Problem #5
A hair dryer is basically a duct of constant diameter in which a few layers of electric resistors are placed. A
small fan pulls the air in and forces it through the resistors where it is heated. If the hair dryer is running
in a steady-state condition with the density of air as 1.20 kg/m³ at the inlet and 1.05 kg/m³ at the exit,
determine
a. The percent increase in the velocity of air as it flows through the dryer [6%]
b. The volumetric and mass flow rates and the inlet and exit if the duct is 5 cm in diameter with an exit
velocity of 21 m/s [4%]
c. The temperature change of the air (use $P_{atm} = 100 \text{kPa}$) [4%]
d. The electrical work used to power the heater and fan if the hair dryer loses half of the input electrical
energy to system inefficiencies, such as heat loss to the ambient air. [6%]
1.05 kg/m³
1.20 kg/m³
