Sample freezing point temperature detection device and method

Abstract

The invention discloses a sample freezing point temperature detection device and method.The air outlet end of an air pump communicates with a cold and hot air flow separation device through an electronic pressure regulating valve, the electronic pressure regulating valve is electrically connected with the first control end of a controller, the second control end of the controller is electrically connected with a temperature sensor, and the temperature sensor is arranged at the cold end of a refrigeration device; and the cold and hot air flow separation device is communicated with the refrigeration device. Compressed air is conveyed into the vortex tube through the air pump, and after a vortex chamber in the vortex tube is expanded and accelerated, airflow is divided into a cold stream and a hot stream. The hot air flow is released to the external environment, and the cold air flow enters the hot end of the Peltier refrigerator. The Peltier refrigerator is powered on for refrigeration, and the hot end absorbs heat from the ultralow-temperature cold air flow, so that the cold end of the Peltier is kept in an ultralow-temperature state. After the sample is placed on the vortex tube, the current direction of the Peltier can be adjusted to switch to a heating mode, meanwhile, airflow of the vortex tube is reduced or stopped, and the freezing point temperature of the sample is observed in the temperature rising process.

Description

Technical Field

[0001] The present application relates to the technical field of freezing point detection, and specifically relates to a device and method for detecting the freezing point temperature of a sample. Background Art

[0002] When detecting the "freezing point" of a sample, it is necessary to carry out the detection in an extremely low temperature environment and also requires precise control of the temperature. However, in the traditional process of detecting the "freezing point" of a sample, the operation process is cumbersome, the cost is relatively high, the risk is relatively large, and it is easily affected by the external temperature.

[0003] In order to create an ultra-low temperature condition, high-pressure equipment (such as a high-pressure reactor or a high-pressure chamber) is traditionally used, and these devices can withstand pressures of several thousand atmospheres. However, the use of these devices requires specialized instruments and technologies, further increasing the cost and complexity of the experiment. In addition, there may be deficiencies in the temperature precision control of high-pressure experiments, bringing potential safety hazards.

[0004] In contrast, liquid nitrogen as a refrigerant can achieve precise temperature control, but its cooling time is long, the efficiency is low, and the raw material supply is limited. This makes the detection of the freezing point by liquid nitrogen also face relatively high costs and safety risks. Summary of the Invention

[0005] In order to solve the above technical problems, the present application proposes the following technical solutions:

[0006] In a first aspect, an embodiment of the present application provides a device for detecting the freezing point temperature of a sample, including: an air pump, the air outlet end of the air pump is connected to a cold and hot air separation device through an electronic pressure regulating valve, the electronic pressure regulating valve is electrically connected to a first control end of a controller, a second control end of the controller is electrically connected to a temperature sensor, the temperature sensor is arranged at the cold end of a refrigeration device, and the cold and hot air separation device is connected to the refrigeration device.

[0007] In a possible implementation manner, the cold and hot air separation device includes a vortex tube connected to the electronic pressure regulating valve, an air outlet of the vortex tube is connected to a vortex chamber, a first port of the vortex chamber is connected to a first end of a cold and hot air separation tube, a second end of the cold and hot air separation tube is connected to the external environment, and a second port of the vortex chamber is connected to a cold air pipeline of the refrigeration device.

[0008] In a possible implementation manner, a conical plug is arranged at the second end of the cold and hot air separation tube, a conical end of the conical plug extends into the cold and hot air separation tube, the other end of the conical plug is arranged in a first muffler, and there is a gap between the conical plug and the inner wall of the cold and hot air separation tube.

[0009] In a possible implementation, the refrigeration device is a Peltier cooler. One end of the cold air flow pipe is connected to the second port of the vortex chamber through a second muffler, and the other end of the cold air flow pipe communicates with the groove body of the hot end of the Peltier cooler.

[0010] In a possible implementation, a method for detecting the freezing point temperature of a sample uses the sample freezing point temperature detection device according to any possible implementation of the first aspect, and includes:

[0011] Using a vortex tube and a vortex chamber to generate a cold air flow from the air pumped in by the air pump to cool the hot end of the Peltier cooler;

[0012] The controller adjusts the working current of the Peltier cooler in real time, and a temperature sensor monitors the temperature of the cold end of the Peltier cooler;

[0013] When controlling the Peltier cooler to reach the preset temperature, the controller controls the electronic pressure regulating valve to adjust the air pressure and flow rate, gradually reduce the output of the cold air in the cold and hot air flow separation device, and at the same time adjust the positive and negative voltages of the Peltier cooler to change the current direction, and increase the temperature of the cold end of the Peltier cooler by an increment of the preset temperature difference to observe the change in the state of the sample.

[0014] In a possible implementation, the step of using a vortex tube and a vortex chamber to generate a cold air flow from the air pumped in by the air pump to cool the hot end of the Peltier cooler includes:

[0015] The air pump passes compressed air with a preset pressure into the air inlet of the vortex tube and inputs it into the vortex chamber;

[0016] After the compressed air expands and accelerates in the vortex chamber, it rotates and enters the cold and hot air flow separation tube and is divided into an outer layer of high-temperature spiral air flow and an inner layer of low-temperature spiral air flow;

[0017] The high-temperature spiral air flow flows out through the gap of the conical plug at the second end of the cold and hot air flow separation tube, and the inner layer of low-temperature spiral air flow is blocked by the conical plug. As the air pressure increases, it flows into the cold air flow pipe from the second end of the opposite vortex chamber.

[0018] In a possible implementation, the step of when controlling the Peltier cooler to reach the preset temperature, the controller controls the electronic pressure regulating valve to adjust the air pressure and flow rate, gradually reduce the output of the cold air in the cold and hot air flow separation device, and at the same time adjust the positive and negative voltages of the Peltier cooler to change the current direction, and increase the temperature of the cold end of the Peltier cooler by an increment of the preset temperature difference includes:

[0019] Determine the temperature error between the current temperature and the target temperature: e(t) = T target -T current , where Ttarget is the target temperature, T current is the current temperature;

[0020] Adjust the Peltier cooler and the cold and hot air separation device according to the temperature error, where:

[0021] The output of the Peltier cooler is:

[0022]

[0023] The output of the vortex tube is:

[0024]

[0025] Combine the output of the Peltier cooler and the output of the vortex tube to form an integrated control:

[0026] U(t) = I peliter (t) + Q cooling (t);

[0027] In the above formula, K p is the proportional gain, K p = 0.6K u is the integral gain, i K is the derivative gain, d T is the integral time constant, T u is the derivative time constant, K U is the proportional gain at which the system exhibits continuous oscillation. u In a possible implementation, the opening β of the electronic pressure regulating valve is adjusted to control the flow rate Q and pressure P of the compressed air to control the output of the vortex tube, where:

[0028]

[0029]

[0030] where: C V is the valve flow coefficient, ρ is the air density, P in is the valve inlet pressure, P out is the valve outlet pressure;

[0031] The controller dynamically adjusts β through the PID algorithm to make the flow rate Q meet the set value:

[0032]

[0033] where: e Q (t) = Q set - Q actual and Q set is the set flow rate value, Qactual The actual flow value is detected by the sensor;

[0034] The cold air temperature T of the vortex tube C and the valve inlet pressure P in and the cold flow ratio μ are related as follows:

[0035]

[0036] where T in is the intake air temperature, ΔT is the fixed temperature drop coefficient of the vortex tube, and P0 is the set intake air pressure.

[0037] In a possible implementation, the power Q of the Peltier cooler p is:

[0038]

[0039] where: I is the reverse current passed into the module, α is the Seebeck coefficient, R is the module resistance, K is the heat conduction coefficient, and ΔT is the temperature difference between the hot and cold ends;

[0040] The controller compensates for the reduced cooling capacity of the cold air of the vortex tube through the reverse current I, and the temperature rise rate is achieved as:

[0041]

[0042] where: Q loss is the system heat loss, C is the sample heat capacity, the reverse current I changes with time, and the specific value of I is:

[0043]

[0044] where: e T (t) = T set (t) - T sensor (t), T set (t) is the set temperature increasing according to the preset temperature rise rate, and T sensor (t) is the sample temperature actually detected by the sensor;

[0045] When the sample undergoes a phase change from solid to liquid or gas, the heat capacity C changes suddenly, and the temperature change rate instantaneously approaches zero, satisfying: ∈ approaches 0, and the temperature recorded at this time is the freezing point T ice .

[0046] In the embodiment of the present application, a compressed air is delivered into the vortex tube by an air pump. After the vortex chamber inside the vortex tube undergoes expansion and acceleration, the air flow is divided into two cold and hot streams. The hot air stream is released into the external environment, while the cold air stream enters the hot end of the Peltier cooler. The Peltier cooler is powered on for refrigeration, and the hot end absorbs the heat from the ultra-low temperature cold air stream, so that the cold end of the Peltier cooler remains in the ultra-low temperature state. When the sample is placed on it, the current direction of the Peltier can be adjusted to switch to the heating mode, and at the same time, the air flow of the vortex tube is reduced or stopped. During the temperature rise process, the freezing point temperature of the sample is observed. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a schematic structural diagram of a device for detecting the freezing point temperature of a sample provided by an embodiment of the present application;

[0048] Figure 2 is a schematic flow diagram of a method for detecting the freezing point temperature of a sample provided by an embodiment of the present application;

[0049] Figure 1-2 In, the symbols are represented as:

[0050] 1 - air pump, 2 - electronic pressure regulating valve, 3 - temperature sensor, 4 - vortex tube, 5 - vortex chamber, 6 - cold and hot air flow separation tube, 7 - cold air flow pipeline, 8 - conical plug, 9 - first muffler, 10 - Peltier cooler, 11 - second muffler. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] The following elaborates on this solution in combination with the accompanying drawings and specific embodiments.

[0052] Refer to Figure 1 , the device for detecting the freezing point temperature of a sample provided in this embodiment includes: an air pump 1, the air outlet end of the air pump 1 is connected to a cold and hot air flow separation device through an electronic pressure regulating valve 2, the electronic pressure regulating valve 2 is electrically connected to the first control end of a controller, the second control end of the controller is electrically connected to a temperature sensor 3, the temperature sensor 3 is arranged at the cold end of a refrigeration device, and the cold and hot air flow separation device is connected to the refrigeration device.

[0053] In this embodiment, the cold and hot air flow separation device includes a vortex tube 4 connected to the electronic pressure regulating valve 2, the air outlet of the vortex tube 4 is connected to a vortex chamber 5, the first port of the vortex chamber 5 is connected to the first end of a cold and hot air flow separation tube 6, the second end of the cold and hot air flow separation tube 6 is connected to the external environment, and the second port of the vortex chamber 5 is connected to the cold air flow pipeline 7 of the refrigeration device.

[0054] A conical plug 8 is provided at the second end of the hot and cold air separation tube 6. The conical end of the conical plug 8 extends into the hot and cold air separation tube 6, and the other end of the conical plug 8 is arranged inside the first muffler 9. There is a gap between the conical plug 8 and the inner wall of the hot and cold air separation tube 6.

[0055] In this embodiment, the refrigeration device is a Peltier cooler 10. One end of the cold air duct 7 is connected to the second port of the vortex chamber 5 through a second muffler 11, and the other end of the cold air duct 7 is communicated with the groove of the hot end of the Peltier cooler 10.

[0056] In this embodiment, compressed air with a pressure of 7 bar is introduced into the air inlet of the vortex tube 4 through an air pump 1 and input into the vortex chamber 5 of the vortex tube 4. After expanding and accelerating in the vortex chamber, it rotates. The air flow enters the inside of the heat pipe along the heat pipe wall at a rotational speed of 1,000,000 rpm. Due to the different angular velocities of the inner and outer layer air flows in the hot end tube, the inner layer has a larger acceleration and the outer layer has a smaller angular velocity. Friction is generated between the two air flows. The internal energy of the inner layer air flow decreases and the kinetic energy increases, so the temperature decreases. While the outer layer air flow obtains kinetic energy due to friction and is converted into more internal energy, and the temperature rises. Therefore, the air flow is divided into an outer layer high-temperature spiral air flow and an inner layer low-temperature spiral air flow.

[0057] At the end of the hot and cold air separation tube 6, the outer layer high-temperature spiral air flow flows out through the gap of the conical plug 8 with a built-in temperature regulating valve, while the inner layer low-temperature spiral air flow is blocked by the conical plug 8. Since too much low-temperature air flow is blocked and accumulates at the hot end tube, the air pressure increases and it is then pressed out from the cold air end outlet in the opposite direction.

[0058] In this embodiment, the cold air temperature and cold air flow can also be adjusted by a built-in temperature regulating valve to reach a suitable cold air temperature. Rotate the regulating valve counterclockwise (outward), the cold air temperature decreases and the cold air flow decreases. Rotate the regulating valve clockwise (inward), the cold air temperature increases and the cold air flow increases.

[0059] Holes are drilled in the groove of the Peltier cooler 10 and connected to the cold air end. A large amount of cold air is input to reduce the heat of the hot end of the Peltier cooler 10 inside the groove, and the cooled air is discharged through the exhaust hole at the other end of the groove. At the same time, the temperature sensor 3 monitors the device temperature in real time and adjusts the working current of the Peltier through the controller, and the pressure regulating valve regulates the air pressure and flow of the compressed air at the air inlet port of the vortex tube 4 to achieve more precise temperature control and reach the target temperature, which helps to optimize the refrigeration effect and improve the stability and accuracy of the whole set of equipment.

[0060] After that, the Peltier is powered on, and two different semiconductor materials (n-type and p-type) are arranged in an alternating manner in the circuit inside the Peltier cooler 10 to form a thermoelectric module. When current passes through these semiconductor materials, a temperature difference will be generated at the junction of the n-type and p-type semiconductors when power is turned on. The forward current cooling property of the Peltier itself continues to cool and perform secondary cooling.

[0061] When the temperature is lowered to -75°C required by the experiment, the controller controls the electronic pressure regulating valve 2 to adjust the air pressure and flow, gradually reducing the output of cold air in the vortex tube 4. At the same time, the positive and negative voltages of the components in the Peltier cooler 10 are adjusted to change the direction of the current to achieve heating of the sample. During the recovery process, the temperature rises in increments of 0.01°C, which is convenient for carefully observing the changes in the sample state.

[0062] If a state transition of the sample is observed at a certain temperature point (such as solid to liquid or solid to gas), the temperature is recorded as the "freezing point" of the sample. If no state transition is observed, the cold air output of the vortex tube 4 is continuously reduced until almost no gas is discharged and the temperature sensor 3 shows a constant. At this time, the vortex tube 4 is turned off, and the sample temperature is continuously raised by reducing the working voltage of the Peltier until the "freezing point" is found before 0°C.

[0063] Corresponding to the sample freezing point temperature detection device provided in the above embodiment, the present application also provides an embodiment of a sample freezing point temperature detection method.

[0064] See also Figure 2 The sample freezing point temperature detection method in this embodiment includes:

[0065] S101, using a vortex tube and a vortex chamber to generate a cold airflow from the air input by the air pump to cool the hot end of the Peltier cooler.

[0066] The compressed air of preset pressure is introduced into the vortex chamber through the air pump to the air inlet of the vortex tube. The compressed air expands and accelerates in the vortex chamber and then rotates into the hot and cold air flow separation tube to be divided into an outer layer of high-temperature spiral airflow and an inner layer of low-temperature spiral airflow. The high-temperature spiral airflow flows out through the gap of the conical plug at the second end of the hot and cold air flow separation tube, and the inner layer of low-temperature spiral airflow is blocked by the conical plug. As the airflow pressure increases, it flows into the cold airflow pipeline from the second end of the vortex chamber in the opposite direction.

[0067] Specifically, in this embodiment, compressed air with a pressure of 7 bar is introduced into the vortex chamber of the vortex tube through an air pump. After expansion and acceleration in the vortex chamber, the air rotates and enters the interior of the heat pipe along the heat pipe wall at a rotational speed of 1,000,000 rpm. Due to the different angular velocities of the inner and outer layer airflows in the hot end tube, the inner layer has a larger acceleration and the outer layer has a smaller angular velocity. Friction is generated between the two airflows. The internal energy of the inner layer airflow decreases and its kinetic energy increases, resulting in a temperature decrease. While the outer layer airflow obtains kinetic energy due to friction and is converted into more internal energy, resulting in a temperature increase. Therefore, the airflow is divided into an outer layer of high-temperature spiral airflow and an inner layer of low-temperature spiral airflow.

[0068] At the end of the hot and cold air separation tube, the outer layer of high-temperature spiral airflow flows out through the gap of the conical plug of the built-in temperature regulating valve, while the inner layer of low-temperature spiral airflow is blocked by the conical plug. Since too much low-temperature airflow is blocked and accumulates at the hot end tube, the air pressure increases, and it is then pressed out from the cold air outlet in the opposite direction and flows into the cold air pipeline.

[0069] S102, the working current of the Peltier cooler is adjusted in real time by the controller, and the temperature sensor is used to monitor the temperature at the cold end of the Peltier cooler.

[0070] The Peltier is powered on. Inside the Peltier cooler, two different semiconductor materials (n-type and p-type) are arranged alternately in the circuit to form a thermoelectric module. When current passes through these semiconductor materials, a temperature difference will be generated at the junction of the n-type and p-type semiconductors when powered on. Due to the property of the Peltier itself to cool down with forward current, it continues to refrigerate for secondary cooling.

[0071] When the temperature is reduced to -75 °C required by the experiment, the controller controls the electronic pressure regulating valve to adjust the air pressure and flow rate, and gradually reduces the output of cold air in the vortex tube. At the same time, the positive and negative voltages of the components in the Peltier cooler are adjusted to change the current direction to achieve heating of the sample.

[0072] S103, when the preset temperature is reached by controlling the Peltier cooler, the controller controls the electronic pressure regulating valve to adjust the air pressure and flow rate, and gradually reduces the output of cold air in the hot and cold air separation device. At the same time, the positive and negative voltages of the Peltier cooler are adjusted to change the current direction, and the temperature at the cold end of the Peltier cooler is increased by the increment of the preset temperature difference to observe the change in the state of the sample.

[0073] Determine the temperature error between the current temperature and the target temperature: e(t) = T target -T current where T target is the target temperature and T current is the current temperature. Adjust the Peltier cooler and the hot and cold air separation device according to the temperature error, where: the output of the Peltier cooler is:

[0074]

[0075] The output of the vortex tube is:

[0076]

[0077] Combine the output of the Peltier cooler and the output of the vortex tube to form an integrated control:

[0078] U(t) = I peliter (t) + Q cooling (t);

[0079] In the above formula, K p is the proportional gain, K p = 0.6K u K i is the integral gain, K d is the derivative gain, T u is the integral time constant, T U is the derivative time constant, K u is the proportional gain at which the system exhibits continuous oscillation.

[0080] Control the output of the vortex tube by adjusting the opening β of the electronic pressure regulating valve to control the flow rate Q and pressure P of the compressed air, where:

[0081]

[0082] Where: C V is the valve flow coefficient, ρ is the air density, P in is the valve inlet pressure, P out is the valve outlet pressure;

[0083] The controller dynamically adjusts β through the PID algorithm to make the flow rate Q meet the set value:

[0084]

[0085] Where: e Q (t) = Q set - Q actual Q set is the set flow rate value, Q actual is the actual flow rate value detected by the sensor;

[0086] The cold air temperature T of the vortex tube C has the following relationship with the valve inlet pressure P in and the cold flow ratio μ:

[0087]

[0088] where T in is the intake air temperature, ΔT is the fixed temperature drop coefficient of the vortex tube, and P0 is the set intake air pressure.

[0089] The Peltier cooler power Q p is:

[0090]

[0091] where: I is the reverse current passed into the module, α is the Seebeck coefficient, R is the module resistance, K is the heat conduction coefficient, and ΔT is the temperature difference between the hot and cold ends;

[0092] The controller compensates for the reduced cooling capacity of the cold air of the vortex tube through the reverse current I, and the temperature rise rate is achieved as:

[0093]

[0094] where: Q loss is the system heat loss, C is the sample heat capacity, the reverse current I changes with time, and the specific value of I is:

[0095]

[0096] where: e T (t) = T set (t) - T sensor (t), T set (t) is the set temperature that increases according to the preset temperature rise rate, and T sensor (t) is the sample temperature detected by the sensor;

[0097] When the sample undergoes a phase change from solid to liquid or gas, the heat capacity C changes suddenly, and the temperature change rate instantaneously approaches zero, satisfying: ∈ approaches 0, and the temperature recorded at this time is the freezing point T ice .

[0098] In the embodiments of the present application, "at least one" means one or more, and "a plurality" means two or more. "And / or" describes the association relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can represent the situation where A exists alone, A and B exist simultaneously, or B exists alone. Where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the front and back associated objects. "At least one of the following" and its similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, and c can represent: a, b, c, a - b, a - c, b - c, or a - b - c, where a, b, and c can be single or multiple.

[0099] The above are only specific embodiments of the present application. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. The protection scope of the present application shall be subject to the protection scope of the claims described above.

Claims

1. A device for detecting the freezing point temperature of a sample, characterized in that, Comprising: An air pump, the air outlet end of the air pump is connected to a cold and hot air separation device through an electronic pressure regulating valve, the electronic pressure regulating valve is electrically connected to the first control end of a controller, the second control end of the controller is electrically connected to a temperature sensor, the temperature sensor is arranged at the cold end of a refrigeration device, and the cold and hot air separation device is connected to the refrigeration device.

2. The sample freezing point temperature detection device according to claim 1, wherein The cold and hot air separation device includes a vortex tube connected to the electronic pressure regulating valve, the air outlet of the vortex tube is connected to a vortex chamber, the first port of the vortex chamber is connected to the first end of a cold and hot air separation tube, the second end of the cold and hot air separation tube is connected to the external environment, and the second port of the vortex chamber is connected to the cold air pipeline of the refrigeration device.

3. The sample freezing point temperature detection device according to claim 2, characterized in that, A conical plug is arranged at the second end of the cold and hot air separation tube, the conical end of the conical plug extends into the cold and hot air separation tube, the other end of the conical plug is arranged in a first muffler, and there is a gap between the conical plug and the inner wall of the cold and hot air separation tube.

4. The sample freezing point temperature detection device according to claim 2, characterized in that The refrigeration device is a Peltier cooler, one end of the cold air pipeline is connected to the second port of the vortex chamber through a second muffler, and the other end of the cold air pipeline is connected to the tank body at the hot end of the Peltier cooler.

5. A method for detecting the freezing point temperature of a sample, characterized in that, Using the sample freezing point temperature detection device according to any one of claims 1-4, comprising: Using a vortex tube and a vortex chamber to generate cold air flow from the air input by the air pump to cool the hot end of the Peltier cooler; Real-time adjusting the working current of the Peltier cooler through a controller, and using a temperature sensor to monitor the temperature at the cold end of the Peltier cooler; When controlling the Peltier cooler to reach a preset temperature, controlling the electronic pressure regulating valve through the controller to adjust the air pressure and flow rate, gradually reducing the output of cold air in the cold and hot air separation device, and at the same time adjusting the positive and negative voltage of the Peltier cooler to change the current direction, increasing the temperature at the cold end of the Peltier cooler by an increment of a preset temperature difference, and observing the change of the sample state.

6. The sample freezing point temperature detection method according to claim 5, wherein The using a vortex tube and a vortex chamber to generate cold air flow from the air input by the air pump to cool the hot end of the Peltier cooler includes: Passing compressed air with a preset pressure into the air inlet of the vortex tube through the air pump and inputting it into the vortex chamber; The compressed air expands and accelerates in the vortex chamber and then rotates into the cold and hot air separation tube and is divided into an outer layer of high-temperature spiral air flow and an inner layer of low-temperature spiral air flow; The high-temperature spiral air flow flows out through the gap of the conical plug at the second end of the cold and hot air separation tube, and the inner layer of low-temperature spiral air flow is blocked by the conical plug, and as the air pressure increases, it flows into the cold air pipeline from the second end of the vortex chamber in the opposite direction.

7. The sample freezing point temperature detection method according to claim 5, characterized in that When controlling the Peltier cooler to reach a preset temperature, controlling the electronic pressure regulating valve through the controller to adjust the air pressure and flow rate, gradually reducing the output of cold air in the cold and hot air separation device, and at the same time adjusting the positive and negative voltage of the Peltier cooler to change the current direction, increasing the temperature at the cold end of the Peltier cooler by an increment of a preset temperature difference includes: Determine the temperature error between the current temperature and the target temperature: e(t) = T target - T current , where T target is the target temperature and T current is the current temperature; Adjusting the Peltier cooler and the cold and hot air separation device according to the temperature error, wherein: The output of the Peltier cooler is: The output of the vortex tube is: Combine the Peltier cooler output and the vortex tube output to form an integrated control: U(t) = I peliter (t) + Q cooling (t); In the above formula, K p is the proportional gain, K p = 0.6K u , K i is the integral gain, K d is the derivative gain, T u is the integral time constant, T U is the derivative time constant, K u is the proportional gain at which the system exhibits continuous oscillation.

8. The method for detecting the freezing point temperature of a sample according to claim 7, characterized in that, Control the output of the vortex tube by adjusting the opening β of the electronic pressure regulating valve to control the flow rate Q and pressure P of the compressed air, where: Where: C V is the valve flow coefficient, ρ is the air density, P in is the inlet pressure of the valve, P out is the outlet pressure of the valve; The controller dynamically adjusts β through the PID algorithm to make the flow rate Q meet the set value: Where: e Q (t) = Q set -Q actual , Q set is the set flow value, Q actual is the actual flow value detected by the sensor; Cold air temperature T of the vortex tube C and the valve inlet pressure P in and the cold flow ratio μ is as follows: where T in is the intake air temperature, ΔT is the fixed temperature drop coefficient of the vortex tube, and P0 is the set intake air pressure.

9. The method for detecting the freezing point temperature of a sample according to claim 7, wherein Peltier cooler power Q p is as follows: Where: I is the reverse current applied to the module, α is the Seebeck coefficient, R is the module resistance, K is the heat conduction coefficient, and ΔT is the temperature difference between the hot and cold ends; The controller compensates for the reduced cooling capacity of the cold air of the vortex tube through the reverse current I to achieve a temperature rise rate of: Where: Q loss is the system heat loss, C is the sample heat capacity, the reverse current I changes with time, and the specific value of the I value is: Where: e T (t) = T set (t) - T sensor (t), T set (t) is the set temperature increasing according to the preset temperature rising rate, and T sensor (t) is the sample temperature detected by the sensor; When the sample undergoes a phase change from solid state to liquid or gaseous state instantaneously, the heat capacity C changes abruptly, and the temperature change rate instantaneously approaches zero, satisfying: ∈ approaches 0, and the temperature recorded at this time is the freezing point T ice .

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