Part 1: Engineering Calculations - University of Idaho



Part 1: Engineering Calculations – 45 Points(20 points) Air enters the compressor at 14.7 psia and 60 °F, and leaves at 119.0 psia. For this calculation, assume the process is reversible and adiabatic (which means isentropic). Calculate the outlet temperature (in °F) of the air using the assumption that specific heats are constant over the temperature range. Calculate the outlet temperature (in °F) of the air using the assumption that specific heats are not constant over the temperature range. Hint….there are some tables in your supplement that are for exactly this sort of thing ? (25 points) You are going to fill an initially empty Acetylene tank (C2H2) tank until it reaches 250 psia. The tank is rigid, and wrapped in adiabatic insulation. The tank is connected to a supply of Acetylene that stays at a constant 500 psia and 75 °F through the filling process. Additionally, the specific heats for Acetylene at 100 °F are: cp = 0.35 Btu/(lbm °R), and cv = 0.27 Btu/(lbm °R)Simplify the equations below as they pertain to this problem. Q-W+imihi+Vi22gc+ggczi-emehe+Ve22gc+ggcze=ddtU+KE+PEimi-eme=dmdtUse substitution, then separate and integrate the equation to get rid of the time derivatives. Simplify the equations for this system, noting things like the tank is initially empty. Box your final answer of the governing equation for this system.Assuming constant specific heats (given in the problem statement), use the calorific equations of state to solve for the final temperature (°F) of the Acetylene gas in the tank after it is filled. Alternatively, you can use EES to find T2, but you will need to attach a PDF printout directly from EES showing your work (the equations, and solution windows). Part 2: Short Calculations – 30 PointsA home freezer is operating with a condenser temperature of 25 °F and an evaporator temperature of 95 °F. What is the maximum theoretical COP for this freezer?Four devices (Carnot heat engine, real heat engine, heat pump, and refrigerator) operate between the same high and low temperature thermal reservoirs. What is the order of the most efficient device to the least efficient device?According to your supplemental tables, the specific volume [ft3/lbm] of R-134a at 500 psia and 50 °F is most nearly what value?Part 3: EES Problems – 25 PointsYou have 5 lbm of air in a sealed container with movable piston. The piston is weighted such that it will maintain a constant pressure in the container of 100 psia. The air starts out at 240 °F, and you are going to heat it until it reaches 1540 °F. You need to figure out how much heat will be required to do this. Use EES to do the following:Note: You must print a PDF directly from the EES software. Scans of printed paper, or screen captures are not acceptable for this submission. Make an array table for the initial and final state that tracks: Pressure [psia], Temperature [°F], specific volume [ft3/lbm], and specific internal energy [Btu/lbm]Create a P-v plot for air, and overlay the initial state, final state, and path on that plot.Calculate the change in total internal energy [Btu] between State 1 and State 2.Calculate the moving boundary work [Btu] between State 1 and State 2.Calculate the heat required [Btu] for this process. ................
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