SU1557499A1 - Apparatus for determining thermophysical parameters of materials - Google Patents

Abstract

The invention relates to the study of the physical properties of substances and materials, namely, devices for determining the thermophysical properties of materials on samples in the form of plates that are not transparent to the radiation of heat. The purpose of the invention is to improve accuracy. A repeater 5, integrators 6, 7, multiplier 11 and subtractor 12 are inserted into the device containing the pulse heating source 1, the thermocouple 3, the amplifier 4, the differentiator 8, the zero-organ 9, the trigger 10 and the source 14 of the reference voltage. replace the double differentiation operation to determine the inflection point of the temperature curve by the integration operation of this curve, which provides improved accuracy. 2 Il.

Description

nat1

The invention relates to the study of the physical properties of substances and materials, namely, devices for determining the thermophysical properties of materials on samples in the form of plates that are not transparent to the radiation of heat, and can be used in research laboratories of material science of various branches of the national economy.

The purpose of the invention is to improve the measurement accuracy.

FIG. 1 shows a functional diagram of the device for determining the thermophysical characteristics of materials; in fig. 2 - time diagrams that show his work.

A device for determining the thermophysical characteristics of materials contains (Fig. 1) a pulse heating source 1 with a pulse start recorder, sample 2 being placed between a pulse heating source 1 and a thermocouple 3, amplifier 4, repeater 5, integrators 6 and 7, differentiator 8, zero - organ 9, trigger 10, multiplier 11, subtractor 12, gauge 13 and reference voltage source 14. The output of thermocouple 3 is connected via amplifier 4 to the information inputs of repeater 5 and integrator 6, the output of which is connected to one input of the subtractor 12. The output of the repeater 5 is connected to one input of the multiplier 11 and to the input of the differentiator 8, the output of which is connected via zero - organ 9 to the counting input of the trigger 10, connected by a zeroing input to the output of the recorder of the beginning of the pulse of the source 1 of the pulse heating and the output to the control inputs of the repeater 5 and the integrators 6 and 7. The integrator 7 is connected by an information input to the output the source 14 of the reference voltage and the output to another input of the multiplier 11, connected by an output to another input of the subtractor 12, the output of which is the output of the device and connected to the meter 13.

FIG. 2 denotes the signal 15 at the output of the amplifier 4i signal 16 at the output of the repeater 5; the signal 17 at the output of the differentiator 8; signal 18 at the output of the trigger 10; signal 19 at the output of the integrator 7; signal 20 at the output of the integrator 6; signal 21

at the output of the multiplier 11; signal 22 n output of the subtractor 12.

A device for determining the thermophysical characteristics of materials works as follows. .

The heat flux from the source 1 of pulsed heating enters the sample under study 2.

At the same time, the trigger 10 and the integrators 6 and 7 are zeroed by the signal from the recorder output of the beginning of the pulse of the pulse heating source 1, thereby switching the integrators 6 and 7 to the integration mode of the input signal, and the repeater 5 to the repeater of the input signal. The temperature on the surface of sample 2, opposite to the heating surface, is measured by thermocouple 3, the signal from the output of which is amplified by amplifier 4 (Fig. 2, signal 15) and fed to the input of integrator 6 and repeater 5. At the output of integrator 6, proportional to the integral of temperature T (signal 20), and the output of the repeater 5 is a signal 16 proportional to temperature.

The integrator 7 integrates the constant reference voltage, so the signal 19 at its output is proportional to the current time. When the maximum temperature Tm is reached, the signal 17 at the output of the differentiator 8 becomes equal to zero, the null organ 9 is triggered, and the trigger 18 is set to one state by the signal 18 from its output. The impulse from the trigger output 10 integrators 6 and 7 and repeater 5 are transferred to the memory mode, thereby the signals proportional to the outputs of the integrators 6 and 7 and repeater 5 are memorized

TdЈ; m and Tm respectively, where

 - analysis time interval; Јt- maximum analysis time interval. The signals from the outputs of the integrator 7 and the repeater 5 are fed to a multiplier 11, at the output of which a voltage appears that is proportional to

 m

 TmdC (signal 21). From this example

In the subtractor 12, the voltage is subtracted from the output of the integrator 6. At the output of the subtractor 12, a voltage appears that is proportional to

noye i | (Tn1-T) d (signal 22), which is measured by the meter 13. When pulsed by radiation from the surface of a flat thermally insulated opaque to radiation of a heated sample of finite thickness L, is determined by the amount of absorbed energy Q by integrating over the time from time t to and in the interval (TSH-T) between the maximum (Tm) and current (T) temperature on the surface opposite to the heating surface, the thermophysical parameters of the sample 2 according to the formulas

 -T7

L2T2 61

Q

Tml

(one)

(2)

(3) (4)

where i

J (Tm- T) dC;

a, b, a-, respectively, the coefficients of thermal diffusivity, thermal conductivity and thermal conductivity of the material of the object; f- volume heat capacity of the material.

. Relations (1) - (4) are derived from solving the problem of temperature distribution T in a thermally insulated plate of finite thickness L when energy is applied to one of the surfaces by an Γ pulse, and the energy is absorbed in the surface layer of infinitely small thickness.

The solution for the plate surface opposite to the heating surface is obtained using a pulse coefficient in the form

 -S- Ь + 2 t (-1) ЬхР (-а ГЬ 1 1

P2 II 2 L

-jj-0

where n is natural since

ABOUT

Yu

15 tt-t

-2T

m

in

I

P: 1

6

(-one)

exp

2lЈV

L2

(6)

Integra (6) cases from G 0 to

J (V Tig Tmg

on time in pre- Ј s, we get

(7)

To theoretical value, when Т Т, in practice the corresponding moment of time answers

- Then, having designated J (T - T) dС I,

I

We obtain the required design formulas (1) - (4) in which the value of T is determined using the proposed device.

The calculation of the coefficients a, v, D, b by formulas (1) - (4) does not represent technical complexity and is implemented by standard algorithms.

The use of the invention makes it possible to increase the accuracy of measuring the thermophysical parameters of materials by about an order of magnitude. So, for examining samples of tungsten in the form of discs with a diameter of 20-32 mm and a thickness of 1-2 mm, heated by a flash lamp IFK-120 (pulse duration 3 ms), having a value of thermal diffusivity a of 6.27 -10 5 (m2 / c), the following results were obtained. With the help of the well-known instrument TAU-1, which determines the coefficient of thermal diffusivity over time, when the second derivative of

temperature over time will be equal to zero, the value of the measured coefficient, obtained as an average of ten measurements with a confidence interval of 0.997,

amounted to a (7.94 ± 0.1) 10 5 (m2 / s), i.e. the deviation from the tabular value is 26.6%. Measured using the proposed device, the corresponding value of the coefficient

thermal conductivity was a (6.4It ± 0.02) -10 (m2 / s), which gives a deviation from the table value of 2.24%.

Claims (1)

Invention Formula I. A device for determining the thermophysical parameters of materials containing a source of pulse heating with a pulse start recorder, a thermocouple, an amplifier, a source of reference voltage, a null organ, a trigger and a differentiator, the output of which is connected via a null organ to a numeric trigger. the input to the output of the recorder of the beginning of the pulse, the thermocouple output is connected to the input of the amplifier , different the fact that, in order to increase the accuracy, two integrators, a multiplier, a subtractor and a repeater, connected by an information input to the output of the amplifier and to the information The first input of the integrator, the control input — to the control inputs of both integrators and the trigger output and output — to the input of the differentiator and to one input of the multiplier, the other input of which is connected to the output of the second integrator, connected by an information input to the output of the reference voltage source, the output of the first integrator is connected to one input of the subtractor, the output of the multiplier is connected to another input of the subtractor, the output of which is the output of the device. 22