Cryogenic recondenser with remote cold box

Apparatus for cooling a bath of cryogen in a cryostat in which a magnetic coil of a magnetic resonance imaging system is cooled, the apparatus comprising:

• a mechanical refrigerator positioned outside of the bath, said refrigerator precooling a volume of gaseous refrigerant;
• a transfer line leading into the cryostat;
• and
• a JT valve at an end of the transfer line in the cryostat, the transfer line transferring the precooled refrigerant from the mechanical refrigerator to the JT valve in heat exchange relation with returning refrigerant, the precooled refrigerant being expanded through the JT valve to form a liquid and gas cryogen mixture at the end of the transfer line in the cryostat, the formed liquid and gas mixture being in heat exchange relation with boil-off from the bath and thereby recondensing said boil-off;
• the refrigerant being returned to the mechanical refrigerator through the transfer line in heat exchange relation with the precooled and expanded refrigerant being transferred to the JT valve.

Apparatus for recondensing boil-off from a bath of cryogen retained in a cryostat comprising:

• cooling and expansion means comprising a mechanical refrigerator positioned outside of the cryostat, said means precooling and expanding a volume of working gas;
• a coaxial transfer line having an inner tube coaxially positioned within an outer tube leading into the cryostat;
• a JT valve at an end of the coaxial transfer line in the cryostat, said precooled and expanded working gas being transferred through the inner tube of the coaxial transfer line to the JT valve in heat exchange relation with the working gas flowing in the outer tube of the coaxial transfer line and being expanded through the JT valve to form a liquid and gas cryogen mixture;
• and
• a coaxial recondensing heat exchanger having an inner tubing coaxially positioned within an outer tubing and positioned at an end of the JT valve for receiving the formed liquid and gas cryogen mixture, the formed cryogen mixture being passed through the inner tubing and the outer tubing in heat exchange relation with the boil-off such that said boil-off is recondensed and said cryogen being returned to the cooling and expansion means through the outer tube of the coaxial transfer line.

A method of condensing cryogen gas comprising the steps of:

• precooling a stream of compressed gas;
• expanding the precooled gas through a first JT valve to form a stream of medium pressure gas;
• cooling the stream of medium pressure gas;
• and
• expanding the cooled stream of medium pressure gas through a second JT valve in a cryostat which is remote from said first JT valve, expansion through the second JT valve forming a cold mixture of liquid and low pressure gas which is in heat exchange relation with cryogen boil-off from a volume of liquid cryogen contained in the cryostat and thereby recondenses the boil-off.

A condenser comprising:

• a mechanical refrigerator for precooling a stream of compressed gas;
• a first JT valve for expanding the precooled stream of compressed gas to a medium pressure stream of precooled gas;
• and
• a heat exchanging and transfer means for further cooling and transferring the medium pressure precooled gas between the first JT valve and a second JT valve, the second JT valve expanding the medium pressure stream of further cooled gas, said expansion by the second JT valve forming a cold mixture of liquid and gas at a pressure below the medium pressure, the first and second JT valves being remotely positioned from each other, the second being in a storage vessel and the first being outside of the storage vessel.