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Question: dustoff or other propellant gas used to clean computer hardware...

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“Dust-off” or other propellant gas used to clean computer hardware is typically difluoroethane (C2H4F2). The vapour pressure is 87 psi at 25°C, the specific heat ratio is

γ = 1.14 and the gas’ molar mass is 66 g/mol. The gas jets through the nozzle orifice,

which acts as a converging nozzle with exit diameter of 2 mm. Assume that the propellant inside the can remains at 25°C for the entire operation, and that it can be assumed to be a perfect gas in its gas form.

a) Determine whether the flow is sonic or not at the exit of the nozzle. Determine the speed, pressure, temperature, and density of the flow at the nozzle exit plane.

b) Suppose one connects a divergent section at the exit of the nozzle. Determine the exit diameter of the divergent section, such that the exit pressure matches the ambient pressure.

c) Suppose that all the liquid inside the can is evaporated, and only 20 psi of gas remains. What will be the Mach number at the nozzle exit, if only the convergent section is used?

d) Repeat part c) assuming that the gas is incompressible.

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