Ultralow-temperature refrigerator with linear pulse tube refrigerator combined with methane thermosiphon

Abstract

The ultralow-temperature refrigerator comprises the pulse tube refrigerator, the thermosiphon and an ultralow-temperature refrigerator heat insulation shell, and the pulse tube refrigerator comprises an oil-free linear compressor, a connecting pipe, an after-stage cooler, a heat regenerator, a cold end heat exchanger, a pulse tube, a hot end heat exchanger, an inertia pipe and a pulse tube refrigerator gas reservoir. The thermosiphon comprises a thermosiphon air reservoir, a thermosiphon connecting pipe, a thermosiphon descending section and a thermosiphon ascending section. By utilizing the advantages of environmental protection, energy conservation and no horizontal vibration of the linear opposed pulse tube refrigerating machine, the problems of high energy consumption of a traditional cascade steam compression refrigerating system and unstable vibration operation of other novel refrigerating machines are solved. And the problem of low heat exchange efficiency caused by insufficient heat exchange is solved by utilizing the bent pipeline at the descending section of the thermosiphon. The problem that the ultralow-temperature refrigerator is unstable and unsafe when the refrigerating machine is shut down is solved by utilizing the advantage that the thermosiphon air reservoir is added to relieve overlarge pressure in the thermosiphon when the refrigerating machine is shut down.

Description

Technical Field

[0001] The present invention relates to a refrigerator, in particular to an ultra-low temperature refrigerator combining a linear pulse tube refrigerator with a methane thermosiphon. Background Art

[0002] With the rapid development of the biological, medical, and aerospace industries, the demand for ultra-low temperature refrigerators for the storage of biological materials such as biological samples, reagents, vaccines, and low-temperature testing of special materials is increasing. Such ultra-low temperature refrigerators generally require a storage temperature of around -100°C to -150°C and a stable refrigeration system to achieve long-term reliable storage of biological materials or the reliability of low-temperature test results. In addition, considering the issues of energy conservation, emission reduction, and environmental protection, such ultra-low temperature refrigerators should also meet energy-saving requirements, and there are certain requirements for the start-stop stability and safety of ultra-low temperature refrigerators. Therefore, this patent proposes a design method for ultra-low temperature refrigerators.

[0003] New cryogenic refrigerators offer relatively high refrigeration efficiency under wide temperature gradients (temperature gradients >60°C). Especially when used in ultra-low temperature refrigerators, these new refrigerators can achieve refrigeration efficiencies more than double those of traditional cascade vapor compression systems, offering significant energy savings. Furthermore, since these new refrigerators are oil-free, they eliminate the common oil blockage problem in vapor compression refrigerators, making the system more stable and reliable. Furthermore, these new refrigerators often utilize refrigerants with low global warming potential (GWP), such as nitrogen and helium, making them more environmentally friendly. With the increasing popularity of ultra-low temperature refrigerators, the application prospects of these new refrigerators are expected to expand. Among these new refrigerators, the linear opposed pulse tube refrigerator is widely used due to its simple structure, reliable operation, lack of horizontal vibration, and long life.

[0004] A thermosyphon is a type of heat pipe. Like conventional heat pipes, it transfers heat by utilizing the vaporization and condensation of a working fluid, as well as its automatic circulation without external power. Heat pipes offer numerous advantages over other heat transfer technologies: superior heat transfer efficiency and speed, reliability, isolation, low resistance, compact size, and controllability. Currently, the main heat pipes used in the refrigeration industry are cored heat pipes and coreless heat pipes (thermosyphons). However, both cored and coreless heat pipes have drawbacks. Cored heat pipes require a wick, making their structure more complex. Coreless heat pipes, also known as thermosyphons or gravity heat pipes, do not require a wick, but are subject to gravity and possess directional characteristics. Current thermosyphon designs lack consideration for stability and safety during chiller startup and shutdown. Without an additional thermosyphon gas reservoir, the liquid in the thermosyphon evaporates into a gaseous state during shutdown due to rising temperature. This increased pressure can pose a safety hazard. Summary of the Invention

[0005] The present invention aims to solve the stability and safety problems of ultra-low temperature refrigerators when starting and stopping due to the pressure increase in the thermosyphon tube when the refrigerator is stopped, and proposes an ultra-low temperature refrigerator combined with a linear pulse tube refrigerator and a methane thermosyphon. The advantages of the linear opposed pulse tube refrigerator, such as being environmentally friendly, energy-saving, free of horizontal vibration and suitable for low-temperature refrigeration, are utilized to solve the problems of traditional cascade vapor compression refrigeration systems being non-energy-saving and non-environmentally friendly and other low-temperature refrigeration systems affecting the operating stability of the refrigerator due to vibration. At the same time, the advantages of the thermosyphon tube, such as simple structure, low cost and outstanding heat transfer performance, are utilized and a corresponding thermosyphon gas reservoir is added to solve the safety hazards caused by the complex structure of the core heat pipe and the increase in the pressure in the thermosyphon tube when the refrigerator is stopped, so that the ultra-low temperature refrigerator is energy-saving, environmentally friendly, stable in operation and safe to start and stop.

[0006] The present invention provides a linear pulse tube refrigerator combined with a methane thermosyphon for ultra-low temperature refrigerators. The refrigerator comprises a pulse tube refrigerator, a thermosyphon, and an insulated ultra-low temperature refrigerator housing. The pulse tube refrigerator includes an oil-free linear compressor, connecting pipes, an aftercooler, a regenerator, a cold-end heat exchanger, a pulse tube, a hot-end heat exchanger, an inertia tube, and a pulse tube refrigerator gas reservoir. The thermosyphon includes a thermosyphon gas reservoir, a thermosyphon connecting pipe, a thermosyphon descending section, and a thermosyphon ascending section. When the pulse tube refrigerator is shut down, the temperature of the cold-end heat exchanger rises, causing the liquid in the thermosyphon to evaporate into a gaseous state, dispersing throughout the pipe and the thermosyphon gas reservoir, thereby preventing excessive pressure in the thermosyphon. When the pulse tube refrigerator is started, the temperature of the cold-end heat exchanger gradually decreases, causing gaseous methane to condense into a liquid state and flow down the curved pipe of the thermosyphon descending section. At the end of the thermosyphon descending section, the temperature rises and the methane returns to a gaseous state, flowing along the ascending section, forming a cycle.

[0007] The working medium in the linear opposed pulse tube refrigerator is helium.

[0008] The working fluid in the thermosiphon is methane (CH4), the working temperature range is -100°C to -150°C, and the filling rate α is 30%-40%.

[0009] The descending section of the thermosiphon tube is bent multiple times, and the angle between the pipes is β, ranging from 30° to 40°, to ensure that the liquid can flow down continuously and slow down the liquid flow speed, thereby increasing the heat exchange area and heat exchange efficiency.

[0010] The beneficial effects of the present invention are as follows: compared with existing low-temperature refrigerators, the ultra-low-temperature refrigerator of the linear pulse tube refrigerator combined with the methane thermosyphon has low energy consumption, stable operation, and guaranteed safety during start-up and shutdown. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is an overall diagram of an ultra-low temperature refrigerator that combines a linear pulse tube refrigerator with a methane thermosyphon. DETAILED DESCRIPTION

[0012] like Figure 1 As shown in the overall diagram of an ultra-low temperature refrigerator incorporating a linear pulse tube refrigerator and a methane thermosyphon, the ultra-low temperature refrigerator includes a pulse tube refrigerator, a thermosyphon, and an insulated shell 11 of the ultra-low temperature refrigerator. The pulse tube refrigerator is located on the upper part of the insulated shell of the ultra-low temperature refrigerator and includes an oil-free linear compressor 1, a connecting pipe 2, a stage aftercooler 3, a regenerator 4, a cold-end heat exchanger 5, a pulse tube 6, a hot-end heat exchanger 7, an inertia tube 8, and a pulse tube refrigerator gas reservoir 9. The thermosyphon includes a thermosyphon gas reservoir 101, a thermosyphon connecting pipe 102, a thermosyphon descending section 103, and a thermosyphon ascending section 104.

[0013] The total length of the thermosyphon descending section 103 and the thermosyphon ascending section 104 is L, the length of the thermosyphon connecting pipe 102 is l, the diameter of the thermosyphon is d, and the volume of the thermosyphon gas reservoir 101 is V. g The low-temperature liquid density of methane in the thermosyphon ultra-low temperature refrigerator is ρ1, and the low-temperature gas density is ρ2. The normal-temperature gas density at the thermosyphon gas reservoir 101 under this pressure is ρ3. The normal-temperature density is ρ4 when the ultra-low temperature refrigerator is shut down. The methane filling rate during operation is α. According to the law of conservation of mass, the formula for solving the volume of the thermosyphon gas reservoir can be obtained.

[0014]

[0015] The working fluid, methane, flows directional within the thermosyphon, flowing counterclockwise through the descending section 103 and ascending section 104. The specific operating principle of the thermosyphon ultra-low temperature refrigerator of the present invention is as follows: when the pulse tube refrigerator is shut down, the temperature of the cold-end heat exchanger rises, and the liquid in the thermosyphon evaporates into a gaseous state, spreading throughout the pipe and thermosyphon gas reservoir 101, preventing excessive pressure in the thermosyphon pipe. When the pulse tube refrigerator is started, the temperature of the cold-end heat exchanger gradually decreases. When the temperature here falls below the methane boiling point of -161.5°C, the gaseous methane begins to condense into a liquid state and flows down the curved pipe of the descending section 103 of the thermosyphon. The refrigeration temperature of the descending section 103 of the thermosyphon is between -150°C and -100°C. As methane condenses into liquid form in the thermosyphon's descending section 103, the pressure decreases, causing the higher-pressure methane in the thermosyphon reservoir 101 to continuously flow from the thermosyphon connecting pipe 102 toward the lower pressure. The temperature at the end of the thermosyphon's descending section 103 rises, transforming it into a gaseous state and flowing along the thermosyphon's ascending section 104, forming a cycle. When the temperature of the cold-end heat exchanger stabilizes and the pressure in the thermosyphon reservoir 101 is equal to the pressure within the thermosyphon, the thermosyphon reservoir 101 no longer flows methane into the thermosyphon. To prevent cold leakage and ensure that the thermosyphon reservoir 101 remains at a constant temperature, the thermosyphon connecting pipe 102 can be made of stainless steel with poor thermal conductivity and insulated. Its length, l, should be at least 15 cm.

[0016] The low-temperature circulating working fluid matches the operating temperature of the ultra-low temperature refrigerator. The present invention is aimed at ultra-low temperature refrigerators with an operating temperature range of -100°C to -150°C. The working fluid in the thermosyphon is methane CH4, and the liquid filling rate α during operation is 30%-40%. Compared with the ethane working fluid, the refrigeration temperature range is lower, but the gas pressure at room temperature is higher when the refrigerator is shut down. Therefore, it is necessary to install a thermosyphon gas reservoir 101 to improve the start-up and shutdown safety of the ultra-low temperature refrigerator.

[0017] The pulse tube refrigerator adopts a linear opposed pulse tube refrigerator, the refrigerant is helium, and there is no horizontal vibration, which can improve the stability and safety of the ultra-low temperature refrigerator.

[0018] The pipe of the descending section 103 of the thermosiphon is bent multiple times, and the angle between the pipes is β, ranging from 30° to 40°, to ensure that the liquid can flow down continuously and slow down the liquid flow speed, thereby increasing the heat exchange area and heat exchange efficiency.

[0019] The linear opposed pulse tube refrigerator of the present invention provides cooling through the cold-end heat exchanger 5, which is then transferred via a thermosyphon, cooling the contents of the ultra-low temperature refrigerator to a low temperature. The thermosyphon descending section 103 features multiple bends to increase heat exchange area and efficiency. The addition of a thermosyphon air reservoir 101 prevents safety hazards caused by excessive thermosyphon pressure during refrigerator shutdown. The linear opposed pulse tube refrigerator eliminates horizontal vibration, enhancing the stability and safety of the ultra-low temperature refrigerator.

Claims

1. A linear pulse tube refrigerator combined with a methane thermosyphon ultra-low temperature refrigerator, characterized in that: It includes a pulse tube refrigerator, a thermosiphon and an insulated shell of an ultra-low temperature refrigerator. The pulse tube refrigerator includes an oil-free linear compressor, a connecting pipe, a stage aftercooler, a regenerator, a cold-end heat exchanger, a pulse tube, a hot-end heat exchanger, an inertia tube, and a pulse tube refrigerator gas reservoir. The thermosiphon includes a thermosiphon gas reservoir, a thermosiphon connecting pipe, a thermosiphon descending section and a thermosiphon ascending section. When the pulse tube refrigerator is shut down, the temperature of the cold-end heat exchanger rises, and the liquid in the thermosiphon evaporates into a gaseous state, spreading throughout the pipe and the thermosiphon gas reservoir to prevent the pipe pressure of the thermosiphon from being too high. When the pulse tube refrigerator is started, the temperature of the cold-end heat exchanger gradually decreases, and the gaseous methane begins to condense into a liquid state and flows down along the curved pipe of the thermosiphon descending section. At the end of the thermosiphon descending section, the temperature rises and turns into a gaseous state, and flows along the thermosiphon ascending section to form a cycle. Assume that the total length of the thermosyphon descending section and the thermosyphon ascending section is L, the length of the thermosyphon connecting pipe is l, the diameter of the thermosyphon is d, and the volume of the thermosyphon gas reservoir is V. g The low-temperature liquid density of methane in the thermosyphon ultra-low temperature refrigerator is ρ1, the low-temperature gas density is ρ2, the normal temperature gas density at the thermosyphon gas reservoir under this pressure is ρ3, and the normal temperature density when the ultra-low temperature refrigerator is shut down is ρ4. The methane filling rate during operation is α. According to the law of conservation of mass, the formula for solving the volume of the thermosyphon gas reservoir can be obtained.

2. The ultra-low temperature refrigerator incorporating a linear pulse tube refrigerator and a methane thermosyphon according to claim 1, characterized in that: The pulse tube refrigerator adopts a linear opposed pulse tube refrigerator without horizontal vibration, which can improve the stability and safety of the ultra-low temperature refrigerator.

3. The ultra-low temperature refrigerator incorporating a linear pulse tube refrigerator and a methane thermosyphon according to claim 1 or 2, characterized in that: The working medium in the thermosiphon is methane (CH4), the working temperature range is -100°C to -150°C, and the liquid filling rate is 30%-40%.

4. The ultra-low temperature refrigerator incorporating a linear pulse tube refrigerator and a methane thermosyphon according to claim 3, characterized in that: The descending section of the thermosiphon tube is bent multiple times, and the angle between the pipes is β, ranging from 30° to 40°, to ensure that the liquid can flow down continuously and slow down the liquid flow speed, thereby increasing the heat exchange area and heat exchange efficiency.

5. The ultra-low temperature refrigerator incorporating a linear pulse tube refrigerator and a methane thermosyphon according to claim 1, characterized in that: In order to prevent cold leakage and ensure that the thermosiphon gas reservoir maintains normal temperature, the thermosiphon connecting pipe uses stainless steel pipes with poor thermal conductivity and adopts insulation measures. Its length should be greater than 15cm.

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