Influence of Excitation Frequency, Phase Shift, and Duty Cycle on Cooling Ratio in a Dynamically Forced Impingement Jet Array

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Arne Berthold ◽  
Frank Haucke
Keyword(s):  
Phase Shift ◽  
Duty Cycle ◽  
Excitation Frequency ◽  
Liquid Crystal Thermography ◽  
Impingement Jet ◽  
Nusselt Numbers ◽  
Cycle Variation ◽  
The Impact ◽  
Frequency Phase ◽  
Jet Array

Abstract The cooling ratio on a dynamically forced 7 × 7 impingement jet array is studied experimentally. The current study is focused on determining the influence of a phase shift between every row of nozzles as well as the impact of a duty cycle variation on the cooling ratio. Both parameters are studied in dependency of the impingement distance (H/D = 2, 3, 5), the (nozzle-) Reynolds-number (ReD = 3200, 5200, 7200), and the excitation frequency (f = 0 Hz − 1000 Hz). For every set of parameters, the phase shift between every row of nozzles is varied between Φ=0% and 90%, while the variation of the duty cycle is performed between duty cycle (DC) = 35% and 65%. During all investigations, the dimensionless distance between adjacent nozzles is fixed at Sx/D = Sy/D = 5, and liquid crystal thermography is used to acquire the wall temperatures, which are further processed to calculate the local Nusselt numbers. Generally, the implementation of an excitation frequency allows a case-depending increase in the cooling ratio of up to 52%. Further implementation of a phase shift yields an additional frequency-depending improvement of the cooling ratio. In case of duty cycle variation, the best case revealed an additional 19% improvement in the cooling ratio.

Influence of Excitation Frequency, Phase-Shift and Duty Cycle on Cooling Ratio in a Dynamically Forced Impingement Jet Array

2019 ◽  
Author(s):  
Arne Berthold ◽  
Frank Haucke
Keyword(s):  
Phase Shift ◽  
Duty Cycle ◽  
Excitation Frequency ◽  
Liquid Crystal Thermography ◽  
Impingement Jet ◽  
Nusselt Numbers ◽  
Cycle Variation ◽  
The Impact ◽  
Frequency Phase ◽  
Jet Array

Abstract The cooling ratio on a dynamically forced 7×7 impingement jet array is studied experimentally. The current study is focused on determining the influence of a phase-shift between every row of nozzles as well as the impact of a duty cycle variation on the cooling ratio. Both parameters are studied in dependency of the impingement distance (H/D = 2, 3, 5), the (nozzle-)Reynolds-number (ReD = 3200, 5200, 7200) and the excitation frequency (f = 0 Hz – 1000 Hz). For every set of parameters, the phase-shift between every row of nozzles is varied between Φ = 0% – 90% while the variation of the duty-cycle is performed between DC = 35% – 65%. During all investigations, the dimensionless distance between adjacent nozzles is fixed at x/D = y/D = 5 and liquid crystal thermography is used to acquire the wall temperatures, which are further processed to calculate the local Nusselt numbers. Generally, the implementation of an excitation frequency allows a case depending increase in cooling ratio of up to 52%. Further implementation of a phase-shift yields an additional frequency-depending improvement of the cooling ratio. In case of duty cycle variation, the best case revealed an additional 19% improvement in cooling ratio.

Crossflows From Jet Array Impingement Cooling: Effects of Hole Array Spacing, Jet-to-Target Plate Distance, and Reynolds Number

2014 ◽  
Author(s):  
Junsik Lee ◽  
Zhong Ren ◽  
Phil Ligrani ◽  
Michael D. Fox ◽  
Hee-Koo Moon
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Hole Array ◽  
Target Plate ◽  
Impingement Jet ◽  
Nusselt Numbers ◽  
Cooling Effects ◽  
Plate Distance ◽  
Jet Array

Data which illustrate the combined and separate effects of hole array spacing, jet-to-target plate distance, and Reynolds number on cross-flows, and the resulting heat transfer, for an impingement jet array are presented. The array of impinging jets are directed to one flat surface of a channel which is bounded on three sides. Considered are Reynolds numbers ranging from 8,000 to 50,000, jet-to-target plate distances of 1.5D, 3.0D, 5.0D, and 8.0D, and steamwise and spanwise hole spacing of 5D, 8D, and 12D, where D is the impingement hole diameter. In general, the cumulative accumulations of cross-flows, from sequential rows of jets, reduce the effectiveness of each individual jet (especially for jets at larger streamwise locations). The result is sequentially decreasing periodic Nusselt number variations with streamwise development, which generally become more significant as the Reynolds number increases, and as hole spacing decreases. In other situations, the impingement cross-flow results in locally augmented Nusselt numbers. Such variations most often occur at larger downstream locations, as jet interactions are more vigorous, and local magnitudes of mixing and turbulent transport are augmented. This occurs in channels at lower Reynolds numbers, where impingement jets are confined by smaller hole spacing, and smaller jet-to-target plate distance. The overall result is complex dependence of local, line-averaged, and spatially-averaged Nusselt numbers on hole array spacing, jet-to-target plate distance, and impingement jet Reynolds number. Of particular importance are the effects of these parameters on the coherence of the shear layers which form around the impingement jets, as well as on the Kelvin-Helmholtz instability vortices which develop within the shear interface around each impingement jet.

WINGLET-PAIR TARGET SURFACE ROUGHNESS INFLUENCES ON IMPINGEMENT JET ARRAY HEAT TRANSFER

2019 ◽  
Vol 26 (1) ◽  
pp. 15-35 ◽  
Author(s):  
Phillip Ligrani ◽  
Patrick McInturff ◽  
Masaaki Suzuki ◽  
Chiyuki Nakamata
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Target Surface ◽  
Impingement Jet ◽  
Jet Array

scholarly journals Impact of Duty Cycle Variation on WSNs

2009 ◽  
Author(s):  
Sithu Sudarsan ◽  
Vimalathithan Subramanian ◽  
Kenji Yoshigoe ◽  
Srini Ramaswamy ◽  
Remzi Seker ◽  
...  
Keyword(s):  
Duty Cycle ◽  
Cycle Variation

scholarly journals Middle atmosphere response to the solar cycle in irradiance and ionizing particle precipitation

2011 ◽  
Vol 11 (10) ◽  
pp. 5045-5077 ◽  
Author(s):  
K. Semeniuk ◽  
V. I. Fomichev ◽  
J. C. McConnell ◽  
C. Fu ◽  
S. M. L. Melo ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Radiative Forcing ◽  
Climate Model ◽  
Middle Atmosphere ◽  
High Energy ◽  
Galactic Cosmic Rays ◽  
Particle Precipitation ◽  
Solar Cycle Variation ◽  
Cycle Variation ◽  
The Impact

Abstract. The impact of NOx and HOx production by three types of energetic particle precipitation (EPP), auroral zone medium and high energy electrons, solar proton events and galactic cosmic rays on the middle atmosphere is examined using a chemistry climate model. This process study uses ensemble simulations forced by transient EPP derived from observations with one-year repeating sea surface temperatures and fixed chemical boundary conditions for cases with and without solar cycle in irradiance. Our model results show a wintertime polar stratosphere ozone reduction of between 3 and 10 % in agreement with previous studies. EPP is found to modulate the radiative solar cycle effect in the middle atmosphere in a significant way, bringing temperature and ozone variations closer to observed patterns. The Southern Hemisphere polar vortex undergoes an intensification from solar minimum to solar maximum instead of a weakening. This changes the solar cycle variation of the Brewer-Dobson circulation, with a weakening during solar maxima compared to solar minima. In response, the tropical tropopause temperature manifests a statistically significant solar cycle variation resulting in about 4 % more water vapour transported into the lower tropical stratosphere during solar maxima compared to solar minima. This has implications for surface temperature variation due to the associated change in radiative forcing.

Analytical and Experimental Simulation of Loose Pedestal Dynamic Effects on a Rotating Machine Vibrational Response

1991 ◽  
Author(s):  
Pavel Goldman ◽  
Agnes Muszynska
Keyword(s):  
Excitation Frequency ◽  
Experimental Studies ◽  
Experimental Simulation ◽  
Physical Parameters ◽  
Vibrational Response ◽  
Rotating Machine ◽  
Qualitative Pattern ◽  
The Impact ◽  
Good Agreement ◽  
Periodic Changes

Abstract This report presents experimental, analytical, and numerical results describing vibrational phenomena in a rotating machine with one loose pedestal. The loose-pedestal machine rotor vibrations represent unbalance-related excited vibrations of synchronous and fractional subsynchronous regimes. In this study the loose-pedestal machine is first simulated by a simple vibrating beam excited by a shaker mounted on it. The shaker simulates an unbalanced machine rotor. The beam occasionally enters in contact with the foundation. The excited vibrations are modified by impacting occurrences, and by periodic changes in system stiffness. A new model of the impact has been developed. The results of analytical and experimental studies stand in a good agreement. They illustrate the existence of the synchronous regime and several subsynchronous fractional regimes in various excitation frequency ranges. The analysis adequately predicts the occurrence of these regimes and determines the physical parameters affecting them. The analytical and experimental results are then compared with the responses of experimental rotor rig with one bearing pedestal looseness. They show the same qualitative pattern.

Quantifying Office Productivity: An Ergonomic Framework

1998 ◽  
Vol 42 (13) ◽  
pp. 974-978 ◽  
Author(s):  
Alan Hedge
Keyword(s):  
Life Cycle ◽  
Duty Cycle ◽  
Office Workers ◽  
Short Term ◽  
Task Time ◽  
Ergonomic Interventions ◽  
The Impact

An ergonomic framework for conceptualizing and measuring office productivity is described. This framework is based on the the analysis of task time, posture and sequence, and the subsequent the determination of the most appropriate pace, posture, and activities for any office job. The framework assesses various measures of pace, proficiency, and posture that currently can be readily assessed by ergonomists, and it uses these measures to quantify the short-term duty cycle productivity (DCP) and in the longer-term life-cycle productivity (LCP) of office workers. The approach that will be described allows companies to evaluate the impact of ergonomic interventions on the productivity of their workers. The benefits of this ergonomic approach to assessing productivity are discussed.

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