DD225875A3 - METHOD FOR THE DYNAMIC MEASUREMENT OF THE HEAT CAPACITITY, TEMPERATURE TEMPERATURE AND HEAT ACCURACY - Google Patents

Abstract

The invention relates to a method for the dynamic measurement of the heat capacity, Temperaturleitfaehigkeit and Waermeleitfaehigkeit on flat plates, in particular for building and Daemmstoffe. The object of the invention consists in the simple realization of the boundary conditions, the rapid transition to the quasi-stationary state and the simultaneous determination of the thermal characteristics heat capacity, Temperaturleitfaehigkeit and Waermeleitfaehigkeit. The task consists in the simultaneous measurement of the thermo-technical parameters without the disadvantages of realizing complicated boundary conditions and the associated high equipment expense, with a short-term method. According to the invention, a sample plate is brought to a constant temperature uO between tempering plates contacted by heat flow meters and then the heat registers recorded during the linear temperature rise of only one tempering plate (xD), the heat flows at the surfaces (xO and xD) for measuring times tD2 / 2a linearly increase in time and from the linear section the quantities DqqDqO at tconst and Dtt (qD) t (qO) at qDqO are determined and from this the calculation of the heat capacity, temperature conductivity and heat conductivity is carried out.

Description

Title of the invention

Method for the dynamic measurement of heat capacity, thermal diffusivity and thermal conductivity.

Field of application of the invention

The invention relates to a method for the dynamic measurement of heat capacity, thermal diffusivity and thermal conductivity of flat plates, which are used in particular for construction and insulation materials.

Characteristic of the known technical solutions

The dynamic measurement of the thermal characteristics of substances is carried out on geometrically shaped bodies (e.g., plates, balls, cylinders) in compliance with specific marginal and initial conditions. In this case, the solution of the heat equation is used taking into account the boundary and initial conditions used for the method for evaluating the measured values.

The application of the heat flow measuring technique has gained in importance, since averaged over large area or volume ranges parameters are obtained. In the commercial patent No. 207 a method for measuring the heat capacity and thermal conductivity is described by a plate-shaped sample in a protective shell by a tempering to a uniform temperature η) ' and then with the aid of a hotplate its surface facing the sample to a temperature of iT * is brought. Temperature control plate and heating

plate are contacted with heat flow meter. The heat flows are tracked at the edges of the sample surfaces facing the temperature control plates. The amount of heat remaining in the test specimen until the steady state is reached is a measure of the heat capacity P c.

The thermal conductivity can be determined with the measured with only one heat flow meter in the steady state heat flux density.

The timing of the transition from the state of the uniform temperature ^ in the stationary state of the heat flow has no influence on the evaluation process. The easily realisieisiden boundary conditions of said method require a sensitive and expensive measurement technique. The measuring method is unsuitable for light insulating materials. The amount of heat remaining in the test piece is so small that it is smaller than the amount of heat absorbed by the Y / heat flow meters. According to the error propagation law, high measurement uncertainties then arise for the thermal parameters. This can be counteracted by reducing the thickness of the heat flow meter. However, the reduction is subject to static and technological limits. Another disadvantage is the necessary storage of the heat flows over the entire measurement period and the execution of the aufv / endigen integration operation to determine the amount of heat remaining in the test specimen.

Object of the invention

The object of the invention ¹ is a method that allows the heat capacity, temperature and thermal conductivity of flat plates, in particular of building and insulating materials, to be measured with low measurement uncertainty quickly and with a low equipment outlay.

Essence of the invention

The object of the invention is to develop a dynamic, interference-free short-term method with which the measurement

the heat capacity and thermal conductivity on flat plates can be made simultaneously. According to the invention the object is achieved in that a sample plate is placed directly between contacted with heat generators Temperierplatten, the sample plate receives a constant temperature -J * , at the Xontaktstelle D heat flow meter with tempering the temperature increases linearly and arranged with the at the contact points 0 and D. Heat flow meters, the heat flows are measured. _O

D In the quasi-stationary state t> p- A q and ^ t are determined for the measurement times, these values being the relations

q = q ^ - q at t = constant and At = t (q _D ) - t (q _Q ) satisfying q _D = q _Q.

(a = thermal conductivity, D = thickness of the sample plate heat flow meter, q = heat flux density).

The heat capacity j c, the thermal diffusivity a and the thermal conductivity \ are calculated from the measured thermal parameters.

Exemplary embodiment

The invention will be explained in more detail using an exemplary embodiment.

FIG. 1 shows a cross section of the arrangement for carrying out the method

FIG. 2: measuring curves

The measurement of the thermal parameters is carried out on optical glass, the sample plate 1 having a thickness of 26.17 mm. The sample plate 1 is placed between contacted with heat flow meter 2 tempering 3. The sample plate 1 has a temperature of 20 ⁰ C.

For the measurement, heat flow meters 2 with the insulation value 0.018 m ² K / W, the heat capacity 970.7 kWs / m ² K and the sensitivity of 26.11 W / m mV were used.

Curve 1 shows the temperature increase (sensitivity 0.42 mV / K) on the heated surface, while curves 2 and 3 represent the Vfärmeströme at constant tempered and heated surface.

The evaluation of the quasi-stationary state provides the following measured variables:

= q _D ) Aq (t = const)

7,058 10 ~ ³ Ks " ¹ 1280 s 274,0 Wm" ²

If the temperature is linearly increased on one side of the constant-temperature sample plate, whose geometry is close to the infinite-sized plate of finite thickness, while the other maintains the starting temperature, the solution is the heat equation

- a

3t

to apply the following boundary and initial conditions:

, t = 0) = 0, 0 = / (0, t) = 0,

= ^ (D, t) = i ^ _o K t.

D = thickness of the sample plate

With the help of the Laplace transform of the heat equation, the following solution results in the subrange

· £ sinh q χ

u = VK- *. (2)

⁰ ρ sinh q D.

To determine the heat exchange-on the sample plate, the heat flow in the sub-range after

w = -λ - = r ^ o, D (3)

calculated.

From equations (2) and (3) follows;

= - / L ^ K -a ^;

⁰ P sinh q D,

q cosh q D

₁₅ = - λ ^ KX

¹ ^ ° p ^ sinh q D.

After the back transformation into the upper region, the solutions are for the quasi-stationary final state

In the quasi-stationary final state, the heat flows have the same linear increase with time when the surface of a surface is raised linearly

 The comparison of both lines yields at t = const

2 Δ.4 'j> c = - * (6)

and at q = q ^

a = - £ - (7)

The thermal conductivity is calculated from equations (6) and (7):

\ = aj c. ' (8th)

If the test plate consists of several substance densities, the quantities obtained according to equations (6) to (8) shall be treated as mean values.

The calculation of the various substance characteristics then takes place on the basis of the following known equations:

K

oo = Y ^ - "> Jn ^c n ^V n (10)

gea ^ _n

R = ^ - = - = thermal resistance of the η-th fabric layer

V = volume fraction of the η-th fabric layer

According to equations (6) to (8), the average values of the thermal parameters of the system heat flow meter-sample plate heat flow meter are calculated

~ a = 3.673 10 " ⁷ m ² / s Jc = 1.816 10 ~ ³ kWs / m ³ K λ = 0.667 W / mK.

Using equations (9) and (10), the thermal parameters of the optical glass are determined

X = 0.938 W / mK J> c = 1962.935 kWs / m ³ K a = 5.038 10 "" ⁷ m ² / s.

Claims (2)

claims 1. A method for dynamic measurement of heat capacity, thermal diffusivity and thermal conductivity, characterized in that a sample plate (1) is brought directly between with heat flow meter (2) contacted tempering (3), the sample plate (1) receives a constant temperature ν , at the Contact point D • Heat flow meter (2) with tempering plate (3) the temperature is increased linearly and with the heat flow meters (2) arranged at the contact points 0 and D the heat flows are measured and in quasi - steady state the. Y / ärmeströmung (t> -p-) Z ^ q and ^ t are determined. 2. The method according to 1, characterized in that in the quasi-stationary state, the thermal parameters ^ q and the relationships = q - q at t = constant and At = t (q _D ) - t (q ₀ ) with q _D = q suffice For this 1 page drawings