Condensation in a Variable Acceleration Field and the Condensing Thermosyphon

1965 ◽  
Vol 87 (4) ◽  
pp. 355-360 ◽  
Author(s):  
J. C. Chato
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Radial Distance ◽  
Constant Cross Section ◽  
Linear Variation ◽  
Temperature Differential ◽  
Acceleration Field ◽  
Nusselt Numbers ◽  
Increasing Temperature ◽  
Limiting Values

The general problem of condensation in a variable acceleration field was investigated analytically. The case of the linear variation, which occurs in a constant cross section, rotating thermosyphon, was treated in detail. The results show that the condensate thickness and Nusselt numbers approach limiting values as the radial distance increases. The effects of the temperature differential and the Prandtl number are similar to those in other condensation problems; i.e., the heat transfer increases slightly with increasing temperature differential if Pr > 1, but it decreases with increasing temperature differential if Pr ≪ 1.

Heat Transfer in an Oblique Jet Impingement Configuration With Varying Jet Geometries

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Simon Schueren ◽  
Florian Hoefler ◽  
Jens von Wolfersdorf ◽  
Shailendra Naik
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Hot Spots ◽  
Thermal Load ◽  
Jet Impingement ◽  
Wall Heat Transfer ◽  
Thermochromic Liquid Crystal ◽  
Numerical Heat Transfer ◽  
Nusselt Numbers ◽  
Sst Turbulence Model

The experimental and numerical heat transfer results in a trapezoidal duct with two staggered rows of inclined impingement jets are presented. The influence of changes in the jet bore geometry on the wall heat transfer is examined. The goal of this project is to minimize the thermal load in an internal gas turbine blade channel and to provide sufficient cooling for local hot spots. The dimensionless pitch is varied between p/djet=3 − 6. For p/djet=3, cylindrical and conically narrowing bores with a cross section reduction of 25% and 50%, respectively, are investigated. The studies are conducted at 10,000≤Re≤75,000. Experimental results are obtained using a transient thermochromic liquid crystal technique. The numerical simulations are performed solving the RANS equations with FLUENT using the low- Re k- ω -SST turbulence model. The results show that for a greater pitch, the decreasing interaction between the jets leads to diminished local wall heat transfer. The area averaged Nusselt numbers decrease by up to 15% for p/djet=4.5, and up to 30% for p/djet=6, respectively, if compared to the baseline pitch of p/djet=3. The conical bore design accelerates the jets, thus increasing the area-averaged heat transfer for identical mass-flow by up to 15% and 30% for the moderately and strongly narrowing jets, respectively. A dependency of the displacement between the Nu maximum and the geometric stagnation point from the jet shear layer is shown.

Heat Transfer in an Oblique Jet Impingement Configuration With Varying Jet Geometries

2011 ◽  
Author(s):  
Simon Schueren ◽  
Florian Hoefler ◽  
Jens von Wolfersdorf ◽  
Shailendra Naik
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Hot Spots ◽  
Thermal Load ◽  
Jet Impingement ◽  
Wall Heat Transfer ◽  
Thermochromic Liquid Crystal ◽  
Numerical Heat Transfer ◽  
Nusselt Numbers ◽  
Sst Turbulence Model

Experimental and numerical heat transfer results in a trapezoidal duct with two staggered rows of inclined impingement jets are presented. The influence of changes in the jet bore geometry on the wall heat transfer is examined. The goal of this project is to minimize the thermal load in an internal gas turbine blade channel and to provide sufficient cooling for local hot spots. The dimensionless pitch is varied between p/djet = 3–6. For p/djet = 3, cylindrical as well as conically narrowing bores with a cross section reduction of 25% and 50%, respectively, are investigated. The studies are conducted at 10,000 ≤ Re ≤ 75,000. Experimental results are obtained using a transient thermochromic liquid crystal technique. The numerical simulations are performed solving the RANS equations with FLUENT using the low-Re k-ω-SST turbulence model. The results show that for greater pitch, the decreasing interaction between the jets leads to diminished local wall heat transfer. The area averaged Nusselt numbers decrease by up to 15% for p/djet = 4.5, and up to 30% for p/djet = 6, respectively, if compared to the baseline pitch of p/djet = 3. The conical bore design accelerates the jets, thus increasing the area-averaged heat transfer for identical mass-flow by up to 15% and 30% for the moderately and strongly narrowing jets, respectively. A dependency of the displacement between the Nu maximum and the geometric stagnation point from the jet shear layer is shown.

Flow and Heat Transfer in Convectively Cooled Underground Electric Cable Systems: Part 2—Temperature Distributions and Heat Transfer Correlations

1978 ◽  
Vol 100 (1) ◽  
pp. 36-40 ◽  
Author(s):  
R. S. Abdulhadi ◽  
J. C. Chato
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Cross Section ◽  
Thermal Boundary Layer ◽  
Electric Cable ◽  
Nusselt Numbers ◽  
Temperature Distributions ◽  
Cable Systems ◽  
Heat Transfer Correlations

Temperature distributions and heat transfer correlations have been obtained experimentally for a wide range of physical, flow and thermal parameters in three models of oil-cooled underground electric cable systems. The results show that in the laminar range, with the oils used, the thermal boundary layer thickness around the heated cables is only of the order of 2–3 mm over the entire length of the test section. Consequently, the best correlation of the heat transfer results is obtained if the Nusselt number, based on the cable diameter, is plotted against Re·Pr0.4, where the Reynolds number is based on the overall hydraulic diameter of the cross section of the flow. For laminar flows, the oil temperatures in the restricted flow channels between three cables or two cables and the pipe wall are about 11°C higher than corresponding bulk temperatures. As the flow becomes turbulent, the thermal boundary layer tends to vanish and the oil temperature becomes uniform over the entire flow cross section. Laminar Nusselt numbers are independent of the skid wire roughness ratio and the flow Reynolds number, but increase with increasing Rayleigh number and axial distance from the inlet, indicating significant natural convection effect. The range of laminar Nusselt numbers was 5–16. Turbulent Nusselt numbers increase with increasing roughness ratios. The Nusselt numbers at Re = 3000 are 30 and 60 for roughness ratios of 0.0216 and 0.0293, respectively.

Rotating Cavity With Axial Throughflow of Cooling Air: Heat Transfer

1992 ◽  
Vol 114 (1) ◽  
pp. 229-236 ◽  
Author(s):  
P. R. Farthing ◽  
C. A. Long ◽  
J. M. Owen ◽  
J. R. Pincombe
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Simple Correlation ◽  
Nusselt Numbers ◽  
Rotating Cavity ◽  
Wide Range ◽  
Effects Of Radiation ◽  
Increasing Temperature ◽  
Cooling Air ◽  
Made In

Heat transfer measurements were made in two rotating cavity rigs, in which cooling air passed axially through the center of the disks, for a wide range of flow rates, rotational speeds, and temperature distributions. For the case of a symmetrically heated cavity (in which both disks have the same temperature distribution), it was found that the distributions of local Nusselt numbers were similar for both disks and the effects of radiation were negligible. For an asymmetrically heated cavity (in which one disk is hotter than the other), the Nusselt numbers on the hotter disk were similar to those in the symmetrically heated cavity but greater in magnitude than those on the colder disks; for this case, radiation from the hot to the cold disk was the same magnitude as the convective heat transfer. Although the two rigs had different gap ratios (G = 0.138 and 0.267), and one rig contained a central drive shaft, there was little difference between the measured Nusselt numbers. For the case of “increasing temperature distribution” (where the temperature of the disks increases radially), the local Nusselt numbers increase radially; for a “decreasing temperature distribution,” the Nusselt numbers decrease radially and become negative at the outer radii. For the increasing temperature case, a simple correlation was obtained between the local Nusselt numbers and the local Grashof numbers and the axial Reynolds number.

scholarly journals Heat Transfer Around Sharp 180 Degree Turns in Smooth Rectangular Channels

1985 ◽  
Author(s):  
D. E. Metzger ◽  
M. K. Sahm
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Forced Convection ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Side Wall ◽  
Bottom Wall ◽  
Channel Depth ◽  
Nusselt Numbers ◽  
Rectangular Channels

Measured Nusselt numbers are presented for forced convection within and around sharp 180 degree turns in smooth channels of rectangular cross section. Separately determined top wall, bottom wall, and side wall values are presented individually along with azimuthal averages. The geometry of the channels and connecting turn is characterized by parameters W*, the ratio of upstream and downstream channel widths; D*, the non-dimensional channel depth; and H*, the non-dimensional clearance at the tip of the turn. Results from nine combinations of these parameters are presented at several values of channel Reynolds number to illustrate the effect of turn geometry on the heat transfer distributions.

Heat Transfer Around Sharp 180-deg Turns in Smooth Rectangular Channels

1986 ◽  
Vol 108 (3) ◽  
pp. 500-506 ◽  
Author(s):  
D. E. Metzger ◽  
M. K. Sahm
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Forced Convection ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Side Wall ◽  
Bottom Wall ◽  
Channel Depth ◽  
Nusselt Numbers ◽  
Rectangular Channels

Measured Nusselt numbers are presented for forced convection within and around sharp 180-deg turns in smooth channels of rectangular cross section. Separately determined top wall, bottom wall, and side wall values are presented individually along with azimuthal averages. The geometry of the channels and connecting turn is characterized by the parameters W*, the ratio of upstream and downstream channel widths; D*, the nondimensional channel depth; and H*, the nondimensional clearance at the tip of the turn. Results from nine combinations of these parameters are presented at several values of channel Reynolds number to illustrate the effect of turn geometry on the heat transfer distributions.

Measurement of the Heat Transfer Coefficient for Mercury Flowing in a Narrow Channel

2002 ◽  
Vol 124 (6) ◽  
pp. 1034-1038 ◽  
Author(s):  
J. M. Crye ◽  
A. E. Ruggles ◽  
W. D. Pointer ◽  
D. K. Felde ◽  
P. A. Jallouk ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cross Section ◽  
Narrow Channel ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
The Heat Transfer Coefficient

The heat transfer coefficient is inferred from measurements for mercury flowing in a channel of cross-section 2 mm×40 mm with flow velocities from 1 m/s to 4 m/s and heat fluxes from 192 kW/m2 to 1.14 MW/m2. Mercury bulk temperatures vary from 67°C to 143°C. Inferred heat transfer coefficients agree with open literature tube data when compared on a Nusselt versus. Peclet number plot, with Nusselt numbers examined from 8 to 17 and Peclet numbers examined from 790 to 3070.

Two-Fluid and Single-Fluid Natural Convection Heat Transfer in an Enclosure

1986 ◽  
Vol 108 (4) ◽  
pp. 848-852 ◽  
Author(s):  
E. M. Sparrow ◽  
L. F. A. Azevedo ◽  
A. T. Prata
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Cross Section ◽  
Convection Heat Transfer ◽  
Immiscible Fluids ◽  
Nusselt Numbers ◽  
Baseline Information ◽  
Vertical Walls ◽  
Predicted Values ◽  
Two Fluid

Natural convection experiments were performed for an enclosure of square cross section containing either a single fluid or two immiscible fluids in a layered configuration. The two vertical walls of the cross section were respectively heated and cooled, while the two horizontal walls were adiabatic. The single-fluid experiments, performed with distilled water and with n-hexadecane paraffin (Pr = 5 and 39.2, respectively), yielded Nusselt numbers whose Rayleigh and Prandtl number dependences were perfectly correlated by a single dimensionless group. These single-fluid results were used as baseline information for the development of methods to predict the heat transfer in two-fluid layered systems. To test the utility of the predictive methods, experiments were carried out for water–hexadecane systems in which the position of the interface separating the liquids was varied parametrically. It was found that the experimentally determined, two-layer Nusselt numbers were in excellent agreement with the predicted values. The prediction methods are not limited to the particular fluids employed here, nor do they require additional experimental data for their application.

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