MEEN 315 Fall 2016 Section 501 505 Professor Strzelec Homework 6 45 pts Due Wednesday October 5 2016 at the START of class NO late homework will be accepted You are encouraged to use the problem solving steps and show all of your work Please use this page as a cover sheet This material will be covered on Exam 1 Student Name Section Questions 1 5 are TRUE or FALSE questions If the statement is FALSE you must correct it to receive full credit 1 2 pts The specific internal energy of ammonia at 0 45 MPa and 50 C is 1564 32 kJ kg 2 2 pts If superheated steam is cooled at constant pressure it will eventually become saturated vapor and with additional cooling at the same pressure it will become a saturated liquid 3 2 pts The pressures listed in the thermodynamic tables are gage pressures 4 2 pts If a closed system containing a simple compressible substance is at equilibrium only one phase can be present 5 2 pts If the value of any property changes with time the system cannot be at steady state Questions 6 10 are short calculations 6 2 pts Calculate the density specific weight mass and weight of a body that occupies 250 ft 3 if its specific volume is 5 ft3 lbm 7 2 pts Two kilograms of air experience the three process cycle shown at the right Calculate the net work 8 2 pts 10 kg of H2 is contained in a rigid insulated tank at 20 C What is the final temperature in C if a 400 W resistance heater operates in the H2 for 50 min 9 2 pts A rigid 2 ft3 volume contains water at 120 F with a quality of 0 5 Calculate the final temperature if 8 BTU of heat is added 10 2 pts A closed system containing 2 kg of mass undergoes an adiabatic process The work done on the system is 3 kJ The velocity of the system changes from 3 m s to 15 m s During the process the elevation of the system increases by 45 m a Write the energy balance that describes this system Start with the full version and defend any simplifications b Determine the change in internal energy of the system Questions 11 15 are work out style problems 11 5 pts A closed system initially at rest on the surface of the Earth undergoes a process for which there is a net energy transfer to the system by work of 200 Btu During the process there is a net heat transfer from the system of 30 Btu At the end of the process the system has velocity 200 ft s at an elevation of 200 ft The mass of the system is 50lb and the local acceleration due to gravity is 32 ft s 2 Determine the change in internal energy of the system for this process in Btu Follow the problem solving steps MEEN 315 Fall 2016 Section 501 505 Professor Strzelec 12 5 pts The frictionless piston has a mass of 16kg Heat is added until the temperature reaches 400 C If the initial quality is 20 find a the initial pressure b the mass of water c the quality when the piston hits the stops d the final pressure and e the work done on the piston 13 5 pts A piston cylinder assembly contains air at a pressure of 30 lb f in2 and a volume of 0 75 ft3 The air is heated at constant pressure until its volume is doubled Assuming the ideal gas model with constant specific heat ratio of k 1 4 for the air determine the work and heat transfer each in BTU 14 5 pts Air is confined to one side of a rigid container divided by a partition The other side is initially evacuated The air is initially at 5 bar 500K and 0 2m3 When the partition is removed the air expands to fill the entire chamber Measurements show that the final volume is double the initial and the final pressure is 25 of the initial Assuming that the air behaves as an ideal gas determine a the final Temperature in K and b the heat transfer in kJ 15 5 pts A piston cylinder device contains 17 lb m of R 134a at 10 psia and 100 F After a constant pressure quasi equilibrium process the enthalpy reaches 1275 BTU a Sketch the process on P v and T v diagrams clearly showing the saturation dome and relevant lines of constant T or P and process points 1 and 2 b Determine the work done in lb f ft c Determine the internal energy change in BTU
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