Steam Jet Refrigeration Cycle

Topics: Pressure, Vapor pressure, Chemical engineering Pages: 53 (7224 words) Published: November 28, 2012
Chemical Engineering and Processing 41 (2002) 551– 561

Evaluation of steam jet ejectors
Hisham El-Dessouky *, Hisham Ettouney, Imad Alatiqi, Ghada Al-Nuwaibit Department of Chemical Engineering, College of Engineering and Petroleum, Kuwait Uni6ersity, P.O. Box 5969, Safat 13060, Kuwait Received 4 April 2001; received in revised form 26 September 2001; accepted 27 September 2001

Steam jet ejectors are an essential part in refrigeration and air conditioning, desalination, petroleum refining, petrochemical and chemical industries. The ejectors form an integral part of distillation columns, condensers and other heat exchange processes. In this study, semi-empirical models are developed for design and rating of steam jet ejectors. The model gives the entrainment ratio as a function of the expansion ratio and the pressures of the entrained vapor, motive steam and compressed vapor. Also, correlations are developed for the motive steam pressure at the nozzle exit as a function of the evaporator and condenser pressures and the area ratios as a function of the entrainment ratio and the stream pressures. This allows for full design of the ejector, where defining the ejector load and the pressures of the motive steam, evaporator and condenser gives the entrainment ratio, the motive steam pressure at the nozzle outlet and the cross section areas of the diffuser and the nozzle. The developed correlations are based on large database that includes manufacturer design data and experimental data. The model includes correlations for the choked flow with compression ratios above 1.8. In addition, a correlation is provided for the non-choked flow with compression ratios below 1.8. The values of the coefficient of determination (R 2) are 0.85 and 0.78 for the choked and non-choked flow correlations, respectively. As for the correlations for the motive steam pressure at the nozzle outlet and the area ratios, all have R 2 values above 0.99. © 2002 Elsevier Science B.V. All rights reserved.

Keywords: Steam jet ejectors; Choked flow; Heat pumps; Thermal vapor compression

1. Introduction
Currently, most of the conventional cooling and refrigeration systems are based on mechanical vapor compression (MVC). These cycles are powered by a
high quality form of energy, electrical energy. The
inefficient use of the energy required to operate such a
process can be generated by the combustion of fossil
fuels and thus contributes to an increase in greenhouse
gases and the generation of air pollutants, such as NOx,
SOx, particulates and ozone. These pollutants have
adverse effects on human health and the environment.
In addition, MVC refrigeration and cooling cycles use
unfriendly chloro-floro-carbon compounds (CFCs),
which, upon release, contributes to the destruction of
the protective ozone layer in the upper atmosphere.

* Corresponding author. Tel.: + 965-4811188x5613; fax: + 9654839498. E -mail address: (H. El-Dessouky).

Environmental considerations and the need for efficient
use of available energy call for the development of
processes based on the use of low grade heat. These
processes adopt entrainment and compression of low
pressure vapor to higher pressures suitable for different
systems. The compression process takes place in absorption, adsorption, chemical or jet ejector vapor compression cycles. Jet ejectors have the simplest configuration among various vapor compression cycles.

In contrast to other processes, ejectors are formed of a
single unit connected to tubing of motive, entrained
and mixture streams. Also, ejectors do not include
valves, rotors or other moving parts and are available
commercially in various sizes and for different applications. Jet ejectors have lower capital and maintenance cost than the other configurations. On the other hand,
the main drawbacks of jet ejectors include the
“ Ejectors are designed to operate at a...
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