I have a small pump that does 6L/min flow-rate. With a pipe size of 0.5 inches and 3 nozzles spaced at a distance of about 1m each, is it possible to do effective misting? My total pipe length will be 4m. I have been trying out calculations from various references but it keeps driving me nuts. What am wondering is, is the pump fit for that job? I have seen similar pumps online with equal flow-rates and pressure ratings of about 130psi. What matters most?
Droplet size through a spray nozzle is a strong function of pressure drop. The higher the pressure drop, the smaller the drop size. So for an atomizer you need high pressure (probably >15 psi). Coarser droplets can be produced down to about 3 psi.
Check out the data sheets for you nozzles. They likely specify acceptable pressure drops and may also rate the droplet size (coarse to fine).
And, as is usual, the pressure drop across the nozzle is related to flow rate. Increasing one increases the other (check out "flow coefficient").
Finally, a small centrifugal pump probably won't let you atomize/mist, although that's not a fixed rule. Try positive displacement pumps like diaphragm or gear pumps to get higher pressures at low flows.