CN101320007A - Material thermal conductivity measurement apparatus by probe method - Google Patents

Abstract

The invention discloses a probe method material thermal conductivity coefficient measurement device based on line heat source principle which is characterized in that the device comprises a probe, a microcomputer processing system and a regulated power supply. The probe comprises an electric heating wire, a probe tube and a thermal coupler. The thermal coupler and the heating wire are arranged in the probe tube. The probe which is inserted in material to be measured for measuring the material sends a temperature electric potential signal into the microcomputer processing system for processing, changing and displaying. The regulated power supply provides constant voltage to the electric heating wire to lead to the constant heating power. The voltage range value is controlled by the microcomputer processing system. The device improves the measuring application range of the line heat method. The probe method can be applied to all substances that can be inserted in the probe. The probe after being processed can guarantee the reproducibility and the accuracy during the measurement. The measured result is directly displayed by computer. Thus, as long as the probe is inserted in material to be measured, the program can be operated automatically by the computer, and the result can be seen on the computer. Therefore, the probe method material thermal conductivity coefficient measurement device based on the line heat source principle has the characteristics of convenient measurement and high precision.

Description

Material thermal conductivity measurement apparatus by probe method

Technical field

The present invention relates to a kind of material thermal conductivity measurement apparatus, particularly a kind of material thermal conductivity measurement apparatus that adopts sonde method.

Background technology

Material thermal conductivity is measured and adopted a kind of heat-pole method measuring instrument at present, and mainly there is following problem in existing heat-pole method measuring instrument: (1) measurement range is narrower, can only measure single materials such as gas or liquid; (2) complicated operation, repeatable poor, accuracy can not guarantee.

Summary of the invention

The present invention be directed to that existing heat-pole method measuring instrument measurement range is narrow, the problem of complicated operation, a kind of material thermal conductivity measurement apparatus by probe method has been proposed, by heating and the thermometric that utilizes sonde method, and with its data transmission to computing machine, and can demonstrate the coefficient of heat conductivity of material in real time by the program that in computing machine, configures, measurement range is wide, and data are accurate, relies on computing machine to reduce Operating Complexity.

Ultimate principle of the present invention: when heating infinitely-great object with heater strip, line heat source can be regarded numerous points thermal source composition as, and each heat point source continues heat release with firm power.Through after a while, because heat conduction, off-line thermal source distance for the temperature rise at r place is in having the medium of normal rerum natura so:

$\mathrm{\&Delta;T}=\frac{\mathrm{<figure-callout\; id="4"\; label="Q"\; filenames="A20081004025300071.png"\; state="\{\{state\}\}">Q</figure-callout>}}{4\mathrm{\&pi;\&lambda;}}{\&Integral;}_{{\mathrm{\&beta;}}^2}^{\mathrm{\&alpha;}}\frac{e^{-u}}{u}\mathrm{du}$

Wherein:

$u=\frac{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="A20081004025300071.png"\; state="\{\{state\}\}">r</figure-callout>}}^2}{4a(t-t_0)}$

$\mathrm{\&beta;}=\frac{r}{2\sqrt{\left(\mathrm{at}\right)}}$

In the formula:

Q: the power of line heat source unit length (w/m);

λ: coefficient of heat conductivity (w/m.K);

α: thermal diffusion coefficient (m2/s);

T, t0: time, initial time;

P: density (kg/m3);

Cp: specific heat (J/kg ℃)

After arrangement and distortion to following formula, when the enough little or sufficiently long words of test duration of diameter of probe, following formula can be deformed into so:

$\mathrm{\&Delta;T}-\mathrm{\&Delta;}{T}_0=\frac{\mathrm{<figure-callout\; id="4"\; label="Q"\; filenames="A20081004025300071.png"\; state="\{\{state\}\}">Q</figure-callout>}}{4\mathrm{\&pi;\&lambda;}}\left[\ln \left(\frac{t}{t_0}\right)\right]$

This formula is exactly the principle equation that sonde method is measured material thermal conductivity time institute foundation.

According to the characteristics of the heater strip of our designed device, as long as (diameter of electrical heating wire is 0.0762mm to the size of detected materials, and 0.0762mm * 25=1.905mm), promptly detected materials can be regarded infinitely-great object as so greater than 1.905mm.

Based on above-mentioned hot line source theoretical principle, technical scheme of the present invention is: a kind of material thermal conductivity measurement apparatus by probe method, be characterized in, it comprises probe, microprocessor system and stabilized voltage supply, described probe comprises electrical heating wire, probe tube and thermopair, thermopair and heater strip place the inside of probe tube, insert the probe of the temperature of measured material measurement material temperature signal is imported in the microprocessor system, by microprocessor system processing, conversion and demonstration; Stabilized voltage supply provides constant voltage to make heating power constant for the heating wire in the described probe, and the voltage range value of stabilized voltage supply is controlled by microprocessor system.

The ratio of described probe length and external diameter is greater than 25, and described heater strip adopts resistance to vary with temperature little constantan, at described constantan wire surface coating tetrafluoroethylene insulation course, injects after the described electrical heating wire doubling in the probe tube, and length is with the probe tube unanimity.Described thermopair adopts T type copper one constantan insulation thermocouple, and the point for measuring temperature of thermopair is arranged in the middle aperture of probe tube, inserts the heat conductive silica gel of insulation in the middle of the probe tube.

Beneficial effect of the present invention is: the present invention has improved the measurement range of application of heat-pole method, and the material that can insert probe all can use sonde method, and no matter solid, liquid, gas all can; Repeatability and accuracy in the time of can guaranteeing to measure after the special processing of probe process; Owing to be to use computing machine directly to show measurement result, only need that probe is inserted detected materials and can pass through the automatic operation program of computer, can find out the result on computers, therefore have the characteristics convenient, that precision is high of measuring.

Description of drawings

Fig. 1 is the principle schematic of material thermal conductivity measurement apparatus by probe method of the present invention;

Material thermal conductivity measurement apparatus by probe method comprises probe, microprocessor system and stabilized voltage supply three parts as shown in Figure 1.The main effect of probe is to insert the temperature of measured material to its heating and mensuration material; Probe comprises electrical heating wire 3, probe tube 4 and thermopair 5, thermopair 5 and electrical heating wire 3 place the inside of probe tube 4, the temperature signal that during measurement probe is recorded is imported microprocessor system 1 by the data acquisition board that is connected with microprocessor system 1 with data.The main effect of microprocessor system 1 is that whole test system is controlled, promptly the temperature measured of acquisition probe, temperature data handled, controls the voltage of stabilized voltage supply 2.The effect of stabilized voltage supply 2 is for heater strip provides constant voltage, so that heater strip is in when heating, heating power is constant.

Choosing probe length is 53mm, and external diameter is 0.7mm, and its length-diameter ratio is 75.7, makes ratio be far longer than 25, satisfies the condition (length-diameter ratio must greater than 25) of Blackwell well.Heater strip 3 adopts resistance to vary with temperature little constantan (diameter 0.0762mm), injects after heater strip 3 doublings in the probe tube 4, and length is with probe tube 4 unanimities, and heater strip 3 surfaces scribble the teflon insulation layer; Thermopair 5 adopts T type copper constantan insulation thermocouple (diameter 0.0762mm), the point for measuring temperature of thermopair 5 is arranged in the aperture of probe tube 4 centres, do not draw from aperture, insert the heat conductive silica gel of insulation in the middle of the probe tube 4, the probe tube root is fixed on the insulcrete.

Utilize the hot line ratio juris by measuring probe in difference temperature rise constantly, obtain the temperature rise slope of logarithm in time, carry it into according to heat-pole method and calculate in the middle of the formula of back institute abbreviation, just can calculate the coefficient of heat conductivity of material again according to the heating power of probe.All computation schemas set in microprocessor system, by obtain temperature-time curve in conjunction with heating power can be very fast calculate material to coefficient of heat conductivity.The characteristics of this measurement mechanism are that measurement is easy to use, and broad application temperature range can be measured frozen material, and suitable material is wide, the precision height.

Claims (4)

1, a kind of material thermal conductivity measurement apparatus by probe method, it is characterized in that, comprise probe, microprocessor system and stabilized voltage supply, described probe comprises electrical heating wire, probe tube and thermopair, thermopair and heater strip place the inside of probe tube, the probe that inserts the temperature of measured material measurement material enters the temperature electric potential signal in the microprocessor system, by microprocessor system processing, conversion and demonstration; Stabilized voltage supply provides constant voltage to make heating power constant for the heating wire in the described probe, and the voltage range value of stabilized voltage supply is controlled by microprocessor system.

According to the described material thermal conductivity measurement apparatus by probe method of claim 1, it is characterized in that 2, the ratio of described probe length and external diameter is greater than 25.

3, according to the described material thermal conductivity measurement apparatus by probe method of claim 1, it is characterized in that the described electrical heating wire that is used for probe adopts constantan wire, at described constantan wire surface coating tetrafluoroethylene insulation course, inject after the described electrical heating wire doubling in the probe tube, length is with the probe tube unanimity.

4, according to the described material thermal conductivity measurement apparatus by probe method of claim 1, it is characterized in that, described thermopair adopts T type copper constantan insulation thermocouple, and the point for measuring temperature of thermopair is arranged in the middle aperture of probe tube, inserts the heat conductive silica gel of insulation in the middle of the probe tube.

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