Because mechanical refrigeration is energy intensive, active collectors are typically restricted to places where there is no supply of water that can be desalinated or purified at a lower cost and that are sufficiently far from a supply of fresh water to make transport uneconomical.
32.
They are also useful for creating low temperatures when mechanical refrigeration is not available, for example to tightly fit two parts of machined metal : one part is soaked in a frigorific mixture, causing it to cool and contract, and then placed into the uncooled second part.
33.
Specific advancements included the introduction of oil fired steam turbine and internal combustion driven steel ships, the development of the airplane, the practical commercialization of the automobile, mass production of consumer goods, the perfection of canning, mechanical refrigeration and other food preservation techniques, and the invention of the telephone.
34.
An additional 100 cars were soon incorporated into the fleet, and small mechanical refrigeration units were installed to keep temperatures constant on hot days . In 2004, Tropicana s rail fleet of 514 cars traveled over 35 million miles a method that is three times more fuel efficient than other shipping methods.
