The most common cooling system simply delivers liquid nitrogen from a bulk storage tank to the point requiring the cooling activity. But, if the designer is aware of these, steps can be taken to mitigate the negative results. When designing cryogenic cooling systems, some common pitfalls befall many designers. How to Design a Cryogenic Cooling System for Industrial Processes Long-period cooling can become expensive when done cryogenically. However, users are cautioned to consider the costs of not only the cryogenic coolant used but also the cost of managing and changing the coolant tanks in facilities that do not have built-in cryogenic liquid coolant delivery systems. If low temperatures are not held for long periods, cryogenic cooling can be cost effective.Ĭryogenic cooling is simple to use, and cryogenic cooling chambers are less expensive to buy. Cryogenic cooling is the better choice for applications that require fast downward temperature transitions or very low temperatures (below the limits of mechanical refrigeration). When plant layouts change, it typically is less costly to relocate the end of a flexible vacuum-insulated hose than to relocate a mechanical freezer. These deficiencies aside, cryogenic cooling has advantages over mechanical cooling. Any device that uses expendable CO 2 or N 2 must be vented to the outside atmosphere or be used in a well-ventilated area with an oxygen monitor. While excessive quantities of carbon dioxide (CO 2) will usually - but not always - manifest with signs of headache or dizziness, nitrogen (N 2) makes up 78 percent of the Earth’s atmosphere, and excessive concentrations that displace oxygen may accumulate without warning. Neither liquid carbon dioxide (LCO 2) nor liquid nitrogen (LN 2) is poisonous to humans, but both have the potential to displace breathable oxygen in a closed room. It is worth noting, however, that cryogenic coolants pose certain health risks that are easily tolerated but important to consider. By contrast, single-stage mechanical refrigeration has temperature limits around -65☏ (-53☌). Liquid nitrogen can reach near -320☏ (-195☌). Generally, from the user’s perspective, the system is simpler, faster and often better performing.Ĭryogenic cooling can deliver extremely low temperatures should they be necessary. One simply buys the coolant, uses it and discards it into the atmosphere. Cryogenic Cooling SystemsĬryogenic cooling systems leave the task of compressing and liquefying the coolant to the coolant supplier. Therefore, unless one has a great deal of time for a ramp down, using a single-stage refrigeration system to achieve -31☏ (-35☌) in a midsize chamber will be possible but tedious. The performance of the chamber will degrade substantially as the limits of the system are approached. The amount of heat that can be removed by a mechanical cooling system is related to the difference between the current temperature of the chamber and the evaporator. Finally, mechanical refrigeration may be the only choice for clean environments and for areas where the spent CO 2 or N 2 exhaust gas could pose a risk to workers. Also, mechanical refrigeration can be advantageous where the time required to ramp down to temperature is not critical. Mechanical refrigeration can be advantageous over expendable gas for cooling applications where expendable liquid nitrogen or liquid carbon dioxide is not readily available for long periods of cooling. Also, mechanical cooling systems are limited by the capacity of the compressors, which are, in turn, limited by available power, space and tolerance for noise and heat. These systems are somewhat complicated and relatively expensive. The system includes at least one compressor, two heat exchanger coils, a fan and several process controls. With a mechanically cooled system, the equipment for recompression and cooling of the spent coolant vapor - in order to convert it back to a reusable liquid - is part of the system.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |