Solution Week 5 Tutorial - 2013 PDF

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CHE2162 Tutorial Problems Semester Two, 2013 Week 5 1. 5) Spray drying is a process in which a liquid containing dissolved or suspended solids is injected into a chamber through a spray nozzle or centrifugal disk atomizer. The resulting mist is contacted with hot air, which evaporates most or all of...

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CHE2162 Tutorial Problems

Semester Two, 2013

Week 5

1. (F&R, 5.17) Spray drying is a process in which a liquid containing dissolved or suspended solids is injected into a chamber through a spray nozzle or centrifugal disk atomizer. The resulting mist is contacted with hot air, which evaporates most or all of the liquid, leaving the dried solids to fall to a conveyor belt at the bottom of the chamber. Milk (70% H2O)

Inlet Air 167°C, - 40 cm H2O

Wet Air 311 m3/min @ 83°C, 1 atm

Dried Milk

Powdered milk is produced in a spray dryer 6 m in diameter by 6 m high. Air enters at 167°C and -40 cm H2O pressure. The milk fed to the atomizer contains 70 wt% water by mass, all of which evaporates. The outlet gas contains 12 mol% water and leaves the chamber at 83°C and 1 atm (absolute) at a rate of 311 m3 /min. a. Calculate the production rate of dried milk and the volumetric flow rate of the inlet air. Estimate the upward velocity of air (m/s) at the bottom of the dryer. b. What problem would you guess would occur if the velocity is too high?

CHE2162 Tutorial Problems

Semester Two, 2013

2. (F&R, 5-27) An adult takes about 12 breaths per minute, inhaling roughly 500 mL of air with each breath. The molar compositions of the inspired and expired gases are as follows: Species Inspired Gas Expired Gas (%) (%) O2 20.6 15.1 CO2 0.0 3.7 N2 77.4 75.0 H2O 2.0 6.2 The inspired gas is at 24°C and 1 atm, and the expired gas is at 37°C and 1 atm. Nitrogen is not transported into or out of the blood in the lungs. Calculate the masses of O2, CO2 and H2O transferred from the pulmonary gases to the blood or viceversa (specify which) per minute. a) Calculate the volume of air exhaled per millilitre (mL) inhaled. b) At what rate (g/min) is this individual losing weight by merely breathing?

CHE2162 Tutorial Problems

Semester Two, 2013

3. Your friend wants to open car service station and wants your help in designing cost effective jacks for raising the cars by 1.80 m for testing and cleaning the underside of the car. You think of an innovative device where instead of hydraulic pressure you use compressed gas to raise a movable piston in a cylinder. Cars are raised by placing them on top of a platform above the piston and then inserting a block of dry ice at the base of the cylinder (see the diagram). A gas tight door at the base is sealed and just enough heat is added to the dry ice to sublimate it and raise the piston by the gas pressure. The final temperature is 30°C and due to safety reasons, the final pressure must not exceed 40 bar. If the combine mass of the car and the piston is 5350 kg, and before the piston rises the cylinder contains 30 L of CO2 at 20°C and 1 atm pressure (hint: neglect dry ice volume), calculate the following– a) Calculate the minimum diameter (mm) of the cylinder for safe operation. b) For the diameter calculated in part (a), how much dry ice (kg) will be required for raising the car if in normal operation the final pressure is 37 bar? Use the SRK equation for state for this calculation. c) If the cost of dry ice is $1.35 / lbm. What will be the annual operating cost of buying dry ice, if the service station operates two such jacks and serves 5 cars on each jack per day. d) For the amount of dry ice calculated in part (b), calculate the elevation (m) of the piston using the compressibility factor equation of state. Why is it different from the SRK equation of state?

1.80 m

Door Dry Ice

CHE2162 Tutorial Problems

Semester Two, 2013

CHE2162 Tutorial Problems

Semester Two, 2013

CHE2162 Tutorial Problems

Semester Two, 2013

4. (F&R, 6.17) Wet air containing 20.0 mol% water vapour initially at 1 atm absolute pressure is cooled in a 1-litre sealed vessel from 200°C to 15°C. a) What is the pressure in the vessel at the end of the process? b) What is the mole fraction of water in the gas phase at the end of the process? c) How much water (grams) condenses?

CHE2162 Tutorial Problems

Semester Two, 2013...