Stoff‐ und Wärmeübergang an umströmten Platten, Zylindern und Kugeln

Brauer, Heinz; Sucker, D.

doi:10.1002/cite.330480903

Cited by 23 publications

(4 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The temperature of the droplet changes due to convective heat transfer to the surrounding air flow, and the Reynolds number (based on the relative velocity of the droplet to the surrounding air) is used to calculate the Nusselt number. The Reynolds number is given by: The Nusselt number is calculated according to the formula of Brauer/Sucker for a sphere [14,15] valid for a range of 0 ≤ Re ≤ 3 ⋅ 10 5 :…”

Section: Temperaturementioning

confidence: 99%

Kinetic and thermal simulation of water droplets in icing wind tunnels

et al. 2021

View full text Add to dashboard Cite

Within the certification process of aircraft, tests under specific icing conditions are required. For such safety relevant tests—which are performed under defined and repeatable test conditions—specially equipped Icing Wind Tunnels (IWT) are required. In such IWTs, supercooled water droplets are created with the aid of a spray system injecting pre-tempered water droplets of specific diameters into the free stream air flow. Especially tests with a droplet size up to 2mm (Supercooled Large Droplets - SLDs) are of great importance. SLDs are difficult to generate under laboratory conditions in IWT since usually the available droplet flight time from the injection location to the impact position on the test object is insufficient to reliably cool down a droplet at least to freezing temperature. To investigate the limitations associated with the application of SLD, the current work provides a method to allow detailed insight into the behavior of droplets on the path from the injection spray nozzle to the test section. In this work a state space model of a single droplet is derived that combines the kinetic aspects, thermal properties as well as the governing differential equations for motion, convective heat transfer at the droplet surface and heat conduction inside the droplet. Beside the states for the droplet’s position and velocity in space, the state space vector comprises various fluid and thermodynamic parameters. The droplet-internal temperature distribution is modelled by a discrete one-dimensional spherical shell model that also incorporates the aggregate phase (freezing mass fraction) at each shell node. This approach allows, therefore, the simulation of potential droplet phase change processes (freezing/melting) as well. With the model at hand, the influence of various boundary conditions (initial droplet temperature, flow field, ambient air temperature, etc.) can be determined and evaluated. As a result, concrete measures to achieve a desired operating condition (e.g. droplet temperature at the test object) for various model assumptions can be derived. In addition, the simulation model facilitates the prediction of the droplet diameter threshold for ensuring a supercooled state upon the impact on the test object. The governing theoretical influences are described, and various simulation results for representative test conditions that occur at the Rail-Tec-Arsenal (RTA) in Vienna are presented.

show abstract

Section: Temperaturementioning

confidence: 99%

Kinetic and thermal simulation of water droplets in icing wind tunnels

et al. 2021

View full text Add to dashboard Cite

show abstract

“…Für die Berechnung der REYNOLDS‐Zahl (Gl. ) wurde das Modell für „längsumströmte Platten“ verwendet, das dem quaderförmigen Mikrospalt ähnelt . Diese ergibt mit einem Wert von Re = 4,28 ein laminares Strömungsprofil unter den verwendeten Reaktionsbedingungen.

true Re = \frac{ul}{v}

…”

Section: Ergebnisse Und Diskussionunclassified

Quaternäre Metall/Metalloxid‐Katalysatoren als Wandkatalysatoren in Mikroreaktoren für Power‐to‐Gas‐Applikationen mittels kombinatorischer Hochdurchsatzmethoden

Pfeifer

Schwarz

Stöwe

2019

Chemie Ingenieur Technik

View full text Add to dashboard Cite

Zur Untersuchung des Sabatier‐Prozesses werden quaternäre Katalysatoren synthetisiert und getestet. Die Synthesen erfolgen durch Imprägnierung und Sol‐Gel. Das Screening der Katalysatoren erfolgt bei Temperaturen zwischen 520 und 670 K, Drücken von 15 bzw. 30 bar, einem H2/CO2‐Verhältnis von 4:1 und wird in einem speziell dafür konstruierten 10‐fach‐Parallel‐Gasphasen‐Strömungsreaktor im sequentiellen Betriebsmodus durchgeführt. Die Katalysatoren werden auf Mikrospaltplatten beschichtet und für das Screening in den Reaktor eingeführt. Die Analyse der Gasphasenzusammensetzung erfolgt mittels GC‐FID.

show abstract

“…For water evaporation from structures with very small dimensions, the Péclet numbers are small and the thickness of the concentration boundary layer is in the range of the microchannel dimensions. Brauer and Sucker 16 solved the differential equations of the concentration field by numerically showing that the boundary layer theory is no longer applicable for flows at low Péclet numbers and that the Sherwood number approaches an asymptote for Pe → 0 given in eqn (7).…”

Section: Convective Mass Transfermentioning

confidence: 99%

“…In the literature, only few data for flow over a flat structure for such low Péclet numbers can be found. For very low Reynolds numbers (Re < 0.1, Stokes flow) and intermediate Reynolds numbers (Re = 1-10), correlations are available for different kinds of geometries such as flat plates, 16 spheres, 17 and cylinders. 18 For all geometries, the influence of air velocity on the mass transfer rate decreases with decreasing air velocity.…”

Section: Introductionmentioning

confidence: 99%

Evaporation from open microchannel grooves

et al. 2014

View full text Add to dashboard Cite

The evaporation of water from open u-shaped microchannel grooves was investigated with particular emphasis on the roles of channel width and air flow conditions. Given the small dimensions of the microchannels, all measurements were conducted in a range where convection and diffusion are of equal importance and known correlations for the calculation of mass transfer coefficients cannot be applied. The evaporation rates were measured using a new optical method and a gravimetric method. Both measurement methods yielded mass transfer coefficients that are in agreement with each other. The observed relation between mass transfer coefficient, air velocity and channel width vastly differs from the predictions obtained from macroscopic structures. With respect to diagnostic devices we conclude that analyte concentration in an open microchannel groove strongly increases even within short times due to the evaporation process and we show that wider channels are more favourable in terms of minimizing the relative evaporation rate.

show abstract

Stoff‐ und Wärmeübergang an umströmten Platten, Zylindern und Kugeln

Cited by 23 publications

References 10 publications

Kinetic and thermal simulation of water droplets in icing wind tunnels

Kinetic and thermal simulation of water droplets in icing wind tunnels

Quaternäre Metall/Metalloxid‐Katalysatoren als Wandkatalysatoren in Mikroreaktoren für Power‐to‐Gas‐Applikationen mittels kombinatorischer Hochdurchsatzmethoden

Evaporation from open microchannel grooves

Contact Info

Product

Resources

About