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.

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.

Maldistributed Inlet Flow Effects on Turbulent Heat Transfer and Pressure Drop in a Flat Rectangular Duct

1983 ◽  
Vol 105 (3) ◽  
pp. 527-535 ◽  
Author(s):  
E. M. Sparrow ◽  
N. Cur
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Inlet Flow ◽  
Heat Transfer Coefficients ◽  
Flow Maldistribution

The effects of flow maldistribution caused by partial blockage of the inlet of a flat rectangular duct were studied experimentally. Local heat transfer coefficients were measured on the principal walls of the duct for two blockages and for Reynolds numbers spanning the range between 6000 and 30,000. Measurements were also made of the pressure distribution along the duct, and the fluid flow pattern was visualized by the oil-lampblack technique. Large spanwise nonuniformities of the local heat transfer coefficient were induced by the maldistributed flow. These nonuniformities persisted to far downstream locations, especially in the presence of severe inlet flow maldistributions. Spanwise-average heat transfer coefficients, evaluated from the local data, were found to be enhanced in the downstream portion of the duct due to the flow maldistribution. However, at more upstream locations, where the entering flow reattached to the duct wall following its separation at the sharp-edged inlet, the average coefficients were reduced by the presence of the maldistribution.

Measured Heat Transfer Coefficients at and Adjacent to the Tip of a Wall-Attached Cylinder in Crossflow—Application to Fins

1981 ◽  
Vol 103 (4) ◽  
pp. 778-784 ◽  
Author(s):  
E. M. Sparrow ◽  
F. Samie
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Visualization ◽  
Cylindrical Surface ◽  
The Other ◽  
Heat Transfer Analysis ◽  
End Effect ◽  
Transfer Coefficients ◽  
End Effects ◽  
Heat Transfer Coefficients

Wind tunnel studies encompassing both heat transfer measurements and flow visualization were performed for a cylinder in crossflow, with one end of the cylinder attached perpendicular to a wall and with the other end free. The focus of the work was to obtain heat transfer coefficients for the tip of the cylinder, for the tip-adjacent portion of the cylindrical surface, and for a portion of the cylindrical surface where there are no end effects. The flow visualization studies were performed to assist in the explanation and rationalization of the heat transfer results. They revealed the presence of spanwise flows adjacent to both ends of the cylinder, with accompanying modifications of the size of the separated region that washes the rear of the cylinder. The flow passing over the tip separates on the fore portion of the tip, but reattaches on the aft portion. The tip heat transfer coefficients are higher than those for the end-effect-free portion of the cylindrical surface, with deviations which grow with increasing Reynolds number (about a factor of two at Re = 25,000). For the tip-adjacent portion of the cylindrical surface, the coefficients are about fifty percent higher than those uninfluenced by end effects. The ramifications of these findings on the heat transfer analysis of fins are discussed.

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.

Experimental Investigation of Local and Average Heat Transfer Coefficients Under an Inline Impinging Jet Array, Including Jets With Low Impingement Distance and Inclined Angle

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Weihong Li ◽  
Minghe Xu ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Design Tool ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Impingement Heat Transfer ◽  
Upstream Direction ◽  
Inclined Angle

Comprehensive impingement heat transfer coefficients data are presented with varied Reynolds number, hole spacing, jet-to-target distance, and hole inclination utilizing transient liquid crystal. The impingement configurations include: streamwise and spanwise jet-to-jet spacing (X/D, Y/D) are 4∼8 and jet-to-target plate distance (Z/D) is 0.75∼3, which composed a test matrix of 36 different geometries. The Reynolds numbers vary between 5,000 and 25,000. Additionally, hole inclination pointing to the upstream direction (θ: 0 deg∼40 deg) is also investigated to compare with normal impingement jets. Local and averaged heat transfer coefficients data are presented to illustrate that (1) surface Nusselt numbers increase with streamwise development for low impingement distance, while decrease for large impingement distance. The increase or decrease variations are also influenced by Reynolds number, streamwise and spanwise spacings. (2) Nusselt numbers of impingement jets with inclined angle are similar to those of normal impingement jets. Due to the increase or decrease variations corresponding to small or large impingement distance, a two-regime-based correlation, based on that of Florschuetz et al., is developed to predict row-averaged Nusselt number. The new correlation is capable to cover low Z/D∼0.75 and presents better prediction of row-averaged Nusselt number, which proves to be an effective impingement design tool.

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.

Experiments on Turbulent Heat Transfer in an Asymmetrically Heated Rectangular Duct

1966 ◽  
Vol 88 (2) ◽  
pp. 170-174 ◽  
Author(s):  
E. M. Sparrow ◽  
J. R. Lloyd ◽  
C. W. Hixon
Keyword(s):  
Heat Transfer ◽  
Rectangular Cross Section ◽  
Heated Wall ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
First Case ◽  
Symmetric Heating

An experimental investigation of the effect of asymmetrical heating on fully developed turbulent heat transfer has been carried out. The test apparatus was a rectangular duct of aspect ratio 5:1. The duct was constructed so that the two long sides of the rectangular cross section could be heated at different preselected rates, while the two short sides were unheated. Two cases of asymmetrical heating were studied: (a) One of the two long sides was heated, while the second was unheated; (b) both of the long sides were heated, with the heating rate at one side being twice that of the other. For the first case, the heat transfer coefficients are lower than those for the symmetrically heated duct. For the second case, the coefficients for the more strongly heated wall are also below the values for symmetrical heating, while the coefficients for the lesser-heated wall are greater than the symmetric heating results. These findings are in qualitative agreement with analytical predictions for the parallel-plate channel. Furthermore, by applying an analytically motivated correlation procedure (reference [10]), it was shown that overall Nusselt number results for asymmetric heating could be brought into virtual coincidence with those for symmetric heating.

Average Nusselt Number for Pressure and Suction Sides of Squealer Turbine Blade Tip

2011 ◽  
Author(s):  
Chaouki Ghenai
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Cavity Depth ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Blade Tip

Numerical simulations of the flow field and heat transfer of squealer blade tip are performed in this study. The effect of Reynolds number (Re = 10000–40000), the clearance gap to width ratios (C/W = 5%–15%) and the cavity depth to width ratios (D/W = 10%, 20% and 50%) on fluid flow and heat transfer characteristics are obtained. The temperature and velocity distributions inside the cavity, the local heat transfer coefficients, and the average Nusselt numbers for the pressure and suction sides of the turbine blade tip are determined. This paper presents the results of the effects of Reynolds number, clearance gap and width ratios on the Nusslet number for the pressure and suction sides of squealer turbine blade tip. The results show a good agreement with the experimental data obtained by Metzger and Bunker. New correlations for the average Nusselt numbers for turbine blade tip pressure and suction sides are presented.

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