CN113941385B - Ultralow-temperature precise constant-temperature device based on liquid nitrogen refrigeration and temperature control method - Google Patents

Ultralow-temperature precise constant-temperature device based on liquid nitrogen refrigeration and temperature control method Download PDF

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CN113941385B
CN113941385B CN202111201247.6A CN202111201247A CN113941385B CN 113941385 B CN113941385 B CN 113941385B CN 202111201247 A CN202111201247 A CN 202111201247A CN 113941385 B CN113941385 B CN 113941385B
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temperature
liquid nitrogen
guide cylinder
tank body
tank
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CN113941385A (en
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余辛波
付杰
孙强
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Guizhou Aerospace Institute of Measuring and Testing Technology
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Guizhou Aerospace Institute of Measuring and Testing Technology
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L7/00—Heating or cooling apparatus; Heat insulating devices
    • B01L7/50—Cryostats
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2300/00—Additional constructional details
    • B01L2300/18—Means for temperature control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2300/00—Additional constructional details
    • B01L2300/18—Means for temperature control
    • B01L2300/1838—Means for temperature control using fluid heat transfer medium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2300/00—Additional constructional details
    • B01L2300/18—Means for temperature control
    • B01L2300/1894—Cooling means; Cryo cooling
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
    • Y02B30/70—Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

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  • Clinical Laboratory Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
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Abstract

The invention discloses an ultralow temperature precise constant temperature device and a temperature control method based on liquid nitrogen refrigeration, wherein the constant temperature device comprises: the heat preservation tank comprises a tank body and a shell; the guide cylinder is arranged in the tank body, and the upper end and the lower end of the guide cylinder are provided with air vents; the air circulation mechanism comprises a circulation fan which is arranged on the inner side of the lower edge of the guide cylinder; the air heating mechanism comprises a temperature sensor and an annular heating belt, the measuring end of the temperature sensor is arranged in the guide cylinder, and the annular heating belt is arranged between the outer side of the guide cylinder and the inner side of the tank body; the liquid nitrogen injection mechanism comprises a fast liquid nitrogen diffusion ring, a slow liquid nitrogen diffusion ring, an ultralow temperature relay and a liquid nitrogen tank; and the programmable temperature controller is electrically connected with the temperature sensor and the ultra-low Wen Ji electric appliance and is electrically connected with the control end of the annular heating belt through the solid-state relay. The invention can rapidly provide a uniform, stable and reliable ultralow-temperature constant-temperature field at the temperature of-80 ℃ to-190 ℃ and can achieve smaller temperature overshoot.

Description

Ultralow-temperature precise constant-temperature device based on liquid nitrogen refrigeration and temperature control method
Technical Field
The invention relates to an ultralow temperature precise constant temperature device and a temperature control method based on liquid nitrogen refrigeration, which are mainly applied to the technical research fields of temperature sensor metering and ultralow temperature test of ultralow Wen Wenou at-80 ℃ to-190 ℃.
Background
In recent years, with the continuous development of China in the fields of aerospace and deep space exploration, ultra-low temperature test technology aiming at ensuring the quality and reliability of aerospace products and spacecraft products is also rapidly advanced. The ultra-low temperature test plays a significant role in product quality and reliability, and has great influence on the development cost, development period and competitive power of the product. The aerospace vehicle flies in deep space and bears severe environments as low as-80 ℃ to-190 ℃, and a constant temperature device capable of realizing ultra-low temperature precise temperature control is urgently needed in the ultra-low temperature reliability test of aerospace-grade products and the ultra-low temperature continuous metering technical field of temperature sensors.
At present, a conventional low-temperature test device adopts a multi-stage compressor refrigeration mode to cool, PID is used for temperature adjustment, and a temperature control sensor senses temperature change to realize temperature adjustment and control. At the temperature region below-100 ℃, the refrigeration equipment is mostly designed and manufactured in a liquid nitrogen refrigeration mode, the temperature of liquid nitrogen at normal pressure is-196 ℃, the existing various ultralow temperature test devices and liquid nitrogen test boxes are usually realized in a fixed point mode, and the temperature region is usually only subjected to fixed point fixed value of a temperature sensor. In addition, due to unreasonable structural design, the temperature control difficulty of liquid nitrogen is extremely high, a uniform, stable and reliable ultralow-temperature constant temperature field is not obtained, and meanwhile, extremely large temperature overshoot is generated in the cooling process, so that various performance indexes of aerospace-grade products under the ultralow-temperature condition cannot be effectively measured, and the temperature measurement accuracy of a temperature sensor under the ultralow-temperature condition cannot be effectively ensured.
Disclosure of Invention
Based on the above, the ultralow temperature precise constant temperature device and the temperature control method based on liquid nitrogen refrigeration can rapidly provide a uniform, stable and reliable ultralow temperature constant temperature field at the temperature of-80 ℃ to-190 ℃ and can achieve smaller temperature overshoot so as to overcome the defects in the prior art.
The technical scheme of the invention is as follows: an ultra-low temperature precision constant temperature device based on liquid nitrogen refrigeration, comprising:
the heat preservation tank comprises a tank body and a shell, wherein the tank body is arranged in the shell, and a working hole is formed in the shell;
the guide cylinder is arranged in the tank body, and air vents are arranged between the upper end and the lower end of the guide cylinder and the inner top surface and the inner bottom surface of the tank body;
the air circulation mechanism comprises a circulation fan, and the circulation fan is arranged on the inner side of the lower edge of the guide cylinder;
the air heating mechanism comprises a temperature sensor and an annular heating belt, the measuring end of the temperature sensor is arranged in the guide cylinder, and the annular heating belt is arranged between the outer side of the guide cylinder and the inner side of the tank body;
the liquid nitrogen injection mechanism comprises a fast liquid nitrogen diffusion ring, a slow liquid nitrogen diffusion ring, an ultralow temperature relay and a liquid nitrogen tank, wherein the fast liquid nitrogen diffusion ring and the slow liquid nitrogen diffusion ring are arranged between the outer side of the guide cylinder and the inner side of the tank body and are connected with the liquid nitrogen tank through an ultralow Wen Ji electric appliance;
and the programmable temperature controller is electrically connected with the temperature sensor and the ultra-low Wen Ji electric appliance, and is electrically connected with the control end of the annular heating belt through a solid relay.
Optionally, the device further comprises a bracket, the bracket comprises:
a base;
the support rod is arranged on the base;
the bottom of the shell is arranged at the top of the supporting rod, the air circulation mechanism further comprises a driving motor and a rotating shaft, the driving motor is arranged on the base, the rotating shaft is rotatably arranged on the base, one end of the rotating shaft is connected with the driving motor, and the other end of the rotating shaft is connected with the circulating fan.
Optionally, an air guide ring is further arranged between the outside of the guide cylinder and the inside of the tank body, a plurality of guide holes are formed in the air guide ring, and the air guide ring is arranged on the side close to the circulating fan.
Optionally, an automatic pressure release valve communicated with the tank body is arranged on the shell.
Optionally, the annular heating belt is a graphene annular heating belt, and a plurality of triangular through holes consistent with the length direction of the guide cylinder are formed in the graphene annular heating belt.
Optionally, the quick liquid nitrogen diffusion ring is provided with nitrogen spraying round holes along the annular inner side surface of the quick liquid nitrogen diffusion ring at intervals, the slow liquid nitrogen diffusion ring is provided with a plurality of capillary spray pipes along the annular inner side surface of the quick liquid nitrogen diffusion ring at intervals, the capillary spray pipes are provided with a plurality of capillary spray nozzles, and the size of the capillary spray nozzles is smaller than the size of the nitrogen spraying round holes.
Optionally, an insulating layer is disposed on the outer side of the tank body and the inner side of the shell.
Optionally, polyurethane low-temperature heat insulation paint is sprayed on the inner side surface and the outer side surface of the tank body and the guide cylinder.
Optionally, the upper end and the lower end of the guide cylinder are connected with the inner top surface and the inner bottom surface of the tank body through a plurality of connecting rods which are arranged on the end surfaces of the guide cylinder at intervals.
The invention also provides a temperature control method of the ultralow temperature precise constant temperature device based on liquid nitrogen refrigeration, which comprises the following steps:
setting a target temperature and starting a circulating fan;
the programmable temperature controller controls the ultralow temperature relay to enable liquid nitrogen in the liquid nitrogen tank to enter the guide cylinder through the rapid liquid nitrogen diffusion ring, and when the temperature sensor detects that the actual temperature value is a preset temperature from the target temperature, the rapid liquid nitrogen diffusion ring is controlled to be closed;
the programmable temperature controller controls the ultralow temperature relay, so that liquid nitrogen in the liquid nitrogen tank enters the guide cylinder through the slow liquid nitrogen diffusion ring, and simultaneously controls the solid relay, so that the annular heating belt heats the gas, and the actual temperature value in the guide cylinder is always in a preset deviation range compared with the target temperature.
The beneficial effects of the invention are as follows: the device has the characteristics of high temperature control speed, small temperature overshoot, high temperature uniformity and high temperature stability, can be designed into a size according to actual requirements, and is mainly used in the fields of temperature sensor calibration and ultralow temperature test research at-80 ℃ to-190 ℃.
Compared with the prior art, the invention has the following main advantages:
1. the invention is different from the method that most liquid nitrogen refrigerating devices adopt liquid nitrogen single-tube direct injection for refrigerating, the constant temperature device adopts the double liquid nitrogen diffusion ring to input liquid nitrogen into the heat preservation tank for cooling, the rapid liquid nitrogen diffusion ring realizes the rapid cooling of the initial section, the slow liquid nitrogen diffusion ring provides a refrigerating source for the temperature control of the constant section, the structure can rapidly and uniformly release liquid nitrogen to the constant temperature device, the temperature field in the constant temperature device cannot be out of control, and the constant and uniform temperature field can be rapidly generated.
2. According to the invention, the graphene annular heating belt is adopted, the graphene heating belt has the characteristics of rapid temperature rise and reduction, good toughness and high efficiency, the honeycomb heating structure formed by the graphene heating film is arranged in the temperature regulation area, and has good heating and flow guiding effects on internal circulating gas.
3. The programmable temperature controller adopted by the invention is used as a brain with intelligent temperature control, each output end has a good PID temperature regulation function, and the precise temperature control can be realized only by writing a simple control program into the programmable controller. The key point of PID temperature control is the debugging of PID parameters, the adjusting mode is divided into manual adjustment and intelligent adjustment, and the theoretical low temperature area can reach the temperature control precision of +/-0.1 ℃.
4. The ultra-low temperature precise constant temperature device is simple to manufacture, easy to realize, low in technical threshold, beneficial to application in actual scientific research production work and good in benefit.
Drawings
FIG. 1 is a general schematic of the present invention;
FIG. 2 is a schematic diagram of a slow liquid nitrogen diffusion ring of the present invention;
FIG. 3 is a schematic view of a graphene annular heating belt of the present invention;
reference numerals:
the liquid nitrogen diffusion device comprises a 1 tank body, a 2 shell, a 3 working hole, a 4 guide cylinder, a 5 circulating fan, a 6 temperature sensor, a 7 annular heating belt, an 8 rapid liquid nitrogen diffusion ring, a 9 slow liquid nitrogen diffusion ring, a 10 ultra-low temperature relay, a 11 liquid nitrogen tank, a 12 programmable temperature controller, a 13 base, a 14 support rod, a 15 driving motor, a 16 rotating shaft, a 17 air guide ring, a 18 automatic pressure relief valve, a 19 capillary spray pipe, a 20 heat insulation layer, a 21 connecting rod and a 22 solid state relay.
Detailed Description
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to the appended drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The invention may be embodied in many other forms than described herein and similarly modified by those skilled in the art without departing from the spirit or scope of the invention, which is therefore not limited to the specific embodiments disclosed below.
Referring to fig. 1 to 3, the ultralow temperature precise thermostat based on liquid nitrogen refrigeration in this embodiment includes a heat preservation tank, a guide cylinder 4, an air circulation mechanism, an air heating mechanism, a liquid nitrogen injection mechanism and a programmable temperature controller 12.
The heat preservation jar, including jar body 1 and casing 2, jar body 1 sets up in casing 2, is equipped with working hole 3 on casing 2. In operation, a sensor or test sample may be placed into the cartridge 4, i.e., the working area, through the working aperture 3. In this embodiment, the tank 1 is a sealed hollow cylindrical housing 2.
In this embodiment, an insulation layer 20 is disposed on the outer side of the tank body 1 and the inner side of the housing 2, and the insulation layer 20 is mainly made of polyurethane foam materials, so as to perform the functions of insulation and heat insulation for the whole insulation tank.
In the embodiment, polyurethane low-temperature heat insulation paint is sprayed on the inner side surface and the outer side surface of the tank body 1 and the guide cylinder 4, so that the heat insulation effect can be further improved.
In this embodiment, the device further comprises a support, the support comprises a base 13 and a plurality of struts 14, the struts 14 are mounted on the base 13, and the bottom of the housing 2 is mounted on the top of the struts 14, so that the housing 2 is in a suspended upright state, and an air circulation mechanism is mounted conveniently.
The guide cylinder 4 is installed in the tank body 1, and ventilation openings are formed between the upper and lower ends of the guide cylinder 4 and the inner top and bottom surfaces of the tank body 1 so as to facilitate the circulation flow of air. The space within the cartridge 4 serves as a working area, i.e. an area into which the sensor or test sample is placed.
In this embodiment, the upper and lower ends of the guide cylinder 4 are connected with the inner top surface and the inner bottom surface of the tank body 1 through a plurality of connecting rods 21 arranged at intervals on the end surfaces of the guide cylinder, and the space between the connecting rods 21 is the air vent.
The air circulation mechanism comprises a circulation fan 5, and the circulation fan 5 is arranged on the inner side of the lower edge of the guide cylinder 4. In the working state, the circulating fan 5 rotates to enable the air in the inner bottom of the guide cylinder 4 to flow upwards, then flows out of the air vent above the guide cylinder 4, then flows into the space below the guide cylinder 4 again through the annular space between the outer side surface of the guide cylinder 4 and the inner side surface of the tank body 1, and the cup is extracted to the upper side by the circulating fan 5, so that the air in the tank body 1, particularly the guide cylinder 4, is kept to flow continuously and uniformly.
In this embodiment, the air circulation mechanism further includes a driving motor 15 and a rotating shaft 16, the driving motor 15 is mounted on the base 13, the rotating shaft 16 is rotatably disposed on the base 13, one end of the rotating shaft 16 is connected with the driving motor 15, and the other end of the rotating shaft 16 is connected with the circulation fan 5. The rotating shaft 16 and the base 13 adopt a sealing rotating structure form so as to ensure that the tank body 1 is airtight.
The air heating mechanism comprises a temperature sensor 6 and an annular heating belt 7, wherein the measuring end of the temperature sensor 6 extends into the guide cylinder 4, and the annular heating belt 7 is arranged between the outer side of the guide cylinder 4 and the inner side of the tank body 1 and is arranged near the middle upper part so as to uniformly heat the circulating air.
In this embodiment, the annular heating belt 7 is a graphene annular heating belt, and the graphene annular heating belt is provided with a plurality of triangular through holes consistent with the length direction of the guide cylinder 4, so that the annular heating belt has the effects of heating and guiding the gas circulated inside.
The liquid nitrogen injection mechanism comprises a fast liquid nitrogen diffusion ring 8, a slow liquid nitrogen diffusion ring 9, an ultralow temperature relay 10 and a liquid nitrogen tank 11, wherein the fast liquid nitrogen diffusion ring 8 and the slow liquid nitrogen diffusion ring 9 are both installed at the middle position between the outer side of the guide cylinder 4 and the inner side of the tank body 1, and are both connected with the liquid nitrogen tank 11 through the ultralow temperature relay 10 respectively. Liquid nitrogen in the liquid nitrogen tank 11 can be quickly led into the tank body 1 through the quick liquid nitrogen diffusion ring 8, and liquid nitrogen in the liquid nitrogen tank 11 can be slowly led into the tank body 1 through the slow liquid nitrogen diffusion ring 9, and the injection area is a temperature regulation area. In particular, the introduced liquid nitrogen is located in the annular space between the outside of the guide cylinder 4 and the inside of the tank body 1 and is separated from the working area in the guide cylinder 4, so that the influence on the temperature fluctuation in the working area can be reduced as much as possible. The liquid nitrogen tank 11 may be a self-pressurizing liquid nitrogen tank 11.
In this embodiment, the fast liquid nitrogen diffusion ring 8 is provided with a plurality of nitrogen spraying round holes along its circumferential inner side surface at intervals, the slow liquid nitrogen diffusion ring 9 is provided with a plurality of capillary spray pipes 19 along its circumferential inner side surface at intervals, the capillary spray pipes 19 are provided with a plurality of capillary spray ports, and the size of the capillary spray ports is smaller than the size of the nitrogen spraying round holes. The number of the capillary nozzles is 7, and liquid nitrogen can be directly and uniformly input into the tank body 1.
And the programmable temperature controller 12 is electrically connected with the temperature sensor 6 and the ultra-low temperature relay 10, and the programmable temperature controller 12 is electrically connected with the control end of the annular heating belt 7 through the solid state relay 22. Furthermore, the programmable temperature controller 12 can receive the temperature value detected by the temperature sensor 6, can realize the switch control of the fast liquid nitrogen diffusion ring 8 and the slow liquid nitrogen diffusion ring 9 by controlling the ultra-low temperature relay 10, and can realize the heating control of the annular heating belt 7 by controlling the solid state relay 22. The programmable temperature controller 12 is used as a brain with intelligent temperature control, each output end has a good PID temperature regulation function, and precise temperature control can be realized only by writing a simple control program into the programmable controller. The key point of PID temperature control is the debugging of PID parameters, the adjusting mode is divided into manual adjustment and intelligent adjustment, and the theoretical low temperature area can reach the temperature control precision of +/-0.1 ℃.
In this embodiment, an air guiding ring 17 is further disposed between the outside of the guiding cylinder 4 and the inside of the tank 1, a plurality of guiding holes are disposed on the air guiding ring 17, and the air guiding ring 17 is disposed on the side close to the circulating fan 5. Specifically, the direction of the diversion hole is consistent with the height direction of the annular space at the inner side of the tank body 1 and the outer side of the diversion cylinder 4, and the flow direction of the liquid nitrogen input by the fast liquid nitrogen diffusion ring 8 and the slow liquid nitrogen diffusion ring 9 can be limited.
In this embodiment, an automatic pressure release valve 18 is provided on the housing 2 and is in communication with the tank 1, and the air pressure inside the thermal insulation tank can be adjusted to maintain balance.
The temperature control method of the ultralow temperature precise constant temperature device based on liquid nitrogen refrigeration in the embodiment comprises the following steps:
first, a target temperature is set, the circulation fan 5 is started, so that air in the guide cylinder 4 flows from bottom to top, enters into an annular space between the outer side of the guide cylinder 4 and the inner side of the tank body 1 from the air vent above the guide cylinder 4, and enters into the guide cylinder 4 for internal circulation through the air vent below the guide cylinder 4.
Secondly, the programmable temperature controller 12 controls the ultra-low temperature relay 10 so that liquid nitrogen in the liquid nitrogen tank 11 enters the guide cylinder 4 through the rapid liquid nitrogen diffusion ring 8, and when the temperature sensor 6 detects that the actual temperature value is a preset temperature from the target temperature, the rapid liquid nitrogen diffusion ring 8 is controlled to be closed.
Finally, the programmable temperature controller 12 controls the ultra-low temperature relay 10 to enable liquid nitrogen in the liquid nitrogen tank 11 to enter the guide cylinder 4 through the slow liquid nitrogen diffusion ring 9, and simultaneously controls the solid relay to enable the annular heating belt 7 to heat the gas, so that the actual temperature value in the guide cylinder 4 is always in a preset deviation range compared with the target temperature, namely, is at ultra-low temperature and constant temperature. During the operation of the device, the automatic pressure relief valve 18 can regulate the air pressure inside the tank 1 to maintain balance.
The ultra-low temperature precise constant temperature device designed by the invention adopts liquid nitrogen refrigeration, and can realize a uniform constant temperature field of-80 ℃ to-190 ℃. The air circulation mechanism completes the rapid circulation and uniformity of the air in the tank body 1, the automatic pressure release valve 18 keeps the balance of the air in the heat preservation tank due to the high pressure in the device caused by the liquid nitrogen input, and the air guide ring 17 can adjust the wind speed and the wind direction along the vertical direction. The precise constant temperature of the whole device is controlled by a programmable temperature controller 12 in a program, the control process is divided into two stages of rapid cooling and precise constant temperature, after the target temperature is set, the programmable temperature controller 12 controls liquid nitrogen to be input into a heat preservation tank from a rapid liquid nitrogen diffusion ring 8 to realize rapid cooling of a working area, when the temperature is close to the target temperature, the programmable temperature controller 12 closes an ultralow temperature relay 10 of the rapid liquid nitrogen diffusion ring 8, and the ultralow temperature relay and a solid state relay 22 of the slow liquid nitrogen diffusion ring 9 are controlled by the program to realize constant temperature of the target temperature. In the whole temperature control process, liquid nitrogen can be uniformly input, the graphene annular heating belt 7 can rapidly and uniformly heat gas, and the gas is rapidly and stably balanced in the heat preservation tank. The whole device has the characteristics of high temperature control speed, small temperature overshoot, high temperature uniformity and high temperature stability. The device can be designed into a size according to actual requirements, and is mainly used in the fields of temperature sensor 6 calibration and ultralow temperature test research at-80 ℃ to-190 ℃.
The foregoing examples illustrate only a few embodiments of the invention and are described in detail herein without thereby limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims (6)

1. Ultra-low temperature precision constant temperature device based on liquid nitrogen refrigeration, which is characterized by comprising:
the heat preservation tank comprises a tank body (1) and a shell (2), wherein the tank body (1) is arranged in the shell (2), and a working hole (3) is formed in the shell (2);
the guide cylinder (4) is arranged in the tank body (1), and ventilation openings are formed between the upper end and the lower end of the guide cylinder (4) and the inner top surface and the inner bottom surface of the tank body (1);
the air circulation mechanism comprises a circulation fan (5), and the circulation fan (5) is arranged on the inner side of the lower edge of the guide cylinder (4);
the air heating mechanism comprises a temperature sensor (6) and an annular heating belt (7), wherein the measuring end of the temperature sensor (6) is arranged in the guide cylinder (4), the annular heating belt (7) is arranged between the outer side of the guide cylinder (4) and the inner side of the tank body (1), the annular heating belt (7) is a graphene annular heating belt, and a plurality of triangular through holes consistent with the length direction of the guide cylinder (4) are formed in the graphene annular heating belt;
the liquid nitrogen injection mechanism comprises a fast liquid nitrogen diffusion ring (8), a slow liquid nitrogen diffusion ring (9), an ultralow temperature relay (10) and a liquid nitrogen tank (11), wherein the fast liquid nitrogen diffusion ring (8) and the slow liquid nitrogen diffusion ring (9) are both arranged between the outer side of the guide cylinder (4) and the inner side of the tank body (1), and are both connected with the liquid nitrogen tank (11) through the ultralow temperature relay (10), nitrogen spraying round holes are formed in the fast liquid nitrogen diffusion ring (8) along the annular inner side surface of the fast liquid nitrogen diffusion ring at intervals, a plurality of capillary spray pipes (19) are formed in the slow liquid nitrogen diffusion ring (9) along the annular inner side surface of the slow liquid nitrogen diffusion ring at intervals, and a plurality of capillary spray pipes are arranged on the capillary spray pipes (19), and the size of each capillary spray pipe is smaller than that of each capillary spray round hole;
the programmable temperature controller (12) is electrically connected with the temperature sensor (6) and the ultralow temperature relay (10), and the programmable temperature controller (12) is electrically connected with the control end of the annular heating belt (7) through the solid state relay (22);
an air guide ring (17) is further arranged between the outer side of the guide cylinder (4) and the inner side of the tank body (1), a plurality of guide holes are formed in the air guide ring (17), and the air guide ring (17) is arranged on the side close to the circulating fan (5);
the temperature control method of the device comprises the following steps:
setting a target temperature and starting a circulating fan (5);
the programmable temperature controller (12) controls the ultralow temperature relay (10) to enable liquid nitrogen in the liquid nitrogen tank (11) to enter the guide cylinder (4) through the rapid liquid nitrogen diffusion ring (8), and when the temperature sensor (6) detects that the actual temperature value is a preset temperature from the target temperature, the rapid liquid nitrogen diffusion ring (8) is controlled to be closed;
the programmable temperature controller (12) controls the ultralow temperature relay (10) to enable liquid nitrogen in the liquid nitrogen tank (11) to enter the guide cylinder (4) through the slow liquid nitrogen diffusion ring (9), and simultaneously controls the solid relay to enable the annular heating belt (7) to heat gas, so that an actual temperature value in the guide cylinder (4) is always in a preset deviation range compared with a target temperature.
2. The ultra-low temperature precise constant temperature device based on liquid nitrogen refrigeration according to claim 1, further comprising a bracket comprising:
a base (13);
a support rod (14) arranged on the base (13);
the bottom of the shell (2) is arranged at the top of the supporting rod (14), the air circulation mechanism further comprises a driving motor (15) and a rotating shaft (16), the driving motor (15) is arranged on the base (13), the rotating shaft (16) is rotatably arranged on the base (13), one end of the rotating shaft (16) is connected with the driving motor (15), and the other end of the rotating shaft (16) is connected with the circulating fan (5).
3. Ultra-low temperature precision thermostat based on liquid nitrogen refrigeration according to claim 1, characterized in that the housing (2) is provided with an automatic pressure relief valve (18) communicating with the tank (1).
4. The ultra-low temperature precise constant temperature device based on liquid nitrogen refrigeration according to claim 1, wherein an insulating layer (20) is arranged on the outer side of the tank body (1) and the inner side of the shell (2).
5. The ultra-low temperature precise constant temperature device based on liquid nitrogen refrigeration according to claim 1, wherein polyurethane low temperature heat insulation paint is sprayed on the inner side surface and the outer side surface of the tank body (1) and the guide cylinder (4).
6. The ultra-low temperature precise constant temperature device based on liquid nitrogen refrigeration according to claim 1, wherein the upper end and the lower end of the guide cylinder (4) are connected with the inner top surface and the inner bottom surface of the tank body (1) through a plurality of connecting rods (21) which are arranged on the end surfaces of the guide cylinder at intervals.
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