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2answers
54 views

Problem regarding heat engines [closed]

We have two different set ups: A 200K brick in a 300K environment A 300K brick in a 200K environment From which one of these can you extract more work? Assume equal mass and heat capacity. Using ...
0
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1answer
61 views

Efficiency of reversible engines

I'm a little confused about something. All reversible engines have the same efficiency, or one could drive the other to move more heat in the reverse direction. Also, no engine has an efficiency ...
0
votes
1answer
59 views

How to define the thermodynamic temperature

I've been reading derivations of the thermodynamic temperature scale. I'm assuming these are using Kelvin's method. I follow the math and the conclusion of the argument, but I don't understand how it ...
2
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3answers
60 views

Intuitive explaination for why higher engine compression ratio is more efficient?

Intuitively to me it seems likes increasing compression ratio would require more work to compress the gasses before ignition, so you'd just end up getting back what you put in - like a spring. What am ...
3
votes
6answers
232 views

Extracting heat energy without a heat engine

Is it possible to extract the molecular kinetic energy from a system directly (without the use of a heat engine / temperature gradient) and convert that to another form of energy, such as electricity, ...
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0answers
56 views

Heat engine efficiency, compression ratio vs temperatures

I want to understand the role or even existence of a cold reservoir in the Otto cycle gasoline engine. The efficiency of the Otto engine is given as a function of compression ratio $$ ...
1
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0answers
49 views

could it be possible to create a pentane steam engine?

I'm questioning if there's a way to make use of the priciple of steam engines again. The idea of a steam engine is a little primitive and outdated maybe, but the principle isn't that at all if you ...
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vote
1answer
95 views

Can you extract energy from “hot” things without a temperature differential?

I've been reading about extracting energy from heat, particularly Sterling engines. There's always a temperature gradient. Heat flows from the hot side to the cold side through the working fluid. As ...
4
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2answers
161 views

What's the efficiency of real heat engines?

Real heat engines always have lower efficiency than the Carnot efficiency. I wonder how efficient real engines can be? Can their efficiency get anywhere near the Carnot-limit?
1
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1answer
34 views

How to increase temperature of small mass using large mass of lesser temperature?

I know that heat flow from higher temperature to lower temperature, but theoretically, is it possible to build heat pump that can move energy from ocean which are at ~295 kelvin to a small boiler ...
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1answer
134 views

Meaning of heat sink in engine analysis [closed]

I am confused with the meaning of sink. What part of vehicle engine acts as reservoir and what does as sink?
3
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2answers
3k views

Maximum theoretical efficiency of internal combustion engine

This Wikipedia article states that: Most steel engines have a thermodynamic limit of 37%. Is it correct? If so then it is not clear where this number comes from. Is it derived somehow from ...
1
vote
0answers
36 views

Maximum temperature of an elliptical thermodynamic process

Given a heat engine made from the curve $$V(t)=V_0 +A \cos(\omega t); \qquad P(t)=P_0-B \sin(\omega t).$$ What are the hottest and coldest points of this cycle, and what are the temperatures at those ...
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1answer
110 views

How do Stirling engines work?

How do Stirling engines work? I understand the heating and cooling of air, but how much faster (or more force, I'm not sure which to use) does the piston move per degree Celsius that the temperatures ...
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vote
2answers
263 views

How does a dehumidifier work?

I have read sites like this, but I am just not getting it yet. I'm looking to understand the variables involved, which I think are: air moisture content air flow (cfm?) condenser surface area? ...
4
votes
1answer
395 views

Why is it that a Carnot heat engine will reject no heat to a zero temperature sink?

Looking at the equation for Carnot efficiency, I notice that as the temperature of the heat sink approaches zero, the efficiency approaches unity: $$ \eta_{rev} = 1 - \frac{0}{T_H} = 1 $$ Seeing ...
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0answers
101 views

diesel steam engine

Let's imagine a diesel engine's cylinder head would be heated by external means, to some hundred degree celsius, and the fuel would be replaced by water. We've made modifications so that water ...
0
votes
2answers
187 views

scaling of motor power

For car engines, the cylinder volume is often associated with the engine power, which suggests scaling of the power as $L^3$ where L is the linear size. Consider a system consisting of a motor and its ...
1
vote
0answers
78 views

How efficient is the Crookes radiometer?

I remember many years ago, I think at 8th grade, seeing the teacher show us a Crookes radiometer. I remember it being very fascinating. Today I read the wiki article on it, after looking up what it ...
0
votes
3answers
494 views

Will this type of engine produce thrust?

I was wondering that if we replace the combustion chambers in a jet engine with heaters heating the compressed air up to temperature near to plasma then what will be the case, will it produce any kind ...
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vote
3answers
893 views

Human as a heat engine

humans are heat engines. heat engines can't operate when the source and the sink are at the same temperatures and also if the temperature of the sink is higher than that of the source. in humans' ...
2
votes
2answers
209 views

Can the vibrational energy of a engine be used to increase efficiency?

In whole mechanics, we never talk about wasted vibrational energy! As we see in our daily life, a lot of energy is wasted as vibrational energy in every engine, for example as we fire our car's ...
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2answers
149 views

Stealing heat, or not?

Say I hook a 1KW steam engine to the steam heat in my apartment, and generate 1KW of electricity (the engine is 1KW mechanical, not 1KW thermal) from it, so I don't have to pay ConEd. That means I ...
3
votes
1answer
61 views

Can exhaust gases be diverted to other cylinders during engine operation?

Here's a description of new combustion engine improvement by Mazda, called SkyActive-G. They claim that in a "generic" engine... when the exhaust manifold is short, the high pressure wave from the ...
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2answers
222 views

Carnot cycle: What happens to the rest of the energy?

In a Carnot cycle, the work potential is $W =Q_{in}( 1-\frac{T_0}{T_R})$ where $T_0$ is the temperature of the sink, $T_{R}$ is the temperature of the source heat reservoir, and $Q_{in}$ is the heat ...