Space velocity

Space velocity

The space velocity of an astronomical object is its "actual motion" relative to the Sun or the Local standard of rest.

Astrometry

Its components in the Galactic coordinate system are usually designated U, V, and W, given in km/s, with U positive in the direction of the Galactic center, V positive in the direction of Galactic rotation, and W positive in the direction of the North Galactic Pole. These velocity components can be calculated from the observed radial velocity, proper motion and parallax [Johnson & Soderblom 1987, Astronomical Journal 93, 864] .

Chemistry

In chemical reactor design, space velocity represents the relation between volumetric flow and reactor volume (or catalyst bed volume). It is often denoted by SV and is related to the residence time in a chemical reactor, τ, by the relationship, SV = volumetric flow/reactor volume = 1/τwhere the space velocity and the residence time are calculated at the same conditions.

The space velocity, in chemical reactor design, indicates how many reactor volumes of feed can be treated in a unit time. For example, a reactor with a space velocity of 7 hr-1 is able to process feed equivalent to seven times the reactor volume each hour.

Space velocities may also be calculated on a weight basis. These are typically used to describe catalytic reactors, and are denoted as weight hourly space velocity, WHSV. WHSV = mass flow/catalyst mass

Notes

References

* cite web
last = Majewski
first = Steven R.
year = 2006
url = http://www.astro.virginia.edu/class/majewski/astr551/lectures/VELOCITIES/velocities.html
title = Stellar Motions
publisher = University of Virginia
accessdate = 2008-02-25
* cite web
url = http://csep10.phys.utk.edu/astr162/lect/motion/space.html
title = The Space Velocity and its Components
publisher = University of Tennessee
accessdate = 2008-02-25

See also

* Astrometry
* Gaia probe
* Hipparcos


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