My dryer does not heat up when it is hot outside?

Hair Dryer Heat Transfer Problem?

• For this problem, I did an energy balance but I can't figure out where to go from there because I do not know the velocity at the exit. If I were to assume that air can be treated ideally, I could find specific volume using PV=RT, but then I would need a mass flow rate in order to find the volume flow rate. I could really use some insight to this problem, thanks! A hair dryer is basically a duct in which a few layers of electric resistors are placed. A small fan pulls air in and forces if to flow over the resistors where it is heated. Air enters a 1200 W hair dryer at 100 kPa and 22 deg.C and leaves at 47 deg.C. The cross-sectional area of the hair dryer at the exit is 60 cm^2. Neglecting the power consumed by the fan and the heat losses through the walls of the hair dryer, determine (a) the volume flow rate of the air at the inlet and (b) the velocity of the air at the exit.

• Answer:

  1200w is raising the temperature of the air by 25C find the specific heat at 100kPa this should let you get a mass rate of flow adjust the volume for the new temperature. Then use exit nozzle area to get exit velocity.