SU1747954A1 - Method of measuring heat flow - Google Patents

Abstract

The invention relates to thermal measurements and is intended to measure heat fluxes in mechanical engineering, energy, and building thermal physics. The purpose of the invention is to increase the reliability of measurements of heat fluxes. The method of measuring the heat flux is that before applying the thermal insulation to the test area of the surface, then a sensor measures the temperature change of this surface, determines the rate of its change and calculates the product of these values, and the heat flux value is determined in accordance with established mathematical dependence. 2 yl

Description

The invention relates to a technique of thermal measurements and can be used in mechanical engineering, power engineering, meteorology, and building thermal physics when measuring heat fluxes.

A device is known for measuring the thermal energy released by a heated body into space, which implements a method for measuring the temperature difference between a heated body and the space surrounding this body by comparing measured temperatures. The device contains a measuring sensor mounted on the surface of the heated body and a comparative sensor located at a specific point in the space surrounding the body.

The disadvantage of this method is its low accuracy of measuring the heat flux due to the fact that the compared point is located in the surrounding space, and not on the surface of the heated body.

According to this method, temperature measurement points are in environments with different thermal conductivities, which leads to incomparable rates of measurement of measured temperatures and, consequently, to a decrease in reliability.

The closest to the proposed method is the method of determining the heat flux, which consists in measuring the change in surface temperature and determining the heat flux from the measured value, and before measuring the change in temperature, the heat to be tested is locally superimposed on the test surface, and the heat flux is determined by mathematical dependence.

The disadvantage of this method is low reliability due to the fact that the obtained value of the heat flux depends on the measurement time and varies over time for stationary heat fluxes.

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In addition, according to a known method, the initial temperature of the heat insulating material at the time it is applied to the test surface is not taken into account.

The purpose of the invention is to increase the reliability of the measurement of the stationary heat flux.

The goal is achieved by preheating the heat insulating pad to the initial temperature of the test surface, measuring the rate of temperature change of this surface after applying the heat insulating pad, and the heat flux is determined at a constant time product of the change in temperature of the test surface by following dependency:

, l A p with V DT h

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1/2

where A, p, C is the thermal conductivity, density and heat capacity of the material of the test surface;

L T - measured value of temperature change;

V is the rate of change of the value L T;

g is the heat flux.

Fig. 1 shows a block diagram of an apparatus for carrying out the proposed method; Fig. 2 is a graph of change in magnitude (Vx AT).

The device includes a temperature sensor 1, a thermal insulating overlay 2, a normalizing amplifier 3, a differential amplifier 4, an adder 5, a multiplication unit 6 and a recording device (recorder) 7.

The proposed method is carried out as follows.

A thermocouple 1 is attached to the test surface, the signal from which via normalizing amplifier 3 goes to differential amplifier 4, where the rate of temperature change is calculated, and adder 5, where the temperature change is calculated. 7. Until the moment when the heat-insulating material is applied with a stationary heat flux, the rate of change of temperature calculated by differential amplifier 4 and the amount of change of surface temperature calculated by sums ator b, equal to zero, which implies

that the recording device 7 receives a zero signal. After applying thermal insulation to the test surface, its temperature begins to increase and the signal from the multiplier unit is different from zero.

registered with the device 7.

At the initial stage, due to transients, there is a time-varying signal in blocks 3-6; however, after a certain period, depending on the quality factor and other characteristics of the amplifiers, the signal from the multiplier b becomes constant in time. The measurement of the heat flux and its calculation is carried out according to the above formula on

Claims (2)

specified site. The change profile of the magnitude (V x A T) is shown in FIG. 2. The invention The method of measuring the heat flux, consisting in a local position on the test surface is insulated with a thermal overlay, measuring the change in temperature of this surface and determining the heat flux from the measured value, taking into account the mathematical dependence on; in order to increase the reliability of the measurement results, the heat insulating pad is preheated to the initial temperature of the test surface, the rate of change of the temperature of this surface after applying the insulating lining, and the heat flux is determined at a time unchanged product of the value of the change in temperature of the test surface by the rate of its change according to the following relationship; „/ -A-o with V-AT h 1/2 g where A, p, C - respectively, thermal conductivity, density and heat capacity of the material of the test surface; A T is the measured value of the change in temperature, V is the rate of change of the value of A T; g is the heat flux & J, c //// phage. one ifar-v) FIG. 2