Fluid Motion Dynamics in a Two-Stage Piston Hybrid Power Machine
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FLUID MOTION DYNAMICS IN A TWO-STAGE PISTON HYBRID POWER MACHINE V. E. Shcherba, A. V. Zanin, and S. F. Khrapskii
UDC 621.512
This article presents a method for calculating the dynamics of fluid motion in a two-stage hybrid energy machine with a gas cap. The developed method is based on the Bernoulli energy conservation equation, taking the linear hydraulic resistances, local hydraulic resistances, and inertial forces into account. The expressions for the current coordinate values of the liquid levels and pressures in the gas cap apply to the second stage compressor section and the first stage pump section. The developed method of calculation can be used for the analysis of working processes in compressor machines based on the principle of the liquid piston. Keywords: piston hybrid power machine, dynamics of fluid motion, liquid piston, gas cooling, compressor, pump.
Given that piston hybrid power machines (PHPMs) combine the functions of a piston pump and a reciprocating compressor, they offer several definite advantages, the main ones being [1–3] — intensive gas cooling and the approximation of compression to an isothermal process, no leaks of compressed gas, a decrease in frictional forces in the cylinder-piston group, an increase in the positive suction head, heat recovery from compressed gas, as well as a significant improvement in the mass and dimensional characteristics of the machine. The listed physical aspects allow the cost-effectiveness and efficiency of the compressor and the pump to be increased. Gas compression to high pressures requires booster compressors utilizing a liquid piston and piston pumps for supplying liquid to the compressor chamber [4, 5]. In a PHPM, gas is also pre-compressed in a compressor, with a pump supplying liquid to the booster stage of the compressor. In the first-stage compressor section, the gas is pre-compressed. Next, it enters the interstage cooler through the discharge pipeline. After that, it arrives at the second-stage chamber through the second-stage suction valve. Through the interstage cooler, fluid from the first-stage pump chamber enters the chamber of the secondstage compressor section, with the excess liquid being led into the gas cap (see Fig. 1). During the upward piston stroke, liquid from the second-stage compressor section and the gas cap through the heat exchanger enters the first-stage pump section. Thus, the second-stage compressor section ensures the intensive cooling of compressed gas (given that the pressure in the pump chamber exceeds the pressure in the compressor section throughout the entire piston stroke, liquid is certain to be present above the first-stage piston) without gas leaks in the cylinder-piston group, with no clearance space in the first- and second-stage compressor sections; the second stage is characterised by an absence of rigid piston and actuator mechanism. This enables the cost-effective and efficient compression of gas to medium and high pressures in a positive displacement twostage PHPM characterized by small overall dimensio
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