SU658456A1 - Method of determining thermal conductivity coefficient of gases - Google Patents

Description

The invention relates to the field of thermophysics and can be used to determine the thermophysical properties of gases.

According to the existing methods of experimental determination of the thermal conductivity of gases, both stationary and non-stationary, measurements are carried out in a quiescent gas in the presence of two heat exchange surfaces, limiting the first layer of the test gas and having different temperatures 1.

Two significant drawbacks are inherent in these methods: the presence of two heat exchange surfaces having different temperatures and the transparency of gases for thermal radiation cause heat to be transmitted through the gas layer not only by conduction, but also by radiation; In a non-isothermal gas layer, natural convection easily occurs, which is difficult to remove in a number of cases and can significantly distort the measurement results.

The closest technical solution to the present invention is a method for determining the isobaric heat capacity of gases, which consists in that the reference and research gases alternately pass a metal tube through an electric current heated and measure the resistance differences of the input and output sections of the tube, according to which the heat capacity of the gas 2 The change in temperature distribution along the length of the tube during the flow of gas can be obtained from solving the system of heat balance equations for the tubes.

However, this method is not accurate in determining the coefficient of thermal conductivity.

The aim of the invention is to reduce errors in determining the thermal conductivity of gases.

This is achieved by changing the flow rate of the reference and test gases and finding the maximum values of the resistance difference between the tube sections.

The method is based on the fact that at a certain flow rate the temperature distribution along the length of the tube depends only on the thermal conductivity of the gas and does not depend on the flow rate and other properties of the gas. The drawing shows the device

Claims (2)

to implement the method. Two thin-walled metal tubes 1, pressed into the massive conductors 2, serve to pass gas through them. The diameter of the tubes is “1 mm. Wires 3 are welded to the tubes so that the halves of the tubes are shoulders from the measuring bridge. A circuit with a current source 4 is used for heating. Gas is supplied to tubes 1 in such a way that it flows through them in opposite directions. Increase gas flow through the tubes. The relative balance of the bridge at the same time increases first and then begins to decrease. Find the maximum value of the difference between the resistances of the tube handles, i.e. maximum imbalance of the bridge. The same operations are done earlier with the reference gas. Regarding the maximum unbalances of the bridge measured for both gases, and the known thermal conductivity of the reference gas, the thermal conductivity of the test gas is determined. To determine the temperature dependence of thermal conductivity, it is sufficient to measure the measuring instrument with a single reference gas at different temperatures. To determine the thermal conductivity coefficient, the instrument is calibrated to a second reference gas. The calculation formulas of the method do not include radiative heat fluxes through the test gas, therefore, this method does not require the introduction of corrections for heat exchange by radiation. The influence of convection on the measurement results is excluded, since the diameter of the pipe is small and the speed of convective currents. if they occur, much less flow rate. The time spent on measuring thermal conductivity at a given temperature is about 10 minutes, since the inertia of the measuring device is small 10 seconds, the measurement time is determined by the time it takes to find the maximum unbalance of the bridge and does not exceed 5 minutes. The method can be applied to measure the thermal conductivity of gases in a wide range of temperatures and pressures, possibly also at high temperatures. Claim Method The method for determining the coefficient of thermal conductivity of gases is that the reference and test gases are alternately passed through a metal tube heated by an electric current and the resistance differences between the inlet and outlet sections of the tube are measured, which determine the thermal conductivity, which is reduce systematic errors, change the flow rate of the reference and test gases and find the maximum values of the resistance difference between the tube sections. Sources of information taken into account in the examination 1. Tsederberg N. V. Thermal conductivity of gases and liquids. M., 1963, p. 48-95. 2.Gruzdev B. A., Shumska A. I. Determination of isobaric heat capacity. IFZH, 13, No. 1, 1967.