JPS6010570B2 - heat flow meter - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat flow meter for measuring the density of heat flow flowing through an object or dissipating from the surface of an object. The measurement principle of most of the heat flow meters currently on the market is that the temperature difference between the front and back surfaces of a thin thermal resistor is proportional to the heat flow density to be measured. When used as is, it is considered to be a measurement method that belongs to the "displacement method" from the classification of measurement methods. This displacement method has a relatively simple structure, is inexpensive, and is easy to handle.However, compared to electrical measurement, it is an analog measurement using a moving coil, so it has a disadvantage in terms of accuracy. It also has In other words, in a heat flow meter using the displacement method, the following measurement errors must be taken into account. There are two types of heat flow meters: the so-called surface-stick type heat flow meter, which measures the heat flow density by attaching it to the surface to be measured, and the so-called buried type heat flow meter, which measures the heat flow density by embedding it in the object to be measured. The measurement errors that should be considered are listed below for each of these heat flow meters. [1] Surface-attached heat flow meter [i] Error due to difference in contact status with the surface to be measured {o}
Error date when the convective heat transfer coefficient of gas or liquid differs from the conditions under which the heat flow sensor was tested Error Q due to differences in thermal conductivity of the material of the measured surface Emissivity of the measured surface and the gas side surface of the heat flow meter Error due to difference

[0] Buried type heat flow meter [A] Error due to the difference in thermal conductivity between the measured object during verification and the measured object during actual measurement. There is a large possibility that voids will occur, and the presence of these voids will cause errors.Of the above error factors, the "difference in emissivity" that was pointed out in surface-attached heat flow meters
Since it is presumed that "matching the emissivity" is usually a necessary condition for surface-attached heat flow meters, it is desirable to solve other error factors. By the way, from the viewpoint of measuring heat flow density with high accuracy, the zero position method is far superior to the above-mentioned displacement method. However, this heat flow meter using the zero & method has not been put into practical use at present, and there was a desire for early development.This invention was made in view of the above points. An object of the present invention is to provide a heat flow meter that can accurately measure heat flow density.An embodiment of the present invention will be described below with reference to the drawings.Before explaining the embodiment, first, this type of heat flow meter will be described. The basic measurement principle will be explained with reference to Fig. 1.Here, we will explain the surface ayu type heat flow meter.As shown in the diagram, the surface to be measured 1
1, the distribution of heat flow density is uniform and the surface temperature is Tw
Consider a slightly expanding region (area) of [K]. At this time, the heat flow density can be expressed as the sum of convection and radiation energy as shown in the following equation.の；日（TW１T＾）JudoWbo（T
W4 -T^4)...[11 However, the convective heat transfer coefficient. ; Stefan-Bormann constant (488×10-8kc
azo/Hi MK4 T^: Temperature of the air sufficiently far away from the surface to be measured [K] Go: Effective emissivity of the surface to be measured Next, the role of a thin heat insulator on a part of this uniformly radiating surface Let us consider a case where a board 12 (hereinafter referred to as heat insulating board 12) is attached. However, the emissivity of the side of the heat insulation plate blade 2 facing the air side is {
1) Assume that it is equal to w in the expression. At this time, "heat insulation plate 1"
2, the temperature of that part of the surface to be measured 11 is △Tw[K
] and becomes (Tw0ATw). Also, heat insulation board 1
According to the heat flow density ′ (<) passing through 2,
The surface temperature of decreases by △T [K] (Tw + △Tw - △
T). Here, if we consider the case where the thermal conductivity of the material of the surface to be measured 11 is infinitely large, △Tw → 0, and if the thermal conductivity is infinitely small, the surface temperature of the heat insulating plate 12 is T
It can be easily estimated that it approaches w. That is, the surface temperature of the heat-insulating plate turtle 2 is in the range of (Tw-ΔT) to Tw, and is always lower than Tw [K]. By the way, "the above heat insulation board 12
As shown in FIG. 2, it is composed of a flat heater 3, a heat flow sensor 14, and a temperature difference measuring element 15. The heat flow sensor 14 includes a thermopile 14 and a thermal resistor 1.
The heat resistor turtle 4
This is a very ordinary heat flow sensor that measures the heat flow density by detecting the temperature difference between the front and back sides of the heat flow sensor blade 2, and the surface of the heat flow sensor blade 4 on the side that comes into contact with the air has the same emissivity as the surface to be measured 1. It is colored in . Further, the temperature difference measuring element 15 has two detection points P, , P2, and the air side surface of the heat flow sensor 14 (
This is to detect the temperature difference between the surface (on the colored side) and the surface of the surface to be measured 11 that is sufficiently distant from the heat flow sensor 14. In such a configuration 1/3, if the thermal conductance of the thermal resistor 142 is k, then when the heater 13 is not generating heat, the thermal conductance due to the temperature difference of the thermal resistor 142 is The target signal v' is output, and 'nikov' eH (Tw 10△Tw-△T-T^) 10ZWhi{(TW+△TW-△T)4-T^4 }
...[There are 21 relationships. Next, heat is applied from the heater 13 so that the difference between the temperature of the blades 1 to be measured (the temperature at the detection point P) which is sufficiently far away from the heat flow sensor 14 and the surface temperature of the heat flow sensor 14 (the temperature at the detection point P2) becomes equal. When continuing, ``If the output signal of the heat flow sensor 14 is v, then tk4V: day (TW-T^) ten Whi (TW4-
T^4)=■ ……'3}. That is, from the above equation [3}, the correct heat flow density is indicated by the output of the heat flow sensor 14, and the thermal conductance k' on the left side of equation [3] is a constant determined by the thermal resistor itself, so it is not affected by any other influence. It turns out that there isn't. This is a measurement error that should be taken into consideration in the displacement method heat flow meter.
This means that measurements can be made while ignoring the 'i}, {〇', and shiichi of 1]. Note that ``from a practical point of view, the thermal conductance k has temperature dependence;
Corrected by
Each surface, that is, the surface of the heat flow sensor 14 and the surface to be measured 1
It is extremely difficult to measure the temperature on the surface of 1.
However, this does not mean measuring the correct surface temperature for each surface temperature, but rather that if each surface temperature can be measured with the same degree of measurement error, the measurement error will be canceled out by the difference. It is. To measure this temperature difference, there are differential thermocouples in which thermocouples are connected in series, and in addition to differential thermocouple groups, side temperature resistors and thermistors can be used in twilled wires. It becomes possible to use a radiation thermometer, which is a non-contact thermometer. In addition, the heat flow sensor 1
Regarding the dimensions of 4, as shown in FIG. 3, it is made smaller than the heater 13 and placed in the center of the heater 13.
A structure may be adopted in which a heat insulating material 31 is arranged around the heat flow sensor turtle 4. This is to prevent the heat from escaping sideways so that the heat applied from the heater 13 passes through the heat flow sensor ear 4 and is dissipated from the surface of the sensor equally. Therefore, the heat flow meter shown in Figures 2 and 3 is controlled so that the output of the temperature difference measuring element is always "0", so it is a zero-level heat flow meter, but this cloud level The heat flow sensor 14 built into the method heat flow meter is a normal displacement method heat flow sensor as described above. Next, FIG. 4 shows an experimental example using a heat flow sensor as shown in FIG. 2. Here, as the heater 13,
A nichrome band wire-wound uniform heater molded with a heat-resistant synthetic resin with a thickness of 6 cm x 6 cm x 1 sail is used, the heat flow sensor 4 is a commercially available one, and the temperature difference measuring element 1 is used.
5, a CRC differential thermocouple is used. and,
The heater 13, the heat flow sensor, and the temperature difference measuring element 15
is installed on the compensation heater surface of the heat flow sensor verification device 21. That is, the heat flow sensor verification device 21 is approximately 35 m x 45 m in length and width, and the surface material is made of an iron plate with a thickness of approximately 5 mm.
The heat flow sensor 14 is placed on top of the heater 13 . Then, one detection point P of the temperature difference measuring element 15 is placed on the central surface of the verification device 21 sufficiently away from the heat flow sensor 4, and the other detection point P2 is placed on the top of the heat flow sensor 1. Although not shown here, "Actually, the detection points P, P2 of the overflow difference measuring element 15 are held down by a holding device.The heater turtle 3 is a proportional, integral, and differential isothermal controller. 22 (hereinafter referred to as the PID isothermal controller 22), the output of the heat flow sensor is connected to the input terminal of the 2-pen recorder 23, and the temperature difference measuring element 15 is connected to the output terminal of the PID isothermal controller 22. In the above configuration, examine how well the results under natural convection and the results under forced convection using two fans agree. 2 shouts = about 2.6
The results obtained under forced convection with a wind of 1000 msec showed relatively good agreement as shown in Figure 5. In FIG. 5, the characteristics shown by solid lines are under natural convection, and the characteristics shown by dotted lines are under forced convection. However, the reason why the results did not match in the above two states is that the detection points P, , P2 of the temperature difference measuring element 15
There was a slight lack of consideration in the arrangement of the
This is thought to be due to the difference in convective heat transfer coefficient due to the difference between the surface to be measured and the position of the heat flow sensor 4, and if these points are taken into consideration, even more accurate measurements can be performed. From the above, it is proven that this device has sufficient practicality as a heat flow meter using the fog level method. As described above, the heat flow meter according to the present invention belongs to the zero-level method in terms of measurement methods, and it can measure heat flow density with higher accuracy than conventional displacement method heat flow meters, and its practical value is There is something very big about it.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the operating principle of a surface-attached heat flow meter, Fig. 2 is a configuration diagram for explaining an embodiment of the present invention, and Fig. 3 is a diagram of the heat flow sensor of Fig. 2. Fig. 4 is a configuration diagram showing a modified example; Fig. 4 is a horizontal diagram showing an experimental example according to the same embodiment;
The figure shows the experimental results. Turtle 1... Surface to be measured, 13... Heater, 14... Heat flow sensor, 15... Temperature difference measuring element. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1 A flat plate-shaped soaking heating body, one side of which is in contact with the soaking heating body and the other side colored to match the emissivity of the surface to be measured, detects the temperature difference between the front and back of the thermal resistor, and calculates the heat flow density. 1. A heat flow meter comprising: a heat flow sensor that measures the temperature of the heat flow sensor; and an element that measures the difference between the temperature of the colored surface and the temperature of the surface to be measured of the heat flow sensor.