MEEN 315 SECTION 503 PRINCIPLES OF THERMODYNAMICS Spring 2013 Homework 9 DUE April 2 2013 N B The enhancement lecture Example Closed System First Law may be helpful on this homework It is located on the elearning website Lectures Enhancement Lectures Example Closed System First Law N B The material on this homework is covered on your Exam 2 Exam 2 is Thursday April 4 from 7 9pm in 102 Zachary This homework will not be graded before the exam Thus make a photocopy of it before submission if you wish to use it as a study guide 1 During your recent dinner creation of spaghetti you wondered about the energy transferring from the stove into the water causing the water to boil Suppose you assume all the energy from the stove goes into the pot and the water Further suppose your pot is 1 kg steel and you have 1 kg of liquid water The water is heated up to its boiling point i e it always remains a liquid at standard pressure How much energy was used to heat up the pot and the water 2 A rigid insulated vessel contains superheated vapor steam at 3 MPa 400 C A valve on the vessel is opened allowing steam to escape as shown below The overall process is irreversible but the steam remaining inside the vessel is assumed to undergo a reversible adiabatic expansion Determine the fraction of steam that has escaped when the final state inside is saturated vapor HINT Draw your control volume around the water that remains in the tank and note that it undergoes a reversible and adiabatic process 3 An insulated piston cylinder arrangement contains R 134a at 1 MPa 50 C with a volume of 100 L The R 134a expands moving the piston until the pressure in the cylinder has dropped to 100 kPa It is claimed that the R 134a does 190 kJ of work against the piston during the process By calculating the entropy generation for this process make a comment on if this process is possible or not Regardless of your answer describe what your result means in terms of the work transferred out of the system relative to ideal 4 A 50 kg iron block and a 20 kg copper block both initially at 80 C are dropped into a large lake at 15 C Thermal equilibrium is established after a while as a result of heat transfer between the blocks and the lake water Determine the total entropy change for this process HINT Example 7 19 might be helpful That is what is the sum of the entropy change of the iron and copper blocks and the entropy change of the lake 5 The expansion process in an internal combustion engine i e the power stroke is modeled as an isentropic process You can model this process by assuming the system is composed of air It s initial state is a pressure of 2200 psia and a temperature of 3600 R The ratio between the volume at the final state to the volume at the initial state is 8 Determine the temperature and pressure at the final state and the work per unit mass transferred during the process During your re ent dinner creation of spaghetti you wondered about the energy transferring from the 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