Nonuniform Jet Array Impingement on a Curved Surface

2017 ◽  
Vol 140 (5) ◽  
Author(s):  
Jahed Hossain ◽  
John Harrington ◽  
Wenping Wang ◽  
Jayanta Kapat ◽  
Steven Thorpe ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Flow Distribution ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Temperature Sensitive ◽  
Transfer Coefficients ◽  
Temperature Sensitive Paint ◽  
Jet Array

Experiments to investigate the effect of varying jet hole diameter and jet spacing on heat transfer and pressure loss from jet array impingement on a curved target surface are reported. The jet plate configurations studied have varying hole diameters and geometric spacing for spatial tuning of the heat transfer behavior. The configuration also includes a straight section downstream of the curved section, where the effect on heat transfer and pressure loss is also investigated. The jet plate holes are sharp-edged. A steady-state measurement technique utilizing temperature-sensitive paint (TSP) was used on the target surface to obtain local heat transfer coefficients. Pressure taps placed on the sidewall and jet plate of the channel were used to evaluate the flow distribution in the impingement channel. For all configurations, spent air is drawn out in a single direction which is tangential to the target plate curvature. First row jet Reynolds numbers ranging from 50,000 to 160,000 are reported. Further tests were performed to evaluate several modifications to the impingement array. These involve blocking several downstream rows of jets, measuring the subsequent shifts in the pressure and heat transfer data, and then applying different turbulator designs in an attempt to recover the loss in the heat transfer while retaining favorable pressure loss. It was found that by using W-shaped turbulators, the downstream surface average Nusselt number increases up to ∼13% as compared with a smooth case using the same amount of coolant. The results suggest that by properly combining impingement and turbulators (in the post impingement section), higher heat transfer, lower flow rate, and lower pressure drop are simultaneously obtained, thus providing an optimal scenario.

Effect of Target Wall Curvature on Heat Transfer and Pressure Loss From Jet Array Impingement

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
John Harrington ◽  
Jahed Hossain ◽  
Wenping Wang ◽  
Jayanta Kapat ◽  
Michael Maurer ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Loss ◽  
Flow Distribution ◽  
Target Surface ◽  
Temperature Sensitive ◽  
Target Plate ◽  
Target Wall ◽  
The Impact ◽  
Jet Array

Experiments to investigate the effect of target wall curvature on heat transfer and pressure loss from jet array impingement are performed. A jet plate configuration is studied with constant hole diameters and spacings. The geometry of the jet plate has streamwise jet spacings of 5.79 jet diameters, spanwise jet spacings of 4.49 jet diameters, and a jet-to-target plate distance of 3 jet diameters. For the curved case, the radius of the target plate is r/D = 31.57. A flat target wall setup with identical geometric spacing is also tested for direct comparison. Jet spacings were chosen such that validation and comparison can be made with open literature. For all configurations, spent air is drawn out in a single direction, which is tangential to the target plate curvature. Average jet Reynolds numbers ranging from 55,000 to 125,000 are tested. A steady-state measurement technique utilizing temperature-sensitive paint (TSP) is used on the target surface to obtain Nusselt number distributions. Pressure taps placed on the sidewall of the channel are used to evaluate the flow distribution in the impingement channel. Alongside the experimental work, CFD was performed utilizing the v2 − f turbulence model to better understand the relationship between the flow field and the heat transfer on the target surface. The main target of the current study is to quantify the impact of target wall radius and the decay of heat transfer after the impingement section, and to check the open literature correlations. It was found that the target wall curvature did not cause any significant changes in either the flow distribution or the heat transfer level. Comparisons with established correlations show similar level but different trends in heat transfer, potentially caused by differences in L/D. CFD results were able to show agreement in streamwise pitch-averaged Nusselt number levels with experimental results for the curved target plate at higher Re numbers.

Non-Uniform Array Impingement on a Curved Surface

2016 ◽  
Author(s):  
John Harrington ◽  
Jahed Hossain ◽  
Christian Garrett ◽  
Wenping Wang ◽  
Jay Kapat ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Distribution ◽  
Target Surface ◽  
Temperature Sensitive ◽  
Transfer Coefficients ◽  
Flat Surfaces ◽  
State Measurement ◽  
Uniform Array ◽  
Curved Section ◽  
Temperature Sensitive Paint

Experiments to investigate the effect of varying jet hole diameter and jet spacing on heat transfer from jet array impingement on a curved target surface are reported. The jet plate configurations studied have varying hole diameters and geometric spacing for spatial tuning of the heat transfer behaviour. The configuration also includes a straight section downstream of the curved section, where the effect on heat transfer and pressure loss is also investigated. For all configurations, spent air is drawn out in a single direction which is tangential to the target plate curvature. First row jet Reynolds numbers ranging from 50,000 to 160,000 are reported. The jet plate holes are sharp-edged. A steady-state measurement technique utilizing temperature sensitive paint (TSP) was used on the target surface to obtain heat transfer coefficients. Pressure taps placed on the sidewall and jet plate of the channel were used to evaluate the flow distribution in the impingement channel. Alongside the experimental work, CFD simulations were performed utilizing the v2-f eddy viscosity turbulence model to understand better the relationship between the flow field and the heat transfer on the target surface. The results from this study are compared against past results for uniform array impingement on flat surfaces.

Effect of Target Wall Curvature on Heat Transfer and Pressure Loss From Jet Array Impingement

2015 ◽  
Author(s):  
John Harrington ◽  
Arash Nayebzadeh ◽  
Jonathan Winn ◽  
Wenping Wang ◽  
Jayanta Kapat ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Loss ◽  
Flow Distribution ◽  
Target Surface ◽  
Temperature Sensitive ◽  
Target Plate ◽  
Target Wall ◽  
The Impact ◽  
Jet Array

Experiments to investigate the effect of target wall curvature on heat transfer and pressure loss from jet array impingement are performed. A jet plate configuration is studied with constant hole diameters and spacings. The geometry of the jet plate has streamwise jet spacings of 5.79 jet diameters, spanwise jet spacings of 4.49 jet diameters, and a jet-to-target plate distance of 3 jet diameters. For the curved case, the radius of the target plate is r/D=31.57. A flat target wall setup with identical geometric spacing is also tested for direct comparison. Jet spacings were chosen such that validation and comparison can be made with open literature. For all configurations, spent air is drawn out in a single direction which is tangential to the target plate curvature. Average jet Reynolds numbers ranging from 50,000 to 150,000 are tested. A steady-state measurement technique utilizing Temperature Sensitive Paint is used on the target surface to obtain Nusselt number distributions. Pressure taps placed on the sidewall of the channel are used to evaluate the flow distribution in the impingement channel. Alongside the experimental work, CFD was performed utilizing the v2-f turbulence model to better understand the relationship between the flow field and the heat transfer on the target surface. The main target of the current study is to quantify the impact of target wall radius, the decay of heat transfer after the impingement section and to check the open literature correlations. It was found that the target wall curvature caused higher heat transfer levels, with array-average Nusselt numbers increasing by an average of 28% when compared to the similar plane case. In the post-impingement section, increases in heat transfer levels were also seen with the curved case by up to 60%. Finally, CFD results were able to show agreement in stagnation point Nusselt number levels with experimental results for the curved target plate.

Use of Rib Turbulators to Enhance Postimpingement Heat Transfer for Curved Surface

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Jahed Hossain ◽  
Andres Curbelo ◽  
Christian Garrett ◽  
Wenping Wang ◽  
Jayanta Kapat ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Curved Surface ◽  
Temperature Sensitive ◽  
Straight Section ◽  
Target Plate ◽  
Cfd Simulations ◽  
Rib Turbulators

The present study aims to investigate the heat transfer and pressure loss characteristics for multiple rows of jets impinging on a curved surface in the presence of rib turbulators. The target plate contains a straight section downstream of the impingement section. The rib turbulators are added only over the straight section, in an attempt to enhance the heat transfer while minimizing the pressure loss. The jet plate configuration in this study has fixed jet hole diameters and hole spacing. For the curved plate, the radius of the target plate is 32 times the diameter of the impingement holes. Impingement array configuration was chosen such that validation and comparison can be made with the open literature. For all the configurations, crossflow air is drawn out in the streamwise direction. Average jet Reynolds numbers ranging from 55,000 to 125,000 were tested. Heat transfer characteristics are measured using steady-state temperature-sensitive paint (TSP) to obtain local heat transfer distribution. The experimental results are compared with computational fluid dynamics (CFD) simulations. CFD results show that CFD simulations predict the heat transfer distribution well in the postimpingement area with turbulators.

Effects of Height-to-Diameter Ratio of Pin Element on Heat Transfer From Staggered Pin-Fin Arrays

2009 ◽  
Author(s):  
Minking K. Chyu ◽  
Sean C. Siw ◽  
Hee Koo Moon
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Diameter Ratio ◽  
Hybrid Technique ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Test Models ◽  
Pin Fin Array

A pin-fin array is a compact heat exchanger and widely used for cooling of turbine airfoils. This study is to experimentally examine the effects of pin height or height-to-diameter ratio (H/D) on the heat transfer from a pin-fin array. The test models are designed to facilitate three different H/D ratios, from 2 to 4, with a staggered pin-fin array of inter-pin spacing 2.5 times the pin diameter (S/D = X/D = 2.5) in both longitudinal and transverse directions. The Reynolds number ranges from 10,000 to 30,000. The experiment uses a hybrid technique based on the transient liquid-crystal imaging to obtain detailed local heat transfer coefficients over both the pin-fin surface and endwalls. Overall array-averaged heat transfer increases with the H/D value or pin height. Most of the heat transfer contribution for H/D>2 comes from the pins rather than the endwall. However, higher H/D leads to a greater pressure loss. As a measure of heat transfer enhancement per pressure loss, H/D = 2 leads to the highest performance index and H/D = 4 is the lowest.

Use of Rib Turbulators to Enhance Post-Impingement Heat Transfer for Curved Surface

2016 ◽  
Author(s):  
Jahed Hossain ◽  
Christian Garrett ◽  
Andres Curbelo ◽  
John Harrington ◽  
Wenping Wang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Curved Surface ◽  
Temperature Sensitive ◽  
Straight Section ◽  
Target Plate ◽  
Cfd Simulations ◽  
Rib Turbulators

The present study aims to investigate the heat transfer and pressure loss characteristics for multiple rows of jets impinging on a curved surface in the presence of rib turbulators. The target plate contains a straight section downstream of the impingement section. The rib turbulators are added only over the straight section, in an attempt to enhance the heat transfer while minimizing the pressure loss. The jet plate configuration in this study has fixed jet hole diameters and hole spacing. For the curved plate, the radius of the target plate is 32 times the diameter of the impingement holes. Impingement array configuration was chosen such that validation and comparison can be made with the open literature. For all configurations, crossflow air is drawn out in the streamwise direction. Average jet Reynolds numbers ranging from 55,000 to 125,000 were tested. Heat transfer characteristics are measured using steady state temperature sensitive paint (TSP) to obtain local heat transfer distribution. The experimental results are compared with CFD simulations. CFD results show that CFD simulations predict the heat transfer distribution well in the post-impingement area with turbulators.

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.

Application of Pressure and Temperature Sensitive Paints for Study of Heat Transfer to a Circular Impinging Air Jet

2005 ◽  
Author(s):  
Quan Liu ◽  
A. K. Sleiti ◽  
J. S. Kapat
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Surface Flow ◽  
Temperature Sensitive ◽  
Number Range ◽  
Air Jet ◽  
Jet Characteristics ◽  
Second Peak

Experimental and computational studies are performed to study pressure and temperature distributions and flow patterns on impingement target surface subject to a single impinging air jet from a plenum. The experiments cover a range of jet-to- target plate distance, Z/D, from 1.5 to 12 for Reynolds number range from 5000 to 60000. The main objective is to investigate the optimal jet-to-target distance (Z/D) for stagnation point heat transfer and location of second peak of local heat transfer at small Z/D value of 1.5. Pressure and temperature sensitive paints measurements techniques are implemented to obtain the distribution of pressure and temperature on target surface. Flow visualization test has also been performed using surface oil and smoke technique to obtain the streamline distribution over the impinged surface and to qualitative study jet characteristics. The optimal (Z/D) is found to be 4.8 and second peak location for Z/D of 1.5 is at radial location (r/D) of 1.8. Comparison of average Nu with correlation from open literature, shows agreement to within experimental uncertainty for Z/D=5, while for Z/D=1.5 a 23% difference is found. Experimental results are compared to computational (CFD) prediction using Realizable κ-ε turbulence model.

Investigation of the Effects of Flow Swirl on Heat Transfer Inside a Cylindrical Cavity

1991 ◽  
Vol 113 (2) ◽  
pp. 348-354 ◽  
Author(s):  
A. Salce ◽  
T. W. Simon
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cylindrical Cavity ◽  
Flow Direction ◽  
Axial Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Sensitive ◽  
Transfer Coefficients ◽  
Cavity Bottom

Experiments were conducted to determine local heat transfer coefficients on the inside surfaces of a cylindrical cavity that is cooled by a swirling air flow. Temperature-sensitive liquid crystals were used as temperature sensors. Five blowing (cooling) modes were tested: three with swirl numbers of 0.36, 0.84, and 1.73; a fourth with no swirl (axial flow), and a fifth that was similar to the fourth but had the flow direction reversed. Flow visualization and static pressure measurements were performed to improve understanding of the situation. The smoke-wire technique was successfully used to picture the flow patterns. Plots of local Nusselt number along the cavity surfaces were obtained for the five blowing modes and for three different Reynolds numbers. The swirling cases had similar flow fields with higher heat transfer rates near the cavity top and lower rates near the cavity bottom (the opposite of the nonswirling cases). A tornadolike structure on the cavity bottom was observed in the swirling cases. This structure became stronger and more violent as the degree of swirl and the Reynolds number were increased. The Nusselt number curves for the two nonswirling cases were of similar shape, although the flow direction was reversed.

Experimental Investigation of the Effect of Synthetic Jets on Local Heat Transfer Coefficients in Minichannels During Laminar and Turbulent Flow Conditions

2013 ◽  
Author(s):  
David M. Sykes ◽  
Andrew L. Carpenter ◽  
Gregory S. Cole
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pressure Loss ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Microchannels and minichannels have been shown to have many potential applications for cooling high-heat-flux electronics over the past 3 decades. Synthetic jets can enhance minichannel performance by adding net momentum flux into a stream without adding mass flux. These jets are produced because of different flow patterns that emerge during the induction and expulsion stroke of a diaphragm, and when incorporated into minichannels can disrupt boundary layers and impinge on the far wall, leading to high heat transfer coefficients. Many researchers have examined the effects of synthetic jets in microchannels and minichannels with single-phase flows. The use of synthetic jets has been shown to augment local heat transfer coefficients by 2–3 times the value of steady flow conditions. In this investigation, local heat transfer coefficients and pressure loss in various operating regimes were experimentally measured. Experiments were conducted with a minichannel array containing embedded thermocouples to directly measure local wall temperatures. Flow regimes ranged from laminar to turbulent. Local wall temperature measurements taken directly beneath the synthetic jet in a laminar flow regime indicated that when a synthetic jet was used, the heat transfer coefficient was increased as much as 2.8 times the value as when synthetic jets were not used. Significant heat transfer coefficient augmentation also propagated to the upstream location, where heat transfer was increased to 2.2 times the value as when the synthetic jets were not used. Additional measurements show that synthetic jets significantly altered the pressure loss coefficient of the minichannels and that this effect was more pronounced in laminar flow than in turbulent flow. The effect of operating frequency on heat transfer and pressure loss is also presented. It was shown that the optimal operating point for the synthetic jet within a minichannel was in transitional to weakly turbulent flow (2600<Re<4500) to maximize the increase in heat transfer coefficient and minimize the increase in pressure loss.

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