1. A horizontal "hot air blower" consists of a fan, an electrical heating element and a nozzle The power input to the fan is 50 J/s and the power input to the heating element is 1.44 kJ/s. The air enters the fan with negligible velocity at a pressure of 1 bar and a temperature of 20 C, the volumetric flow rate being 0.5 m3 /min. After passing over the heating element, the air leaves the nozzle with a velocity of 25 m/s and a pressure of 1.1 bar. Treating the complete arrangement as a steady flow system and ignoring any heat loss from the system, determine: (a) The mass flow rate of air entering the fan in kg per second (b) The kinetic energy of the air leaving the nozzle per second (c) The change in enthalpy of the air occurring per second between entering the fan and leaving the nozzle
1. A horizontal "hot air blower" consists of a fan, an electrical heating element and a nozzle
The power input to the fan is 50 J/s and the power input to the heating element is 1.44 kJ/s. The
air enters the fan with negligible velocity at a pressure of 1 bar and a temperature of 20 C, the
volumetric flow rate being 0.5 m3
/min. After passing over the heating element, the air leaves
the nozzle with a velocity of 25 m/s and a pressure of 1.1 bar. Treating the complete
arrangement as a steady flow system and ignoring any heat loss from the system, determine:
(a) The mass flow rate of air entering the fan in kg per second
(b) The kinetic energy of the air leaving the nozzle per second
(c) The change in enthalpy of the air occurring per second between entering the fan and leaving
the nozzle
(d) The temperature of the air as it leaves the nozzle.
(e) The density of the air as it leaves the nozzle
(f) The flow area at the nozzle exit.
Take R = 0.287 kJ/kgK and cp = 1.005 kJ/kgK
Step by step
Solved in 4 steps
