KR20230121187A - Superconducting magnet cooling system using a heat pipe - Google Patents

Abstract

A superconducting magnet cooling system using a heat pipe is disclosed. An objective of the present invention is to provide the superconducting magnet cooling system that can efficiently cool superconducting magnets by using heat pipes with very high thermal conductivity instead of metal cooling channels used in an existing conduction cooling method. The superconducting magnet cooling system according to one example includes a cryogenic refrigerator, a vacuum vessel, a heat pipe, a superconducting magnet, a pressure reduction device, and a radiation shield.

Description

Superconducting magnet cooling system using a heat pipe}

The present invention relates to a superconducting magnet cooling system using a heat pipe. More specifically, it relates to a superconducting magnet cooling system capable of efficiently cooling a superconducting magnet by using a heat pipe having a very high thermal conductivity instead of a metal cooling channel used in a conventional conduction cooling method.

The cooling method of the system including the superconducting magnet can be divided into a refrigerant circulation method in which low-temperature gas (helium, neon, hydrogen) is circulated and cooled, a method in which cooling is performed in a cryogenic liquid, and a method in which a cryogenic freezer is directly connected to the cooling method.

In the cryogenic gas circulation method, devices such as a refrigerator, a heat exchanger, and a blower are added to cool the gas. In the method of direct cooling with a cryogenic liquid, a gas is generated by evaporating the cryogenic fluid, and a recondensation system is required to recondense the gas generated by evaporation. The conduction cooling method using a cryogenic freezer has the simplest system configuration and uses the least amount of power required to cool the superconducting magnet.

However, the conduction cooling method has a problem in that a temperature gradient occurs in the cooling object, and more power is used or a refrigerator with a large capacity is required to cool the superconducting magnet below the operating temperature.

In order to solve this problem, a heat pipe may be used instead of a braided wire or a copper block in a cooling channel connecting the refrigerator and the superconducting magnet.

A heat pipe is a device for efficiently transferring heat, and heat is transferred while gas and liquid move to a high temperature part and a low temperature part by a phase change of a fluid inside the heat pipe. Helium (4 K), hydrogen (20 K), and neon (27 K) may be used as the fluid used in the heat pipe for cooling the superconducting magnet.

Since a superconducting magnet maintains a superconducting state below a critical temperature, cooling is very important in a system using a superconducting magnet.

Methods for cooling superconducting magnets include a gas circulation cooling method in which low-temperature gas is circulated and cooled, and a conduction cooling method in which a superconducting magnet is directly coupled to a refrigerator.

In the gas circulation cooling method, a system for cooling is added, and the cost of configuring the system also increases.

In the conduction cooling method, a refrigerator and a superconducting magnet are directly connected to a cooling channel to be cooled by conduction, and a temperature difference occurs due to thermal resistance caused by the connection of the cooling channel.

A superconducting magnet cannot achieve its target performance if it does not reach its target temperature, and temperature control in the conduction cooling method is the most important factor.

This problem can be solved by replacing the cooling channel connecting the refrigerator and the superconducting magnet with a heat pipe.

The present invention has been conceived to solve the above problems, and a superconducting magnet capable of efficiently cooling a superconducting magnet by using a heat pipe having a very high thermal conductivity instead of a metal cooling channel used in the conventional conduction cooling method. It is an object to provide a magnetic cooling system.

A superconducting magnet cooling system according to an example includes a cryogenic freezer, a vacuum container, a heat pipe, a superconducting magnet, a pressure reducer, and a radiation shield.

The present invention provides a superconducting magnet cooling system capable of efficiently cooling a superconducting magnet by using a heat pipe having a very high thermal conductivity instead of a metal cooling channel used in the conventional conduction cooling method. there is

In addition, if the present invention is used, first, the superconducting magnet can be cooled by being attached to a cryogenic refrigerator. Second, the thermal conductivity is tens to hundreds of times higher than that of copper blocks or braided wires used in the conventional conduction cooling method, and effective cooling is possible. Third, since the size is small and heat transfer is possible over a long distance, the temperature gradient can be reduced by attaching it to several places on the cooling target. Fourth, by applying the wick structure, the degree of freedom in installing the heat pipe can be increased by pumping force by capillary force rather than by thermosiphon. Fifth, the pressure inside the heat pipe according to the temperature change can be kept constant by using a pressure reducer.

1 is a view showing an example of a superconducting magnet cooling system using a heat pipe;
FIG. 2 is a diagram illustrating a flow of a fluid inside a heat pipe in the superconducting magnet cooling system of FIG. 1 .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In order to apply the heat pipe to the cooling system, it is necessary to consider the selection of the working fluid according to the operating temperature of the superconducting magnet, the filling amount and pressure of the fluid inside the heat pipe according to the cooling capacity. The present inventors have performed research tasks on heat reduction systems using heat pipes, and have know-how on operation characteristics and operation of heat pipes for efficient cooling of superconducting magnet cooling systems.

1 is a diagram showing an example of a superconducting magnet cooling system using a heat pipe.
As shown in FIG. 1 , a superconducting magnet cooling system using a heat pipe includes a cryogenic freezer, a vacuum container, a heat pipe, a superconducting magnet, a pressure reducer, and a radiation shield.
The heat pipe has a thermal conductivity that is tens to hundreds of times higher than that of a cooling channel made of generally used copper material, and enables effective cooling. Since the heat pipe can be used semi-permanently and can be manufactured in a small size, the temperature of the entire superconducting magnet can be reduced within a certain range by attaching it to a part with a high temperature gradient generated by the superconducting magnet.
Since the heat pipe operates as a thermosiphon by gravity, the cryogenic freezer must be installed at the top of the system, but using a porous wick inside the heat pipe allows the fluid to be transported between the low temperature and high temperature sections by pumping by capillary force. And the installation location of the cryogenic freezer can be installed in a different location than the top.
When the heat pipe is applied to the conduction cooling system, the internal pressure of the fluid inside the heat pipe is reduced due to the temperature difference between normal temperature and cryogenic temperature. This problem can be solved by applying a pressure reducing device (PRR) to solve the temperature imbalance.
A superconducting magnet cooling system using a heat pipe can be applied to NMR (Nuclear magnetic resonance) and MRI (Magnetic resonance imaging) using high-temperature superconducting magnets.
FIG. 2 is a diagram illustrating a flow of a fluid inside a heat pipe in the superconducting magnet cooling system of FIG. 1 .
To cool the superconducting magnet, a heat pipe is connected to the cold head of the cryogenic freezer, and the heat pipe transfers heat by a temperature difference by injecting a fluid into a metal tube such as copper having high thermal conductivity.
The low-temperature part of the heat pipe is attached to the cryogenic freezer, and the high-temperature part is attached to the superconducting magnet. Since the low-temperature part is maintained at a low temperature by the cryogenic freezer, the fluid inside the heat pipe is liquefied and moves to the high-temperature part, and the fluid that has moved to the high-temperature part has a relatively high temperature. It evaporates according to the temperature and cools the superconducting magnet by the latent heat of vaporization.
As this process is repeated, the superconducting magnet is cooled. As the cooling system is cooled from room temperature to cryogenic temperature, the pressure inside the heat pipe due to the temperature difference between room temperature and cryogenic temperature is lowered, and the pressure inside the heat pipe can be kept constant by connecting a pressure reducer to the heat pipe.
The pressure reducing device is a container that is very large compared to the volume inside the heat pipe, and is filled with a sufficiently large amount of fluid so as not to affect the pressure change inside the heat pipe due to temperature change.
Cooling systems using heat pipes can be used to efficiently cool temperatures below 100 K. Nitrogen (77 K), neon (27 K), hydrogen (20 K), and helium (4 K) can be used inside the heat pipe to apply to a system for use at various temperatures, and in a cryogenic fluid storage system, constant It can be used for systems for maintaining temperature, etc.
In addition, it is very important to cool to operating temperature in order to reach the target performance of the superconducting magnet in the system including the superconducting magnet. When a superconducting magnet is cooled by the conduction cooling method among existing cooling methods, the cryogenic refrigerator and the superconducting magnet are connected to a cooling channel made of a metal material having high thermal conductivity such as copper to be cooled.
In conduction cooling, a temperature gradient is generated by thermal resistance, and depending on the shape of a superconducting magnet, cooling to the target temperature of the system may occur due to a large temperature gradient.
In this case, the problem can be solved by selecting a refrigerator with a large cooling capacity. Due to the high price of the cryogenic freezer, it leads to an increase in the cost of system configuration.
According to the present invention, when a previously used cooling channel is replaced with a heat pipe having excellent heat transfer efficiency, the temperature gradient can be reduced at low cost, and the cost required for system configuration can be reduced. Heat pipes are used to remove heat in various fields such as electronic products and spacecraft, and the heat transport ability of heat pipes has already been proven with sufficient performance through many studies and actually used products.
In addition, using the present invention, the present invention enables effective cooling by applying a heat pipe with high thermal conductivity to improve the existing cooling method of superconducting magnets, and the temperature gradient due to thermal resistance, which is a disadvantage of the conduction cooling method, is applied. cooling problem can be solved.
In addition, if the present invention is used, a system to which superconducting magnets are applied can be applied to medical, aviation, transportation, and energy fields, and a heat pipe can be used as the most essential element of a cooling system. In order to apply the heat pipe to the cooling system, it is necessary to design a cooling system according to the purpose, and technology to configure a system for use in a wide temperature range from room temperature to cryogenic temperature is transferred to related companies or through start-ups. can make a profit.

Claims (1)

A superconducting magnet cooling system using a heat pipe, including a cryogenic freezer, a vacuum container, a heat pipe, a superconducting magnet, a pressure reducing device, and a radiation shield.