Air is contained in a rigid well-insulated tank with a volume of 0.6 m3 . The tank is fitted with a paddle wheel that transfers energy to the air at a constant rate of 4 W for 1 h. The initial density of the air is 1.2 kg/m3 . If no changes in kinetic or potential energy occur, determine
(a) the specific volume at the final state, in m3 /kg
(b) the energy transfer by work, in kJ.
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(c) the change in specific internal energy of the air, in kJ/kg.
A gas is contained in a closed rigid tank. An electric resistor in the tank transfers energy to the gas at a constant rate of 1000 W. Heat transfer between the gas and the surroundings occurs at a rate ofĂ‚Â 50t, where is in watts, and t is time, in min.
(a) Plot the time rate of change of energy of the gas for 0Ă‚Â t Ă‚Â 20 min, in watts.
(b) Determine the net change in energy of the gas after 20 min, in kJ.
(c) If electricity is valued at $0.08 per what is the cost of the electrical input to the resistor for 20 min of operation?