A theory for predicting the size and velocity of droplets from pressure nozzles
1996
Sidahmed, M.M.
This article presents generalized theoretical and semitheoretical atomization equations, and examines their validity using published experimental data. It was postulated that atomization can be explained by energy balance in a process where a small mass (deltam) of liquid (with no initial surface) separates from a liquid sheet into a single droplet. This leads to drop-size/velocity correlation equations, which describe the behavior of droplets just after (or near) their formation. It also allows prediction of the lower limit for the minimum diameter (dfMIN) and the upper limit for the maximum diameter (dfMAX) in a spray. When viscosity is negligible, dfMIN is associated with Weber's number (Nwe), and dfMAX is associated with Bond's number (Nbo). When surface tension is negligible, dfMIN is associated with Reynold's number (Nre), and dfMAX is associated with a dimensionless group equivalent to NboNre/Nwe. The semitheoretical equation agreed well with the experimental data. The theoretical equation showed discrepancies at sizes below 100 micrometers, but overall agreement was reasonable. Also, 4.57% of the energy extracted from the liquid sheet was unaccounted for. While only 13.3% of that was attributed to the grouping of the data, the effect of grouping on velocities of smaller droplets was significant.
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