Nozzle flow model for high pressure variable-rate spraying is indispensable when orchard sprayer is controlling liquid flow based on Pulse Width Modulation (PWM) technology. Three flow models for Teejet AITXA 8002, 8003 and 8004 nozzles are obtained by using nozzle flow model test system which is established in this paper. The results from equation hypothesis test and test for lack of fit of flow model shows that those three flow models work well. Nozzle flow model validation trials show that the relative errors of model flow and actual flow are small, while the maximum relative error is 6.50%; the flows characteristics of different nozzles with the same type are almost the same.
Single-hole (SH)
injectors were compared with multi-hole (MH) injectors
to reveal the differences in nozzle internal flow and spray propagation.
The multi-phase flow inside the nozzles was numerically investigated.
The nonevaporating near-field spray images were captured to observe
the spray dispersion profile near the nozzles using a microscopic
imaging technique. Moreover, the laser diagnostics technique of laser
absorption scattering (LAS) was implemented to measure the mixture
concentration distribution under evaporating condition. The result
indicates that a sharp change in the flow direction of MH injector
can lead to the cavitation region downstream to the hole axis. However,
the cavitation inside the SH injector only occurs on the wall of the
hole. The unstable cavitation flow inside the MH nozzle hole is an
important cause for spray perturbations in nozzle near-field. Furthermore,
at the beginning of the needle raising process, the injection rate
curve of SH injector with smaller discharge area rises faster than
that of MH injector, caused by the higher sac pressure. The lower
sac pressure, worse second breakup, and spray plumes interference
result in the sprays of MH injector entraining less ambient gas per
unit mass of fuel, compared with that of SH injectors. Moreover, the
larger the hole diameter is, the larger the gap of evaporation ratio
between the SH and MH injectors would be.
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