Abstract
Accurate prediction of the discharge coefficient (CD) for internal-mixing twin-fluid (IMTF) atomizers is challenging, the effect of control factors remains inadequately understood, and comparative data on the CD of IMTF atomizers are unavailable. This work presents an experimental study on CD for different IMTF atomizers with a wide range of factors, including the gas-to-liquid ratio (GLR), the inlet-overpressure ratio (∆pmix/pamb), the orifice length-to-diameter ratio (Lo/do), and the liquid viscosity (µL). 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 CD is governed mainly by GLR, and reduces if GLR, Lo/do, or µL is increased. An increase in ∆pmix/pamb causes a CD reduction up to ∆pmix/pamb = 0.98, and CD increases for a higher ∆pmix/pamb. Surprisingly, differences in CD 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 CD correlation fitting with an R2 ≥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.
Highlights
Twin-fluid (TF) atomizers were found to be more advantageous over other liquid atomization devices in numerous applications including gas turbines [1,2,3], scramjet [4], internal combustion engines [5,6], furnaces, and boilers [7,8,9]
CD features a sharp decrease when increasing the gas-to-liquid ratio (GLR) to ≈30%, while a further GLR increase has little effect on CD. This behavior results from the link between the GLR and the flow area occupied by the liquid inside the exit orifice [26]
The actual area available for the liquid flow decreases with any increase in the gas flow rate
Summary
Twin-fluid (TF) atomizers were found to be more advantageous over other liquid atomization devices in numerous applications including gas turbines [1,2,3], scramjet [4], internal combustion engines [5,6], furnaces, and boilers [7,8,9]. They have been used for spray drying in the food industry [10,11,12,13,14,15], humidification, dust control, gas cooling, spray coating [16], pharmaceutical or consumer products [17], and water mist fire suppression systems [18]. This effect can be achieved by exposing the bulk liquid to a sudden and sharp pressure drop (during an isothermal expansion process) or by isobaric heating
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