PRACTICE PASSAGE 8 Artificial snowmaking illustrates the Joule-Thomson effect as

Question

PRACTICE PASSAGE 8 Artificial snowmaking illustrates the Joule-Thomson effect as a mixture of air and water vapor is throtled from 20 atm of pressure through an insulated valve into the surrounding atmosphere. Snowmaking is costly, and its efficiency is dependent on appropriate weather conditions The wet bulb temperature is used to determine when snowmaking is possible. The bulb of a standerd, dry bulb thermometer is wrapped in wet cloth. The wet bulb temperature reading results from the evaporation of the water on the cloth in a manner dependent on the relative humidity or moisture content of the surrounding air passing by. Humidity levels also influence the dew point, or maximum temperature where condensation can occur. An engineer refers to the data in Table 1 and Figure 1 to plan snowmaking operations at a mountain ski resort. The snowmaking curves in Figure 1 mark the boundaries between good, possible, and impossible conditions to make snow. Table 1 Physical Properties of Water Enthalpy of formation -285.85 kJ mol- (at 25°C) Enthalpy of vaporization 4505 J mo (et C Enthalpy of vaporization 45.05 kJ mol (at 0°C) 40.66 kJ mol (at 100°C) Enthalpy of fusion 6.01 kJ mol (at 0'C) 6.35 kJ mol (at 82°C) Snow Making Curves Impossible o Possible Snowmaking -2 Good 0 10 20 30 40 50 60 70 80 90 100 Relative Humidity (%) Figure 1

Explanation / Answer

5. For water vapor turning to snow during throttling,

A) q > U

6. In a wet bulb thermometer, the true statement is,

C) work is done by the expaning water vapor

7. Snow making is least likely under the following wet bulb temperature,

A) 0 oC, 50%

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