![]() Loy Upp, in Fluid Flow Measurement (Third Edition), 2014 Flow NozzlesĪnother important flow element is the flow nozzle. The results showed that an increase in temperature had the effect of enhancing cavitation due to lower viscosity and weaker molecular bounding. The effect of viscosity was only evident during early stage of cavitation with a delay on the onset of the cavitation and less intense cavitation with blends at higher viscosity the latter was less evidence at CN = 2.2 and above when cavitation was more or less developed. It is expected to affect spray outside the nozzles which needs to be quantified in future study by high speed spray visualization and the droplets velocity/size measurements by a PDA system. It was found that the flow with the larger L/D are more developed and stable than those in the shorter L/D nozzle due to longer time which allows the flow to be diffused more and become more uniform. The main effect of L/D was observed to be at the exit of the nozzle where different types of in-nozzle flow would be experienced due to different length of the nozzles. This was expected as the geometrical boundary condition upstream of the nozzle were exactly the same and therefore similar hydrodynamic forces. The effect of L/D on the in-nozzle flow structures over the same length of the nozzle from the entrance was negligible at all operating conditions. The effect of needle lift on the onset cavitation with both models was considerable so that a reduction of the needle lift suppressed the cavitation intensity, in particular, the vortex cavitation for example, the onset of the cavitation was delayed from a CN ≈ 1.1 at full lift to CN = 1.9 at 25% of the full where no VC could be observed. In-nozzle flow comparison between the first model, M1, and those observed by in a 30 times enlarged model similar similar two-phase in-nozzle flows with a dominant well-known horseshoe geometrical cavitation and a central dynamic vortex cavitation they found to be highly complex, transient and unstable.
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