Talk:Why an efficient air compressor matters

The original article was just a blog musing of Archimerged's, and not very well communicated. It does need revision. Archimerged 04:51, 3 July 2006 (UTC)

Primitive firestarter
Please explain how a primitive fire starter works in view of the above article. This device consists of a wood or bamboo tube, closed at one end, 5 or 6" long and about 1/4" ID. A close fitting sliding plunger/piston with a recess in the end filled with a bit of tinder and provided with a seal of waxed fibers like a piston ring nearby is inserted into the open end of the tube. When sharply forced into the tube and quickly withdrawn it is found that the tinder is aglow with fire. Where is the heat reservoir that supplied the heat to ignite the tinder?


 * The proper understanding of how an/any air compressor works is essential to the design and use of a system incorporating an air compressor or the compression and expansion of air or any other gaseous medium.


 * The primitive fire starter is a heat pump taking work plus heat from the surroundings and rejecting the heat into the tinder. The total heat rejected into the tinder is at most the total work plus the total heat absorbed from the surroundings.  Although since this isn't a cyclic process it appears that essentially all of the heat came from the work. Archimerged 11:12, 1 July 2006 (UTC)


 * The primitive fire starter is an Air Compressor, pure and simple, it is NOT a heat pump! There is no heat Rejected to anything. When the plunger/piston is forcibly/quickly rammed into the cylinder the heat of compression is sufficient to ignite the tender. As the piston is withdrawn the tinder continues to burn with the oxygen present and the air cools back to outside air temperature by expansion. The tinder is burning and you quickly use it to start your fire. Showmehow2 1:12, 2 July 2006 (EDT)


 * The original idea (not well expressed) was that an efficient air compressor is half of a heat engine and if put together with an efficient isothermal expansion engine, it makes a good low ΔT heat engine.  However, I will argue (just because I am perverse) that the firestarter rejects heat into the tinder.  Rejecting heat simply means that heat flows out of the working gas.  The heat that started the fire went to break certain chemical bonds (mostly C-C bonds), and the heat of the fire came from formation of certain other bonds (H-O-H and O-C-O bonds), so one can argue that the heat rejected into the tinder stayed there...  But its not very important and certainly calling the firestarter a heat pump is a stretch.  Archimerged 04:51, 3 July 2006 (UTC)


 * I worked for several years in the utilities department of a large institution where dried compressed air was distributed to laboratories and work shops at 100 psig. A 100 HP dual cylinder, double acting air compressor took in atmospheric air compressed it to an intermediate pressue, discharging it into a water cooled inter-cooler from which it entered the intake chambers of the high pressure cylinder to be discharged into a water cooled after-cooler. It then went through a silica gel drier system and then to distribution at 100 psig. All of the work of compression was converted to heat which had to be removed by cooling water! Showmehow2 1:12, 2 July 2006 (EDT)


 * That's correct -- all of the work of compression is converted to heat. When the air is returned to its original temperature, it contains exactly as much energy as it did before compression started, namely, nRT.  So, a cooled piston is not like a spring storing what looks like "potential energy," although an adiabatic dashpot stores the energy in the higher temperature and converts the heat back to work if the load is removed.  I realized this during a heated discussion on halfbakery.  It may be easier to read in the archived copy here, see the 2006-04-21 20:56:24 version down at the bottom of the history page.  However, the important stuff is on the current page Hydrostatic Stirling cycle air compressor, search for "answer for required energy conversion efficiency."  Also look at "eventually returns all of the heat energy absorbed..." Archimerged 04:51, 3 July 2006 (UTC)

Original article needs revision
The original article needs explanation/revision as to why and where located,the high and low temperature storage tanks are used/required. This of course brings on a question. Why, if this is so important, that air compressor manufacturers have not already incorporated this/these feature(s) into the the equipment they sell? Showmehow2 1:12, 2 July 2006 (EDT)


 * Because they don't need super efficient air compressors. It only matters when half a percent of efficiency makes the difference between a heat engine that produces work, and one that only operates if work is done on it.  This is not the case when the compressed air is being used for something other than operating an isothermal expansion engine.  Clearly, the original article is not clear at all...  Archimerged 04:51, 3 July 2006 (UTC)