US 6,854,276 B1Granted

Method and apparatus of cryogenic cooling for high temperature superconductor devices

AssigneeSuperPower, Inc.

InventorsXing Yuan, Susumu Mine

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Abstract

A method and apparatus for providing cryogenic cooling to HTS devices, in particular those that are used in high-voltage electric power applications. The method involves pressurizing liquid cryogen to above one atmospheric pressure to improve its dielectric strength, while sub-cooling the liquid cryogen to below its saturation temperature in order to improve the performance of the HTS components of the device. An apparatus utilizing such a cooling method consists of a vessel that contains a pressurized gaseous cryogen region and a sub-cooled liquid cryogen bath, a liquid cryogen heating coupled with a gaseous cryogen venting scheme to maintain the pressure of the cryogen to a value in a range that corresponds to optimum dielectric strength of the liquid cryogen, and a cooling system that maintains the liquid cryogen at a temperature below its boiling point to improve the performance of HTS materials used in the device.

Claims26

Dependent claims

A method for achieving and maintaining cryogenic cooling for a cryogenic cooling system having a cryogen containment vessel that stores cryogen in a liquid state and a gaseous state, wherein the liquid state includes a subcooled region and a thermal gradient layer (TGL) boundary region adjacent the gaseous region and having at least one superconductor, the method comprising the steps of:

maintaining a pressurized cryogen region within the cryogen containment vessel;
maintaining the temperature of the subcooled region of the liquid cryogen at or below its boiling temperature using sub-cooling means;
and
maintaining an optimum thickness of the TGL, wherein the optimum thickness of such TGL in the case of a stagnat liquid cryogen is expressed by the equation k×S×(ΔT)/Q, wherein “S” is the surface area of the TGL, and wherein “ΔT” is the temperature difference across the TGL region, and wherein “k” is the thermal conductivity of the cryogen in the TGL, and wherein “Q” is the heat input to the TGL through the boundary surface between the TGL and the gaseous regions;
and
maintaining a physical barrier between the TGL and subcooled liquid cryogen regions, wherein such barrier is thermally coupled to a cryocooling means, wherein the thermal conductive characteristics of such barrier allows the heat input “Q” to the TGL to be transferred to the subcooled region and/or the coupled cryocooling means.

3 more elements

A cyrogenic cooling system having an inner vessel, at least one high temperature superconductor, and an outer vessel, the inner vessel adapted to be contained inside the outer vessel and adapted to store pressurized cryogen in a liquid state and a gaseous state, wherein the liquid state includes a subcooled region and a thermal gradient layer (TGL) boundary region adjacent the gaseous region, the cooling system comprising:

liquid heating means for boiling off liquid cryogen in the TGL region in order to increase the pressure at the gaseous region;
gas venting means for releasing gas in order to reduce the pressure at the gaseous region;
and
cryogenic cooling means for maintaining a portion of the liquid cryogen in the subcooled region within a sub-cooled temperature range that is at and below its boiling temperature;
and
thermal gradient layer means for maintaing an optimum thickness of the TGL, wherein the optimum thickness of such TGL in the case of a stagnant liquid cryogen is expressed by the equation k×S×(ΔT)/Q, wherein “S” is the surface area of the TGL, and wherein “ΔT” is the temperature difference across the TGL region, and wherein “k” is the thermal conductivity of the cryogen in the TGL, and wherein “Q” is the heat input to the TGL through the boundary surface between the TGL and the gaseous regions;
physical barrier means between the TGL and subcooled liquid cryogen regions, wherein such barrier is thermally coupled to a cryocooling means, wherein the thermal conductive characteristics of such barrier allows the heat input “Q” to the TGL to be transferred to the subcooled region and/or the coupled cryocooling means.

4 more elements

Dependencies are inferred from the claim text.