Jyri Juhala

Hydraulic Accumulator as Energy Storage

Most of the hydraulically operated systems have potential to improve the energy efficiency of the system by using energy regeneration. The recovered energy can be stored in various ways. However, previous studies made by the authors have shown that in hydraulically operated regenerative systems a pressure accumulator seems to be potential option as energy storage. Hydraulic accumulator has also some disadvantages, e.g., energy losses in form of heat transfer. The efficiency can be improved by using different heat recovery methods. To compare these methods numerically, a reliable model of an accumulator is needed. The primary aim of this study is to build a multidisciplinary model of a basic piston type hydraulic accumulator and to validate the model with experimental measurements. The second aim is to experimentally test the effects of a honeycomb heat regenerator by efficiency point of view. The results manifest that multidisciplinary modeling is useful and valid tool for modeling the piston type hydraulic accumulator. The results also indicate that the heat regenerator attached inside the accumulator’s gas volume improves energy efficiency significantly.Copyright

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.Copyright