Liquid metal heat soaking blackbody furnace based on induction heating

Abstract

This invention provides a liquid metal homogenizing blackbody furnace based on induction heating, belonging to the technical field of infrared radiation temperature measurement equipment. It includes a coaxial graphite tube, liquid metal, insulation material, a water-cooled coil, a temperature measuring device, and a high-frequency power control module. The coaxial graphite tube consists of an inner and outer graphite tube, forming an annular gap between them. The inner cavity of the inner graphite tube constitutes the blackbody cavity. The liquid metal fills the annular gap, generating eddy current heat under an alternating magnetic field. The insulation material covers the outer graphite tube. The water-cooled coil is wound around the outside of the insulation material. The temperature measuring device is attached to the wall of the coaxial graphite tube. The high-frequency power control module is electrically connected to the water-cooled coil to provide high-frequency current, causing it to generate an alternating magnetic field. This invention achieves high spatial temperature uniformity and long-term operational stability of the blackbody radiation cavity wall at high temperatures without relying on precise coil arrangement or mechanical motion compensation.

Description

Technical Field

[0001] This invention belongs to the field of infrared radiation temperature measurement equipment technology, specifically relating to a liquid metal homogenizing blackbody furnace based on induction heating. Background Technology

[0002] A blackbody furnace is a standard radiation source used to provide high emissivity, high temperature stability, and excellent spatial uniformity. It is widely used in the calibration and standardization of optical and thermal measurement equipment such as infrared thermometers, radiation thermometers, and remote sensors. Especially in high-temperature (e.g., above 1000℃) metrology, the uniformity of the temperature field on the blackbody cavity wall is extremely demanding. Therefore, achieving high-precision temperature uniformity of the blackbody radiation cavity at high temperatures has always been a core technical challenge in blackbody furnace design.

[0003] Currently, most existing blackbody furnaces employ resistance heating or induction heating. For example, Chinese utility model patent CN205209245U discloses a high-frequency heating micro-tube blackbody furnace, which achieves heating by winding a high-frequency coil around a metal conductor rod and utilizing the eddy current effect. However, this solution relies on the thermal conductivity of the metal rod itself to achieve temperature uniformity. Limited by the thermal conductivity of solid materials, temperature differences in the axial and radial directions are still difficult to avoid, and it is only suitable for teaching or low-precision scenarios, failing to meet the requirements of high-precision measurement.

[0004] Another approach, such as the high-precision blackbody furnace described in Chinese utility model patent CN202195889U, uses graphite as the blackbody cavity material and incorporates induction heating. However, its temperature uniformity is highly dependent on the precise spiral arrangement of the induction coils and the thermal homogeneity of the graphite cavity itself. Even a slight deviation in coil winding or anisotropy in the graphite material can lead to localized hot or cold spots, affecting the consistency of the radiation field. Furthermore, this structure requires complex sealing, water cooling, and atmosphere protection systems, increasing equipment cost and maintenance difficulty.

[0005] Furthermore, Chinese invention patent application CN117824846A proposes a uniform high-temperature blackbody furnace based on rotary heating, which dynamically compensates for temperature unevenness by mechanically rotating the heating rod in conjunction with an axial telescopic mechanism. Although this method improves the circumferential and axial uniformity to some extent, it introduces moving parts such as a rotary table and telescopic motor, which not only complicates the structure and reduces reliability, but may also interfere with the stability of radiation measurements due to mechanical vibration. Moreover, long-term operation poses risks of wear and failure, making it difficult to meet the stringent requirements of national metrological standards for long-term stability and maintenance-free operation.

[0006] The above solutions are all based on the heat conduction and homogenization mechanism of solid-phase materials. The heat transfer rate is limited by the thermal conductivity of the material, and it is impossible to overcome the bottleneck of thermal resistance between the heating source and the cavity wall. Under high-temperature conditions (>2000℃), even with expensive highly oriented pyrolytic graphite, it is still difficult to control the axial temperature gradient within ±2℃. At the same time, in order to meet the temperature homogenization requirements, the induction coil needs to be designed as segmented adjustable or supplemented with a precision motion mechanism, resulting in a complex system structure, high cost, and reduced reliability. Summary of the Invention

[0007] To address the technical challenges of existing blackbody homogenization methods that rely on mechanical motion, increase manufacturing burden, and fail to overcome the physical limitations of solid-state material thermal conductivity, thus hindering rapid, adaptive, and full-area temperature uniformity in blackbody cavities above 2000℃, this invention provides a liquid metal homogenization blackbody furnace based on induction heating. This furnace achieves a highly uniform temperature distribution within the blackbody cavity and enables stable operation at high temperatures (depending on the boiling point of the selected filler metal), meeting the stringent requirements for temperature uniformity and stability in the calibration of infrared thermometers and thermal radiation standard sources. This invention utilizes liquid metal simultaneously as both the heating element and the homogenizing medium, achieving rapid adaptive homogenization through electromagnetic-thermal-fluid multi-field coupling and without mechanical motion. It simultaneously optimizes temperature uniformity, response speed, and structural reliability, and can be applied to the calibration and standardization of infrared thermometers, thermal imagers, radiometers, and other infrared temperature measurement equipment. This invention achieves high spatial temperature uniformity and long-term operational stability of the blackbody radiation cavity wall at high temperatures without relying on precise coil arrangements or mechanical motion compensation.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A liquid metal homogenizing blackbody furnace based on induction heating includes a coaxial graphite tube, liquid metal, insulation material, a water-cooled coil, a temperature measuring device, and a high-frequency power control module. The coaxial graphite tube consists of an inner graphite tube and an outer graphite tube, with a closed annular gap between them. The inner cavity of the inner graphite tube forms the blackbody cavity. The liquid metal fills the annular gap to generate eddy current heat under an alternating magnetic field, while simultaneously providing high thermal conductivity and natural convection to achieve dynamic, real-time, axial, and radial temperature equilibrium. The insulation material covers the outer graphite tube. The water-cooled coil is wound around the outside of the insulation material. The temperature measuring device is attached to the wall of the coaxial graphite tube. The high-frequency power control module is electrically connected to the water-cooled coil to provide high-frequency current, causing it to generate an alternating magnetic field. The high-frequency power control module is signal-connected to the temperature measuring device to receive the temperature signal measured by the temperature measuring device and adjust the output power according to the temperature signal.

[0010] This invention employs an induction-heated blackbody furnace with a double-layer graphite tube structure and filled with low-melting-point liquid metal. Its beneficial effects include:

[0011] 1. Highly Uniform Temperature Field: The low-melting-point, high-boiling-point metal (such as gallium indium tin alloy with a melting point of approximately 29℃ and a boiling point of approximately 2400℃) filling the space between the inner and outer graphite tubes forms a liquid metal upon heating. The liquid metal generates eddy current heat in a high-frequency alternating magnetic field. Simultaneously, due to its excellent electrical conductivity, high thermal conductivity, and fluidity, it uniformly transfers heat to the inner graphite tube wall through heat conduction and convection. Even if there is uneven heating in some areas, the temperature can be quickly balanced, significantly improving the uniformity of the temperature field on the blackbody cavity wall.

[0012] 2. Wide temperature range and high extreme temperature: Utilizing high-frequency induction heating technology, the high temperature resistance of graphite materials, and the high boiling point of liquid metal, the system can achieve a working temperature of up to 2000℃ or more, breaking through the temperature limits of traditional constant temperature baths or resistance furnaces.

[0013] 3. Rapid Response and High Energy Efficiency: An external water-cooled high-frequency induction coil simultaneously induces eddy currents in both the graphite tube and the internal liquid metal, resulting in rapid and uniform heating. The excellent thermal conductivity and convective heat transfer characteristics of the liquid metal significantly improve heating efficiency. Attaching thermocouples or platinum resistance sensors to the graphite tube wall for real-time temperature measurement, and adjusting the high-frequency power supply through feedback, effectively compensates for disturbances, achieving rapid temperature stabilization and dynamic fast response.

[0014] 4. Compact structure and easy operation: It eliminates the need for complex stirring machinery and bulky liquid circulation systems, simplifying the equipment structure, making maintenance convenient and operation simple. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a liquid metal homogenizing blackbody furnace based on induction heating according to the present invention.

[0016] In the attached diagram, the following labels are used: 1 is a water-cooled coil; 2 is thermal insulation material; 3 is a coaxial graphite tube; 4 is liquid metal; 5 is a temperature measuring device; and 6 is a high-frequency power control module. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0018] like Figure 1As shown, the present invention discloses a liquid metal homogenizing blackbody furnace based on induction heating, comprising a water-cooled coil 1, insulation material 2, a coaxial graphite tube 3, liquid metal 4, a temperature measuring device 5, and a high-frequency power control module 6. The water-cooled coil 1 is wound around the outside of the insulation material 2 of the coaxial graphite tube 3 to conduct high-frequency current and generate an induced magnetic field; the insulation material 2 is disposed between the water-cooled coil 1 and the coaxial graphite tube 3, i.e., covering the outside of the coaxial graphite tube 3, to reduce heat loss; the coaxial graphite tube 3 is composed of two layers of graphite tubes, inner and outer.

[0019] Specifically, the coaxial graphite tube 3 is made of high-purity graphite and has a U-shaped coaxial structure with one end closed and the other open. It consists of an inner graphite tube and an outer graphite tube coaxially fitted together. An annular gap is formed between the inner and outer graphite tubes, and the inner cavity of the inner graphite tube constitutes a blackbody cavity, realizing blackbody radiation. Liquid metal 4 fills the annular gap between the inner and outer graphite tubes of the coaxial graphite tube 3. It has excellent electrical conductivity, high thermal conductivity, and strong fluidity at high temperatures, and can generate eddy current heat in an alternating magnetic field. At the same time, through high thermal conductivity and natural convection, it makes the temperature field of the inner graphite tube wall uniform. The annular gap is closed. The temperature measuring device 5 is attached to the inner wall of the inner graphite tube facing the annular gap and is used to measure the temperature of the blackbody cavity. The high-frequency power supply control module 6 includes a heating power adjustment and temperature control feedback unit and is connected to the water-cooled coil 1. The insulation material 2 has an opening at the same position as the coaxial graphite tube 3.

[0020] Preferably, the temperature measuring device 5 is a thermocouple or a platinum resistance thermometer.

[0021] When the blackbody furnace is working, the water-cooled coil 1 is energized with a high-frequency current to generate an alternating magnetic field, which heats the coaxial graphite tube 3 and the liquid metal 4 inside it. The liquid metal 4 melts and circulates, transferring heat evenly to the tube wall of the inner graphite tube. The temperature measuring device 5 sends the temperature signal to the high-frequency power control module 6, which automatically adjusts the heating power of the water-cooled coil 1 to achieve precise control and stable maintenance of the temperature inside the blackbody cavity.

[0022] Preferably, the inner wall of the inner graphite tube 3 of the coaxial graphite tube forms a blackbody cavity, and the surface is frosted and coated with a high emissivity coating. Graphite has excellent high-temperature resistance properties.

[0023] Preferably, the liquid metal 4 is a low-melting-point, high-boiling-point metal, such as a gallium-indium-tin alloy. This metal changes from a solid to a liquid state when heated, and it has high thermal conductivity and fluidity. It transfers heat to the inner graphite tube wall through its own convection motion, resulting in a uniform temperature distribution.

[0024] Preferably, the water-cooled coil 1 is a high-frequency induction coil wound around the outside of the coaxial graphite tube 3. The water-cooled coil 1 generates an alternating magnetic field when a high-frequency alternating current is applied, induction heating the coaxial graphite tube 3 and the liquid metal 4. The water-cooled coil 1 adopts a water-cooled structure. Preferably, the water-cooled coil 1 is a spiral coil wound around a hollow copper tube, uniformly wound around the outside of the insulation material 2. Inlet and outlet water outlets are respectively provided at both ends of the hollow copper tube for connecting to an external cooling water circulation system. During equipment operation, the Joule heat generated by the coil is removed by deionized circulating cooling water, maintaining the normal operating temperature of the coil and ensuring the long-term safe operation of the coil and electronic components. Induction heating causes the coaxial graphite tube and the internal liquid metal 4 to heat up uniformly and quickly reach the set temperature.

[0025] Preferably, the high-frequency power control module 6 is electrically connected to the water-cooled coil 1 and simultaneously signal-connected to the temperature measuring device 5, for realizing high-frequency power output and closed-loop temperature control. Specifically, the high-frequency power control module 6 includes a heating power adjustment unit and a temperature control feedback unit; wherein, the temperature control feedback unit includes a signal amplification circuit, a 16-bit AD conversion circuit, and a PID control circuit connected in sequence, which can receive the millivolt-level temperature analog signal output by the temperature measuring device 5, amplify it, convert it from analog to digital, and input it to the PID control circuit. The PID control circuit outputs a power adjustment signal based on the difference between the preset temperature and the measured temperature, as well as the axial temperature gradient data; the heating power adjustment unit includes a rectifier circuit, an IGBT inverter circuit, and an impedance matching circuit connected in sequence, with the control terminal of the IGBT inverter circuit electrically connected to the output terminal of the PID control circuit, which can adjust the high-frequency current power output to the water-cooled coil 1 according to the power adjustment signal. The temperature signal is fed back to the high-frequency power control module 6 through the temperature measuring device 5, and the high-frequency power control module 6 adjusts the power output of the inductive power supply to achieve high-precision temperature control and maintenance.

[0026] Preferably, the liquid metal 4 can be other low-melting-point, high-boiling-point alloys, such as gallium-indium alloys, gallium-lead alloys, etc.

[0027] Preferably, the material and thickness of the insulation material 2 can be adjusted according to the application.

[0028] In this invention, the role of liquid metal is not simply heat transfer, but rather to encapsulate it between two layers of graphite tubes, forming a closed, self-circulating heat exchange system. In this structure, the liquid metal simultaneously plays a dual role of high thermal conductivity and natural convection, achieving dynamic, real-time, axial, and radial temperature equilibrium. This heat exchange mechanism is independent of the uniformity of the heating source; even if there are slight non-uniformities in the water-cooled coil 1, the liquid metal can automatically compensate. In other words, unlike existing solutions that rely on solid heat conduction or external mechanical regulation, this invention introduces liquid metal into the blackbody furnace cavity structure for the first time, utilizing its high fluidity and high thermal conductivity at high temperatures to form a forced convection heat transfer loop within the cavity wall, thereby achieving high temperature field uniformity without moving parts.

[0029] This invention is applicable to high-temperature blackbody radiation sources with temperatures ranging from 1500°C to 2500°C, and preferably exhibits significantly better temperature uniformity than existing technologies at temperatures of 2000°C and above.

[0030] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A liquid metal homogenizing blackbody furnace based on induction heating, characterized in that, The system includes a coaxial graphite tube, liquid metal, insulation material, water-cooled coil, temperature measuring device, and high-frequency power control module. The coaxial graphite tube consists of an inner graphite tube and an outer graphite tube, with a closed annular gap between them. The inner cavity of the inner graphite tube forms a blackbody cavity. The liquid metal fills the annular gap and is used to generate eddy current heat under an alternating magnetic field. It also plays a dual role of high thermal conductivity and natural convection, achieving dynamic, real-time, axial, and radial temperature equilibrium. The insulation material is wrapped around the outside of the outer graphite tube; the water-cooling coil is wound around the outside of the insulation material; the temperature measuring device is attached to the wall of the coaxial graphite tube; the high-frequency power control module is electrically connected to the water-cooling coil to provide high-frequency current to the water-cooling coil, so that it generates an alternating magnetic field; the high-frequency power control module is signal connected to the temperature measuring device to receive the temperature signal measured by the temperature measuring device and adjust the output power according to the temperature signal.

2. The liquid metal homogenizing blackbody furnace based on induction heating according to claim 1, characterized in that, The liquid metal is a low-melting-point, high-boiling-point metal.

3. A liquid metal homogenizing blackbody furnace based on induction heating according to claim 2, characterized in that, The liquid metal is a gallium-indium-tin alloy, a gallium-indium alloy, or a gallium-lead alloy.

4. The liquid metal homogenizing blackbody furnace based on induction heating according to claim 1, characterized in that, The coaxial graphite tube is a U-shaped coaxial structure with one end completely closed and the other end open. The open end is equipped with a high-purity graphite end cap identical to that of the coaxial graphite tube. The high-purity graphite end cap is bonded to the open end face of the inner graphite tube and the open end face of the outer graphite tube using a high-temperature resistant graphite adhesive. The annular gap is completely sealed by high-temperature sintering, forming an integrated all-graphite sealed structure without interface gaps.

5. The liquid metal homogenizing blackbody furnace based on induction heating according to claim 4, characterized in that, The outer graphite tube has an injection hole that communicates with the annular gap. The injection hole is equipped with a high-temperature resistant sealing plug for injecting and sealing liquid metal.

6. A liquid metal homogenizing blackbody furnace based on induction heating according to claim 1, characterized in that, The temperature measuring device is a thermocouple or a platinum resistance thermometer.

7. A liquid metal homogenizing blackbody furnace based on induction heating according to claim 1, characterized in that, The inner wall surface of the blackbody cavity is frosted and coated with a high emissivity coating.

8. A liquid metal homogenizing blackbody furnace based on induction heating according to claim 1, characterized in that, The water-cooled coil is a spiral coil wound with a hollow copper tube. The two ends of the hollow copper tube are respectively provided with water inlet and water outlet for connecting to an external cooling water circulation system, and the coil's working temperature is maintained by circulating cooling water.

9. A liquid metal homogenizing blackbody furnace based on induction heating according to claim 1, characterized in that, The high-frequency power supply control module includes a heating power adjustment unit and a temperature control feedback unit.

10. A liquid metal homogenizing blackbody furnace based on induction heating according to claim 9, characterized in that, The temperature control feedback unit receives the signal from the temperature measuring device and transmits it to the heating power adjustment unit, which adjusts the heating power of the water-cooled coil according to the signal.

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