Experimental analysis of heat losses in different types of hydraulic accumulators

Even though an accumulator seems to be an ideal energy storage component, it also has some disadvantages. Further energy losses in form of heat transfer from gas to walls of the accumulator and to surroundings is a well-known problem. Especially the fast filling of the accumulator is nearly adiabatic process where the temperature of gas increases significantly. A part of this stored energy escapes from gas through the walls of the accumulator to the environment in form of heat reducing the energy efficiency. Several methods for improving the energy efficiency of the accumulator can be found in the literature. However, the previous studies made by the authors have concentrated to piston type accumulator but the knowledge of differences in performance characteristics of different type of accumulators is also important. The aim of this study is to compare different type of accumulator; piston, bladder and diaphragm type. The results of this study consist of experimental measurements of different types of hydraulic accumulators. The results demonstrate that the membrane inside the bladder type accumulator acts as a thermal insulator between the gas and the hydraulic fluid resulting to smaller thermal losses whereas in diaphragm and piston type accumulators the membrane is not protecting the nitrogen from heat losses.