SU146542A1 - Device for determining the heat transfer coefficient - Google Patents

Description

The known devices for determining the heat transfer coefficient, made in the form of an Archimedean cylinder and two thermocouples, have a low measurement accuracy, since they do not take into account the temperature difference inside the tested sample and determine the average value of the heat transfer coefficient during the entire measurement time.

In the proposed device, the working junctions of thermocouples are placed on two isothermal surfaces. One of the surfaces corresponds to the temperature average over the surface of the entire heat sink, and the second surface corresponds to the temperature average by mass. This will significantly increase the accuracy of heat transfer coefficient determination.

The drawing in the section shows the proposed device containing the Archimedean cylinder, the diameter D of which is equal to its height, and two thermocouples.

The cylinder is easy to manufacture, and its temperature field is easy to calculate, since the heat flow in the radial and axial direction goes the same way.

The ends of thermocouples are located on isothermal surfaces with temperatures equal to the temperature, average over the surface, and temperature, average by weight. For an Archimedean cylinder of diameter D, the isothermal surfaces are spheres with diameters O „and).„, With O „1.18 /), and D Q, 8SD. Here, Л „is the diameter of an isothermal surface, the temperature of which corresponds to the temperature average over the surface of the entire heat exchanger, and D is the diameter of an isothermal surface with a temperature corresponding to the temperature average by mass.

The intersection of these spheres with the sectional plane of the drawing is shown by a dotted (for a sphere with a diameter D „), an opposing (for a sphere with a diameter Dj,) LINES.

In the manufacture of the device it is especially important to ensure the accuracy of the installation of thermocouple condos on isothermal surfaces, as well as

create a reliable contact with thermocouples and the heat sink itself.

For the manufacture of the Archimedean cylinder of metal, the ends of thermocouples are welded to the bottom of drilled holes, and in the manufacture of other materials, such as graphite or refractories, special plugs and clamps are used.

The determination of the heat transfer coefficient is reduced to the fact that a uniformly heated cylinder is immersed in the test medium and the change in temperature, average over the surface and average by mass, is recorded, but with which they are plotted over time. The obtained heating or cooling curves are divided into a number of calculation intervals, for which the average heat transfer coefficient is determined for the given interval and for the entire surface of the cylinder.

The proposed device for determining the heat transfer coefficient can be widely used in the metallurgical and chemical industries to study and control various non-stationary processes of heat transfer.

Subject invention

A device for determining the heat transfer coefficient, made in the form of an Archimedean cylinder and two thermocouples, characterized in that, in order to improve the accuracy of determining the heat transfer coefficient, the working spades of thermocouples are placed on two isothermal surfaces, one of which corresponds to a temperature average over the surface of the entire heat sink and the second is the temperature, the average but the mass.