|
According to the EPA and Eaton, accumulators are 96-99% efficient. They are referring to the bladder type. The spring piston type can handle higher pressures but are much heavier. There are also inert gas piston types, as well as many others that are not very commonly encountered.
The bladder is precharged to several hundred PSI, pumping the fluid into the containment vessel outside the bladder collapses the bladder and increases the pressure.
The heat rises as the gas in the bladder (usually Nitrogen) is compressed. That increase in temperature increases the effective pressure necessary to push more fluid into the liquid portion of the accumulator.
Heat losses are minimal. If that was not true the efficiency calculations would be lower. When the charge in the accumulator is released the temperature of the gas falls off to the same temperature that existed before the charge cycle began.
Few energy storage sources can compete with hydraulic accumulators. The closest competitor is a flywheel battery, but you are talking about 150,000 RPM, magnetic bearings, in a perfect vacuum vessel.
That NASA developed flywheel battery can store 10 KWH in a vessel the size of a gallon gas can, but it cost several hundred thousand dollars.
Accumulators do not use air for a spring generally speaking. This is because if you used any gas containing oxygen, that allowed the combination of a volatile liquid and that same oxygen at pressures above the compression pressure of a Diesel engine, you could have spontaneous combustion.
Conceptually speaking that phenomena could potentially be exploited as a form of an engine, creating spontaneous combustion intentionally to increase pressure significantly with a single combustion event.
regards
Mech
|