Question

air is passing over a 20kw electric wire in a duct at a flow rate of 150 m3/min 100 kpa and 17°c.calculate the temperature of the air at the duct exit and the help transfer to the surrounding from the duct is 200 W.

Answer 1

Answer:$T_2=23.55 ^{\circ}$

Step-by-step explanation:

Given

Power=20 kW

air flow rate$=150 m^3/min$

P=100 KPa

$T=17 ^{\circ}\approx 290 K$

Heat transfer to surrounding is =200 W

Net heat supplied $=20\times 10^3-200=19.8 kW$

Mass flow rate $\dot{m}$

$P\dot{v}=\dot{m}RT$

$100\times 150=\dot{m}\times 0.287\times 290$

$\dot{m}=3.004 kg/s$

To calculate exit temperature

$Q=\dot{m}\times c_p\left ( T_2-17\right )$

$19.8=3.004\times 1.005\times \left ( T_2-17\right )$

$T_2=23.55 ^{\circ}$