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Magnetic heat pumps
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news
No u velles de I'in dustrie II
I
Magnetic heat pumps The change in the temperature of magnetic materials when subjected to a magnetic field is the principle behind the design of a magnetic heat pump. While most materials only produce temperature changes of one to two degrees, researchers at NASA's Lewis Centre have found that gadolinium will change temperature by up to 14°C. By using a process called regeneration, this can be increased to over 60°C, which is similar to the temperature range of a conventional heat pump, which can both heat buildings and provide refrigeration. The researchers have built a model heat pump which consists of a gadolinium refrigerant assembly, a 100 cm long, 5 cm diameter fluid-filled tube called a regenerator, and an electro-magnet. The gadolinium refrigerant assembly is composed of 36, one mm thick Gd plates assembled in a cylindrical stainless steel canister. The canister is suspended in a fixed position within the regenerator, which is filled with a mixutre of 50% water and 50% alcohol. A doughnut-shaped magnet surrounds the regenerator and is in the same fixed position as the refrigerant canister. The only moving part of the pump is the regenerator, which is driven up and down electrically, an action that serves to position the Gd canister alternately at either end of the regenerator. When the Gd is at the hot end of the regenerator, the magnet is turned on, heating the Gd which, in turn, heats the surrounding fluid. The
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regenerator is then driven in the opposite direction so as to position the Gd at the cold end. At this point the magnet is turned off and the temperature of the Gd decreases and absorbs heat from the surround. ing fluid, thus cooling it. Repetition of this process creates a cumulative effect at each end of the regenerator: the hot end gets hotter and the cold end gets cooler. In one recent test run, the magnetic heat pump achieved a temperature range from 55°C at the hot end to -30°C at the cold end. The researchers believe that their heat pumps could achieve an efficiency of 60% as compared to 40% for conventional heat pumps, thus resulting in considerable energy savings. They forsee it being able to replace all but the smallest conventional units, including those used in industrial refrigeration plants for such purposes as freeze drying, food processing and cold storage, and others used for the heating and cooling of medium to large buildings, plants and ships. Other possible applications, at much lower temperatures, include the liquefaction and separation of air (eg to supply oxygen for steel mills), the liquefaction of natural gas and the liquefaction of lower-boiling gases such as hydrogen and helium. Lewis Research Center, 2 1 0 0 0 Brookpark Road, Cleveland, Ohio 4 4 1 3 5 , USA.
Control. This is one of the applications for which they recommend their Maxicarb filters. Activated carbon cells are arranged in a V formation to present the maximum filter area to the air flow. The cells consist of granules contained in honeycomb laminates which are asymmetrically arranged and are pressure-bonded on each side to plastic-covered steel wire screens. The company claim that this design prevents the cells sagging in use and destroying the efficiency of the filter. The screens forming the outside faces of the filter cell are bonded to foam plastic sheets which contain the granules, and which are carried up the sides of the cell to seal the entire unit. This construction is very light but of high mechanical strength, and as well as containing the granules so that voids are eliminated, provides a large number of adsorption sites with low resistance to the passage of air. The effective "stay' time of a contaminant within each cell is high, providing good adsorption efficiency. A foam plastic prefilter panel is normally fitted to the filters, to remove dust from the air stream. Machine Control Ltd, Blatchord Road, Horsham, West Sussex, UK
Carbon stops smells Reciprocal transfer of odours in refrigerated warehouses can be prevented by activated carbon filters, say Machine
Filling a cell of carbon filter The filter bed vibrates during this process to ensure void free packing of the granules
International Journal of Refrigerahon
news
No u velles de I'in dustrie II
I
Magnetic heat pumps The change in the temperature of magnetic materials when subjected to a magnetic field is the principle behind the design of a magnetic heat pump. While most materials only produce temperature changes of one to two degrees, researchers at NASA's Lewis Centre have found that gadolinium will change temperature by up to 14°C. By using a process called regeneration, this can be increased to over 60°C, which is similar to the temperature range of a conventional heat pump, which can both heat buildings and provide refrigeration. The researchers have built a model heat pump which consists of a gadolinium refrigerant assembly, a 100 cm long, 5 cm diameter fluid-filled tube called a regenerator, and an electro-magnet. The gadolinium refrigerant assembly is composed of 36, one mm thick Gd plates assembled in a cylindrical stainless steel canister. The canister is suspended in a fixed position within the regenerator, which is filled with a mixutre of 50% water and 50% alcohol. A doughnut-shaped magnet surrounds the regenerator and is in the same fixed position as the refrigerant canister. The only moving part of the pump is the regenerator, which is driven up and down electrically, an action that serves to position the Gd canister alternately at either end of the regenerator. When the Gd is at the hot end of the regenerator, the magnet is turned on, heating the Gd which, in turn, heats the surrounding fluid. The
242
I
regenerator is then driven in the opposite direction so as to position the Gd at the cold end. At this point the magnet is turned off and the temperature of the Gd decreases and absorbs heat from the surround. ing fluid, thus cooling it. Repetition of this process creates a cumulative effect at each end of the regenerator: the hot end gets hotter and the cold end gets cooler. In one recent test run, the magnetic heat pump achieved a temperature range from 55°C at the hot end to -30°C at the cold end. The researchers believe that their heat pumps could achieve an efficiency of 60% as compared to 40% for conventional heat pumps, thus resulting in considerable energy savings. They forsee it being able to replace all but the smallest conventional units, including those used in industrial refrigeration plants for such purposes as freeze drying, food processing and cold storage, and others used for the heating and cooling of medium to large buildings, plants and ships. Other possible applications, at much lower temperatures, include the liquefaction and separation of air (eg to supply oxygen for steel mills), the liquefaction of natural gas and the liquefaction of lower-boiling gases such as hydrogen and helium. Lewis Research Center, 2 1 0 0 0 Brookpark Road, Cleveland, Ohio 4 4 1 3 5 , USA.
Control. This is one of the applications for which they recommend their Maxicarb filters. Activated carbon cells are arranged in a V formation to present the maximum filter area to the air flow. The cells consist of granules contained in honeycomb laminates which are asymmetrically arranged and are pressure-bonded on each side to plastic-covered steel wire screens. The company claim that this design prevents the cells sagging in use and destroying the efficiency of the filter. The screens forming the outside faces of the filter cell are bonded to foam plastic sheets which contain the granules, and which are carried up the sides of the cell to seal the entire unit. This construction is very light but of high mechanical strength, and as well as containing the granules so that voids are eliminated, provides a large number of adsorption sites with low resistance to the passage of air. The effective "stay' time of a contaminant within each cell is high, providing good adsorption efficiency. A foam plastic prefilter panel is normally fitted to the filters, to remove dust from the air stream. Machine Control Ltd, Blatchord Road, Horsham, West Sussex, UK
Carbon stops smells Reciprocal transfer of odours in refrigerated warehouses can be prevented by activated carbon filters, say Machine
Filling a cell of carbon filter The filter bed vibrates during this process to ensure void free packing of the granules
International Journal of Refrigerahon