The technique to be used for "self-refilling" compressed air tanks, is sometimes referred to as "free expansion," and standard engineering practice considers it as being thermodynamically irreversible, and not to be considered an investment. That train of thought is not applicable to applying “free expansion” to "self-refilling” compressed air tank technology.
The facts behind the efficacy of “self-refilling” a compressed air tank using the compressed air already inside the tank, are derived from the ability of the Sun to store vast quantities of heat energy in the ambient atmosphere.
The Sun has already stored ~ 500º ̊ F, at +40º F ambient temperature, of heat in every particle of matter in the atmosphere. There is approximately 5.5 Quadrillion Tons of atmosphere surrounding planet Earth. All of that heat energy is resident in the atmosphere, “free air.” That heat energy is free for the taking. No meters may be interposed between the “free air” you breathe, and your lungs. (More . . . )
If "free expansion" is put to work in the right context, a phenomena presently considered to be a disadvantage, the attribute can be converted into an advantageous source of sheer raw brute power.
Scuba tank filling stations know all about it: when filling a heavy duty, high pressure, safety-factor-of-167%, well made, correctly maintained scuba tank, TOO FAST, you had better be hiding around the corner. Scuba cylinders are hydrostatically safety tested to a pressure 1.67 (167%) (5/3) times the Maximum Available Working Pressure (MAWP) rating stamped on the tank.
For example: Scuba tank stamped pressure rating is 3300 psig, this tank would be hydrostatically tested to a pressure of 5500 psig. (1.67 x 3300 = 5511).
Hydrostatic testing measures the ability of the scuba tank to (1) expand under pressure, (2) maintain containment integrity, (3) show no signs of leaks, and (4) recover its original volume to within 10% of pre-test volume. i.e., if the cylinder volume increased 100 ml at test pressure, after test pressure is removed, the tank should recover to less than 10 ml larger volume than the pre-test volume. The MAWP should be strictly observed to prevent frequent tank expansion and contraction which causes metal fatigue, fractures, and eventual failure of the pressure vessel.
The established dogma behind pressure equalization is that there is no "work" done because the actual instantaneous temperature is discounted and factored into the math as though there was no (heat) temperature change (Joule's first law). But that train of thought is purposed to protect certain physical “laws” held to be sacred, even in the face of their fallibility. All of the facts are not considered in order to maintain the status quo. In reality, the present establishment dogma is focused upon “complete equalization,” where there is no NET temperature change. (Physics . . .)
Ask anyone who has filled scuba tanks about the concern for big temperature change. Dangerous temperature change. Temperature change caused just by moving compressed air, at ambient temperature, from a big tank into a smaller tank at ambient temperature. If the procedure is performed too quickly, there is a very real danger that the smaller tank could explode like a bomb, putting life and limb in great jeopardy.
The question to ponder is, "Where does the energy come from to explode the scuba tank if the max air pressure in the storage tank does not exceed the scuba tank safety test pressure?"
Exploding compressed air tanks constitutes an argument against the "conventional" air car like the MDI which stops to fill its tanks about every 30 miles. Yes, filling can take place in a minute or less, but you would be prudent to be hiding around the corner.
The reason for this dangerous circumstance is based upon the characteristics of suddenly compressing air. Sudden compression of air generates an enormous amount of heat.
When lightning occurs, the air through which the lightning travels is instantaneously superheated to enormously high temperatures. The heat from the lightning instantaneously causes compression of the air to such a degree that the matter in the air attains velocities greater than the speed of sound, thereby, breaking the sound barrier and causing a loud sonic BOOM. We call it thunder. The heat of the lightning compresses the air against the containment of colder atmosphere at 0 psig.
HEAT energy compresses AIR. Compressing AIR releases HEAT energy.
This phenomena, sudden compression, if properly harnessed, can release the enormous heat energy stored in the air by the Sun, which can then, be captured and put to work. Free energy.
Through experience, and daily use of heat pumps, it is known that the heat energy delivered by a heat pump, is on average, three (3) to four (4) times the amount of heat energy consumed by the heat pump compressor and fans. This phenomena has been designated as Coefficient of Performance, (COP), in order to compartmentalize the facts away from some of those previously mentioned "laws."
The best technique for capturing and putting to work the heat energy derived from sudden compression, that is presently known and understood, is:
The Main Tank has a much larger volume than the equalizer. The whole air volume of the Main Tank, even if its temperature goes down less than a degree, contributes a vast amount of energy to the air in the smaller equalizer containing atmosphere. When the control valve is opened suddenly, compression takes place inside the EQT, (equalizer tank), and the air inside the EQT gets very hot instantly, causing another tremendous compression to take place. HEAT causes compression. Before the heat of compression inside the EQT can cool to ambient temperature, the atmosphere air and the Main Tank air that has been added to the EQT, now at a pressure much higher than Main Tank air pressure, enters the Main Tank through the EQT discharge check valve.
It sounds unlikely: use Main Tank air to put more air into the Main Tank, until the EQT (Equalizer), cycle is comprehended. The one, very small, expenditure of energy to operate the equalizer cycle, is that the control valve will have to be powered to open and close. (Maxwell's Secret . . .)
If the Main Tank air pressure was 200 psig and the EQT (equalizer) pressure was 1 psig, then, equalizing the two pressures would raise the EQT pressure to maybe 199 psig, because the Main Tank pressure will drop, 1 psig, because of moving the EQT volume of air out of the Main Tank into the EQT. At that point, and pressure, the EQT air would not go into the Main Tank without being increased to a value greater than 199 psig. That circumstance is predicated upon “complete equalization,” which is discounting, or eliminating the heat created in the EQT when the Main Tank air suddenly enters.
The equalizer can be used in a manner that doesn't allow complete equalization, it's called unbalanced expansion (or free expansion) for a reason. It's like anything elastic that stores potential energy, store energy, cause the energy to be released, the released energy will attempt to return, in ever decreasing cycles, to equilibrium. The cycles are waves, periodic oscillations or the overshooting of equilibrium as the unbalanced condition seeks balance, causing the tension to gradually dissipate, overshooting equilibrium in both directions till finally it comes to rest at ambient temperature and 199 psig.
The design of the EQT equalizer injection system doesn't allow enough time for “complete equalization.” When the actual pressure in the equalizer exceeds the Main Tank air pressure the injection control valve has already closed.
Fill the equalizer suddenly with Main Tank air and the heat generated is extremely high, except that as soon as the heat is generated, extreme pressurization of the equalizer expansion zone causes all of the EQT air to blast through the EQT discharge check valve into the Main Tank because the equalization zone pressure exceeds the Main Tank air pressure, and due to the Kadenacy Effect (like 2-stroke engine tuning). A suction is left behind in the EQT expansion zone that is easily filled by “free air” being sucked in through the EQT inlet check valve.
The following is an attempt to illustrate the EQT equalizer cycle.
This cycle explanation is based on time instantaneous (Ti).
The pressures used in this explanation are for the purposes of
illustration only. Actual pressures and temperatures must be acquired by
SEQUENCE — 2
SEQUENCE — 3