Mathematical Modelling of the Entrainment Ratio of High Performance Supersonic Industrial Ejectors

Dario Friso

doi:10.3390/pr10010088

Abstract

For many years now, manufacturers have been producing supersonic ejectors with a high entrainment ratio for the chemical, oil, and food industries. In the present work, mathematical modelling of the entrainment ratio of such industrial ejectors is carried out, in which a variation of the diffuser efficiency is also assumed to be a function of the Mach number of the motive gas. To determine this unknown relationship, the mathematical modelling was overturned by inserting the entrainment ratios of ten different high-performance industrial ejectors, as identified through an experimental investigation. The mathematical modelling, completed through the use of the relationship between the diffuser efficiency and the Mach number of the motive gas, was applied to sixty-eight ejectors, built and tested experimentally over the last twenty years as part of research aimed at the development of thermal ejector refrigeration systems (ERSs), to obtain the entrainment ratios proposed by the manufacturers (industrial entrainment ratios). A comparison of the experimental entrainment ratios with respect to the industrial ones demonstrated that the former were always lower, ranging from a minimum of −17% to a maximum of −82%. These results indicate that the lab-built ejectors for ERS prototypes can be improved. Therefore, in the future, researchers should apply numerical analysis iteratively, starting from a given geometry of the ejector, and modifying it until the numerical analysis provides the industrial value of the entrainment ratio.

Highlights

An ejector, or jet pump, is an apparatus (Figure 1) of which the task is the compression of a fluid—called the induced fluid—by molecular entrainment and diffusion, through a jet produced by the expansion of another fluid—called the motive fluid [1,2]
The mathematical modelling, completed through the use of the relationship between the diffuser efficiency and the Mach number of the motive gas, was applied to sixty-eight ejectors, built and tested experimentally over the last twenty years as part of research aimed at the development of thermal ejector refrigeration systems (ERSs), to obtain the entrainment ratios proposed by the manufacturers
A comparison of the experimental entrainment ratios with respect to the industrial ones demonstrated that the former were always lower, ranging from a minimum of −17% to a maximum of −82%. These results indicate that the lab-built ejectors for ERS prototypes can be improved

Summary

Introduction

Jet pump, is an apparatus (Figure 1) of which the task is the compression of a fluid—called the induced fluid—by molecular entrainment and diffusion, through a jet produced by the expansion of another fluid—called the motive fluid [1,2]. The vapor resulting from boiling liquid is thermodynamically requalified and reused to heat the boiling liquid itself This ejector–heat exchanger system is, a heat pump, and the ejector is called a thermo-compressor. Various studies focused on the use of supersonic ejectors as thermo-compressors in heat-driven ejector refrigeration systems (ERSs), where both fluids are refrigerating gases, have been underway for many years. This type of system, which has been known for more than a century [3], is being re-proposed for environmental reasons, as they can operate on solar energy [4]

Methods

Results

Conclusion