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Old Feb 7th 2018, 07:33 AM   #1
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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.
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Old Feb 7th 2018, 08:47 AM   #2
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So how have you started this question, and where have you got stuck?

It is a very straightforward question.
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Old Feb 7th 2018, 09:26 AM   #3
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I found Qlow, Q high. I know that density =mass / volume. But how can i apply the energy balance eqn?
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Old Feb 7th 2018, 09:35 AM   #4
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Originally Posted by casperneo View Post
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?
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Old Feb 7th 2018, 09:38 AM   #5
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75kW
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Old Feb 7th 2018, 10:10 AM   #6
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And 75kW is 75 kJ per second.

So what mass of fuel per second has this energy content?
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Old Feb 7th 2018, 06:40 PM   #7
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Okay, i got it. Thanks
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Old Feb 8th 2018, 12:36 AM   #8
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Hopefully this style of reply has helped you more in the long run than just me writing out the answer.

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Old Feb 9th 2018, 05:27 AM   #9
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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.
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Old Feb 9th 2018, 07:33 AM   #10
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Originally Posted by casperneo View Post
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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