MEEN 315 Fall 2016 Section 501 505 Professor Strzelec Homework 10 60 pts Due Monday November 7th 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 Student Name Section 1 2pts A reversible power cycle R and an irreversible power cycle I operate between the same two reservoirs If each cycle receives the same amount of energy Q H from the hot reservoir which cycle discharges more Qc to the cold reservoir How would this impact actual power cycles 2 2pts A reversible power cycle R and an irreversible power cycle I operate between the same two reservoirs If each cycle develops the same net work which cycle receives more Q H Why How would this impact actual power cycles 3 2pts Heat engines and heat pumps and refrigerators are energy conversion devices that alter the amount of energy transferred between Q and W Are either of the conversion directions Q to W or W to Q limited Unlimited Explain 4 2pts A coal fired power plant operates with a high T of 600 C whereas a jet engine has a high T of about 1400K Does that mean that we should replace all power plants with jet engines 5 2pts Assume a heat engine with a given QH Can you say anything about QL from the Clausius inequality if the engine is reversible If it is irreversible 6 5pts An electric baseboard heater receives 1500 W of electrical power that heats the room air which loses the same amount out through the walls and windows Specify exactly where entropy is generated in that process 7 5pts A Carnot engine operates with air using the cycle shown in the figure Determine the thermal efficiency and the work output for each process in the cycle shown on the right 8 5pts A thermal storage is made with a rock granite bed of 2 m3 which is heated to 400 K using solar energy A heat engine receives a QH from the bed and rejects heat to the ambient at 290 K The rock bed cools down and as it reaches 290 K the process stops Find the energy the rock bed can give out What is the heat engine efficiency at the beginning of the process and what is it at the end of the process 9 5pts Water at 100 C quality 50 in a rigid box is heated to 110oC How do the properties P v x u and s change increase stay about the same or decrease 10 5pts Carbon dioxide is compressed to a smaller volume in a polytropic process with n 1 4 How do the properties u h s P T change up down or constant 11 4pts A piston cylinder device contains an ideal gas Will the entropy always sometimes or never increase for the following processes a For reversible isothermal processes b For reversible adiabatic processes c For irreversible isothermal processes d For irreversible adiabatic processes MEEN 315 Fall 2016 Section 501 505 Professor Strzelec 12 6pts Find the missing properties of T P s and x for water at the following points and draw and label the points on P v and T s diagrams a P 25 kPa s 7 7 kJ kgK b P 10 MPa u 3400 kJ kg c T 150oC s 7 4 kJ kgK 13 5pts A rigid insulated container fitted with a paddle wheel contains 5 lb of water initially at 260 F and a quality of 60 The water is stirred until the temperature is 350 F For the water determine the work in Btu and the amount of entropy produced in Btu R 14 10pts Consider a Carnot cycle heat pump with R 134a as the working fluid Heat is rejected from the R 134a at 100 F during which process the R 134a changes from saturated vapor to saturated liquid The heat is transferred to the R 134a at 30 F a Show the cycle on a T s diagram b Find the quality of the R 134a at the beginning and end of the isothermal heat addition process at 30 F c Determine the coefficient of performance for the cycle
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