RU2550699C1 - Digital heat flux sensor - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: digital heat flux sensor comprises two parallel heat batteries. Heat sensitive elements are digital temperature sensors, which are located in the same plane and are connected in parallel in each heat battery.

EFFECT: increased accuracy of measurement of heat flux value with the possibility of studying structure of investigated materials.

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Description

The invention relates to measuring thermophysics and can be used to measure the thermophysical properties of materials and study and heterogeneity of the material structure.

A known heat flux sensor, consisting of a thermopile with heat-sensitive elements - junctions, the design and recommendations for the manufacture of which are described in GOST 26263-84. In most cases, this type of sensor is used in devices to determine the coefficient of thermal conductivity of various materials by the method of a flat layer. A disadvantage in the design of the sensor is that the dimensions of the sensor must coincide with the dimensions of the test sample in the plane of their contact. If the dimensions of the sample are smaller than the corresponding sizes of the sensor, then part of the junctions of the sensor is in contact not with the sample, but with air. Since the thermoelectric signal of the heat flux sensor is composed of all signals coming from each junction, the signal from junctions that are not in contact with the sample carries an unaccounted error. This error is greater, the larger the sample size differs from the fixed size of the sensor in the plane of their contact.

A heat flow sensor is known in which a method for mechanically changing the number of junctions is proposed, but it is a question of changing the sensitivity of the sensor, while the dimensions of the site where the number of junctions varies, do not change (SU No. 1696910 A1).

The technical result of the invention is to improve the accuracy of measuring the magnitude of the heat flux with the possibility of studying the structure of the materials under study. This is achieved by the fact that the digital heat flux sensor (CCTT) consists of two thermal batteries of digital temperature sensors 1 and 2 (Fig. 1), in each thermal battery there are digital temperature sensors 3 are located in one plane and are connected in parallel via the 1 - Wire system. Thermopiles are parallel to each other at a fixed distance. The space between them is filled with a layer of material with known thermal conductivity and similar to the material of the sensor housing. Both terminals from two thermal batteries are connected to a PC or other device.

A feature of the digital temperature sensor is that each digital temperature sensor has an individual identification number, this allows you to first connect them in parallel, and then use the PC to isolate the signal from each temperature sensor separately. For example: we put in a device where this sensor 4 is involved, a sample of material 5 with sizes smaller than the sensor, as an example we take the dimensions of a digital heat flow sensor - 10 × 10 cm, the dimensions of the sample - 4 × 4 cm. Using a heater 6 (Fig. 2) we will form a uniform heat flow through the heat flux sensor 4. In this case, the temperature distribution along the axis marked by the dashed line 7 in Fig. 2 from the thermopiles 1 and 2 will be as follows (Fig. 3 and Fig. 4). Where in Fig.3 shows the temperature distribution according to the first thermopile on contact with the heater, Fig.4 - temperature distribution according to the second thermopile on contact with the sample. These graphs can be represented in the form of thermograms of the surfaces of the heat flux sensor 4 from the side of contact with the heater and the sample (Fig. 5 and Fig. 6).

Under the condition of uniform heat flux from the heater, the temperature at the contact of the heat flux sensor with the heater is the same at all points both along the dashed line 7 and on the entire surface of the sensor (Fig. 5 and 6).

From figure 4 it is seen that there is a decrease in temperature at the contact point "heat flow sensor - sample" due to heat removal from the heat flow sensor due to the heat-conducting properties of the sample. Temperature sensors included in the second thermopile and not in contact with the sample are in contact with air. For the reason that the thermal conductivity of the air is small, the incoming heat is not removed and the temperature at the border “heat flow sensor - air” is higher than the temperature at the border “heat flow sensor - sample”. Therefore, knowing the indicated temperature distribution on the surface of both the first and second thermal batteries (Fig. 4 and Fig. 6), all digital temperature sensors emerging from the area of contact with the sample are excluded from further calculations. Therefore, the error introduced by digital temperature sensors in contact with air is eliminated.

This makes it possible to use the specified heat flux sensor for a wide range of samples with different geometric dimensions (in the plane of contact of the samples with the heat flux sensor).

, где величина $$\left(\frac{\lambda }{L}\right)$$

находится из калибровочных экспериментов.The calculation of the desired value of the heat flux density q [W / m ² ] is as follows: at the calculated average temperature at the border “heater-DSC” and “sample-DAC”, the following is calculated: $$q=-\left(\frac{\lambda }{L}\right)\Delta T$$

where the quantity $$\left(\frac{\lambda }{L}\right)$$

found from calibration experiments.

This sensor as part of a device for determining thermal conductivity can be used to detect and study the inhomogeneity of the material structure caused by defects, inclusions, uneven density of the material, etc., by the heat wave method, provided that the dimensions of the inhomogeneities are comparable to the dimensions of a single digital temperature sensor and the thickness of the sample along the Z axis (FIG. 1), as well as the condition that the thermophysical characteristics of the inhomogeneities and the base material composing the sample are different.

The experiment is carried out as follows (figure 2): on one side of the sample 5, the heater 6 forms a short uniform heat flux. Using the second heat flux sensor 8, namely the thermal battery, a temperature field is fixed at the contact with sample 9, which can be used to judge the presence of inclusions, regions with different densities, etc., if the temperature field is not uniform; and uniformity of the structure of the sample, if the temperature at all points is the same.

Literature

1. GOST 26263-84 Soils. Laboratory method for determining the thermal conductivity of frozen soils. - M .: Publishing house of standards, 1985. - 9 p.

2. Heat flow sensor. Patent SU 1696910 A1; G01K 17/08. Cheryukanov S.D., Grishchenko T.G., Dekusha L.V. and etc.

Claims (1)

A digital heat flow sensor, including a thermopile of connected thermosensitive elements, characterized in that it consists of two parallel thermopiles, as thermosensitive elements, digital temperature sensors are used, which are located in the same plane and connected in parallel in each thermopile.

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