Available online
Description
The operation of a helium liquifier is examined in terms of thermodynamics.
The operation of a helium liquifier is examined in terms of thermodynamics.
| Module code and title: | ST285, "Solids, liquids and gases" |
|---|---|
| Item code: | ST285; 14 |
| First transmission date: | 11-08-1973 |
| Published: | 1973 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:24:30 |
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| Producer: | Andrew Millington |
| Contributors: | Paul Clark; Alan Walton |
| Publisher: | BBC Open University |
| Keyword(s): | Helium liquifier; Hydrogen; Inversion temperature; Nitrogen |
| Footage description: | Paul Clark introduces the programme. He has with him in the studio a helium liquifier of the type used at Cambridge University. He points out the more important component parts and explains their function. Alan Walton uses a diagram of a throttle valve to explain the basic throttling process which is essential to the helium liquifier. Alan Walton at Clarendon Laboratory, Oxford with an experimental apparatus which demonstrates that the process of throttling can lower the temperature of the gas. He explains how the apparatus works. Walton performs the experiment by raising the pressure of nitrogen gas at the throttle from 10 to 25 and then to 40 atmospheres. The gas cools. Walton repeats the experiment using helium gas. The temperature rises in this case as pressure increases. To explain this anomaly, Paul Clark performs some systematic analysis on a flow process. He uses diagrams and several captions to aid. Clark arrives at a conservation of energy equation which is simplified by Alan Walton. Clark continues and determines that enthalpy, as a function of state, is conserved. Alan Walton with a pressure temperature diagram which has plotted on it the result of the nitrogen throttling experiment. He points out the limitations of this graph. Paul Clark uses a pressure-temperature diagram for nitrogen, which has plotted on it a series of curves of constant enthalpy, to explain that a rise or fall in temperature during throttling depends on the pressure and temperature of the experiment. Clark does the same for helium using a helium pressure-temperature diagram. He derives an inversion curve for both gases which explains the anomaly of the above experiment. Paul Clark and Alan Walton explain how liquification is achieved. A nitrogen liquification apparatus in the studio acts as an aid. Clark and Walton then explain how expansion and heat exchange achieve liquification of helium. They use the helium liquifier shown at the beginning of the programme to illustrate how the process works. Clark sums up. |
| Master spool number: | 6HT/70990 |
| Production number: | 00525_1038 |
| Videofinder number: | 691 |
| Available to public: | no |
