Heat Transfer From Arrays of Impinging Jets with Large Jet-to-Jet Spacing

1978 ◽  
Vol 100 (2) ◽  
pp. 352-357 ◽  
Author(s):  
B. R. Hollworth ◽  
R. D. Berry
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Turbulent Jets ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Turbine Cooling ◽  
Heat Transfer Coefficients

Local and average convective heat transfer coefficients were measured for arrays of widely spaced impinging air jets and correlated in terms of system geometry, air flow, and fluid properties. The configurations were square arrays of circular turbulent jets (spaced from 10–25 diameters apart) incident upon a flat isothermal target surface. Independent parameters were varied over ranges generally corresponding to gas turbine cooling applications. Local heat transfer coefficients were influenced by interference from neighboring jets only when the target plate and the jet orifice plate were less than five jet diameters apart. Average heat transfer coefficients were nearly equal for all the arrays tested as long as the coolant flow per unit area of target surface was held constant. In fact, there was a tendency for the more widely spaced configurations to produce slightly higher average heat transfer under such conditions.

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2001 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Roughened Surface

Abstract Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with cross-flow in one direction which is a common method for cooling gas turbine components such as the combustion liner. Jet angle is varied between 30, 60, and 90 degrees as measured from the impingement surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer efficiency and pressure loss is determined along with the various interactions among these parameters. Peak heat transfer coefficients for the range of Reynolds number from 15,000 to 35,000 are highest for orthogonal jets impinging on roughened surface; peak Nu values for this configuration ranged from 88 to 165 depending on Reynolds number. The ratio of peak to average Nu is lowest for 30-degree jets impinging on roughened surfaces. It is often desirable to minimize this ratio in order to decrease thermal gradients, which could lead to thermal fatigue. High thermal stress can significantly reduce the useful life of engineering components and machinery. Peak heat transfer coefficients decay in the cross-flow direction by close to 24% over a dimensionless length of 20. The decrease of spanwise average Nu in the crossflow direction is lowest for the case of 30-degree jets impinging on a roughened surface where the decrease was less than 3%. The decrease is greatest for 30-degree jet impingement on a smooth surface where the stagnation point Nu decreased by more than 23% for some Reynolds numbers.

Heat Transfer Enhancement by Turbulent Impinging Jets

2000 ◽  
Author(s):  
M. Kumagai ◽  
R. S. Amano ◽  
M. K. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stokes Equations ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Abstract A numerical and experimental investigation on cooling of a solid surface was performed by studying the behavior of an impinging jet onto a fixed flat target. The local heat transfer coefficient distributions on a plate with a constant heat flux were computationally investigated with a normally impinging axisymmetric jet for nozzle diameter of 4.6mm at H/d = 4 and 10, with the Reynolds numbers of 10,000 and 40,000. The two-dimensional cylindrical Navier-Stokes equations were solved using a two-equation k-ε turbulence model. The finite-volume differencing scheme was used to solve the thermal and flow fields. The predicted heat transfer coefficients were compared with experimental measurements. A universal function based on the wave equation was developed and applied to the heat transfer model to improve calculated local heat transfer coefficients for short nozzle-to-plate distance (H/d = 4). The differences between H/d = 4 and 10 due to the correlation among heat transfer coefficient, kinetic energy and pressure were investigated for the impingement region. Predictions by the present model show good agreement with the experimental data.

Arrays of Impinging Jets with Spent Fluid Removal through Vent Holes on the Target Surface—Part 1: Average Heat Transfer

1980 ◽  
Vol 102 (4) ◽  
pp. 994-999 ◽  
Author(s):  
B. R. Hollworth ◽  
L. Dagan
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Impinging Jets ◽  
Superior Performance ◽  
Jet Flows ◽  
Target Plate ◽  
Average Heat ◽  
Fluid Removal

Measurements of average convective heat transfer are reported for square arrays of impinging air jets. The target plate on which the jets impinge is perforated so that spent air is withdrawn through the plate rather than at one or more edges of the array, as is usually the case in such investigations. Jet holes and vent holes had the same diameters, but the spacing of the jet holes was twice that of the vent holes. This information is especially relevent to the design of hybrid cooling configurations, in which a surface is cooled by the combined mechanisms of impingement and transpiration. Tests were conducted for both inline arrangements (with a vent hole opposite each jet orifice) and for staggered arrangements; and the latter always yielded higher average heat transfer. The degradation of performance of inline arrays was most pronounced when the clearance between the jet orifice plate and the target plate was small. Under these conditions, a significant portion of each jet flows directly out through the opposing vent without “scrubbing” the target surface. Arrays with staggered vent holes yield heat transfer rates consistently higher (sometimes by as much as 35 percent) than the same jet array with edge venting. The authors attribute the superior performance of the former geometry to high local heat transfer due to boundary layer suction in the vicinities of the vent holes.

Local and Average Heat Transfer and Pressure Drop for Refrigerants Evaporating in Horizontal Tubes

1960 ◽  
Vol 82 (3) ◽  
pp. 189-196 ◽  
Author(s):  
M. Altman ◽  
R. H. Norris ◽  
F. W. Staub
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Test Facility ◽  
Transfer Coefficients ◽  
Local Pressure ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes

A test facility is described that has been constructed to investigate local heat transfer and pressure drop for evaporating or condensing refrigerants. The empirical method of B. Pierre [1] for correlating the average heat-transfer coefficients of refrigerants evaporating in horizontal tubes is presented in conjunction with the data of several authors [3–6]. Data on local heat-transfer coefficients and pressure drop are presented for Refrigerant-22 evaporating in two 4-ft-long, 0.343-in-ID straight horizontal tubes, and are correlated by a refinement of the curve proposed in [1]. The procedure of Martinelli-Nelson [9] correlated the data for local pressure drop within 15 per cent.

Numerical Analysis of Local Heat Transfer From a Flat Plate to a Pair of Circular Air Impingining Jets

2004 ◽  
Author(s):  
X. Terry Yan ◽  
Yavaraj Saravanan
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Flat Plate ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Local heat transfer from a flat plate to a pair of circular air impinging jets is investigated numerically. A pair of impinging jets from fully-developed pipe flows are used for the numerical simulations. The Reynolds Averaged Navier-Stokes equations(RANS) and energy equation are solved for the three dimensional flow. Eddy-viscocity based turbulence models, RNG k-epsilon and V2F models, are used. Hybrid meshes are used for the three dimensional flows and mesh independent solutions are obtained. The flow Reynolds number, which is based on the jet diameter, is kept at 23,000. In the analysis, local heat transfer coefficients are obtained for the jet-to-plate distance, L/D, ranging from 2 to 10 and the jet-to-jet spacing, S/D, in the range of 1.75 to 7.0. Both local and average heat transfer coefficients are evaluated and compared with available experimental data under same flow conditions. The effect of using different turbulence models in the numerical analysis is evaluated and the selection of proper turbulence models under such a flow condition is suggested.

Forced-Convective Condensation of Pure Steam and Ammonia-Steam Vapor Mixtures in a Shell-Tube Condenser

1999 ◽  
Author(s):  
Ratnesh K. Sharma ◽  
Vahab Hassani ◽  
Roop L. Mahajan
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Ammonia Concentration ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
Pure Steam ◽  
Convective Condensation ◽  
Tube Condenser

Abstract In this paper, we present our experimental findings for the forced-convective condensation of pure steam and ammonia-steam vapor mixture in a horizontal annulus in a counter-current shell-tube condenser. Experiments with ammonia-steam mixtures were conducted for ∼ 90% ammonia concentration (by wt.) for vapor inlet mass fluxes ranging from 2 to 5 kg/m2s. The local heat transfer coefficient varied considerably along the condenser and this variation was strongly linked to the condensate flow patterns in the annulus. Based on a condensate drainage model, the flow in the annulus was mapped on to flow maps for horizontal in-tube condensing flows. The delineated flow regimes were utilized to explain augmentation or deterioration of local heat transfer in the condenser. The average heat transfer coefficients are presented as a function of the condensate and vapor Reynolds number for both steam and ammonia-steam mixture. The results for pure steam are higher than those predicted by annular flow correlation developed in the past. For ammonia-steam mixtures, the average heat transfer coefficients are about 16% of those for pure steam due to the vapor layer resistance at the interface.

Entrainment Effects on Impingement Heat Transfer: Part II—Local Heat Transfer Measurements

1985 ◽  
Vol 107 (4) ◽  
pp. 910-915 ◽  
Author(s):  
B. R. Hollworth ◽  
L. R. Gero
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Air Jet ◽  
Impingement Heat Transfer ◽  
Local Recovery ◽  
The Difference

Convective heat transfer was measured for a heated axisymmetric air jet impinging on a flat surface. It was found that the local heat transfer coefficient does not depend explicitly upon the temperature mismatch between the jet fluid and the ambient fluid if the convection coefficient is defined in terms of the difference between the local recovery temperature and target surface temperature. In fact, profiles of local heat transfer coefficients defined in this manner were found to be identical to those measured for isothermal impinging jets.

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

2013 ◽  
Vol 34 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Cfd Simulation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

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