Compressed-Gas Spray

volume

moles

temperature

pressure

stop at -5 °C

adjust stopping time

initial volume fraction of liquid

0.75

spray gas

Compressed-gas dusters can be used to remove dust from electronics by spraying a refrigerant gas (in this case, DFE, 1,1-difluoroethane). As gas exits through the valve, liquid DFE vaporizes to maintain vapor-liquid equilibrium, and the energy required for vaporization is drawn from the remaining liquid, which is thereby cooled. When the temperature decreases, the saturation pressure decreases, and thus the gas flow rate decreases because the driving force for gas flow decreases. For smaller initial volume fractions of liquid (change the volume fraction with the slider), the time to cool the liquid decreases.

Select a plot (volume, moles, temperature, or pressure versus time) using the buttons. To animate the liquid volume in the can, click the play button next to "spray gas." Select "adjust stopping time" to set the length of time gas is released from the can; otherwise, spray continues until the liquid temperature is

-5

°C. The DFE in the can is assumed to be in vapor-liquid equilibrium at all times, and the process is assumed to be adiabatic. As the spray time increases and as the liquid temperature decreases, heat transfer increases and the adiabatic approximation becomes less accurate.