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1.
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
2.
An experimental and three-dimensional numerical study on the convective heat transfer inside a trapezoidal duct under constant wall temperature 总被引:1,自引:0,他引:1
In this study, steady-state forced convection heat transfer and pressure drop characteristics for hydrodynamically fully developed
thermally developing three-dimensional turbulent flow in a horizontal smooth trapezoidal duct with corner angle of 75° and
hydraulic diameter of 0.043 m were both experimentally and numerically investigated in the Reynolds number range from 2.6 × 103 to 67 × 103 for isothermal conditions. Results have shown that there is a good agreement between the present experimental and numerical
results. 相似文献
3.
A numerical and experimental study has been made on the flow and heat transfer in inclined air-filled cavities with aspect
ratios 1–18 at Ra numbers from 2·104–5·105 and angles of inclination from 40 to 90°. Core stratification influences the flow. Due to this there arises a torque with
two components depending on angle of inclination. On basis of the two torques the computed effects on flow and temperature
fields can be explained. For the heat transfer a scaling law could be derived. Experimental data validate the numerical studies. 相似文献
4.
Local heat transfer coefficients and temperature distributions within the fluid for air flow around a 180° square-sectioned bend have been measured. The ratio of bend radius to hydraulic diameter of the duct is 3.35:1 and the flow entering the bend is sensibly fully developed. Measurements of air and wall temperatures span a range of Reynolds numbers from 9.9 × 103 to 9.2 × 104 with the principal emphasis given to the case of Re ? 5.6 × 104. This Reynolds number and geometric configuration coincide with that of a companion LDA study carried out by Chang et al1 which provides detailed maps of the mean and turbulent velocity fields. The data show that by 45° into the bend the heat transfer coefficients on the inner convex wall of the bend drop markedly while those on the other walls increase. By 90° the ratio of the heat transfer coefficients at the mid positions of the concave and convex walls is more than 2:1. Nevertheless this ratio is less than would be anticipated from considering two-dimensional flow on weakly curved surfaces. There is a general consistency between the velocity and the temperatyre field data in the heated fluid 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.
S. A. Nada 《Heat and Mass Transfer》2008,44(8):929-936
In the present study, an experimental investigation of heat transfer and fluid flow characteristics of buoyancy-driven flow
in horizontal and inclined annuli bounded by concentric tubes has been carried out. The annulus inner surface is maintained
at high temperature by applying heat flux to the inner tube while the annulus outer surface is maintained at low temperature
by circulating cooling water at high mass flow rate around the outer tube. The experiments were carried out at a wide range
of Rayleigh number (5 × 104 < Ra < 5 × 105) for different annulus gap widths (L/D
o = 0.23, 0.3, and 0.37) and different inclination of the annulus (α = 0°, 30° and 60°). The results showed that: (1) increasing
the annulus gap width strongly increases the heat transfer rate, (2) the heat transfer rate slightly decreases with increasing
the inclination of the annulus from the horizontal, and (3) increasing Ra increases the heat transfer rate for any L/D
o and at any inclination. Correlations of the heat transfer enhancement due to buoyancy driven flow in an annulus has been
developed in terms of Ra, L/D
o and α. The prediction of the correlation has been compared with the present and previous data and fair agreement was found. 相似文献
7.
Sayed Ahmed E. Sayed Ahmed Emad Z. Ibrahiem Osama M. Mesalhy Mohamed A. Abdelatief 《Heat and Mass Transfer》2014,50(8):1091-1102
An experimental and numerical study has been conducted to clarify heat transfer characteristics and effectiveness of a cross-flow heat exchanger employing staggered wing-shaped tubes at different angels of attack. The water-side Rew and the air-side Rea were at 5 × 102 and at from 1.8 × 103 to 9.7 × 103, respectively. The tubes arrangements were employed with various angles of attack θ1,2,3 from 0° to 330° at the considered Rea range. Correlation of Nu, St, as well as the heat transfer per unit pumping power (ε) in terms of Rea and design parameters for the studied bundle were presented. The temperature fields around the staggered wing-shaped tubes bundle were predicted by using commercial CFD FLUENT 6.3.26 software package. Results indicated that the heat transfer increased with the angle of attack in the range from 0° to 45°, while the opposite was true for angles of attack from 135° to 180°. The best thermal performance and hence the efficiency η of studied bundle occurred at the lowest Rea and/or zero angle of attack. Comparisons between the experimental and numerical results of the present study and those, previously, obtained for similar available studies showed good agreements. 相似文献
8.
Natural convective heat transfer from an isothermal narrow flat plate embedded in a plane adiabatic surface and inclined at
moderate positive and negative angles to the vertical has been numerically and experimentally studied. The solution has the
Rayleigh number, the dimensionless plate width, the angle of inclination, and the Prandtl number as parameters. Attention
was restricted to a Prandtl number of 0.7. The numerical results have been obtained for Rayleigh numbers between 103 and 107 for dimensionless plate widths of between 0.3 and 1.2 and for angles of inclination between +45° and −45°. In the experimental
study, results have been obtained for Rayleigh numbers between 4 × 102 and 105 for dimensionless plate widths of 0.4 and 2.5 and for angles of inclination between +45° and −45° to the vertical. Empirical
equations for the heat transfer rate have been derived. 相似文献
9.
An experimental study was conducted to investigate the heat transfer characteristic of a vertical copper plate with rectangular micro-channels. In this research, Cu/R141b nanofluids were used as the working fluid. Three different volume concentrations—0.001, 0.01, and 0.1 %—of Cu nanoparticles with an average diameter of 20 nm dispersed in R141b were prepared. Experiments were performed to measure thermal resistance of the microchannel surface under a steady operating pressure range of 0.86 × 105 Pa to 2 × 105 Pa. Thermal resistance weakened with addition of nanoparticles into the base fluid. The maximum reduction effect of the thermal resistance was 50 %, which corresponds to 0.01 % volume concentration of nanofluid at low operating pressure. The operating pressure significantly affects thermal performance of the microchannel surface. This paper also studied heat transfer characteristics for a Cu nanoparticle-coated surface with rectangular microchannels, which were produced by heating in different volume concentrations from 0.001 to 0.1 %. Nanoparticle layer on the micro-channel surface is responsible for enhanced heat transfer of nanofluids with 0.001 and 0.01 % volume concentrations. 相似文献
10.
Experiments are carried out to study flow and heat transfer characteristics over NACA0018 aerofoil when the body approaches the wall of a wind tunnel. Investigations have been done to study the effect of wall proximity due to flow separation around the body at Reynolds number 2.5 × 105, different height ratios and various angles of attack. The static pressure distribution has been measured on upper and lower surfaces of the aerofoil. The results have been presented in the form of pressure coefficient, drag coefficient for different height ratios. Pressure coefficient values are decreased and then increased on the lower surface of the aerofoil and decreased on the upper surface of the aerofoil at all angles of attack. The negative pressure coefficient and drag coefficient decreases as the body approaches the upper wall of wind tunnel. The maximum value of drag coefficient has been observed at an angle of attack 30° for the aerofoil at all height ratios. The Heat transfer experiments have been carried out under constant heat flux condition. Heat transfer coefficients are determined from the measured wall temperature and ambient temperature and presented in the form of Nusselt number. The variation of local as well as average Nusselt number has been shown with non dimensional distance for different angles of attack and for various height ratios. The local as well as average Nusselt number decreases as the height ratio decreases for all non-dimensional distance and angles of attack respectively. Maximum value of average Nusselt number has been observed at an angle of attack 40°. 相似文献
11.
This paper presents the comparative studies on the effect of duct height on heat transfer and flow behavior between co-angular
and co-rotating type finned surface in duct. Experiments were performed to investigate the effect of duct height on heat transfer
enhancement of a surface affixed with arrays (7 × 7) of short rectangular plate fins of a co-angular and a co-rotating type
pattern in the duct. An infrared imaging system with the camera of TVS 8000 was used to measure the temperature distributions
to calculate the local heat transfer coefficients of the representative fin regions. Pressure drop and heat transfer experiments
were performed for both types of fin pattern varying the duct to fin height ratio (H
d/H
f) of 2.0–5.0. The friction factor calculated from the pressure drop shows that friction factor decreases with increasing the
duct to fin height ratio (H
d/H
f) regardless of fin pattern and this is expected because the larger friction occurs for smaller duct to fin height ratios.
Detailed heat transfer distribution gives a clear picture of heat transfer characteristics of the overall surface as well
as the influence of the duct height. In addition, different flow behavior and flow structure developed by both patterns were
visualized by the smoke flow visualization technique. 相似文献
12.
GH. R. Kefayati 《Theoretical and Computational Fluid Dynamics》2013,27(6):865-883
In this paper, the effects of a magnetic field on natural convection flow in filled long enclosures with Cu/water nanofluid have been analyzed by lattice Boltzmann method. This study has been carried out for the pertinent parameters in the following ranges: the Rayleigh number of base fluid, Ra = 103–105, the volumetric fraction of nanoparticles between 0 and 6 %, the aspect ratio of the enclosure between A = 0.5 and 2. The Hartmann number has been varied from Ha = 0 to 90 with interval 30 while the magnetic field is considered at inclination angles of θ = 0°, 30°, 60° and 90°. Results show that the heat transfer decreases by the increment of Hartmann number for various Rayleigh numbers and the aspect ratios. Heat transfer decreases with the growth of the aspect ratio but this growth causes the effect of the nanoparticles to increase. The magnetic field augments the effect of the nanoparticles at high Rayleigh numbers (Ra = 105). The effect of the nanoparticles rises for high Hartmann numbers when the aspect ratio increases. The rise in the magnetic field inclination improves heat transfer at aspect ratio of A = 0.5. 相似文献
13.
Experimental study of developing turbulent flow and heat transfer in ribbed convergent/divergent square ducts 总被引:4,自引:0,他引:4
Liang-Bi Wang Wen-Quan Tao Qiu-Wang Wang Tsun Tat Wong 《International Journal of Heat and Fluid Flow》2001,22(6):603-613
The local heat transfer and pressure drop characteristics of developing turbulent flows of air in three stationary ribbed square ducts have been investigated experimentally. These are: ribbed square duct with constant cross-section (straight duct), ribbed divergent square duct and ribbed convergent square duct. The convergent/divergent duct has an inclination angle of 1°. The measurement was conducted within the range of Reynolds numbers from 10 000 to 77 000. The heat transfer performance of the divergent/convergent ducts is compared with the ribbed straight duct under three constraints: identical mass flow rate, identical pumping power and identical pressure drop. Because of the streamwise flow acceleration or deceleration, the local heat transfer characteristics of the divergent and convergent ducts are quite different from those of the straight duct. In the straight duct, the fluid flow and heat transfer become fully developed after 2–3 ribs, while in the divergent and convergent ducts there is no such trend. The comparison shows that among the three ducts, the divergent duct has the highest heat transfer performance, the convergent duct has the lowest, while the straight duct locates somewhere in between. 相似文献
14.
Numerical studies were conducted to investigate the natural convection heat transfer around a uniformly heated thin plate
with arbitrary inclination in an infinite space. The numerical approach was based on the finite volume technique with a nonstaggered
grid arrangement. For handling the pressure–velocity coupling the SIMPLE-algorithm was used. QUICK scheme and first order
upwind scheme were employed for discretization of the momentum and energy convective terms respectively. Plate width and heating
rate were used to vary the modified Rayleigh number over the range of 4.8×106 to 1.87×108. Local and average heat transfer characteristics were compared with regarding to the inclination angle. The empirical expressions
for local and average Nusselt number were correlated. It has been found that for inclination angle less than 10∘, the flow and heat transfer characteristics are complicated and the average Nusselt number can not be correlated by one equation
while for inclination angle larger than 10∘, the average Nusselt number can be correlated into an elegant correlation.
Received on 18 April 2001 / Published online: 29 November 2001 相似文献
15.
Assistant Prof. S. Aiba Assistant Prof. T. Ota Assistant H. Tsuchida 《Heat and Mass Transfer》1979,12(3-4):221-231
An experimental study was conducted on the heat transfer under the condition of constant heat flux and the flow around a circular cylinder with tripping-wires, which were affixed at ± 65° from the forward stagnation point on the cylinder surface. The testing fluid was air and the Reynolds number Red, based on the cylinder diameter, ranged from 1.2 × 104 to 5.2×104. Especially investigated are the interactions between the heat transfer and the flow in the critical flow state, in relation to the static pressure distribution along the cylinder surface and the mean and turbulent fluctuating velocities in the wake. It is found that the heat transfer from the cylinder to the cross flow is in very close connection with the width of near wake. 相似文献
16.
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
17.
Experimental study on the pressure drop and heat transfer characteristics of tubes with internal wave-like longitudinal fins 总被引:11,自引:0,他引:11
Experiments were performed to determine the heat transfer and pressure drop characteristics in the entrance and fully developed
regions of tubes with internal wave-like longitudinal fins. The test tube has a double-pipe structure, with the inner tube
as an insertion. The wave-like fins are in the annulus and span its full width. Experiments were conducted for two cases:
one with the inner tube blocked (no air flowing through it) and the other with the inner tube unblocked. The outer tube was
electrically heated. Local and average heat transfer coefficients and friction factors were measured. The friction factor
and Nusselt number correlations in the fully developed region were obtained in the Reynolds number range of 9×102 to 3.5×103. It has been found that the wave-like fins enhance heat transfer significantly with the blocked case being superior. In addition,
the in-tube heat transfer process is characterized by an earlier transition from laminar to turbulent flow and Reynolds number-dependent
thermal entrance length.
Received on 12 May 1998 相似文献
18.
Z. B. Yan F. Duan T. N. Wong K. C. Toh K. F. Choo P. K. Chan Y. S. Chua L. W. Lee 《Heat and Mass Transfer》2013,49(7):985-990
An inclined spray chamber with four multiple nozzles to cool a 1 kW 6U electronic test card has been designed and tested in this study. The multiple inclined sprays can cover the same heated surface area as that with the multiple normal sprays but halve the volume of the spray chamber. The spray cooling system used R134a as a working fluid in a modified refrigeration cycle. It is observed that increasing mass flow rate and pressure drop across the nozzles improved the heat transfer coefficient with a maximum enhancement of 117 %, and reduced the maximum temperature difference at the heated surface from 13.8 to 8.4 °C in the inclined spray chamber with a heat flux of 5.25 W/cm2, while the heat transfer coefficient of the normal spray increased with a maximum enhancement of 215 % and the maximum temperature difference decreased from 10.8 to 5.4 °C under similar operating conditions. We conclude that the multiple inclined sprays could produce a higher heat transfer coefficient but with an increase in non-uniformity of the surface temperature compared with the multiple normal sprays. 相似文献
19.
Tang Guiming 《Acta Mechanica Sinica》1998,14(2):139-146
An experimental study was conducted on shock wave turbulent boundary layer interactions caused by a blunt swept fin-plate
configuration at Mach numbers of 5.0, 7.8, 9.9 for a Reynolds number range of (1.0∼4.7)×107/m. Detailed heat transfer and pressure distributions were measured at fin deflection angles of up to 30° for a sweepback
angle of 67.6°. Surface oil flow patterns and liquid crystal thermograms as well as schlieren pictures of fin shock shape
were taken. The study shows that the flow was separated at deflection of 10° and secondary separation were detected at deflection
of ϑ≥20°. The heat transfer and pressure distributions on flat plate showed an extensive plateau region followed by a distinct
dip and local peak close to the fin foot. Measurements of the plateau pressure and heat transfer were in good agreement with
existing prediction methods, but pressure and heating peak measurements atM≥6 were significantly lower than predicted by the simple prediction techniques at lower Mach numbers.
The project supported by China Academy of Launch Vehicle Technology 相似文献
20.
Abdelmoumène Hakim Benmachiche Chérif Bougriou Said Abboudi 《Heat and Mass Transfer》2010,46(11-12):1367-1377
In this work, we present the numerical results of the average heat transfer coefficients, $ \overline{{h_{\varphi } }} $ , over a circular plane fin in a finned-tube bundle for both aligned and staggered arrangements as well as the fin efficiency and the heat flux dissipated from the whole fin. The study covers a wide range of Reynolds number (2 × 103–3 × 104), for three different positions of the finned tube inside the heat exchanger. The temperature distribution on the fins surfaces was obtained experimentally using infrared thermography technique. The predicted values of the heat transfer coefficient were obtained numerically using the finite element method in conjunction with the conjugate gradient algorithm and the measured temperatures. 相似文献