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Cooling Technique, 1, 1, Bath, 1, It is a direct or indirect cooling…
Cooling Technique
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the ‘Open Loop’, where the boil-off goes out of the system to be re-liquefied somewhere else before refilling the reservoir permanently to avoid a dry-out
the ‘Closed Loop’, where the vapour is re-condensed in a closed reservoir with a heat exchanger.
In a vertical configuration, two-phase flow circulation loops also have high heat transfer rates.
In a horizontal configuration, the heat transfer is as high as that for the vertical case, but there are flow instabilities at low heat flux flow
an auto-tuned mass flow rate system in which the flow is created by the weight unbalance between the heated branch and the feeding branch of the loop due to vaporization or decreased vapour density
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needs to have a ‘heavier’ cryogenic installation to ensure a periodic re-cooling for operation and to maintain a pressure above Pcrit in the system
Disadvantages includes the pressurization system, the implementation of the heat exchanger system to sub-cool the fluid and the temperature range limitation due to finite sub-cooling.
the guarantee of having an almost isothermal flow due to the high heat transfer,
the limited range of temperature cooling & non-uniform cooling if the vapour and the liquid are not homogeneous
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An OHP generally consists of a capillary tube, wound in a serpentine manner, connecting the ends to the inlets.
a small natural circulation loop coupled with a cryocooler can be used to serve as a self-sustaining thermal link at cryogenic temperatures.
cryocoolers can provide sufficient power to cool down and maintain a small cryomagnetic system at low temperature
Even if the obvious advantages of easy implementation are very attractive, one has to be very accurate in the thermal design
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Indirect method - a cryogenic fluid is used without direct contact with the device but only
through intermediate components.
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simplicity of the cryogenic design and operation, the high heat transfer due to nucleate boiling, and,
therefore, an almost constant surface temperature.
a large quantity of cryogen has to be handled, particularly in case of a quench of a cryomagnetic system
methods used to reduce the amount of cryogen, especially in indirect cooling composed of a network of peripheral tubes.
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if the heat flux q > qcr, then there is film boiling and the heat transfer rate becomes an order of magnitude smaller
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