Space velocity

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The space velocity of a star is its velocity relative to the Sun or the Local standard of rest. 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 ^[1].

Also in chemical reactor design space velocity represents how fast a molecules (volume) move inside the reactor. It is often denoted by SV and it is related to the residence time in a chemical reactor, τ.

In the relationship, SV = 1/τ

When 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.