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Q: Percent efficiency in transforming energy ( Answered,   2 Comments )
Subject: Percent efficiency in transforming energy
Category: Science > Technology
Asked by: gmm765-ga
List Price: $10.00
Posted: 20 Nov 2006 19:11 PST
Expires: 20 Dec 2006 19:11 PST
Question ID: 784410
I am looking for a table or list which has the percentage of efficiency
when you transform energy from one from to another. I'd like to find a
comprehensive list.

Please start by listing the major forms of energy--electrical, light,
chemical etc, etc ( i don't know them all), then all the ways they can
be transformed and the percentage efficiency.

It would seem to me that this would be essential foundation knowledge
for all engineers, but I haven't been able to find it on the web.

I'd am willing to go upward in price to get this, so let me know how
long you think it will take, where you will search, and how much you

Clarification of Question by gmm765-ga on 20 Nov 2006 19:23 PST
Oh about the e=mc squared stuff. This isn't something I am
particularly concerned with, but it would be nice to see some thoughts
on the efficiency  of transforming matter into energy.
Subject: Re: Percent efficiency in transforming energy
Answered By: hedgie-ga on 22 Nov 2006 22:04 PST

1)  Limit on efficiency of conversion, based  on energy type is given by
  Carnot's formula.
  Sadi Carnot was an engineer who wondered what is a limit on efficiency
of steam engines.éonard_Sadi_Carnot

 The formula (better then list, certainly) may be complex, and the concept
 is very complex and often misinterpreted in popular presentations

but  your statement

" It would seem to me that this would be essential foundation knowledge "

and your intuition are correct. Carnot's answer became  foundation
of thermodynamics, which today applies to all conversion precesses, not
just to heat engines.

2)  E=m *c^2   , contrary to popular opinion, does not refer to
conversion of one from of energy into another, nor conversion of
matter into energy.

This is best seen when we use 'planck units' in which  c=1

the formula is then


and means that two physical quantities of Newtonian physics, E and m
are replaced by one quantity in the relativistic physics. This quantity
(a forth component of four-vector for linear momentum) can be interpreted
as sum of mass and all energies in the  classical (Newtonian) limit.

This formula:

from this article
under 'Kinetic energy' heading

  ilustrates this: when  v/c tends to zero, the higher order terms tend to zero
  and we are left with  E as sum of mass and kinetic energy.

The formula (eq 9) is derived here

SEARCH TERMS;     entropy, 2nd law of thermodynamics

example of application

SEARCH TERMS;              STR, special theory of relativity

 In both case, it is advisable to be critical. There is a lot of 'entropy'
on the web, on both topics.

You are invitied to ask for clarification before you rate the answer,
but not to argue with the current mainstream theories of physics.

Request for Answer Clarification by gmm765-ga on 25 Nov 2006 17:27 PST
I thought that carnot's efficiency theorum (1- Temp-cold/temp-hot)only
applied to heat engines? I do understand how this applies to internal
combustion engines, but electrical energy into heat? Or the other

Let's start with the types of energy:
Mechanical, electrical, heat, gravitational, magnetic, chemical .Are
you saying that carnot theorum applies in all these cases? How?
Please list other types of energy besides the ones I've listed.I am
not familiar with how energy is conceptually broken down, and maybe
you could clarify that for me.

More. The carnot efficiency is an idealized and theoretical approach.
I am more interested in a practical , empirical look at the best
energy transfers percentage that we know of. Is there someplace that
knowledge has been collected?

I would think that such a collection of knowledge would be a godsend
to engineers that design things for the real world, but I have not
been able to find it.

Oh and I am only interested in learning about what IS accepted by
physicists. That is, I am not one of those perpetual motion guys, or 
one of those people who is challenging the accepted laws of physics.
Also,sticking with Newtonian physics is fine!


Hope to hear from you


Clarification of Answer by hedgie-ga on 25 Nov 2006 18:56 PST
Hi Geoff, nice hearing from you

  Let me finish the section 2) first,
  then we will stick with non-relativistic mechanics, 
  with thermodynamics really.

re 2) mc^c
  PBS has a nice presentation on the famous eq. (search term) mc2

How do physicists explain Einstein's equation to curious non-physicists?
 Listen online by selecting Play All or choose individual clips below.
Listen offline by downloading clips,

they asked 10 physicists to explain - and explanations differ
 not because it is an open question, but because in 3 minutes it is not
possible to explain 

What is energy?
what is matter?

we talk about that a bit in:
Pure Energy...Yes or No?

  Part of the differences is in treating  expression 'nuclear energy'
 differently. Formula E=Mc^2  covers all processes, all energy conversions,
 chemical, nuclear, etc. But it more useful in nuclear and elementary
particles (annihilation of positron and electron) then in case of
chemical reaction. That's why people, even physicist, quote in the
nuclear and particle
physics is if it would be specific to those processes.

re 1)  Carnot's formula applies to the heat engines. 
        It is  very practical (Carnot was an engineer) and is clever
since it pioneered the use of Carnot cycle. There are many different
substances, steam-water, freon, etc which can be used to build a heat
engine. One can go and try different substances, hoping to Find most
'efficient one' . Carnot reasoning did show that WITH ANY substance,
efficiency is limited by his formula.

That was the beginning of Thermodynamics.  Today it applies to all
energy conversions, from heat to nuclear.

Today's answer to your question is the 2nd law:

 Best conversion process you can invent, is the one in which entropy
 does not change ( an isentropic or quasi-stationer process).

 All other processes have entropy going up, more or less, and so are
'less efficient'  The formulas for entropy may be complex. Carnot's
 is a simple formula which applies to heat engines.

  Second law applies to all processes, all conversions.

  Expression 'forms of energy' is not exactly defined.
'Wind energy' can be a category in itself, or it can be kinetic
and internal energy of atmosphere gases.

Here are few 'official' lists:

  When you have a rock on a high platform , at height h, in gravity field g ..
 it has potential energy   m*g*h   right?

You kick it down, before it hits, it has kinetic energy corresponding
to m*g*h  .. nothing is lost, because entropy did not change.

After it hits, most energy is dissipated (not LOST!!)  and entropy
increased.  That increase depends on the properties of the rock and
floor, and can be calculated. That's how it is.

Subject: Re: Percent efficiency in transforming energy
From: stanmartin1952-ga on 21 Nov 2006 00:22 PST
Generally, the percentage efficiency depends on the characteristics of
the process you use. There is a wide range of efficiencies. Think of
automobile engines. Some are fairly efficient and some aren't. You can
change the efficiency by changing the operating temperature, fuel,
carburetion, combustion chambers, valves, timing, exhaust system, etc.
Subject: Re: Percent efficiency in transforming energy
From: gmm765-ga on 21 Nov 2006 19:39 PST
Well, I am aware that the characteristics of the process can effect
the efficiency. Maybe I didn't make this clear, but the whole point of
answering this question is to get a fix on what is most efficient in
transforming energy from one type to another.

In the case of the internal combustion engines, I think it's generally
agreed that gasoline engines are able to get around 18% efficiency in
turning the energy in the liquid into motion, Diesel is about 38% and
the stirling is 50% plus.

I don't need a detailed explanation of the history of carburetion, or
the development of computer controlled combustion, but if the hemi
engine ( a cylindrical top to the combustion chamber which prevents
btu's from escaping the cylcinders) represents the most efficient
internal combustion engine, then engineers should know this, and I'd
like to see that in the chart.

Does the hemi diesel give us the the best efficiency for internal
combustion ---that we know of? That is the sort of thing I'd like to
know. And the percentage efficiency would go into the row( in our
effieciency chart) entitled "chemical energy to physical motion."

Hope that clarifies.

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