Performance
The performance of the cooler is determined mainly by the quality of the regenerator. It has to satisfy conflicting requirements: it must have a low flow resistance (so it must be short with wide channels), but the heat exchange should also be good (so it must be long with narrow channels). The material must have a large heat capacity. At temperatures above 50 K practically all materials are suitable. Bronze or stainless steel is often used. For temperatures between 10 and 50 K lead is most suitable. Below 10 K one uses magnetic materials which are specially developed for this application.
The so-called Coefficient Of Performance (COP) of coolers is defined as the ratio between the cooling power and the compressor power P. In formula: . For a perfectly reversible cooler, is given by the famous relation
| (1) |
which is also called the Carnot COP. However, a pulse-tube refrigerator is not perfectly reversible due to the presence of the orifice, which has flow resistance. Therefore equation (1) does not hold. Instead, the COP of an ideal PTR is given by
| . | (2) |
Comparing relations 1 and 2 shows that the COP of PTR’s is lower than that of ideal coolers.
Read more about this topic: Pulse Tube Refrigerator
Famous quotes containing the word performance:
“No performance is worth loss of geniality. ‘Tis a cruel price we pay for certain fancy goods called fine arts and philosophy.”
—Ralph Waldo Emerson (1803–1882)
“What avails it that you are a Christian, if you are not purer than the heathen, if you deny yourself no more, if you are not more religious? I know of many systems of religion esteemed heathenish whose precepts fill the reader with shame, and provoke him to new endeavors, though it be to the performance of rites merely.”
—Henry David Thoreau (1817–1862)
“True balance requires assigning realistic performance expectations to each of our roles. True balance requires us to acknowledge that our performance in some areas is more important than in others. True balance demands that we determine what accomplishments give us honest satisfaction as well as what failures cause us intolerable grief.”
—Melinda M. Marshall (20th century)