Apparatus for recondensing helium for cryostat
Provided is a helium recondensation apparatus for a cryostat, which can stably recondense vapor of helium in the cryostat while preventing a pipeline for the recondensation from being clogged. A recondensation apparatus includes a freezer, a first heat exchanger, a first recondensing chamber, and a first connection part. The first heat exchanger stores heat-exchanging helium in a helium tank included in an NMR apparatus, and permits the heat-exchanging helium to evaporate owing to heat of vaporization taken from vapor of coolant helium in the helium tank, thereby permitting the coolant helium to recondense through heat exchange with the heat-exchanging helium. The first connection part is separated from the coolant helium in the helium tank and permits the heat-exchanging helium to flow between the first heat exchanger and the first recondensing chamber therethrough.
1. A helium recondensation apparatus for a cryostat which includes a helium tank closed to store coolant helium in liquid and accommodates a cooled object immersed in the coolant helium, the apparatus being connected to the cryostat for recondensing vapor of the coolant helium in the helium tank, and comprising:
a freezer located away from the cryostat and including a main cooling part kept at a cryogenic temperature; and
a helium recondensing unit which recondenses the coolant helium in the helium tank by receiving cold energy from the main cooling part of the freezer, wherein
the helium recondensing unit includes:
a first heat exchanger located above a liquid surface of the coolant helium in the helium tank, and having a first inner space separated from the coolant helium in the helium tank for storing heat-exchanging helium in liquid, the first heat exchanger taking heat of vaporization for evaporation of the heat-exchanging helium in the inner space, from the vapor of the coolant helium in the helium tank;
a first recondensing chamber located away from the cryostat but in thermal contact with the main cooling part, and configured to receive vapor of the heat-exchanging helium in the first inner space, recondense and liquefy the received vapor of the heat-exchanging helium by receiving the cold energy from the main cooling part, and discharge the recondensed and liquefied heat-exchanging helium;
a housing which supports the first recondensing chamber so that the first recondensing chamber is at a higher position than the helium tank; and
a first connection part continuously extending downward from the first recondensing chamber to the first heat exchanger located in the cryostat to define a flow passage for permitting the heat-exchanging helium to flow between the first recondensing chamber and the first heat exchanger so that the heat-exchanging helium discharged from the first recondensing chamber flows to the first inner space of the first heat exchanger by gravity.
2. The helium recondensation apparatus for a cryostat according to claim 1 , wherein
the first connection part has:
a forward section which connects the first inner space of the first heat exchanger and the first recondensing chamber to each other for permitting the vapor of the heat-exchanging helium in the first inner space to flow into the first recondensing chamber; and
a backward section which is independent of the forward section and connects the first inner space of the first heat exchanger and the first recondensing chamber to each other for permitting the heat-exchanging helium recondensed in the first recondensing chamber to flow into the first inner space.
3. The helium recondensation apparatus for a cryostat according to claim 2 , wherein
the first recondensing chamber has:
an inlet connection port for permitting the heat-exchanging helium to flow into the first recondensing chamber from the forward section; and
an outlet connection port located below the inlet connection port for permitting the heat-exchanging helium to flow out to the backward section from the first recondensing chamber.
4. The helium recondensation apparatus for a cryostat according to claim 1 , wherein
the first connection part includes a single pipeline connecting the first inner space of the first heat exchanger and the first recondensing chamber to each other for permitting the vapor of the heat-exchanging helium in the first inner space to flow into the first recondensing chamber, and permitting the heat exchanging helium recondensed in the first recondensing chamber to flow into the first inner space.
5. The helium recondensation apparatus for a cryostat according to claim 1 , wherein
the first recondensing chamber has a first lower surface slanting downward to the first connection part.
6. The helium recondensation apparatus for a cryostat according to claim 1 , wherein
the first connection part has a first flexible section made of a flexible member and arranged at least between the first heat exchanger and the first recondensing chamber.
7. The helium recondensation apparatus for a cryostat according to claim 1 , wherein
a helium buffer tank connected to the first recondensing chamber for transferring the heat-exchanging helium between the helium buffer tank and the first recondensing chamber, and having a capacity which is larger than a sum of a capacity of the first recondensing chamber and a capacity of the first inner space.
8. The helium recondensation apparatus for a cryostat according to claim 7 , further comprising:
a helium reservoir tank which is independent of the first recondensing chamber and connected to the helium buffer tank for transferring the heat-exchanging helium between the helium reservoir tank and the helium buffer tank; and
a pressure regulating assembly including a pump and valves which regulates a transfer amount of the heat-exchanging helium between the helium buffer tank and the helium reservoir tank so that a pressure in the helium buffer tank falls within a predetermined range.
9. The helium recondensation apparatus for a cryostat according to claim 8 , wherein
the pump of the pressure regulating assembly includes a helium pump arranged between the helium buffer tank and the helium reservoir tank,
the valves of the pressure regulating assembly include:
an intake-side switch valve disposed on an intake side of the helium pump for switching a supply source of supplying the heat-exchanging helium to the helium pump between the helium buffer tank and the helium reservoir tank; and
a discharge-side switch valve disposed on a discharge side of the helium pump for switching a discharge destination to which the heat-exchanging helium is discharged between the helium buffer tank and the helium reservoir tank.
10. The helium recondensation apparatus for a cryostat according to claim 8 , wherein
the helium reservoir tank has:
a low-pressure reservoir tank part having a lower pressure than the helium buffer tank; and
a high-pressure reservoir tank part having a higher pressure than the helium buffer tank,
the pump of the pressure regulating assembly includes a helium pump arranged between the low-pressure reservoir tank part and the high-pressure reservoir tank part; and
the valves of the pressure regulating assembly include:
a helium low-pressure valve disposed between the helium pump and the low-pressure reservoir tank part, and openable to permit the heat-exchanging helium to flow out to the low-pressure reservoir tank part from the helium buffer tank in response to an operation of the helium pump; and
a helium high-pressure valve disposed between the helium pump and the high-pressure reservoir tank part, and openable to permit the heat-exchanging helium to flow into the helium buffer tank from the high-pressure reservoir tank part in response to an operation of the helium pump.
11. The helium recondensation apparatus for a cryostat according to claim 1 , wherein
the cryostat further includes an auxiliary coolant tank surrounding the helium tank and closed to store a thermally-insulating auxiliary coolant in liquid, and
the freezer further includes a sub-cooling part arranged at a position different from the main cooling part and kept at a cryogenic temperature, the apparatus further comprising:
an auxiliary coolant recondensing unit which recondenses the thermally-insulating auxiliary coolant in the auxiliary coolant tank by receiving cold energy from the sub-cooling part of the freezer,
the auxiliary coolant recondensing unit includes:
a second heat exchanger located above a liquid surface of the thermally-insulating auxiliary coolant in the auxiliary coolant tank, and having a second inner space separated from the thermally-insulating auxiliary coolant in the auxiliary coolant tank for storing a heat-exchanging auxiliary coolant in liquid, the second heat exchanger taking heat of vaporization for evaporation of the heat-exchanging auxiliary coolant in the second inner space, from the vapor of the thermally-insulating auxiliary coolant in the auxiliary coolant tank;
a second recondensing chamber located away from the cryostat but in thermal contact with the sub-cooling part, supported by the housing at a higher position than the auxiliary coolant tank, and configured to receive vapor of the heat-exchanging auxiliary coolant in the second inner space, recondense and liquefy the received vapor of the heat-exchanging auxiliary coolant by receiving the cold energy from the sub-cooling part, and discharge the recondensed and liquefied heat-exchanging auxiliary coolant; and
a second connection part continuously extending downward from the second recondensing chamber to the second heat exchanger located in the cryostat to define a flow passage for permitting the heat-exchanging auxiliary coolant to flow between the second recondensing chamber and the second heat exchanger so that the thermally-insulating auxiliary coolant discharged from the second recondensing chamber flows to the second inner space of the second heat exchanger by gravity.
12. The helium recondensation apparatus for a cryostat according to claim 11 , wherein
the second recondensing chamber has a second lower surface slanting downward to the second connection part.
13. The helium recondensation apparatus for a cryostat according to claim 11 , wherein
the second connection part has a second flexible section made of a flexible member and arranged at least between the second heat exchanger and the second recondensing chamber.
14. The helium recondensation apparatus for a cryostat according to claim 11 , wherein
the freezer further includes:
a cylinder having a cylindrical shape and a central axis extending in an up-down direction;
a displacer arranged in the cylinder reciprocatively movable upward and downward in the up-down direction for generating cold energy by expanding coolant gas in the cylinder; and
a drive part located below the cylinder for generating a drive force to reciprocatively move the displacer upward and downward,
the sub-cooling part is connected to the cylinder above the drive part for cooling the second recondensing chamber by receiving the cold energy, and
the main cooling part is connected to the cylinder above the sub-cooling part for cooling the first recondensing chamber at a lower temperature than a temperature of the second recondensing chamber by receiving the cold energy.