Entropomechanical converters store energy by converting the sorage medium in a lower entopy form or vice versa. [Todo: incorrect needs rewrite] They use energy storage cells containing an appropriate medium that's only partially in machine phase. They are a subclass of molecular power converters. Chemomechanical converters like radical batteries use similar zip style reactor cells.
Compressed gas above its inversion point (wikipedia) is one of the simplest entropic batteries conceivable. The temperature drops when work is extracted. With APM capabilities micro sized gas capsules with a size below the limit of what is perceptible by the human eye can make storage of pressurized gas inherently safe even at around 1000 bars (at room temperature) which is around the point where the gas molecules begin to "touch" each other that is where the density of a liquid is archived. To get out the full energy stored in a short period of time one needs to supply the storage with environmental ambient temperature heat (e.g. with pellet warming and air medium movers) or else the storage cool down quickly and energy output will temporarily run dry. (till..)
Alternativels an entropic battery may be implemented with a set of linear alkane molecules which are on both sides bond to handles. Those handles can be either pulled apart and fixated at their maximum separation thereby stretching the alkane completely straight or put together rather close allowing the alkane great freedom of movement.
H H H H H H H H H H H H H H H | | | | | | | | | | | | | | | Handle1-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-Handle2 | | | | | | | | | | | | | | | H H H H H H H H H H H H H H H
In the nano-comos every degree of freedom on average absorbs a package of energy that is proportional to the environments temperature (this energy is E = 3/2kT; see equipartition theorem). When the alkanes are completely stretched they have only a few degrees of freedom (DOFs) and store less thermal energy than in a natural unconstrained state. When the alkanes are contracted and chaotically curled up they provide many DOFs and store a maximal amount of thermal energy.
At non-zero temperatures the alkanes pull the handles together. So to draw energy from your battery you simply remove the handles from their locked positions and let them drive your workload. The emerging DOFs in the alkanes suck up the thermal energy of the environment effectively cooling the battery down. The reason behind this seemingly paradox behavior is that not the total energy but the Gibbs free energy is subject to minimization. Some more information can be found here: "rubber elasticity" and here: "entropic force"
To store energy into the entropic battery all the handles are pulled apart. The thermal energy is effectively wrung out out of the alkanes increasing the environments temperature.
Expected features of entropic batteries:
- recyclability: potentially excellent - depends on AP - system design
- durability: probably acceptable - carbon chains are especially sensitive to radiation damage - too fast charging can lead to thermal destruction
- measurability: excellent - one can count used handle pairs - zero self discharge
- power density: probably good - power extraction is limited by self cooling
- efficiency: probably acceptable for some applications - significant thermal losses since it's an inherent thermal process
- energy density: probably mediocre
- recource consumption: absolutely no scarce elements are needed
- health hazards: probably very low - no heavy metals are used
- danger (when crushed): inherently safe since it freezes when shorted - the use of silicone polymers would make it even safer.
Note that mechanosynthesis of the needed floppy polymers is beyond basic capabilities of productive APM systems and will require specialized tools.
[Todo: can this be considered as a latent heat storage system too?]
Relation to quantum effects
Just as the Joule-Thomson effect (see cooling) this effect is
predominantly not originating from quantum effects
like e.g. quantum mechanical unfreezing of DOFs (which causes heat capacity jumps in muti-atomic gases).
(TODO: questionable correctness - check in more detail)
Relation to machine phase
Giving crystolecules increasing space to frewheel on an axle or freereciprocate on a sliderail could exert ectropic forces on the motion limiters. Given the forces can be balanced out delicately. The effect to expect is likely to be much smaller than what one can observe in polymers though, since each relatively big crystolecule gets just one single thermal energy package according to the equipartitioning theorem. Thus each crystolecule acts just equivalently to one much smaller DOF in a polymer chain.
The downside of the much more effective polymer chains is that they are
- harder to mechanosynthesize due to their total lack of stiffness (not impossible: see molecule spanning method)
- more amenable to high energy radiation (including UV light) (just one break in a single bonded chain leads to failure)
Robust gases as alternative to delicate polymer chains
Gas spring capsules (as used in Diamondoid heat pump systems) might be a solution solving both issues. There are no bonds to break in mono-atomic gasses. But this is basically just a pneumatic ultra high pressure (~1000atm - contacting gas atoms) energy storage. Energy density is lower than chemical and easy to calculate. (wiki-TODO: do that)
(TODO: Explore if energy densities comparable to conventional chemical energy storage can be reached somehow.)
Known potential for extreme safety
Sidenote: Experiments (long before time of writing 2018) with state of the art metal hydride energy storage (in which strong entropic effects are present) have shown that very high energy density storages can be exceptionally safe. So safe that in case they are majorly abused (shot at, driven over with a tank) they just freeze instead of going off in a violent and dangerous explosion.
The ideal energy storage
One could imagine a combination of conventional energy storage and entropic energy storage such that the catastrophic event thwarting entropic part just slightly overcompensates the catastrophic event fostering conventional part and one gets the maximum possible energy density but still retains very high safety.
- Wikipedia: Equipartition_theorem