Message text written by Randall Young
>> Since the car is producing no output at idle (it
>> is merely turning itself over producing no work) the efficiency is zero
>> with or without vacuum retard.
>
>Hmmm, what term would you apply to how much fuel it takes to keep the
engine
>turning ?
I would call that overhead. Unless the desired result of the process is
the exhaust note then there is no primary output (forward propulsion) and
hence all energy consumed is wasted. Of course you could redefine the
definitions to include battery charging but that's a bit of a streach.
>My refrigerator doesn't produce any net work either (viewed from
>outside), but we talk about it's efficiency ...
Again, what is the desired outcome of the process? In the case of a
refrigerator it is to maintain the temperature of the inside of the box. A
fridge's job is to cool down warm items placed therein and to move thermal
energy that leaks in (through the insulation and whenever the door is open)
back out to a higher temperature environment (basically up hill in a
thremodynamic sense). In essence you are creating a potential energy
difference in a quantity of mass which calculates into work. Running the
defrost cycle is overhead.
Dave (got an A in Thermo in college but I forgot most of it)
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