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:
“Just as the performance of the vilest and most wicked deeds requires spirit and talent, so even the greatest demand a certain insensitivity which under other circumstances we would call stupidity.”
—G.C. (Georg Christoph)
“Tennis is more than just a sport. It’s an art, like the ballet. Or like a performance in the theater. When I step on the court I feel like Anna Pavlova. Or like Adelina Patti. Or even like Sarah Bernhardt. I see the footlights in front of me. I hear the whisperings of the audience. I feel an icy shudder. Win or die! Now or never! It’s the crisis of my life.”
—Bill Tilden (1893–1953)
“The child to be concerned about is the one who is actively unhappy, [in school].... In the long run, a child’s emotional development has a far greater impact on his life than his school performance or the curriculum’s richness, so it is wise to do everything possible to change a situation in which a child is suffering excessively.”
—Dorothy H. Cohen (20th century)