A tank is fitted with an electrical resistor holds 2 kg of nitrogen (N2), initia

Question

A tank is fitted with an electrical resistor holds 2 kg of nitrogen (N2), initially at 27 degree C, 100 kPa. Over a period of 10 minutes, electricity is provided to the resistor at a rate of 0.12 kW. During this period, the tank is cooled by transferring 12.59 kJ of heat from the nitrogen to its surroundings. Show the thermodynamic system and the energy interactions labeled appropriately. Treat nitrogen as an ideal gas & determine the nitrogen's filial temperature, in degree C. Begin your analysis with the first law of thermodynamics. Find the final pressure, in kPa.

Explanation / Answer

for 10 minutes time heat transferred -> into the system = 0.12*10*60 = 72 KJ -> out of system = 12.59 KJ net heat transferred into system = 72-12.59 = 59.41 KJ considering nitrogen to be ideal diatomic gas, Cv for nitrogen = (5/2)R moles of nitrogen, n = (2000/28) = 71.43 so, n*Cv*dT = 59410 put values, dT = 40 so final temp of nitrogen is (40+27) = 67 deg C now for constant volume system with ideal gas (P/T) = const so, (100/300.15) = (P/340.15) so, final pressure, P = 113.33 kPa

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