Energy and Environment I NAME: ANSWERS

Quiz #2

15 minutes

25 points

Closed books and notes

ANSWERS IN RED

 

The picture on the backside of this page shows a cycle. The picture is taken from your text (p. 114). The warm seawater has a temperature of 30 degrees C and that of the cold seawater, drawn from several hundred meters deep, is 15 degrees C.

  1. What is the name of this cycle?

    2. RANKINE CYCLE or OTEC CYCLE
  2. Does the cycle represent a heat engine?

    3. YES, THIS IS A HEAT ENGINE. THE HEAT SOURCE IS THE WARM SEAWATER NEAR THE SURFACE, AND THE HEAT SINK IS THE COLD SEAWATER SEVERAL HUNDRED METERS BELOW THE SURFACE.
  3. Estimate the efficiency of the cycle. Be sure to show how you determined this.

    4. ONE CAN ESTIMATE THE EFFICIENCY (OR MORE PRECISELY, THE MAXIMUM POSSIBLE EFFICIENCY) BY USING THE EQUATION:

    h = 1 – TC/TH

    WHERE TC = 15 + 273 = 288 K

    TH = 30 + 273 = 303 K

    THUS: h = 1 – TC/TH = 1 – 288/303 = 0.05

    NOTE: THE ACTUAL EFFICIENCY WILL BE LESS THAN THE 5% VALUE – PROBABLY ABOUT 3%.
  4. If the cycle has a power output of 100 MW, how many MW of heat (from the warm seawater) must be provided? Be sure to show how you determined this.

THIS IS FOUND USING:

h = W/QH

OR

h = POWER/RATE OF HEAT ADDITION

THEN: RATE OF HEAT ADDITION = POWER/h

RATE OF HEAT ADDITION = 100 MW/0.05

RATE OF HEAT ADDITION = 2000 MW

(THIS IS VERY LARGE RATE OF HEAT ADDITION. THUS, THE FLOW RATE OF SEAWATER THROUGH THE HEAT EXCHANGER OF THE BOILER MUST BE HUGE.)