CN101788513A - Measurement device of thermal conductivity of materials and method thereof - Google Patents

Abstract

The invention discloses a measurement device of thermal conductivity of materials and method thereof. The device comprises a probe, a regulated power supply, a computer processing system, Wheatstone BR bridges and a data-test acquisition system. The Wheatstone BR bridges are connected with the probe, the regulated power supply and the data-test acquisition system respectively. The data-test acquisition system is connected to the processing system of the computer. The measurement method is composed of two steps: standardizing the instrumental constants of the probe from the materials with identified coefficient of heat conductivity, calculating the corresponding coefficient of heat conductivity of different materials according to the linear relation between the detected voltage difference and the natural logarithm of the time, and the standardized instrumental constants.The invention can provide a fast, convenient and precise measurement method, available on line and widely applicable.

Description

A kind of measurement mechanism of material thermal conductivity and measuring method

Technical field:

The present invention relates to measure the material thermal conductivity field, be specifically related to a kind of device of measuring the material heat-conducting system, also relate to a kind of measuring method of measuring heat-conducting system based on this device simultaneously.

Background technology:

Coefficient of heat conductivity has reflected the ability of material conduction heat, and is closely related with diabatic process, is the very important thermophysical property parameter of material, also is to carry out insulated design and the indispensable key parameter of analytical calculation; Have a wide range of applications in industries such as the energy, chemical industry, refrigeration, biology, food.

The measuring method of coefficient of heat conductivity generally can be divided into steady state method and unstable state method two big classes, steady state method refer to sample reach thermally-stabilised after, the heat, thermograde etc. that flow through sample by measurement are determined the coefficient of heat conductivity of sample material by Fourier's law, the starting point of its analysis is the heat conduction differential equation of stable state, be characterized in that empirical formula is simple, experimental period is long, needs large-sized sample in the test, needs to measure the temperature of heat conduction amount (directly or indirectly) and some points.

The unstable state method refers to that specimen temperature changes in time in the experiment measuring process, and the starting point of its analysis is the unstable conduction differential equation.Measuring principle is the sample that is in thermal equilibrium state to be applied certain heat disturb, and measures the response (temperature over time) that sample disturbs heat simultaneously, determines the numerical value of sample material coefficient of heat conductivity then according to response curve.For the unstable state assay method, heat-pole method is used comparatively extensive, but in actual applications, because the diameter of heated filament is minimum, is difficult to directly be inserted with in the specimen material of certain degree of hardness, has limited the application of heat wire method.

Chinese patent CN 101320007A discloses a kind of material thermal conductivity measurement apparatus by probe method based on the line heat source principle, this device comprises probe, microprocessor system and stabilized voltage supply, its middle probe comprises electrical heating wire, probe tube and thermopair, thermopair and heater strip place the inside of probe tube, insert measured material and measure the probe of material the temperature electric potential signal is sent in the microprocessor system, handle, conversion and demonstration; Stabilized voltage supply provides constant voltage to make heating power constant to electrical heating wire, and its voltage range value is controlled by microprocessor system.This technical scheme is by measuring the coefficient of heat conductivity that time dependent probe temperature rise and heating power obtain the material of measuring and monitoring the growth of standing timber.In the test, require to use thermopair to carry out thermometric, the point for measuring temperature of thermopair is arranged in the aperture in the middle of the probe tube, has increased manufacture difficulty, and occurs fault such as loose contact in using easily, is unfavorable for data stability and accuracy.

Summary of the invention:

The object of the present invention is to provide a kind of device of the measurement material thermal conductivity based on the unstable state method, be used to solve problems such as existing measurement mechanism sample requirement is big, test specification is little and measuring accuracy is low.

Another object of the present invention is to provide a kind of method of measuring material thermal conductivity, and this measuring method is implemented based on above-mentioned measurement mechanism, is used to solve problems such as existing measuring method test duration length and operation steps complexity.

In order to achieve the above object, the present invention adopts following technical scheme:

A kind of measurement mechanism of material thermal conductivity, this device comprises probe, stabilized voltage supply, computer processing system; Described measurement mechanism also comprises Wheatstone bridge and data test acquisition system, described probe is used for heating and thermometric, insert in the detected materials sample, described stabilized voltage supply imposes stabilized voltage supply by Wheatstone bridge to thermal probe, it is poor that described data test acquisition system is gathered the output voltage of Wheatstone bridge, and after amplifying conversion, transferring to computer processing system, described computer processing system calculates the coefficient of heat conductivity of detected materials sample according to the numerical signal that receives.

Described probe comprises enamel-cover copper wire and probe tube, and described enamel-cover copper wire scribbles insulation course, and evenly is covered with in probe tube inside, middle heat-conducting silicone grease of filling insulation, and the tube head of described probe tube and pipe tail seal with epoxide-resin glue.

Described Wheatstone bridge comprises three adjustable resistance casees.

A kind of measuring method of material heat-conducting system, this measuring method is implemented based on last measurement mechanism, and it comprises the steps:

(1) in constant temperature oven, put into the material of known coefficient of heat conductivity, probe is inserted, and constant temperature is to the temperature of required test;

(2) resistance of resistance box in the output voltage of adjusting stabilized voltage supply and the Wheatstone bridge, the control circuit output voltage signal is to predetermined value;

(3) closed circuit, probe is heated disconnecting circuit after a period of time, gather the output voltage difference of Wheatstone bridge and the variable quantity of heat time heating time, output potential difference and the logarithm of gathering of time carried out linearity period process of fitting treatment, principle by degree of correlation maximum obtains the output voltage difference linear changing relation of natural logarithm in time;

(4) the output voltage difference that obtains according to step (3) in time the linear changing relation of natural logarithm calculate the instrument constant of probe;

(5) test substance is tested according to step (1) to step (3), obtained the respective output voltages difference linear changing relation of natural logarithm in time, the instrument constant value that obtains according to step (4) is again tried to achieve the coefficient of heat conductivity of test substance.

The output voltage of stabilized voltage supply is 2-8V in the described step (2), described circuit output voltage signal＜10 ^-5V.

In the described step (3) probe being carried out heat time heating time is 20-40S, and with the output voltage difference of 0.5 second speed acquisition Wheatstone bridge of every and the variable quantity of heat time heating time.

In order further to improve the precision of measuring method, described step (4) can take multiple measurements, and obtains many group numerical value, and is the instrument constant of probe with the average of many groups numerical value.When taking multiple measurements, each time interval of measuring is more than the 5min again.

Further, also comprise verification step in the measuring method provided by the invention, the instrument constant that is used for the probe that verification step (4) obtains, described verification step is as follows: other material of selecting known coefficient of heat conductivity, test according to step (1) to step (3) down temperature required, obtain the output voltage difference linear changing relation of natural logarithm in time, the instrument constant value of determining according to step (5) is tried to achieve the coefficient of heat conductivity of this material again, and with the known coefficient of heat conductivity of this material relatively, come the reliability of the instrument constant that verification step (5) determines.

Measurement mechanism provided by the invention has following advantage:

1, simple in structure, realize easily, easy to operate;

2, applied widely, can be used for accurately measuring the coefficient of heat conductivity solid-state, liquid, that gaseous material comprises the material that self can conduct electricity;

3, amount of samples is few;

4, can on-line measurement;

5, measuring accuracy height.

Measuring method provided by the invention has the following advantages:

1, test duration weak point, operation steps is simple;

2, the temperature rise of mensuration process sample is little, and the thermal perturbation of environment influence is little during measurement;

3, for biomaterial, tissue damage is little and involved area is little;

4, measuring accuracy height.

Description of drawings:

Further specify the present invention below in conjunction with the drawings and specific embodiments.

Fig. 1 is the structural representation of measurement mechanism among the present invention.

Fig. 2 is the structural representation of middle probe of the present invention.

Fig. 3 is the process flow diagram of measuring method among the present invention.

Embodiment:

For technological means, creation characteristic that the present invention is realized, reach purpose and effect is easy to understand, below in conjunction with concrete diagram, further set forth the present invention.

Based on the line heat source transient model, can set up the one dimension Transient Heat Transfer differential governing equation radially in infinity, the isotropic medium:

Copper wire $\frac{1}{r}\frac{\∂}{\∂r}\left(r\frac{{\∂\mathrm{\θ}}_w}{\∂r}\right)+\frac{q}{{\mathrm{\πr}}_w^2{\mathrm{\λ}}_w}=\frac{1}{a_w}\frac{{\∂\mathrm{\θ}}_w}{\∂t}(0\≤r\≤r_w,t>0)---\left(1\right)$

Metal sleeve $\frac{1}{r}\frac{\&PartialD;}{\&PartialD;r}(r-\frac{{\&PartialD;\mathrm{\&theta;}}_p}{\&PartialD;r})=\frac{1}{a_p}\frac{{\&PartialD;\mathrm{\&theta;}}_p}{\&PartialD;t}(r_w<r\&le;r_p,t>0)---\left(2\right)$

Sample $\frac{1}{r}\frac{\&PartialD;}{\&PartialD;r}\left(r\frac{{\&PartialD;\mathrm{\&theta;}}_m}{\&PartialD;r}\right)=\frac{1}{a_m}\frac{{\&PartialD;\mathrm{\&theta;}}_m}{\&PartialD;t}(r>r_p,t>0)---\left(3\right)$

Boundary condition

θ _w(r _w，t)＝θ _p(r _w，t) (4)

${\mathrm{\&lambda;}}_w{\left(\frac{{\&PartialD;\mathrm{\&theta;}}_w}{\&PartialD;r}\right)}_{r_w}={\mathrm{\&lambda;}}_p{\left(\frac{{\&PartialD;\mathrm{\&theta;}}_p}{\&PartialD;r}\right)}_{r_p}---\left(5\right)$

θ _p(r _p，t)＝θ _m(r _p，t) (6)

${\mathrm{\&lambda;}}_p{\left(\frac{{\&PartialD;\mathrm{\&theta;}}_p}{\&PartialD;r}\right)}_{r_p}={\mathrm{\&lambda;}}_m{\left(\frac{{\&PartialD;\mathrm{\&theta;}}_m}{\&PartialD;r}\right)}_{r_m}---\left(7\right)$

Starting condition:

θ _w(r，0)＝θ _p(r，0)＝θ _m(r，0)＝0 (8)

θ in the formula: the difference of copper wire temperature and initial room-temperature

λ: coefficient of heat conductivity

α: thermal diffusion coefficient

T: heat time heating time

R: radial coordinate value

Q: the heating power of unit length copper wire

Subscript w, p, m represent copper wire, metal sleeve, testing medium respectively.

Obtain the exact solution of differential governing equations with Laplace transform, as a that satisfies condition _mT/r _p ²Enough big, the sample coefficient of heat conductivity can be expressed as:

${\mathrm{\&lambda;}}_m=-\frac{{\mathrm{AU}}^3}{R_b^2}/\frac{d\left(\mathrm{\&Delta;V}\right)}{d\left(\ln t\right)}---\left(9\right)$

This formula is exactly the measurement relational expression of entire measuring device institute foundation.In the following formula, a _mBe the thermal diffusivity of testing sample, unit is m ²/ s; r _pBe the radially radius of probe, unit is m; λ _mBe the coefficient of heat conductivity of testing sample, unit is W/ (mK); U is the voltage of stabilized voltage supply, and unit is V; R _pBe the initial resistance of probe, unit is Ω; Δ V is that circuit output voltage is poor, and unit is V; T is heat time heating time, and unit is s; A=0.005 α ₀R ₀/ L is an instrument constant, and L represents copper wire length; R ₀The resistance of the copper wire when representing 0 ℃; α ₀Copper wire temperature coefficient when representing 0 ℃.

Based on above-mentioned principle as can be known, as long as can know the circuit output voltage difference linear changing relation of natural logarithm (d (Δ V)/d (lnt)) in time, according to formula (9) just can obtain the coefficient of heat conductivity of respective material.

For this reason, the invention provides a kind of device of the measurement material thermal conductivity based on the unstable state method, as shown in Figure 1, this device comprises probe 100, stabilized voltage supply 200, computer processing system 500, Wheatstone bridge 300 and data test acquisition system 400.

Referring to Fig. 2, probe 100 is used for heating and thermometric, and it inserts in the detected materials sample when test, probe 100 mainly is made up of enamel-cover copper wire 104 and probe tube 105 two parts, wherein the enamel-cover copper wire scribbles insulation course, evenly is covered with in probe tube 105 inside, and connects power supply by lead-in wire 101.

Probe tube 105 adopts medical needle, and the ratio of length and external diameter is greater than 25; The tube head of probe tube 105 is provided with insulation end socket 102, fills simultaneously the heat-conducting silicone grease 103 of insulation in the middle of the probe tube, and at the tube head of probe tube 105 and pipe tail with epoxide-resin glue 106 sealings.

Wheatstone bridge 300 among the present invention mainly is made up of three adjustable resistance casees 301, and it is the core of whole device, by regulating the resistance of resistance box, regulates the output voltage signal of circuit in the measurement mechanism.Wheatstone bridge 300 joins with stabilized voltage supply 200, and probe 100 is applied the firm power that source of stable pressure 200 provides, and Wheatstone bridge 300 also joins with data test acquisition system 400 simultaneously.It is poor that data test acquisition system 400 will be gathered the output voltage of Wheatstone bridge 300, and transfer to computer processing system 500 after amplifying conversion.

Adjustable in order to realize voltage, the stabilized voltage supply 200 that the present invention adopts is adjustable D.C. regulated power supply.

According to the measurement mechanism that technique scheme obtains, it is as follows at operational process:

Probe 100 is inserted in the testing sample 700 that is placed in the adjustable thermostatic case 600, according to the characteristic that has linear relationship between copper resistance and the temperature, impose firm power by stabilized voltage supply 200 by 300 pairs of probes 100 of Wheatstone bridge, the intensification of being heated of the copper wire of probe 100 inside, probe tube and testing sample 700 are also along with intensification simultaneously, the resistance that causes copper wire changes, thereby the output voltage difference of Wheatstone bridge 300 is changed thereupon, after data test acquisition system 400 is amplified conversion with the output voltage difference signal that collects, input computer processing system 500 is handled, obtain the output voltage difference linear changing relation d of natural logarithm (Δ V)/d (lnt) in time, can obtain the coefficient of heat conductivity of institute's test sample product according to formula (9).

Based on said apparatus with and operation logic, specifically measure material heat-conducting system step following (referring to Fig. 1 and Fig. 3):

(1), in adjustable thermostatic case 600, put into the material of known coefficient of heat conductivity, and probe 100 inserted (if this material is a solid matter, probe 100 can directly thrust; If this material is a liquid substance, can liquid substance be poured in the small beaker of 50ml in advance), regulate the temperature of constant temperature oven 600 constant temperature then to required test.

(2), regulate stabilized voltage supply 200, make that the circuit input voltage of measurement mechanism is about 2～8V; Regulate the resistance Rs of resistance box in the Wheatstone bridge 300, control circuit output voltage signal Δ Vi＜10 ^-5V.

(3), the circuit of closed measurement mechanism, probe is heated disconnecting circuit behind 20～40s, with the output potential difference of 0.5 second speed acquisition Wheatstone bridge 300 of every and the variable quantity of heat time heating time, the output potential difference Δ V of collection and the logarithm lnt of time are carried out linearity period process of fitting treatment with the Excel ChartWizard, principle by degree of correlation maximum obtains the output voltage difference linear changing relation d of natural logarithm (Δ V)/d (lnt) in time.

(4), by d (Δ V)/d (lnt) that step (3) obtains, calculate the instrument constant value of probe 100 again according to formula (9).

(5), repeating step (3) is to (4), each measuring intervals of TIME is more than the 5min, obtains many group instrument constant values, asks its mean value then, determines the instrument constant of probe.

(6), select other material of known coefficient of heat conductivity, test the d that is obtained accordingly (Δ V)/d (lnt) according to step (1) to (3) down temperature required; Try to achieve the coefficient of heat conductivity of this material in the instrument constant value that obtains according to step (5), and with the known coefficient of heat conductivity (being literature value) of this material relatively, come the reliability of the instrument constant that verification step (5) determines.

(7) test substance is tested according to step (1) to step (3), obtained corresponding d (Δ V)/d (lnt), the instrument constant value of verifying according to step (6) is again tried to achieve the coefficient of heat conductivity of test substance.

The instantiation that adopts above-mentioned measurement mechanism and measuring method to measure is as follows:

At first, pure glycerine is poured in the small beaker of 50ml, put into the adjustable thermostatic case, and probe is inserted, regulate the probe temperature of constant temperature oven constant temperature to 20 ℃ then;

Then, regulate stabilized voltage supply, make that the circuit input voltage is 3.05V, the resistance to regulating resistance box in the Wheatstone bridge before the probe heating makes output voltage signal Δ Vi (be generally less than 10 near 0 ^-5V);

Then, closed whole test circuit, probe is heated, and with 0.5 second every speed acquisition output potential difference and the variable quantity of heat time heating time, the output potential difference Δ V of collection and the logarithm lnt of time are carried out linearity period process of fitting treatment with the Excel ChartWizard, principle by degree of correlation maximum calculates d (Δ V)/d (lnt);

Moreover, by measuring relational expression, the standard coefficient of heat conductivity of known glycerine calculates the instrument constant of probe, test is eight times under the identical conditions, twice measuring intervals of TIME is more than the 5min, so that probe and sample return to initial balance attitude (following test is same), ask its mean value then, obtain the final instrument constant of probe;

At last, choice criteria sample pure water (resistivity 18.4M Ω cm) is analyzed pure ethylene glycol and analysis straight alcohol solution, at room temperature tests, and tries to achieve each sample coefficient of heat conductivity according to the instrument constant value that preceding step obtains, and with literature value relatively, concrete outcome is as shown in table 1:

The test result of table 1 sample coefficient of heat conductivity

In the actual measurement, the environment temperature of high precision pure water is 15 ℃; The environment temperature of ethylene glycol is 20 ℃; The environment temperature of absolute ethyl alcohol is 16 ℃.As can be seen from Table 1, the coefficient of heat conductivity of high precision pure water and ethylene glycol and literature value deviation are less than 1%, and the coefficient of heat conductivity of measurement absolute ethyl alcohol and literature value deviation are less than 2%, so the present invention can be used for testing the coefficient of heat conductivity of testing sample more exactly.

More than show and described ultimate principle of the present invention, principal character and advantage of the present invention.The technician of the industry should understand; the present invention is not restricted to the described embodiments; that describes in the foregoing description and the instructions just illustrates principle of the present invention; without departing from the spirit and scope of the present invention; the present invention also has various changes and modifications, and these changes and improvements all fall in the claimed scope of the invention.The claimed scope of the present invention is defined by appending claims and equivalent thereof.

Claims (9)

1. the measurement mechanism of a material thermal conductivity, this device comprises probe, stabilized voltage supply, computer processing system; It is characterized in that, described measurement mechanism also comprises Wheatstone bridge and data test acquisition system, described probe is used for heating and thermometric, insert in the detected materials sample, described stabilized voltage supply imposes stabilized voltage supply by Wheatstone bridge to thermal probe, it is poor that described data test acquisition system is gathered the output voltage of Wheatstone bridge, and transfer to computer processing system after amplifying conversion, and described computer processing system calculates the coefficient of heat conductivity of detected materials sample according to the numerical signal that receives.

2. the measurement mechanism of a kind of material thermal conductivity according to claim 1, it is characterized in that, described probe comprises enamel-cover copper wire and probe tube, described enamel-cover copper wire scribbles insulation course, and evenly be covered with in probe tube inside, middle heat-conducting silicone grease of filling insulation, the tube head of described probe tube and pipe tail seal with epoxide-resin glue.

3. the measurement mechanism of a kind of material thermal conductivity according to claim 1 is characterized in that, described Wheatstone bridge comprises three adjustable resistance casees.

4. the measuring method of a material heat-conducting system, this measuring method is implemented based on the described measurement mechanism of claim 1, it is characterized in that described measuring method comprises the steps:

(1) in constant temperature oven, put into the material of known coefficient of heat conductivity, probe is inserted, and constant temperature is to the temperature of required test;

(2) resistance of resistance box in the output voltage of adjusting stabilized voltage supply and the Wheatstone bridge, the control circuit output voltage signal is to predetermined value;

(3) closed circuit, probe is heated disconnecting circuit after a period of time, gather the output voltage difference of Wheatstone bridge and the variable quantity of heat time heating time, output potential difference and the logarithm of gathering of time carried out linearity period process of fitting treatment, principle by degree of correlation maximum obtains the output voltage difference linear changing relation of natural logarithm in time;

(4) the output voltage difference that obtains according to step (3) in time the linear changing relation of natural logarithm calculate the instrument constant of probe;

(5) test substance is tested according to step (1) to step (3), obtained the respective output voltages difference linear changing relation of natural logarithm in time, the instrument constant value that obtains according to step (4) is again tried to achieve the coefficient of heat conductivity of test substance.

5. the measuring method of a kind of material heat-conducting system according to claim 4 is characterized in that, the output voltage of stabilized voltage supply is 2-8V in the described step (2), described circuit output voltage signal＜10 ^-5V.

6. the measuring method of a kind of material heat-conducting system according to claim 4, it is characterized in that, in the described step (3) probe being carried out heat time heating time is 20-40S, and with the output voltage difference of 0.5 second speed acquisition Wheatstone bridge of every and the variable quantity of heat time heating time.

7. the measuring method of a kind of material heat-conducting system according to claim 4 is characterized in that, described step (4) can take multiple measurements, and obtains many group numerical value, and is the instrument constant of probe with the average of many groups numerical value.

8. the measuring method of a kind of material heat-conducting system according to claim 7 is characterized in that, the described step (4) of stating is when taking multiple measurements, and each time interval of measuring is more than the 5min.

9. the measuring method of a kind of material heat-conducting system according to claim 4, it is characterized in that, also comprise verification step in the described measuring method, the instrument constant that is used for the probe that verification step (4) obtains, described verification step is as follows: other material of selecting known coefficient of heat conductivity, test according to step (1) to step (3) down temperature required, obtain the output voltage difference linear changing relation of natural logarithm in time, the instrument constant value of determining according to step (5) is tried to achieve the coefficient of heat conductivity of this material again, and with the known coefficient of heat conductivity of this material relatively, come the reliability of the instrument constant that verification step (5) determines.

Images