ASican University of sharah American University of Sharjah M

ASican University of sharah American University of Sharjah Mechanical Engineering MCE 241 Sample Exam 2 (20 Points each) 1) Fill in the blank or circle the correct answer as necessary 14 Points for each): a. A machine design which violates the 2nd Law of Thermodynamics is called a b. A reversible Carnot cycle engine is more efficient than a reversible Otto engine because it exchangers heat with zero delta T. (True or False) C The 2d law statement that requires a heat engine to reject heat to a low temperature res d. The temperature of Helium passing through a throttling valve would be expected to (increase ervoir is called the remain the same, decrease). It is impossible to isothermally compress an i ideal gas in an adiabatic piston/cylinder. (True or False) e. One half kilogram of steam is compressed from 200 kPa and 40°C to 20OC in an isobaric process. Calculate the boundary work and heat transfer during this process. (ans: -46.4 kJ and-203 k) 2) 3) Helium (k 5/3) is initially in a piston cylinder with a spring (as shown) at 200kPa and 0.05 m\' before heated to 300kPa and 0.10 m2. work. (ans: 48.8 k) Calculate the amount of heat added assuming only reversible boundary A 0.25 m2 P1 = 200 kPa v, = 0.05 mi Heat

Solution

1)

a) A perpetual motion machine of second kind,

b) T

c) Kelvin–Planck statement states that sink is required for low temperature heat rejection reservoir

d) increase

e)False