KR20000021120A - Ultra low temperature freezer using reverse brayton cycle - Google Patents

Abstract

PURPOSE: A very low temperature refrigerator using reverse Brayton cycle is provided to suitably apply to the very low temperature refrigerator for electric elements and superconducting elements by reducing the size and simplifying the composition. CONSTITUTION: A very low temperature refrigerator using reverse Brayton cycle includes a first element(100) formed with an electric power introduction part(102) coming into in the one side end, and a compressor(104) and a small refrigerating fan(106) driven by the electric power came into through the electric power introduction part in the inside, a second element(110) formed with a counter flow heat exchanger(122) in which high-pressure gas and low-pressure gas exchanges heat, and an expander(126) in the inside for forming a low temperature, and a third element(120) between the compressor and the counter flow heat exchanger for controlling the electric power to a motor driving the compressor.

Description

Cryogenic Chiller with Reverse Brayton Cycle

TECHNICAL FIELD The present invention relates to cryogenic chillers, and more particularly, to chillers that form cryogenic temperatures by powering from outside in a small volume using a reverse braton cycle.

Ultra-low temperature cryogenic cooler that causes cooling effect of liquid nitrogen temperature (approximately 77K) is mainly used to cool infrared sensor.In the future, semiconductor devices such as CMOS, GaAs, HEMT, SQUID, RF filter using high temperature superconductor, etc. Will be enlarged.

For example, CMOS logic circuits operate at 80K for two to three times faster than at room temperature, while GaAs devices have 77K at 10 GHz. As described above, the electronic circuits operated at cryogenic temperatures may also benefit not only from the operation speed of the semiconductor device itself, but also from the additional characteristics such as the reduction of thermal noise, the increase in the capacity of the communication circuit, the sensitivity of the sensing element, and the area expansion. Doing.

Meanwhile, important technical developments in the field of cryogenic refrigerators include miniaturization, convenience, price, and durability of cryogenic chillers. In particular, when cooling the electronic device and the superconducting device is very small cryogenic cooler is advantageous, how to apply the existing cooler in this field was the biggest problem.

The ultra-small cryogenic cooler according to the prior art was a J-T (Joule-Thomson) cooler using a compressor that generates a high pressure of about 300 atmospheres or a Stirling cryogenic cooler using a linear compressor.

JT cooler is a cooler that only miniaturizes the heat exchanger and the expansion part and only JT expansion (insulation expansion). Since it requires about 300 atm of compressed gas, the compressor is very large and needs to be installed separately from the cooling part. I had a problem.

On the other hand, as is well known in the case of a very small sterling cryogenic chiller using a linear compressor, the compressor, the expander and the regenerator are operated by reversing a sterling cycle consisting of two constant temperature processes and two static processes. It is manufactured by Mechanical System) technology and operates depending on high frequency pulsating flow.

A detailed description of this can be found in US Pat. No. 5,457,956 "Microminiature Stirling Cycle Cryocoolers And Engines".

As described above, the JT cooler of the related art can be miniaturized in size, but as the compressor driving the cooler always occupies the largest volume, the size of the entire cooler becomes large and it is inconvenient to use. The ultra-low temperature cryogenic cooler uses a high-frequency pulsating flow, so its structure is very complicated. Therefore, in order to commercialize high-temperature superconductor application electronic devices that can be used at liquid nitrogen temperature, a more compact and convenient cryogenic cooler is needed. .

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art as described above, and an object thereof is to provide a micro cryogenic cooler using an inverse Brayton cycle to form cryogenic temperature in a miniaturized volume.

1A is a three-dimensional schematic diagram illustrating a cryogenic chiller using a reverse Brayton cycle according to an embodiment of the present invention;

FIG. 1B is a plan view of the cryogenic cooler using the reverse Braton cycle shown in FIG.

FIG. 2 is a T-s diagram illustrating the thermodynamic cycle of a cryogenic chiller using an inverse Braton cycle in accordance with one embodiment of the present invention. FIG.

♠ Explanation of symbols on the main parts of the drawing ♠

100: first device 102: power introduction unit

104: centrifugal compressor 106: small cooling fan

110: second device 112: electrical circuit portion

120: third apparatus 122: counterflow heat exchanger

124: vacuum insulation 126: turbo expander

128: vacuum insulation reinforcement

According to the present invention for achieving the object as described above, there is provided a power inlet for introducing power at one end thereof, the centrifugal compressor and the small cooling fan respectively driven by the power introduced through the power introduction unit therein A first device installed; A counter flow heat exchanger in which high pressure and low pressure gas exchanges heat, and a second device having a low temperature expander formed therein; An ultra-small cryogenic cooler is provided, comprising a third device for controlling electric power for a motor driving a centrifugal compressor between the centrifugal compressor and the counterflow heat exchanger.

In the following, with reference to the accompanying drawings, a preferred embodiment of a micro cryogenic cooler according to the present invention will be described in detail.

As shown in FIGS. 2A and 2B, the ultra-low temperature cryogenic cooler is composed of three devices 100, 110, and 120, and a power introduction part 102 into which power is drawn at one end of the first device 100. ) Is installed, and inside the centrifugal compressor 104 and the small cooling fan 106 are driven by the power drawn through the power introduction unit 102, respectively.

The centrifugal compressor 104 has a radius of about 1 cm and a thickness of about 5 mm, and is manufactured by using deep reactive ion etching, and a small cooling fan positioned directly above the nitrogen gas, which is a working fluid, is compressed. 106) suppresses the temperature rise as much as possible. The small cooling fan 106 is a small axial flow fan is installed on the same shaft as the centrifugal compressor 104 and is manufactured to have a rotational speed of about 1 million rpm electrostatic micromotor.

The counter-flow heat exchanger 122 inside the third apparatus is manufactured by lithography (lithography) in the form of microchannels to have a sufficient heat exchange area while having a maze shape.

In addition, between the counterflow heat exchanger 122 and the turbo expander 126, a vacuum insulator 124 for minimizing heat transfer from the outside to the cryogenic cooler is provided, and the third device has a columnar shape. The vacuum insulation reinforcement 128 is provided in a number of longitudinal directions.

On the other hand, between the first apparatus 100 and the third apparatus 120, the power supply and turbo for the motor driving the centrifugal compressor 104 between the centrifugal compressor 104 and the counterflow heat exchanger 122 There is provided a second device provided therein with an electrical circuit portion for controlling the power regenerated by the expander 126.

Preferably, the three devices 100, 110, 120 have a small volume of approximately 2 cm × 10 cm × 1 cm when their one or both side circumferences are connected to one structure by welding or the like. In addition, the figure has a rectangular parallelepiped shape, but a round cross-sectional shape like a cylinder is also possible.

The centrifugal compressor 104 and the turbo expander 126 is made of single crystal silicon or composite material to improve the strength per unit density, reduce the loss due to friction by applying the gas bearing technology that can be used at high speed, and the thermal insulation efficiency It is desirable to be able to increase.

On the other hand, since the ultra-low temperature cryogenic cooler using the reverse braton cycle configured in the present embodiment is used for electronic devices, the size of the micro cryogenic cooler must be very small. LIthography Galvanoformung Abfonnung) technology.

The manufacturing process steps of each component manufactured by MEMS technology and LIGA technology are as follows. First, a space for the refrigerant to move is designed to create a sophisticated optical plate. Second, in order to partially etch the material made of silicon or glass, the material is partially etched using the dry plate prepared in the first step. Third, additionally fabricate the necessary components separately to perform a fine assembly process. Fourth, the device is covered with a cover structure and sealed with UV adhesive or other EPOXY for refrigerant and vacuum tightness.

The reference pressure ratio designed in this embodiment is about 10, which is to compress nitrogen gas of 1 atm to 10 atm by the micro centrifugal compressor 104. The total cooler was designed to have a large thickness (about 1 cm) to enable multi-stage compression, and the thickness of one compression stage was about 2 mm, considering current etching technology.

In addition, according to the present exemplary embodiment, the counterflow heat exchanger 122 and the high pressure gas side and the low pressure gas side are formed side by side in a maze form, and the heat transfer area of each other is sufficiently secured and the width of the channel is about 1 mm. As a result, even if the wall thickness of the channel is thin (about 0.1 mm or less), there is no risk of rupture.

Hereinafter, the operation of cooling and operating the electronic device and the superconducting device at a liquid nitrogen temperature (77 K) much lower than room temperature using the cryogenic cooler for the electronic device according to the present embodiment will be described.

As shown in FIGS. 2A to 3, the incoming power through the power introduction unit 102 first drives the centrifugal compressor 104 and the small cooling fan 106, and the high pressure and low pressure in the counterflow heat exchanger 122 space. The gas achieves effective heat exchange and eventually forms low temperatures in the turbo expander 126. At this time, in the temperature region lower than room temperature, heat transfer from the outside to the low temperature portion is minimized by the vacuum insulation portion 124, and the stress due to the pressure difference of the gas is reduced by the vacuum insulation reinforcement 128 having the pillar shape. Sustained.

Meanwhile, pure nitrogen gas at room temperature and 1 atm is compressed to 10 atm through isothermal compression (1-> 2), and is cooled to about 150 K by the nitrogen gas at low pressure through the counterflow heat exchanger 122. (2-> 3), low temperature is formed by the adiabatic expansion process (3-> 4).

At this time, the above-mentioned (1-> 2) process is difficult to become an isothermal process in actuality, and the effective cooling should lower the gas temperature in the final compression process. Processed in the heat exchange process (2-> 3), the heating process of the low pressure nitrogen gas (4-> 1) is the process of cooling the gas of high pressure in the counter-flow heat exchanger 122 and return to the compression process.

According to this embodiment, when 0.1 g / s of nitrogen gas circulates into the working fluid, it is designed to provide a cooling capacity of about 1 W in the 80 K region, where the centrifugally compressed nitrogen gas is supplied to the counterflow heat exchanger ( Cooling at 122 results in a sufficiently cold nitrogen gas entering the turboexpander 126 to rotate the radial vanes and reduce enthalpy.

At this time, the regeneration of the turbo expander 126 is absorbed by the electrostatic generator that is connected to the turbo expander 126 in one axis, the temperature of the nitrogen gas after the expansion process is very low.

The power supply to the motor driving the centrifugal compressor 104 and the control of the regenerated power at the turbo expander 126 are controlled by the electrical circuitry 112 between the counterflow heat exchanger 122 and the centrifugal compressor 104. In order to minimize the heat loss to the outside which is a problem in the cryogenic cooler, the turbo expander 126, which is the coldest part of the cooler, is kept away from the centrifugal compressor 104, which is the hottest part, to suppress heat transfer by conduction.

In addition, according to the present embodiment, the total space of the cooler occupied by the working fluid is initially vacuumed and filled with pure nitrogen gas, and the amount of nitrogen gas charged at this time is virtually reversed when the cooler reaches a steady state. When the Layton cycle is formed, the pressure conditions of the high and low pressure sections are determined, so the filling amount must be carefully controlled from the cooler's internal volume and manufacturing experience.

As described in detail above, the present invention has an effect that can be suitably applied to the cryogenic cooler for electronic devices and superconducting devices because the size of the cryogenic cooler that generates cryogenic temperature is much smaller and simpler than the conventional cooler.

Although the technical idea of the ultra-low temperature cryogenic cooler of the present invention has been described with the accompanying drawings, this is illustrative of the best embodiment of the present invention and is not intended to limit the present invention. In addition, it is obvious that any person skilled in the art can make various modifications and imitations without departing from the scope of the technical idea of the present invention.

Claims (6)

A first device having a power introduction unit configured to receive electric power at one end thereof and having a compressor and a small cooling fan respectively driven therein by the electric power introduced through the electric power introduction unit; A second apparatus in which a counterflow heat exchanger in which a gas of high pressure and a low pressure exchange heat and a expander forming a low temperature are respectively installed therein; And A third device for controlling power to a motor driving the compressor between the compressor and the counterflow heat exchanger, The compressor, expander, counterflow heat exchanger is cryogenic cooler, characterized in that produced by MEMS technology. The method of claim 1, wherein the compressor, the expander, the counter flow heat exchanger is a first step of manufacturing an optical dry plate by designing a space in which the refrigerant moves, a second step of etching using the dry plate produced in the first step, Cryogenic cooler, characterized in that it is manufactured in a third step of assembling the components produced by the above process. The cryogenic cooler of claim 1, wherein the compressor is a multi-stage compressor. 4. The cryogenic cooler of claim 3, wherein the expander is a turbo expander. The cryogenic cooler according to claim 4, wherein an electrostatic generator is provided which absorbs the work generated by the turboexpander and generates electricity for use as a power of the refrigerator. The cryogenic cooler of claim 1, wherein a vacuum insulator is installed between the counterflow heat exchanger and the expander to minimize heat transferred from the outside to the cryogenic cooler.