Binary Fluid Ejector

Binary Fluid Ejector

  • A BFE is a thermally-driven fluidic compressor that replaces the electro-mechanical compressor in reverse-Rankine thermal cycles (refrigeration cycles).
  • A BFE system essentially acts as a highly-efficient heat pump, and results in energy and economic savings.
  • BFE units can be driven by many types of low-grade thermal energy, including: solar thermal, geothermal, waste heat, stack flue gas, engine exhaust, biogas, biomass or natural gas and other fossil fuels.
  • BFE is a cross-cutting technology, applicable to a broad swath of applications in many economic sectors, including: air conditioning, space heating, water heating, refrigeration, industrial-scale desiccation, distillation and desalination, waste heat recovery and re-use, etc.

Background
Innovation
Benefits
Project Development
In Summary

Background
No high-performance, thermally driven heat pump or refrigeration cycle currently exists, though such a device would play a critical role in unlocking the wide spread use of renewable energy such as waste heat, solar thermal, and geothermal. Even in the absence of renewable energy, such a device would enable fuel switching from electricity to natural gas, which would save 65 to 75% on energy costs, reduce GHG production, and relieve the power grid during peak times. The Binary Fluid Ejector (BFE) has the potential to fill this important technology gap. Because refrigeration type thermal dynamic cycles cut across all sectors of the economy, the BFE is a platform technology with the potential for transformational impact on global energy use and the global water supply.

BFE is designed to replace the mechanical compressor used in traditional refrigeration systems. These thermal cycles consume billions of kWh of electric energy and produce hundreds of millions of metric tonnes of atmospheric carbon each year in North America. These traditional systems include space cooling (air conditioning), heat pumps (space heating), refrigerators (food storage, water chillers, etc.). Additionally, vapor recompression type thermal cycles are used for such important applications as distillation, desalination, and desiccation/drying systems.

Innovation
The critical measure for energy efficiency for any refrigeration cycle or thermal cycles employing refrigeration is overall Coefficient of Performance (COP), defined as the work done over the energy consumed doing that work. For a reverse Rankine thermal cycle, for which the BFE qualifies, this translates into the energy efficiency of compression and expansion; BFE technology addresses the energy and cost efficiency of compression.
MRT’s Binary Fluid Ejector technology represents a new class of ejector that is self-consistent for binary fluid functionality. This means that the ejector does not simply employ a binary fluid, but rather, it is specifically designed for binary fluid operation; this design approach represents novel art. Unlike traditional ejectors that employ a single fluid, the use of a binary fluid allows for one fluid to optimize ejector efficiency, while the other optimizes refrigeration efficiency.

BFE has the potential for high operating COP for two primary reasons: 1) superior mass entrainment ratio; and 2) a superior capacity to exploit the differential enthalpy between the two working fluids. (The term “differential enthalpy” refers to the change in equilibria enthalpy between condenser/boiler conditions for the drive fluid, versus condenser/evaporator conditions for the refrigerant fluid.)

Mass entrainment ratio is the mass flow rate of the secondary fluid over the mass flow rate of the primary fluid, an indication of entrainment performance. Low mass entrainment ratio for traditional ejectors is a result of employing shear turbulence as a method of secondary fluid entrainment. This entrainment method is plagued by irreversible thermodynamic energy transforms that result in significant system entropy gain. The BFE employs a unique method termed Braiding Entrainment that exploits a type of direct energy transfer known as pressure exchange. In an ideal model, pressure exchange is an intrinsically reversible process. When applied properly in the real world, Braiding Entrainment via pressure energy exchange is far more energy efficient than shear turbulent entrainment, presenting significantly less irreversible energy transforms. Braiding Entrainment involves spatial bilateral oscillation of the primary jet, accomplished by means of an unsteady state fluidic oscillator, the performance of which is realized in the frequency domain. Unlike all prior art, the cross sectional shape of the body and the primary jet are rectangular instead of round. This coupled with secondary mass entrainment accomplished in the frequency domain represents an innovative and unique fluid compression technology, novel to all prior art. A detailed description of primary jet flow mechanics is available upon request.

Mass entrainment ratio is also influenced by the molecular mass of the working fluids. In the case of traditional single fluid ejectors, the ratio of molecular mass is always 1. Although there is an extremum involved in the transfer function, generally, a drive fluid with a higher molecular mass than the refrigerant fluid will result in a higher mass entrainment ratio and superior COP. MRT has identified a base-case binary fluid consisting of water as the refrigerant and HFE-7500, a 3M product, as the drive fluid. For this combination, the differential molecular mass (414:18 g/mol) would significantly increase the mass entrainment ratio of the BFE over that of two fluids having the same molecular mass equilibrated in a standard ejector.
Another significant advantage of Binary Fluid Ejector compression technology is differential enthalpy. This refers to the change in equilibria enthalpy between condenser/boiler conditions for the drive fluid, versus condenser/evaporator conditions for the refrigerant. Again, for traditional ejectors employing a single fluid, this ratio is always 1. By contrast, the BFE is specifically designed to equilibrate two chemically distinct fluids, and therefore can exploit this ratio as leverage for increasing COP. For the base case binary fluid cited above, the ratio of the differential equilibria enthalpy is 2,362/217 kJ/kg = 10.88. The BFE is superior to all prior art because of its capacity to exploit one fluid optimized as a driver having low phase change enthalpy and high molecular mass, and another fluid optimized as a refrigerant having high phase change enthalpy and low molecular mass.

Benefits
By no measure does BFE technology represent an incremental improvement over existing and emerging refrigeration cycles; because the BFE thermal cycle can be adapted to many applications, it represents a platform technology with the potential for transformational impact on global energy security and economies over a broad range of energy consuming sectors.
The BFE's low operating and capital costs could transform the economics for many applications using renewable energy. BFE can be driven by many forms of low grade thermal energy: waste heat, stack flue gas heat, solar thermal, geothermal, or biogas. When renewable energy is not available or intermittent (such as solar), natural gas (NG) or other fossil fuels may be combusted. Fuel choice can depend on emissions targets, price, or availability.

Although the fractionating condenser will be more expensive, the ejector itself is far less expensive than a conventional electromechanical compressor, equalizing or lowering BFE capital costs. A BFE should have much lower operational and maintenance costs, due to their solid state design, fuel options and energy efficiency. Heat exchangers represent additional capital cost for renewable BFE installations, but payback periods are shortened when the cost of the collector can be amortized over several functions. BFE can provide refrigeration, a/c, and hot water heating simultaneously or individually from the same collector. Expected payback periods should be acceptable to consumers.

A BFC should have higher energy performance than other thermally-driven technologies, resulting in smaller heat exchangers or collectors, and lower incremental capital costs for renewable installations. Due to their COP, NG-driven BFE units will show GHG reductions over similar electrical and natural gas driven appliances. Take air conditioning systems as an example. BFE is predicted to be far more efficient, and should save money on operating costs.


Project Development
MRT has conducted an extensive research effort collecting international patents, patent applications (where available), conference papers, published research papers, university studies, Masters’ and Ph.D. level dissertations, association proceedings, and commercial literature. We know of no prior art, commercial product, or emerging system that is remotely similar to Binary Fluid Ejector technology. US and PCT patents applications have been filed, and patent is pending.

A preliminary binary fluid assay has been completed, to identify promising candidate binary fluid components according to a Figure of Merit analytical tool developed for this task. A small number of candidate binary fluid pairs have been identified, such as HFE-7500 and water, which combine high thermal performance with high environmental performance (i.e. low global warming potential, atmospheric life, toxicity, etc.).
The next research steps are to expand the analytical model and binary fluid assay, conduct in-depth three-dimensional computational fluid dynamic modeling predictive of BFE performance under various operating conditions, and prototype construction and testing to verify BFE performance and validate model accuracy.

MRT has been awarded $569,000 from Alberta’s Climate Change and Emissions Management Council, towards development of BFE technology. (See the News Bulletin describing the award.) This project was submitted with partners 3M Canada, ENMAX and Worley Parsons, with support from Shell Canada and Electrotherm. Research partners include Dr. Saffa Riffatt from the University of Nottingham, as well as other scientific experts in the field such as Dr. Richard Powell (father of R-134a), Dr. D. Buyadgie (lead binary fluid researcher at Odessa State Academy of Refrigeration), and Dr. Garris (Department head of Aeronautical Engineering, Gorge Washington University, world expert in pressure energy exchange).

Currently, MRT has formed a new company, May-Ruben Thermal Solutions, Inc. ("MRTS") to develop and commercialize the BFE technology. MRTS has retained a staff of highly qualified PhD’s in Mechanical and Chemical engineering to design and construct a bench top prototype. This initial prototype will be designed as a distillation unit. Distillation, desalination, and desiccation are considered important opportunities that are well matched to an ejector driven refrigeration cycle. It is scheduled to be completed by the fall of 2013. MRTS is pleased to be working with the University of Calgary in this endeavour.

MRT has had positive feedback from many corporations interested in BFE technology. They are interested in acting as hosts for BFE demonstration projects, and/or furthering BFE commercialization, if the results of BFE prototype testing confirm predicted levels of performance.

In Summary
The Binary Fluid Ejector (BFE) is a high-performance, thermally-driven heat pump that can increase adoption of renewable energy like waste heat, solar thermal, geothermal, and biogas, and enable fuel switching from electricity to natural gas; reducing energy costs, GHG emissions, and peak demand on power grids. BFE applications cut across economic sectors, including air conditioning, space heating, water heating, refrigeration, and industrial scale distillation, desalination, and desiccation/drying. It can also upgrade marginal waste or geothermal heat streams to temperatures more useful to industrial processes, or for Organic Rankine Cycle electricity generation. BFE could have a transformational impact on global energy use and water supplies.