An apparatus and method for measuring the specific heat of a solid sample.

Abstract

This invention discloses an apparatus and method for measuring the specific heat of solid test samples. The apparatus includes a container, a data acquisition and processing system, a storage compartment, and a heater. Based on the 3ω method, this invention constructs an apparatus for measuring the specific heat of solid test samples, which solves the technical problems of measurement interference from conductive materials in molten samples, the impact of oxidation on accuracy during measurement, and damage to the measuring wire during the addition and melting of molten samples. Specifically, separating the storage compartment and the container, and then using a protective gas to transport and inject the solid test sample into the first chamber after melting in the storage compartment, reduces disturbance to the measuring wire and ensures that the experiment is conducted under a protective gas atmosphere, thereby improving the success rate of the experiment.

Description

Technical Field

[0001] This invention belongs to the field of fluid thermophysical property measurement technology, and specifically relates to an apparatus and method for measuring the specific heat of a solid sample. Background Art

[0002] Liquid metals generally refer to metallic materials that remain liquid within a normal or operating temperature range, possessing advantages such as a wide liquid temperature range, high thermal conductivity, and high electrical conductivity. With industrial progress, liquid metal materials are finding increasingly widespread applications in fields such as chemical engineering, electronics, energy, industrial safety, and computers. For example, lead-bismuth alloys have become the preferred material for fourth-generation fast reactor targets and coolants (explanatory, operating temperature 200℃~600℃); liquid gallium thermal grease offers chip heat dissipation performance dozens of times higher than traditional thermal grease (explanatory, operating temperature 30℃~125℃); and aluminum-lithium metals have broad application prospects in aerospace structural materials (explanatory, operating temperature above 150℃). Against the backdrop of the important "dual carbon" goal, high-temperature molten salt thermal storage (explanatory, operating temperature 60℃~1000℃) is of great significance for promoting green energy transition, responding to extreme events, ensuring energy security, and promoting high-quality energy development. Therefore, it is essential to study the heat dissipation performance and specific heat of liquid metals and molten salts in their applications in relevant fields.

[0003] Currently, commonly used methods for measuring the specific heat of fluids mainly include flow-type calorimetry, adiabatic calorimetry, and differential scanning calorimetry. Flow-type calorimetry is a steady-state isothermal calorimetry suitable for experimental measurements of various low-viscosity fluids. It has advantages such as simple structure, convenient operation, and high measurement accuracy. However, its measurement temperature is below 200℃, molten metals and molten salts have poor fluidity and can clog the measurement pipe, and the sample volume required is relatively large. The intermittent heating method, commonly used in adiabatic calorimetry, is a steady-state measurement method widely used in actual isobaric heat capacity measurements. However, its measurement temperature is below 400℃, and measuring easily vaporized samples can contaminate the instrument's interior; failure to clean it promptly can affect subsequent measurement accuracy. Differential scanning calorimetry is a non-steady-state thermal conductivity calorimetry with advantages such as low sample consumption, short measurement time, high sensitivity, and wide application. However, its measurement temperature is below 550℃. Based on the further explanation of the above measurement methods, the steady-state method has the advantages of high test accuracy and simple data processing, but it is difficult to establish thermal equilibrium, the measurement time cost is high and it is easily affected by convection; the unsteady-state method has the advantages of short test cycle, small sample size, and can generally measure multiple thermophysical property data at the same time, and has been widely studied and used in recent years.

[0004] With the widespread application of computer data in recent years, experimental equipment and methods have been greatly improved, making it possible to acquire and process data that was previously difficult to achieve using conventional instruments and calculation methods. This has also made unsteady-state methods increasingly important in the testing of thermophysical properties. Among them, the 3ω method has a wide temperature range, short measurement time, is insensitive to thermal radiation and thermal convection, has low requirements for sample size and cleanliness outside the measurement chamber, can measure bulk materials, thin films, gases and liquids, has low microfabrication requirements, the test system is easier to assemble, and the measuring components are easy to replace. By adjusting the algorithm, a variety of thermophysical parameters can be obtained, making it an ideal measurement method.

[0005] In summary, existing methods present challenges in measuring the specific heat of high-temperature molten samples (interpretive, especially above 600°C), and the application requirements of high-temperature molten metals and salts necessitate improvements in these methods. Currently, no apparatus is available to measure the specific heat of high-temperature molten metals or salts using the 3ω method, primarily due to the following unresolved technical issues:

[0006] The 3ω method for measuring high-temperature molten metals and molten salts requires addressing the technical challenges of maintaining insulation between the micron-sized measuring wire and solder joints and the molten sample at high temperatures; the technical challenge of damaging the precision measuring wire when the molten sample, which is solid at room temperature, is added to the apparatus or melts and flows; and the technical challenge of affecting the accuracy of measurements due to oxidation of the easily oxidized molten sample during heating and measurement. Summary of the Invention

[0007] The purpose of this invention is to provide an apparatus and method for measuring the specific heat of a solid sample, thereby solving one or more of the aforementioned technical problems. The technical solution of this invention utilizes the 3ω method to construct an apparatus and method for measuring the specific heat of a solid sample, which can solve the technical problems of measurement interference from conductive matter in molten samples, accuracy issues caused by oxidation during measurement, and damage to the measuring wire during the addition and melting process of the molten sample.

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

[0009] The present invention provides an apparatus for measuring the specific heat of a solid sample, comprising: a container, a data acquisition and processing system, a storage compartment, and a heater;

[0010] The container section and the storage section are disposed in the heating chamber of the heater, and the heater is used to heat and melt the solid sample to be tested into a molten sample to be tested;

[0011] The container is provided with a first chamber, a second chamber, a first connecting pipe, and a second connecting pipe; wherein, the first chamber is connected to the second chamber, and a measuring wire for measurement is provided in the first chamber; one end of the first connecting pipe is connected to the second chamber, and the other end is connected to the outside for the outlet of protective gas; the inlet of the second connecting pipe is connected to the first chamber, and the outlet is used to introduce protective gas or a molten sample to be tested; wherein, the molten sample to be tested is molten metal or molten salt to be tested;

[0012] The acquisition end of the data acquisition and processing system is electrically connected to the measuring wire; the data acquisition and processing system is used to acquire the third harmonic voltage of the measuring wire, perform data processing based on the acquired third harmonic voltage, and output the specific heat of the molten sample to be tested;

[0013] The storage section is provided with a third chamber for storing the solid sample to be heated and melted. The inlet of the third chamber is equipped with a first sealing cover, which is provided with a vent pipe for introducing protective gas. The outlet of the third chamber is connected to the outlet of the second connecting pipe for introducing protective gas into the first chamber and the second chamber, or for introducing the molten sample to be tested into the first chamber through the second connecting pipe via the protective gas.

[0014] A further improvement of the present invention is that, in the data acquisition and processing system, in the step of data processing based on the acquired third harmonic voltage, the expression for calculating the specific heat of the molten sample to be tested is:

[0015]

[0016]

[0017] In the formula, λ is the thermal conductivity, and U ω It is the first harmonic voltage, α is the temperature coefficient of resistance of the measuring wire, l is the length of the measuring wire, R is the resistance of the measuring wire, ρ is the density of the molten sample to be tested, ω is the frequency, r is the radius of the measuring wire, and U 3ω It is the third harmonic voltage, γ is the Euler constant, and i is the complex unit.

[0018] A further improvement of the present invention is that the heater is a molybdenum heating device with a rated temperature of 1800°C.

[0019] A further improvement of the present invention is that,

[0020] The first chamber is equipped with a replaceable liquid storage chamber;

[0021] The third chamber is equipped with a replaceable storage chamber;

[0022] The second connecting pipe is a replaceable delivery pipe.

[0023] A further improvement of the present invention is that the specific structure of the measuring wire provided in the first chamber includes: a clamp, a measuring wire, and two conductive rods of different lengths;

[0024] The clamp is fixedly installed in the first chamber or the second chamber; the two conductive rods of different lengths are fixedly installed on the clamp; the two ends of the measuring wire are respectively fixedly set on the two conductive rods of different lengths, and the measuring wire, the two conductive rods of different lengths, and the fixed connection between the measuring wire and the conductive rods are all provided with an insulating coating.

[0025] A further improvement of the present invention is that,

[0026] The measuring wire is a platinum wire whose resistance is linear with temperature and can withstand high temperatures up to 870℃.

[0027] The conductive rod is made of platinum with a melting point of 1772℃;

[0028] The coating material is CrAlN;

[0029] The clamp is made of ceramic.

[0030] A further improvement of the present invention is that both the container section and the storage section are made of 310S stainless steel.

[0031] A further improvement of the present invention is that it further includes:

[0032] Temperature and pressure measurement and control system, used to measure and control the ambient temperature and ambient pressure of the molten sample to be tested;

[0033] The temperature and pressure measurement and control system includes a thermocouple and a pressure gauge; the thermocouple is used to measure the temperature of the heating chamber of the heater, and the pressure gauge is used to monitor the inflow and outflow pressure of the protective gas.

[0034] A further improvement of the present invention is that the data acquisition and processing system includes an adjustable resistor box, a first adder, a second adder, a lock-in amplifier, an electrode flange, and a LabVIEW program module; wherein,

[0035] The adjustable resistor box and the measuring wire are connected in series via the electrode flange. The adjustable resistor box is used to adjust the bridge balance to achieve differential signal input in the subsequent measurement process.

[0036] The first adder and the second adder are used to amplify the signals at both ends of the measuring wire and the adjustable resistor box, respectively, and are connected to the A input terminal and the B input terminal of the lock-in amplifier, respectively.

[0037] The lock-in amplifier is used to provide circuit voltage and receive measurement signals, which are then input into the LabVIEW program module via a data acquisition card.

[0038] The LabVIEW program module is used to process data based on the acquired third harmonic voltage and output the specific heat of the molten sample to be tested.

[0039] The present invention provides a method for measuring the specific heat of a solid sample, based on the above-mentioned device for measuring the specific heat of a solid sample, wherein the venting pipe is provided with a first valve and the first connecting pipe is provided with a second valve.

[0040] The method for measuring the specific heat of a solid sample includes the following steps:

[0041] Add the solid metal or salt to be tested to the third chamber of the storage section;

[0042] Open the first valve and the second valve, introduce protective gas into the first chamber and the second chamber of the container through the first valve, and release the protective gas through the second valve, so that the first chamber and the second chamber are filled with protective gas, and then close the first valve and the second valve.

[0043] The solid sample to be tested is heated and melted into a molten sample by a heater. The first valve is opened and the second valve is kept closed. A protective gas for oxidizing the molten sample is introduced, allowing the molten sample to be tested to slowly flow into the first chamber until it meets the preset required amount. The first valve is then closed and the measurement begins. The slow inflow is to prevent the molten sample to be tested from splashing.

[0044] After the measurement begins, the third harmonic voltage of the measuring wire is acquired through the data acquisition and processing system. Based on the acquired third harmonic voltage, data processing is performed to output the specific heat of the molten sample to be tested.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] In this invention, a device for measuring the specific heat of molten metals and molten salts is constructed based on the 3ω method. This device solves the technical problems of measurement interference from the conductivity of the molten sample, the impact of oxidation on accuracy during measurement, and damage to the measuring wire during the addition and melting of the molten sample. Specifically, many molten metals and molten salts are solid at room temperature. In traditional device designs, the addition and melting of the molten sample can damage the precision measuring wire. This invention separates the storage section and the container section (i.e., the measurement section). After the solid sample is melted in the storage section, it is injected into the first chamber (i.e., the measurement chamber) using a protective gas. This reduces disturbance to the measuring wire and ensures that the experiment is conducted under a protective gas atmosphere, thereby improving the success rate of the experiment.

[0047] Furthermore, to address the technical problem of interference from conductive molten samples in the measurement, this invention employs a vacuum ion plating technique on the conductive rod and measuring wire, ensuring that the conductive rod, measuring wire, and fixed connection points all possess high-temperature resistance and insulation properties. Since most molten metals and molten salts are conductive, the above method can lead to an expansion of the measurement range.

[0048] Furthermore, to address the technical problem of oxidation during the measurement of easily oxidized molten samples, this invention employs a protective gas inlet / outlet passage and a pressure gauge, which ensures that the experiment is conducted under a protective gas atmosphere and that the pressure remains constant during the experiment, thereby improving the accuracy of the measurement results. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art are briefly introduced below; obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0050] Figure 1 This is a partial structural schematic diagram of a device for measuring the specific heat of a solid sample according to an embodiment of the present invention.

[0051] Figure 2 This is a partially enlarged structural diagram of the measuring wire in the container section in an embodiment of the present invention;

[0052] Figure 3 This is a schematic diagram of the circuit structure of the data acquisition and processing system in an embodiment of the present invention;

[0053] In the diagram, 1 is a lock-in amplifier; 2 is the first adder; 3 is the second adder; and 4 is an adjustable resistor box.

[0054] 5. First valve; 6. Pressure gauge; 7. First sealing cover; 8. Storage section; 9. Replaceable storage chamber; 10. Replaceable delivery pipe; 11. Second valve; 12. Thermocouple; 13. Second sealing cover; 14. Electrode flange; 15. Buffer chamber; 16. Container section; 17. Replaceable liquid storage chamber; 18. Heater; 19. Conductive rod; 20. Clamp; 21. Measuring wire. Detailed Implementation

[0055] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0056] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0057] The present invention will now be described in further detail with reference to the accompanying drawings:

[0058] Please see Figure 1 The present invention provides an apparatus for measuring the specific heat of molten metal or molten salt, comprising: a container section 16 and a data acquisition and processing system;

[0059] The container section 16 is provided with a first chamber (i.e., a measuring chamber), a second chamber (i.e., a buffer chamber 15), a first connecting pipe, and a second connecting pipe; wherein, the first chamber is connected to the second chamber, and a measuring wire 21 for measurement is provided in the first chamber; one end of the first connecting pipe is connected to the second chamber, and the other end is connected to the outside for the passage of protective gas; one end of the second connecting pipe is connected to the first chamber, and the other end is connected to the outside for the passage of the molten sample to be tested or the protective gas; wherein, the molten sample to be tested is molten metal to be tested or molten salt to be tested; the second connecting pipe can be a replaceable delivery pipe 10;

[0060] The acquisition end of the data acquisition and processing system is electrically connected to the measuring wire 21 to obtain the third harmonic voltage of the measuring wire 21, and to perform data processing based on the obtained third harmonic voltage to output the specific heat of the molten sample to be tested.

[0061] In data processing, the expression for calculating the specific heat of the molten sample to be tested is as follows:

[0062]

[0063]

[0064] In the formula, λ is the thermal conductivity, and U ω It is the first harmonic voltage, α is the temperature coefficient of resistance of the measuring wire, l is the length of the measuring wire, R is the resistance of the measuring wire, ρ is the density of the molten sample to be tested, ω is the frequency, r is the radius of the measuring wire, and U 3ω It is the third harmonic voltage, γ=0.57721566… is Euler's constant, and i is the complex unit.

[0065] In the above embodiments of the present invention, a storage section 8 is further provided; the storage section 8 is provided with a third chamber and a heater 18; wherein, the third chamber is used to store solid materials to be heated and melted, and the heater 18 is used to provide heat to melt the materials; the inlet of the third chamber is provided with a removable first sealing cover 7; the first sealing cover 7 is provided with a vent pipe for introducing protective gas; the outlet of the third chamber is connected to the outlet end of the second connecting pipe; wherein, the vent pipe is provided with a first valve 5, and the protective gas can be an inert gas such as argon or nitrogen, used for oxidation protection of the sample to be tested at high temperature; the heater 18 can be a molybdenum heating device with a rated temperature of 1800℃.

[0066] Specifically, the storage section is mainly used to heat and melt the solid sample to be tested and then inject it into the first chamber of the container section to prevent the solid sample to be tested from melting directly in the measuring chamber and damaging the measuring wire used for measurement; the first sealing cover is used to isolate air and prevent the molten sample to be tested from oxidizing at high temperature; the first valve is used to control the inflow and sealing of the protective gas.

[0067] In this embodiment of the invention, the preferred material for the container part 16 is 310S stainless steel (melting point 1470℃, softening temperature 800℃), which is resistant to high temperature, corrosion and oxidation.

[0068] In a further preferred embodiment of the present invention, a replaceable storage chamber 9 is provided in the third chamber.

[0069] A further preferred embodiment of the present invention includes: a temperature and pressure measurement and control system for controlling and measuring the temperature and pressure of the molten material to be measured; the thermocouple 12 is an armored platinum-rhodium thermocouple with a temperature measurement range of 0 to 1700°C; wherein, the temperature and pressure measurement and control system includes a hollow heating cavity (i.e., the heating chamber of the heater 18 mentioned above), and a fixed storage part 8 and a container part 16 are fixed inside the heating cavity; the thermocouple 12 is inserted into the preset gap between the heating cavity and the container part 16 for temperature measurement and control; the heating cavity is installed entirely in an insulation box, and the space between the insulation box and the heating cavity is filled with insulation material; the pressure measurement and control is achieved by connecting a pressure gauge 6 to the gas path before the first valve 5 and after the second valve 11 to monitor the pressure of gas inflow and outflow.

[0070] The embodiments of the present invention are illustrative in that the storage section, the second chamber, and the first chamber are arranged vertically from top to bottom. The main component of the storage section is a replaceable storage chamber 9, which is connected to the replaceable liquid storage chamber 17 in the first chamber via a replaceable delivery pipe 10 (exemplarily a replaceable thin pipe). The replaceable storage chamber 9 is mainly used to store solid test samples and to heat the solid test samples to melt them using a heating device. The melted samples flow directly into the replaceable liquid storage chamber 17 through the replaceable thin pipe along the inner wall of the replaceable liquid storage chamber 17, preventing the molten material from splashing and protecting the measuring wire 21.

[0071] Explanatoryly, since the measured molten material may remain in the storage chamber and the inner wall of the replaceable capillary tube after each experiment, or even cause blockage of the capillary tube, the replaceable containers and replaceable capillary tubes used are disposable consumables to eliminate the impact of contamination from previous experiments on subsequent experiments and improve experimental accuracy.

[0072] Please see Figure 2 In a specific exemplary embodiment of the present invention, the measuring wire 21 for measurement in the first chamber comprises a clamp 20, two coated conductive rods 19 of different lengths, and the measuring wire 21. The two coated conductive rods 19 are mounted in parallel on the clamp 20, and the measuring wire 21 is fixedly disposed (or welded) between the two coated conductive rods 19. The measuring wire 21 serves both as a heating element to provide heat to the molten sample to be tested and as a measuring element to measure the voltage signal change caused by the temperature rise.

[0073] In this embodiment of the invention, vacuum ion plating (CrAlN, temperature resistance 1000℃, resistance 10) is performed on the surfaces of the measuring wire 21 and the conductive rod 19. 6 The Ω) is insulated to prevent the conductivity of the molten sample from affecting the measurement. Specifically, the measuring wire 21 is a platinum wire with a linear resistance to temperature and a high temperature resistance of 870℃, the conductive rod 19 is a platinum rod with a melting point of 1772℃, and the clamp 20 is circular, with a size slightly larger than the diameter of the first chamber and smaller than the diameter of the second chamber, and is made of ceramic material (95 ceramic, insulating, temperature resistance of 1500℃); the upper end is connected to the data acquisition and processing system through the electrode flange 14.

[0074] In a specific and exemplary embodiment of the present invention, the container part 16 may be a cylinder, with a second chamber and a first chamber sequentially excavated from the center of its top surface to its bottom surface. Both the second chamber and the first chamber are cylindrical cavities, and the diameter of the second chamber is larger than that of the first chamber, serving as a buffer chamber 15 and a measuring chamber, respectively. Further illustratively, the buffer chamber 15 has a larger diameter, is located above the measuring chamber, and has a much larger volume than the measuring chamber. During the experiment, the buffer chamber 15 and the measuring chamber are filled with protective gas. When the molten sample to be tested flows into the measuring chamber from the storage part 8 to displace the protective gas, it can buffer the chamber pressure. At the same time, if the experimental temperature rises and causes the molten sample to be tested to expand and overflow the measuring chamber, it can buffer the pressure and improve experimental safety. The measuring chamber has a smaller diameter, is located below the buffer chamber 15, and is the main location for the measurement experiment. The second chamber has a second sealing cap 13 at its opening. An electrode flange 14, the first connecting pipe, and the second connecting pipe are fixedly mounted on the second sealing cap 13. The electrode flange 14 can be connected to the data acquisition and processing system via a wire led from the conductive rod 19 of the coated material, while ensuring a tight seal. The first connecting pipe is equipped with a second valve 11 to control the outflow of gas and ensure sealing during the experiment. The second sealing cap 13 acts as a seal to isolate air, preventing oxidation of the molten material and improving experimental accuracy. The replaceable sleeve inside the measuring chamber is a disposable consumable, functioning similarly to a replaceable container or thin tube, eliminating the impact of previous experiments on the measuring chamber's contamination of subsequent experiments.

[0075] Please see Figure 3 In this embodiment of the invention, the data acquisition and processing system consists of an adjustable resistor box 4, a first adder 2, a second adder 3, a lock-in amplifier 1, a measurement circuit, and a LabVIEW program module. The adjustable resistor box 4 and the measuring wire 21 are connected in series via a connecting line led out from the electrode flange 14. The adjustable resistor box 4 is used to adjust the bridge balance for differential signal input in subsequent measurement processes. The first adder 2 and the second adder 3 amplify the signals at both ends of the measuring wire 21 and the adjustable resistor box 4, and are respectively connected to the A and B input terminals of the lock-in amplifier 1. The lock-in amplifier 1 provides circuit voltage and receives measurement signals, which are then input to the computer via a data acquisition card. The LabVIEW program module on the computer is used to record and process experimental data.

[0076] This invention provides a method for measuring the specific heat of molten metal or molten salt, including data acquisition and data processing, with the specific steps as follows:

[0077] At the start of the experiment, the storage section, testing section, and container are assembled. The assembled experimental body is then fixed inside the heating chamber. Solid metal or salt to be tested is added to the storage chamber. Protective gas is then introduced into the measuring chamber through the first valve 5 and discharged through the second valve 11, filling the first chamber (measuring chamber) and the second chamber (buffer chamber 15) inside the container with protective gas. The first valve 5 and the second valve 11 are then closed. The test temperature is adjusted to the set value using the heater 18 in the temperature and pressure control system, and the pressure is maintained at the measurement condition using the pressure gauge 6, heating the storage chamber and measuring chamber until the sample melts. The first valve 5 is then opened while the second valve 11 remains closed, allowing a small flow of protective gas to slowly flow into the measuring chamber of the container until the required amount is reached. The first valve 5 is then closed, and the measurement begins.

[0078] At the start of the measurement, the lock-in amplifier 1 is first locked to the first harmonic ω, and then the resistance of the precision adjustable resistor box 4 is adjusted to be equal to the internal resistance of the measuring wire 21; then, the lock-in amplifier 1 is locked to the third harmonic 3ω, and the given voltage amplitude is adjusted; the frequency of the initial voltage is changed, and the third harmonic voltage change of the measuring wire 21 at different frequencies is recorded by LabVIEW.

[0079] During data processing, the specific heat of the molten sample to be tested is calculated using the collected data.

[0080] In a specific embodiment of the present invention, the lock-in amplifier 1 provides a first-harmonic voltage to the measurement circuit. Due to the Joule heating effect and the linear relationship between the resistance and temperature of the measuring wire 21, the composite voltage (first-harmonic and third-harmonic) generated across the measuring wire 21 is input to the lock-in amplifier 1. Simultaneously, the first-harmonic voltage across the adjustable resistor box 4 connected in series with the measuring wire 21 is also input to the lock-in amplifier 1. The differential input of the two signals to the lock-in amplifier 1 yields a precise third-harmonic voltage, which is then acquired and processed by the subsequent LabVIEW program module. The storage section is mainly used to heat and melt the solid sample to be tested and inject it into the measurement chamber of the container section 16, preventing the solid sample to be tested from melting directly in the measurement chamber and damaging the measuring wire 21. The container section 16 mainly includes a measurement chamber and a buffer chamber 15. The measurement chamber is the main location for the measurement experiment, and the buffer chamber 15 can buffer the pressure increase caused by dripping the molten material to be measured and improve the safety of the experiment. The testing section includes the measuring wire 21, the conductive rod 19, and the clamp 20. A lock-in amplifier 1 provides a voltage with a frequency of ω to the conductive rod 19 of the coating. This voltage generates a current with a frequency of ω within the measuring wire 21. Due to the Joule heating effect, the measuring wire 21 heats the molten material at a frequency of 2ω. Since the resistance of the measuring wire 21 is linearly related to its temperature, the resistance of the measuring wire 21 oscillates at a frequency of 2ω. The increased resistance, together with the alternating current at a frequency of ω, generates a voltage component with a frequency of 3ω. This voltage component, along with the voltage at a frequency of ω, is input to the lock-in amplifier 1 via wiring. The temperature and pressure control system is used to control and measure the temperature and pressure of the molten material to be measured. The experimental body is heated to a given temperature by the heater 18, causing the solid sample to be measured in the storage chamber to melt and flow into the measuring chamber. Since the measuring wire 21 heats the molten sample to be measured at a frequency of 2ω, the third harmonic voltage change of the measuring wire 21 at different frequencies can be obtained by changing the frequency of the initial voltage, thereby allowing the calculation of the specific heat of the molten sample at a given temperature and frequency.

[0081] In summary, the specific process of this invention embodiment is as follows:

[0082] (1) Install the experimental body and test the circuit:

[0083] The storage section, measuring section, and container section 16 are assembled to form the experimental body. The assembled experimental body is then connected to the temperature and pressure control system. The continuity of the measuring circuit is checked by inspecting the resistance. After the inspection is completed, the solid sample to be tested is loaded into the storage chamber.

[0084] (2) Heating the experimental body:

[0085] Open the first valve 5 and the second valve 11, and introduce protective gas into the container section 16 through the first valve 5 until all the air in the container section 16 is expelled. Then close the first valve 5 and the second valve 11. Adjust the temperature to the set value through the temperature and pressure control system. After the solid sample to be tested is heated to a molten state, open the first valve 5 and introduce a small flow of protective gas to allow the molten sample to drip into the measuring chamber until the amount meets the experimental requirements. Then close the first valve 5.

[0086] (3) Adjusting the bridge balance:

[0087] When the lock-in amplifier 1 is locked to the first harmonic ω, the resistance of the adjustable resistor box 4 is adjusted to be equal to the internal resistance of the measuring wire 21. This makes it easier to eliminate the first harmonic voltage component through signal differential input during subsequent measurements, thereby obtaining the pure third harmonic voltage component.

[0088] (4) Data acquisition:

[0089] Lock-in amplifier 1 is locked to its third harmonic, 3ω. The initial voltage amplitude is then adjusted to ensure it is neither too high, leading to excessive temperature rise in measuring wire 21, nor too low, resulting in minimal changes in experimental data and reduced measurement accuracy. After adjusting the voltage, the third harmonic voltage variation of measuring wire 21 at different frequencies is obtained by changing the frequency of the initial voltage.

[0090] (5) Data processing: The specific heat of the molten sample to be tested is calculated using the collected data by the following formula, and the calculation expression is as described above;

[0091] In summary, this invention specifically discloses an apparatus and method suitable for measuring the specific heat of molten metals and molten salts. Currently, no existing apparatus or method can measure the specific heat of molten metals and molten salts using the 3ω method. The apparatus of this invention has a compact structure, is easy to manufacture and experiment with, and uses LabVIEW to acquire the third harmonic voltage change of the measuring wire at different frequencies, calculating the specific heat of the molten sample using relevant formulas. This invention has a wide measurement temperature range (room temperature to above 600℃), can measure samples that are solid at room temperature but melt at high temperatures, and can measure samples that are easily oxidized at high temperatures and have high conductivity. The testing system is easy to assemble, and various information can be obtained by adjusting the algorithm, making it a relatively ideal measuring device.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An apparatus for measuring the specific heat of a solid sample, characterized in that, include: Container section (16), data acquisition and processing system, storage section (8) and heater (18); The container section (16) and the storage section (8) are disposed in the heating chamber of the heater (18), and the heater (18) is used to heat and melt the solid sample to be tested into a molten sample to be tested; The container (16) is provided with a first chamber, a second chamber, a first connecting pipe, and a second connecting pipe; wherein, the first chamber is connected to the second chamber, and a measuring wire (21) for measurement is provided in the first chamber; one end of the first connecting pipe is connected to the second chamber, and the other end is connected to the outside for the purpose of releasing protective gas; the inlet of the second connecting pipe is connected to the first chamber, and the outlet is used to release protective gas or a molten sample to be tested; wherein, the molten sample to be tested is molten metal or molten salt to be tested; The acquisition end of the data acquisition and processing system is electrically connected to the measuring wire (21); the data acquisition and processing system is used to acquire the third harmonic voltage of the measuring wire (21), perform data processing based on the acquired third harmonic voltage, and output the specific heat of the molten sample to be tested; The storage section (8) is provided with a third chamber for storing solid test samples to be heated and melted; the inlet of the third chamber is equipped with a first sealing cover (7), and the first sealing cover (7) is provided with a vent pipe for introducing protective gas; the outlet of the third chamber is connected to the outlet of the second connecting pipe for introducing protective gas into the first chamber and the second chamber, or for introducing the molten test sample into the first chamber through the second connecting pipe via the protective gas.

2. The apparatus for measuring the specific heat of a solid sample according to claim 1, characterized in that, In the data acquisition and processing system, during the data processing step based on the acquired third harmonic voltage, the expression for calculating the specific heat of the molten sample to be tested is as follows: In the formula, λ is the thermal conductivity, and U ω It is the first harmonic voltage, α is the temperature coefficient of resistance of the measuring wire, l is the length of the measuring wire, R is the resistance of the measuring wire, ρ is the density of the molten sample to be tested, ω is the frequency, r is the radius of the measuring wire, and U 3ω It is the third harmonic voltage, γ is the Euler constant, and i is the complex unit.

3. The apparatus for measuring the specific heat of a solid sample according to claim 1, characterized in that, The heater (18) is a molybdenum heating device with a rated temperature of 1800℃.

4. The apparatus for measuring the specific heat of a solid sample according to claim 1, characterized in that, The first chamber is provided with a replaceable liquid storage chamber (17); The third chamber is provided with a replaceable storage chamber (9); The second connecting pipe is a replaceable delivery pipe (10).

5. The apparatus for measuring the specific heat of a solid sample according to claim 1, characterized in that, The first chamber is equipped with a measuring wire (21) for measurement. The specific structure includes: a clamp (20), a measuring wire (21), and two conductive rods (19) of different lengths. The clamp (20) is fixedly installed in the first chamber or the second chamber; the two conductive rods (19) of different lengths are fixedly installed on the clamp (20); the two ends of the measuring wire (21) are respectively fixedly set on the two conductive rods (19) of different lengths, and the measuring wire (21), the two conductive rods (19) of different lengths, and the fixed connection between the measuring wire (21) and the conductive rods (19) are all provided with an insulating coating.

6. The apparatus for measuring the specific heat of a solid sample according to claim 5, characterized in that, The measuring wire (21) is a platinum wire whose resistance is linear with temperature and can withstand high temperatures up to 870℃; The conductive rod (19) is made of platinum with a melting point of 1772°C; The coating material is CrAlN; The clamp (20) is made of ceramic.

7. The apparatus for measuring the specific heat of a solid sample according to claim 1, characterized in that, Both the container section (16) and the storage section (8) are made of 310S stainless steel.

8. The apparatus for measuring the specific heat of a solid sample according to claim 1, characterized in that, Also includes: Temperature and pressure measurement and control system, used to measure and control the ambient temperature and ambient pressure of the molten sample to be tested; The temperature and pressure measurement and control system includes a thermocouple (12) and a pressure gauge (6); the thermocouple (12) is used to measure the temperature of the heating chamber of the heater (18), and the pressure gauge (6) is used to monitor the inflow and outflow pressure of the protective gas.

9. The apparatus for measuring the specific heat of a solid sample according to claim 1, characterized in that, The data acquisition and processing system includes an adjustable resistor box (4), a first adder (2), a second adder (3), a lock-in amplifier (1), an electrode flange (14), and a LabVIEW program module; among which, The adjustable resistor box (4) and the measuring wire (21) are connected in series via the connecting wire led out from the electrode flange (14). The adjustable resistor box (4) is used to adjust the bridge balance to realize the signal differential input in the subsequent measurement process. The first adder (2) and the second adder (3) are used to amplify the signals at both ends of the measuring wire (21) and the adjustable resistor box (4), respectively, and are connected to the A input terminal and the B input terminal of the lock-in amplifier (1), respectively. The lock-in amplifier (1) is used to provide circuit voltage and receive measurement signals, which are input into the LabVIEW program module via the acquisition card; The LabVIEW program module is used to process data based on the acquired third harmonic voltage and output the specific heat of the molten sample to be tested.

10. A method for measuring the specific heat of a solid sample, characterized in that, Based on the device for measuring the specific heat of a solid sample as described in claim 1, the ventilation pipe is provided with a first valve (5), and the first connecting pipe is provided with a second valve (11); The method for measuring the specific heat of a solid sample includes the following steps: Add solid metal or salt to be tested to the third chamber of the storage section (8); Open the first valve (5) and the second valve (11), introduce protective gas into the first chamber and the second chamber of the container section (16) through the first valve (5), and release the protective gas through the second valve (11) so that the first chamber and the second chamber are filled with protective gas, and close the first valve (5) and the second valve (11). The solid sample to be tested is heated and melted into a molten sample to be tested by the heater (18). The first valve (5) is opened and the second valve (11) is kept closed. A protective gas for oxidizing the molten sample to be tested is introduced, and the molten sample to be tested slowly flows into the first chamber until it meets the preset required amount. The first valve (5) is closed and the measurement begins. The slow flow is used to prevent the molten sample to be tested from splashing. After the measurement begins, the third harmonic voltage of the measuring wire (21) is acquired through the data acquisition and processing system. Based on the acquired third harmonic voltage, data processing is performed to output the specific heat of the molten sample to be tested.

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