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Research Papers: Flows in Complex Systems

Onset of Flash Atomization in a Propellant Microjet

[+] Author and Article Information
Farzin M. Shemirani

Mem. ASME
Department of Mechanical Engineering,
University of Alberta,
4-9 Mechanical Engineering,
Edmonton, AB T6G 2G8, Canada
e-mail: farzin.shemirani@gmail.com

Tanya K. Church

Chiesi Ltd. Inc.,
Bath Road Industrial Estate,
Chippenham, Wiltshire SN14 0AB, UK
e-mail: t.church@chiesi.com

David A. Lewis

Chiesi Ltd. Inc.,
Bath Road Industrial Estate,
Chippenham, Wiltshire SN14 0AB, UK
e-mail: d.lewis@chiesi.com

Warren H. Finlay

Department of Mechanical Engineering,
University of Alberta,
5-08F Mechanical Engineering,
Edmonton, AB T6G 2G8, Canada
e-mail: warren.finlay@ualberta.ca

Reinhard Vehring

Department of Mechanical Engineering,
University of Alberta,
5-01G Mechanical Engineering,
Edmonton, AB T6G 2G8, Canada
e-mail: reinhard.vehring@ualberta.ca

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received November 29, 2014; final manuscript received March 14, 2015; published online April 29, 2015. Assoc. Editor: John Abraham.

J. Fluids Eng 137(9), 091101 (Sep 01, 2015) (9 pages) Paper No: FE-14-1713; doi: 10.1115/1.4030089 History: Received November 29, 2014; Revised March 14, 2015; Online April 29, 2015

The parameters affecting the onset of flashing in microjets were studied. A custom atomizer assembly was designed to produce jets of propellant mixtures at different temperatures. Propellants chosen were HFA134a and HFA227ea, which are used in most pressurized metered dose inhalers (pMDIs). Ethanol was added to the propellants to investigate its effect on flashing. Orifices used ranged from 5 to 35 μm in diameter. A critical jet diameter above which flashing was the dominant mechanism of atomization was found at each temperature and formulation. A correlation was developed to relate the critical jet diameter to the thermophysical properties of the formulation.

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Figures

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Fig. 1

Schematic of different components of a MDI: (1) formulation, (2) container, (3) metering volume, (4) metering valve, (5) valve stem, (6) actuator, and (7) actuator orifice

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Fig. 2

Schematic of heat and mass transfer processes involved in an isolated droplet with a bubble located at its center: T0 is the initial droplet diameter, Tb is the boiling point at pamb, Twb is the wet-bulb temperature, and d0 is the initial bubble diameter

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Fig. 3

(a) The atomizer used in the current study: (1) nozzle head, (2) orifice cup, (3) T-type thermocouple, (4) tubes for feed solution, (5) atomizer body, (6) base, (7) thermostatic liquid inlet tubing, (8) thermostatic liquid outlet tubing, (9) EPDM O-ring, and (10) micro-orifice plate. (b) Schematic of the feed reservoir: (1) orifice cup, (2) EPDM O-ring, (3) nozzle head, (4) micro-orifice plate, (5) T-type thermocouple, (6) thermostatic liquid, and (7) tubes to feed the reservoir.

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Fig. 4

Schematic diagram of the experimental setup

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Fig. 5

Images taken from HFA134a jets: (a) thin stable jet below critical temperature and (b) expanded unstable spray above critical temperature

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Fig. 6

Critical jet diameter depicted versus critical initial jet temperature for mixtures containing HFA134a (n = 3), 25 °C as a typical room temperature is specified by a dashed-dotted line

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Fig. 7

Critical jet diameter depicted versus critical initial jet temperature for mixtures containing HFA227ea (n = 3), 25 °C as a typical room temperature is specified by a dashed-dotted line

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Fig. 8

Plot of Π6 versus Π4 using a quadratic curve fit

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