MEEN 315 Fall 2016 Section 501 505 Professor Strzelec Homework 9 40 pts Due Monday October 31 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 With Thanksgiving coming up consider the process of cooking a turkey in the oven Can the hot air inside the oven be treated as a thermal energy reservoir Why or why not 2 2pts An inventor claims to have raised the temperature of a small amount of water to 150 C by transferring heat from high pressure steam at 120 C Is this a reasonable claim Why or why not 3 2pts When two liquid streams one hot one cold pass each other in a heat exchanger which irreversibility is present What type internal external total of irreversibility is it 4 2pts An unknown perfect gas has an enthalpy of 703 6 kJ kg at 380K and an enthalpy of 549 8 kJ kg at 298K Estimate the value of cp for this gas 5 2pts A heat engine converts 600 BTU of high temperature thermal energy into 250 BTU of work and rejects the remaining energy to a thermal reservoir at 70 F What is the minimum temperature that the high temperature thermal reservoir can be 6 2pts A heat pump requires 1 kW to transfer 1 kW of thermal energy from a low temperature space at 30 C What is the heat pump s maximum possible COP 7 2pts Water as a saturated liquid with initial temperature of 40 C exchanges thermal energy with the surroundings during a reversible process until it reaches the saturated vapor state What is the temperature of the surroundings 8 2pts Does the Clausius statement of the second law mean that we cannot transfer thermal energy from a cold space to a warmer space at all Why or why not What does it require 9 3pts A Carnot heat engine produces 10 hp by transferring energy between two reservoirs at 40 F and 212 F Calculate the rate of heat transfer from the high temperature reservoir 10 3pts Determine the maximum pressure increase across a 10 hp pump if the inlet water velocity is 30 ft s the inlet diameter is 1 and the exit diameter is 1 5 11 3pts A refrigerator is rated with a COP of 4 The refrigerated space that is cooled requires a peak cooling rate of 30 000 kJ hr What size electrical motor in hp is required 12 5pts A Carnot power cycle is run using water as the working fluid in a piston cylinder device Saturated liquid water is isothermally expanded at 50 bar until it is a saturated vapor The vapor is then adiabatically expanded to 5 bar while 364 31 kJ kg of work is extracted Evaluate the specific thermal energy transfer per unit mass and the specific work for each of the processes in kJ kg What is the thermal efficiency of the cycle Sketch this process on a P v diagram 13 5pts An initially empty bottle is filled with water from a line at 0 8MPa and 350 C Assume that there is no heat transfer and that the bottle is closed when the pressure reaches the line pressure If the final mass is 0 75 kg find the final temperature and volume of the bottle 14 5pts A power utility company would like to use a geothermal reservoir i e an underground spring of hot water as the high temperature reservoir in a heat engine cycle The company draws hot water MEEN 315 Fall 2016 Section 501 505 Professor Strzelec from the reservoir at the rate of 0 5 lbm s and using a steady state heat exchanger transfers thermal energy from the hot water to the heat engine cycle The temperatures of the hot water entering and exiting the heat exchanger are 200 F and 160 F respectively The heat engine rejects thermal energy to the atmosphere at 80 F A rendition of the system is shown in the figure below Determine the thermal energy transfer rate added to the engine from the geothermal reservoir Suppose the heat engine was operating such that the thermal energy added by the geothermal reservoir is done at constant temperature leading to a thermal efficiency of 18 What is the maximum power in hp available from the heat engine
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