CEE361: Introduction to Environmental Engineering - Mass and Energy Balances - Engineering Assignment Help

Assignment Task:

MASS AND ENERGY BALANCES

PROBLEMS

1. In a lab experiment gone wrong, two students create hydrogen sulfide (H2S, a non-reactive chemical that smells like rotten eggs) that instantaneously mixes through the entire portion of the laboratory bench enclosed by the fume hood (the enclosed portion of the lab where the experiment is done). Assume the initial concentration of H2S is 2 x10-3 g/L, the volume of the fume hood is 2 m³ , and the clean air exchange rate is 220 m³ /hr. a. Draw a diagram of the problem, including the control volume) b. Calculate the time required for the concentration to decrease to an acceptable level of 1 x 10-6 g/L.

2. A bar with a volume of 600 m³ has 40 smokers in it, each smoking 2 cigarettes per hour. An individual cigarette emits, among other things, 1.4 mg of formaldehyde (HCHO). Formaldehyde converts to carbon dioxide with a reaction rate coefficient k = 0.40/hr. Fresh air enters the bar at steady rate of 1,000 m³ /hr, and stale air leaves at the same rate. a. Draw a diagram of the system, including the control volume b. Assuming complete mixing, estimate the steady-state concentration of formaldehyde in the air of the bar in mg/m³ .

3. A residential water heater has a capacity of 175 liters and delivers 10 kW of power. Unfortunately, your housemate took a very long shower and used all the hot water. If you want to take a shower with water that is at least 55ºC and the water entering the water heater is 15ºC, how long will you have to wait to take a shower? Assume that all power goes into heating the water.

4. Consider a 354-mL can of soda cold enough to cause moisture from the air to condense on the outside of the can. If all of the heat released when 5 mL of vapor condenses on the can is transferred into the soda, how much would the soda temperature increase? Assume the density and specific heat of the soda are the same as water and neglect the thermal capacitance of the can itself.

5. The lowest flow in the Menominee River in July is about 40 m³ /s. If the river temperature is 18ºC and a power plant discharges 2 m³ /s of cooling water at 80ºC, what is the final river temperature after the cooling water and the river have mixed? Ignore radiative and convective losses to the atmosphere as well as conductive losses to the atmosphere as well as conductive losses to the river bottom and banks.

6. A 600 MW power plant has an efficiency of 36% with 15% of the waste heat being released to the atmosphere as stack heat and the other 85% taken away in the cooling water. The cooling water that is withdrawn from a local river with an upstream flow of 100 m³ /s and a temperature of 20ºC. a. If the cooling water is only allowed to rise in temperature by 10ºC, what flow rate from the river would be required? b. How much would the river temperature rise as it receives the heated cooling water?

7. A 600 MW power plant has an efficiency of 36% with 15% of the waste heat being released to the atmosphere as stack heat and the other 85% taken away in the cooling water. The plant uses an evaporative cooling tower, where the cooling water is converted to water vapor by the waste heat. At what rate must 15ºC makeup water be provided from the river to offset the water lost in the cooling tower?

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