RU2149388C1 - Method testing thermophysical characteristics of materials - Google Patents

Abstract

FIELD: experimental physics. SUBSTANCE: two point electric heaters releasing certain quantity of heat at moment of start of measurement and working ends of two heat converters ( thermocouples ) registering temperature in specified points are positioned on heat-insulated surface of tested material. Thermophysical characteristics ( thermal conductivity and thermal diffusivity ) of material are computed on basis of obtained data by formulas given in description of invention. EFFECT: reduced energy consumption by heat source. 2 dwg

Description

 The invention relates to theoretical physics, in particular to thermophysical measurements.

 There is a method of determining thermophysical characteristics, which consists in supplying a heat pulse from a heat source previously placed in a reference body to the test material and recording the values of excess temperatures in one of the sections of the reference and test bodies at two predetermined times (Copyright Certificate N 1117512 of the USSR MKI G 01 N 25/18, 1984).

 The disadvantage of this method is the need for introducing into the sample thermocouple (thermocouple), that is, conducting destructive testing.

 There is also a method of non-destructive testing of thermophysical characteristics, which consists in a pulsed thermal effect in a straight line on the thermally insulated surface of the studied material with subsequent registration of the time of equality of the excess temperature at a given distance from the source line of action, and the difference between the excess temperature on the source line of action and at a given distance from it, on the surface of the studied material (Copyright certificate N 1728755 of the USSR, MKI G 01 N 25/18, 1992).

 The disadvantage of this method is the high energy consumption of the heat source.

 In the well-known technical solution closest to the proposed one (Copyright certificate N 834480 of the USSR, MKI G 01 N 25/18, 1979), they perform a pulsed thermal effect in a straight line on the heat-insulated surface of the investigated material (product) and fix the time when the ratio between excess temperatures in two differently spaced points on the surface of the investigated material will reach a predetermined predetermined ratio.

 However, with this method, the energy consumption of the heat source is also large.

 The technical result of the invention is to reduce energy consumption by a heat source.

от второго, а вторую термопару, регистрирующую температуру T₂, - на одинаковом расстоянии

от обоих источников.The essence of the invention is as follows: two point heat sources and the working ends of two thermocouples (thermocouples) are placed on the heat-insulated surface of the test material, and one thermocouple that records the temperature T ₁ is placed at a distance R from the first point source and at a distance

from the second, and the second thermocouple, recording the temperature T ₂ , at the same distance

from both sources.

At the moment the measurement starts (τ = 0), the first and second point sources simultaneously emit heat quantities Q and 2Q, respectively. After the supply of thermal pulses, the instant of time τ _{0 is} fixed for the temperature T ₁ and T ₂ to be equal on the surface of the test material and the temperature T (τ ₀ ) is recorded at one of the locations of the thermocouples.

According to the measured values of time τ ₀ and temperature T (τ ₀ ), the coefficients of heat and thermal diffusivity are determined by the formulas below.

коэффициент теплопроводности, (1)

коэффициент температуропроводности. (2)
На фиг. 1 показана схема реализации предлагаемого способа. На теплоизолированную поверхность исследуемого материала 1 помещают точечные источники тепла 2 и 3, выделяющие энергии Q и 2Q соответственно и рабочие концы 4 двух термопар, регистрирующих соответственно температуры T₁ и T₂. Причем термопару, регистрирующую температуру T₁, располагают на расстоянии R от первого точечного источника тепла, выделяющего энергию Q и на расстоянии

от второго точечного источника тепла, выделяющего энергию 2Q, а термопару регистрирующую температуру T₂, - на одинаковом расстоянии

от обоих точечных источников, после чего определяют коэффициенты тепло- и температуропроводности исследуемого материала согласно приведенному выше описанию. На фиг. 2 приведены графики изменения температур T₁ и T₂ во времени.

thermal conductivity coefficient, (1)

thermal diffusivity coefficient. (2)
In FIG. 1 shows a diagram of the implementation of the proposed method. Point heat sources 2 and 3 are placed on the heat-insulated surface of the test material 1, emitting energies Q and 2Q, respectively, and the working ends 4 of two thermocouples, recording temperatures T ₁ and T ₂ , respectively. Moreover, the thermocouple that records the temperature T ₁ is placed at a distance R from the first point heat source that generates energy Q and at a distance

from the second point source of heat, emitting 2Q energy, and the thermocouple registering temperature T ₂ , at the same distance

from both point sources, after which the coefficients of thermal and thermal diffusivity of the test material are determined according to the above description. In FIG. 2 shows graphs of the temperature changes T ₁ and T ₂ over time.

An IBM 486 / DX-4 personal computer was used to simulate the process of measuring the thermophysical characteristics by the proposed method at R = 0.001 m and Q = 0.1 J. The material with the thermal conductivity λ = 0.9 W / m • K and thermal diffusivity was taken as the test one a = 2.8 • 10 ^-6 m ² / s. During the simulation, the values of time τ ₀ = 0.129 s and temperatures T (τ ₀ ) = 48.364 ^o C were obtained and the corresponding coefficients were calculated by formulas (1) and (2):
- thermal conductivity coefficient λ = 0.898 W / m • K,
- thermal diffusivity a = 2.796 • 10 ^-6 m ² / s.

 The use of the invention allows to increase the efficiency of measurements and significantly reduce the energy consumption of a heat source.

Claims (1)

A method for determining the thermophysical characteristics of materials, including a pulsed thermal effect on a thermally insulated surface of a test material, measuring a surface temperature at two predetermined points, characterized in that there are two point heat sources emitting energy Q and 2Q on the surface of the test material, respectively, and two thermal converters, respectively the first at a distance R from the first point source of heat emitting energy Q, and at a distance

from the second point source of heat emitting 2Q energy, and the second at the same distance

from both sources, they act on the heat-insulated surface of the material under study by point sources of heat, after which the time for reaching the temperature equality at the points of location of the thermal converters is recorded, and the coefficients of heat and thermal diffusivity are calculated by the formulas

where λ is the coefficient of thermal conductivity;
a is the coefficient of thermal diffusivity;
Q is the amount of heat generated by a point heat source;
R is the distance between the first thermal converter and the heat source of energy Q;
τ ₀ - the time to achieve equal temperatures at two given points on the surface of the investigated material;
T (τ ₀ ) is the excess temperature at the given control points of the surface of the investigated material at time τ ₀ .

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