Liquids cryogenic

Special hazards associated with cryogenic liquids include  

Special precautions include the use of protective clothing, including eye or face protection and heavy leather gloves. Transfer operatioits, especially ttiose involving open containers such as Dewars, should be carried out slowly and carefully to control boiling and splashing of the liquid. Ventilation must be adequate to handle any gas evolved. 

In system design, materials of construction must be compatible with the liquids handled at the low temperatures to be encoimtered. Apparatus must have proper pressure relief. Where liquid can be trapped between valves, the possibility of high pressure due to partial vaporization or thermal expansion must be considered. Again, pressure relief devices may be called for. 

Because of their different physical and chemical properties, the various cryogenic liquids have their own peculiar requirements, some of which are discussed below. 

Because of its explosive reactivity with many substances, oxygen presents unique problems. Any system that wUl contain oxygen must be cleaned and kept free of 

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Cryogenics Cryogenic liquids are too cold for most seals. Use a metal bellows mechanical seal with no elastomer parts. 

Every gas has a critical temperature above which it cannot be liquefied by application of pressure alone (Chapter 4). As a result, gases used, e.g., as an inert medium to reduce oxygen content of atmospheres containing flammable gas or vapour (Chapter 6) are often shipped and stored as cryogenic liquid for convenience and economy. 

Wear protective clothing which avoids the possibility of cryogenic liquid becoming trapped near the skin avoid turnups and pockets and wear trousers over boots, not tucked in. 

Table 8.4 Physical properties of selected cryogenic liquids ...

They are widely employed in the manufacture, storage and distribution of liquified gases, particularly on sea and road tankers. The most popular alloy for cryogenic applications is 4.5% magnesium alloy (N8). Table 3.33 gives the boiling points of the most common cryogenic liquids and the minimum temperatures at which various materials can be used. 

Using the data given in Fig. 1.17 we consider the deviation of the isothermic dependence of 1 from linear (binary) relationship (1.124). The dependence of l/(xj(v)) on i/ in a liquid is presented in Fig. 1.23. The experimental results practically coincide with a straight line corresponding to a binary approximation up to a critical point. Hence the impact approximation is not too bad even for moderately condensed gases. However, the abrupt increase in 1/tj observed in the cryogen liquid is too sharp to be described even with the hard-sphere correction... 

Excessive generation of e.g. nitrogen or helium gas from cryogenic liquids. 

Also, because the boiling points of these cryogenic liquids are lower than that of oxygen, if exposed to air they can cause oxygen to condense preferentially, resulting in hazards similar to those of liquid oxygen. 

Ensure that pipework and control systems are adequate to cope with the pressures associated with storage and conveyance of carbon dioxide, which are higher than those encountered with most other cryogenic liquids. 

Accidents due to thermcil shock mixtures of cryogenic liquids with water at ambient temperature. There will be an explosion if the difference in temperature of the mixture of molten metals with water is greater than 90°C. 

Interest in permanent magnets is increasing in non-medical NMR imaging. One reason is obviously the lower costs, permanent magnets do not need a power supply or cryogenic liquids. Only the temperature has to be kept very stable,... 

See also cryogenic liquids (reference 10), liquefied petroleum gases... 

See Ozone Hydrogen (Liquid) See other cryogenic liquids... 

See Other CRYOGENIC LIQUIDS, IRRADIATION DECOMPOSITION INCIDENTS... 

All dewars of cryogenic liquids must be equipped with safety valves, so that pressure cannot raise to dangerous values in case of an accident. 

It is important to note that some types of dewar necks are made of plastic materials which are permeable to gases and in particular to He. The permeation phenomenon has a strong dependence on temperature and is negligible at 4K (see e.g. ref. [6]). If the dewar remains for a long time at room temperature in an atmosphere containing He gas, the vacuum space is slowly filled with He which must be pumped before the filling with cryogenic liquids. 

In containers for cryogenic liquids, we must be able to determine the level of the liquid. Since most dewars are metallic, we cannot detect the level optically. 

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