Statement of Dr. Gregory W. Swift Physics Division Los Alamos National Laboratory

Transcription

1 Statement of Dr. Gregory W. Swift Physics Division Los Alamos National Laboratory before Ad Hoc Subcommittee on Consumer and Environmental Affairs Senate Committee on Governmental Affairs United States Senate Washington DC May 15, 1992 INTRODUCTION Thank you for the opportunity to testify on this important topic today. As recently as 10 years ago, only a few experts appreciated the potentially disastrous consequences of stratospheric ozone depletion by manufactured chemicals such as chlorofluorocarbons (CFCs). But today, it is widely believed that such chemicals are destroying stratospheric ozone, which shields the earth from the sun s ultraviolet radiation, and that the resulting increased ultraviolet radiation will soon lead to unacceptable numbers of cataracts, fatal and nonfatal skin cancers, other dangers to human health, and potentially severe dangers to agriculture and ecosystems. To prevent these serious effects, the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer and its 1990 revision have committed the United States and most other nations to a 50 per cent reduction in CFC production by 1995 and to 1

2 complete elimination by the year CFCs, previously believed to be completely safe, have until now been used extensively as refrigerants in refrigerators and air conditioners, as solvents in electronics and sheet metal fabrication, and as foaming agents in foam insulation and cushions. Of these three common uses of CFCs, the use as a refrigerant in refrigerators and air conditioners appears to be the most difficult to eliminate, in part because CFC-based cooling systems are the most efficient on the market. Cooling systems use a significant amount of electric power: about 20 per cent of the nation s electricity, at a cost of tens of billions of dollars per year. Kitchen refrigerators alone use 8 per cent of the nation s electricity. lost of that electricity is produced by burning fossil fuels. Clearly, cooling-system efficiency has major economic and environmental impacts. Recognizing this, Congress is requiring ever more efficient cooling equipment; for example, 1993 kitchen refrigerators must use 30 per cent less electricity than 1990 models, and additional improvements will be required in subsequent years. Thus, the appliance industry and other cooling industries are facing the double challenge of eliminating CFCs and simultaneously improving energy efficiency. These challenges will force this industry to make tremendous changes and to work out many difficult problems, ranging from choice of technology through production-line retooling to product-liability concerns. CFC elimination and efficiency improvement should not proceed without simultaneous attention to cost, reliability, safety, compactness, and other such issues of practicality. I can address only a small part of this challenge. I have firsthand knowledge of three new cooling technologies--sonic compression, thermoacoustic refrigeration, and Malone refrigeration--which have been developed in part at Los Alamos National Laboratory. I will discuss the principles, features, and status of each. With these three examples I hope to establish that potentially practical cooling methods exist other than mechanical compression and subsequent evaporation of CFCs. I believe that enough new cooling technologies exist and that the probability for success of each technology is high enough to enable both the elimination of CFCs and the reduction of 2

3 electricity consumption, without prohibitively high production costs. THE SONIC COMPRESSOR In conventional small refrigeration systems such as kitchen refrigerators, the CFC refrigerant vapor is compressed mechanically, usually by a reciprocating piston, whose motion pulls the CFC vapor into a cylinder through a one-way valve at low pressure and then pushes the CFC vapor out through another one-way valve at high pressure. The piston and associated crankshaft parts are lubricated with oil to reduce friction and promote long compressor life. Because the oil is in constant contact with the refrigerant vapor, a high degree of chemical compatibility between oil and refrigerant is required. In addition, compressor losses consume a large fraction of the electric power supplied to small refrigeration systems. A new small-compressor technology, called the Sonic Compressor, has shown the potential to compress refrigerant vapors with greater efficiency, comparable to that of much larger conventional compressors. The Sonic Compressor has no piston or crankshaft to produce friction; it uses a resonant sound wave and a pair of one-way valves to compress the refrigerant. The Sonic Compressor is powered by an acoustic driver, which converts electrical power into acoustic power. The principle is similar to that which operates in a bass (low- frequency) loudspeaker. As in a loudspeaker, the flexible perimeter around the acoustic driver permits motion of the driver without any sliding seal, which would require lubrication. The Sonic Compressor is fairly well developed and has several appealing features. Because it has no parts that produce friction, the Sonic Compressor requires no lubricating oil. This characteristic provides compatibility with all CFC replacements, such as HFC-134a. It should also be extremely efficient: The developer of the Sonic Compressor projects a 30 to 40 per cent reduction in annual electricity consumption compared with the electricity consumption of a standard 1990 kitchen refrigerator. In other words, it should be possible to meet 1993 efficiency standards by using a 1990 refrigerator with a Sonic Compressor and a non-cfc refrigerant, with no other 3

4 modifications. As a drop-in replacement for current compressors, the Sonic Compressor will require little or no retooling by refrigerator manufacturers: cabinets, heat exchangers, piping, and control circuits need not change. The projected manufacturing cost of the Sonic Compressor is low, roughly comparable to that of conventional small compressors. Tim Lucas of Sonic Compressor Systems, Inc., invented the Sonic Compressor, and afterwards came to Los Alamos for help in designing and building acoustic resonators that suppress acoustic shock-wave formation at the high pressure differences required for refrigeration. Sonic Compressor Systems is now completing development of this new compressor technology and plans to test its product in standard home refrigerators within one year. Large-scale production could begin within two years because of the Sonic Compressor s inherent simplicity and compatibility with other components of refrigeration systems. A U.S. refrigerator manufacturer has offered to participate in a joint program with Sonic Compressor Systems to adapt the Sonic Compressor to existing refrigerators. Other applications of interest include freezers, window air conditioners, dehumidifiers, and other small-scale cooling systems. THERMOACOUSTIC REFRIGERATION In conventional refrigeration systems, the evaporation of the CFC refrigerant produces the cooling. But evaporation is not the only physical effect that produces cooling. Thermoacoustic refrigeration relies on the heating and cooling that accompany the compression and expansion of a gas in a sound wave. Although ordinary, conversational-level sound produces only tiny heating and cooling effects, extremely loud sound waves confined in sealed cavities produce heating and cooling effects large enough to be useful. Thermoacoustic refrigeration works best with inert gases such as helium and argon, which are environmentally harmless, nonflammable, and nontoxic. The most reliable current estimates show that thermoacoustic refrigeration may be efficient enough to meet 1993 appliance efficiency standards. At the 4

5 current rate of progress, a year or two of further work will be required to determine the efficiency of thermoacoustic refrigeration more accurately. Thermoacoustic refrigeration requires no moving parts; it has only one flexing part much like a loudspeaker. Thus, we expect it to be a reliable, long-lived technology. We expect thermoacoustic refrigeration to be inexpensive to manufacture because it requires neither exotic materials nor exacting construction tolerances. However, thermoacoustic refrigeration would require considerable manufacturer retooling because all subsystems such as heat exchangers would be quite different from those of conventional refrigeration systems. Thermoacoustic refrigeration was invented at Los Alamos National Laboratory 10 years ago. Small proof-of-principle thermoacoustic cooling systems have been built at Los Alamos and more recently at the Naval Postgraduate School at Monterey. With mixed government and corporate support, the Naval Postgraduate School is ready to begin practical development of a model suitable for a kitchen refrigerator. MALONE REFRIGERATION Malone refrigeration relies on the cooling that accompanies the expansion of a liquid. Significant cooling accompanies the expansion of some pressurized liquids, without expanding them enough to produce the evaporation that is used for cooling in conventional refrigeration technology. This effect contrasts with the common misconception that liquids behave much like idealized hydraulic fluid and hence are thermodynamically useless. In fact, many liquids are significantly compressible and cool significantly when expanded, and they have other attractive properties such as large heat capacity. Malone refrigerators use such liquids in a closed cycle of expansion and compression, powered by electric-motor-driven pistons. Malone refrigerators can have extremely compact heat exchangers if the refrigerator cools a liquid stream, such as water, and transfers its waste heat to water. Thus, Malone 5

6 refrigeration is naturally suited to large-capacity applications in which water or other liquid streams are already involved for heat transfer. Such applications include air conditioning of large buildings and ground-coupled heat-pumping for residences. Our most reliable current estimates show that Malone refrigeration should be more efficient than large-capacity conventional refrigeration equipment. At the current rate of progress, several years of further work will be required to determine its efficiency accurately. Even if Malone refrigerators are only 10 per cent more efficient than conventional equipment, and if Malone technology is eventually used in half of all cooling applications nationwide, then about 1 per cent of the nation s electricity use will be eliminated, a reduction corresponding to millions of tons of fossil-fuel savings each year. Liquid carbon dioxide and dilute mixtures of methanol or ethanol in liquid carbon dioxide are efficient, safe, and environmentally benign working fluids for Malone refrigeration. The amount of carbon dioxide used has negligible environmental impact compared with the effect of the pounds per capita per day we each exhale; the amount of alcohol also has negligible environmental impact. Malone refrigeration equipment will be more compact, but heavier, than conventional equipment. It may be expensive to manufacture because some dimensional tolerances are critical. Malone refrigeration was. invented at the University of California at San Diego in the 1970s. The only proof-of-principle Malone refrigerator to date was built and studied at Los Alamos National Laboratory in the 1980s. Second prototypes are now under construction with government support at Los Alamos and at the David Taylor Research Center at Annapolis. SUMMARY The preceding examples are only three of many alternative cooling technologies. No new technology can be guaranteed successful before 6

7 development is complete, from either an economic or an engineering point of view. But enough alternative cooling technologies exist, and the probability for success of each technology is high enough, that manufacturers can almost certainly produce one or more of these technologies at reasonable cost, eliminate CFCs, and reduce the consumption of electricity. The Sonic Compressor and other, similarly mature alternatives could easily reach production in less than two years. Thermoacoustic refrigeration, Malone refrigeration, and other immature technologies require only a few million dollars each for development until their suitability for production can be assessed. FOR MORE INFORMATION Sonic Compressor: Tim Lucas, Sonic Compressor Systems, Inc., Glen Allen, VA (804) Thermoacoustic refrigeration: Thermoacoustic Steven L. Garrett and Thomas J. Hofler, Refrigeration, Proceedings of the Second National Technology Transfer Conference and Exposition, 5 December 1991, San Jose, California, and references therein; Gregory W. Swift, Thermoacoustic Engines, Journal of the Acoustical Society of America, Vol. 84, pp (1988)) and references therein. Malone refrigeration: Gregory W. Swift, Malone Refrigeration, ASHRAE Journal, November 1990, pp , and references therein; Gregory W. Swift, A Stirling Engine with a Liquid Working Substance, Journal of Applied Physics, Vol. 65, p , and references therein. 7