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The low temperature system data theory

From the above introduction method of cooling relief as you can see, if you want to get 1 k under low temperature, the key is to reduce the liquid saturation vapour pressure. On the surface of the liquid saturation vapour pressure can reduce to what extent, depends on several factors.

( 1) The size of the experimental dewar exhausting and exhaust of the exhaust pipe thickness and length.

( 2) Heat and flow into the liquid helium leak within the dewar is attached to the size of the calorific value of thing.

( 3) The inner diameter of the experimental dewar and crawling of superfluid helium film, etc.

this several factors influence each other, mutual restriction, columns, such as, to get a very low temperature ( Low pressure) Requires not only large vacuum pump, large diameter pipeline, and need to the appropriate diameter, the adiabatic efficiency high dewar, at the same time, he needs to find ways to customer service, super flow membrane crawling.

when decompression for cryogenic system, liquid temperature drop, the required cold quantity is to achieve by part of the liquid evaporation absorbs heat. Due to the latent heat of liquid helium is very small, so the liquid evaporation loss particularly significant. When the evaporation liquid helium, helium absorb heat from the remaining liquid helium and make the liquid temperature drop, when the evaporation process has no heat leak ( Not including the building heat loss during the relief) When can I get some conclusions from the experiment.

in fact, because of system heat leak and ancillary pieces of the heat capacity of dewar, effect is compared with theoretical results is, in effect, there are differences, but the solid specific heat is small liquid helium heat, so the difference is smaller. From the experiment experience shows: when the liquid helium from 4. When the 2 k to 2 k, drawdown height is about 1/3 of the original height, including by the density of liquid helium from 0. 125 g/L up to 0. 145 g/L liquid level height caused by falling ( Because of its high density, liquid level drops it is bigger than 1/3) 。 When the liquid helium decompression, can find the final temperature from the table and the corresponding relationship between the number of residual liquid helium.
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