SU949449A1 - Comparator for express-measurements of material thermal conductivity factors - Google Patents

Description

(54) COMPARATOR FOR EXPRESS MEASUREMENT OF THERMAL CONDUCTIVITY FACTOR

one

The invention relates to thermophysical instrumentation, and more specifically to devices for express measurements of the thermal conductivity of materials of arbitrary forgl bodies, and can be used in those national industries that require a high-speed determination of the thermal conductivity of materials of real bodies, including finished products without disturbing them. integrity.

Instruments for measuring the coefficient of thermal conductivity of materials are known, based on probing the surface of the object under study with probes and then comparing with the results of tests on standard reference materials fl. A disadvantage of the known device for measuring the coefficient of thermal conductivity is the need to conduct a measurement process for a long period of time.

The closest in technical essence and the achieved result is a comparator for express measurement of the coefficient of thermal conductivity of materials, containing two MATERIALS

remote rod-like probes, a unit for creating and undercutting a constant temperature difference between the probe ends that are not in contact with the surface of the test material, a circuit for measuring the temperature difference between the probe ends that are in contact with the surface of the test material.

Using a known device

10, the thermal conductivity coefficient of materials having a polished horizontal surface 2 can be measured.

The disadvantages of the known device

15 consists in the fact that during repeated measurements the configuration of the probe ends contacting with the surface of the test material is disturbed and, consequently, the area of the contact of the probes with the test body changes. This, in turn, leads to a violation of the calibration characteristics of the device and the emergence of additional measurement errors. With

25 measurements of the same elastic, for example, rubber, and dispersed, in particular, bulk and fibrous materials, the contact area varies within large limits and can vary greatly

30 from that which was used when calibrating the instrument on solid standard samples, due to the partial introduction of thermal probes into such materials. This leads to low accuracy measurements of the thermal conductivity of elastic and dispersed materials.

The aim of the invention is to reduce the measurement error of the thermal conductivity coefficient by automatically taking into account the surface topography.

The goal is achieved by the fact that in a comparator for ekrepress measurements of the coefficient of thermal conductivity of materials containing two remote rod-like probes, one ends of which are in contact with the surface of the material under study, a unit for creating and maintaining a constant temperature difference between the ends of the probes that are not in contact with the surface of the material under test, the scheme for measuring the difference temperatures between the probe tips that are in contact with the surface of the test material, the probes are further provided with tips flat bases connected to the probes by ball spheres so that the inner parts of the hinges are the tips of probes in contact with the surface of the test material, made in the form of balls with a diameter greater than the diameter of the probes, and probes and tips have parameters determined from the conditions

T), L „S

(one)

 (2)

where l s

probe length

probe cross-sectional area;

D is the diameter of the base of the tip;

З / иcoefficients of thermal conductivity of the probe and tip / AO materials - approximate value

thermal conductivity of the test material. Such a solution of the problem allows stabilizing the area of KOHTiaKTa probes with materials, keeping it equal to the area of the bases of the tips when measuring on solid, elastic and dispersed materials. The measurement error offered by the comparator becomes minimal when the relation (1) is fulfilled, which is obtained on the basis of experimental and computational studies and should serve as a criterion for the choice of parameters of thermal probes and a tip for a given range of measured values

water content. At the same time, for the AO, the average of this range is taken. The low thermal resistance of the ball joints, together with the condition (2), contributes to temperature registration,

close to the surface temperature of the material at the points of sounding, and therefore increase the sensitivity of the device.

The drawing shows a diagram of a thermal comparator for express measurements of the coefficient of thermal conductivity of materials.

The comparator has two probes 1 in the form of round rods, which

5 ends that are not in contact with the surface of the material under investigation are clamped into copper plates 2 installed on a semiconductor thermoelectric battery 3. The ends of probes 1 in contact with the surface of the test material, made in the form of balls 4 with integral thermocouple splices 5 built into them, are connected by ball joints tips b, having,

for example, conical shape. The tips 6 with flat bases are brought into thermal contact with the surface of the material under study 7. An automatic current regulator 8 with a connected thermocouple 9 and thermopile 3 connected to it maintains the temperature difference between the plates 2 and therefore between the non-contacting surfaces

5 of the test material by the ends of the probes are constant. Millvoltmeter 10 with a differential thermocouple connected to it 5 register the temperature difference between the lower ends

0 thermal probes to judge o

material thermal conductivity coefficient 7.

The measurement process with the help of a comparator is reduced to the fact that thermal probes are pressed against the surface of the material under investigation by the tips of the tips and after the establishment of a stationary thermal regime.

(2-3 min) readout of millivoltmeters was measured. Then, according to the calibration curve of the data obtained as a result of the same measurements on standard samples of the coefficient of heat conductivity, we find the desired value. I.

The proposed tep / uovy comparator was tested on solid, elastic (rubber) and dispersed (powder) materials. In the experimental sample, the instrument thermoprobes and tips had the parameters L S 2 10 10 m; Dx 100 W / (m.K) (brass), Dts

5,400 W / (mK) (copper).

Claims (1)

Claim Comparator for rapid measurements of the thermal conductivity of materials, containing two remote rod-shaped probes' ^, one ends of which are in contact with the surface of the material being studied, a unit for creating and maintaining a constant temperature difference between the ends of the probes not in contact with the surface of the material being tested, a circuit for measuring the temperature difference between those in contact with the surface of the test material with probe ends, characterized in that, in order to reduce the error in measuring the coefficient of thermal conductivity due to automatic accounting of the surface topography, the probes are additionally equipped with tips with flat (bases connected to the probes by 10 ball joints so that the inner parts of the joints are the ends of the probes in contact with the surface of the test material made in the form of balls with a diameter exceeding the diameter of the probes, and the outer the parts of the hinges are the tips themselves, and the probes and tips have parameters determined from the conditions S to - probe length; - cross-sectional area of the probe / - diameter of the base of the tip; - thermal conductivity coefficients of the probe and tip materials; - approximate value of the coefficient of thermal conductivity of the test material.