Patent Application
20050274130
This invention relates to refrigeration systems.
Conventional refrigeration systems employ the compression technology of chlorofluorocarbon (CFC), hydrofluorocarbon (HFC), hydrochlorofluorocarbon (HCFC), and ammonia (NH3) refrigerants. Gaseous refrigerants are compressed to the liquid state through heat exchanges with the environment. Evaporations of liquefied CFC or NH3 refrigerants provide the cooling mechanism. Because the heat of vaporization of NH3 is larger than those of CFCs, and that NH3 is easily compressible to a condensed phase, NH3 compression refrigeration systems are widely utilized in various manufacturing industries and in large storage facilities. On the other hand, the corrosive characteristics of NH3 require that special operational precautions to be imposed. Thus, domestic refrigerators and air-conditioners (including motor vehicle ACs) invariably utilize the compression technology of CFC refrigerants. The formidable issues of ozone depletion and the greenhouse effect caused by CFC and HCFC refrigerants demand a new refrigeration technology.
In the prior art, water is not used as the refrigerant for a compression cycle refrigerating system. A. D. Althouse, C. H. Turnquist, A. F. Bracciano, “Modern Refrigeration and Air Conditioning,” The Goodheart-Willcox Co., South Holland, Ill., 1988, p. 295. However, water is the refrigerant for steam jet refrigeration used in connection with air conditioning systems. Id. A steam jet refrigeration chiller employs the momentum of steam to pump away gaseous water molecules. Thus, evaporation of water in the chill tank under reduced pressure cools down the water reservoir in the chill tank. This is an inefficient method that relies on an inexpensive supply of high pressure steam and can only cool the water reservoir to about 4° C.
In the prior art, such as U.S. Pat. Nos. 2,159,251, 2,386,554, 4,866,947, 5,046,321, and 6,672,091, atomizers have been used instead of the expansion valve in conventional compression cycle refrigerating systems to improve the evaporation rate of the refrigerant.
Thus, what is needed is a refrigerant system that (1) employs a refrigerant that is environmental-friendly, chemically non-corrosive, non-flammable, and physiologically harmless, and (2) provides the same or better performance while consuming the same or less energy as conventional technologies.
Use of the same reference numbers in different figures indicates similar or identical elements.
In one embodiment of the invention, a system for controlling temperature includes an atomizer that forms micron-sized hydrogen-bonded refrigerant droplets within a chamber. A vacuum pump is coupled to the chamber to lower its interior pressure. Under these conditions, the refrigerant droplets evaporate while lowering the temperature of its immediate surrounding. In one embodiment, the atomizer includes a pump that forces a hydrogen-bonded liquid refrigerant through a nozzle.
In one embodiment, a method for controlling temperature includes lower the pressure within a chamber and generating micron-sized hydrogen-bonded refrigerant droplets within the chamber. Under these conditions, the refrigerant droplets evaporate while lowering the temperature of its immediate surrounding. In one embodiment, the refrigerant droplets are generated by pumping a hydrogen-bonded liquid refrigerant through a nozzle.
A liquid jet refrigeration system utilizes the atomization of hydrogen-bonded liquid refrigerants to meet environmental needs, occupational safety standards, and fast cooling rates. The evaporation efficiencies of environmental-friendly hydrogen-bonded liquid refrigerants are greatly enhanced by atomizing them into streams of micron-sized refrigerant droplets. In addition to the advantage of the large heats of vaporization of hydrogen-bonded liquid refrigerants, these gaseous refrigerants are easily condensed under compression. Energy consumptions of the liquid jet refrigeration system are more efficient in comparison with those of conventional technologies.
After 1950, refrigerants that are liquids at room temperatures (25° C.) and 1 atmosphere have never been considered for refrigeration systems using compression technologies. However, there are many hydrogen-bonded liquids that are environmental-friendly, chemically non-corrosive, non-flammable, and physiologically harmless (e.g., alcohol/water mixtures, such as ethyl alcohol (C2H5OH)). Above all, they exhibit heats of vaporization larger than those of NH3 (ΔH0vap=40.6 kJ/mole, 43.5 kJ/mole, and 23.35 kJ/mole for water, ethyl alcohol, and ammonia, respectively).
According to their phase diagrams and thermodynamic properties, these liquid refrigerants evaporate spontaneously under reduced pressure. Meanwhile, the evaporated molecules that escape from the surface carry away the internal energy of the liquid (heats of vaporization). Thus, the evaporation of the liquefied refrigerant, e.g., at 25° C. initially, cools the remaining liquid into a state of lower temperature under reduced pressure. This refrigeration mechanism can be maintained in principle as long as a good vacuum environment (better than 10−2 mbar) is created above the liquid surface.
In practice, the rate of evaporation is not controlled thermodynamically but kinetically. According to the kinetic theory of gases, the rate of evaporation dN/dt is given by:
where ΔP is the pressure difference between the equilibrium vapor pressure of the liquid at temperature T and the gaseous pressure of the environment, NA is the Avogadro number, M is the molecular weight, R is the gas constant, and A is the surface area of the liquid phase. When a 1 cm3 liquid droplet is dispersed into 1 μm micro-spheres, the surface area is increased by four orders of magnitude (104). Consequently, the rate of cooling is substantially enhanced by atomizing the liquid into micron-sized droplets (i.e., dispersing a liquid into mist).
There are many techniques to atomize liquids into micron-sized droplets, including (1). liquid jet atomization by pumping a liquid through micron-sized pinholes, (2) ultrasonic atomization, (3) piezoelectric atomization, and (4) DC-discharge atomization. Presently, experiments demonstrate that liquid jet atomization serves the refrigeration purpose quite well. For example, a refrigeration chamber can be cooled from 21° C. to −20° C. around 6 minutes. The cooling mechanism is provided by the evaporation of micron-sized refrigerant droplets under reduced pressure. The micron-sized refrigerant droplets are created by pumping the liquid refrigerant through a nozzle having an array of micron-sized pinholes.
From liquid refrigerant 17 in reservoir 12, an atomizer 13 generates micron-sized refrigerant droplets 20. In one embodiment, atomizer 13 includes a liquid pump 14 and a nozzle 16. Liquid pump 14 forces liquid refrigerant 17 through nozzle 16 to inject micron-sized refrigerant droplets 20 into a low-pressure chamber 18 (e.g., a heat exchanger). In one embodiment, liquid pump 14 (e.g., a NP-CX-100 from Nihon Seimitsu Kagaku of Tokyo, Japan) delivers a flow rate of 80 ml/min at a pressure of 30 bar.
In one embodiment, pinholes 58 have a diameter of 80 μm and generate refrigerant droplets 20 having a diameter of approximately 10 μm. In this embodiment, nozzle plate 56 is a stainless steel plate having a diameter of 13 mm and a thickness of 1 mm. In this embodiment, six or more pinholes 58 are laser-drilled into nozzle plate 56 (e.g., by a COMPEX 200 and SCANMATE 2E laser system made by Lambda Physik of Göttingen, Germany).
Nozzle 16 may include a heater 60 (e.g., an electric heater or a water heater that circulates room temperature water around the nozzle) to prevent liquid refrigerant 17 from clogging nozzle 16 when it freezes. Parameters such as the flow rate, the applied pressure, the number of pinholes in the nozzle array, and the pinhole size may be modified to generate the micron-sized refrigerant droplets of the appropriate size.
Referring back to
In one embodiment, system 10 is an open loop refrigeration system because liquid refrigerant, like water, can be safely expelled into the environment. In this embodiment, vacuum pump/compressor 22 simply expels the gaseous refrigerant into the atmosphere. In this embodiment, reservoir 12 can be replaced by a water supply line (e.g., a city supplied water line to a home or a business).
In one embodiment, system 10 is a closed cycle refrigeration system because liquid refrigerant 17 cannot be safely expelled into the environment. In this embodiment, vacuum pump/compressor 22 compresses the gaseous refrigerant into an atmospheric pressure chamber 26 (e.g., another heat exchanger).
Referring back to
For a fast cooling rate and an ultimate low temperature, methanol/water or ethanol/water refrigerant may be used in system 10. For an environmentally friendly, chemically non-corrosive, non-flammable, and physiologically harmless refrigerant, pure water or ethanol/water refrigerant may be used in system 10. Thus, water systems can find their roles in the market of domestic appliances, while pure ethanol, ethanol/water, and methanol/water refrigeration systems can be employed in manufacturing industries and in large storage facilities.
Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention. For example, hydrogen-bonded liquid refrigerants are not limited to the specific chemical compounds mentioned above. The material, the fabrication method, and the characteristics of the nozzle are not limited to those mentioned above. Liquid atomization by other well-known techniques, such as ultrasonic, piezoelectric, and electric discharge methods, can be used in place of the pump and the nozzle. Numerous embodiments are encompassed by the following claims.
