Counter flow atomizer: Effect of the area ratio of the outlet orifice and the inlet air canal

The need to reduce the energy demand of processes also creates pressure to make atomizers more efficient. A promising development path could be counterflow atomizers (CFA). An atomizer, or synonymously a nozzle, is a device that turns a liquid into a spray. The CFA is a twin-fluid type of atomizer because both the liquid and the atomizing gas are fed into it. Initial results suggest that CFA is capable of the same quality of atomization but using half the air mass flow rate compared to conventional twin-fluids atomizers when operated at identical inlet pressure. This means half the energy requirements with the same efficiency. This atomizer also shows a great promise in the atomization of highly viscous substances such as waste-based fuels and biomass oils. In CFA, the air expands twice; first, at the discharge from the air inlet canal into the mixing tube, and second, at the discharge from the atomizer to the surrounding atmosphere. Therefore, one of the main control parameters is the area ratio of the exit orifice and the air inlet canal. This study experimentally investigates the effect of this ratio on the spray quality for two different CFA atomizers using Phase Doppler Anemometry (PDA), which provides the velocity and size of individual droplet in the spray. The atomizers were operated at the air inlet pressure of 100 and 200 kPa and gas-to-liquid mass (GLR) ratios of 5, 10 and 20%. The effect of the double expansion can be well observed in the pressure differences between the air inlet and the pressure inside the mixing tube. The length of the air counterflow insert had a significant effect on the atomizer performance. For the shorter counterflow channel, a minimal effect on flow was observed; this atomizer behaved like a conventional twin-fluid atomizer and all expansions occurred downstream of the exit orifice. The longer counterflow canal changed the internal expansion ratios, larger droplets, wider spray and higher discharge coefficients (Cd) were obtained