Arrays of Impinging Jets With Spent Fluid Removal Through Vent Holes on the Target Surface, Part 2: Local Heat Transfer

1983 ◽  
Vol 105 (2) ◽  
pp. 393-402 ◽  
Author(s):  
B. R. Hollworth ◽  
G. Lehmann ◽  
J. Rosiczkowski
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Impinging Jets ◽  
Extensive Study ◽  
Heat Transfer Characteristics ◽  
Fluid Removal ◽  
Air Jets ◽  
Approximate Mathematical Model

An extensive study was conducted to determine the heat transfer characteristics of arrays of turbulent air jets impinging on perforated target surfaces. Spent air was withdrawn through vent holes on the surface, rather than along one or more of its edges, as had been done in all previous investigations. An earlier publication presented average heat transfer data for such systems; this paper gives results of comprehensive measurements of local heat transfer. Also given are the results of flow visualization studies, and an approximate mathematical model which predicts distributions of local heat transfer which agree satisfactorily with test 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 The target plate on which the jets impinge is perforated so that spent air is withdrawn through the plate rather than at one or more edges of the array, as is usually the case in such investigations.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.

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

2004 ◽  
Vol 127 (3) ◽  
pp. 532-544 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Temperature Data ◽  
Test Rig ◽  
Surface Temperature Data

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 crossflow in one direction. Jet angle is varied between 30, 60, and 90deg as measured from the target 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 and pressure loss is determined along with the various interactions among these parameters.

Heat Transfer of Confined Circular Jet Impingement

2001 ◽  
Vol 17 (1) ◽  
pp. 29-38
Author(s):  
Shou-Shing Hsieh ◽  
Jung-Tai Huang ◽  
Huang-Hsiu Tsai
Keyword(s):  
Heat Transfer ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Plate Spacing ◽  
Single Jet

ABSTRACTExperiments for heat transfer characteristics of confined circular single jet impingement were conducted. The effect of jet Reynolds number, jet hole-to-plate spacing and heat flux levels on heat transfer characteristics of the heated target surface was examined and presented. The local heat transfer coefficient along the surface is measured and correlations of the stagnation point, local and average Nusselt number are developed and discussed. Finally, comparisons of the present data with existing results were also made.

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.

scholarly journals Experimental and Numerical Investigations of Heat Transfer Characteristics for Impinging Swirl Flow

2014 ◽  
Vol 6 ◽  
pp. 631081 ◽  
Author(s):  
Sami D. Salman ◽  
Abdul Amir H. Kadhum ◽  
Mohd S. Takriff ◽  
Abu Bakar Mohamad
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Swirl Flow ◽  
Twisted Tape ◽  
Heat Transfer Characteristics ◽  
Cfd Modelling ◽  
Transfer Characteristics ◽  
Air Jets ◽  
Swirl Intensity

This paper reports experimental and computational fluid dynamics (CFD) modelling studies to investigate the effect of the swirl intensity on the heat transfer characteristics of conventional and swirl impingement air jets at a constant nozzle-to-plate distance ( L = 2 D). The experiments were performed using classical twisted tape inserts in a nozzle jet with three twist ratios ( y = 2.93, 3.91, and 4.89) and Reynolds numbers that varied from 4000 to 16000. The results indicate that the radial uniformity of Nusselt number (Nu) of swirl impingement air jets (SIJ) depended on the values of the swirl intensity and the air Reynolds number. The results also revealed that the SIJ that was fitted with an insert of y = 4.89, which corresponds to the swirl number Sw = 0.671, provided much more uniform local heat transfer distribution on the surface. The CFD-predicted results help to explain the experimental measurements in terms of the turbulence intensity. Furthermore, the predicted and measured local Nusselt numbers were consistent with each other.

Effect of Angle and Separation Distance on Heat Transfer on an Inclined Surface Subject to Airflow

2003 ◽  
Author(s):  
Srinivasan C. Rasipuram ◽  
Karim J. Nasr
Keyword(s):  
Heat Transfer ◽  
Fluid Velocity ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Separation Distance ◽  
Convective Heating ◽  
Air Jets ◽  
Inclined Surface

Impinging jets may be used to achieve enhanced local heat transfer for convective heating, cooling, or drying. The issuing jet may contact the surface normally or obliquely. Factors such as jet attachment, surface angle, jet angle, separation distance between jet orifice and surface of impingement, and trajectory influence heat transfer dramatically. This study addresses the thermal problem of jet impingement on an inclined surface. This investigation is motivated by the practical application of air jets issuing out of a defroster’s nozzles and impinging on the inclined windshield surface of a vehicle. Effect of incoming fluid velocity, angle that the inclined surface makes with the horizontal plane and angle of impinging jet on heat transfer will be examined. The results are correlated in terms of governing dimensionless parameters. The end-result will be a numerically-based correlation that is capable of predicting heat transfer on an inclined surface subject to impinging airflow.

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.

Mechanism of Novel Streamlined Roughness Element Enhancing the Flow and Heat Transfer Performance From Arrays of Impinging Jets

2020 ◽  
Author(s):  
Zhuang Wu ◽  
Hui-ren Zhu ◽  
Cun-liang Liu ◽  
Lin Li ◽  
Qiang Gao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Stagnation Point ◽  
Roughness Element ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Impinging Jets ◽  
Remarkable Effect ◽  
Flow And Heat Transfer

Abstract The numerical investigation of the flow and heat transfer characteristics from arrays of impinging jets with the roughed target surface is presented in this paper. Three novel streamlined roughness elements are proposed: similar round protuberance, similar trapezoidal straight rib, and similar trapezoidal curved rib. The jet Reynolds number ranges from 15000 to 30000, the protuberance height is h/H = 0.36, the rib height is h/H = 0.3, 0.5, and 0.7 respectively. The results show that the protuberance can shorten the nozzle to the stagnation point distance, increasing the heat transfer at the stagnation point by nearly 40%. The rib has a remarkable effect of guiding the flow in span-wise direction and away from the target surface, weakening the cross-flow effect. The straight rib gets a better guidance performance, the curved rib provides a larger surface area. An appropriate increase of rib height can improve local heat transfer, continuing to increase mainly enlarge heat transfer area. The decent aerodynamic shape decreases the flow discharge coefficient by only 2% at the rib height of 0.3H.

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