This paper addresses the issue of understanding the dynamic phenomena in piston type accumulators; and how this leads to improved numerical accumulator models. Developing a numerical model has two challenges. First; the unsteady heat transfer between the accumulator gas and the wall has to be described. Secondly; a suitable real gas model had to be identified and employed. To verify the model; a series of experiments were conducted at Fritz Schur Energy in Glostrup; Denmark. The experiments were designed to investigate gas dynamical properties at various precharge pressures; maximum pressures; and ambient temperatures. These parameters are varied to obtain parameter independent conclusions. During controlled piston movements; hydraulic and gas pressures are measured together with the piston position and the gas temperature.
It was found that the simple thermal time constant approximation by Rotth√§user was suitable and stable for the application. It was also found that the Soave-Redlich-Kwong equation; was overall best suited with experimental data. The Soave-Redlich-Kwong equation is as much as six times faster than the widely used Benedict-Webb-Rubin equation; independent of the ambient temperature; maximum pressure and precharge pressure.
This project concludes that the Soave-Redlich-Kwong equation should be used in simulation of piston type accumulators. It is noted that the pressure available after expansion is some 5-10 bar lower than predicted by any model. Therefore; it is suggested that more research is conduced to obtain an improved model for the heat transfer. finally; measurement quality was confirmed by comparing measured pressure data by pressure calculations based on measured temperature<
Keywords: Hydraulics; Accumulator; Thermodynamics; Modelling; SIMULINK; Matlab; Verification; Thermal time constant
13th Scandinavian International Conference on Fluid Power; June 3-5; 2013; Link√∂ping; Sweden
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