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Ionocaloric Refrigeration
February 27, 2023
The baseline
standard of living has vastly increased from the
mid-20th century to the present day. In the 1955-1956
television sitcom,
the honeymooners, the principal
characters, Ralph Kramden (played by
Jackie Gleason, 1916-1987) and his wife Alice (played by
Audrey Meadows, 1922-1996) lived in a
spare two room
apartment with no
telephone and an
ice box for
refrigeration. Today, people would think themselves to be
abused if they didn't own a
smartphone, have a
widescreen television, and an electric
refrigerator/freezer well stocked with
junk food.
Our present
cozy lifestyle is a direct consequence of the
labors of the many
scientists and
engineers who have created our
technological society. The technological advances in refrigeration are a good example of our progress, and there's a
website that lists a
timeline of events in refrigeration
history.[1] Some of these are as follow:
• 1834 - Jacob Perkins (1766-1849), who is known as the father of the refrigerator, is granted the first patent for a vapor-compression refrigeration system.
• 1906 - Willis Carrier (1876-1950) patents the modern air conditioner.
• 1923 - Kelvinator attains 80% of the electric refrigerator market.
• 1926 - General Electric markets the first hermetic compressor refrigerator.
• 1926 - Albert Einstein (1879-1955) and Leo Szilard (1898-1964) invent a refrigerator having no moving parts.[2]
• 1955 - 80% of American households have a refrigerator.
• 2005 - 99.5% of American households have a refrigerator.
A graph of the frequency of occurrence by year of the word "refrigeration" via the Google Ngram Viewer (https://books.google.com/ngrams). The curve, not unexpectedly, resembles the graph known as the technology adoption life cycle. (Click for larger image.)
Albert Einstein, who was familiar with the patent process from his time as a
patent examiner at the
Swiss Patent Office, teamed with Leo Szilard on the
design of a refrigerator. Their
motivation was the report that an entire
family had been
killed as they
slept by leaking refrigerator
fumes.[2] The "
Einstein refrigerator" still used the
toxic refrigerants known at that time, but it was
safer since it had no moving parts and did not require
rotary seals (see figure).[3].
Figure from US Patent No. 1,781,541, "Refrigeration," by Albert Einstein and Leo Szilard, dated November 11, 1930.
The "Einstein refrigerator" is an absorption refrigerator in which the cooling evaporate is absorbed by another liquid, which is run through a heat exchanger to recover the refrigerant for another refrigeration cycle.
(Via Google Patents.)[3]
The common refrigeration method, as used in
domestic and
commercial refrigerators and air conditioners, is the
vapor-compression cycle that utilizes the liquid to gas
phase transition of a
refrigerant, such as
R-600a (isobutane, HC(CH
3)
3). The refrigerant vapor is compressed, and the higher
pressure results in a higher
temperature. This hot, compressed vapor is then
condensed into a liquid by a
heat exchanger where it is cooled. The condensed liquid refrigerant flows through an
expansion valve where the abrupt reduction in pressure causes it to cool in a
Joule expansion. It then flows through heat exchanger
coils within the refrigerator to cool its interior. The interior warms the refrigerant to change it into a gas to feed again through the compressor, restarting the cycle.
Aside from the vapor-compression cycle, there are several other methods of cooling. One of these is
thermoelectric cooling in which a
thermoelectric Seebeck effect device is used in inverse to cool one
surface while heating another, rather than generating
electricity from a hot-cold temperature difference. While this has the advantage of having no moving parts, it's far less
efficient. I wrote about the thermoelectric effect in an
earlier article (Thermopower on the Cheap, December 21, 2012). Far more interesting is the
magnetocaloric effect, the subject of another of my articles (
Magnetic Refrigeration, September 3, 2014).
In 1881,
German physicist Emil Warburg (1846-1931) found that
iron, a
magnetic material, would cool about a degree
Celsius when subjected to an
applied magnetic field of one
tesla, the equivalent of 10,000
gauss.[4] The
Earth's magnetic field is about half a gauss; so the effect is very small. This effect can be used in a
magnetic refrigeration cycle (see figure).
The thermodynamic cycle of a magnetic refrigerator.
Refrigeration is achieved by using the entropy associated with the alignment of the magnetic moments of the atoms in a solid as a heat pump.
(Click for larger image.)
The magnetocaloric effect is greatest near the vicinity of a magnetic
phase transition, and some
alloys of
gadolinium, such as
Gd5Si2Ge2, exhibit a "giant magnetocaloric effect" (GMCE) around
room temperature.[5] I wrote about this effect in a
previous article (Giant Magnetocaloric Effect, September 10, 2018). Some of my former
colleagues worked on magnetocaloric
materials in the
1990s.[6]
A recent article in
Science describes a new refrigeration principle,
ionocaloric refrigeration, which uses
ions to drive solid-to-liquid phase transitions in a thermal cycle.[7-10] This technology was developed by
Drew Lilley and
Ravi Prasher, both at
Lawrence Berkeley National Laboratory (Berkeley, California) and the
University of California (Berkeley, California).[7]
Unfortunately, even today's newer
hydrofluorocarbon refrigerants have a
global warming potential, and this problem is
exacerbated by increased use of air conditioning in our warming world.[7-8,10] Hydrofluorocarbons are
greenhouse gases that are thousands of times as powerful as
carbon dioxide.[9] A
2022 climate agreement called the Kigali Amendment commits
signatory nations to reduced
production and
consumption of hydrofluorocarbons by at least 80% over the next 25 years.[10] This has encouraged
research on on alternatives to vapor-compression refrigeration, and ionocaloric cooling is one such technology.[9]
Magnetocaloric refrigeration requires large applied fields, and they have low efficiency and offer just a small temperature change.[7,10] Ionocaloric cooling works by using ions to drive solid-to-liquid phase changes; and, having a liquid as part of the cycle makes it easier to exchange heat in the system.[9] The
researchers have
calculated that ionocaloric cooling has the potential to work at least as efficiently as vapor-compression systems.[9] The
published ionocaloric cooling system uses an
environmentally friendly salt and
solvent.[10]
The operating principle of ionocaloric cooling is the same
freezing point depression principle by which added salt will cause water to freeze at lower temperature. A
saturated solution of
salt water has a freezing point of -21°C; but, to make this large temperature change useful in refrigeration, the process needs to be
reversible.[7-8] The ionocaloric cycle used the flow of
sodium iodide (NaI) ions from
ethylene carbonate ((CH2O)2CO) as the reversible part of the cycle.[9-10] The sodium iodide is removed from the ethylene carbonate by
electrodialysis, causing the ethylene carbonate to
recrystallize and expel
heat.[10]
Animation of the ionocaloric cooling process. Electric current flow causes ions to induce a solid to liquid phase transition in a material, and the material absorbs heat from the surroundings. Reversed current flow removes the ions, causing the material to recrystallize into a solid and release heat. (Lawrence Berkeley National Laboratory image by Jenny Nuss.)
Experiments have shown a larger
adiabatic temperature change and
entropy change per unit
mass and
volume for the ionocaloric system as compared with other caloric effects at equivalent low applied field strengths.[7] There's a 30%
Carnot cycle efficiency and a temperature change as high as 25°C at about 0.22
volts.[7] Says study
author, Drew Lilley,
"There's potential to have refrigerants that are not just GWP [global warming potential]-zero, but GWP-negative... Using a material like ethylene carbonate could actually be carbon-negative, because you produce it by using carbon dioxide as an input. This could give us a place to use CO2 from Carbon capture."[9]
The ionocaloric cycle can be used for
heating as well as cooling.[9] What's needed before
commercialization are experiments on different combinations of materials and development of the components for an actual refrigeration unit.[9] Lilley and Prasher have filed a
provisional patent application for the ionocaloric refrigeration cycle.[9]
Research funding was provided by the
United States Department of Energy in its
Energy Efficiency and Renewable Energy Building Technologies Program.[7,9]
References:
- Timeline of Refrigerators and Low-Temperature Technology, History of Refrigeration Website.
- Gene Dannen, The Einstein-Szilard Refrigerators, Scientific American, January 1997, pp. 90-95.
- Albert Einstein and Leo Szilard, "Refrigeration," US patent No. 1,781,541, November 11, 1930 (via Google Patents).
- Anders Smith, "Who discovered the magnetocaloric effect?" The European Physical Journal H, vol. 38, no 4 (September,2013), pp 507-517.
- V. K. Pecharsky and K. A. Gschneidner, Jr., "Giant Magnetocaloric Effect in Gd5(Si2Ge2)," Phys. Rev. Lett., vol. 78 (June 9, 1997), Document No. 4494, DOI: http://dx.doi.org/10.1103/PhysRevLett.78.4494.
- J. M. Elbicki, L. Y. Zhang, R. T. Obermeyer, and W. E. Wallace, "Magnetic studies of (Gd1−x M x )5Si4 alloys (M=La or Y)," J. Appl. Phys., vol. 69, no. 8 (April 15, 1991), pp. 5571ff.
- Drew Lilley and Ravi Prasher, "Ionocaloric refrigeration cycle," Science, vol. 378, no. 6626 (December 22, 2022), pp. 1344-1348, DOI: 10.1126/science.ade1696.
- Emmanuel Defay, "Cool it, with a pinch of salt," Science, vol. 378,no. 6626 (December 22, 2022), p. 1275, DOI: 10.1126/science.adf5114.
- Lauren Biron, "Berkeley Lab Scientists Develop a Cool New Method of Refrigeration," Lawrence Berkeley National Laboratory Press Release, January 3, 2023.
- Presenting "ionocaloric" refrigeration: A new approach to efficient and sustainable cooling, American Association for the Advancement of Science Press Release, December 22, 2022.
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