Ocean Energy Questions for Exams on “Ocean Thermal Energy”.
1. What type of working fluids do closed-cycle ocean thermal energy conversion (OTEC) systems use?
a) Low boiling point fluids at atmospheric pressure
b) High boiling point fluids at atmospheric pressure
c) Low boiling point fluids at 100 bar
d) High boiling point fluids at 100 bar
Answer: a
Clarification: Closed-cycle ocean thermal energy conversion systems use low boiling point fluids at atmospheric pressure. An example of a low boiling point at atmospheric pressure is ammonia with a boiling point around -33 degree Celsius.
2. What is the warm surface seawater pumped through in a closed-cycle ocean thermal energy conversion (OTEC) system?
a) Heat compressor
b) Heat exchanger
c) Fluid compressor
d) Turbine
Answer: b
Clarification: The warm surface seawater is pumped through a heat exchanger in a closed-cycle ocean thermal energy conversion system. This is to vapourise the working fluid to run the turbine.
3. How is the vapourised working fluid condensed in a closed-cycle ocean thermal energy conversion system?
a) Warm surface seawater
b) Fresh warm water
c) Cold water from deep ocean
d) Fresh cold water
Answer: c
Clarification: The vapourised working fluid is condensed using the cold water from deep ocean in a closed-cycle ocean thermal energy conversion system. The cold water is pumped through a second heat exchanger to perform condensation.
4. Which of the following organisations developed the “mini OTEC”?
a) CERN
b) NASA
c) ISRO
d) Natural Energy Laboratory
Answer: d
Clarification: In 1979, the Natural Energy Laboratory and several private-sector partners developed the “mini OTEC” experiment. They successfully produced electrical power from a closed-cycle OTEC on the Hawaiian coast.
5. The open-cycle OTEC uses working fluid.
a) False
b) True
Answer: a
Clarification: The open-cycle OTEC does not use a working fluid. It directly uses the warm surface seawater to produce electricity.
6. Which of the following best describes the open-cycle OTEC?
a) Warm surface seawater → heat exchanger → working fluid → turbine
b) Warm surface seawater → low-pressure container → turbine/generator
c) Deep seawater → heat exchanger → working fluid → turbine
d) Deep seawater → low-pressure container → turbine/generator
Answer: b
Clarification: In an open-cycle OTEC, the warm surface seawater is first pumped into a low-pressure container. Then this fluid is used to drive the turbine to generate electricity.
7. Why does an open-cycle OTEC use low-pressure container?
a) To solidify the warm surface seawater
b) To evaporate the deep seawater
c) To boil and evaporate the warm surface seawater
d) To solidify the warm surface seawater
Answer: c
Clarification: Open-cycle OTEC uses a low-pressure container to boil the warm surface seawater. Due to decrease in pressure, the seawater boils and expands to form vapour. This vapour is then used to drive the turbines to generate electricity.
8. Which of the following produces desalinized fresh water?
a) Closed-cycle OTEC
b) Fracking
c) Ammonia
d) Open-cycle OTEC
Answer: d
Clarification: Open-cycle OTEC produces desalinized fresh water because it directly uses the warm surface water to drive the turbines. Closed-cycle OTEC does not use the warm surface seawater directly. Ammonia is used as working fluid in closed-cycle OTEC.
9. Why does open-cycle OTEC produce desalinized fresh water?
a) Because the vapourised surface seawater leaves all the salts and contaminants in the low-pressure container
b) Because of the working fluid
c) Because the warm surface seawater is mixed with deep ocean water
d) Because of thermohaline circulation
Answer: a
Clarification: Open-cycle OTECH produces desalinized fresh water because the vapourized surface seawater leaves all the salts and contaminants in the low-pressure container. Since the vapour is pure, it generates desalinized fresh water on condensation.
10. Where is the desalinized fresh water used?
a) Sent back into ocean
b) Used for irrigation and aquaculture
c) Used to generate electricity
d) Used to generate tides
Answer: b
Clarification: Desalinized fresh water has many applications. It is suitable for irrigation and aquaculture. On further processing, it could also be used for drinking purposes. It is not used to generate electricity and tides.
11. Which of the following best describes hybrid ocean thermal energy conversion?
a) Warm surface seawater → low-pressure container → turbine/generator
b) Deep seawater → vacuum chamber → flash-evaporated → steam vapourises ammonia → turbine
c) Warm surface seawater → vacuum chamber → flash-evaporated → steam vapourises ammonia → turbine
d) Deep seawater → low-pressure container → turbine/generator
Answer: c
Clarification: In hybrid OTEC, warm surface seawater is pumped into a vacuum chamber. Due to low pressure, the water boils and expands into vapour. This vapour is then used to vapourise the working fluid which runs the turbine.
12. How does hybrid OTEC provide desalinized water?
a) By evaporating the warm surface seawater
b) By solidifying the warm surface seawater
c) By condensing the steam generated from deep seawater
d) By condensing the steam generated from warm surface seawater
Answer: d
Clarification: Hybrid ocean thermal energy conversion systems generate desalinized water by condensing the steam generated from warm surface seawater. Due to low pressure in vacuum chamber, the incoming surface seawater is vapourised to generate steam. This steam does not contain salts and contaminants as it is left behind in the chamber.
13. Which of the following is a good choice for working fluid?
a) CFCs
b) Steam
c) Surface seawater
d) Deep seawater
Answer: a
Clarification: CFCs are a good choice for working fluid. Unlike ammonia, they are not toxic or flammable. However, they contribute to ozone layer depletion.
14. As the vapour pressure of working fluid increases the size of turbine ________
a) increases
b) decreases
c) does not change
d) first increases then decreases
Answer: b
Clarification: As the vapour pressure of working fluid increases the size of turbine and heat exchanger decreases. The power plant size is dependent upon the vapour pressure of the working fluid.
15. The wall thickness of pipes used to transport the vapour increases as the vapour pressure of working fluid increases.
a) True
b) False
Answer: a
Clarification: The wall thickness of pipes used to transport the vapour increases as the vapour pressure of working fluid increases. This is because these pipes need to support the vapours without breaking apart.