Velocity and space

It may be more convenient to measure the volumetric feed rate at some standard state, especially when the reactor is to operate at a number of temperatures. If, for example, the material is gaseous when fed to the reactor at high temperature but is liquid at the standard state, care must be taken to specify precisely what state has been chosen. The relation between the space-velocity and space-time for actual feed conditions (unprimed symbols) and at standard conditions (designated by primes) is given by... 

In most of what follows, we deal with the space-velocity and space-time based on feed at actual entering conditions however, the change to any other basis is easily made. 

Process technology and chemical engineering as we understand it today began with the successful realization of the technical ammonia synthesis. Continuous production with high space velocities and space yields combined with the ammonia oxidation process developed immediately thereafter enabled chemical industry for the first time to compete successfully with a cheap natural bulk product, namely, sodium nitrate from Chile. The synthesis of ammonia thus became exemplary for all subsequent chemical mass production processes. 

When an external field is present, a coupling between velocity and space is established, making it necessary to replace Eq. (1.4) with... 

The ratio (1 /v) is the volume of mixture in the reactor divided by the volume of mixture fed to the reactor per unit time and is called the space time, t. The inverse of the space time is called the space velocity. In each case, the conditions for the volume of the feed must be specified temperature, pressure (in the case of a gas), and state of aggregation (liquid or gas). Space velocity and space time should be used in preference to contact time or holding time since there is no unique residence time in the CSTR (see below). Why develop this terminology Consider a batch reactor. The material balance on a batch reactor can be written [from Equation (3.2.1)] ... 

SECTION 3-6 SPACE VELOCITY AND SPACE TIME IN TUBULAR-FLOW REACTORS... 

Space Velocity and Space Time in Tubular-flow Reactors... 

The advantage to be gained from a high current density it has been seen in section 2.5 that the reactor performance (as evidenced by, for example, the fractional conversion, mass-transport coefficient, space velocity and space-time yield) is enhanced at higher currents. 

---