Abstract
The article is devoted the design of working process of liquid-vapor ejector of a vacuum unit with conical mixing chamber, working on principle of stream thermocompression, research of influence of thermodynamic parameters and descriptions of active and passive streams on the process of mixing with the purpose of achievement of most vacuum unit efficiency. The main content of the article is study the nature of passive mixing flows with different thermodynamic properties on the geometric parameters of the mixing chamber. Experimental study of liquid-vapor ejector with conical mixing chamber on a transparent model allowed to confirm the mechanism of the working process at pressures below atmospheric pressure, namely the boiling of metastable superheated liquid, characterized by the presence of three critical sections expiry of expanding the channels to the definition section of flow separation from the walls of the channel and its position relative to the nozzle exit of active flow. Also the nature of the mixing process in the chambers of conical shape is investigated. It allows establishing maximum efficiency by optimizing the flow of liquid-vapor ejector with conical mixing chamber. The estimation of the appropriateness of units on the basis of LVE in vacuum systems through a comparative exergy analysis of basic and alternative schemes offered by the method of J. Tsatsaronis.
Highlights
At the present stage of human development technological processes that can be taken only at pressures below atmospheric are more widely used in various industries
For the design of vacuum units based on liquid-vapor ejector (LVE) with conical mixing chamber it is necessary to develop a method of calculation that would authentically reflect its workflow
The use of conical mixing chamber with contraction angles > 10° is impractical, since already in experimental research of chambers with 8° contraction angle condensation jumps in section 1-1 were observed and there was a shift in modes in which there was «choking» of mixing chamber with the emergence of return currents along the LVE length (Fig. 4)
Summary
At the present stage of human development technological processes that can be taken only at pressures below atmospheric are more widely used in various industries. Greater degree of pressure increases at one stage lead to a sharp decline in the ejector efficiency, which is associated with choking losses during the mixing of supercritical active and subcritical passive streams In view of this situation, it is very relevant to use liquid-vapor ejector (LVE), which works on the principle of. Jet thermal compression (JTC) [1] This principle is based on the fact that the passage of the working environment of active flow through Laval nozzle is accompanied by relaxation vaporization of the part that is expanding. In the initial section of the LVE active flow nozzle is formed supersonic jet of finely-divided vapor-drop structure with a pressure that is less than the pressure of the environment It injects hydraulic fluid of passive flow entering the rec eiving chamber. Vapor that compressed in LVE is separated in a separator from which liquid is extracted in circulation circuit by the pump and after the heating in the heat exchanger is fed to the active LVE nozzle
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