ProblemsetProperties&PracticeFirstExam.pdf

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Unformatted text preview: Department of Bioresource Engineering BREE301 Biothermodynamics PROBLEM SET – Properties of pure substances 1) Complete this table for H2O T, °C P, kPa h, kJ/kg Quality x Phase description 200 0.7 140 1800 950 0.0 80 5000 800 3162.2 2) A piston‐cylinder device contains 0.85 kg of refrigerant‐134a at ‐10°C. The piston that is free to move has a mass of 12 kg and a diameter of 11 cm. The local atmospheric pressure is 88 kPa. Now, heat is transferred to refrigerant‐134a until the temperature is 10°C. Determine (a) the final pressure, (b) the change in volume of the cylinder and (c) the change in the enthalpy of the refrigerant‐134a. 3) 100‐kg of refrigerant‐134a at 200 kPa are contained in a piston‐cylinder device whose volume is 12.322 m3. The piston is now moved until the volume is one‐half its original size. This is done such that the pressure of the R‐134a does not change. Determine the final temperature and the change in the total internal energy of the R‐134a. 4) Saturated steam coming off the turbine of a steam power plant at 30°C condenses on the outside of a 3‐cm outer diameter, 35 m long tube at a rate of 45 kg/h. Determine the rate of heat transfer from the steam to the cooling water flowing through the pipe. 5) Water in a 5‐cm deep pan is observed to boil at 98°C. At what temperature will the water in a 40‐cm deep pan boil? 6) Carbon‐dioxide gas at 3 MPa and 500 K flows steadily in a pipe at a rate of 0.4 kmol/s. Determine (a) the volume and mass flow rates and the density of carbon dioxide at this state. If CO2 is cooled at constant pressure as it flows in the pipe so that the temperature of CO2 drops to 450 K at the exit of the pipe, determine (b) the volume flow rate at the exit of the pipe. 7) Determine the specific volume of nitrogen gas at 10 MPa and 150 K based on (a) the ideal‐gas equation and (b) the generalized compressibility chart. Compare these results with the experimental value of 0.002388 m3/kg, and determine the error involved in each case. 8) The piston‐cylinder assembly shown here fitted with stops contains 0.1 kg of water initially at 1 MPa, 500°C. The water undergoes two processes in series: Process 1‐2: Constant pressure cooling until the piston face rests against the stops. The volume occupied by the water is then one‐half of its initial volume. Process 2‐3: With the piston face resting against the stops, the water cools to 25°C. Sketch the two processes in series on a p‐v diagram. Neglect changes in potential and kinetic energy. Evaluate for each process the work and heat transfer in kJ. Department of Bioresource Engineering First MidTerm Examination BREE 301 Biothermodynamics Pre‐Exam Practice Open book examination (textbook is allowed along with a calculator and one “cheat‐sheet”) This exam is worth 15% of the total grade (2 points) 1) A system with a mass of 5 kg, initially moving horizontally with a velocity of 40 m/s, experiences a constant horizontal deceleration of 2m/s2 due to the action of a resultant force. As a result, the system comes to rest. Determine the length of time in seconds taken to come to rest and the amount of energy transfer by work of this system, in kJ. (3 points) 2) A water pipe is connected to a U‐shaped manometer as presented here. The atmospheric pressure is 102 kPa. Determine the absolute pressure at the centre of the water pipe. (3 points) 3) As seen in the schematic, 5 kg of steam contained within the piston‐cylinder assembly undergoes an expansion from state 1, where the specific internal energy is u1 = 2709.9 kJ/kg, to state 2, where u2 = 2659.6 kJ/kg. During the process, there is heat transfer to the steam with a magnitude of 80 kJ. Also a paddle wheel transfers energy to the steam by work in the amount of 18.5 kJ. There is no significant change in the kinetic or potential energy of the steam. Determine the energy transfer by work from the steam to the piston during the process. (3 points) 4) Determine the phase or phases (for a‐e) and the specific internal energy (for a‐d) in a system consisting of H2O at the following conditions (a) P = 5 bar, T = 151.9°C. (b) P = 5 bar, T = 200°C (c) P = 2.5 MPa, T = 200°C (d) P = 4.8 bar, T = 160°C (e) P = 1 bar, T = ‐12°C (4 points) 5) Steam is contained in a closed rigid container with a volume of 1 m3. The pressure and temperature of the steam are initially 700 kPa and 500°C. The temperature drops as a result of heat loss to the surroundings. Determine the temperature at which point condensation first occurs in °C and the fraction of the total mass that has condensed when the pressure reaches 50 kPa. ...
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  • Winter '16
  • Heat Transfer, steam power plant, local atmospheric pressure, piston face, bioresource engineering

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