WO2020248204A1

WO2020248204A1 - A cold head with extended working gas channels

Info

Publication number: WO2020248204A1
Application number: PCT/CN2019/091176
Authority: WO
Inventors: Kui YANG
Original assignee: Yang Kui
Priority date: 2019-06-13
Filing date: 2019-06-13
Publication date: 2020-12-17

Abstract

A cold head of cryocooler, which is intricately constructed with various forms of object to be cooled. The cold head deforms the void volume and constructs extended gas channels i.e. gaps, holes or grooves as part of expanding space for working gas. Moreover the working gas circulation mechanism is established to achieve larger energy exchange area, in the meantime, enhance temperature uniformity and stability at cryogenic temperature.

Description

A Cold Head With Extended Working Gas Channels

Technical Field

The invention mainly apply in cryogenic temperature generation and distribution apparatus, for instance, cryocooler which is capable of reaching desirable temperature by cyclical compression and expansion of working gas (hereinafter refer as gas) such as helium or hydrogen.

Background Art

Stirling cycle based cryocooler generate low temperature by adiabatic expansion of gas in cylinder. The cold end of expansion cylinder is generally defined as cold head. Between object to be cooled (hereinafter referred as sample) and cryocooler cold head, extra heat exchanger or cold acceptor with desirable heat conductivity and large contacting surface are normally mounted as sampler holder and energy transfer interface. In the case of high requirement on temperature uniformity, extra coolant is applied to circulate between cold head and samples..

Summary of Invention

A cold head with predefined gas channels to accommodate various forms and states of samples to achieve temperature uniformity stability around the samples. Built-in gas channels might sacrifice the engine performance as it increase the void volume. However such sacrifice is worthwhile for certain application which demands decent temperature uniformity. To better accommodate sample shapes and minimize the void volume, maximum length of certain gas channel in one dimension is normally more than threes times of minimum length of other two dimensions. The gas channels, including the gaps, deep holes or grooves are built integrally as part of gas expanding space. Compression and expansion operation during Stirling cycle did accomplish mixing and heat exchange for the gas inside the channel. Therefore the sample location surrounded by gas channels achieve good temperature uniformity and stability. This design is valid for various types of cryocoolers, pulse tube, GM, Stirling as long as the engine apply gas adiabatic expansion to generate cryogenic temperature.

In this invention some channels receive more gas from regenerator than its direct output to regenerator and other channels output more gas than that they directly received from the regenerator. To achieve better temperature uniformity for samples with remarkable unequal length in different dimensions, this invention designed a gas circulation mechanism to drive certain amount of gas flow unidirectionally through entry channels to other return channels rather than compressing and expanding gas turbulently in the same channel bidirectionally.

Technical Problem

One of cold distribution mechanism of cryocooler is direct contact. However cold head is of too small area to suitably accommodate samples with various forms and large surface. It demands heat transfer device and/or sample holder located on top of cold head. In this case, despite of its apparent simplicity, the existence of extra device constitutes physical barrier between samples and the cryocoolder cold head, restricts the energy transfer and deteriorates samples temperature uniformity and stability.

To apply extra coolant circulate between cold head and samples cause the system unduly large and complex. Moreover it might not advisable to apply extra coolant around liquid Nitrogen range of cryogenic temperature.

Solution to Problem

Solution to problem is described with reference of first embodiment and along with Fig 1, Fig2, Fig3. The second embodiment is of share the same principle but with simpler structure as channels openings are connected to regenerator directly with separation in cold end space.

Replace extra devices/adapters/holders conventionally fitted between samples and expansion cylinder by special cold head with customized geometry to accommodate various sample forms. This special cold head normally with concave forms as sample holder 4 is cast, welded and mechanically built integrally as indispensable part of the cylinder. The gas channels including the gaps, deep holes or grooves are built integrally around distant and irregular samples contacting area as part of gas expanding space.

The whole gas thermodynamic cycle is roughly divided into two basic periods: compression operation period that compression chamber pressure is normally higher than expansion chamber and expansion operation period that compression chamber pressure is lower than expansion chamber. To better assisting the circulation of gas, whole cryocooler cold space end is separated physically into two sections by cap ceiling fixture 14 to displacer piston cylinder 9: entry space 5 where compressed gas squeezed to entry channels 1 and exit space 6 where expanded gas exit from return channels 2. Ideally significant amount of gas from compression chamber is compressed into entry channels 1 through entry space 5 during compression operation and then vacuumed into regenerator 13 from exit space 6 by other return channels 2 during expansion operation. One entry channel is capable of inputting gas to multiple return channels and vice versa. Displacer piston cylinder 9 is closely surrounding the displacer piston and concentric with cylinder 12 which is surrounding the regenerator and cold end exchanger. Agap opening 8 is built in displacer piston cylinder 9 at position below the zero point of displacer i.e. middle point of its full stroke to control the gas migration between these two sections. Gap opening can be opened in compressing piston as well to differentiate gas flow for different channels. The dome of displacer piston 10 and other bends in gas passage are built with proper round angle to reduce gas turbulence.

During the compression operation the gas is pushed from regenerator 13 and cold end exchanger 11 to entry space 5, sequentially compressed into entry channel 1, return route connection 3, return channel 2 and enclosed in exit space 6. At this operation, the displacer locates above the its zero point and blocks the gap opening 8 to defense the integrity of physical separation of entry and exit spaces. Reinforced framework or beam are installed inside the displacer piston on this particular area to resist momentary pressure.

During expansion operation, the displacer piston normally locate below the gap opening 8 and the gas is expanding from below two channels.

A. Entry channel 1 and entry space 5 gas directly purged into regenerator 13.

B. Return channel 2 and exit space 6 purged into entry space 5 and regenerator 13 through the gap opening 8 which is opened by displacer piston. During expansion operation, return channels 2 and exit space 6 with large volume purged more gas back to regenerator 13 than the gas they received directly from entry space 5 during compression operation. In this way the position and width of this gap 8 actually activate and regulate the gas passage in right time without causing leakage and generate gas flow circulation all the way from channel 1 to channel 2.

To sum up, gas passages indicated by the dashed arrow in Fig. 1, Fig. 2 and Fig. 3 are motivated by gap cyclic on and off triggered by displacer piston movement. The position and width of the gap openings are technically defined with reference of stroke length and pressure differential curve between hot end and cold end.

The main purpose of gap opening is to generate imbalance of gas flow in different channels and spaces. Displacer piston cylinder 9 and cap ceiling fixture 14 is not necessarily to block two spaces completely. Therefore besides application the gap opening 8 in piston cylinder 9, any material with anisotropic property on flow rate can be applied. Such anisotropic materials with asymmetric porosity or micro structures or geometrical distribution create different flow rates from by different direction and serve the similar purpose as the function of gap opening 8. Mechanical construction such as geometrical design in gas passing route also differentiate gas flow rate bidirectionally. The main circulation loop is indicated by dashed arrow in Fig. 1. Gap opening, mechanical construction and material with anisotropic property, these solutions can be applied separately in its own right or in parallel.

Advantageous Effects of Invention

This invention creates larger sample contacting surface. It applies cryocooler working gas directly as heat transfer coolant and eliminates the extra coolant circulation, therefore it reduces system weight, size and complexity. Especially this invention reach lower temperature faster than the system with extra coolant circulation could with better temperature uniformity and stability.

Brief Description of Drawings

Fig. 1 is schematic diagram in axial section of cold head of embodiment which heat regenerator locates annularly surrenders the displacer. Gas flow circulation is indicated by dashed arrow.

Fig. 2 is perspective view of displacer piston cylinder 9 with gap opening 8 during expansion operation. Gas flow direction is indicated by dashed arrow.

Fig. 3 is perspective view of displacer piston cylinder 9 with gap opening 8 and displacer piston 10 during compression operation. Gas flow direction is indicated by dashed arrow.

Fig. 4 is schematic diagram in axial section of cold head of the embodiment which heat regenerator locates inside the displacer during the compression operation. Gas flow circulation is indicated by dashed arrow.

Fig. 5 is schematic diagram in axial section of cold head of the embodiment which heat regenerator locates inside the displacer during the expansion operation. Gas flow circulation is indicated by dashed arrow.

In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific term so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar mannerto accomplish a similar purpose.

Description of Embodiments

The first embodiment that regenerator locates annularly surrounding the displacer

As illustrated in drawing 1, cryocooler with physical displacer and annular regenerator 13 is selected to present the embodiment. The whole cold end space is divided into two spaces by cap ceiling fixture 14 to displacer piston cylinder 9. One gap opening 8 is constructed around and below zero point of displacer in displacer piston cylinder 9. For each adiabatic expansion, displacer basically locate between its zero point and full stroke end at hot space, the gap is opened and the gas purge out of return channels 2 into annular regenerator 13 through exit space 6. However during compression cycle of cryocooler, this gap opening 8 is blocked by displacer itself and most gas is driven into entry channels 1. The circulation mechanism for gas are well established.

Besides gap opening 8 in displacer piston cylinder 9, extra cold end exchanger 7 normally made of porous or corrugated material with large contacting surface (hereinafter refer as matrix material) located between entry space and exit space providing differentiating gas flow rate for different direction as well. This exchanger 7 in cold end mainly serve as gas flow direction regulator between spaces providing imbalance of gas flow. As result channel 1 mainly serve as entry and channel 2 serve as return in term of gas net mass output from or input to regenerator 13.

Another main function of matrix material locate between entry space and exit space is to achieve energy exchange, each compression operation pushed gas with relatively high temperature into the pores or crevices inside the matrix materials, on the other hand, each expansion operation push low temperature gas into the pores or crevices from the other side. Amyriad of these micro structures provides desirable large heat exchange surface to balance temperature difference. This exchanger 7 could be merged with original cold end exchanger 11 which normally is built by corrugated metal on top of regenerator 13. In this case, matrix material with anisotropic micro structures locates in the opening of entry channels. It contribute to gas circulation by assisting the vertical flow into the entry channels 1 from space 5 during compression operation and restrict gas flow the other way around during expansion operation.

The second embodiment that the regenerator locates inside the displacer

As illustrated in drawing 4 and drawing 5, cryocooler with regenerator inside the displacer is selected to present the embodiment. The top ceiling of displacer is closed and internally installed a gas diverter 15. In the meantime, the side wall in top section of displacer 16 is perforated or slotted to act as gas passage. The rest of displacer wall 17 is of full integrity with decent sealing to its cylinder 9.

As illustrated in drawing 4, during compression operation, the top section of displacer 16 locate and travel overlapped with the channel opening 8a. The gas out of regenerator 13 is diverted by gas diverter 15, passing through top section of displacer 16 into channel 1, connector 3, channel 2, eventually blocked and enclosed by side wall of displacer main body 17.

As illustrated in drawing 5, during expansion operation, the top section of displacer 16 locates and travels overlapped with the opening 8b. The gas expanded from channel opening 8a, channel 1, connector 3, channel 2, channel opening 8b and top section of displacer 16, eventually purge into regenerator 13. The circulation mechanism for gas are well established.

Industrial Applicability

The invention applies in temperature control apparatus, mainly with Stirling cycle based cryocooler which is capable of freezing, heating and stabilizing samples with various dimensions. It can be applied in thermostatic bath, cold shield for instruments, heat or cold exchanger for cryostat, freezer...etc...

The detailed description in connection with drawing is intended principally as a description of presently preferred embodiment of invention, and is not intended to represent the only form in which the present invention may be constructed or utilized. The description set forth the designs, functions, means and methods of implementing the invention in connection with illustrated embodiments. It is to be understood, however, that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention and that various modifications may be adopted without departing from the invention or scope of the following claims.

Claims

A cold head comprising extended gas channels built integrally around distant and irregular samples contacting area according to various sample shapes including but not limited to narrow gaps, deep holes or groove as part of cold end space for working gas.
A cold head comprising gas circulation mechanism that certain amount of gas purged out of regenerator, travels into entry channels and return from return channels before being recollected by regenerator, sweeping the sample contacting area.
A cold head in accordance to claim 2 wherein channels openings are connected to regenerator through the perforated or slotted sidewall of displacer.
A cold head in accordance to claim 3, wherein the position and width of the channel openings and perforated or slotted area in displacer sidewall are technically defined with reference of stroke length and pressure differential between hot end and cold end.
A cold head in accordance to claim 3, wherein entry channel opening locate in the position which entry channels opening directly connects to perforated or slotted area of displacer during the compression operation.
A cold head in accordance to claim 3, wherein return channel opening locate in the position which return channels opening directly connects to perforated or slotted area of displacer during the expansion operation.
A cold head in accordance to claim 3, gas diverter is internally constructed at ceiling of displacer to facilitate gas migration through perforated or slotted sidewall of displacer.
A cold head in accordance to claim 2 wherein displacer cyclic movement opens and closes the channel openings completely or partially.
A cold head in accordance to claim 2 wherein entry and return channels are connected to different sections of cold end space separated by cap ceiling fixture or displacer piston cylinder 9.
A cold head in accordance to claim 9, wherein gas migrates between different sections in cold end space through one or mulitple gap openings in cap ceiling fixture or displacer piston cylinder 9.
A cold head in accordance to claim 10, wherein displacer cyclic movement opens and closes the gap openings completely or partially.
A cold head in accordance to claim 10, wherein the position and width of the gap openings are technically defined with reference of stroke length and pressure differential between hot and cold end.
A cold head in accordance to claim 2 characterized in application of matrix materials with anisotropic resistance to different gas flow directions.