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0answers
26 views

Exhaust liquefaction in internal combustion engines

Does an internal combustion engine provide enough efficiency to still deliver mechanical power, if it is forced to liquify it's own exhaust gases by compression? If gas containers would be added to ...
1
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0answers
36 views

Self-powered heat exchanger w/energy profit? [closed]

It is possible, considering the laws of physics, to build a heat exchanger that runs on the power it gathers from the environment? A typical heat exchanger uses less power to harvest heat for a ...
1
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2answers
84 views

Heat diffusion in a house

I was wondering about this problem (which is NOT homework, it's one of my mental problems due to what surrounds me): supposing I'm in a room, and it's winter. Heating is on, the boiler works and the ...
3
votes
0answers
45 views

What is the best material to use in a solar heater box to convert solar energy into heat energy?

Suppose you want to design a solar heater box with the dimensions: 1 sq meter x 30.48 cm H. 5 sides of the box's interior will be insulated and the interior will be totally black. Ideal glass will be ...
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0answers
47 views

Why isn't Hydrogen used as fuel in Internal combustion engine?

I was looking at hydrogen cars and found out that hydrogen is mainly used in hydrogen cells to produce electricity instead of combusting it like gasoline in a cylinder to produce heat energy. Why ...
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4answers
72 views

Why do coal power stations not directly use combustion to turn the turbines?

Why do coal power stations run by creating steam rather than from the expansion due to combustion? I understand that in order to generate electricity in a coal power plant, steam is usually produced ...
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0answers
61 views

Carnot cycle's paradox

Carnot cycle is a reversible cycle. By definition a reversible cycle must have an infinitesimal temperature difference. That means ($T_{high}-T_{low}$) is very very small. Any finite temperature ...
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0answers
26 views

Turning Heat into Work [closed]

Q) I was told to create a machine which could turn heat into work. The lower its cost, the better it would be(Max around 10 bucks). The higher its efficiency, th.e better it would also be.My attemp is ...
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vote
0answers
9 views

microturbine heat loss

Would the hot combustion gasses in the millimeter-wide turbine in http://thefutureofthings.com/3063-engine-on-a-chip/ lose heat so quickly that the engine efficiency would be low? The velocity of ...
2
votes
1answer
44 views

Why must the total change in entropy be 0 for a heat cycle to be as efficient as possible?

If $\Delta S_{total}$ were not zero, then heat flow would take place at different temperatures. It is easy to see why this is true by examining the opposite: that when heat flow takes place at the ...
1
vote
1answer
98 views

Ways to increase efficiency of carnot refrigerator and a four stroke engine? [closed]

What are ways to increase the efficiency of a Carnot refrigerator. I remember something about decreasing the temperature but also about something about the flow rate, and fins? Also, for four stroke ...
1
vote
0answers
37 views

Is it possible to use stainless steel for 3d printed liquid rocket engine powered by kerosene and oxygen? [closed]

There is no possible to print from copper at this moment, so, I need a replacement material. There is rocket engine with regenerative cooling system. It's cooling by liquid propellant (it uses gaseous ...
2
votes
3answers
290 views

How is the efficiency of a heat engine related to the entropy produced during the process?

I'm reading Schroeder's An Introduction to Thermal Physics. Regarding heat engines, it is stated: Unfortunately, only part of the energy absorbed as heat can be converted to work by a heat engine. ...
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1answer
49 views

Efficiency in a thermodynamic cycle

Question The area on a PV diagram within one thermodynamic cycle of a heat engine is 610J. THe total thermal energy transferred out of the gas in one cycle is 1300J. Determine the efficiency of ...
2
votes
1answer
63 views

Heating up water with a heat pump

Suppose we wish to heat 1 litre of 0°C water up to 50°C during wintertime by using an ideal heat pump (Carnot cycle in "reverse"). We will place this water amount in an initally empty container, in ...
2
votes
2answers
170 views

Why can't the Carnot cycle be used to operate automobiles, if its the most efficient?

Since the cycle proposed by Carnot (consisting of two isothermal and two adiabatic processes) is the most efficient one on which to run a heat engine, why do we use other, less efficient ones (like ...
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0answers
60 views

Ericsson cycle: what happens if you add more mass?

We recreated the Ericsson cycle using a heat engine apparatus, with air as the working fluid (assumed an ideal gas). During the isothermal compression and isobaric expansion processes, a mass of ...
-1
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2answers
94 views

More torque or more horsepower? Which engine is more powerful [closed]

Two internal combustion engines : $250\,\mathrm{hp}$ and $900\,\mathrm{Nm}$ torque $770\,\mathrm{hp}$ and $790\,\mathrm{Nm}$ torque Which of the above two engines will be more powerful? P.S. ...
2
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3answers
747 views

Questions on Carnot's theorem

This article on Carnot's theorem states that All heat engines between two heat reservoirs are less efficient than a Carnot heat engine operating between the same reservoirs. However, it only ...
0
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0answers
92 views

Efficiency of a compressed air engine

I am doing some personal research on the efficiency of compressed air cars. I am currently trying to come up with an 'ideal' cycle to use as a reference for efficiency (c.f. Otto Cycle for petrol ...
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1answer
52 views

How long will pressure exist in this case?

I'm currently fabricating my project, which currently exists only on paper, and there's one question to which I have stumbled today. Suppose, that I have a pressure vessel capable of holding upto ...
0
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0answers
59 views

Theoretical efficiency Diesel vs Otto

The efficiency for the otto cycle is defined as: equation 1: $$ n_{otto} = 1 - \frac{T_4-T_1}{T_3-T_2} $$ which can be expressed in terms of the compression ratio: equation 2:$$ n_{otto} = 1 - ...
1
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1answer
82 views

COP of Stirling engine

If we consider the theoretical maximum of COP for a heat pump, we will see that it is possible to make it infinite by approaching the temperatures of each source to each other. Yet, in a real engine ...
0
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0answers
35 views

Water as heat source in a heat pump

Consider we have water flowing in a pipe, which is working as a hot source for a heat pump. We are able to know the temperature of the water in both ends of the pipe, yet we don't have information ...
2
votes
1answer
300 views

Carnot vs. Otto

Otto cycle is reversible and according to Carnot theorem should have the same efficiency as Carnot $\eta_{Carnot}=1-T_C/T_H$. The efficiency of Otto is $\eta_{Otto}=1-\frac{T_4-T_1}{T_3-T_2}$ (see ...
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vote
1answer
127 views

Efficiency of a real engine

Can anyone tell me what is wrong with the following argument? Consider a Carnot engine and an engine $X$ whose efficiencies are $\eta_c$ and $\eta_x$ respectively. Let us assume that ...
3
votes
5answers
374 views

What is the heat sink in an internal combustion engine?

I believe that the heat source is the spark plug because it heats up the fuel-air mixture and that the working substance is the fuel-gas mixture. Then, I know that the explosion created by the fuel ...
2
votes
1answer
92 views

How to heat water at very high temepratures?

I am working on a project and recently came through a situation where I'll be working with water evaporation. On searching the internet I found that water heated at 350Celsius would generate almost ...
2
votes
1answer
180 views

How to move liquid uphill against a thermal gradient, without moving parts

I am looking for a conceptual way of dealing with the following. I am not looking for a set of blueprints. Consider a 5 meter x 10 cm vertical closed tube filled with a substance in the gas and ...
0
votes
1answer
498 views

Efficiency larger than one?

The efficiency of a heat engine is the work we can do divided by the heat we take out of the hot reservoir. This quantity is always $ \le 1$. The efficiency of a heat pump is the heat we can release ...
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votes
3answers
1k views

How much heat from a fire actually warms your home?

A fire in a hearth disperses heat to, I guess, three places: the bricks of the chimney out the hearth (where the person tending the fire is standing) out the chimney, above the house How would you ...
0
votes
2answers
71 views

Create air stream from heat

We know that heating the air inside a bounded box raises its pressure. And if there is a hole in the box, then air flows out until the pressure inside and outside balances. So in this case we would ...
3
votes
2answers
471 views

Why is the Carnot engine the most efficient?

It seems that the only condition used in proving that the Carnot engine is the most efficient is that it is reversible. More specifically, the Carnot engine can be run in reverse as a refrigerator. ...
4
votes
2answers
329 views

Why does a cooling car engine crackle?

Why does a cooling car engine crackle? What determines the frequency of the crackles?
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1answer
167 views

Speedy Cooling - Ice based Cooler - Efficient Way

Ice is used in a cooler in order to cool its contents. Which of the following will speed up the process? A) Wrap the ice in a metal foil B) Drain the water from the cooler periodically C) Put the ...
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votes
2answers
565 views

What is a simple model of internal combustion engine? [closed]

Let's look at an internal combustion engine (more precisely a standard gasoline car engine) as a black box (so without going too much into details about internal processes). The inputs of this system ...
2
votes
2answers
180 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 ...
1
vote
1answer
615 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
150 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
votes
3answers
498 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 ...
2
votes
6answers
573 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, ...
1
vote
1answer
101 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 ...
1
vote
1answer
542 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
votes
2answers
1k 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
vote
1answer
38 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
1k 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?
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3answers
16k 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
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0answers
40 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 ...
0
votes
1answer
154 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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2answers
570 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? ...