Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum 
Feb 7th 2018, 07:33 AM

#1  Junior Member
Join Date: Feb 2018
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 Finding volumetric flow rate of heat engine
A Heat Engine has a thermal efficiency of 40% at a steady power output of 30kW. Calculate the required volumetric fuel flow in L/Hr ( litres/hour) if the fuel has a density of 850 kg/m^3 and an energy content of 45 MJ/kg.

 
Feb 7th 2018, 08:47 AM

#2  Senior Member
Join Date: Apr 2015 Location: Somerset, England
Posts: 1,031

So how have you started this question, and where have you got stuck?
It is a very straightforward question.

 
Feb 7th 2018, 09:26 AM

#3  Junior Member
Join Date: Feb 2018
Posts: 9

I found Qlow, Q high. I know that density =mass / volume. But how can i apply the energy balance eqn?

 
Feb 7th 2018, 09:35 AM

#4  Senior Member
Join Date: Apr 2015 Location: Somerset, England
Posts: 1,031

Originally Posted by casperneo I found Qlow, Q high. I know that density =mass / volume. But how can i apply the energy balance eqn? 
Not sure what you are trying to do here.
If the efficiency is 40% what is the input power?

 
Feb 7th 2018, 09:38 AM

#5  Junior Member
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75kW

 
Feb 7th 2018, 10:10 AM

#6  Senior Member
Join Date: Apr 2015 Location: Somerset, England
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And 75kW is 75 kJ per second.
So what mass of fuel per second has this energy content?

 
Feb 7th 2018, 06:40 PM

#7  Junior Member
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Okay, i got it. Thanks

 
Feb 8th 2018, 12:36 AM

#8  Senior Member
Join Date: Apr 2015 Location: Somerset, England
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Hopefully this style of reply has helped you more in the long run than just me writing out the answer. 
 
Feb 9th 2018, 05:27 AM

#9  Junior Member
Join Date: Feb 2018
Posts: 9

I have another question regarding thermodynamics,
A ship's anchor, made of 500kg of steel and initially at a temperature of 20 degree is dropped into the ocean which has a temperature of 7 degree. Determine the entropy change of the anchor.
Can i assume that since the ocean has a huge volume, the ocean water would not change temperature. Thus, the steel anchor will have a final temperature of 7 degree.
Solving it, using Cp= 4.002KJ/KG.K
The answer is 0.18162 KJ/K.

 
Feb 9th 2018, 07:33 AM

#10  Senior Member
Join Date: Apr 2015 Location: Somerset, England
Posts: 1,031

Originally Posted by casperneo I have another question regarding thermodynamics,
A ship's anchor, made of 500kg of steel and initially at a temperature of 20 degree is dropped into the ocean which has a temperature of 7 degree. Determine the entropy change of the anchor.
Can i assume that since the ocean has a huge volume, the ocean water would not change temperature. Thus, the steel anchor will have a final temperature of 7 degree.
Solving it, using Cp= 4.002KJ/KG.K
The answer is 0.18162 KJ/K. 
I'm sorry but this is not correct since the temperature of the anchor varies during the cooling.
In any case you should have started a new thread for this.
I will do this for you and we can continue the discussion there.
Here is the new thread. The entropy change of solids and incompressible liquids
Last edited by studiot; Feb 10th 2018 at 03:44 AM.

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