Go Back   Physics Help Forum > High School and Pre-University Physics Help > Thermodynamics and Fluid Mechanics

Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

Reply
 
LinkBack Thread Tools Display Modes
Old May 23rd 2009, 07:55 AM   #1
C.E
Member
 
Join Date: Apr 2009
Posts: 71
A powerplant near a river- entropy question

Hi, I am stuck on Termodynamics again (and I have an exam really soon)!

A typical coal-fired power plant generates 1000 MW of usable power at an overall thermal efficiency of 40%.

1. The river's temperature is 18.0 degrees celcius before it reaches the

power plant and 18.6 degrees celcius after it has received the plant's

waste heat. Calculate the river's flow rate, in cubic meters per second.

(the answer you should get is V =597 m^3/s )

2.By how much does the river's entropy increase each second?

(the answer is $\displaystyle \Delta S$ =5.15106 J/K ).

I don't know how to start 1, please help. I am in a similar position with 2.

Usually I use $\displaystyle \Delta S=\int_{T_1}^{T_2} \frac{mcdT}{T}$

for this type of problem (as I can't find any other relevant formulas in my notes)

but as I don't know the mass of the river I don't this is not an option. Am

I missing something really obvious?

Last edited by C.E; May 23rd 2009 at 07:58 AM.
C.E is offline   Reply With Quote
Old Jun 6th 2009, 03:19 AM   #2
Senior Member
 
Join Date: Dec 2008
Location: Udupi, Karnataka, India
Posts: 292
Efficiency = (Q1 - Q2)/Q1
(Q1 - Q2) is the energy output. In the given problem energy output is 1000 MJ per second. Using efficiency as 0.4 calculate Q1 and Q2. Q2 is the amount of heat given to the cooling water. Rise in temperature of the water is given. Using Q = mcΔt. you can find mass of the water flowing per second. Using density of water you can find the volume of the water flowing out.
sa-ri-ga-ma is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Thermodynamics and Fluid Mechanics

Tags
entropy, powerplant, question, river



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Entropy question Nrt Thermodynamics and Fluid Mechanics 1 Oct 12th 2011 09:42 AM
Jumping a river CalculusCrazed Kinematics and Dynamics 1 Sep 20th 2010 11:53 AM
Designing coal feeders for a powerplant. Yander Advanced Thermodynamics 0 Jul 29th 2010 06:40 AM
[SOLVED] Swimming across a river mybrohshi5 Kinematics and Dynamics 0 Feb 2nd 2010 07:25 PM
velocity question - Jeep jumping river lindsayboyle Kinematics and Dynamics 2 Feb 12th 2009 05:18 PM


Facebook Twitter Google+ RSS Feed