#$&*
course Phy 232
7/14 10
Question: univ phy problem 20.45 11th edition 20.44 (18.40 10th edition) ocean thermal energy conversion 6 C to 27 C
At 210 kW, what is the rate of extraction of thermal energy from the warm water and the rate of absorption by the cold water?
YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY
Your Solution:
First off, we know that the total change in momentum = .07. Thus, the work / thermal energy = .07. Therefore, thermal energy = work / .07.
So, the thermal energy = 210 kW/ .07 = 3000 kW.
confidence rating #$&*:
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.............................................
Given Solution:
** work done / thermal energy required = .07 so thermal energy required = work done / .07.
Translating directly to power, thermal energy must be extracted at rate 210 kW / .07 = 3,000 kW. The cold water absorbs what's left after the 210 kW go into work, or 2,790 kW.
Each liter supplies 4186 J for every degree, or about 17 kJ for the 4 degree net temp change of the water entering and exiting the system. Needing 3,000 kJ/sec this requires about 180 liters / sec, or about 600 000 liters / hour (also expressible as about 600 cubic meters per hour).
Comment from student: To be honest, I was surprised the efficiency was so low.
Efficiency is low but the energy is cheap and environmental impact in the deep ocean can be negligible so the process can be economical. **
Your Self-Critique:
Where did the 4186 J for every degree come from? I understand the amount of work, but when it comes to converting it into liters/sec I become confused.
Your Self-Critique Rating: 2
@& The specific heat of water and its heats of fusion and vaporization, as well as those of a number of other substances, are given in the text.
A liter of water requires 4186 J to raise it by one degree Celsius. The temperature is lowered by 21 Celsius, so you can figure out how much energy is obtained from each liter.
210 kW tells you how many Joules are extracted per second.
You know how many Joules are extracted from each liter, and how many Joules are extracted each second. So you can figure out how many liters are required each second.
*@
"
Self-critique (if necessary):
------------------------------------------------
Self-critique rating:
"
Self-critique (if necessary):
------------------------------------------------
Self-critique rating:
#*&!
&#This looks good. See my notes. Let me know if you have any questions. &#