A rigid tank has a volume of 0.06m3 and initially contains a two-phase liquid-vapour mixture of H2O at a pressure of 15 bar and a quality of 20%. As the tank contents are heated, a pressure- regulating valve keeps the pressure constant in the tank by allowing saturated vapour to escape. Neglecting kinetic and potential energy effects.
a. Determine the total mass in the tank, in kg, and the amount of heat transfer, in kJ, if heating continues until the final quality is x = 0.5.
b. Plot the total mass in the tank, in kg, and the amount of heat transfer, in kJ, versus the final quality x ranging from 0.2 to 1.0.
2. One kilogram of air as an ideal gas executes a Carnot power cycle having a thermal efficiency 50%. The heat transfer to the air during isothermal expansion is 50 kJ. At the end of the isothermal expansion, the pressure is 574 kPa and the volume is 0.3 m3. Determine
a. The maximum and minimum temperatures for the cycle, in K
b. The pressure and volume at the beginning of the isothermal expansion in kPa and m3.
c. The work and heat transfer for each of the four processes in kJ
d. Sketch the cycle on P-v coordinates
3. Electronic components are mounted on the inner surface of a horizontal cylindrical duct whose inner diameter is 0.2m. To prevent overheating of the electronics, the cylinder is cooled by a stream of air flowing through it and by convection from its outer surface. Air enters the duct at 25oC, 1 bar and a velocity of 0.3 m/s and exits at 40oC with negligible changes in kinetic energy and pressure. Convective cooling occurs on the outer surface to the surroundings, which are at 25oC, in accord with hA = 3.4 W/K, where h is the heat transfer coefficient and A is the surface area (the rate of cooling by convection is given by Q = hA(Ts-Tsurr)) . The electronic components require 0.2 kW of electric power. For a control volume enclosing the cylinder, determine at steady state
a. The mass flow rate of the air, in kg/s
b. The temperature on the outer surface of the duct, Ts, in oC
c. The rate of entropy generation, in W/K
Assume the ideal gas model for air.
Do the problems in a systematic way. Include the units in the calculations. State any assumptions.
Dear Student, Your assignment is in... View the full answer