Heat Transfer by Natural Convection in Liquids Confined by Two Parallel Plates Which Are Inclined at Various Angles With Respect to the Horizontal

1965 ◽  
Vol 87 (1) ◽  
pp. 77-82 ◽  
Author(s):  
D. Dropkin ◽  
E. Somerscales
Keyword(s):  
Heat Transfer ◽  
Test Results ◽  
Parallel Plates ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Prandtl Numbers ◽  
The Relationship ◽  
Rayleigh Numbers ◽  
Vertical Case ◽  
Made In

This paper presents results of an experimental investigation of convective heat transfer in liquids confined by two parallel plates and inclined at various angles with respect to the horizontal. The experiments covered a range of Rayleigh numbers between 5(10)4 and 7.17(10)8, and Prandtl numbers between 0.02 and 11,560. Tests were made in rectangular and circular containers having copper plates and insulating walls. The liquids used were water, silicone oils, and mercury. The test results indicate that the heat transfer coefficients for all liquids investigated at the various angles, from horizontal to vertical, may be determined from the relationship Nu=C(Ra)1/3(Pr)0.074 The constant, C, is a function of the angle of inclination. It varies from C = 0.069 for the horizontal case when heated from below to C = 0.049 for the vertical case. For the test cells used, no effect on the Nusselt number had been detected for the vertical case by the change of the ratio of height of cell to distance between plates. The ratio for these tests was varied from 4.41 to 16.56.

Natural-Convection Heat Transfer in Liquids Confined by Two Horizontal Plates and Heated From Below

1959 ◽  
Vol 81 (1) ◽  
pp. 24-28 ◽  
Author(s):  
Samuel Globe ◽  
David Dropkin
Keyword(s):  
Heat Transfer ◽  
Silicone Oil ◽  
Convection Heat Transfer ◽  
Test Results ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Silicone Oils ◽  
Prandtl Numbers ◽  
The Relationship ◽  
Rayleigh Numbers

This paper presents results of an experimental investigation of convective heat transfer in liquids placed between two horizontal plates and heated from below. The liquids used were water, silicone oils of 1.5, 50, and 1000 centistoke kinematic viscosities, and mercury. The experiments covered a range of Rayleigh numbers between 1.51(10)5 and 6.76(10)8. and Prandtl numbers between 0.02 and 8750. Tests were made in cylindrical containers having copper tops and bottoms and insulating walls. For water and silicone oils the container was 5 in. in diam and 2 in. high. For mercury, two containers were used, both 5.28 in. in diameter, but one 1.39 in. high and another 2.62 in. high. In all cases the bottom plates were heated by electric heaters. The top plates were air-cooled for the water and silicone-oil experiments and water-cooled for the mercury tests. To prevent amalgamation, the copper plates of the mercury container were chromium plated. Surface temperatures were measured by thermocouples embedded in the plates. The test results indicate that the heat-transfer coefficients for all liquids investigated may be determined from the relationship Nu=0.069Ra13Pr0.074 In this equation the Nusselt and Rayleigh numbers are based on the distance between the copper plates. The results of this experiment are in reasonable agreement with the data reported by others who used larger containers and different fluids.

An Experimental Study of Free Corrective Heat Transfer in a Parallelogrammic Enclosure

1983 ◽  
Vol 105 (3) ◽  
pp. 433-439 ◽  
Author(s):  
N. Seki ◽  
S. Fukusako ◽  
A. Yamaguchi
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Nusselt Number ◽  
Correlation Equation ◽  
Transformer Oil ◽  
Experimental Measurements ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Prandtl Numbers ◽  
Rayleigh Numbers

Experimental measurements are presented for free convective heat transfer across a parallelogrammic enclosure with the various tilt angles of parallel upper and lower walls insulated. The experiments covered a range of Rayleigh numbers between 3.4 × 104 and 8.6 × 107, and Prandtl numbers between 0.70 and 480. Those also covered the tilt angles of the parallel insulated walls with respect to the horizontal, φ, of 0, ±25, ±45, ±60, and ±70 deg under an aspect ratio of H/W = 1.44. The fluids used were air, transformer oil, and water. It was found that the heat transfer coefficients for φ = −70 deg were decreased to be about 1/18 times those for φ = 0 deg. Experimental results are given as plots of the Nusselt number versus the Rayleigh number. A correlation equation is given for the Nusselt number, Nu, as a function of φ, Pr, and Ra.

Effect of Insulated/Uninsulated Channel Walls on Heat Transfer From a Horizontal Finned Tube in a Vertical Channel

1987 ◽  
Vol 109 (2) ◽  
pp. 388-391 ◽  
Author(s):  
E. M. Sparrow ◽  
M. A. Ansari
Keyword(s):  
Heat Transfer ◽  
Radiation Heat Transfer ◽  
Vertical Channel ◽  
Finned Tube ◽  
Radiation Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Metallic Sheet ◽  
Rayleigh Numbers ◽  
Metal Wall

Measurements were made of the combined natural convection and radiation heat transfer from a horizontal finned tube situated in a vertical channel open at the top and bottom. In one set of experiments, both walls of the channel were heavily insulated, while in a second set of experiments, one of the insulated walls was replaced by an uninsulated metallic sheet. In general, the heat transfer coefficients were found to be lower with the metal wall in place, but only moderately. With the finned tube situated at the bottom of the channel, the differences in the heat transfer coefficients corresponding to the two types of walls were only a few percent. When the tube was positioned at the mid-height of the channel, larger differences were encountered, but in the practical range of Rayleigh numbers, the differences did not exceed 5 percent.

The Use of Organic Coatings to Promote Dropwise Condensation of Steam

1987 ◽  
Vol 109 (3) ◽  
pp. 768-774 ◽  
Author(s):  
K. M. Holden ◽  
A. S. Wanniarachchi ◽  
P. J. Marto ◽  
D. H. Boone ◽  
J. W. Rose
Keyword(s):  
Heat Transfer ◽  
Atmospheric Pressure ◽  
Polymer Coatings ◽  
Organic Coatings ◽  
Major Constituent ◽  
Dropwise Condensation ◽  
Test Results ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Sustained Performance

Fourteen polymer coatings were evaluated for their ability to promote and sustain dropwise condensation of steam. Nine of the coatings employed a fluoropolymer as a major constituent; four employed hydrocarbons and one a silicone. Each coating was applied to 25-mm-square by approximately 1-mm-thick metal substrates of brass, copper, copper–nickel, and titanium. While exposed to steam at atmospheric pressure, each coating was visually evaluated for its ability to promote dropwise condensation. Observations were also conducted over a period of 22,000 hr. Hardness and adhesion tests were performed on selected specimens. On the basis of sustained performance, six coatings were selected for application to the outside of 19-mm-dia copper tubes in order to perform a heat transfer evaluation. These tubes were mounted horizontally in a separate apparatus through which steam flowed vertically downward. Steam-side heat transfer coefficients were inferred from overall measurements. Test results indicate that the steam-side heat transfer coefficient can be increased by a factor of five to eight through the use of polymer coatings to promote dropwise condensation.

Crossover Jet Impingement in a Rib-Roughened Trailing-Edge Cooling Channel

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Mohammad E. Taslim ◽  
Fei Xue
Keyword(s):  
Heat Transfer ◽  
Numerical Results ◽  
Test Results ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Numerical Work ◽  
Edge Channel ◽  
Heat Transfer Coefficients ◽  
The Cross ◽  
Rib Roughened

Airfoil trailing-edge cooling is the main focus of this study. The test section was made up of two adjacent trapezoidal channels, simulating the trailing-edge cooling cavity of a gas turbine airfoil and its neighboring cavity. Eleven racetrack-shaped holes were drilled on the partition wall between the two channels to produce 11 cross-over jets that impinged on the rib-roughened wall of the trailing-edge channel. The jets, after impinging on their respective target surface, turned toward the trailing-edge channel exit. Smooth target wall, as a baseline case, as well as four rib angles with the flow of 0 deg, 45 deg, 90 deg, and 135 deg are investigated. Cross-over holes axes were on the trailing-edge channel center plane, i.e., no tilting of the cross-over jets. Steady-state liquid crystal thermography technique was used in this study for a range of jet Reynolds number of 10,000–35,000. The test results are compared with the numerical results obtained from the Reynolds-averaged Navier–Stokes and energy equation. Closure was attained by k–ω with shear stress transport (SST) turbulence model. The entire test rig (supply and trailing-edge channels) was meshed with variable density hexagonal meshes. The numerical work was performed for boundary conditions identical to those of the tests. In addition to the impingement heat transfer coefficients, the numerical results provided the mass flow rates through individual cross-over holes. This study concluded that: (a) the local Nusselt numbers correlate well with the local jet Reynolds numbers, (b) 90 deg rib arrangement, that is, when the cross-over jet axis was parallel to the rib longitudinal axis, produced higher heat transfer coefficients, compared to other rib angles, and (c) numerical heat transfer results were generally in good agreement with the test results. The overall difference between the computational fluid dynamics (CFD) and test results was about 10%.

Effect of Nano-Particles on Pool Boiling Heat Transfer of Refrigerant 141b

2007 ◽  
Author(s):  
Da-Wei Liu ◽  
Chien-Yuh Yang
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
Nano Particles ◽  
Test Results ◽  
Tube Surface ◽  
Transfer Coefficients ◽  
Pool Boiling Heat Transfer ◽  
Heat Transfer Coefficients

Fluids with nano-sized particles have been proved that may effectively enhance the single-phase convective heat transfer performance. For pool boiling heat transfer, the published test results seems conflicted to each other. Some measured heat transfer coefficient decreased with increasing particle concentration but some showed no appreciable difference. This study provides an experimental investigation on pool boiling heat transfer performance of refrigerants R-141b with and without nano-sized Au particles on horizontal plain tubes. The test results show that the boiling heat transfer coefficients increase with increasing nano-particles concentration. At particles concentration of 1.0%, the heat transfer coefficient is more than twice higher than those without nano-particles. However, the heat transfer coefficients decreased for each test after every 5 days and finally close to those of R-141b without nano-particles. The SPM investigation shows that the test tube surface roughness decreased from 0.317 μm before boiling test to 0.162 μm after test. Further investigation by TEM and Dynamic Light Scattering particle analyzer shows that the nano-particles aggregated from 3 μm before test to 110 μm after test. This results show that the nano-sized Au particles are able to significantly increase pool boiling heat transfer of refrigerant R-141b on plain tube surface. The tube surface roughness and particle size changed after boiling test. Both of these effects degrade the boiling heat transfer coefficients.

Modeling Subcooled Flow Film Boiling in a Vertical Tube

2010 ◽  
Vol 2 (2) ◽  
Author(s):  
Meamer El Nakla ◽  
D. C. Groeneveld ◽  
Shui-Chih Cheng
Keyword(s):  
Heat Transfer ◽  
Film Boiling ◽  
Average Error ◽  
Parallel Plates ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Rms Error ◽  
Rms Errors ◽  
Flow Film Boiling

A two-fluid one-dimensional model has been developed to predict the wall temperature of an internally heated tube during inverted annular flow film boiling (IAFB). The model is derived using basic conservation equations of mass, momentum, and energy. To simplify the derivation of the constitutive heat transfer relations, flow between two parallel plates is assumed. The model features shear stress and interfacial relations that make it accurately predict the parametric effects and heat transfer characteristics of IAFB over a wide range of flow conditions. The model predicts wall temperatures of R-134a-cooled tubes with an average error of −1.21% and a rms error of 6.37%. This corresponds to average and rms errors in predicted heat transfer coefficients of 1.33% and 10.07%, respectively. Using water data, the model predicts wall temperatures with an average error of −1.76% and a rms error of 7.78%, which corresponds to average and rms errors in predicted heat transfer coefficients of 4.16% and 15.06%, respectively.

Development of an Outdoor Test Facility for Wind Convectors

1990 ◽  
Vol 112 (4) ◽  
pp. 287-292 ◽  
Author(s):  
P. F. Monaghan ◽  
D. P. Finn ◽  
P. H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Heat Pumps ◽  
Test Facility ◽  
Transfer Performance ◽  
Test Results ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Heat Transfer Coefficients ◽  
Outdoor Test

This paper deals with measurement of heat transfer performance of wind convectors, an alternative air source evaporator system for heat pumps. An automatically controlled and monitored outdoor wind convector test facility that is capable of measuring heat transfer rates and overall heat-transfer coefficients to within ± 5 percent measurement uncertainty for up to three wind convectors has been designed, built, and tested. Data on air temperature and humidity, solar radiation, and wind speed and direction are simultaneously collected. The choice of measurement technique for each variable and an error analysis for each sensor is discussed. Typical graphical test results are presented.

Condensation Measurement of Horizontal Cocurrent Steam/Water Flow

1984 ◽  
Vol 106 (2) ◽  
pp. 425-432 ◽  
Author(s):  
I. S. Lim ◽  
R. S. Tankin ◽  
M. C. Yuen
Keyword(s):  
Heat Transfer ◽  
Water Flow ◽  
Water Layer ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Wavy Interface ◽  
Prandtl Numbers ◽  
Inlet Conditions

Condensation of steam on a subcooled water layer was studied in a cocurrent horizontal channel at atmospheric pressure. The heat transfer coefficients were found to vary from 1.3 kW/m2°C to 20 kW/m2°C, depending on whether the liquid interface was smooth or wavy, increased with increasing steam flow rates and water flow rates. For all cases, 50 to 90 percent of the steam condensed within 1.2 m from the entrance. The average Nusselt numbers were correlated with average steam and water Reynolds numbers and average liquid Prandtl numbers, for both smooth and wavy interface flows. Finally, a correlation of the average heat transfer coefficient and condensation rate for wavy interface flow was obtained as a function of inlet conditions and distance downstream.

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