Chapter 10 homework old book
1. A professor is looking for absolute-200 proof ethyl alcohol (for unstated reasons) in
his lab at 5 am. In going through the solvent cabinet he unintentionally breaks a bottle
of ethyl chloroform (MCF) which contains 2 kg of pure liquid. The spill covers an area of
0.3 m2 . He is rather embarrassed and does not want his graduate students to find out,
although things of this nature are reported to the Univ. Dept. of Heath and Safety. He
first looks for the new bag of kitty litter which turns out to be an excellent absorbent for
solvent spills. Unfortunately the cleaning people moved the kitty litter to the rat
exposure chambers a few days (also for unknown reasons). He next opens up the door
and turns on all the hoods in the lab. He gets a hot wire anemometer from Dr. Leith’s
lab and measures the air speed one meter over the spill and gets a steady 3.895 m/sec.
The lab temperature is 77 oF. As luck would have it, the GC in the lab is set up for
measuring MCF and works, which is not always the case!! He measures 1ng/m3 (which
can be assumed to be almost nothing) just above the spill because it is being rapidly
diluted by the air. How much time will it take for the MCF to evaporate? Will the
students find out? What will happen if they do? Hint: write a gas-liquid flux expression
for MCF. Assume the gas boundary layer above the MCF gas-liquid interface is
saturated with MCF, and assume the spill does not change in surface area or
temperature as it evaporates.
2.
2. cont. equations H10-H-13 are the set I gave you at the end of class that relate the
loss rate constant to the Flux.
3a. Assume that our Cane Creak Reservoir has a surface area of 500 acres and an
average depth of 18 feet During a period of drought (assume summer time in Chapel
Hill), the average relative humidity during the day light hours is ~25% and during
darkness ~60%. Assume no wind during darkness with average temperatures of 83oF
and average winds of 7mph during daylight and temperatures of 98oF. What is the rate
of evaporation in gallons per 24 hour period.
3b. Assume the local water authority can use all of the 18 ft of water depth (When I
asked they told me this) If there is no rain, how many days at the above evaporation
rate will water be available for public consumption.
3c. During these periods, the local government has called on its citizens to conserve
water. Assume there are 50,000 people in the Chapel Hill-Carrboro area during the
summer months drawing on the reservoir, and each on average uses 200 gallons of
water/day. How does this consumption rate compare with the evaporation rate? Will
conservation efforts which reduce water consumption by 80% have a substantial impact
on how long the water will last in the reservoir. What are some conservation efforts?