JPS5915846A - Heat conductivity measuring cell using heat generator - Google Patents

Abstract

PURPOSE:To measure heat conductivity in good preciseness, by a method wherein a current is supplied to an electric hating wire having resitance independent of a temp. to heat a heat generator and a metal pipe encircling the outside thereof is controlled to a predetermined temp. to detect the temp. difference of the heat generator and the metal pipe by a thermocouple or a thermopile. CONSTITUTION:An electric heating wire 3 having resistance independent of a temp. is sealed in a heat generating pipe 1 comprising a metal fine pipe and a current is supplied to the electric heating wire 3 to heat the heat generating pipe 1. The outer pipe 2 made of a metal encircling the heat generating pipe 2 is controlled to a definite temp. to detect the temp. difference of the heat generating pipe 1 and the outer pipe 2 by a thermocouple 4 and the heat conductivity of a heat conductivity measuring cell is measured. Because the thermocouple is used in the measurement of a temp., highly precise measurement is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION In a steady state, the amount of heat released from the heating element is equal to the amount of heat generated, but the amount of heat released is not only due to heat conduction through the gas, but also due to radiation and heat conduction through solid parts. In the two-constant-temperature equation, the radiation and heat conduction through solid parts are both considered to be independent of the presence of gas, so they are corrected by measurements in vacuum. If the two-temperature equation is not used, the amount of heat dissipated by radiation and heat conduction through the solid part depends on both temperatures, so measurement in vacuum will not be sufficiently corrected.

In this way, the two-constant temperature formula is better;
There are the following two methods.

1) Both temperatures are controlled separately to a predetermined temperature.

it) control the temperature of one side to a predetermined temperature,
The temperature difference between the two is controlled to be a predetermined temperature difference.

When considering which of these two methods is more advantageous for a thermal conductivity measurement cell, assuming that the measurement errors of temperature and temperature difference are of the same degree (for example, assuming that both are 1°C), the thermal conductivity measurement cell It is known that the effect of temperature error on the measured value of temperature is approximately twice that of temperature difference error. Also, when controlling temperature and temperature difference,
It is also known that temperature difference control should be performed as accurately as possible, and temperature control does not need to be performed as precisely as possible.

If the temperature difference is detected using a thermocouple or thermopile, the temperature difference will be 0.
Since it is not difficult to obtain an accuracy of 1° C., in the present invention, a thermocouple or thermopile is used to detect the temperature difference.

In the cell of the present invention, the temperature of the heating element is not measured.

Therefore, it is desirable that the calorific value be known easily, so
The heating element is heated by a heating wire whose resistance does not depend on temperature.

The temperature of the outer tube may be measured with an appropriate thermometer, but a thermometer in which a thermocouple or thermopile for measuring temperature differences is connected to a platinum resistance thermometer or the like is most suitable.

FIGS. 1, 2, and 3 are explanatory diagrams showing different embodiments of the thermal conductivity measurement cell according to the present invention, and FIG. 1 shows that the heating element has a resistance that does not depend on the temperature. A measurement cell is shown in which the heating wire is housed in a thin metal right circular tube. That is, a metal thin tube (exothermic tube) 2 with an outer diameter of 2r and a length of t is installed coaxially with a metal right circular tube (outer tube) 2 with an inner diameter of 2r2,
Inside it is a heating wire 3 whose resistance does not depend on the temperature.
The temperature difference between the heat generating tube and the outer tube is measured by the thermopile 4. The thermopile is connected to a platinum resistance thermometer (not shown). It is assumed that r, -r is so small that the shielding convection is ignored (for example, 1.5 m). Assume that the resistance of the heating wire is R regardless of temperature, so the amount of heat generated per unit time when current 1 is flowing is R1''.0 Figures 2 and 3 both show the resistance of the thermocouple. An example in which one of the wires is used as a heating element is shown. Figure 2 shows the case where the resistance of all the pixel wires of the thermocouple does not depend on the temperature, and Figure 3 shows the case where the resistance does not depend on the temperature of the wire. However, the resistance of the other wire of the thermocouple may or may not depend on temperature.

The embodiment shown in FIG. 2 and the embodiment shown in FIG. 3 differ in the method of measuring the temperature difference.

In FIG. 2, a thin manganin wire 5 with a length t has an inner diameter of 12r.
, (approximately 3 mm) is stretched in a straight line at the axis of a metal right circular thin tube (outer tube) 2. At both ends P and PL of the manganin thin wire 5, there is a manganin thin wire PBN with equal resistance,
P'B' N are connected. Manganin thin wire P
At the midpoint M of P' (i.e. 5), draw a constantan thin line M
A is connected. Point A and point B in PBN are
If the temperature is kept the same as the outer tube temperature t3℃, L point B
Assume that is grounded.

The resistance of constantan thin wire AM is R8, and the resistance of manganese thin wire M is
Let the resistance of PB be RM, and select a point C in the mumanganin thin wire BNO so that the resistance of BC is RM+2Ro. 6 is a power source, and sections from the power source 6 to A and N are conducting wires. A voltage is applied to NA, an AMK current 21 flows, and one manganin thin wire is heated. The constantan thin wire AM has a relatively small resistance R6 so that the temperature rise of the constantan thin wire is about the same as the temperature rise of the manganin thin wire PP'.

Let the potentials of point A and point C be vA and VB, respectively. Also,
The temperature at both junctions of the manganin-constantan thermocouple is t.
The thermoelectromotive force at 0℃ and t2℃ is β(1,-t2)
Suppose that Assuming that the temperature change due to the Peltier effect is ignored, when the temperature of point M and the thin wire PMP' is t°C, ■A=2Roi+β(t, -t2) 1RMi,
Vo=-(RM+2Ro)i
(1), so by the operational amplifier, V
=VA10V.

When creating, V=VA+Vo=/(tl-ts)
(2) becomes. Therefore, by measuring ■, the temperature difference (tyo-t2)°C is known.

In Fig. 3, a wire whose resistance does not depend on temperature (manganin thin wire or constantan thin wire) is placed coaxially inside the outer tube 2 as a heating element, and another wire (constant thin wire) which becomes a thermocouple is placed at the midpoint M of the outer tube 2. In this case, the resistance may be chromel, which depends on temperature, or the resistance may be manganin, which does not depend on temperature). The difference from FIG. 2 is that current is passed only through the heating element. To do this, a conducting wire CE with a very high impedance is connected to the strand MC connected to the heating element at point M, and even if a current flows through the heating element AMB, the strand MC connected to it
The current flowing through is ignored. Since no current flows, there is no need for the resistance of the wire to be independent of temperature.

It is assumed that the resistances of the two parts AM and MB of the heating element are R regardless of the temperature. Also, point A.

It is assumed that the temperature of both B and C is kept the same as the temperature t2°C of the outer tube, and when a current 1 is flowing through AMB, the temperature including point M is 70°C. 6 is a power supply, and 7 is a variable resistor.

If the potentials of points A, IB, and C are vA, vo, and vo, respectively, ■A-Vo: R1+β(t□ t,), VB V
o:= −R1 β(tl−t2)
(3), so V==V, V. -1-VB-Vo==V, +VB-2
Vo=2β(tl-t2) (4). By using an operational amplifier to determine ■, and measuring it, the temperature difference (tl - t2) °C can be found. It's the same. That is, the current when t2°C and (tyo-t,)°C each reach a predetermined value is 1 for a sample gas with a thermal conductivity of K, and 1* for a reference gas with a thermal conductivity of K*. .

Assuming that the vacuum is 1°, K is known as .

io and 1* can be measured in advance and do not need to be measured when measuring the sample gas.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 are explanatory diagrams showing different embodiments of the thermal conductivity measuring cell according to the present invention. 1...Metal thin tube (heating tube) 2...Metal right circular tube (outer tube) 3...Heating wire 4...Thermopile 5...Manganin Thin wire 6... Power supply 7... Variable resistance patent applicant Shisaka Institute Co., Ltd. Agent (
7524) To the top main part, size

Claims (1)

[Claims] A thin right cylindrical heating element, whose resistance does not depend on temperature, is heated by passing a current through the heating wire, is placed on the axis of a metal right circular tube to form a measurement chamber, and the outer metal tube is placed in a specified position. The temperature difference between the heating element and the metal outer tube is detected by a thermocouple or thermopile, so that
A thermal conductivity measurement cell that heats a heating element.