Exited energy dissipation

Example 3.3 Energy dissipation in a nozzle Steam enters a nozzle at 30 psia and 300°F, and exits as a saturated vapor at 300°F. The steam enters at a velocity of 1467 ft/s, and leaves at 75 ft/s. The nozzle has an exit area of 0.5 ft2. Determine the rate of energy dissipation when the environmental temperature is T0 = 500 R. 

In practice, it is often not possible to calculate the selectivity for this type of process from first principles. Experimental studies have to be done under various conditions, leading to an empiricd optimum on a small scale. It has been shown in section 5.2.2 that the selectivity can be sensitive to the meso-mixe(hiess, and that these can both decrease on larger scales. It may be practical to study the reaction first in a well mixed semi-batch reactor, preferably equipped with an effective turbine impeller, or propeller. The feed tube should end in the exit flow of the impeller. With this equipment one measures the influence of the feed rate on the selectivity. It may be that a sufficiently high selectivity is obtained when the feeding time has a certain minimum value. The specific energy dissipation should be measured or calculated. 

Example 3.4 Energy dissipation in a compressor Air enters a compressor at 15 psia and 80°F, and exits at 45... 

Equation (6-95) is valid for incompressible flow. For compressible flows, see Benedict, Wyler, Dudek, and Gleed (J. E/ig. Power, 98, 327-334 [1976]). For an infinite expansion, A1/A2 = 0, Eq. (6-95) shows that the exit loss from a pipe is 1 velocity head. This result is easily deduced from the mechanic energy balance Eq. (6-90), noting that Pi =pg. This exit loss is due to the dissipation of the discharged jet there is no pressure drop at the exit. 

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