Vortex shedding from confined micropin arrays
Summary (1 min read)
- The present work is an attempt to obtain information on the rheological behaviour of sewage 11 sludge by performing electrical resistivity measurements.
- In simple electrolytic solutions, the relationship between resistivity and viscosity is linear and 14 straightforward.
- For rheological and electrical measurement, samples 9 were submitted to a slow ramp, from 4 to 35°C by using a thermostatic bath, also known as 8 Temperature dependence.
Temperature dependence 2
- When the temperature increased, the sludge became fluider, its apparent viscosity decreased 3 (fig. 2).
- Considering that the current flow through the structure is 19 due to surface charges and that surface charges give a picture of the solid structure and its 20 interactions, the authors can write: 21 ( ) == η η ρρ ;chargesurface;chargesfree fsf (5) 22 24.
- Nevertheless, additional works are needed in order to determine the physical meaning of the 1 parameters highlighted in the relationships between resistivity and viscosity.
- The use of rheology for sludge characterization.
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Cites background from "Vortex shedding from confined micro..."
...Micro pin–fins have been demonstrated to be viable for single-phase interlayer cooling of 3D-IC stacks [26,42–44]....
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Frequently Asked Questions (16)
Q1. What are the contributions in "Vortex shedding from confined micropin arrays" ?
The hydrodynamics in microcavities populated with cylindrical micropins was investigated using dynamic pressure measurements and fluid pathline visualization. The pathline visualization technique provided direct optical access to the flow field without any intermediate post-processing step and could be used to interpret the frequencies determined through pressure measurements.
Q2. What is the importance of the study of the detailed flow behavior?
Given the clear coupling of thermal transport with fluidics, the investigation of the detailed flow behavior is of paramount importance.
Q3. What is the effect of the reduced cavity height on the vortex shedding?
While high packaging densities and short TSVs are preferred for integrated water-cooled electronics, the reduced cavity height is expected to affect the flow behavior significantly.
Q4. What is the way to resolve flow fluctuations in microcavities?
The two-frame cross-correlation technique in lPIV resolves flow processes with a high temporal resolution in the microsecond time scale to instantly freeze flow fluctuation patterns in microcavities (Natrajan and Christensen 2010; Renfer et al. 2011).
Q5. What is the role of fluidics in microelectromechanical systems?
for compact systems as concentrated photovoltaics, power amplifiers and integrated circuits, the fluidics and related cooling at the microscale and nanoscale are becoming a crucial technology to further improve their performance.
Q6. What is the way to capture flow dynamics?
Visualization methods in general require high intensity light sources and fast charge coupled device (CCD) cameras to capture the fluid dynamics with a high temporal resolution.
Q7. How many data sets were used to calculate the frequency peak for a given Reynolds number?
Each frequency peak for a given Reynolds number was calculated by averaging 20 data sets in the frequency domain; each calculated from the FFT of the pressure signal acquired over a time interval of 500 ms.
Q8. Why do the pathlines capture the entire flow fluctuation period?
The pathlines capture the entire flow fluctuation period simply because with a longer exposure time the subsequent shedding cycles are superimposed on the same image.
Q9. What is the role of the hydrodynamics of flow past obstacles in microcavities?
Hydrodynamics of flow past obstacles confined in microcavities is relevant to a variety of microfluidic applications such as microfluidic memory and control elements (Groisman et al. 2003), micro-reactors (Moghtaderi 2007), electronics cooling (Renfer et al. 2011) and microporous media (Sen et al. 2012).
Q10. How does the reduction in aspect ratio affect vortex shedding?
For micropin arrays, using lPIV the authors previously reported that the reduction in aspect ratio suppresses the vortex shedding for a cavity height h = 100 lm up to Re = 330, whereas vortex shedding for the same pin diameter but with h = 200 lm already started at Re = 200 (Renfer et al. 2011).
Q11. Why was the dominant pressureoscillation Stmed observed in the FFT spectrum?
Due to the incompressibility of water, however, the dominant medium pressureoscillation Stmed starting downstream was still observed in the FFT spectrum from the inlet measurements (see in Fig. 9c for Re = 335).
Q12. Why were the low signal fluctuations only detected by the local measurements?
As noted above, due to their high sensitivity, the low signal fluctuations corresponding to Stlow and Sthigh were only detected by the local measurements.
Q13. What is the impact of fluid dynamics on heat transfer in integrated devices?
With respect to the latter, there is a clear impact of fluid dynamics on heat transfer in integrated devices: with the advancing miniaturization of high power density electrical devices, liquid based cooling solutions will become a conceivable strategy in the near future.
Q14. What is the frequency of unsteady vortices in the shear layer scales?
the frequency of unsteady vortices formed in the shear layer scales as f *Re1.67 (Prasad and Williamson 1997), whereas the measured fluctuation frequencies in their study vary linearly with Re.
Q15. What frequency component was assigned to the vortex shedding?
In the frequency spectrum at the outlet, for Re = 335 only the medium frequency component fmed was measured and therefore, it was assigned to vortex shedding as visualized in Fig. 9a.
Q16. What effect was observed for the longitudinal confinement of the flow between individual micropins?
A similar effect was observed for the longitudinal confinement of the flow between individual micropins, since the Strouhal number increased with smaller pitch-to-pin diameter ratios.