CN110763723A - Device and method for measuring specific heat capacity of metal material - Google Patents

Device and method for measuring specific heat capacity of metal material Download PDF

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CN110763723A
CN110763723A CN201911196995.2A CN201911196995A CN110763723A CN 110763723 A CN110763723 A CN 110763723A CN 201911196995 A CN201911196995 A CN 201911196995A CN 110763723 A CN110763723 A CN 110763723A
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sample
temperature
laser
measuring
furnace body
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周逸
林鸿
张金涛
冯晓娟
邱萍
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Zhengzhou Institute Of Advanced Measurement Technology
National Institute of Metrology
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Zhengzhou Institute Of Advanced Measurement Technology
National Institute of Metrology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity

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Abstract

The invention relates to a device for measuring the specific heat capacity of a metal material, which comprises a laser heater and a control module thereof; a heating furnace body and a control module thereof; a sample holder; measuring the thermocouple group; a data acquisition module; a base; and the PC with control and measurement function software and the equipment connecting line thereof. The device can realize carrying out the measurement of specific heat capacity to the specified small-size metal sample after carrying out corresponding processing and handling, can be comparatively accurate the specific heat capacity that obtains the metal sample that awaits measuring according to the absolute method measurement model that proposes and correction model. The deviation of the measurement result of the specific heat capacity at normal temperature to 300 ℃ is less than +/-3%, the repeatability is better than 2%, wherein the deviation of the measurement at normal temperature is less than +/-1%, and the repeatability is better than 1%. The invention also provides a method for measuring by using the device for measuring the specific heat capacity of the metal material.

Description

Device and method for measuring specific heat capacity of metal material
Technical Field
The invention relates to a measuring device and a measuring method thereof, in particular to a measuring device for the specific heat capacity of a metal material and a measuring method based on the measuring device.
Background
The specific heat capacity is one of the most important thermophysical parameters of the material, represents the heat energy required to be consumed by the material at the temperature of 1 ℃ under the unit mass, is used as the important property of the material and the data of theoretical analysis, is the basis for evaluating the thermal property of the material, is widely applied to actual production and life, and particularly has important application value in the fields of materials, energy, spaceflight, environmental protection, synthesis and application development of the material, medicine, engineering thermodynamics and the like.
The specific heat capacity of the solid material is measured mainly by a calorimeter method, a comparison method and the like, wherein the comparison method mainly comprises a Differential Scanning Calorimeter (DSC) method, a laser flash method and the like, and synthetic sapphire (α -Al) is generally used internationally2O3) As a standard substance of specific heat capacity, a DSC method is one of the methods with the widest application and higher measurement precision at present, the specific heat capacity measurement precision of commercial DSC instruments on the market can be alleged to reach 2% -3%, but the measurement results of equipment produced by different manufacturers are greatly different, and the measurement deviation of the same material can reach more than 20%.
The laser flash method is one of the most important methods for measuring the thermal physical property parameters of the current materials, is suitable for measuring the thermal diffusion coefficient and the specific heat capacity of the metal materials, has the advantages of high measuring speed, small sample size and high accuracy, and is one of the standard methods for measuring the thermal diffusion coefficient at present. However, the deviation of the specific heat capacity of the material measured by a commercial flash method series heat conduction instrument is large, generally, the deviation is claimed to be 5% -10%, mainly because the flash method laser pulse heating time is extremely short, the front surface of the sample is sprayed with graphite to improve the heat absorption rate and other treatments, and the accurate determination of the heat absorption energy of the front surface is difficult; meanwhile, no matter the rear surface of the sample is measured by a thermocouple or an infrared thermometer, the heat loss causes large deviation in the measurement of the maximum temperature rise of the rear surface of the sample, so that the specific heat capacity deviation of the material obtained by the measurement of the relative method is large, and the repeatability is poor.
At present, a laser flash method measuring instrument usually uses copper or graphite as a standard sample for measuring specific heat capacity, the sample lacks corresponding quantity value tracing, and the accuracy of a nominal value of the sample cannot be guaranteed, so that the uncertainty of the specific heat capacity of the standard sample directly affects the accuracy of a measurement result of a relative method, and the heat conductivity coefficient obtained by the flash method measuring instrument through equivalent calculation of the measured heat diffusion coefficient, the specific heat capacity and the density introduces larger uncertainty, and the reliability of the measurement result is poor.
Disclosure of Invention
The invention aims to improve on the basis of a flash method measuring principle and a device, provides a measuring device for measuring the specific heat capacity of a metal material by using continuous laser heating, and obtains the specific heat capacity of the metal material by an absolute method based on a quasi-steady state temperature rise process established by the continuous laser heating.
The invention provides a device for measuring the specific heat capacity of a metal material, which comprises a laser heater, a laser temperature sensor, a temperature sensor and a temperature sensor, wherein the laser heater is used for providing irradiation laser beams; a heating furnace having a temperature controlled within a predetermined temperature range; and a control module; the method is characterized in that: the heating furnace comprises a fixed furnace body and a movable furnace body, wherein the fixed furnace body and the movable furnace body can be combined and separated, and a sample rack is arranged between the fixed furnace body and the movable furnace body; and the sample to be tested is positioned on the sample frame, micropores are formed in the side part and the surface of the sample to be tested, and thermocouples are arranged in the micropores.
Wherein the predetermined temperature range is a temperature range of room temperature to 300 ℃.
Wherein, the furnace temperature and the uniformity are measured by adopting a temperature thermocouple group, the furnace temperature deviation is less than +/-1 ℃, and the uniformity is less than 1 ℃.
The thermocouple group comprises two extremely-thin k-shaped armored thermocouples, the diameter of each thermocouple is 0.15mm, and the thermocouples are used for measuring the internal temperature of the perforated metal sample.
The control module controls the laser heater shutter, reads the thermocouple temperature, and can process and store data.
Wherein, further comprising a data acquisition module.
The invention relates to a method for measuring the specific heat capacity of a metal material, which comprises the following steps:
step 1, preparing a metal sample with a size in a specified range, and punching micropores with the size in the specified range on the metal sample by using a micro-punching technology;
step 2, uniformly spraying a graphite spray on the front surface of the metal sample to be tested, and drying and then loading the metal sample on a sample rack;
step 3, selecting the thermocouple of the thermocouple group to be measured according to the punching position, plugging the superfine thermocouple into the micropore,
step 4, respectively connecting the data acquisition equipment and the laser heater controller with the control module by using a data connecting line, opening a matching program on the control module, setting port connection, operating the program and testing the connection state of the connection equipment;
step 5, setting the output power of the laser heater through the laser heating controller, and stabilizing for more than 30 min;
step 6, closing the fixed furnace body and the movable furnace body, setting the temperature to be measured through the furnace temperature controller, and waiting for the temperature of the furnace temperature controller to reach the set temperature;
and 7, irradiating the sample by using a laser heater, and acquiring the temperature rise of the thermocouple by using a measuring system in real time, wherein the temperature rise is repeatedly measured for at least 3 times.
In the step 5, the laser heater is stabilized for more than 30min when the furnace temperature reaches a set value and the uniformity deviation of the furnace temperature is less than 1 ℃, and the laser heating pulse time, namely the shutter off time interval, is set, wherein the pulse heating time of the laser heater is generally 20 s.
The invention provides a device for measuring the specific heat capacity of a metal material, which comprises a laser heater and a control module thereof; a heating furnace body and a control module thereof; a sample holder; measuring the thermocouple group; a data acquisition module; a base; PC with control and measurement function software and equipment connecting line thereof
The laser heater is a continuous laser, the highest output power can reach 1W, and the laser heater is provided with a programmable shutter, and the response time of the shutter is less than 1 ms.
The heating furnace is designed into a split mode, and can be separated from the middle part, wherein the left furnace body is a fixed furnace body, and the right furnace body can be combined and separated manually; the heating furnace body can meet the measurement requirement within the temperature range of room temperature to 300 ℃, the furnace temperature and the uniformity are measured by using the thermocouple group, the furnace temperature is controlled by using the control module, the furnace temperature deviation is less than +/-1 ℃, and the uniformity is less than 1 ℃.
The measuring thermocouple group comprises two extremely thin k-shaped armored thermocouples, the diameter of each thermocouple is 0.15mm, and the measuring thermocouples are used for measuring the internal temperature of the perforated metal sample.
The control software of the PC is based on the laser heater shutter control and thermocouple temperature reading written by LabVIEW, and can process and store data, and the connecting lines are two USB-B connecting lines which are respectively connected with the data acquisition module and the laser heater control module.
The invention provides a method for measuring specific heat capacity of a metal material by using a measuring device, which comprises the following steps:
step 1, preparing a metal sample with a size in a specified range, and punching micropores with the size in the specified range on the metal sample by using a micro-punching technology;
step 2, measuring the mass of the metal sample by using a 0.001g resolution balance;
step 3, uniformly spraying a graphite spray on the front surface of the metal sample to be tested, and drying and then loading the metal sample on a sample rack;
step 4, selecting the thermocouple of the thermocouple group to be measured according to the punching position, plugging the superfine thermocouple into the micropore,
step 5, connecting the data acquisition equipment and the laser heater controller with a PC (personal computer) respectively by using a USB-B (universal serial bus-B) connecting line, opening a matched program on the PC, setting port connection, operating the program and testing the connection state of the connecting equipment;
step 6, setting the output power of the laser heater through the laser heating controller, and stabilizing for more than 30 min;
step 7, manually rotating the right furnace body handle to close the furnace body, setting the temperature to be measured through the furnace temperature controller, and waiting for the temperature of the furnace temperature controller to reach the set temperature;
step 8, when the temperature in the furnace reaches a set value and the uniformity deviation of the furnace temperature is less than 1 ℃, stabilizing the laser heater for more than 30min, and setting the pulse heating time of the laser heater, namely the shutter turn-off time interval, wherein the pulse heating time of the laser heater is generally 20 s;
step 9, clicking a PC program to start measurement button, starting measurement, and acquiring and measuring the temperature rise of the thermocouple in real time by the measurement system;
step 10, inputting the mass of a sample, displaying the specific heat capacity of the measured metal sample after the measured temperature rise data is processed by software, cooling for more than 10min, and measuring again, wherein the measurement is repeated for not less than 3 times;
and step 11, after the measurement is finished, closing the power supply of the heating furnace body, closing the power supply of the laser heater, opening the furnace body when the temperature in the furnace is reduced to be below 60 ℃, pulling out the measurement thermocouple, and taking out the measured metal sample.
The measuring device mainly comprises a laser heater and a control module thereof; a heating furnace body and a control module thereof; a sample holder; measuring the thermocouple group; a data acquisition module; a base; and the PC with control and measurement function software and the equipment connecting line thereof. The method comprises the following steps of processing and micropore punching of a metal sample to be measured according to the size requirement, and spraying a graphite spray on the front surface of the metal sample before measurement to improve the heat absorption rate of the sample; the inside of the sample is measured by using a superfine thermocouple, so that the influence of contact thermal resistance, surface convection and the like on temperature measurement is reduced. The device can realize the measurement of absolute most metal material specific heat capacity under room temperature to 300 ℃, and the sample needs to satisfy the requirement of regulation size, can be comparatively accurate the specific heat capacity that obtains the metal sample that awaits measuring according to the absolute method measurement model that proposes and correction model. The deviation of the measurement result of the specific heat capacity at normal temperature to 300 ℃ is less than +/-3%, the repeatability is better than 2%, wherein the deviation of the measurement at normal temperature is less than +/-1%, and the repeatability is better than 1%. The device for measuring the specific heat capacity of the metal material is a quasi-steady state temperature rise established based on continuous laser heating, the specific heat capacity of the metal material is obtained by an absolute method, the measuring principle is simple, and the accuracy is high.
The invention improves the specific heat capacity measurement by the laser flash method on the basis of using laser to heat the sample, develops an absolute method with higher accuracy, is beneficial to further improving the measurement capability of the laser flash method series measuring instrument on the specific heat capacity and the heat conductivity coefficient of the material, and realizes the accurate measurement of the multiple thermophysical parameters.
Drawings
FIG. 1 is a schematic structural view of a device for measuring specific heat capacity of a metallic material according to the present invention;
FIG. 2 is a schematic view of the punching position of the metal sample according to the present invention;
FIG. 3 is a schematic view of the structure of a sample holder according to the present invention;
FIG. 4 is a schematic diagram of simulated temperature rise at various points on a 316L sample under uniform laser heating;
FIG. 5 is a schematic diagram of simulated temperature rise fitting slopes of 45 steel samples at various points on the samples under Gaussian laser heating;
FIG. 6 is a schematic diagram of temperature rise curve of red copper sample simulation and experimental measurement.
Detailed Description
To facilitate an understanding of the present invention, embodiments of the present invention will be described below with reference to the accompanying drawings, and it will be understood by those skilled in the art that the following descriptions are provided only for the purpose of illustrating the present invention and are not intended to specifically limit the scope thereof.
FIG. 1 is a schematic structural view of a device for measuring a specific heat capacity of a metallic material according to the present invention. The measuring device includes: the laser heater 1 is a continuous laser used in the device, the laser is preferably a 532mm continuous laser, the maximum output power is 2W, the laser is provided with a shutter, and the response time of the shutter is less than 1 ms; the optical path guide tube 2 is preferably made of a PVC (polyvinyl chloride) plastic tube and is used for connecting a laser output port of the laser heater to a laser input port of the heating furnace body to prevent laser from being reflected and refracted; the heating furnace can meet the temperature control within a preset temperature range, the preset temperature range is preferably room temperature to 300 ℃, the furnace body of the heating furnace comprises at least three layers of structures, namely an outer shell layer 4, a heating layer 5 and a furnace inner layer 6, wherein the heating layer 5 is heated by using resistance wires, the furnace inner layer 6 is made of refractory materials, and the heating resistance wires are insulated and isolated; three heat insulation plane plates 3 are used for carrying out furnace temperature heat insulation at the laser inlet, and the heat insulation plane plates 3 are preferably heat insulation plane glass, so that heat leakage in the furnace is prevented, and the laser of a heating laser is ensured to be effectively shot into the furnace body; the furnace body of the heating furnace comprises at least two parts, as shown in figure 1, the left part is a fixed furnace body 4, the right part is a movable furnace body 12, preferably, the structures of furnace body layers on the left side and the right side are consistent, and a furnace body temperature thermocouple group 8 is used for measuring the furnace temperature and the uniformity; the right furnace body 12 can move along the guide rail 14 by manually rotating the rotary table 13, and can be completely closed and locked with the fixed furnace body 4 by moving leftwards; the sample frame 9 is positioned on one side of the fixed furnace body 4 and used for placing a sample to be measured.
The measuring thermocouple group comprises a vertical thermocouple 10 and a horizontal thermocouple 11, the vertical thermocouple 10 and the horizontal thermocouple 11 are preferably superfine armored k-type thermocouples, the diameter after armoring is 0.15mm, the thermocouple is selected for use according to the punching position of a metal sample, and the sample rack 9 can adjust the height according to the diameter of the sample to ensure that heating laser irradiates the center of the front surface of the sample; a groove is arranged between the fixed furnace body 4 and the movable furnace body 12 and is used for accommodating a supporting column of the sample rack 9, so that perfect closing between the fixed furnace body 4 and the movable furnace body 12 is ensured.
The laser heater 1, the fixed furnace body 4 and the movable furnace body 12 are preferably all positioned above the base 15; the device power supply, operation and alarm display lamp 16 is positioned on the right side of the front surface of the base 15 and is used for displaying the operation condition of the device; the data acquisition module 17 is embedded in the base 15, is used for measuring and acquiring data of the vertical thermocouple 10 and the horizontal thermocouple 11, and is connected with the control module 20 through a first data connection line 18, and the control module is preferably a PC (personal computer) provided with a LabVIEW measurement program; the furnace temperature controller 19 can also be embedded in the device base 15 and connected with the furnace body temperature thermocouple group 8 to display the temperature in the heating furnace in real time, and is connected with the furnace body heating layer 5 through a continuous line 25 to control the resistance wire heating power of the heating layer according to the set temperature and the real-time temperature measured by the temperature thermocouple group 8; the laser heater control module 22 is connected with the laser heater 1 through a control connecting wire 24, can set the output power of the laser heater 1, can also manually control a shutter switch, is connected with the control module 20 through a second data connecting wire 21, and can control the opening and closing of the shutter of the laser heater 1 and the pulse time thereof through a LabVIEW measuring program; the power line 23 is the general power line of the measuring device and provides power for the laser heater 1 and the control module 22 thereof, the heating furnace bodies 4 and 12, the furnace temperature controller 19 and the like.
Fig. 2 is a schematic diagram showing the punching position of the metal sample. The metal sample is required to be an ideal cylinder, and generally, the diameter D of the metal sample is within the range of 8 mm-13 mm, and the thickness H of the metal sample is within the range of 5 mm-7 mm. The metal sample is punched in a laser punching mode, the punching position can be preferably arranged on the side part and the surface, wherein, the side hole of the metal sample 2-1 is punched on the side surface of a cylinder of the metal sample, and the micropores are deep to the central axis of the cylinder; and (3) drilling a micropore in the circle center of the bottom surface of the metal sample cylinder, wherein the micropore is vertical to the metal sample 2-2 with the center hole. Diameter d of micropore on metal sample by laser drilling technology1,2The thickness can reach 0.22 +/-0.02 mm, the insertion of an armored k-type thermocouple with the diameter of 0.15mm can be ensured, and the influence of micropores on the overall measurement of a metal sample can be reduced as much as possible; depth of micro-hole in general side hole metal sample 2-115 +/-0.2 mm, and the depth h of the micropores in the metal sample 2-2 with the vertical central hole 22 + -0.2 mm or 3 + -0.2 mm.
Fig. 3 is a schematic structural diagram of the sample holder according to the present invention. The schematic structural diagram of the sample holder is an enlarged schematic diagram of the sample holder 9 in fig. 1, the sample holder is made of high-temperature-resistant and low-heat-conductivity metal, and the support columns are preferably square columns which are just placed in the furnace layer 6 in fig. 1 for measuring once and only one metal sample to be measured is placed. The vertical thermocouple 3-1 and the horizontal thermocouple 3-7 are preferably k-type armored thermocouples with the diameter of 0.15mm, and the connecting wire 3-5 comprises an extension wire of the vertical thermocouple 3-1 and the horizontal thermocouple 3-7 and is used for leading out from the heating furnace and connecting to a data acquisition module 17 in the figure 1; the vertical thermocouple 3-1 is used for measuring the internal temperature rise of the metal sample 2-1 with the punched hole in the figure 2, and the horizontal thermocouple 3-7 is used for measuring the internal temperature rise of the metal sample 2-2 with the punched hole in the figure 2; the metal sample 3-2 is positioned on the sample groove 3-3, the sample groove 3-3 is semicircular, the inner diameter is 14mm, and the central position of the front surface of the metal sample 3-2 irradiated by heating laser can be ensured according to the diameter of the metal sample 3-2 by adjusting the end 3-6; the upper end part of the sample rack can be controlled to move back and forth by adjusting the knob 3-4; the upper end pressing plate can be controlled by the control knob 3-8, the height of the vertical thermocouple 3-1 is adjusted, and the vertical thermocouple is used for fixing the metal sample 3-2 on the sample groove 3-3.
Fig. 4 is a schematic diagram showing the simulated temperature rise of each point on the 316L sample under uniform laser heating. The reference metal specimen 316L stainless steel has a thermal conductivity of 13.07W/(m.K) and a density of 7912kg/m3The specific heat capacity is 472J/(kg.K), the COMSOL simulation software of the sample sets the material parameters, the diameter of the 316L sample is 10mm, the thickness is 5mm, the boundary is a heat insulation boundary, the heat absorption power is 0.5W, and the temperature rise rate of each probe point tends to be consistent after a certain time.
FIG. 5 is a graph showing the simulated temperature rise fitted slope of the 45 steel sample at each point on the sample under Gaussian laser heating. The 45 steel reference has a thermal conductivity of 51.5W/(m.K) and a density of 7850kg/m3The specific heat capacity is 473J/(kg. K); the COMSOL simulation software of the sample sets the material parameters, the diameter of the 45 steel sample is 10mm, the thickness is 5mm, the radius of the Gaussian beam is 1.25mm, the laser power is 0.5W, and the heat absorption rate of the sample is 1; considering that in the actual measurement process, contact heat transfer exists between the sample and the sample holder, heat convection and heat radiation simultaneously exist to cause heat loss of the metal sample during heating, the surface heat transfer coefficient is set to be 50W/(m)2K) to obtain the fitting slope of the temperature rise of each point on the sample through simulation, and it can be seen that the temperature rise rates of each point on the metal sample are still consistent after a certain time.
FIG. 6 is a schematic diagram showing temperature rise curves of simulation and experimental measurement of a red copper sample, wherein accurate determination of the heat absorption rate β of the front surface of the sample is a key factor influencing the accuracy of specific heat capacity measurement in the experimental measurement, the red copper sample is processed according to the punching position shown in FIG. 2-2, simulation setting is carried out according to the diameter and thickness of the measured sample, and the heat conductivity coefficient and specific heat of the red copper sample are considered as industrial pure copperThe accuracy of the reference value of the capacity and density parameters is high, the probe point is set to be consistent with the position of the thermocouple endpoint, and the deviation of temperature rise is small when the probe point in the sample is set to deviate from the actual one due to the high thermal conductivity coefficient of copper, as shown in FIG. 6, when the simulated heating power is set to be the actual laser output power, and the heat absorption rate β is set to be 1, the surface heat transfer coefficient is 70W/(m2K), the simulated temperature rise curve of the red copper sample is basically consistent with the actually measured temperature rise curve, and the heat absorption rate β of the sample after the graphite spray is sprayed on the surface of the sample can be basically judged to be about 1.
The invention relates to a device for measuring the specific heat capacity of a metal material, which is based on a quasi-steady state temperature rise process established by continuous laser heating, and obtains the specific heat capacity of the metal material by an absolute method.
Figure BDA0002294912190000061
In the formula: t (x, y, z, T) is the real-time temperature, DEG C, of each point on the sample when heated; t is0The initial temperature of the sample is DEG C, and α is the thermal diffusivity, mm2S; phi is volume heat source, W/mm3(ii) a Rho is the density of the sample, g/mm3；cpThe specific heat capacity of the sample is J/(kg. K); t' is the second derivative, which is a small, negligible amount of total temperature rise when the heating time is longer. In this way, it can be determined that the temperature rise rates of the respective points on the sample are consistent when the constant heat source is continuously heated, as shown in fig. 4, when the temperature rise rate is an ideal case, the temperature rise rate of the respective points is simulated by 316L under the heating of the constant power laser uniform beam, and it can be seen that after the sample is heated for a certain time, by measuring the temperature rise condition of any point on the sample and fitting the temperature rise slope m, the following analytical formula can be obtained:
Figure BDA0002294912190000071
wherein β is the surface heat absorption rate of the sample, I0Is the laser power density, W/mm2；P0Is the laser power, W; l is the thickness of the sample, mm; a is the area of the front surface of the sample, mm2Ideally, the laser spot area is consistent with the heated area of the sample, and the sample is cylindrical; v is the sample volume, mm3(ii) a M is the sample mass, g. The specific heat capacity analytical formula based on continuous laser heating can be expressed as:
under the ideal condition, according to the formula, the specific heat capacity of the metal sample can be accurately measured only by accurately obtaining the front surface absorption heat power of the metal sample, the mass of the sample and measuring the continuous temperature rise in the sample.
The actual continuous laser heater used, not an ideal uniform beam, usually a gaussian beam, has a beam profile with a power density expressed as:
Figure BDA0002294912190000073
in the formula: r is the radius of the Gaussian beam, mm; at the effective cross-section x of the Gaussian beam2+y2≤R2The internal accounts for 86.5% of the total energy of the laser, under the condition of adiabatic boundary, when the heating power is constant, the temperature rise rate of each point on the metal sample still tends to be consistent after the metal sample is heated for a certain time, and the specific heat capacity of the metal sample can still be obtained by measuring the temperature rise rate of any point on the metal sample. In the actual measurement process, the metal sample is not an ideal heat insulation boundary, contact heat transfer exists between the metal sample and the sample holder, heat loss is generated when the metal sample is continuously heated due to convection heat transfer, heat radiation and the like, and as shown in FIG. 5, the heat transfer coefficient is set to be 50W/(m) on the surface2K), the temperature rise rate of each probe point on the simulated 45 steel sample still tends to be consistent after a certain time, but the temperature rise m is reduced along with the increase of the heating time, so the actually measured temperature rise slope curve is requiredThe line is corrected to obtain a more accurate calculated slope m', and the correction formula is as follows:
m＝nt+m′
in the formula: n is the coefficient of the temperature rise slope decreasing with time; and m' is the temperature rise slope after correction. Wherein the heating time reaches t for the general case0Later, the temperature rise slope reaches a quasi-steady state, and the temperature rise data time period is selected as follows:
Figure BDA0002294912190000074
wherein L is the thickness of the metal sample in mm, and α is the thermal diffusivity of the metal sample in mm2/s。
According to the temperature rise curve of the simulation and experimental measurement of the red copper sample shown in fig. 6, the surface heat absorption rate β of the sample after being sprayed with the graphite spray can be regarded as 1 for calculation processing.
In the process of measuring by using the measuring device, the following steps are adopted for measurement:
step 1, preparing a metal sample with a size in a specified range, wherein the metal sample is generally 8-13 mm in diameter and 5-7 mm in thickness and is an ideal cylinder, and punching micropores with the size in the specified range on the metal sample by using a micro-punching technology according to a graph 2-1 or 2-2, wherein the pore diameter is generally 0.22 +/-0.02 mm;
step 2, measuring the mass of the metal sample by using a 0.001g resolution balance;
step 3, uniformly spraying a graphite spray on the front surface of the metal sample to be tested, drying the graphite spray, loading the dried graphite spray on a sample groove 3-3 on a sample rack 9, adjusting the graphite spray by 3-6 according to the diameter of the metal sample, and ensuring that laser irradiates the central position of the front surface of the metal sample to be tested 3-2;
step 4, selecting a vertical thermocouple 3-1 or a horizontal thermocouple 3-7 of a measuring thermocouple group according to the punching position 2-1 or 2-2 of the metal sample, plugging the superfine thermocouple into the micropore of the metal sample, and adjusting a pressure plate 3-8 at the upper end of a sample frame 9 to tightly press the metal sample 3-2;
step 5, respectively connecting the data acquisition equipment 27 and the laser heater controller 22 with the control module 20 by using the first data connection line 18 and the second data connection line 21, opening a matched program on the control module 20, setting port connection, running the program and testing the connection state of the connection equipment;
step 6, setting the output power of the laser heater 1 through the laser heating controller 22, and stabilizing for more than 30 min;
step 7, combining the fixed furnace body 4 and the movable furnace body 12; preferably, the right furnace body handle 13 is rotated manually, the fixed furnace body 4 and the movable furnace body 12 are closed and locked, and an automatic closing and locking mode can also be adopted; setting the temperature to be measured through the furnace temperature controller 19, and waiting for the temperature display of the furnace temperature controller 29 to reach the set temperature;
step 8, when the temperature in the furnace reaches a set value and the uniformity deviation of the furnace temperature is less than 1 ℃, stabilizing the laser heater 1 for more than 30min, and setting the pulse heating time of the laser heater, namely the shutter turn-off time interval, wherein the pulse heating time of the laser heater is generally 20 s;
step 9, clicking a program starting measurement button in the control module 20 to start measurement, and acquiring and measuring the temperature rise of the thermocouple 3-1 or 3-7 in real time by a measurement system;
step 10, inputting the measured quality of the metal sample into a measuring system of the control module 20, processing the measured temperature rise data, displaying the specific heat capacity of the measured metal sample, cooling for more than 10min, performing re-measurement, and repeatedly measuring for not less than 3 times;
and 11, after the measurement is finished, closing a power supply of the heating furnace body, closing a power supply of the laser heater 1-1, opening the furnace body when the temperature in the furnace is reduced to be below 60 ℃, pulling out the measuring thermocouple 3-2 or 3-7, taking out the measured metal sample 3-2, and continuing the measurement according to the steps 1-10 after the sample is replaced. The deviations of some of the materials measured using the apparatus of the invention from theoretical reference values at ambient temperature (20. + -. 1 ℃ C.) are shown in the following table;
Figure BDA0002294912190000081
the invention improves the specific heat capacity measurement by the laser flash method on the basis of using laser to heat the sample, develops an absolute method with higher accuracy, is beneficial to further improving the measurement capability of the laser flash method series measuring instrument on the specific heat capacity and the heat conductivity coefficient of the material, and realizes the accurate measurement of the multiple thermophysical parameters.
It is to be understood that while the present invention has been described in conjunction with the preferred embodiments thereof, it is not intended to limit the invention to those embodiments. It will be apparent to those skilled in the art from this disclosure that many changes and modifications can be made, or equivalents modified, in the embodiments of the invention without departing from the scope of the invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.

Claims (8)

1. A measuring device for the specific heat capacity of a metal material comprises a laser heater, a laser processing device and a measuring device, wherein the laser heater provides an irradiation laser beam; a heating furnace having a temperature controlled within a predetermined temperature range; and a control module; the method is characterized in that: the heating furnace comprises a fixed furnace body and a movable furnace body, wherein the fixed furnace body and the movable furnace body can be combined and separated, and a sample rack is arranged between the fixed furnace body and the movable furnace body; and the sample to be tested is positioned on the sample frame, micropores are formed in the side part and the surface of the sample to be tested, and thermocouples are arranged in the micropores.
2. The measurement device of claim 1, wherein: the predetermined temperature range is the temperature range of room temperature to 300 ℃.
3. The measurement device of claim 1, wherein: the temperature and uniformity of the furnace temperature are measured by adopting a temperature thermocouple group, the furnace temperature deviation is less than +/-1 ℃, and the uniformity is less than 1 ℃.
4. The measurement device of claim 1, wherein: the thermocouple group comprises two extremely thin k-shaped armored thermocouples with the diameter of 0.15mm, and is used for measuring the internal temperature of the perforated metal sample.
5. The measurement device of claim 1, wherein: the control module controls the laser heater shutter, reads the thermocouple temperature, and can perform data processing and storage.
6. The measurement device of claim 1, wherein: further comprising a data acquisition module.
7. A method for measuring a specific heat capacity of a metal material using the measuring apparatus of any one of claims 1 to 6, comprising:
step 1, preparing a metal sample with a size in a specified range, and punching micropores with the size in the specified range on the metal sample by using a micro-punching technology;
step 2, uniformly spraying a graphite spray on the front surface of the metal sample to be tested, and drying and then loading the metal sample on a sample rack;
step 3, selecting the thermocouple of the thermocouple group to be measured according to the punching position, plugging the superfine thermocouple into the micropore,
step 4, respectively connecting the data acquisition equipment and the laser heater controller with the control module by using a data connecting line, opening a matching program on the control module, setting port connection, operating the program and testing the connection state of the connection equipment;
step 5, setting the output power of the laser heater through the laser heating controller, and stabilizing for more than 30 min;
step 6, closing the fixed furnace body and the movable furnace body, setting the temperature to be measured through the furnace temperature controller, and waiting for the temperature of the furnace temperature controller to reach the set temperature;
and 7, irradiating the sample by using a laser heater, and acquiring the temperature rise of the thermocouple by using a measuring system in real time, wherein the temperature rise is repeatedly measured for at least 3 times.
8. The method of claim 7, wherein: and 5, when the temperature in the furnace reaches a set value, the uniformity deviation of the furnace temperature is less than 1 ℃, the laser heater is stabilized for more than 30min, the laser heating pulse time, namely the shutter turn-off time interval, is set, and the pulse heating time of the laser heater is generally 20 s.
CN201911196995.2A 2019-11-29 2019-11-29 Device and method for measuring specific heat capacity of metal material Pending CN110763723A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114062413A (en) * 2020-08-04 2022-02-18 中国科学院大连化学物理研究所 Sample packaging mode for measuring heat capacity

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114062413A (en) * 2020-08-04 2022-02-18 中国科学院大连化学物理研究所 Sample packaging mode for measuring heat capacity

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