Mechanische Energiespeicher konstanten Volumens
In this paper general directives are developed for the improvement of accumulators, which use compressed air (or a gas which is chemically passive against metals and moisture) as working substance or only as an elastic link. In the second case water serves as working liquid the surface of which is loaded with an air cushion. In each case the storing capacity is caused by a change of pressure in connection with a constant volume. At first the equations for the calculation of the stored energy are developed in the adiabatic and the isothermal condition, that is for the two limiting cases. Then it is shown that the expenditure of iron for the pressure vessels with a prescribed volume does not depend on the diameter or whether the given volume consists of one or more containers. The same applies to the energy which can be stored per kp of the container material. For the compressed-air accumulator this exploitation of the weight raises steadily with the accumulator pressure up to about 40 kp/cm^2. But it is remarkable that the energy which may be stored per kg of material is practically independent on the pressure if the accumulator is operated with water under compressed gas. In this case there exists also an optimal proportion for the discharge, that is the proportion of the highest to the lowest pressure in the accumulator, of e = 2,718 But the expenditure of material per energy unit for this accumulator is much higher than for the one operated with compressed air only, because the water which does not store energy demands a considerable part of the volume of the tank. But the efficiency is very good and considerably higher than for the accumulator operated with compressed air. Besides that the operation is much simpler, because it is not necessary to cool at charging and to heat at discharging the accumulator. It is even possible to come near to 100% efficiency if one approaches to isothermal change of state in the air cushion by means of heat exchange between air and water volume. That is also possible if one separates the volumes for air and water and connects them by heat exchangers in the junction.