EVALUATION OF EFFICIENCY IN COMPRESSIBLE FLOW EJECTORS

摘要

A steady-flow ejectors are fluid dynamic flow induction devices that directly transfer energy and momentum from a high energy primary fluid to a low energy secondary fluid through the work provided by entrainment and turbulent mixing. A variety of applications from refrigeration svstems that are thermally energized and capable of using environmentally friendly refrigerants such as water and air, to desalination of water are currently being explored with this technology. The potential benefit of using environmentally friendly refrigerants makes it extensively useful for commercial air conditioning and refrigeration, particularly in applications where a source of waste heat is readily available. While steady-flow ejectors operate on entrainment and turbulent mixing between the primary (driving) flow, and the secondary (driven) flow, eliminating mechanically moving parts, the turbulent entrainment mechanism itself, is inherently dissi-pative of energy and little can be done to improve it. The process of mixing, which is irreversible is not accounted for explicitly in the existing definitions of ejector efficiency. Moreover, efficiency of ejectors is based on the concepts of a indirect flow induction viz., turbine-compressor analogy and compressor efficiency, and entrainment ratio. An experimental steady flow ejector with compressed air as the motive fluid and ambient air as suction fluid was fabricated and tested in this study. Comparisons of efficiency are made with the assumption of adiabatic and complete mixing of primary and secondary fluids before fluid discharge from the ejector. An important goal in our research is the definition of a proper measure of ejector efficiency which is appropriate for non-dissipative. non-steady ejectors. Such a definition would enable a more systematic methodology for evaluating ejector performance. There are three proposed methods that will be presented and compared.