The Effect of Geometrical, Operational, Mixing Methods, and Rheological Parameters on Discharge Coefficients of Internal-Mixing Twin-Fluid Atomizers

Accurate prediction of the discharge coefficient (C-D) for internal-mixing twin-fluid (IMTF) atomizers is challenging, the effect of control factors remains inadequately understood, and comparative data on the C(D)of IMTF atomizers are unavailable. This work presents an experimental study on C-D for different IMTF atomizers with a wide range of factors, including the gas-to-liquid ratio (GLR), the inlet-overpressure ratio (Delta p(mix)/p(amb)), the orifice length-to-diameter ratio (L-o/d(o)), and the liquid viscosity (mu(L)). Five atomizers with different internal-mixing principles were probed on a cold test rig, including the frequently studied outside-in-gas (OIG) and inside-out-gas (IOG) effervescent types, the recently-introduced outside-in-liquid (OIL) and air-core-liquid-ring (ACLR) atomizers, and our new design named the swirling-air-core-liquid-ring (SACLR) atomizer. The results demonstrate that C-D is governed mainly by GLR, and reduces if GLR, L-o/d(o), or mu(L)is increased. An increase in Delta p(mix)/p(amb)causes a C-D reduction up to Delta p(mix)/p(amb)= 0.98, and C-D increases for a higher Delta p(mix)/p(amb). Surprisingly, differences in C-D amid examined atomizers were found negligible, although the flow visualization inside the orifice showed a significantly different flow character for each one of the atomizers. Finally, a general C-D correlation fitting with an R-2 >= 0.99 for all the tested nozzles was proposed. The results amend the present knowledge, allow design optimization, and provide flow rate prediction for a variety of IMTF atomizers.