Charles A. Garris

Non-Steady Three-Dimensional Flow Field Analysis in Supersonic Flow Induction

In this paper, supersonic pressure-exchange ejectors were studied through numerical analysis, CFD modelling. The critical role played by the geometry on ejector performance was clearly established. CFD simulations (3D) are capable of predicting all trends in the performance curves. Results show the effect that non-steady flow can achieve over the steady flow ejector.Copyright

Evaluation of Efficiency in Compressible Flow Ejectors

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 systems 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 dissipative 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.Copyright

Non-Steady Pressure-Exchange Ejector

This paper will examine development of practical pressure-exchange ejector to useful level of performance, using our knowledge of aerodynamic design of a compressible fluid. A novel supersonic rotor-vane/pressure-exchange ejector system has been investigated both experimentally and numerically.Copyright

The Influence of Shear Layer Turbulence on Stationary Pseudoblades in Supersonic Pressure Exchange Inducing Flow Fields

The pressure exchange process can be initiated by nonsteady pressure forces that arise due to moving fluid dynamic interfaces in the laboratory frame of reference. The fluid interfaces are flow features of “pseudoblades” that can be generated by an expanding supersonic primary flow, impinging on freely spinning cone-vane type of rotors. These pseudoblades are fluidic vanes that interface with an entrained, compressible secondary fluid and can mimic the action of impellers as in conventional turbomachinery. The overarching goal of this research is the development of a novel fluid impeller-based ejector. The authors’ motivation towards this study was in understanding the boundary conditions leading to spatial deterioration of pseudoblades. Flow around stationary, axisymmetrically aligned rotors (the ramp vane and double cone type), held in a primary supersonic flow field (Mach 1.44 jet), were investigated by laser Doppler velocimetry (LDV) measurements of shear layer turbulence intensity (TI) under alternative seeding of primary and entrained secondary flows. Rotors were tested and compared for shear layer TI distribution-based boundary conditions, anticipated pseudoblade conditions and an “effective persistence length of stationary pseudoblades.” The results suggest that the double cone rotor is most conducive for pseudoblade stability. The TI distribution-based boundary conditions for this rotor indicate that the effective pseudoblade persistence length approximately equals the exit diameter of the supersonic nozzle.

Analysis of Application of Pressure Exchange Device in Thermal Vapor Compression Desalination System

Recent advances in direct fluid-fluid flow induction provide potential for major improvement in performance of thermal distillation systems based on the pressure exchange phenomenon compared to the conventional turbulent mixing controlled ejectors. Pressure exchange devices utilize the work of nonsteady pressure forces acting across moving interfaces. Optimal performances of such devices can be determined through the use of the ideal turbomachinery analog. The analog is configured as a turbine-compressor unit, where the high energy primary fluid expands through the turbine that drives a compressor which compresses the low energy secondary fluid and the two then discharges in a common mixing chamber at a common intermediate pressure. The overall functioning of the turbomachinery analog is similar to the conventional ejector. Thus the turbomachinery analog provides the highest possible performance that an ejector can achieve ideally. An analytical single effect thermal vapor compression (TVC) desalination model is developed. The turbomachinery analog which is the simplest kind of pressure exchange device is simulated in place of the conventional ejector. The objective of the research is to investigate the performance of the system for various ejector efficiencies, so as to achieve the minimum production cost of distilled water. Such a development would make the process comparable with reverse osmosis and mechanical vapor compression desalination system. The system performance is expressed in the form of thermal performance ratio. For similar systems employing conventional steady-state ejectors, thermal performance ratios as high as 2 has been achieved for low compression ratio and low boiling temperature but at a price of high pressure primary steam. This paper reveals that the application of pressure exchange device can achieve even greater performance ratios for lower primary pressure and temperatures, contributing to a significant decrease in production cost. The model is designed for 5m3 /day capacity, with an aim of achieving highest possible thermal efficiency. The system is analyzed by varying the critical operating parameters, like compression ratio, top brine temperature, primary pressure and ejector efficiency. The results show that with increase in primary pressure, the required primary temperature goes down. Also the application of pressure exchange device results in a phenomenal 3 fold rise in thermal performance ratio, as compared to conventional ejectors. The results achieved from the simulations are quite encouraging and promising for the future development of more efficient and compact device called the supersonic pressure exchange ejector.Copyright

Pressure Exchange Heat Pump: Natural Gas Residential Air Conditioning

There is a strong societal need for a thermally-based air conditioning system which can provide cooling in the summer to small homes and businesses. There is currently no technology available today that can fill this vast market in a cost-effective manner. This paper discusses a potentially important technology which has the potential of contributing to this need, as well as helping to reduce carbon emissions. The paper discusses this technology, it potential, and describes some of the preliminary computational work that will lead to its ultimate development.Copyright

Effect of Fluid Dynamic Parameters on the Performance of a Radial Flow Pressure Exchange Ejector

The “Pressure exchange” is a novel concept in turbomachinery whereby two fluids, at different energy levels, come in direct contact with each other to transfer energy and momentum between them through non-steady interface pressure forces. The rotating jets of the high pressure primary fluid, often referred to as pseudoblades, resemble solid blades on the impeller of a conventional turbomachine. The low pressure secondary fluid, ahead of the pseudoblades, is pressurized by the action of interface pressure forces.The current paper seeks to provide an insight into the complex flow phenomena occurring inside the radial flow pressure exchange ejector. This research presents the results of the first successful numerical simulation to explore the effects of primary to secondary total pressure ratio and primary to secondary total temperature ratio on the performance of a radial flow pressure exchange ejector.Copyright

Two-Dimensional Discontinous Galerkin Simulations of Crypto-Steady Supersonic Pressure Exchange

This paper reports the development of a third-order discontinuous Galerkin (DG) method for supersonic inviscid flow on a moving grid, as well as simulations of a simple model of crypto-steady supersonic pressure exchange (CSSPE) by solving 2D inviscid Euler equations. A total variation bounded (TVB) limiter is implemented for shock capturing. The third-order DG method is firstly validated using a case of supersonic vortex flow. Subsequently, the method is successfully employed to predict the crypto-steady supersonic flat-plate flow under various pressure ratios. In particular, at high pressure ratios between primary gas and secondary gas, a detached shock away from the trailing edge of the flat plate is accurately predicted. This study is our first step in approaching to developing a 3D numerical tool and modeling a novel pressure-exchange ejector.Copyright

Effect of Geometric Parameters on the Performance of a Radial Flow Pressure Exchange Ejector

The “Pressure exchange” is a novel concept in turbomachinery whereby two fluids, at different energy levels, come in direct contact with each other to transfer energy and momentum between them through non-steady interface pressure forces. The rotating jets of the high pressure primary fluid, often referred to as pseudoblades, resemble solid blades on the impeller of a conventional turbomachine. The low pressure secondary fluid, ahead of the pseudoblades, is pressurized by the action of interface pressure forces. The current paper seeks to provide an insight into the complex flow phenomena occurring inside the radial flow pressure exchange ejector. This research presents the results of the first successful numerical simulation to explore the effects of spin angle, rotor cone angle and number of nozzles on the performance of a radial flow pressure exchange ejector. If this new concept is shown to be viable for gas compression at sufficiently high pressure ratios, then, in refrigeration applications, it would enable environmentally benign refrigerants to replace the harmful chlorofluorocarbons (CFC) and reduce the effluence of greenhouse gases. Applications in many other areas, where conventional ejectors are currently used, are also possible.Copyright

Energy Analysis of Single Effect Thermal Vapor Compression Desalination Process Based on Pressure Exchange Phenomenon

A closed loop single effect thermal vapor compression desalination process is simulated based on pressure exchange phenomenon. Here the conventional ejector is replaced by a compressor-turbine device, where the high energy primary fluid expands over the turbine that drives the compressor through an ideal drive shaft. The compressor in turn compresses the low energy secondary fluid. Both the fluids are discharged at a constant pressure in a common mixing chamber where they undergo adiabatic mixing and then are discharged at an intermediate energy level. The functionality of the compressor-turbine device is similar to that of an ejector, hence this is also known as the turbomachinery analog of an ejector. The medium of energy transfer between the two fluids in case of compressor-expander device is pressure exchange. Energy analysis of the model is performed under various operating conditions. Key functional parameter like the boiling temperature, compression ratio, compressor-expander efficiencies and primary pressure are varied and its effect on the energy consumption per unit of distillate produced is examined. The system performance is evaluated based on the standard factors that affect the cost of the distillate like, thermal performance ratio, energy performance ratio and specific flow rate of cooling water. The model takes into consideration the inlet seawater conditions and its fouling effects as well as the use of superheated primary steam and its effects on performance of the system. With increase in the analog efficiency the energy consumption and thermal performance ratio improves steadily, where as it is observed that the flow rate of the distillate produced decreases. Initial results have shown performance ratios as high as 5.5 for ideal conditions at low primary pressures and low boiling temperature.Copyright