Pressure dependence of hot-wire anemometer readings

Nekrasov, Yu. P.; Savostenko, P. I.

doi:10.1007/bf00975261

Cited by 4 publications

(5 citation statements)

References 1 publication

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“…Durst et al 1996) and pressure drift (e.g. Nekrasov & Savostenko 1991); problems with wire degradation such as change in material properties due to incomplete cleaning (Willmarth & Bogar 1977), electromigration (see Willmarth & Sharma 1984) and wire fouling (Wyatt 1953); and wider problems with the facility such as pressure gradients (Fernholz & Warnack 1998) and elevated free-stream intensities (Hancock & Bradshaw 1989;Barrett & Hollingsworth 2003;Stefes & Fernholz 2004). Many of the data included in figures 1 and 2 use U τ values obtained using the Clauser method (see § 2.4 for a description of the errors associated with this technique).…”

Section: Experimental Errormentioning

confidence: 99%

Hot-wire spatial resolution issues in wall-bounded turbulence

et al. 2009

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Careful reassessment of new and pre-existing data shows that recorded scatter in the hot-wire-measured near-wall peak in viscous-scaled streamwise turbulence intensity is due in large part to the simultaneous competing effects of the Reynolds number and viscous-scaled wire length l+. An empirical expression is given to account for these effects. These competing factors can explain much of the disparity in existing literature, in particular explaining how previous studies have incorrectly concluded that the inner-scaled near-wall peak is independent of the Reynolds number. We also investigate the appearance of the so-called outer peak in the broadband streamwise intensity, found by some researchers to occur within the log region of high-Reynolds-number boundary layers. We show that the ‘outer peak’ is consistent with the attenuation of small scales due to large l+. For turbulent boundary layers, in the absence of spatial resolution problems, there is no outer peak up to the Reynolds numbers investigated here (Reτ = 18830). Beyond these Reynolds numbers – and for internal geometries – the existence of such peaks remains open to debate. Fully mapped energy spectra, obtained with a range of l+, are used to demonstrate this phenomenon. We also establish the basis for a ‘maximum flow frequency’, a minimum time scale that the full experimental system must be capable of resolving, in order to ensure that the energetic scales are not attenuated. It is shown that where this criterion is not met (in this instance due to insufficient anemometer/probe response), an outer peak can be reproduced in the streamwise intensity even in the absence of spatial resolution problems. It is also shown that attenuation due to wire length can erode the region of the streamwise energy spectra in which we would normally expect to see kx−1 scaling. In doing so, we are able to rationalize much of the disparity in pre-existing literature over the kx−1 region of self-similarity. Not surprisingly, the attenuated spectra also indicate that Kolmogorov-scaled spectra are subject to substantial errors due to wire spatial resolution issues. These errors persist to wavelengths far beyond those which we might otherwise assume from simple isotropic assumptions of small-scale motions. The effects of hot-wire length-to-diameter ratio (l/d) are also briefly investigated. For the moderate wire Reynolds numbers investigated here, reducing l/d from 200 to 100 has a detrimental effect on measured turbulent fluctuations at a wide range of energetic scales, affecting both the broadband intensity and the energy spectra.

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Section: Experimental Errormentioning

confidence: 99%

Hot-wire spatial resolution issues in wall-bounded turbulence

et al. 2009

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“…Contrarily, the air flow is caused by the continuous action of the pump (until the leak rate equals the pump rate) and therefore decays much slower. For practical use of our models, we would highly recommend either directly measuring the air velocity over time within the chamber (accounting for the decreasing pressure [ 66 ] ) or measuring the drying dynamics of a simple reference, for example, pure solvent film, and then use k u and u 0,start as free fit parameters (we have not done this herein because we prefer model validation from general principles to pure mathematical fitting of parameters).…”

Section: Resultsmentioning

confidence: 99%

Modeling and Fundamental Dynamics of Vacuum, Gas, and Antisolvent Quenching for Scalable Perovskite Processes

Ternes,

Laufer,

Paetzold

2024

Advanced Science

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Hybrid perovskite photovoltaics (PVs) promise cost‐effective fabrication with large‐scale solution‐based manufacturing processes as well as high power conversion efficiencies. Almost all of today's high‐performance solution‐processed perovskite absorber films rely on so‐called quenching techniques that rapidly increase supersaturation to induce a prompt crystallization. However, to date, there are no metrics for comparing results obtained with different quenching methods. In response, the first quantitative modeling framework for gas quenching, anti‐solvent quenching, and vacuum quenching is developed herein. Based on dynamic thickness measurements in a vacuum chamber, previous works on drying dynamics, and commonly known material properties, a detailed analysis of mass transfer dynamics is performed for each quenching technique. The derived models are delivered along with an open‐source software framework that is modular and extensible. Thereby, a deep understanding of the impact of each process parameter on mass transfer dynamics is provided. Moreover, the supersaturation rate at critical concentration is proposed as a decisive benchmark of quenching effectiveness, yielding ≈ 10−3 − 10−1s−1 for vacuum quenching, ≈ 10−5 − 10−3s−1 for static gas quenching, ≈ 10−2 − 100s−1 for dynamic gas quenching and ≈ 102s−1 for antisolvent quenching. This benchmark fosters transferability and scalability of hybrid perovskite fabrication, transforming the “art of device making” to well‐defined process engineering.

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“…Drift which is not uniquely associated with changes in temper ature has been less extensively studied. Changes in other thermophysical properties, such as humidity [18] or pres sure [19], can also cause a hot-wire to drift, and both [18] and [19] provide compensation techiques to account for this. However, like the aforementioned temperature compensation Resistance of a 2.5 µm diameter tungsten wire as a function of total hours of operation of the sensor.…”

Section: Literature Reviewmentioning

confidence: 99%

Drift compensation in thermal anemometry

Hewes

Medvescek

Mydlarski

et al. 2020

Meas. Sci. Technol.

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The drift of the resistance of sensors used in thermal (such as hot-wire and hot-film) anemometry remains a perpetual concern for users of constant-temperature anemometers (CTAs). Even small changes in the resistance of such sensors result in error if the sensor was calibrated prior to the occurrence of the drift. In the present work, modified forms of the relationship between the output voltage of a constant-temperature anemometer and the fluid velocity, which take into account the sensor resistance as well as other resistances involved in the Wheatstone bridge (top resistance, operating resistance, cable and probe resistances), are used to minimize the sensitivity of the CTA to changes in the sensor resistance. These new relationships are tested using (i) two different CTAs and (ii) three hot-wires of differing resistances (3-17 Ω), and are shown to collapse the calibration data, even though the sensor resistances had drifted. It is expected that use of this method would reduce the frequency of calibrations needed to maintain satisfactory degrees of accuracy and repeatability in experimental measurements of fluid flows made using CTAs.

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Pressure dependence of hot-wire anemometer readings

Cited by 4 publications

References 1 publication

Hot-wire spatial resolution issues in wall-bounded turbulence

Hot-wire spatial resolution issues in wall-bounded turbulence

Modeling and Fundamental Dynamics of Vacuum, Gas, and Antisolvent Quenching for Scalable Perovskite Processes

Drift compensation in thermal anemometry

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