Entropy in everyday life

[wegs]

Well, it's a good way to show that the energy in a closed system doesn't change - like if you're trying to understand entropy...

Okay, so entropy is basically:

The amount of disorder in a system and the amount of unavailable energy in a system.

And, I'm assuming this is always the case in a closed system.

 

[Michael 345]

What is the unit of "aging"? What is the mechanism by which it acts upon things to increase entropy?

No unit of aging

Change occurs in everything which exists

Something does not change, it does not age

Change can be as small as you mentioned the vibrations of a objects atoms or a rocket going into orbit

Where incidentally it ages less because it's speed is greater

What is the mechanism by which it acts upon things to increase entropy?

Existence could be said to be the mechanism ie stuff which exists has its own built in mechanism (vibration of its atoms)

Very strange - stuff which does not exist does not age

How about that

 

[DaveC426913]

No unit of aging

Perfect. It can't be measured. So it's philosophy, not science.

Existence could be said to be the mechanism ie stuff which exists has its own built in mechanism (vibration of its atoms)

Existence is not a mechanism. Vibration of atoms doesn't make things age.

You're beginning to sound like River.

 

[Michael 345]

Perfect. It can't be measured. So it's philosophy, not science.

No units of AGE

But arbitrary measurements have been given various arbitrary names

This is 1 second old

This is 4 years old

Not science, not philosophy

Existence is not a mechanism. Vibration of atoms doesn't make things age.

Existence could be said to be the mechanism ie stuff which exists has its own built in mechanism (vibration of its atoms)

The vibrations change the brick and

A clay brick will slowly disintegrate as the atoms jostle and vibrate.
The number of atoms spontaneously sticking to a brick to reform it are vastly exceeded by the atoms falling off.

disintegrate - change

You're beginning to sound like River.

Could be - he might have me on Iggy if he thinks I post stupidity

 

[exchemist]

Okay, this is so helpful - thanks!

So, why do we care about measuring the amount of energy unavailable to do work?

The other name for this is "waste heat". It is essential to understanding the efficiency of any heat engine, such as in a car or a power station. All our attempts to use energy with less waste need to be aware of the "waste heat" that is generated.

The rule of thumb is that the higher the temperature of a given amount of heat, the more work it can do as its temperature falls. So for example a steam turbine's efficiency is improved if it runs on superheated steam rather than steam at the temperature at which it boils off. The formula for it is efficiency, η, = 1- T(out)/T(in), in which T in is the temperature of the heat going in (e.g. the superheated steam) and T out is the temperature of the exhaust steam on its way to the condenser. The efficiency is the ratio of work extracted to heat input.

If you look at the formula, you can see you can only get 100% efficiency if either T out is absolute zero (impossible) or if T in is infinite (impossible). It is in practice a huge struggle to get η up to 50%, though some power stations can get a bit better. Basically you nearly always waste at least half the heat input - and often a lot more. A car engine does well to get better than 30% efficiency.

 

[wegs]

The other name for this is "waste heat". It is essential to understanding the efficiency of any heat engine, such as in a car or a power station. All our attempts to use energy with less waste need to be aware of the "waste heat" that is generated.

Ah! Gotcha, that makes sense.

The rule of thumb is that the higher the temperature of a given amount of heat, the more work it can do as its temperature falls. So for example a steam turbine's efficiency is improved if it runs on superheated steam rather than steam at the temperature at which it boils off. The formula for it is efficiency, η, = 1- T(out)/T(in), in which T in is the temperature of the heat going in (e.g. the superheated steam) and T out is the temperature of the exhaust steam on its way to the condenser. The efficiency is the ratio of work extracted to heat input.

If you look at the formula, you can see you can only get 100% efficiency if either T out is absolute zero (impossible) or if T in is infinite (impossible). It is in practice a huge struggle to get η up to 50%, though some power stations can get a bit better. Basically you nearly always waste at least half the heat input - and often a lot more. A car engine does well to get better than 30% efficiency.

Okay, thanks. This might be a silly question, but why does a car ''over heat?'' When a car over heats, it ceases to operate efficiently, or at all.

 

[billvon]

Okay, thanks. This might be a silly question, but why does a car ''over heat?'' When a car over heats, it ceases to operate efficiently, or at all.

That's a bit different.

90% of a car's waste heat goes out the tailpipe. The car takes (cool) air and gasoline in and exhausts (hot) exhaust. The cooler the exhaust is the more efficient the car is, but even the most efficient cars out there are only about 40% efficient, so that's a lot of heat.

The remaining 10% goes towards heating up the exhaust system, the engine block, the manifold etc. There are also frictional losses that heat up bearings and gears. There are active systems (coolant and oil) that transfer that heat from the engine to the environment via the radiator. When that system can't get the heat out fast enough then the temperature keeps rising and eventually the car overheats.

 

[wegs]

That's a bit different.

90% of a car's waste heat goes out the tailpipe. The car takes (cool) air and gasoline in and exhausts (hot) exhaust. The cooler the exhaust is the more efficient the car is, but even the most efficient cars out there are only about 40% efficient, so that's a lot of heat.

The remaining 10% goes towards heating up the exhaust system, the engine block, the manifold etc. There are also frictional losses that heat up bearings and gears. There are active systems (coolant and oil) that transfer that heat from the engine to the environment via the radiator. When that system can't get the heat out fast enough then the temperature keeps rising and eventually the car overheats.

Thanks for this - what do you mean, most efficient cars are only 40% efficient?

I feel like I take science for granted.

 

[billvon]

Thanks for this - what do you mean, most efficient cars are only 40% efficient?

The most efficient engine on the market is in the Gen-IV Prius, and it converts about 40% of the energy in the gasoline into mechanical energy. It does this by doing a lot of tricks, the biggest one being the Atkinson cycle engine*.

Most car engines are much lower than that, between 20 and 30%. The only other engines that are close to the Prius engine in efficiency are diesels.

You can get much higher efficiencies in non-internal-combustion engines, of course - electric vehicles are 90%+ efficient.

(Atkinson cycle engines are super efficient but can't be used in most cars since they can't really idle. Hybrids, of course, don't have to idle.)

 

[DaveC426913]

Most car engines are much lower than that, between 20 and 30%.

What is the baseline here (i.e. what is the 100% reference mark)? At 100% efficiency, the byproducts would be CO2 and water - and zero heat*. Is that right?

*(which, of course, is impossible, even in principle, even with theoretically perfect recovery systems. After all, some energy goes into heat and energy of the air from the moving vehicle.)

 

[wegs]

The most efficient engine on the market is in the Gen-IV Prius, and it converts about 40% of the energy in the gasoline into mechanical energy. It does this by doing a lot of tricks, the biggest one being the Atkinson cycle engine*.

Most car engines are much lower than that, between 20 and 30%. The only other engines that are close to the Prius engine in efficiency are diesels.

You can get much higher efficiencies in non-internal-combustion engines, of course - electric vehicles are 90%+ efficient.

(Atkinson cycle engines are super efficient but can't be used in most cars since they can't really idle. Hybrids, of course, don't have to idle.)

Okay, interesting. So, I did a quick Google search and found --> "for an engine to be 100% efficient, there would need to be no friction, no heat, no pollution, no emissions, etc." So, basically an impossible engine to construct.

So, it's depressing to learn this fact - my car's engine is only capable of 25% (?) efficiency.

 

[DaveC426913]

So, basically an impossible engine to construct.

A fact that an alarming number of Perpetual Motion Machine inventor-wannabes are in denial about.

 

[wegs]

A fact that an alarming number of Perpetual Motion Machine inventor-wannabes are in denial about.

It's a hard fact to swallow, I gotta be honest.

I'm going to visit with some friends over the weekend, and I'm going to see if they realize this. ''Did you know that....?''

So, most cars are 75% inefficient. That's pathetic, when you think about it. I get the science behind it, but I don't know many industries manufacturing products that offer 25% efficiency. Hmm. They wouldn't be in business long.

 

[DaveC426913]

I don't know many industries manufacturing products that offer 25% efficiency.

Name a product that gets 100% efficiency. Name a product that gets even 50% efficiency.

I think, first, you'll have define "efficiency" for a given product.

If we're talking anything that converts energy into work, you're going to have to come up with one that produces no heat. (Which, again, can't be done, even in principle, because work generates heat.)

 

[wegs]

Name a product that gets 100% efficiency. Name a product that gets even 50% efficiency.

I think, first, you'll have define "efficiency" for a given product.

If we're talking anything that converts energy into work, you're going to have to come up with one that produces no heat. (Which, again, can't be done, even in principle, because work generates heat.)

I'm not asking for 100% - but 25%? lol

I can't believe it. I did a quick Google search, and I can't find a product that operates at even 50% efficiency.

 

[wegs]

Wait, an electric car would be roughly 85-90% efficient.

 

[DaveC426913]

Wait, an electric car would be roughly 85-90% efficient.

The batteries don't produce heat?

 

[Michael 345]

Wait, an electric car would be roughly 85-90% efficient.

That might well be true

But before you pop the champagne think about the efficiency of all of of the machinery and equipment and used to produce the electricity pumped into the car

If you want to move a 10 lb package from X to Y it will take E energy

That E might come from a few or many sources but it will always total exactly E

Anything over E is the waste heat

 

[DaveC426913]

That might well be true

But before you pop the champagne think about the efficiency of all of of the machinery and equipment and used to produce the electricity pumped into the car

If you want to move a 10 lb package from X to Y it will take E energy

That E might come from a few or many sources but it will always total exactly E

Anything over E is the waste heat

Then we're back to open versus closed systems.

It is up to wegs to decide if the "system" includes anything more than just the car and charged battery. In which case, the manufacturing is irrelevant.

 

[wegs]

The batteries don't produce heat?

Electric cars generate next to no heat so...

That might well be true

But before you pop the champagne think about the efficiency of all of of the machinery and equipment and used to produce the electricity pumped into the car

If you want to move a 10 lb package from X to Y it will take E energy

That E might come from a few or many sources but it will always total exactly E

Anything over E is the waste heat

That's true. There may also be the problem of coal used for electricity to power the electric cars, so that's not exactly environmentally friendly. There's always a catch.