28-06-2012, 12:54 PM
CRYOGENICS AS FUEL
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ABSTRACT
Cryogenics is described by the Britannica Concise Encyclopedia as the "study and use of low-temperature phenomena”. Applications of cryogenics include the storage and transport of liquefied gases, food preservation, cryosurgery, rocket fuels, and super conducting electromagnets. We're talking about a range of temperatures from -238°F i.e. (-150°C) to absolute zero colder than cold.
Cryogenics has also made possible the commercial transportation of liquefied natural gas. In contrast, cryogenic tempering is used widely and effectively in a variety of industries for manufacturing metal tools, machine parts, firearms, aerospace equipment, even golf club heads.
INTRODUCTION
Science concerned with the production and maintenance of temperatures much below normal, down to almost absolute zero Kelvin. Low-temperature physics is also known as cryogenics, from the Greek meaning "producing cold." Low temperatures are achieved by removing energy from a substance. This may be done in various ways. The simplest way to cool a substance is to bring it into contact with another substance that is already at a low temperature. Ordinary ice, dry ice (solid carbon dioxide), and liquid air may be used successively to cool a substance down to about 80°K (about -190°C). The heat is removed by conduction, passing from the substance to be cooled to the colder substance in contact with it. If the colder substance is a liquefied gas considerable heat can be removed as the liquid reverts to its gaseous state, since it will absorb its latent heat of vaporization during the transition.
MINIATURE COOLER:
The miniature cooler is designed to support the operation of a low power focal plane assembly in the 60 to 150 Kelvin temperature range. The miniature cooler will have a mass of nominally 1 kg and an input power of 10 to 20 watts.
VIBRATION FREE COOLER:
Depending on the cooling power requirement. The vibration free cooler is designed to support instruments whose performance would be degraded by the residual vibration from linear coolers. Because of the extremely high efficiency of the turbo-Brayton cooler in the 4 to 10 Kelvin temperature range, payloads requiring cryogenic cooling at 10 Kelvin or below may choose to use this vibration free cooler technology. TURBO BRAYTON COOLER technology is used in vibration free cooler.
Adiabatic Demagnetization Refrigerator:
Goddard began work on the first space-based Adiabatic Demagnetization Refrigerator (ADR) in 1979. The ADR developed by Goddard is a heat pump that operates between liquid helium temperature and very low temperatures. Goddard developed an ADR for the X-RAY Spectrometer (XRS) to cool detectors to 0.065 Kelvin (65 mK). Ground-based ADRs have been constructed that have reached approximately 2 mK. The ADR for the X-Ray Spectrometer has an efficiency of approximately 50% of Carnot. To obtain temperature below 1k ADR is specially used.
WORKING:
The Adiabatic Demagnetization Refrigerator (ADR) is a cyclic cooling system. It has two states of working.
Operating state
In the operating state the magnetic field is kept low there the paramagnetic
Material absorbs heat from the system which is to be cooled. At this time the
Heat switch is switched off to restrict the heat flow from the salt to the helium
Bath. By absorbing the heat the paramagnetic salt will realign itself to it’s
Original structure
Recycling state
In the recycling state the magnetic field was kept high this forces the
Paramagnetic material to be aligned with the magnetic field. Then the
Paramagnetic salt looses its heat energy at that time the heat switch is
Switched on to allow the heat flow from the salt to the helium bath.