Effects of Interactions Between Adjoining Rows of Circular, Free-Surface Jets on Local Heat Transfer From the Impingement Surface

1994 ◽  
Vol 116 (1) ◽  
pp. 88-95 ◽  
Author(s):  
S. J. Slayzak ◽  
R. Viskanta ◽  
F. P. Incropera
Keyword(s):  
Heat Transfer ◽  
Free Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Separation Distance ◽  
Interaction Zone ◽  
Wall Jets ◽  
Local Coefficients ◽  
Surface Jets

Experiments have been conducted to obtain single-phase local heat transfer coefficient distributions associated with impingement of one or two rows of circular, free-surface water jets on a constant heat flux surface. The nozzle diameter, the centerline-to-centerline distance between nozzles in a row, and the nozzle-to-heater separation distance were fixed at 4.9, 6.3, and 89.7 mm, respectively. Two row-to-row separations (81 and 51 mm) were considered, and nozzle discharge Reynolds numbers were varied over the range from 16,800 to 30,400. The interaction zone created by opposing wall jets from adjacent rows is characterized by an upwelling of spent flow (an interaction fountain) for which local coefficients can approach those of the impingement zones. Interactions between wall jets associated with nozzles in one row can create sprays that impact the adjoining row with sufficient momentum to induce a dominant/subordinate row behavior. In this case the interaction zone is juxtaposed with the subordinate row, and local coefficients in the impingement and wall jet regions of the affected row may be significantly enhanced. This result contrasts with the deleterious effects of crossflow reported for submerged jets throughout the literature. Spray-induced enhancements, as well as interaction zone maxima, increase with decreasing row-to-row pitch and with increasing Reynolds number.

scholarly journals Natural Convection From Isothermal Horizontal Cylinders

2009 ◽  
Author(s):  
Ian M. O. Gorman ◽  
Darina B. Murray ◽  
Gerard Byrne ◽  
Tim Persoons
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Separation Distance ◽  
Thermal Plume ◽  
Number Range ◽  
Vertically Aligned ◽  
Isothermal Cylinders ◽  
Horizontal Cylinders

The research described here is concerned with natural convection from isothermal cylinders, with a particular focus on the interaction between a pair of vertically aligned cylinders. Prime attention was focused on how the local heat transfer characteristics of the upper cylinder are affected due to buoyancy induced fluid flow from the lower cylinder. Tests were performed using internally heated copper cylinders with an outside diameter 30mm and a vertical separation distance between the cylinders ranging from two to three cylinder diameters. Plume interaction between the heated cylinders was investigated within a Rayleigh number range of 2×106 to 6×106. Spectral analysis of the associated heat transfer interaction is presented showing that interaction between the cylinders causes oscillation of the thermal plume. The effect of this oscillation is considered as a possible enhancement mechanism of the heat transfer performance of the upper cylinder.

Effect of Film Extraction on Impingement Heat Transfer Characteristics of Jet Arrays on Spherical-Dimpled Surfaces

2015 ◽  
Author(s):  
Xing Yang ◽  
Zhao Liu ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Coupling Effect ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Separation Distance ◽  
Plate Spacing

Detailed heat transfer distributions are numerically investigated on a multiple jet impingement target surface with staggered arrays of spherical dimples where coolant can be extracted through film holes for external film cooling. The three dimensional Reynolds-averaged Navier-Stokes analysis with SST k-ω turbulence model is conducted at jet Reynolds number from 15,000 to 35,000. The separation distance between the jet plate and the target surface varies from 3 to 5 jet diameters and two jet-induced crossflow schemes are included to be referred as large and small crossflow at one and two opposite exit openings correspondingly. Flow and heat transfer results for the dimpled target plate with three suction ratios of 2.5%, 5.0% and 12.0% are compared with those on dimpled surfaces without film holes. The results indicate the presence of film holes could alter the local heat transfer distributions, especially near the channel outlets where the crossflow level is the highest. The heat transfer enhancements by applying film holes to the dimpled surfaces is improved to different degrees at various suction ratios, and the enhancements depend on the coupling effect of impingement and channel flow, which is relevant to jet Reynolds number, jet-to-plate spacing and crossflow scheme.

Flow Boiling in Mini and Microchannels

2004 ◽  
Author(s):  
M. Cortina Di´az ◽  
H. Boye ◽  
I. Hapke ◽  
J. Schmidt ◽  
Y. Staate ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Outer Wall ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Convective Boiling ◽  
Inconel 600

Flow boiling heat transfer characteristics of water and hydrocarbons in mini and microchannels are experimentally studied. Two different test section geometries are employed; a circular channel with a hydraulic diameter of 1500 μm, and rectangular channels with height values of 300–700 μm and a width of 10mm. In both facilities the fluid flows upwards and the test sections, made of the nickel alloy Inconel 600, are directly electrically heated. Thus the evaporation takes place under the defined boundary condition of constant heat flux. Mass fluxes between 25 and 350 kg/(m2s) and heat fluxes from 20 to 350 kW/m2 at an inlet pressure of 0.3 MPa are examined. Infrared thermography is applied to scan the outer wall temperatures. These allow the identification of different boiling regions, boiling mechanisms and the determination of the local heat transfer coefficients. Measurements are carried out in initial, saturated and post-dryout boiling regions. The experimental results in the region of saturated boiling are compared with available correlations and with a physically founded model developed for convective boiling.

Natural Convection Local Heat Transfer on Constant-Heat-Flux Inclined Surfaces

1969 ◽  
Vol 91 (4) ◽  
pp. 511-516 ◽  
Author(s):  
G. C. Vliet
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Plate Theory ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Transfer Data ◽  
Inclined Surfaces

Experimental local heat transfer data are presented for natural convection on constant-heat-flux inclined surfaces using water and air. The data extend to Grz* Pr = 1016, cover angles from the vertical to 30 deg with the horizontal, and include the laminar, transition, and turbulent regimes. In the laminar regime the data correlate well with vertical plate theory when the gravitational component parallel to the surface is used. Transition is strongly affected by inclination, the transition Grz* Pr decreasing from near 1013 for vertical surfaces to approximately 108 for a surface at 30 deg to the horizontal. The turbulent local heat transfer data correlate using the actual gravity rather than the parallel component, and indicates a change in the Grz* Pr exponent from near 0 22 for a vertical surface to approximately 1/4 as the inclination decreases. The turbulent data can be correlated quite well by Nuz = 0.30(Grz* Pr)0.24.

scholarly journals Numerical Simulation of Turbulent Heat Transfer and Flow in a Rotating Multiple-Pass Square Channel

1997 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Wei-Jyh Wang ◽  
Dong-Yuo Lai
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Straight Channel ◽  
Turbulent Fluid Flow ◽  
Square Channel

Three-dimensional turbulent fluid flow and heat transfer characteristics are analyzed numerically for fluids flowing through a rotating periodical two-pass square channel. The two-pass channel is characterized by three parts: (1) a radial-inward straight channel, (2) 180-deg sharp turns, and (3) a radial-outward straight channel. The smooth walls of the two-pass channel are subject to a constant heat flux. A two-equation k-ε turbulence model with modified terms for Coriolis and rotational buoyancy is employed to resolve this elliptic problem. The effects of rotational buoyancy are examined and discussed. It is found that adjacent the 180-deg turn, the rotational buoyancy effect on the local heat transfer is nearly negligible due to the relatively strong entrance effect of 180-deg turns. Downstream the entrance length, the changes in local heat transfer due to the rotational buoyancy in the radially outward flow are more significant than those in the radially inward flow. However, the channel averaged heat transfer is affected slightly by the rotational buoyancy. Whenever the buoyancy effects are sufficiently strong, the flow reversal appears over the leading face of the radial outward flow channel. A comparison of the present numerical results with the available experimental data by taking buoyancy into consideration is also presented.

Local Heat-Transfer Measurements during Forced-Convection Boiling in a Helically Coiled Tube

1969 ◽  
Vol 184 (3) ◽  
pp. 52-58 ◽  
Author(s):  
K. J. Bell ◽  
A. Owhadi
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Flow Structure ◽  
High Pressures ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Two Phase ◽  
Radial Acceleration ◽  
Local Coefficients ◽  
Small Density

Forced-convection boiling heat transfer to water at atmospheric pressure was studied in two helically coiled tubes. Temperature measurements were made at four positions round the tube at each of nine stations along the tube, permitting calculation of the local heat-transfer coefficient at each point. The local coefficients are correlated by the Lockhart-Martinelli parameters for two-phase flow, using the Seban-McLaughlin correlation for liquid phase heat transfer in coiled tubes. The curves for each of the four peripheral positions, compared to that previously obtained for the peripheral mean coefficient, are consistent with a flow structure having a vapour core with a strong secondary flow serving to distribute the liquid over the entire surface of the tube. The correlation and its interpretation in terms of flow structure may fail at high pressures as a result of the much smaller change in the radial acceleration in systems with small density difference between liquid and vapour.

Jet Impingement Heat Transfer on a Circular Cylinder by Radial Slot Jets

2005 ◽  
Author(s):  
Neil Zuckerman ◽  
Noam Lior
Keyword(s):  
Heat Transfer ◽  
Numerical Models ◽  
Pressure Rise ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Correlation Equation ◽  
Local Heat ◽  
Wall Jets ◽  
Cylindrical Target

To better understand and facilitate design of an impinging jet device, the heat transfer on a cylindrical target exposed to radial impinging slot jets was investigated using numerical methods. Numerical models were created to test the performance of the Shear Stress Transport (SST), Standard and Realizable k-epsilon, v2f, and Reynolds Stress Model (RSM) turbulence models versus published test data. Based on the validation study the v2f model was ultimately selected for further work. Models were then constructed to simulate a cylinder exposed to a radial array of slot jets. Parametric variations were conducted to produce information about the influence of jet speed, nozzle count, and other independent design variables upon heat transfer. Nozzle count was varied from 2 to 8, jet Reynolds number ranged from 5,000 to 80,000, and target diameter varied from 5 to 10 times the nozzle hydraulic diameter. The interaction of adjacent opposed wall jets caused a static pressure rise and resulted in flow separation on the surface of the cylindrical target. This separation and the fountain flow between the two wall jets greatly influenced the local heat transfer, causing a rise in Nu of an order of magnitude. The resulting average Nu values varied from 19 to 217 and were condensed into a correlation equation incorporating target curvature, number of nozzles, Re, and Pr.

Effect of Variation of Local Film Coefficients on Fin Performance

1969 ◽  
Vol 91 (1) ◽  
pp. 21-26 ◽  
Author(s):  
J. W. Stachiewicz
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Single Equation ◽  
Transfer Coefficients ◽  
Base Surface ◽  
Heat Transfer Coefficients ◽  
Local Coefficients ◽  
Film Coefficient

Local heat-transfer coefficients on the surface of a longitudinal, constant area fin were measured experimentally. Turbulent flow was maintained in all tests and the range of fin spacing-to-height ratios from 0.25 to 0.5 was covered. The film coefficients do not increase monotonically from the base of the fin as suggested by an earlier investigation, but increase to a maximum at about 50 percent of fin height, then dip, and then increase again near the tip. The distribution of local coefficients along the height of the fin was similar at all Reynolds numbers and fin spacings investigated. This distribution yields lower fin efficiencies than those computed assuming a constant film coefficient, but, taking advantage of the fact that the distribution is remarkably similar at all fin spacings and all Reynolds numbers, a simple correction factor can be applied to the conventional, constant “h” efficiency to allow for the effect of variation of h. The integrated average heat-transfer coefficients on the surface of the fin were correlated at all fin spacings by a single equation. The coefficients along the base surface between fins were also measured.

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