CN111443106A - Method and system for testing equivalent thermal conductivity coefficient of heterogeneous material - Google Patents
Method and system for testing equivalent thermal conductivity coefficient of heterogeneous material Download PDFInfo
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- CN111443106A CN111443106A CN202010412999.6A CN202010412999A CN111443106A CN 111443106 A CN111443106 A CN 111443106A CN 202010412999 A CN202010412999 A CN 202010412999A CN 111443106 A CN111443106 A CN 111443106A
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Abstract
The invention discloses a method and a system for testing equivalent thermal conductivity of a heterogeneous material. And then establishing a one-dimensional heat transfer model in finite element software, applying a temperature field, and drawing temperature rise curves of the upper surface of the test piece under different heat conductivity coefficients. Wherein the upper and lower lines closest to the temperature rise curve obtained by actually measuring the temperature are the initial range of the equivalent thermal conductivity coefficient. And repeatedly selecting different heat conductivity coefficients in the range for simulation and comparison until the heat conductivity coefficient used in the finite element model is the equivalent heat conductivity coefficient of the sample to be measured when the temperature change curves obtained by the test and the finite element model are close or coincident. The method can not damage the sample to be tested, simplify the measurement process of the heat conductivity coefficient, reduce the requirement of test conditions, improve the accuracy of the measurement result and reduce the test cost.
Description
Technical Field
The invention belongs to the technical field of heat conductivity coefficient testing, and particularly relates to a method and a system for testing equivalent heat conductivity coefficient of a heterogeneous material.
Background
Heat transfer is a phenomenon commonly existing in nature, and particularly in the industrial field, a large number of heat transfer problems need to be researched. Thermal conductivity is an important thermal property of a material, which directly reflects the heat transfer capability of the material. Current methods for measuring thermal conductivity can be broadly divided into two broad categories, namely steady state and unsteady state. In the steady state method, a sample to be measured is placed in a constant temperature field, and after the overall temperature of the sample reaches balance, the heat conductivity coefficient can be directly measured according to the measured heat flow passing through the sample in unit area, the temperature gradient of the sample in the heat conduction direction and the overall dimension of the sample. In the unsteady state method, temperature disturbance is applied to the interior or the boundary of a sample to be tested, then the change condition of the temperature of a sample testing area along with time is obtained, further the thermal diffusion coefficient of the sample to be tested is obtained, and finally the thermal conductivity coefficient of the material is obtained.
The heterogeneous material is composed of a solid framework structure and a pore structure, the distribution of the solid framework structure and the pore structure has certain variability, and particularly the pore structure can seriously influence the heat transfer. By adopting the conventional steady-state and unsteady-state measurement methods, the influence of the material space distribution cannot be effectively considered, so that the experimental test result has great deviation.
Disclosure of Invention
The invention aims to provide a method and a system for testing equivalent thermal conductivity of a heterogeneous material, which can not damage a sample to be tested and can reduce the requirement of test conditions aiming at the defects of the prior art.
The invention provides a method for testing equivalent thermal conductivity of a heterogeneous material, which comprises the following steps:
sampling, namely measuring the density and specific heat capacity of a sample, and placing the sample to be measured in a constant temperature environment for heat preservation for 4-6 h;
heating the bottom of a sample to be measured, measuring the temperature of the upper surface of the sample, and drawing a time-temperature curve;
step three, establishing a finite element heat transfer model of the sample to be measured;
selecting a heat conductivity coefficient, applying a constant temperature boundary equivalent to the constant temperature boundary in the step two to the bottom end of the model, and recording a time-temperature curve of the upper surface of the finite element heat transfer model under the heat conductivity coefficient;
step five, comparing the time-temperature curve measured by the finite element model with the actually measured time-temperature curve;
step six, if the measured time-temperature curve of the finite element model is higher than the measured time-temperature curve, the heat conductivity coefficient is reduced by 0.N, and then the step four and the step five are repeated,
if the measured time-temperature curve of the finite element model is lower than the measured time-temperature curve, adding 0.N on the basis of the heat conductivity coefficient, and repeating the fourth step and the fifth step;
step seven, repeating the step six until two adjacent heat conduction coefficients X.Y and X.Y +/-0. N are respectively positioned at the upper side and the lower side of the actual measurement time-temperature curve, and then judging that the actual heat conduction coefficient is positioned between the two heat conduction coefficients;
step eight, if accurate calculation is not needed, judging the common position X of the two heat conduction coefficients as an actual heat conduction coefficient;
step nine, if accurate calculation is needed, selecting the gradient value of the thermal conductivity coefficient to be 0.0N, repeating the step six to the step eight between X.Y and X.Y +/-0. N, and determining the thermal conductivity coefficient X.Y;
step ten, repeating the step nine to determine the thermal conductivity coefficients X.YZ, X.YZZ, … and X.YZ … Z; and if the time-temperature curve corresponding to the thermal conductivity selected in the comparison process is coincident with the time-temperature curve measured by the test, the thermal conductivity is the corresponding equivalent thermal conductivity.
The sample to be detected is a sample with flat upper and lower bottom surfaces, and has no shape requirement; the sample to be tested is surrounded by a heat insulating layer.
Preferably, the heat insulating layer is a heat insulating foam material.
Preferably, the temperature for heat preservation in the first step is between 20 and 30 DEG C
Preferably, the heating in the second step is constant temperature heating, and the heating temperature is between 50 and 60 ℃.
The invention also provides a system for testing equivalent thermal conductivity of the heterogeneous material, which is used for heating and measuring the temperature of the sample to be tested.
The system comprises a constant temperature heating device and a temperature measuring device; the temperature measuring device is used for measuring the temperature of a sample to be measured in the heat insulation layer.
Preferably, the constant-temperature heating device is a stainless steel constant-temperature heating plate capable of keeping the surface temperature of the device constant, and the temperature control range is 20-100 ℃.
In order to ensure the heating effect, the sample to be measured is provided with a flat base surface which can be in close contact with the constant-temperature heating device.
In one embodiment, the temperature measuring device is an infrared thermal imager.
The invention compares the time temperature curve obtained by finite element software simulation with the time temperature curve obtained by actual measurement, finds out the interval range of the equivalent heat conductivity coefficient by a plurality of comparisons, and repeatedly selects different heat conductivity coefficients in the range for simulation comparison until the heat conductivity coefficient used in the finite element model is the equivalent heat conductivity coefficient of the sample to be measured when the test is similar to or coincident with the temperature change curve obtained by the finite element model. In the whole use, a constant-temperature heat source is provided through the constant-temperature heating device, the test requirement is simple, the average temperature data of the surface of the sample is obtained by adopting the infrared thermal imager, the complex sensor connection is not needed, and the data acquisition is convenient. And finally, establishing a heat transfer model through finite element software, and comparing the change relation of the temperature along with time to obtain the equivalent heat conductivity coefficient of the heterogeneous material. The method has the advantages of not damaging the sample to be tested, simplifying the measurement process of the thermal conductivity, reducing the requirement of test conditions, improving the accuracy of the measurement result of the thermal conductivity of the heterogeneous material and reducing the test cost.
Drawings
Fig. 1 is a schematic view of a preferred embodiment of the present invention in use.
FIG. 2 is a schematic diagram of a finite element simulation of the preferred embodiment.
Fig. 3 is a process block diagram of the preferred embodiment.
Sequence numbers of the drawings:
1-a sample to be tested; 2-constant temperature heating device; 3, heat insulating layer; 4-temperature measuring device.
Detailed Description
As shown in fig. 1, the system for testing equivalent thermal conductivity of heterogeneous material disclosed in this embodiment is used to heat and measure the temperature of a sample 1 to be tested. The sample 1 to be measured has a flat base surface so as to be able to be brought into close contact with the constant-temperature heating apparatus, and the sample 1 to be measured is selected to be a cylinder in this embodiment.
The test system comprises a constant temperature heating device 2, a heat insulation layer 3 and a temperature measuring device 4, wherein the constant temperature heating device 2 is a stainless steel constant temperature heating plate (model DB-3AB) capable of keeping the surface temperature of the device constant, the temperature control range is 20-100 ℃, the heat insulation layer 3 is made of heat insulation foam materials and is adhered to the outside of a sample 1 to be tested, then the sample to be tested coated with the heat insulation layer 3 is placed on the stainless steel constant temperature heating plate, and then the surface temperature of the sample to be tested is measured through the temperature measuring device 4 (model F L IR).
Selecting a cylinder with the diameter of 10cm and the height of 10cm as a sample to be tested, and testing the density and the specific heat capacity of the sample to be tested to obtain the density of 2.12g/cm3The specific heat capacity is 734J/(kg. cndot.). The ambient temperature was 25 ℃ and the heating device temperature was set to 50 ℃. The initial temperature of the surface of the sample to be measured was measured using a temperature measuring device, and then the surface temperature of the sample to be measured was measured every 15 minutes. The time and temperature table is shown in Table 1
A finite element heat transfer model was created using ABAQUS software based on measured test parameters as shown in figure 2,
assuming that the density and specific heat capacity of the sample to be tested do not change with time, the transient heat balance can be expressed by a matrix:
wherein [ C ]]Is a matrix of specific heat, and is,
is a derivative matrix of the node temperature with respect to time, [ K]Is a heat conduction matrix, [ T ]]Is a node temperature matrix, [ Q ]]Is a node heat flow rate matrix.
Selecting a heat conductivity coefficient of 1.10W/(m.K), applying equivalent thermal load to the bottom end of the model, and recording a time-temperature curve of the surface of the finite element heat transfer model under the heat conductivity coefficient; then comparing the value with the measured value, if the value is smaller than the measured value, increasing the value by 0.02W/(m.K) on the basis of the thermal conductivity coefficient of 1.10W/(m.K), namely selecting the thermal conductivity coefficient of 1.12W/(m.K), repeating the simulation to obtain another set of time-temperature data, obtaining the change situation of the upper surface temperature of the sample to be measured under different thermal conductivity coefficients, recording the change situation in the table 1, and repeating the steps until the simulated value is larger than the measured value.
And (4) drawing temperature rise curves under different heat conductivity coefficients and a temperature rise curve obtained by actually measuring the temperature. Wherein the upper and lower lines closest to the temperature rise curve obtained by actually measured temperature are in the range of equivalent thermal conductivity coefficient.
The actual thermal conductivity is found to be between 1.12W/(mK) and 1.14W/(mK). If the requirement on the accuracy of the equivalent thermal conductivity is not high, the equivalent thermal conductivity is 1.1W/(m.K). If higher, the test can be repeated within the interval of 1.12-1.14W/(m.K).
In order to verify the test result, a thermal conductivity tester (the model is DRE-2C) based on the transient flat plate heat source method is adopted to measure the sample to be tested for many times, the average thermal conductivity is 1.12W/(m.K), and the difference between the test data obtained by the test method is not great, which indicates that the test result of the method is accurate.
Claims (10)
1. A method for testing equivalent thermal conductivity of a heterogeneous material is characterized by comprising the following steps:
sampling, namely measuring the density and specific heat capacity of a sample, and placing the sample to be measured in a constant temperature environment for heat preservation for 4-6 h;
heating the bottom of a sample to be measured, measuring the temperature of the upper surface of the sample, and drawing a time-temperature curve;
step three, establishing a finite element heat transfer model of the sample to be measured;
selecting a heat conductivity coefficient, applying a constant temperature boundary equivalent to the constant temperature boundary in the step two to the bottom end of the model, and recording a time-temperature curve of the upper surface of the finite element heat transfer model under the heat conductivity coefficient;
step five, comparing the time-temperature curve measured by the finite element model with the actually measured time-temperature curve;
step six, if the measured time-temperature curve of the finite element model is higher than the measured time-temperature curve, the heat conductivity coefficient is reduced by 0.N, and then the step four and the step five are repeated,
if the measured time-temperature curve of the finite element model is lower than the measured time-temperature curve, adding 0.N on the basis of the heat conductivity coefficient, and repeating the fourth step and the fifth step;
step seven, repeating the step six until two adjacent heat conduction coefficients X.Y and X.Y +/-0. N are respectively positioned at the upper side and the lower side of the actual measurement time-temperature curve, and then judging that the actual heat conduction coefficient is positioned between the two heat conduction coefficients;
step eight, if accurate calculation is not needed, judging the common position X of the two heat conduction coefficients as an actual heat conduction coefficient;
step nine, if accurate calculation is needed, selecting the gradient value of the thermal conductivity coefficient to be 0.0N, repeating the step six to the step eight between X.Y and X.Y +/-0. N, and determining the thermal conductivity coefficient X.Y;
step ten, repeating the step nine to determine the thermal conductivity coefficients X.YZ, X.YZZ, … and X.YZ … Z; and if the time-temperature curve corresponding to the thermal conductivity selected in the comparison process is coincident with the time-temperature curve measured by the test, the thermal conductivity is the corresponding equivalent thermal conductivity.
2. The method for testing equivalent thermal conductivity of a heterogeneous material of claim 1, wherein: the sample to be detected is a sample with flat upper and lower bottom surfaces, and has no shape requirement; the sample to be tested is surrounded by a heat insulating layer.
3. The method for testing equivalent thermal conductivity of a heterogeneous material of claim 2, wherein: the heat insulation layer is made of heat insulation foam material.
4. The method for testing equivalent thermal conductivity of a heterogeneous material of claim 1, wherein: the temperature of the first step is 20-30 ℃.
5. The method for testing equivalent thermal conductivity of a heterogeneous material of claim 1, wherein: and in the second step, constant-temperature heating is adopted, and the heating temperature is 50-60 ℃.
6. A system for testing equivalent thermal conductivity of a heterogeneous material, the system being adapted to heat and measure the temperature of a sample according to claim 1.
7. The heterogeneous material equivalent thermal conductivity test system of claim 6, wherein: the system comprises a constant temperature heating device and a temperature measuring device; the temperature measuring device is used for measuring the temperature of a sample to be measured in the heat insulation layer.
8. The heterogeneous material equivalent thermal conductivity test system of claim 7, wherein: the constant temperature heating device is a stainless steel constant temperature heating plate capable of keeping the surface temperature of the device constant, and the temperature control range is 20-100 ℃.
9. The heterogeneous material equivalent thermal conductivity test system of claim 8, wherein: the sample to be measured is provided with a flat base surface which can be in close contact with the constant-temperature heating device.
10. The heterogeneous material equivalent thermal conductivity test system of claim 7, wherein: the temperature measuring device is an infrared thermal imager.
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Cited By (2)
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| CN114858849A (en) * | 2022-07-11 | 2022-08-05 | 中国空气动力研究与发展中心低速空气动力研究所 | Method for obtaining thermal conductivity coefficient of dynamic ice |
| CN116757007A (en) * | 2023-08-23 | 2023-09-15 | 中南大学 | Method for predicting influence of low-temperature phase-change material on temperature and ice condensation of asphalt pavement |
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| CN116757007B (en) * | 2023-08-23 | 2023-11-03 | 中南大学 | Method for predicting influence of low-temperature phase-change material on temperature and ice condensation of asphalt pavement |
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