SU1004844A1 - Material thermal physical property determination method - Google Patents

Description

renna. temperature depends on the energy input, the thermal properties of the sample, the heat exchange of the free surface of the sample with the environment, etc.

In addition, additional errors arise due to temperature measurements in the contact plane of the sample and the control sample. The behavior of isothermal lines in the contact zone of two bodies shows that when measuring temperature in the contact plane, the sensor can be either in the zone of a single thermal spot or in the zone of increased thermal resistance, which leads to significant random errors.

The aim of the invention is to improve the accuracy of determining the thermophysical properties of materials. 29-oAl / 5e / -M, VW -t fe o l / S - fe o 4-AxVa; o / 2c o K, ... ...,; (v ().). nr-s t-uKVouo / iao 1 H-Ay / gtijCarcco lS j .ГГГ where, a, U - thermal conductivity, thermal diffusivity and thickness of the sample under investigation, respectively; OHO thermal conductivity, temperature permeability of control samples; go / u; - amplitude and frequency of sinusoidal oscillations of the heat flux; to amplitude of sinusoidal fluctuations of the recorded temperature; m is the phase shift of sinusoidal oscillations of the recorded temperature relative to sinusoidal biases of the heat flow; the distance between the surface of the first control sample, the contact with the test sample, and the temperature recording point.

The goal is achieved by the fact that, according to the method for determining the thermophysical properties of materials, which consists in that the test sample is brought into thermal contact in the form of a plate and the control sample in the form of a semi-infinite body, then the surface of the test sample, opposite to the control sample, is affected by periodic oscillations heat flux and record the temperature change of the control sample, the sample surface exposed to heat is brought into thermal contact with the second a control sample in the form of a semi-infinite body, made from the same material as the first control sample, and the determination of its thermophysical properties is carried out using the formulas 5 e -H1; - b (-f-) - -4iib% | C05-Jf The drawing shows a diagram explaining a method for determining the thermal properties of materials. The scheme contains semi-infinite bodies 1 and 2 (from the point of view of the propagation of thermal vibrations with known and equal thermal properties, for example fused quartz or polymethyl methacrylate, a flat source of thermal vibrations 3 representing, for example, a metal foil heater, the sample 4 in the form of a plate or films and a temperature sensor 5. Derivation of the calculated expressions for determining the thermal properties of materials is obtained from solving a mathematical problem. The initial temperature is considered to be zero, and the density . Heat flow heater pasHa Qo (t) -% C05 (.Wc, t) eada5 mathematical formulation for the three-layer model has the following form in dimensionless koordinaTax:) .1,, fo70. .lX№. , F, (y, Fo) .9VtfX, fo), 3Fo eh iVO, a), Fo), 2, i; 6) X “O.W (V, Fo) Wi (x, Fo7: .9waOt, Fo),. Aw,. EH EH) XH, Wa (4, fo) Wi {V, o), A .Fo) .- & W tyvFo) 9X-eh "eint / Wi (X, Fo) / ,, Fo) The solution to this problem, regardless of its initial conditions, for similar oscillations, they are searched for in the form oCX, Fo) Uj (xe; .jr, ", i. A common solution to the differential equations for UjCX) is written in the following way: O, W-Se, anda (V4uJ7A . tH (x) C4e Constants C,, C, and Q |. are determined based on the boundary conditions C, Cd, 1-t: t, (c -, - c.) 1 g Cv6 -GjfC V MV (fe) (fe) V --- - bonds, 0 S AX- / CUo / 2ao

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and (l. | ш: -ъте- ° «(th, g o / uJTA .. -ViSVAT, - lt (1Ш (г v, t, e-С, е; -Сд For the control sample, in which the measurement is made sine oscillations, temperature, you can write - -11Нш) - / (- й-л) Ч -ГГ- 1 Since the reduced temperature is 9) CXfo) ReOj (X), then, taking a real acTbj, you can write the solution of the problem) Ap - H ng-e, {X, Fo) "17t T OH R-" n) .h) YUJ / AVclS | a nCCOS L. y ho (u "r-tarccoa k / liA p) where the constants ot. } B. and dimensionless parameters are expressed as follows. ((.ATV t -A - lsin / ll; | A - bsA -% U -52:, -.Shi; U) TO 1 a OQ f Q-h W From the solution obtained by simple transformations, we obtain the following for actlitud and phase shift: sinusoidal oscillations of temperatura in size coordinates 2. (Sr) "" Vb: ® -AU () "Lo ° -4 € -fe - -4i-IH Method for determining thermal properties materials is carried out as follows. A fixed frequency and amplitude of sinusoidal thermal oscillations in the heater are set. Then the amplitude and phase shift of sinusoidal oscillations are measured The measured amplitude and phase shift of the sinusoidal oscillations of the temperature using the given formulas determine the thermal conductivity and thermal diffusivity of the sample under investigation. Experimental studies of the thermal properties of the proposed method are carried out on samples in the form of plates with a thickness of 1 to 15 mm at different phase states of a substance. Example. Sample (argellit) 2 mm thick and 30 mm in diameter. placed between control samples (polymethyl methacrylate) 40 mm thick and 30 mm in diameter, thermal conductivity - 0.195 and thermal diffusivity - 11.15 X / s. The heat flux with an amplitude of 157.6 W / m and a frequency of 0.0942 Hz is set from a quartz oscillator of thermal oscillations. The temperature is measured with a thermo couple whose working junction is located 1 mm from the surface of the first control sample and the cold one on the opposite surface of this sample. In this case, the amplitude of the temperature fluctuations is 0.111 K, and the phase shift is 2.04 rad. For this sample, the following values of thermal characteristics are obtained: thermal conductivity 1.16, thermal diffusivity 6.06 X 10 m / s and heat capacity 1863 J / kg K. Example 2: sample (bitumen oil), gap 1 mm, heat flux with amplitude 157, 6 W / m and a frequency of 0.047 Hz, control samples of polymethyl methacrylate. The vibration amplitude is measured at a temperature O, and the phase shift is 1.55 rad. Thermal properties are determined; thermal conductivity - 0.110, temp.

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Claims (1)

at 1C V-uXVci5 j2JQ7 i5t, the thermal conductivity is 0.61 x and the heat capacity is 1898 J / kg K. PRI me R 3. Sample (air). The experiment was carried out analogously to example 2. The amplitude of temperature fluctuations was measured to be .127k and. phase shift - 1.80 happy. Thermal properties are determined; thermal conductivity - 0.025 W / m «K, thermal diffusivity - 194 x x 1SGmUS and heat capacity - 1071 J / kg K. Reduction of the sample surface into thermal contact with the second control sample in the proposed invention provides improved accuracy compared with the known method. In addition, it becomes possible to conduct studies of samples in different phase states, which is of great importance in drilling and developing frozen ground layers, and it is easier to determine the thermal properties of materials, since there is no need to measure the temperature on the free surface of the sample. The invention The method for determining the thermophysical properties of materials, which consists in bringing the test sample into thermal contact in the form of a plate and a control sample in the form of a semi-infinite body, then affects the surface of the test sample opposite to the control sample, periodic fluctuations in heat flow and a change in the temperature of the control sample is recorded, characterized in that, in order to improve the determination accuracy, the sample surface exposed to heat iu (brought into thermal contact with the second additional control sample in the form of a semi-infinite body made of the same material as the first control sample, and the determination of the thermophysical properties is carried out by the formulas (Ji-fel c "{J§ i-K € -fe. () "А1с- / Щ - Я: агссо% (-fc№ () -., de L., a, 14 — warm thermal conductivity, thermal diffusivity, and thickness of the sample under investigation, respectively;  - thermal conductivity, thermal diffusivity of control samples; Qf. (tto amplitude and frequency of sinusoidal fluctuations of the heat flow. to - amplitude of sinusoidal oscillations of the recorded temperature, f is the phase shift of sinusoidal oscillations of the recorded temperature relative to sinusoidal oscillations of the heat flow, X is the distance between the surface of the first control sample, which is in contact with the test sample, and the point of the register temperature.