Malone Refrigeration An Old Solution to a New Problem Gregory W. Swift he refrigeration and air- Tconditioning industries are in crisis due to the discovery that chlorofluorocarbons (CFCs), the working fluid in virtually all cooling equipment, cause unacceptable environ- mental damage. A few of us in the Laboratory’s Condensed Matter and Thermal Physics Group are trying to help resolve the crisis by developing a new Malone’s first liquid-based heat engine, 1925 112 Los Alamos Science Number 21 1993 Malone Refrigeration/CFCs and Cooling Equipment CFCs and Cooling Equipment: The Size of the Problem s recently as ten years ago, dollars per year. Kitchen refrigera- their chlorine to the stratosphere, Aonly a few experts appreciated tors alone use 8 percent of the na- and hydrofluorocarbons, which the potentially disastrous conse- tion’s electricity. Most of that contain no chlorine at all. One quences of releasing chlorofluoro- electricity is produced by burning German manufacturer is using or- carbons (CFCs) into the environ- fossil fuels. Congress is accord- dinary hydrocarbons (a mixture of ment. Today it is generally be- ingly requiring ever more efficient propane and butane) as working lieved that chlorine from CFCs is cooling equipment; for example, fluids, recognizing that their flam- destroying stratospheric ozone, kitchen refrigerators built in 1993 mability poses negligible danger which shields the earth from the must use 30 percent less electricity since only small quantities are sun’s ultraviolet radiation, and that than those built in 1990. Clearly used. the resulting increased ultraviolet the elimination of CFCs should not But these new chemicals have radiation will soon lead to millions involve making refrigerators that disadvantages. They are less com- of fatal and nonfatal skin cancers are much less efficient than present patible with lubricants than are and cataracts, to other threats to models. Therefore the use of CFCs CFCs, so they may cause present human health, and to severe dam- in cooling is the most difficult of compressors to wear out more age to agriculture and ecosystems. their common uses to eliminate. quickly. HCFCs and HFCs also To mitigate those effects, the Unit- The cooling industry is enor- significantly reduce the efficiency ed States and most other countries mous. Cooling equipment worth of cooling machinery. They are have committed themselves, $40 billion is sold in the United also greenhouse gases, with rough- through the 1987 Montreal Proto- States each year, and, since it has a ly 1000 times the global-warming col on Substances That Deplete the long useful lifetime, the total value potential of carbon dioxide per Ozone Layer and its later revi- of installed equipment is about molecule, so their use will proba- sions, to rapid elimination of CFC $200 billion. Thus the appliance bly eventually be limited by inter- production. industry and other cooling-equip- national agreements. Finally, as The rate of CFC production, ment manufacturers face a daunt- they do not occur in nature, their though being reduced, is on the ing challenge. The prospects of release into the environment in order of a million tons per year. millions of fatal cancers, tens of million-ton quantities, like the re- CFCs are used extensively as millions of cataracts, and contin- lease of CFCs, will be an experi- working fluids in refrigerators and ued enormous energy consumption ment in atmospheric chemistry air conditioners, as cleaning sol- and attendant greenhouse-gas emis- with unpredictable consequences. vents in electronics and sheet- sions have led to government regu- Completely different cooling metal fabrication, and as foaming lations that are driving a $40-bil- technologies that don’t use any of agents in foam insulation and cush- lion-per-year industry to an un- these chemicals are still needed. ions. CFCs have the advantage for precedented crisis. The situation Many are being developed, includ- many purposes of being almost dwarfs the problems of the DOE’s ing Rankine cycles using CO2, chemically inert (their behavior in nuclear-weapons complex, a mere Stirling cycles using helium, and the upper atmosphere is an excep- $12-billion-per-year industry re- cooling by the Peltier (thermoelec- tion); in particular they present no sponsible for less environmental tric) effect. Almost by accident fire or poison danger. In addition and human-health damage. three new cooling technologies— their lack of interaction with the Stopgap solutions to the CFC thermoacoustic refrigeration, the lubricants used in refrigerator com- crisis are required immediately and related Sonic Sompressor, and pressors improves the efficiency are, in fact, in progress. Industry Malone refrigeration—have been and the lifetime of the refrigerator. has begun extensive recycling of developed in part here at the Labo- Cooling-system efficiency has CFCs, especially in air-conditioner ratory; each may become part of major economic and environmental repair. Some new appliances will intermediate or long-term solutions impacts. Cooling consumes about soon use hydrochlorofluorocar- to the CFC problem. They are 20 percent of the nation’s electrici- bons, which tend to break down described in the accompanying ty, at a cost of tens of billions of and then rain out before carrying articles. 1993 Number 21 Los Alamos Science 113 Malone Refrigeration type of cooling machinery. Its de- the mature descendants of those small thermal-expansion coefficients sign takes advantage of modern fab- nineteenth-century inventions, work (part of a larger misconception that rication techniques and environmen- unobtrusively and reliably—but not liquids resemble idealized hydraulic tally benign materials but is inspired so well that further improvement is fluid) and therefore do not couple by a turn-of-the-century invention. impossible. heat to work well enough for use in Refrigerators and air conditioners In the 1970s, John Wheatley, then engines and heat pumps. In heat are based on heat pumps, machines a physics professor at the University pumps, working fluids must cool as that exploit mechanical power to of California, San Diego, and at the the fluid is depressurized in order to pump heat from low temperature to height of a distinguished career of absorb heat from the area to be high temperature. They operate by academic research into the proper- cooled; in engines, working fluids taking a working fluid through cy- ties of liquid helium, became inter- must expand on heating in order to cles of temperature and pressure ested in improving the efficiency of do work. The cooling on depressur- changes in which the working fluid such ubiquitous heat-engine machin- ization and thermal expansion of a absorbs heat at low temperature ery. But there was trouble at UCSD. material are both proportional to one (from the air inside the refrigerator, Some faculty thought that the work thermodynamic property: its ther- say) and loses (“rejects”) heat at the was “not really physics,” and mal-expansion coefficient. The higher temperature in the room. Wheatley shared their concern that thermal-expansion coefficients of Figure 1 shows an example of such heat-engine research would not pre- gases are large, those of liquid-gas a thermodynamic cycle, the Rankine pare graduate students for a tradi- mixtures at the boiling point are es- cycle used in all present household tional career in academia. Further- sentially infinite (a fact that ex- refrigerators, in which the cooling more, the research required more plains why evaporation and conden- (absorption of heat at low tempera- sophisticated fabrication techniques sation are so useful in the Rankine ture) is produced by the evaporation than were available at universities. cycle), but those of liquids are usu- of the CFC working fluid. Revers- So (with much encouragement from ally small. However, as Figure 2 il- ing the cycle of a heat pump makes Jay Keyworth, then leader of the lustrates, near their critical points a heat engine, which converts heat Laboratory’s Physics Division) liquids do have large thermal-expan- to mechanical power as heat flows Wheatley moved to Los Alamos in sion coefficients, larger in fact than from high temperature to low. For early 1981 and assembled a team that of an ideal gas. (The critical example, the steam turbines that that included Al Migliori, Tom point is the temperature, Tcritical, drive electric generators in large Hofler, Heikki Collan, and me, to and pressure, Pcritical, above which power plants use the reverse of the begin fundamental investigations of the liquid and gas phases of a sub- Rankine cycle shown in Figure 1. old and new concepts in the fields of stance are indistinguishable.) Water is the working fluid; its ex- refrigeration and power generation. Hence liquids can indeed serve as pansion on evaporation drives the One of our research areas is de- working fluids in engines and refrig- turbines. scribed in “Thermoacoustic Engines erators. Heat pumps and engines are and Refrigerators.” Liquids also have advantages among the wonderful machines de- This article discusses another area over gases as working fluids. For veloped during the nineteenth centu- of our investigations: refrigerators instance, as shown in Figure 3, liq- ry, when pistons, crankshafts, fly- and heat engines that use liquids, uids are far less compressible than wheels, and automatically timed without change of phase to gas, as gases; that is, a given volume valves began to replace the labor of the working fluid. We called such change causes a larger pressure horses, oxen, and people. Engines devices Malone refrigerators and en- change in a liquid than in a gas. removed water from mines and later gines after the first engineer to build Large pressure changes are desirable propelled ships and trains. Refriger- such machines (see “John Malone because the heat transferred in the ators preserved beef on the two- and the Invention of Liquid-Based heat exchangers is proportional to month voyage from Argentina or Engines”).