CN117074461A - Equipment for measuring low-temperature heat conduction characteristics of heat insulation material - Google Patents
Equipment for measuring low-temperature heat conduction characteristics of heat insulation material Download PDFInfo
- Publication number
- CN117074461A CN117074461A CN202311009426.9A CN202311009426A CN117074461A CN 117074461 A CN117074461 A CN 117074461A CN 202311009426 A CN202311009426 A CN 202311009426A CN 117074461 A CN117074461 A CN 117074461A
- Authority
- CN
- China
- Prior art keywords
- temperature
- measuring
- container
- heat conduction
- sample
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 239000012774 insulation material Substances 0.000 title claims abstract description 12
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 68
- 239000007788 liquid Substances 0.000 claims abstract description 50
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 34
- 230000008859 change Effects 0.000 claims abstract description 25
- 239000011810 insulating material Substances 0.000 claims abstract description 10
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 41
- 229910052697 platinum Inorganic materials 0.000 claims description 20
- 238000009834 vaporization Methods 0.000 claims description 14
- 230000008016 vaporization Effects 0.000 claims description 14
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 9
- 229910052802 copper Inorganic materials 0.000 claims description 9
- 239000010949 copper Substances 0.000 claims description 9
- 238000012545 processing Methods 0.000 claims description 8
- 238000000926 separation method Methods 0.000 claims description 8
- 229920000742 Cotton Polymers 0.000 claims description 6
- 239000010409 thin film Substances 0.000 claims description 6
- 238000009413 insulation Methods 0.000 claims description 4
- 238000000034 method Methods 0.000 abstract description 45
- 238000005259 measurement Methods 0.000 abstract description 28
- 230000008569 process Effects 0.000 abstract description 10
- 239000000523 sample Substances 0.000 description 41
- 239000000463 material Substances 0.000 description 31
- 238000002474 experimental method Methods 0.000 description 12
- 238000005303 weighing Methods 0.000 description 8
- 238000012360 testing method Methods 0.000 description 7
- 238000010586 diagram Methods 0.000 description 6
- 239000010408 film Substances 0.000 description 6
- 230000001052 transient effect Effects 0.000 description 6
- 238000009529 body temperature measurement Methods 0.000 description 4
- 230000004907 flux Effects 0.000 description 4
- 230000000704 physical effect Effects 0.000 description 4
- 238000013461 design Methods 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 238000012546 transfer Methods 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 239000002390 adhesive tape Substances 0.000 description 2
- 239000004566 building material Substances 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 238000010146 3D printing Methods 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000003574 free electron Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000005457 ice water Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000005764 inhibitory process Effects 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 238000012067 mathematical method Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000002984 plastic foam Substances 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 239000003507 refrigerant Substances 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
Classifications
-
- 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
Abstract
The application relates to a device for measuring low-temperature heat conduction characteristics of a heat insulating material, which is characterized in that a plurality of resistors which are arranged on a first container and are in contact with a sample to be measured are utilized to measure the change data of resistance values of the resistors along with time, pressure sensors respectively arranged under the first container and a second container are utilized to measure the change data of quality along with time, and finally, the heat conduction coefficient of the sample to be measured is calculated by utilizing the unsteady state heat conduction theory of a semi-infinite object. Compared with the prior art, the application adopts the first type of boundary conditions, does not need to set a heat source, provides constant boundary temperature by using the liquid constant temperature cold source in the measuring process, has certain boundary temperature, thereby realizing the low-temperature heat conduction characteristic measurement of the heat insulation material, and liquid nitrogen is the liquid constant temperature cold source commonly used in a laboratory, so the device can be well applied to a laboratory scene.
Description
Technical Field
The application relates to the field of laboratory material physical property measurement, in particular to a device for measuring low-temperature heat conduction characteristics of a heat insulation material.
Background
Thermal conductivity (also known as thermal conductivity) is an important physical quantity reflecting the conductive properties of materials. Heat conduction is one of three basic forms of heat exchange (heat conduction, convection and radiation), and is the subject of various research fields such as engineering thermophysics, material science, solid physics, energy sources, environmental protection and the like. The thermal conduction mechanism of a material depends to a large extent on its microstructure, and the transfer of heat depends on the vibration of atoms, molecules around equilibrium positions, and the migration of free electrons. In metals, electron flow dominates, and in insulators and most semiconductors, lattice vibration dominates. Thus, the thermal conductivity of a material is not only closely related to the kind of substance constituting the material, but also to its microstructure, temperature, pressure and impurity content. The numerical value of the material is different from material to material, and the research and test of the accurate numerical value of the material has important significance for researching the physical properties of the material. In scientific experiments and engineering design, the heat conductivity coefficient of the materials needs to be accurately measured by an experimental method.
The measurement methods of the thermal conductivity coefficient are mainly classified into two types, namely a transient method and a steady state method. The steady state method is a method in which measurement is performed after the temperature distribution of the liquid to be measured has stabilized. The principle is based on the Fourier law under one-dimensional steady-state heat transfer, and the heat conductivity coefficient is calculated by directly measuring the heat flux and the temperature gradient. In the aspect of measuring the low-temperature coefficient of heat conductivity of materials, liquid nitrogen or a temperature-controllable refrigerator is commonly used as a cold source to be contacted with the materials, the other end of the materials is contacted with a heater with fixed power, so that stable temperature distribution is formed among the materials, and the coefficient of heat conductivity of the materials at low temperature is measured according to the Fourier law.
The transient method is opposite to the steady-state method, and when the thermal conductivity coefficient is measured, the temperature distribution of the object to be measured changes along with time, and the theoretical model is based on an unsteady-state thermal conductivity differential equation. During experiments, the change relation of the temperature distribution of the object along with time is recorded through a measuring instrument, and then the heat conductivity coefficient is calculated according to a theoretical relation. The transient method has the advantages of short measurement time, effective inhibition of natural convection influence in a short time and high precision. With the rapid development of modern electronic science technology, the measurement data of micro signals are more and more accurate, and an unsteady state method gradually becomes a mainstream method. The unsteady state method mainly comprises a transient hot wire method, a transient hot needle method, a transient tropical method, a constant power heat source method, a normal state method, a point heat source method, a laser flash method and the like. The method is mainly used for measuring the heat conductivity coefficient of the material at normal temperature and high temperature, and the measurement of the heat conductivity coefficient of the material at low temperature is less.
Chinese patent publication No. CN103293184A discloses an experimental device for testing the heat conductivity coefficient of a building material based on a quasi-unsteady state method, and relates to the technical field of testing the thermal physical property parameters of the building material. The problem that the existing thermophysical parameter experimental device cannot bear the measuring processes of a quasi-steady state method, a constant power method and a thermal pulse method at the same time is solved; the one-time test is longer, and the maximum relative error of the measurement is larger. The positive pole and the negative pole of the low potential potentiometer are correspondingly connected with a switch control interface of the oil immersed key change-over switch, and the thermoelectromotive signals output by the thermocouples are respectively connected with a thermoelectromotive signal input end of the oil immersed key change-over switch; cold ends of the thermocouples are respectively inserted into ice bottles for containing ice-water mixtures; the measuring ends of the thermocouples are respectively contacted with a test piece to be tested; the heating resistor is used for heating the test piece to be tested.
The application applies the unsteady heat conduction theory of a semi-infinite large object, but adopts a second type of boundary condition, namely that boundary thermal power is certain, namely a common constant-power plane heat source method, and a plane heat source is needed and is mainly applied to heat conduction physical property measurement at normal temperature and high temperature. The test in the above application for low temperature and cryogenic conditions requires the use of a quasi-steady state method. In summary, a device for measuring the low-temperature heat conduction characteristics of a heat insulating material based on a semi-infinite object theory is lacking currently.
Disclosure of Invention
The application aims to overcome the defects of the prior art and provide a device for measuring the low-temperature heat conduction characteristics of a heat insulating material, so as to realize measurement of the heat conduction characteristics of a low-temperature sample to be measured based on a semi-infinite object theory.
The aim of the application can be achieved by the following technical scheme:
the application provides a measuring device for low-temperature heat conduction characteristics of a heat insulating material, which comprises the following components:
the first container is internally provided with a first cavity communicated with the outside, the first cavity is used for containing a liquid constant-temperature cold source, the bottom of the first cavity is provided with a second cavity, the inner wall of the second cavity is provided with an opening, and the first cavity is separated from the second cavity through a separation sheet;
the sample to be tested is arranged in the second cavity, matched with the second cavity and fully contacted with the separation sheet;
the platinum resistors are arranged in the openings and are in contact with the sample to be measured, and are used for measuring the change data of the resistance value of the position along with time;
the second container is arranged in the same environment as the first container and is used for containing a liquid constant-temperature cold source with the same specific vaporization heat;
the first pressure sensor and the second pressure sensor are respectively arranged at the bottoms of the first container and the second container and are used for measuring the change data of the quality along with time;
the data processing module is used for calculating the heat conductivity coefficient of the sample to be measured by utilizing the unsteady state heat conductivity principle of the semi-infinite large object based on the size and initial temperature of the sample to be measured, the change data of the resistance value along with time and the change data of the quality along with time.
As an optimal technical scheme, the number of the resistors is three, the length of the sample to be measured is L, the plane of the sample to be measured, which is in contact with the separating sheet, is used as a reference, one end far away from the separating sheet is in a positive direction, and the three resistors are respectively arranged in x 1 、x 2 And L and satisfies 0.05 L.ltoreq.x 1 ≤0.2L。
As a preferred solution, the three resistors are also arranged to satisfy |x 1 -x 2 I is greater than five times the thickness of the resistor.
As the preferable technical scheme, the sample to be detected is cylindrical, and the outside is wrapped with heat insulation cotton.
As an optimal technical scheme, the liquid constant temperature cold source is liquid nitrogen.
As a preferable technical scheme, the resistor is a Pt100 film platinum resistor.
As a preferred technical scheme, the method further comprises:
and the data acquisition card is used for acquiring the data of the first pressure sensor and the second pressure sensor.
As a preferred technical scheme, the method further comprises:
and the constant current source is connected with each resistor in series.
As an optimized technical scheme, the first pressure sensor and the second pressure sensor are resistance strain gauge type sensors, and the resistance strain gauge type sensor comprises an unbalanced bridge measurement circuit and a plurality of strain gauges which are symmetrically arranged on a sensor bracket and connected in a bridge mode.
As a preferable technical scheme, the separating sheet is made of copper.
Compared with the prior art, the application has the following advantages:
(1) The low-temperature heat conduction characteristic measurement of the heat insulation material is realized: according to the application, the plurality of resistors which are arranged on the first container and are in contact with the sample to be measured are utilized to measure the change data of the resistance value of the resistor along with time, the pressure sensors respectively arranged under the first container and the second container are utilized to measure the change data of the quality along with time, and finally the heat conductivity coefficient of the sample to be measured is calculated by utilizing the unsteady state heat conductivity theory of the semi-infinite object. Different from the prior art that the second type boundary condition (namely, the boundary thermal power is certain), the heat source is required to be additionally arranged, the first type boundary condition is adopted, the heat source is not required to be arranged, the constant boundary temperature is provided by the liquid constant temperature cold source in the measuring process, the boundary temperature is certain, the low-temperature heat conduction characteristic measurement of the heat insulation material is realized, and the liquid nitrogen is the liquid constant temperature cold source commonly used in a laboratory, so that the device can be well applied to a laboratory scene.
(2) The measurement error of the heat conductivity coefficient is small: aiming at the problem of larger measurement error caused by smaller temperature change range of resistance measurement in measurement time limit, the application aims at the range of the position of the resistance, and the resistance is respectively arranged at x 1 、x 2 And L and satisfies 0.05 L.ltoreq.x 1 Not more than 0.2L and |x 1 -x 2 The thickness of the resistance is larger than five times, so that x can be 1 The temperature change range of the temperature sensor is larger, the influence of the temperature sensor on the measurement of the thermal conductivity coefficient of the sample material can be reduced by limiting the resistor spacing, the measurement error is reduced, and the measurement accuracy is improved.
(3) The pressure sensor has high precision: the pressure sensor is a resistance strain gauge sensor, and comprises an unbalanced bridge measuring circuit and a plurality of strain gauges which are symmetrically arranged on a sensor bracket and connected in a bridge mode, and the accuracy is high when the external force of a stress point is calculated according to the output voltage of the unbalanced bridge.
Drawings
FIG. 1 is a schematic diagram of a measurement apparatus in an embodiment;
FIG. 2 is a front view of a second container;
FIG. 3 is a top view of the second container;
FIG. 4 is a front view of the upper portion of the first container;
FIG. 5 is a top view of the upper portion of the first container;
FIG. 6 is a front view of the lower portion of the first container;
FIG. 7 is a top view of the lower portion of the first container;
FIG. 8 is a circuit diagram of a pressure sensor measurement circuit;
FIG. 9 is a front view of a pressure sensor;
FIG. 10 is a schematic perspective view of a pressure sensor;
FIG. 11 is a schematic diagram of a resistor and constant current source connection;
FIG. 12 is a schematic illustration of the heat flow rate of the absorption of liquid nitrogen by the first and second containers, and the heat flow rate at the interface of the liquid nitrogen and the icicle;
fig. 13 shows three resistors (x 1 、x 2 A schematic diagram of the temperature of the location where L) is located over time;
FIG. 14 is x 1 、x 2 Schematic diagram of change of the heat flow of the treatment plane with time;
FIG. 15 is a graph showing the thermal conductivity of ice as a function of temperature;
figure 16 is a schematic view of the measurement process,
wherein, 1, a first container, 2, a second container, 3, a separation sheet, 4, a sample to be tested, 5, a resistor, 6, a liquid constant temperature cold source, 7, a first pressure sensor, 8, a second pressure sensor, 9, a data acquisition card, 10, a data processing module, 11, a constant current source, 12, a sensor bracket, 13 and a strain gauge.
Detailed Description
The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present application without making any inventive effort, shall fall within the scope of the present application.
Example 1
Referring to fig. 1, the present embodiment provides a thermal insulation material low-temperature thermal conductivity property measuring apparatus including:
the first container 1 (hereafter referred to as container 1) is internally provided with a first cavity communicated with the outside, the first cavity is used for containing a liquid constant temperature cold source 6, liquid nitrogen is adopted in the embodiment, the bottom of the first cavity is provided with a second cavity, the inner wall of the second cavity is provided with an opening, and the first cavity is separated from the second cavity by a copper separation sheet 3.
The sample 4 to be measured is arranged in the second cavity and matched with the second cavity, and is fully contacted with the separation sheet 3, the sample 4 to be measured is cylindrical, and the outside is wrapped with heat insulation cotton.
The resistor 5 is arranged in the opening and is in contact with the sample 4 to be measured and used for measuring the change data of the resistance value of the resistor at the position along with time, the resistor 5 is a Pt100 film platinum resistor, the number of the resistors is three, the length of the sample 4 to be measured is L, the plane of the sample 4 to be measured, which is in contact with the separating sheet 3, is taken as a reference, one end far away from the separating sheet 3 is in a positive direction, and the three resistors are respectively arranged at x 1 、x 2 And L and satisfies 0.05 L.ltoreq.x 1 ≤0.2L，|x 1 -x 2 I is greater than five times the thickness of the resistor.
The second container 2 (hereinafter referred to as container 2) is disposed in the same environment as the first container 1 and is used for containing a liquid constant temperature cold source 6 having the same specific vaporization heat.
The first pressure sensor 7 and the second pressure sensor 8 are respectively arranged at the bottoms of the first container 1 and the second container 2 and are used for measuring the change data of mass along with time, and the sensors are resistance strain gauge type sensors and comprise an unbalanced bridge measuring circuit and a plurality of strain gauges 13 which are symmetrically arranged on a sensor bracket 12 and are in bridge connection.
The data acquisition card 9 is configured to acquire data of the first pressure sensor 7 and the second pressure sensor 8, and the embodiment is implemented by using NI 9219.
The data processing module 10 is configured to calculate the thermal conductivity of the sample 4 to be measured according to the unsteady thermal conductivity principle of the semi-infinite object based on the size and initial temperature of the sample 4 to be measured, the data of the resistance value change with time, and the data of the quality change with time.
A constant current source 11 connected in series with each resistor 5.
The first container 1 and the second container 2 are made of plastic foam and can be manufactured by using a 3D printing technology. The front view and the top view of the second container 2 are shown in fig. 2 and 3, and the second container is a cylindrical container with a depth of 100mm and a diameter of 60mm and is used for performing a comparative experiment and measuring the natural vaporization rate of liquid nitrogen in an experimental environment.
The first container 1 is composed of an upper part, a front view and a side view of which are shown in fig. 4 and 5, and a lower part, a front view and a side view of which are shown in fig. 6 and 7. Note that the design of the first container 1 of the present application is only for the case that the height of the sample material is 130mm, the diameter is less than 50mm, and the first, second and third temperature measuring points are respectively 15mm, 25mm and 130mm, and other sample measuring containers can be used as references. The upper part of the first container 1 is embedded with a cylindrical copper sheet (namely a separation sheet 3) with the thickness of 1mm and the diameter of 80mm at the position of 100mm deep, the upper part is divided into two parts, liquid nitrogen is put on the upper part of the copper sheet, and the lower part of the copper sheet is contacted with a sample, so that the convective heat resistance generated by direct contact of the liquid nitrogen and the sample is reduced. The lower part of the first container 1 is used for storing sample materials, the depth of the container is 120mm, and the container is combined with the depth of 10mm below the copper sheet at the upper part of the first container 1 to just form the height of 130mm, so that the container 1 is ensured to completely wrap the sample. Meanwhile, 3 small holes with the diameter of 5mm are reserved at the positions 5mm, 15mm and 120mm away from the upper bottom surface of the lower part of the container 1, and the Pt100 thin film resistor can be inserted into a sample material through the small holes for temperature measurement.
The structure of the weighing sensor is shown in fig. 9 and 10, the sensor is symmetrically stuck on the beam of the sensor bracket 12 by 4 strain gauges 13, and is connected through an unbalanced circuit, when the stress point is subjected to external force, the beam arm is deformed, so that the output voltage of an unbalanced bridge is changed, and the weighing sensor is required to calibrate voltage-quality by using standard weights with known quality before experiments. A, B in fig. 9 represents a stress point and a support point, respectively.
The circuit diagram of the load cell is shown in fig. 8, wherein R1, R2, R3, and R4 respectively represent 4 strain gauges. Referring to fig. 11, three Pt100 thin film platinum resistors are electrically connected to a constant current source, and the present application measures the resistance of the Pt100 thin film platinum resistor in the sample by four-wire method to determine the temperature of each measurement point in the sample. The resistor is connected in series at two ends of the constant current source, the voltage at two ends of the resistor is measured to obtain the resistance value, and the constant current source generally adopts 1mA current in order to reduce the heating of the resistor.
The measuring process of the data of the change of the quality with time and the data of the change of the resistance value with time comprises the following steps:
referring to fig. 16, the measurement comprises the steps of:
(1) Making the sample to be measured into a cylinder, wrapping the cylinder with heat insulation cotton, measuring the initial temperature of the sample to be measured to be T, wherein the whole sample is L in length and D in diameter 0 ；
(2) The first container was removed and a cylindrical sample wrapped with insulating cotton was inserted into the lower portion of the first container. Three Pt100 platinum resistors were inserted into the sample through small circular holes in the lower portion of the first container, and connected to a circuit. Combining the upper part and the lower part of the first container, compacting by using an adhesive tape, and ensuring that the copper sheet in the upper part is fully contacted with the upper bottom surface of the sample;
(3) Respectively placing a first container and a second container which are wrapped with a sample on two high-precision weighing sensors, pouring liquid nitrogen with the same volume into the upper part of the first container and the second container, and collecting the mass m of the first container and the mass m of the second container measured by the two weighing sensors at different tau moments in an experimental environment by a computer 1 (τ) and m 2 (τ)；
(4) Measuring each moment x by four-wire method while measuring quality 1 ，x 2 Resistance R (x) of Pt100 film platinum resistance at L 1 ,τ)，R(x 2 T), R (L, T) is dependent on the resistance of the platinum resistor and the temperatureEach time x can be calculated 1 ，x 2 Temperature T (x) 1 ,τ)，T(x 2 ,τ)，T(L,τ)；
The data processing module is internally provided with data processing instructions, and the data processing process relates to the following principles:
(1) Law of fourier
The principle of measuring the thermal conductivity is the thermal conductivity equation given by the french mathematics, the physicist josephson fourier. The equation indicates that when heat is transferred in a heat-conductive manner only in a uniform, isotropic medium, the amount of heat transferred per unit area per unit time is proportional to the temperature gradient, expressed as
In the middle ofIs heat flux, i.e. heat passing through unit area in unit time, in W.m -2 The method comprises the steps of carrying out a first treatment on the surface of the Lambda is a proportionality coefficient, called thermal conductivity coefficient, in W.m -1 ·K -1 ；/>Is a unit normal vector; />Is->Temperature gradient in the direction in K.m -1 The method comprises the steps of carrying out a first treatment on the surface of the Negative sign indicates that the direction of heat transfer is directed in the direction of temperature decrease.
(2) Unsteady state heat conduction theory of semi-infinite large object
The infinitely thick large plate has only one interface, called a "semi-infinite large object". The length and width of the object are also infinite, and the heat flow direction is perpendicular to the plane of x=0. "semi-infinite large objects" have wide engineering applications such as case hardening and quenching of large parts. The long rod with insulated periphery has uniform initial temperature, and is an equivalent semi-infinite large object when one end is cooled or heated.
A semi-infinite object with an initial temperature of T 0 At time τ=0, the surface temperature of x=0 suddenly rises to T f And remain unchanged, the temperature distribution inside the object and thus the heat flux at any one location is now determined.
Differential equations and boundary conditions describing this problem are
x＝0，T(x,τ)＝T f ，x→∞，T(x,τ)＝T 0
The analysis solution can be obtained by Laplace transformation
In which there are no dimensional variableserf (eta) is called an error function, the value of the error function can be obtained through Matlab calculation or table lookup, and a is a heat conduction coefficient.
The heat flux at any point can be obtained from fourier's law:
wherein S is the sectional area of an infinitely large object, and lambda is the heat conductivity coefficient.
The heat flow through the contact surface is:
(3) Specific vaporization heat of liquid nitrogen
Liquefied nitrogen (abbreviated as liquid nitrogen) has a boiling point of about-196 ℃ (77K), which is one of the most commonly used refrigerants in modern laboratories to achieve low temperatures. The process of converting a substance from a gaseous state is called vaporization. At a certain pressure (e.g. 1 atmosphere) the temperature is kept constant and the amount of heat absorbed per unit mass of liquid to gas is called the specific heat of vaporization P of the substance. The specific vaporization heat value is related to the temperature at the time of vaporization, and if the temperature is increased, the specific vaporization heat value is reduced. If the liquid nitrogen specific vaporization heat P in the laboratory environment is known in the experiment, the liquid nitrogen absorption heat can be calculated by measuring the liquid nitrogen vaporization mass delta M.
(4) The relation between the platinum resistance and the temperature is expressed by the following formula within the range of 0-630.74 DEG C
R T ＝R 0 (1+AT+BT 2 )
At a temperature ranging from-200 to 0 DEG C
R T ＝R 0 [1+AT+BT 2 +C(T-100℃)T 3 ]
Wherein R is 0 And R is T The resistance values of platinum resistance at 0 ℃ and temperature T ℃ respectively, A, B, C is the temperature coefficient, and a= 3.90802 ×10 is determined by experiments -3 ℃ -1 ,B＝-5.80195×10 -7 ℃ -2 ,C＝-4.27350×10 -12 ℃ -4 。
Specifically, the process of calculating the thermal conductivity of the sample to be measured includes the following steps:
s1, according to τ 1 And τ 2 Moment first container, liquid nitrogen, sample and second container, total mass m of liquid nitrogen 1 (τ 1 )，m 1 (τ 2 ) And m 2 (τ 1 )，m 2 (τ 2 ) Calculation ofRate of change of mass of liquid nitrogen in first vessel at timeLiquid nitrogen mass change rate in second container +.>Under the condition of knowing the specific heat of vaporization P of liquid nitrogen in the experimental environment, the +.>Heat flow rate of contact surface between sample and liquid nitrogen at moment
S2, according to τ 1 And τ 2 Time x 1 ，x 2 Resistance R (x) of Pt100 film platinum resistance at L 1 ,τ 1 ),R(x 2 ,τ 1 )，R(L,τ 1 ) And R (x) 1 ,τ 2 )，R(x 2 ,τ 2 )，R(L,τ 2 ) And the relation between the resistance value of the platinum resistor and the temperature can calculate tau 1 And τ 2 Time of day, x 1 ，x 2 Temperature T (x) 1 ,τ 1 )，T(x 2 ,τ 1 )，T(L,τ 1 ) And T (x) 1 ,τ 2 )，T(x 2 ,τ 2 )，T(L,τ 2 ) ThenTime x 1 ，x 2 The temperature at L is ∈ ->
S3, according toTime x 1 ，x 2 Temperature at->Initial material temperature T 0 Temperature T of liquid nitrogen f -196 ℃, and formula +_>Calculate->Time x 1 ，x 2 Position->And->Is a value of (2);
s4, according toHeat flow of material and liquid nitrogen contact surface at moment +.>Position-> And the value of (1) and the arbitrary point heat flow +.>Calculate->Time of day Material x 1 ，x 2 Heat flow of the surface>
S5, according toTime of day Material x 1 ，x 2 Heat flow at-> Temperature->Calculate->Average heat flow rate atAverage temperature>
S6, according to the Fourier heat conduction lawCalculate->Time of day Material->Where the material temperature is +.>Is>Wherein->Is the area of the bottom surface of the cylinder.
The measurement is performed below using ice as an example.
Ice block size and first temperature measuring point x 1 Is designed according to the following steps: according to the coefficient of thermal conductivity λ=2.22W/(m·k) of ice at 0 ℃, density ρ=913 kg/m 3 The specific heat capacity c=2100J/(kg·k) is estimated to approximate the thermal conductivity of ice at 0 ℃ a=λ/ρc= 1.157 ×10 -6 m 2 Design measurement time τ Limiting the limit =15 min, according toSince l=0.129 m was calculated, the length of the ice piece was designed to be l=130 mm, and the bottom surface was designed to be a circle having a diameter d=30 mm. According to 0.05 L.ltoreq.x 1 Less than or equal to 0.2L, at x 1 Pt100 thin film platinum resistor was placed at 15mm and designed as the first temperature measurement point.
Sample materials are needed between the second temperature measuring point and the first temperature measuring point, and the thickness of the sample materials exceeds 5 times of the thickness of the sensor, so that the influence of the temperature measuring sensor on the measurement of the heat conductivity coefficient of the sample materials is reduced. The thickness of the Pt100 film platinum resistor is about 1mm, and the distance between the second temperature measuring point and the first temperature measuring point is designed to be 10mm, namely, in x 2 Pt100 thin film platinum resistor was placed at =25mm and designed as the second temperature measurement point. Meanwhile, the Pt100 film platinum resistor is placed in the L=130 mm to be designed into a third temperature measuring point, the temperature of the third temperature measuring point in the experiment is reduced by 1 ℃, the experiment does not accord with a semi-infinite unbalanced heat conduction model, and the experiment is ended.
The specific measurement process is as follows:
step1, the container 1 is taken out, and a cylindrical icicle wrapped with heat insulating cotton is inserted into the lower portion of the container 1. Three Pt100 platinum resistors were inserted into the icicles through small circular holes in the lower part of the vessel 1, and connected to a circuit. The upper part and the lower part of the container 1 are combined together and compacted by using adhesive tape, so that the copper sheet in the upper part is ensured to be fully contacted with the upper bottom surface of the icicle;
step2, respectively placing the container 1 and the container 2 wrapped with the icicles in two high-precision stagesOn the weighing sensor, pouring liquid nitrogen with the same volume into the upper part of the container 1 and the container 2, collecting the mass m of the container 1 and the mass m of the container 2 measured by the two weighing sensors at different tau moments under the experimental environment by a computer 1 (τ) and m 2 (τ)；
Step3, collecting each tau moment x by a computer while measuring the quality 1 、x 2 Resistance R (x) of Pt100 platinum resistance at L 1 ,τ)、R(x 2 τ) and R (L, τ) based on the relation between the resistance value of Pt resistance and temperature, the time x can be calculated 1 、x 2 Temperature T (x) 1 ,τ)、T(x 2 ,τ)、T(L,τ)；
The data processing process is as follows:
step4, the experimental environment is standard atmospheric pressure, the temperature is 21 ℃, the specific vaporization heat of liquid nitrogen is tested to be P=180.1J/g according to experiments, and the mass m of liquid nitrogen at different moments of the container 1 and the container 2 1 (τ) and m 2 By mathematical methods such as polynomial fitting and difference, the heat flow rate Q of the container 1 can be calculated 1 (τ) and the thermal flow Q of the vessel 2 2 (τ), and the heat flow rate Δq (τ) =q of the contact surface of liquid nitrogen and the icicle 1 (τ)-Q 2 (τ) as shown in fig. 12.
Step5, first temperature measuring point (x 1 =15 mm), a second temperature measuring point (x 2 The change in temperature between the third temperature measurement point (l=130mm) =25 mm) is shown in fig. 13. According to the time period, the first temperature measuring point (x 1 =15 mm), a second temperature measuring point (x 2 Temperature T (x) =25 mm 1 ,τ)，T(x 2 τ) and formulaIce initial temperature T 0 = -10.40 ℃, liquid nitrogen temperature T f = -196 ℃, calculate τ time x 1 ，x 2 Position->And->Is a value of (2);
step6, according to the formulaWherein->For the heat flow of the contact surface of liquid nitrogen and the ice column, the time x of tau is calculated 1 ，x 2 Position->And->Can obtain the value of x passing by the time tau 1 ，x 2 Heat flow Q at the plane of the treatment x1 (τ)、Q x2 (τ) as shown in fig. 14;
step7, passing x according to time τ 1 ，x 2 Heat flow at the plane of the processCalculate position +.>Heat flow of the surface>Position->Temperature at->
Step8 according toWherein S is the area of the bottom surface of the cylinder->Calculate position +.>The temperature at the point is->As shown in fig. 15.
According to the embodiment, liquid nitrogen is used as a constant-temperature cold source, the unsteady state heat conduction theory of a semi-infinite large object is used as a basis, two temperature measuring points are arranged in the heat insulation material, physical quantities such as local heat flow and temperature gradient of the material are researched, and the low-temperature heat conduction coefficient of the heat insulation material can be measured in a wider range; measuring the heat flow of the contact surface of the material and the liquid nitrogen by a high-precision weighing sensor through a weighing method and a comparison experiment;
compared with the conventional constant-power heat source planar heat source method, the method is mainly used for measuring the low-temperature heat conductivity coefficient of the material, and the instrument used in the method is simple and easy to obtain and can be completed in a common physical laboratory.
Example 2
On the basis of embodiment 1, the liquid constant temperature cold source 6 of this embodiment may be implemented by using other liquid constant temperature cold sources available in the laboratory.
While the application has been described with reference to certain preferred embodiments, it will be understood by those skilled in the art that various changes and substitutions of equivalents may be made and equivalents will be apparent to those skilled in the art without departing from the scope of the application. Therefore, the protection scope of the application is subject to the protection scope of the claims.
Claims (10)
1. A thermal insulation material low-temperature heat conduction characteristic measuring apparatus, characterized by comprising:
the first container (1) is internally provided with a first cavity communicated with the outside, the first cavity is used for containing a liquid constant temperature cold source (6), the bottom of the first cavity is provided with a second cavity, the inner wall of the second cavity is provided with an opening, and the first cavity and the second cavity are separated by a separation sheet (3);
the sample (4) to be tested is arranged in the second cavity, matched with the second cavity and fully contacted with the separation sheet (3);
the platinum resistors (5) are arranged in the openings and are in contact with the sample (4) to be measured, and are used for measuring the change data of the resistance value of the position with time;
the second container (2) is arranged in the same environment as the first container (1) and is used for containing a liquid constant temperature cold source (6) with the same specific vaporization heat;
a first pressure sensor (7) and a second pressure sensor (8) which are respectively arranged at the bottoms of the first container (1) and the second container (2) and are used for measuring the change data of the quality along with the time;
the data processing module (10) is used for calculating the heat conductivity coefficient of the sample (4) to be detected by utilizing the unsteady heat conduction principle of a semi-infinite large object based on the size and initial temperature of the sample (4) to be detected, the change data of the resistance value along with time and the change data of the quality along with time.
2. The apparatus according to claim 1, wherein the number of the resistors (5) is three, the length of the sample (4) to be measured is L, one end far from the separator (3) is positive with respect to the plane where the sample (4) to be measured contacts the separator (3), and the three resistors are respectively arranged in x 1 、x 2 And L and satisfies 0.05 L.ltoreq.x 1 ≤0.2L。
3. The apparatus for measuring low-temperature heat conduction characteristics of heat insulating material according to claim 2, wherein the three resistances are set so as to satisfy |x 1 -x 2 I is greater than five times the thickness of the resistor.
4. The device for measuring the low-temperature heat conduction characteristics of the heat insulation material according to claim 1, wherein the sample (4) to be measured is cylindrical and is externally wrapped with heat insulation cotton.
5. The device for measuring the low-temperature heat conduction characteristics of the heat insulation material according to claim 1, wherein the liquid constant-temperature cold source (6) is liquid nitrogen.
6. The device for measuring the low-temperature heat conduction characteristics of the heat insulating material according to claim 1, wherein the resistor (5) is a Pt100 thin film platinum resistor.
7. The apparatus for measuring low-temperature heat conduction characteristics of heat insulating material according to claim 1, further comprising:
and the data acquisition card (9) is used for acquiring data of the first pressure sensor (7) and the second pressure sensor (8).
8. The apparatus for measuring low-temperature heat conduction characteristics of heat insulating material according to claim 1, further comprising:
and the constant current source (11) is connected with each resistor (5) in series.
9. The device for measuring the low-temperature heat conduction characteristics of the heat insulating material according to claim 1, wherein the first pressure sensor (7) and the second pressure sensor (8) are resistance strain gauge type sensors, and comprise an unbalanced bridge measuring circuit and a plurality of strain gauges (13) symmetrically arranged on a sensor bracket (12) and connected in a bridge mode.
10. The device for measuring the low-temperature heat conduction characteristics of the heat insulating material according to claim 1, wherein the separating sheet (3) is made of copper.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311009426.9A CN117074461A (en) | 2023-08-11 | 2023-08-11 | Equipment for measuring low-temperature heat conduction characteristics of heat insulation material |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311009426.9A CN117074461A (en) | 2023-08-11 | 2023-08-11 | Equipment for measuring low-temperature heat conduction characteristics of heat insulation material |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN117074461A true CN117074461A (en) | 2023-11-17 |
Family
ID=88718750
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202311009426.9A Pending CN117074461A (en) | 2023-08-11 | 2023-08-11 | Equipment for measuring low-temperature heat conduction characteristics of heat insulation material |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN117074461A (en) |
-
2023
- 2023-08-11 CN CN202311009426.9A patent/CN117074461A/en active Pending
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Finegold et al. | Low-temperature heat capacities of solid argon and krypton | |
| Anis-ur-Rehman et al. | Measurement of thermal transport properties with an improved transient plane source technique | |
| CN117074461A (en) | Equipment for measuring low-temperature heat conduction characteristics of heat insulation material | |
| Bronson et al. | On the specific heats of tungsten, molybdenum, and copper | |
| Zandt et al. | Capabilities for dielectric-constant gas thermometry in a special large-volume liquid-bath thermostat | |
| Wakeham et al. | Thermal conductivity measurement | |
| Bowers | The Thermal Conductivity of Liquid Helium I | |
| CN100425977C (en) | Method for measuring polymer-base foam material linear expansion coefficient by displacement sensor | |
| CN116990345A (en) | Thermal insulation material low-temperature heat conduction characteristic measurement method based on semi-infinite object | |
| Lyon et al. | New technique for measuring the heat of solid deformation | |
| Mosqueira et al. | Measurements of pool boiling heat transfer from ceramic Y1Ba2Cu3O7-delta superconductors to liquid nitrogen | |
| WO1996018871A1 (en) | Temperature sensor system using thin film of microcrystalline semiconductor | |
| Vargas et al. | A versatile and high-precision solution—reaction isoperibol calorimeter | |
| Cowan et al. | An Investigation of the β-γ Transition in Oxygen | |
| Kar et al. | Cryogenic temperature sensors | |
| Korolev et al. | A microcalorimeter for studying the magnetocaloric effect and the heat capacity in magnetic fields | |
| CN218896062U (en) | Insulating material coefficient of heat conductivity measuring device | |
| McIldowie | Introducing temperature scales | |
| CN110687095B (en) | Device for in-situ high-temperature and high-pressure experiment | |
| Trowbridge | Thermal conductivity of air at low pressures | |
| JP3146357B2 (en) | Precise measurement method of thermal conductivity of liquid material using short-time microgravity environment | |
| Walker et al. | Spontaneous ignition of wool. III. Calorimetry of slow oxidation reactions in materials of low thermal conductivity | |
| Karadağ et al. | Thermophysical properties of NPG solid solution in the NPG–SCN organic system | |
| Kang et al. | Self-testable industrial platinum resistance thermometers integrated with miniature mercury and indium fixed-point cells | |
| Mzali et al. | Measurement of temperature-dependent thermal conductivity of moist bricks using the transient hot-bridge sensor |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |