Modern Engineering Thermodynamics

14.11 Commercial and Household Refrigerators 563
CRITICAL THINKING
Visit an antique store and find an old icebox. Note the current price. Look it over to understand how it worked. Inspect it
for insulation in the walls and measure the size of the food storage compartment. How do you think your diet would
change if you had to use an icebox every day? How cold do you think iceboxes were able to keep the food?
WHERE DID BIRDS EYE FROZEN FOOD COME FROM?
Clarence Birdseye (1886–1956) was a very successful businessman and inventor. In 1912, he went to Labrador as a fur
trader and discovered that fish caught in weather 50° below zero froze almost instantly and were still fresh months later,
when they were thawed out. Slow freezing allows ice crystals to form in the cells of plants and animals, causing them to
burst. However, with quick freezing, the cells remain intact, preserving the flavor and nutrition of the food.
After returning from Labrador, Birdseye developed a quick freezing process that preserved the original taste of a variety of
foods such as fish, fruits, and vegetables. In 1924, he helped found the General Seafood Company (later to become
General Foods Corporation), which successfully marketed his frozen food products, and he became very wealthy. Birds Eye
frozen food products are still available in supermarkets.
Birdseye’s patented freezing process consisted of placing two flat refrigerated metal plates at −40°F on either side of a food
package, causing the food to freeze very quickly. Birdseye was granted nearly 300 patents in his lifetime. In addition to his
frozen food patents, he developed infrared heat lamps for home use, a recoilless gun for firing a harpoon, and a method
for freeze-drying foods.
refrigerant flow control mechanism that would not let liquid refrigerant enter and subsequently destroy the
compressor. Commercial refrigeration systems often required constant refrigerant flow adjustment by a
human operator.
The first problem was solved with the development of an effective central electrical power system by Thomas
Edison between 1895 and 1920. Inexpensive electric motors then became available as suitable power sources for a
household compressor. The second problem was solved with the development of the hermetically sealed motorcompressor
unit in 1918. Many of the refrigerants used were dielectrics and did not conduct electricity. Therefore,
they could come in direct contact with the motor windings and even act as a coolant for the motor. Numerous
float-valve (as found in a toilet tank) refrigerant flow control mechanisms were tried during this period, but the
automatic flow control problem was not completely solved until 1926, when Harry Thompson developed the
thermostatic expansion valve to automatically control the flow of liquid refrigerant into the evaporator.
The Kelvinator Corporation of Detroit, Michigan, was one of the first companies to build electrical refrigerators.
They launched the first household vapor-compression refrigerator in 1918 and sold 67 units that year. By 1921,
over 20 manufacturers of home refrigerators sold a total of 5000 units that year. Growth in the domestic refrigeration
market was phenomenal, with 75,000 units sold in 1925, 850,000 in 1930, and 1.7 million in 1935.
Even during the Depression, sales of home refrigerators remained high. As production increased, the prices fell.
In 1920, the average price for a refrigerator was $600; in 1930, it was $275; and in 1935, it was $160. In 1929,
as many mechanical refrigerators were produced as old-fashioned iceboxes.
The first commercial refrigeration system appeared in large hotels in the early 1900s for air conditioning and
food preservation. By the 1930s, glass-covered self-service display cabinets were available in small groceries and
supermarkets for chilled or frozen ice cream, meat, poultry, fish, eggs, and dairy products. Since cold air is heavier
than room air, the glass cover disappeared from most horizontal display cases in the 1950s to encourage
customer access. Vertical freezer display cases, however, still require glass doors.
At the same time as vapor-compression domestic refrigerators were reaching the market, a major breakthrough
was made in absorption refrigeration. In 1925, the Swedish engineers G. Munters and B. von Platen successfully
eliminated the mechanical pump between the high- and low-pressure regions by introducing hydrogen gas into
the system. Hydrogen lowers the partial pressure of the refrigerant (ammonia) vapor in the evaporator, allowing
it to boil at a lower temperature. A percolation or siphon action transports the fluid from the low-pressure
absorber into the high-pressure generator (the pressure difference is only a few inches of height in these systems)
and gravity forces the fluid to circulate through the remaining system (see Figure 14.22). This refinement opened
the way for the development of a household absorption refrigerator that had no moving parts, was completely