Turbulent Heat Transfer Downstream of an Unsymmetric Blockage in a Tube

1978 ◽  
Vol 100 (4) ◽  
pp. 588-594 ◽  
Author(s):  
K. K. Koram ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Initial Increase ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Tube Cross Section ◽  
Nusselt Numbers ◽  
Prandtl Numbers

Pipe flow experiments were performed to study the heat transfer in the separation, reattachment, and redevelopment regions downstream of a wall-attached blockage in the form of a segmental orifice plate. Water was the working fluid, and the Reynolds number encompassed the range from about 10,000–60,000. The extent of the flow blockage was varied from one-fourth to three-fourths of the tube cross section. Heat transfer coefficients were determined both around the circumference of the uniformly heated tube and along its length. The axial distributions of the circumferential average Nusselt numbers show an initial increase, then attain a maximum, and subsequently decrease toward the fully developed regime. These Nusselt numbers are much higher than those for a conventional thermal entrance region. The unsymmetric blockage induces variations of the Nusselt number around the circumference of the tube. Axial distributions of the Nusselt number at various fixed angular positions reveal the presence of two types of maxima. One of these is associated with the reattachment of the flow and the other occurs due to the impingement of flow deflected by the blockage onto the tube wall. The circumferential variations decay with increasing downstream distance, but the rate of decay for the case of the smallest blockage is remarkably slow. Although most of the tests were performed for Pr = 4, supplementary experiments for Pr = 8 showed that the results are valid for a range of Prandtl numbers.

scholarly journals Nusselt number correlation for turbulent heat transfer of helium–xenon gas mixtures

2021 ◽  
Vol 32 (11) ◽  
Author(s):  
Biao Zhou ◽  
Yu Ji ◽  
Jun Sun ◽  
Yu-Liang Sun
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Prandtl Number ◽  
Liquid Metals ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Heat Transfer Correlation ◽  
Heat Transfer Correlations ◽  
Prandtl Numbers

AbstractA gas-cooled nuclear reactor combined with a Brayton cycle shows promise as a technology for high-power space nuclear power systems. Generally, a helium–xenon gas mixture with a molecular weight of 14.5–40.0 g/mol is adopted as the working fluid to reduce the mass and volume of the turbomachinery. The Prandtl number for helium–xenon mixtures with this recommended mixing ratio may be as low as 0.2. As the convective heat transfer is closely related to the Prandtl number, different heat transfer correlations are often needed for fluids with various Prandtl numbers. Previous studies have established heat transfer correlations for fluids with medium–high Prandtl numbers (such as air and water) and extremely low-Prandtl fluids (such as liquid metals); however, these correlations cannot be directly recommended for such helium–xenon mixtures without verification. This study initially assessed the applicability of existing Nusselt number correlations, finding that the selected correlations are unsuitable for helium–xenon mixtures. To establish a more general heat transfer correlation, a theoretical derivation was conducted using the turbulent boundary layer theory. Numerical simulations of turbulent heat transfer for helium–xenon mixtures were carried out using Ansys Fluent. Based on simulated results, the parameters in the derived heat transfer correlation are determined. It is found that calculations using the new correlation were in good agreement with the experimental data, verifying its applicability to the turbulent heat transfer for helium–xenon mixtures. The effect of variable gas properties on turbulent heat transfer was also analyzed, and a modified heat transfer correlation with the temperature ratio was established. Based on the working conditions adopted in this study, the numerical error of the property-variable heat transfer correlation was almost within 10%.

Heat Transfer and Flow Characteristics of an Oblique Turbulent Impinging Jet Within Confined Walls

1995 ◽  
Vol 117 (2) ◽  
pp. 316-322 ◽  
Author(s):  
K. Ichimiya
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Flow Characteristics ◽  
Local Heat Transfer ◽  
Flow Region ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Impingement Surface

Experiments were conducted to determine the turbulent heat transfer and flow characteristics of an oblique impinging circular jet within closely confined walls using air as a working fluid. The local temperature distribution on the impingement surface was obtained in detail by a thermocamera using a liquid crystal sheet. A correction to the heat flux was evaluated by using the detailed temperature distribution and solving numerically the three-dimensional equation of heat conduction in the heated section. Two-dimensional profiles of the local Nusselt numbers and temperatures changed with jet angle and Reynolds number. These showed a peak shift toward the minor flow region and a plateau of the local heat transfer coefficients in the major flow region. The local velocity and turbulent intensity in the gap between the confined insulated wall and impingement surface were also obtained in detail by a thermal anemometer.

Effect of Plenum Length and Diameter on Turbulent Heat Transfer in a Downstream Tube and on Plenum-Related Pressure Losses

1981 ◽  
Vol 103 (3) ◽  
pp. 415-422 ◽  
Author(s):  
S. C. Lau ◽  
E. M. Sparrow ◽  
J. W. Ramsey
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Loss ◽  
Reynolds Numbers ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Turbulent Regime ◽  
Transfer Coefficients ◽  
Pressure Loss Coefficient

A systematic experimental study was carried out to determine how the heat transfer characteristics of a turbulent tube flow are affected by the length and diameter of a cylindrical plenum chamber which delivers fluid to the tube. The net pressure loss due to the presence of the plenum was also measured. The experimental arrangement was such that the fluid experiences a consecutive expansion and contraction in the plenum before entering the electrically heated test section. Air was the working fluid, and the Reynolds number was varied over the range from 5,000 to 60,000. It was found that at axial stations in the upstream portion of the tube, there are substantially higher heat transfer coefficients in the presence of longer plenums. Thus, a longer plenum functions as an enhancement device. On the other hand, the plenum diameter appears to have only a minor influence in the range investigated (i.e., plenum diameters equal to three and six times the tube diameter). The fully developed Nusselt numbers are independent of the plenum length and diameter. With longer plenums in place, the thermal entrance length showed increased sensitivity to Reynolds number in the fully turbulent regime. The pressure loss coefficient, which compares the plenum-related pressure loss with the velocity head in the tube, increases more or less linearly with the plenum length. With regard to experimental technique, it was demonstrated that guard heating/cooling of the electrical bus adjacent to the tube inlet is necessary for accurate heat transfer results at low Reynolds numbers but, although desirable, is less necessary at higher Reynolds numbers.

Heat Transfer Downstream of a Fluid Withdrawal Branch in a Tube

1979 ◽  
Vol 101 (1) ◽  
pp. 23-28 ◽  
Author(s):  
E. M. Sparrow ◽  
R. G. Kemink
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Test Section ◽  
Turbulent Pipe Flow ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Axial Distribution ◽  
Thermal Entrance

Experiments have been performed to study how fluid withdrawal at a branch point in a tube affects the turbulent heat transfer characteristics of the main line flow downstream of the branch. Air was the working fluid. The experiments were carried out for several fixed test section Reynolds numbers and at each Reynolds number the ratio of the withdrawn flow to the test section flow (hereafter designated as the flow split number) was varied systematically. Local heat transfer coefficients were determined both around circumference and along the length of the tube, and circumferential average coefficients were also evaluated. The circumferential average Nusselt numbers in the thermal entrance region are much higher than those for a conventional turbulent pipe flow having the same Reynolds number, and the differences are accentuated at higher values of the flow split number. When normalized by the corresponding fully developed value, the axial distribution of the circumferential average Nusselt number is relatively insensitive to the Reynolds number for a fixed flow split. The thermal entrance lengths, based on a five percent approach to fully developed conditions, are in the 20 to 30 diameter range, which is substantially greater than that for conventional turbulent air flows. Circumferential variations on the order of ±20 percent are induced by the fluid withdrawal process. For the most part, these variations are dissipated upstream of x/D = 10.

Experiments on Turbulent Heat Transfer in a Tube With Circumferentially Varying Thermal Boundary Conditions

1967 ◽  
Vol 89 (3) ◽  
pp. 258-268 ◽  
Author(s):  
A. W. Black ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boundary Conditions ◽  
Wall Heat Flux ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Turbulent Diffusivity ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

An experimental investigation, supported by analysis, was performed to determine the heat transfer characteristics for turbulent flow in a circular tube with circumferentially varying wall temperature and wall heat flux. Air was the working fluid. The desired boundary conditions were achieved by electric heating within the wall of a tube whose thickness varied circumferentially. In this way, ratios of maximum-to-minimum wall heat flux as large as two were attained. Local heat transfer coefficients, deduced from the experimental data, display a circumferential variation that is substantially smaller than the heat flux variation. In general, lower heat transfer coefficients correspond to circumferential locations of greater heating, while higher coefficients correspond to locations of lesser heating. The predictions of prior analyses appear to overestimate the circumferential variation of the heat transfer coefficient. A specially designed probe was employed to measure the radial and circumferential temperature distributions within the flowing airstream. On the basis of these measurements, as well as from the heat transfer results, it is concluded that, in the neighborhood of the wall, the tangential turbulent diffusivity is greater than the radial turbulent diffusivity. The axial thermal development was found to be more rapid on the lesser-heated side of the tube than on the greater-heated side. Experimentally determined circumferential-average heat transfer coefficients agreed well with the predictions of analysis.

Effect of Tip-to-Shroud Clearance on Turbulent Heat Transfer From a Shrouded, Longitudinal Fin Array

1986 ◽  
Vol 108 (3) ◽  
pp. 519-524 ◽  
Author(s):  
E. M. Sparrow ◽  
D. S. Kadle
Keyword(s):  
Heat Transfer ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Fin Efficiency ◽  
Heat Transfer Coefficients ◽  
Thermal Development ◽  
Flow Through

Experiments were performed to determine the response of the heat transfer from a longitudinal fin array to the presence of clearance between the fin tips and an adjacent shroud. During the course of the experiments, the clearance was varied parametrically, starting with the no-clearance case; parametric variations of the fin height and of the rate of fluid flow through the array were also carried out. Air was the working fluid, and the flow was turbulent. The fully developed heat transfer coefficients corresponding to the presence and to the absence of clearance were compared under the condition of equal air flowrate, and substantial clearance-related reductions were found to exist. For clearances equal to 10, 20, and 30 percent of the fin height, the heat transfer coefficients were 85, 74, and 64 percent of those for the no-clearance case. The ratio of the with-clearance and no-clearance heat transfer coefficients was a function only of the clearance-to-fin-height ratio, independent of the air flowrate, the fin height, and the fin efficiency model used to evaluate the heat transfer coefficients. The presence of clearance slowed the rate of thermal development in the entrance region.

Heat Transfer and Fluid Flow Experiments With a Tube Fed by a Plenum Having Nonaligned Inlet and Exit

1983 ◽  
Vol 105 (1) ◽  
pp. 56-63 ◽  
Author(s):  
E. M. Sparrow ◽  
L. D. Bosmans
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Visualization ◽  
Turbulent Heat Transfer ◽  
Geometrical Parameters ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Development Section

Local turbulent heat transfer coefficients for airflow were measured in a tube situated downstream of a cylindrical plenum chamber in which the inflow was radial and the outflow was axial. Pressure drop measurements and flow visualization were performed to supplement the heat transfer experiments. The plenum length and diameter were varied systematically during the experiments, and the Reynolds number ranged from 10,000 to 60,000. Substantially higher Nusselt numbers in the tube were encountered for the present nonaligned plenum inlet/exit configuration than for a plenum with axially aligned inlet and exit or for an upstream hydrodynamic development section. For a given Reynolds number, the Nusselt numbers corresponding to the present plenum configuration were quite insensitive to the investigated geometrical parameters. The thermal development length was found to be substantially elongated due to swirl carried into the tube from the plenum; the presence of the swirl was confirmed by flow visualization. The net pressure loss due to the presence of the plenum was about 1.75 velocity heads and was guite insensitive to the geometrical parameters and to the Reynolds number.

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.

Periodically Converging-Diverging Tubes and Their Turbulent Heat Transfer, Pressure Drop, Fluid Flow, and Enhancement Characteristics

1984 ◽  
Vol 106 (1) ◽  
pp. 55-63 ◽  
Author(s):  
P. Souza Mendes ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Surface Area ◽  
Equal Mass ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Friction Factors

A comprehensive experimental study was performed to determine entrance region and fully developed heat transfer coefficients, pressure distributions and friction factors, and patterns of fluid flow in periodically converging and diverging tubes. The investigated tubes consisted of a succession of alternately converging and diverging conical sections (i.e., modules) placed end to end. Systematic variations were made in the Reynolds number, the taper angle of the converging and diverging modules, and the module aspect ratio. Flow visualizations were performed using the oil-lampblack technique. A performance analysis comparing periodic tubes and conventional straight tubes was made using the experimentally determined heat transfer coefficients and friction factors as input. For equal mass flow rate and equal transfer surface area, there are large enhancements of the heat transfer coefficient for periodic tubes, with accompanying large pressure drops. For equal pumping power and equal transfer surface area, enhancements in the 30–60 percent range were encountered. These findings indicate that periodic converging-diverging tubes possess favorable enhancement characteristics.

Experimental Investigation of Coil Curvature Effect on Heat Transfer and Pressure Drop Characteristics of Shell and Coil Heat Exchanger

2014 ◽  
Vol 7 (1) ◽  
Author(s):  
M. R. Salem ◽  
K. M. Elshazly ◽  
R. Y. Sakr ◽  
R. K. Ali
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Average Nusselt Number ◽  
Transfer Coefficients ◽  
Nusselt Numbers ◽  
Fanning Friction Factor ◽  
Coil Heat

The present work experimentally investigates the characteristics of convective heat transfer in horizontal shell and coil heat exchangers in addition to friction factor for fully developed flow through the helically coiled tube (HCT). The majority of previous studies were performed on HCTs with isothermal and isoflux boundary conditions or shell and coil heat exchangers with small ranges of HCT configurations and fluid operating conditions. Here, five heat exchangers of counter-flow configuration were constructed with different HCT-curvature ratios (δ) and tested at different mass flow rates and inlet temperatures of the two sides of the heat exchangers. Totally, 295 test runs were performed from which the HCT-side and shell-side heat transfer coefficients were calculated. Results showed that the average Nusselt numbers of the two sides of the heat exchangers and the overall heat transfer coefficients increased by increasing coil curvature ratio. The average increase in the average Nusselt number is of 160.3–80.6% for the HCT side and of 224.3–92.6% for the shell side when δ increases from 0.0392 to 0.1194 within the investigated ranges of different parameters. Also, for the same flow rate in both heat exchanger sides, the effect of coil pitch and number of turns with the same coil torsion and tube length is remarkable on shell average Nusselt number while it is insignificant on HCT-average Nusselt number. In addition, a significant increase of 33.2–7.7% is obtained in the HCT-Fanning friction factor (fc) when δ increases from 0.0392 to 0.1194. Correlations for the average Nusselt numbers for both heat exchanger sides and the HCT Fanning friction factor as a function of the investigated parameters are obtained.

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