HP Ejector Research Papers - Academia.edu (original) (raw)

Numerical and experimental analyses are performed on a supersonic air ejector to evaluate the effectiveness
of commonly-used computational techniques when predicting ejector flow characteristics. Three
series of experimental curves at different operating conditions are compared with 2D and 3D simulations
using RANS, steady, wall-resolved models. Four different turbulence models are tested: k–e, k–e realizable,
k–w SST, and the stress–w Reynolds Stress Model. An extensive analysis is performed to interpret
the differences between numerical and experimental results. The results show that while differences
between turbulence models are typically small with respect to the prediction of global parameters such
as ejector inlet mass flow rates and Mass Entrainment Ratio (MER), the k–w SST model generally performs
best whereas e-based models are more accurate at low motive pressures. Good agreement is found
across all 2D and 3D models at on-design conditions. However, prediction at off-design conditions is only
acceptable with 3D models, making 3D simulations mandatory to correctly predict the critical pressure
and achieve reasonable results at off-design conditions. This may partly depend on the specific geometry
under consideration, which in the present study has a rectangular cross section with low aspect ratio.

- by and +1
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- Thermodynamics, Fluid Dynamics, Computational Fluid Dynamics (CFD) modelling and simulation, Refrigeration Air Conditioning

Supersonic ejectors can be used in heat powered chillers to transfer mechanical energy between the motive and the inverse
cycle. Within the ejector, momentum is exchanged between a high speed flow produced by a primary nozzle and a slow
current coming from the chiller evaporator. Due to the supersonic regime of the primary flow, the mixing of the two streams
causes significant loss and impairs the system efficiency. Up to now, second law efficiency of ejector chillers is quite low
and optimization is highly needed. The fluid dynamics of the whole ejector involves turbulent mixing, shock trains and
complex wall flow, requiring CFD analyses for an adequate description. However, in order to attempt an optimization,
mathematically workable models are advantageous.
An analytical scheme that captures the basic features of the turbulent mixing zone is discussed here in view of a Constructal
design of an ejector chiller.

Encompassing both practical applications and recent research developments, this book takes the reader from fundamental physics, through cutting-edge new designs of ejectors for refrigeration. The authors’ unique vision marries successful design, system optimization, and operation experience with insights on the application of cutting-edge Computational Fluid Dynamics (CFD) models. This robust treatment leads the way forward in developing improved ejector technologies. The book covers ejectors used for heat powered refrigeration and for expansion work recovery in compression refrigerators, with special emphasis on two-phase flows of “natural” fluids within the ejector, i.e. steam and carbon dioxide. It features worked examples, detailed research results, and analysis tools.

A supersonic ejector chiller for industrial use is currently being developed and tested as
part of a project cooperation between Frigel s.p.a and DIEF (Department of Industrial Engineering,
University of Florence). The refrigerator was built following a “ready to market”
setup criterion and is intended for applications on the industrial refrigeration market or in
air conditioning. The plant has a nominal cooling power of 40 kW and is powered by low
temperature heat (from 90 up to 100 C). The ejector is equipped with a movable primary
nozzle and 9 static pressure probes along the mixing chamber/diffuser duct. The working
fluid is R245fa. An extensive numerical campaign was performed to analyze the internal
dynamics of the ejector. All the simulations were carried out by accounting for the real gas
properties of the refrigerant. Comparison with experimental data resulted in close agreement
both in terms of global and local parameters. Analyses showed that in order to
achieve an accurate matching with the experimental data, it is necessary to correctly account
for the surface roughness of the ejector. This is especially true for off-design operating
conditions.

- by Adriano Milazzo and +1
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- Thermodynamics, Fluid Dynamics, Ejector, HP Ejector

High pressure is never expected in process or process flow system. Such a problem is remaining in Jamuna fertilizer Company Limited (JFCL) since 1991. All equipments of the process are damaged due to high pressure, which are connected... more

- by Dr. MD. Mamunur Rashid
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- Urea Synthesis, HP Ejector