MEEN 315, SECTION 503 PRINCIPLES OF THERMODYNAMICS Spring 2013 Homework #2 DUE January 29, 2013 N.B. The following Enhancement Lectures may be helpful for you in working this assignment. 1. Electric Motors 2. English Units 3. Reversible and Irreversible Processes 1. An electric motor draws a current of 10 amp with a voltage of 110V. The output shaft develops a torque of 10.2 N-m and a rotational speed of 1000 RPM. For operation at steady state, determine for the motor, (a) the electrical power required (in kW), (b) the power developed by the output shaft (in kW), (c) the rate of heat transfer (in kW), and (d) the efficiency of the motor. The energy transfer due to heat transfer is associated with what thermodynamic concept? 2. Each line in the following table gives information about a process of a system. Each entry has the same energy units. Fill in the blank spaces in the table. Can you determine from this table if any of these processes are possible? Process Q W E1 E2 ΔE a -20 50 70 b 50 20 50 c -60 60 20 d -90 50 0 e 50 150 20 3. As shown below, 5 kg of steam contained within a piston-cylinder assembly undergoes an expansion from state 1, where the specific internal energy is u1 = 2709.9 kJ/kg to state 2, where u2 = 2659.6 kJ/kg. During the process, there is heat transfer to the steam with a magnitude of 80 kJ. Also, a paddle wheel transfers energy to the steam by work in the amount of 18.5 kJ. There is no significant change in the kinetic or potential energy of the steam. Determine the energy transfer by work from the steam to the piston during the process, in kJ. Consider the work transfer by the piston; is this reversible or irreversible? Consider the work transfer by the paddle wheel; is this reversible or irreversible?4. A vertical cylindrical mass of 10 lb undergoes a process during which the velocity decreases from 100 ft/s to 50 ft/s, while the elevation remains unchanged. The initial specific internal energy of the mass is 0.5 Btu/lbm and the final specific internal energy is 0.8 Btu/lbm. During the process, the mass receives 2 Btu of energy by heat transfer through its bottom surface and loses 1 Btu of energy by heat transfer through its top surface. The lateral surface experiences no heat transfer. For this process, evaluate (a) the change in kinetic energy of the mass in Btu, and (b) the work in Btu. 5. Large wind turbines with blade span diameters of over 100 m are available for electric power generation. Consider a wind turbine with a blade span diameter of 100 m installed at a site subjected to steady winds at 8 m/s. Taking the overall efficiency of the wind turbine to be 32 percent and the air density to be 1.25 kg/m3, determine the electric power generated by this wind turbine. Also, assuming steady winds of 8 m/s during a 24-hour period, determine the amount of electric energy and the revenue generated per day for a unit price of $0.06/kW-hr for