25362
Chemical
- Jan 5, 2003
- 4,826
Tests and accumulated experience have shown that pumps can handle hydrocarbons and some alcohols with less NPSH than would be necessary for cold degassed water. The Hydraulic Institute (1983, 14th Ed.) NPSH depicted these reductions in a graph.
The admissible NPSH reduction is apparently a function of vapor pressure and the density of the liquids pumped.
From this graph one can learn that if the NPSH3% for an available pump handling cold water is, say, 7 m, when planning to pump butane at 40oC (VP: 4 bar) with this pump, a reduction in NPSH3% of 1.4 m is in line. If butane were to be pumped at 80oC (VP:10 bar) the allowable reduction would be 3.0 m.
Practicing engineers are advised to use caution and treat these possible reductions as additional safety margins.
Having said that, here is my question: is there another underlying explanation for these facts to take place, apart from a reduction in the volume of vapors at higher temperatures (and corresponding pressures) ?
