Construction of vortex compressors

Abstract

Vortex compressing machines (VC), viz., compressors, vacuum compressors, vacuum pumps, etc., possess the merits of dynamic machines [absence of complicated kinematic and friction couples, reliability, safety, long service life, "dry" flowthrough part (casing), relatively small size and weight, etc.] and of positive-displacement machines [ability to develop high heads at low outputs (capacities)]. These compressors are distinguished by simple design, technological effectiveness (adaptability to manufacture), low manufacturing cost, serviceability, minimum operational cost, stability, steady characteristics in the whole range of variation in operating conditions, in particular, absence of stalling and surging typical of centrifugal compressors, and so on. Maximum efficiency of a VC is attained at a relatively low rotation speed and peripheral rotor speed, which makes it possible to make them without boosters.Vortex compressors (VC) are well researched [1][2][3][4][5][6][7][8][9]. The best known work is [10] where theoretical hypotheses about the operating process of VCs are reviewed, experimental data are summarized and analyzed, and a procedure for calculating geometric parameters and operating conditions of a single-stage VC, making use of regenerative hypothesis, is given. It is indicated there as well that the characteristics of the stage may also be calculated for variation (with a definite step) in the flow factor.Vortex compressors find application in the domain of relatively low outputs (capacities) and high heads (the head factor of a VC in the rated operating conditions may be > 2), where they successfully compete with centrifugal compressors and compressors of the rotor type, especially of the type of liquid-packed ring, gear, and other compressors. In terms of energy conversion method, VCs are dynamic type of machines: gas particles in the flow-through part move in a spiral-like path from the inlet to the outlet of the machine, repeatedly interacting with the impeller vanes and gradually receiving energy from the impeller. This longitudinal-vortex flow is the primary flow with the energy being exchanged between the VC vanes and the gas particles in the casing channel; the flow intensity is geatly influenced by the type of the flow-through part and the geometric parameters that characterize both the stage as a whole (ratio of the diameter of the flow-through part to the diameter of the VC, ratio of the area of the inlet/outlet pipe to the area of the flow-through part, and so on) and its individual elements (angles of mounting and inclination, number of vanes of the VC, angles of inclination of the inlet and outlet pipe, etc.).A distinctive feature of the operating process of a vortex compressor (VC) is transfer of a part of the working medium through the cutoff device from the outlet to the inlet of the stage, which causes (especially when working with a compressible medium) further energy loss, lowering of efficiency of the machine as a result of mixing and change in the thermodynamic state of the str...