulent Measurement. Iowa City,
Iowa, U.S.A., 1985 相似文献
3.
4.
Shuang-Ying Wu Ying-Ying Wu Lan Xiao 《Journal of Mechanical Science and Technology》2014,28(8):3353-3360
The effect of thermal radiation on convection heat transfer in flat-box type cooling channel of photovoltaic thermal system with tilt angle of 30 degree was studied by 3D numerical simulation under constant heat flux boundary condition. The temperature contours and velocity fields of fluid near the outlet were obtained. The variations of wall temperature and convection Nusselt number along flow direction for all the separate walls composing the cooling channel were compared and analyzed. The results show that due to thermal radiation, the deflection of the maximum velocity region to heated top wall, together with the asymmetry of temperature field is weakened. For natural convection, radiation promotes the formation of multi-vortices. For mixed convection, heat transfer on all the cooling channel walls is enhanced under the condition of lower heat flux while heat transfer on heated top wall is deteriorated when the heat flux is relative high. Also, pressure re-rising is promoted by thermal radiation. 相似文献
5.
J. Lee P. Kandaswamy M. Bhuvaneswari S. Sivasankaran 《Journal of Mechanical Science and Technology》2008,22(9):1779-1784
Natural convection heat transfer fluid flow past an inclined plate embedded in a fluid-saturated porous medium is investigated
by Lie group analysis. The governing partial differential equations are reduced to a system of ordinary differential equations
by the scaling symmetries. From numerical results, it is found that the thermal and momentum boundary layer thicknesses are
increased as the radiation parameter is increased. Also, it is observed that the velocity is increased and the temperature
is decreased for increasing the buoyancy parameter and the porosity parameter. 相似文献
6.
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
7.
Numerical modeling is carried out to investigate forced convective heat transfer to nearcritical water in developing laminar
flow through a circular tube. Due to large variations of thermo-physical properties such as density, specific heat, viscosity,
and thermal conductivity near thermodynamic critical point, heat transfer characteristics show quite different behavior compared
with pure forced convection. With flow acceleration along the tube unusual behavior of heat transfer coefficient and friction
factor occurs when the fluid enthalpy passes through pseudocritical point of pressure in the tube. There is also a transition
behavior from liquid-like phase to gas-like phase in the developing region. Numerical results with constant heat flux boundary
conditions are obtained for reduced pressures from 1.09 to 1.99. Graphical results for velocity, temperature, and heat transfer
coefficient with Stanton number are presented and analyzed. 相似文献
8.
Liu Jiazeng Gao Jianmin Gao Tieyu 《Journal of Mechanical Science and Technology》2012,26(4):1291-1298
An experimental study of heat transfer characteristics of steam in a square channel (simulating a gas turbine blade cooling
passage) with two opposite surfaces roughened by 60 deg parallel ribs was performed. The ranges of key governing parameters
were: Reynolds numbers (Re) based on the channel hydraulic diameter (30000–140000), entry gauge pressure (0.2Mpa–0.5Mpa),
heat flux of heat transfer surface area (5kWm−2–20kWm−2), and steam superheat (13°C–51°C). The test channel length was 1000mm, while the rib spacing (p/e) was 10, and the ratio
of rib height (e) to hydraulic diameter (D) was 0.048. The test channel was heated by passing current through stainless steel
walls instrumented with thermocouples. The local heat transfer coefficients on the ribbed wall from the channel entrance to
the fully developed regions were measured. The semi-empirical correlation was fitted out by using the average Nusselt numbers
in the fully developed region to cover the range of Reynolds number. The correlation can be used in the design of new generation
of gas turbine blade cooled by steam. 相似文献
9.
In this paper, the evaluation of a measurement method is discussed which can determine the heat transfer coefficient in convection reflow ovens. Nowadays the reflow ovens apply forced convection heating with nozzle-matrix blower system. In these ovens the heat transfer coefficients of the heater gas streams determine mainly the efficiency of heating. A method is presented which has two steps: in the first step, the heat transfer coefficient of the heater gas streams is studied above the assembly in function of height; in the second step, the heating efficiency of the nozzle-lines is compared as a distribution of the heat transfer coefficient in the oven. The heat transfer coefficients are calculated from the heat equation of the reflow oven. It is also presented with the distributions of the heat transfer coefficient that how the contamination of the nozzles affects the heating efficiency of the reflow oven. 相似文献
10.
Namjin Kim Jaeyong Lee Taebeom Seo Chongbo Kim 《Journal of Mechanical Science and Technology》2002,16(12):1725-1732
Combined convection and radiation heat transfer in a circular tube with circumferential fins and circular disks is investigated
for various operating conditions. Using a finite volume technique for steady laminar flow, the governing equations are solved
in order to study the flow and temperature fields. TheP- 1 approximation and the weighted sum of gray gases model (WSGGM) are used for solving the radiation transport equation. The
results show that the total Nusselt number of combined convection and radiation is higher than that of pure convection. If
the temperatures of the combustion gas and the wall in a tube are high, radiation becomes dominant. Therefore, it is necessary
to evaluate the effect of radiation on the total heat transfer. Key Words: Convection, Radiation, Nongray Radiation,P- 1 Approximation, Weighted Sum of Gray Gases Model 相似文献
11.
Topological design of heat dissipating structure with forced convective heat transfer 总被引:2,自引:0,他引:2
Gil Ho Yoon 《Journal of Mechanical Science and Technology》2010,24(6):1225-1233
This paper discusses the use of the topology optimization formulation for designing a heat dissipating structure that utilizes
forced convective heat transfer. In addition to forced convection, there is also natural convection due to natural buoyancy
forces induced by local heating inside fluid. In the present study, the temperature distribution due to forced convection,
neglecting buoyancy and viscous dissipation inside fluid, was simulated and optimized. In order to analyze the heat transfer
equation with forced convective heat loss and the Navier-Stokes equation, a common sequential computational procedure for
this thermo/hydraulic characteristic was implemented. For topology optimization, four material properties were interpolated
with respect to spatially defined density design variables: the inverse permeability in the Navier-Stokes equation, the conductivity,
density, and the specific heat capacity of the heat transfer equation. From numerical examples, it was found that the balance
between the conduction and convection of fluid is of central importance to the design of heat dissipating structures. 相似文献
12.
Numerical approach based on the spectral collocation method has been utilized for analyzing heat convection and conduction in eccentric annuli. An eccentric instead of concentric annular duct is sometimes used as a fluid-flow and heat-transfer device especially in nuclear power plants. The hydrodynamically and thermally fully developed laminar flow with uniform heat flux through the inner and outer walls has been analyzed. Also, the conductive heat transfer problem, with uniform rate of internal heat generation in long hollow cylinder, has been solved. The governing equation for the present analysis is Poisson’s equation with constant nonhomogeneous term. Considering temperature and velocity distributions in eccentric annuli, Nusselt numbers and wall shear stresses are presented for various range of eccentricities. The spectral collocation method used in this study is verified by comparing the numerical solutions from the existing analytical solution and it is clear that this method is appropriate for assessing a more complicated heat transfer problem. 相似文献
13.
Kui-Soon Kim 《Journal of Mechanical Science and Technology》1993,7(4):349-363
Accurate determination of convective heat transfer coefficients on complex surfaces with high spatial resolution is essential in the design and analysis of thermal systems. This study focuses on the implementation of a recently developed true color image-processing technique for the quantitative interpretation of liquid crystal images obtained from a curved surface. The interpretation includes the use of a linear hue versus temperature relation as an accurate temperature measuring tool, a color image analysis system and a transient heat transfer model for the conversion of time accurate temperature information into heat transfer coefficient maps. A square to rectangular transition duct is used as a heat transfer model representative of a curved geometry. The transient heat transfer experiments are performed with ambient temperature air in the transition duct model which is preheated by a custom designed electric heater. The measurements are performed on the curved bottom surface of the transition duct. Two dimensional surface distributions of heat transfer coefficient on the curved surface are presented with high spatial resolution. The hue-capturing technique provides extremely fine details of heat transfer coefficient when compared to other conventional discrete sensor methods. The technique is a highly automated heat transfer measurement method which reduces lengthy data reduction processes and significantly improves spatial resolution. 相似文献
14.
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
15.
Hi-Yong Pak Kyoung-Woo Park Moon-Suk Choi 《Journal of Mechanical Science and Technology》1998,12(2):310-319
The flow and heat transfer characteristics of combined forced convection and radiation in the entrance region of internally
finned tubes are investigated numerically in this paper. The uniform flow is considered for an inlet flow condition. A three
dimensional parabolic problem is solved by a marching-type procedure envolving a series of two dimensional elliptic problems
in the cross-stream plane. The SIMPLER-algorithm and Raithby's pressure-velocity coupling method are employed to analyze the
flow and heat transfer characteristics. For the calculation of radiative heat transfer, the P1-approximation and the weighted sum of gray gases method (WSGGM) are used. The effects of fin height, number of fins, optical
thickness, reference temperature, and Planck number on the flow and heat transfer characteristics are examined. It was found
that the effect of fin-height on the heat transfer characteristic is more dominant than that of number of fins. The present
results show that the optimal non-dimensional fin height and number of fins are 0.4 and 16, respectively. 相似文献
16.
Journal of Mechanical Science and Technology - The influence of an external magnetic field and thermal radiation on Cu-water nanofluid flow and heat transfer over a shrinking sheet with slip... 相似文献
17.
Asterios Pantokratoras 《Journal of Mechanical Science and Technology》2014,28(5):1909-1915
The flow of a fluid past a flat plate of finite length and infinite width (two-dimensional flow) is considered. The plate is heated by convection from a fluid with constant temperature T f with a constant heat transfer coefficient h f . In all previous works, the problem was considered using boundary layer theory whereas, in the present work, the solution is based on the full Navier-Stokes equations. The problem is investigated numerically with a finite volume method using the commercial code ANSYS FLUENT. The governing parameters are the Reynolds number, the new heat transfer parameter, and the Prandtl number. In addition, the influence of these three parameters on the temperature field is investigated. It is found that high Reynolds and high Prandtl numbers the wall temperature increases along the plate. They reach a maximum near the trailing edge then decrease. The same occurs as the heat transfer parameter increases. When the Reynolds and Prandtl numbers are low, the plate temperature tends to become symmetric, with a maximum at the middle of the plate. The temperature profiles become thicker as the Reynolds number and the Prandtl number is reduced while the temperature profiles become thicker as the heat transfer parameter increases. 相似文献
18.
Soo Whan Ahn ByungChang Lee WonCheol Kim Myung- Whan Bae Yoon Pyo Lee 《Journal of Mechanical Science and Technology》2002,16(9):1175-1182
The commercial viability of heat exchanger is mainly dependent on its long-term fouling characteristic because the fouling
increases the pressure loss and degrades the thermal performance of a heat exchanger. An experimental study was performed
to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with circulating various
solid particles. The present work showed that the higher densities of particles had higher drag force coefficients, and the
increases in heat transfer were in the order of sand, copper, steel, aluminum, and glass below Reynolds number of 5,000. 相似文献
19.
Chang-Yong Choi 《Journal of Mechanical Science and Technology》1999,13(6):496-503
This paper presents a study of the dual reciprocity boundary element method (DRBEM) for the laminar heat convection problem in a concentric annulus with constant heat flux boundary condition. DRBEM is one of the most successful technique used to transform the domain integrals arising from the nonhomogeneous term of the Poisson equation into equivalent boundary only integrals. This recently developed and highly efficient numerical method is tested for the solution accuracy of the fluid flow and heat transfer study in a concentric annulus. Since their exact solutions are available, DRBEM solutions are verified with different number of boundary element discretizations and internal points. The results obtained in this study are discussed with the relative error percentage of velocity and temperature solutions, and potential applicability of the method for the more complicated heat convection problems with arbitrary duct geometries. 相似文献
20.
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