1999 Progress Report: A Novel Pressure-Exchange Ejector Refrigeration System with Steam as the RefrigerantEPA Grant Number: R825324
Title: A Novel Pressure-Exchange Ejector Refrigeration System with Steam as the Refrigerant
Investigators: Mavriplis, Catherine , Garris Jr., Charles A.
Institution: George Washington University
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1996 through September 30, 1999
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $175,000
RFA: Technology for a Sustainable Environment (1996) RFA Text | Recipients Lists
Research Category: Economics and Decision Sciences , Sustainability , Pollution Prevention/Sustainable Development
Ejector refrigeration has continued to draw considerable attention due to its potential for low cost, its utilization of low-grade energy for refrigeration, simplicity, versatility in the type of refrigerant, being particularly amenable to the use of water as the refrigerant, and low maintenance due to the absence of moving parts. However, the main disadvantage of ejector refrigeration as it exists today is that it has a relatively low Coefficient of Performance as a result of the irreversible nature of the processes employed in conventional steady-flow ejectors. The Principal Investigator (PI) has invented a novel ejector, which operates on non-steady flow principles that are thermodynamically reversible, and therefore capable of much higher levels of performance.
The purpose of this research program is to study from the experimental, the computational, and the theoretical perspectives the complex non-steady flow processes and induction mechanisms within the pressure-exchange ejector, how they relate to overall ejector performance, and to obtain fundamental design information that would allow this technology to be applied to ejector refrigeration systems. If this new concept in ejector technology based on non-steady flow processes can be shown to be viable, the impact on refrigeration and air conditioning in the commercial, automotive, and residential sectors would be enormous. It also would enable environmentally benign refrigerants such as water to replace harmful CFCs, and reduce the effluence of greenhouse gases by reducing fuel consumption through the use of waste heat and improved efficiency.
First-generation and second-generation radial flow pressure-exchange ejectors, as patented by the PI, were designed, fabricated, and incorporated into a complete test rig. For convenience, air was used as the working fluid. Based on our experience with these test rigs, it was realized that there were several concurrent and often competing design requirements that must be met: (1) the aerodynamic design is critical, and small variations can have large effects on performance; (2) the primary fluid leakage around the periphery of the rotor must be kept to a minimum, necessitating very high machining tolerances; (3) free-spinning conditions are necessary to achieve high efficiency, necessitating very low friction between the rotor and the housing; (4) high rotational speeds are needed because the greater the rotational speed, the greater the work of interface pressure forces; (5) very high axial thrust loading occurs, because on one side of the rotor is the high primary pressure, and on the opposite side is the very low secondary pressure; and (6) precision balancing and avoidance of critical speeds is necessary.
With the first and second generation designs, although aerodynamically excellent, it was found that balancing all of these requirements was extremely challenging. The sealing requirements created friction, which prevented the attainment of free-spinning operation. The high axial thrust was difficult to manage in conjunction with the required high angular velocities causing rapid destruction of bearings and difficulties in providing lubrication.
A truly exciting new concept emerged?the supersonic vane rotor. A considerable amount of effort was expended on the new design and we applied for a second patent. A sectional view of the supersonic rotor-vane pressure-exchange ejector is shown in Figure 1 and a typical rotor is shown in Figure 2. It should be noted that there are no nozzles in the rotor, and consequently, no seals. In operation, a supersonic flow exits from the nozzle and produces an attached weak shock on the apex of the cone. The flow is diverted over the wedge-shaped vanes supersonically, whence an expansion fan is generated at the rear of the vane. This draws the secondary flow into the primary flow interstices behind the vanes, whereby pressure-exchange takes place. Because the flow is supersonic as it passes over the rotor, the pressure level is much lower than in the previous configurations, thereby facilitating the management of thrust loading, and facilitating the use of gas radial and thrust bearings. The design is not sensitive to tolerances. The design has the potential to exploit the advantages of pressure-exchange, while maintaining extreme simplicity and reduced manufacturing costs.
A preliminary test rig was fabricated to roughly evaluate the relative importance of some key parameters. Computational fluid dynamic (CFD) studies are being conducted in parallel with the experimental work to gain further insight into the fundamental nature of the supersonic flow induction process. Preliminary data are encouraging. Nevertheless, optimal gas bearings to provide nearly frictionless rotation are needed. An industrial team agreement has been established with a leader in gas bearing design for turbomachinery, and preliminary meetings have provided assurance that the bearing design requirements can be met. It is expected that once the gas bearings are perfected, optimization of the ejector will proceed rapidly and we will be able to move onto the next phase of the program, which is the study of two-phase operation as appropriate for refrigeration.
Figure 2: Rotor for Supersonic Rotor-Vane Pressure-Exchange Ejector
Journal Articles:No journal articles submitted with this report: View all 18 publications for this project
Supplemental Keywords:We plan to: (1) continue experimental and computational studies of flow induction by pressure exchange in supersonic flow, (2) design and fabricate a pressure-exchange ejector test facility using water as refrigerant, and (3) extend collaborative relations with industry and government agencies such as NIST and the Department of Energy., RFA, Scientific Discipline, Sustainable Industry/Business, cleaner production/pollution prevention, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, Environmental Engineering, in-process changes, refrigeration, cleaner production, waste minimization, waste reduction, hazardous emissions, novel refrigeration cycles, alternative materials, ozone depleting chemicals, process modification, innovative technology, alternative refrigerants, industrial innovations, pollution prevention, source reduction