Super Cool Apps
January 1, 2011
The applications where cryogenic solids, liquids and gases are involved continue to grow as OEMs search for innovative ways to develop products and processes in economical, ecological ways.
Research and far-reaching concepts will, in many cases, involve the use of cryogens in the future. Scientists and engineers are always striving to find that one process where the principle of minimum energy will, in effect, apply in the creation of a new, innovative product. The use of cryogens can reduce the energy losses that would be seen if it were not a part of the process. In addition, in many cases their absence would limit the ability to advance these developments at all.
While the National Institute of Standards and Technology (NIST) defines the field of cryogenics as involving temperatures below -292°F (-180°C, or 93.15 K), many processes require temperatures well below this standard. The following examples of processes using cryogenic cooling demonstrate the diversity of this low-temperature tool.
Plastics ProcessingIn the automotive industry, two manufacturing applications where cryogenic cooling often is applied are:
- The process of blow-molding or
- The process of shrink-fitting two metals that have a very tight tolerance.
Once molded, a delay in production to allow for cooling would have an unacceptable impact on profits if not reduced. Tanks formed in cryogenically cooled molds using liquid nitrogen can be removed almost immediately and proceed to the next phase of production.
Likewise, valve seat shrink-fitting is a common cryogenically cooled automotive application. Shrink-fitting at liquid nitrogen temperatures is a method used when one metal part must be inserted into a housing or another assembly that requires an extremely tight tolerance fit. This cryogenically cooled technique allows a mechanical fit that otherwise could not be accomplished via mechanical force - that is, press fitting with both parts at room temperature. The necessary clearance is obtained by shrinking the part to be inserted (instead of expanding the outer one) by immersing the inner component in a bath of liquid nitrogen at a temperature of -320°F (-196°C).
Figure 1 shows a valve seat freeze chamber at an engine assembly plant where multiple units are in place for both the intake and exhaust. The image illustrates an application where the valve seats are automatically fed through the top assembly of each cooling tube and immersed in a bath of liquid nitrogen prior to pressing into the warm engine block. Temperature, insertion speed and liquid level control are all automated to ensure proper force is used when the part is press fit. Expansion of the part is nearly immediate due to the extreme temperature differential of these two parts.
High Temperature SuperconductivityWith the ability to carry up to 10 times more power than conventional cable, high temperature superconductivity (HTS) cables are used for electricity transmission and distribution. HTS cable can meet the increased power demands in urban areas while using a reduced footprint of the conventional cable design. These superconducting cables have the potential to create a new electric superhighway with reduced loses, a more environmentally friendly footprint and reduced energy costs to the consumer. Additional applications include testing currently being conducted for a power grid capable of withstanding lightning strikes and even terrorist attacks. (The latter is funded in part by the Department of Homeland Security to address concerns for power delivery in New York’s financial district, a vital part of the nation’s economy.)
Standard conventional conductors of copper or aluminum are replaced by high temperature superconductivity wire, enabling the cable to carry greater amounts of current with fewer losses due to resistance. The cable requires a cooling system that uses liquid nitrogen as a refrigerant for the HTS conductors. The cryogenic cooling keeps the cable at a temperature (approximately -320°F [-196°C]) where resistance is minimized. This liquid nitrogen cools the cables until they experience zero electrical resistance, which allows them to carry up to 10 times more power than copper cabling of the same size.
These cables also use a high-temperature superconductor material that experiences zero electrical resistance at relatively high temperatures compared to other superconductors. Many manufacturers are developing and testing these materials, but in all cases, the cables still must be cooled to liquid nitrogen temperatures. The superconducting wires also are designed to automatically suppress surges that could otherwise damage system equipment. Real-time testing has been proven in various cities across the United States and abroad.
Experiment Cooling in SpaceAlthough not strictly a process cooling application, many aeronautics innovations ultimately make their way into commercial use. So, it should come as no surprise that cryogenic cooling, which has a growing importance in process applications, is a key component of many space missions.
For instance, not long ago, a NASA mission was launched to study the atmosphere of the Earth and the chemicals that are affecting the ozone layer. This satellite, known as the Upper Atmosphere Research Satellite (UARS), was equipped with 10 instruments to study the physical and chemical processes of the Earth’s stratosphere, mesosphere and lower thermosphere. Among them is the Cryogenic Limb Array Etalon Spectrometer (CLAES). The CLAES instrument is a spectrometer that determines the concentrations and distributions of nitrogen and chlorine compounds, ozone, water vapor and methane. It does this by inferring the amount of gases in the atmosphere by measuring the unique infrared signature of each gas.
In order to differentiate the relatively weak signature of trace gases from the background radiation in the atmosphere, CLAES had to have high resolution and sensitivity. To achieve this, the instrument combined a telescope with an infrared spectrometer. The whole instrument was cryogenically cooled to keep heat from the instrument from interfering with the readings.
The cryogenic system consists of an inner tank of solid neon at -430°F (-257°C) and an outer tank of solid carbon dioxide at -238°F (-150 C). As the neon and carbon dioxide evaporated, they kept the instrument cool for a period of over 19 months. The entire instrument was kept under vacuum during ground test and launch, and then exposed to the vacuum of space when the telescope door was opened on orbit. Additionally, a vacuum-jacketed emergency vent line was required should there be any failure with the solid neon, which could have jeopardized any of the additional nine experiments being conducted. Liquid neon has more than 40 times the refrigerating capacity of liquid helium and three times that of liquid hydrogen (on a per unit volume basis). One reason that neon typically is not used as a refrigerant is that liquid neon is expensive: For small quantities, its price can be more than 55 times that of liquid helium. The driver for expense is the rarity of neon, not the liquefaction process.
As noted, applications where cryogenic solids, liquids and gases are involved continue to grow. It is hoped that the examples in this article help demonstrate cryogenics’ ever-widening possible applications and suggest new and more innovative uses.