Question

As shown in the figure, a building with an internal volume of 400 m³ is heated by an electric heater with a power of 30 kW. The electric heater is located in an adiabatic canal and the canal is inside the building. Initially, the air inside the building is at 14 ° C and the atmospheric pressure at the location of the building is 95 kPa. There is a heat output of 450 kJ per minute from the building. In order to distribute the air in the duct properly, a 250 W fan is also placed at the duct inlet. The temperature difference between the duct outlet and the inlet is 5 ° C. Calculate the time it takes for the average internal temperature of the building to be 24 ° C as [s] and the average flow rate of the air in the channel as [kg / s].

HEAT DISCHARGE T, =T,+5°C V = 400 m P = 95 kPa ELECTRIC HEATER INPUT FAN INPUT

Answer 1

ot BU= Wht W fan m Cv (T2-TI) = of (Wn twofer -0) m = PV RTI 95 xyoo = 461.3386 86 kg 0.287*(273+14) 4161.338X0.718x C24-14) = 0+ (30 +0.2-7.5) At=145.92 sec nhat Wsen + Whenha s = Wfant wn 0.2+30 न CPDT 1.005x5 m= 6 kg/sec