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Problem 5-33
| A mixture of CO2 containing 20 percent solid mass, 20 percent liquid, and 60 percent vapor enters a pipe and emerges all vapor at the inlet pressure of 0 oF. The flow rate is 4 lbm/s. What is the rate at which energy is transferred as heat to the pipe? |
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Problem 5-43
| Freon 12 will be used as the propellant for a small portable jet rocket for maneuvering parts during assembly of a space station. The device will consist of a small spherical tank containing saturated Freon 12 at 80 oF, a valve, and a nozzle. The user will attach the jet to the package, open the valve momentarily, and let some gas escape through the nozzle. Energy transfer as heat from the walls to the Freon 12 will keep the pressure constant in the cylinder during a short burst, and the flow through the nozzle may be considered steady. The valve will throttle the Freon 12 to 20 psia, and the nozzle discharge state will be 2 psia and -80 oF. The thrusting force is approximately given by F = MV/gc, where M is the mass-flow rate and V the exit velocity. Use requirements call for a thrust of 10 lbf. Determine the specific impulse of this device, SI=F/M, in lbf/(lbm/s). By comparison, a good chemical rocket has an SI of the order of 250 lbf/(lbm/s). Specify the size of tamk required to hold enough Freon 12 for 1000s of operation, assuming that the heat-transfer rate is sufficient to keep the pressure constant for short-duration bursts. Compute the total amount of energy which must be transferred from the walls to the Freon 12 during this 1000 s of operation in order to maintain the pressure (Fig. B.7, Table B.5). This requires a careful energy analysis. |
| SI = -373.6 lbf/(lbm/s) |
| V = 4.44 ft3 |
| Q = 21313 Btu |
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Problem 5-46
| A geothermal power plant in California uses steam produced underground by natural sources. Steam enters the adiabatic turbine at 180 oC and 0.6 MPa and emerges at 0.01 MPa with 8 percent moisture (92 percent quality). It is condensed at 0.01 MPa and then pumped back up to atmospheric pressure. The plant produces 12.5 MW of electric power. Assuming and electric generator efficiency of 0.95, and neglecting the pump power, determine the steam flow rate and the condenser heat-transfer rate. Why do you think the system has a condenser? Why does it need the pump? |
| m = 32 kg/s |
| Q = 70.4 MW |
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Problem 7-13
| Thermal power systems for use in space normally reject energy as heat by radiating it into space. Since fluid-filled radiators are generally quite heavy, it has been suggested that this energy be converted to electricity and the current run through lighter resistors to dissipate the energy as heat. What do you think of this idea? Energy transfer as heat from a space vehicle must take place by radiation. The weight of a space radiator is proportional to its area, which is determined by the rate at which the energy must be radiated as heat: the rate of energy radiation is proportional to the product of the area and the fourth power of the radiator temperature. Consider a reversible 2T engine giving a fixed amount of power and operating with a fixed source temperature. Show that the least radiator weight is obtained when the radiator temperature is 0.75 times the source temperature. |
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Problem 7-24
| Steam enters an adiabatic diffuser as 400 m/s as a saturated vapor at 0.4 MPa. What is the maximum possible discharge pressure? |
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