A New Thermodynamics

Blog: Efficiency

By Kent W. Mayhew

www.newthermodynamics.com

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Efficiency

No manmade mechanical device or process is 100% efficient. Consider an engine that requires an energy input (Qin, or dQin), to power a bus that being Wout. Since the engine is not 100% efficient, the energy input is always greater than the work out, i.e.:

          dQin > or = Wout        (1)

In its simplest context: The engine’s efficiency (@) is simply the work out divided by the energy input:

         @=Wout/dQin      (2)

Eqn (2) lacks specifics. How we now advance eqn (2) depends upon we specify systems. Reconsider the first law. We in terms of heat into the system (dQ) and changes to a system’s internal energy (dE) plus any work done by that system (W) gives:

 

                       dQ=dE+W     (3)

 

   And if the only work that is the work done onto the surrounding atmosphere by an expanding system i.e. lost work = PdV, then eqn (1a) becomes:

 

dQ=dE+PdV     (4)

 

   In the case of the bus’s movement, work is provided by an engine which does work onto the surrounding atmosphere plus work done in moving the bus (Wbus) :

 

                       dQ=dE+PdV+Wbus     (5)

 

    Now dE is a function the engine’s temperature increase i.e. dE= CvenginedT,  while PdV is the work done onto the atmosphere and Wbus is the work done in moving the bus. However we must also consider friction between the bus and the atmosphere i.e. drag, as well other sources of friction both within the bus, as well as between the bus’s wheels and the road.    

 

 Obviously we can make this as complicated as we need to. Perhaps we care to analyze the bus’s movement in terms of the gasoline air mixtures combustion. Not only does the combustion process involve increasing the atmosphere’s energy (W=PdV=PatmdV) but all of the energy of combustion cannot be extracted to do work, as was discussed in the work vs energy blog.   

Interestingly in traditional thermodynamics all of the above inefficiencies was (wrongly?) blamed upon the second law. Inefficiencies can be complicated enough. Do we really have to explain such things terms of phase space, entropy and the second law. I guess it depends upon how complicated one wants to makes things and one’s preferred chosen definition of entropy.

Of course to this author all that was wrongly explained by the second law can be explained in simpler terms. It is like making scrambled eggs. You can say put the fork in a hand and then wisk eggs & milk vigorously and then cook in fry pan. Or you can put elemental parts of various components of the yolk into its own infinitesimal volumes and get into the vortices of each volume. If the object is to eat breakfast then the wisking and cooking explanation will do just fine.  

Understandably, no cyclic engine that has friction in any form and/or displaces our atmosphere can never ever be 100% efficient hence power the elusive perpetual motion machine. For those of you not familiar with the concept: A perpetual motion machine is a machine that keeps on going and going, without the need of the addition of energy from an external source, into one (or more) of its cycles. As we are about to find out there is more to understanding efficiency than this i.e. the above described efficiencies are idealistic, let us now investigate the reality.

 

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This website is copyright of Kent W. Mayhew who in 2018 resides in Ottawa Ontario Canada
 
   This website is full of new ideas, which are the property of Kent W. Mayhew.  
 
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 The following quote by Authur Eddington demonstrates the purity of human arrogance that can lend itself to the complete indoctrination of a poorly conceived science

“The law that entropy always increases, holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.”