Centreline velocity characteristics of local exhaust ventilation hoods

Recent experimental studies of centreline velocities in front of plain and flanged local exhaust ventilation hoods have shown that design equations based on the work of Dalla-valle hand Silverman are not valid in general. However, these equations form the basis of today's design methods and are still widely used and advocated by authors despite the large errors in the velocities predicted by them. Garrison compared his experimental data obtained recently for high velocity/low volume exhaust nozzles with results predicted by Dallavalle's and Silverman's equations and found significant variations. Some of Garrison's data are compared here with the formula developed by Fletcher and are found to give very close agreement.