JPS6266147A - Measuring method for heat constant by temperature step thin wire heating - Google Patents

Abstract

PURPOSE:To measure a thermal conductivity and a thermal diffusivity being heat constants of a medium from a relation of DELTAT and Q(t) by raising a temperature instantaneously by DELTAT with a cylindrical heat transmission body of a heat balanced state in the medium, and thereafter, maintaining a prescribed temperature by giving a heating value Q(t). CONSTITUTION:A cylindrical conductor thin wire of a radius (a) is placed in a medium being in a heat balanced state, and when raising a temperature stepwise by DELTAT, a heating value Q(t) flowing out of a unit length surface and DELTAT have a prescribed relation. By using long and short resistances RL, RS by the thin wire, an influence of a heat flow in the axial direction of the thin wire is negated, a Wheatstone bridge is constituted in an initial state by using together R1-R3 and an output is led to a servo-amplifier, and its output is fed back to the bridge. When one of R1-R3 is changed by a minute quantity, and they have been balanced again, RS and RL are brought to a temperature rise by DELTAT and a generated heat flows out into the medium, and from an effective length of the thin wire, Q(t) is known by an expression. In this way, heat constants such as a thermal conductivity lambda, a thermal diffusivity (k), etc. can be derived from a relation of Q(t) and DELTAT.

Description

Detailed Description of the Invention The present invention performs unsteady diffusion of heat in a medium by using a thin wire (cylindrical thermal conductor) that serves as a heat source element and a temperature setting element, and the thermal constant of the medium is It relates to a method of measuring thermal conductivity, thermal diffusivity, etc.

The present invention is characterized by arranging a cylindrical heat conductor in a medium in a thermally balanced state, and instantaneously changing the temperature of the cylindrical heat conductor by a constant temperature amount ΔT stepwise from a certain time. To break the thermal equilibrium and maintain the temperature of the cylindrical hot rice conductor at a constant value from then on, the heat is regressed to a function related to a known time t, and the thermal constant of the medium is determined from the regression coefficient.

Temperature gradients occur when there is a non-uniform distribution of temperature in a medium.

Depending on the magnitude of thermal conductivity and thermal diffusivity, the entire system is in equilibrium.
Heat moves closer to the state. When a cylindrical conductor (thin wire) with radius a is placed in a medium in a state of thermal equilibrium, and the temperature of the thin wire is increased stepwise by ΔT from a certain time 1 = 0 by some kind of operation, A heat flow Q (t) expressed by the following equation flows out into the medium per unit length from the surface of the thin wire.

However, σ=er (r=0.5772..., Euler's number) r """ 4/a2σ2.λ are the thermal conductivity and thermal diffusivity of the thermal constants, respectively.Coefficient A
” I BnrCo can be determined by strictly solving the equation, but Table 1 shows the range necessary for measurement.

Table 1 AnBoC.

2 -0.5772157 1 03 -1.31
17561 0.84556867-54 0.252
0158-7.39856242-25.227843
45 3.9969267-14.73301048-
13.64260106 5.0637282-7.4
4478 343.8177 -6.9278195
The following omitted The following omitted 8 -36.38
34740 9 -46.9795573 10 78.1068987 11 464.675 Based on the above principle, a specific example of the method for determining the thermal constant will be described with reference to FIG.

FIG. 1 shows a state in which the output voltage of a Wheatstone bridge consisting of resistors R1, R2, R3, Rs, and RL is introduced into a servo amplifier, and the output voltage is fed back as a power source for the bridge. Rs and Rt are the electrical resistances created by the thin wires mentioned above, and the subscripts S and L are the shortness of the thin wires,
Two complementary wire resistors are used to cancel the effect of heat flow that travels in the axial direction within the thin wire. R+, R
2. R3 is used to balance the bridge in the initial state.

Generally, the resistivity of electrical conductors depends on temperature, so R3
, RL is a function of temperature. Rs in initial state
, achieve bridge equilibrium by making the Joule heat generated in RL negligible, and from a certain moment r R+ +
When the resistance of either R2+R3 is changed by a minute amount,
The servo system operates so that the bridge output becomes zero again.

When the bridge is in equilibrium again, resistor R5,
RL increases by the temperature difference ΔT and has a value different from the initial state. At this time, the Joule heat generated at + Rs + Rt is the current value flowing at + Rs + Rt.

It can be easily calculated from the resistance value. This Joule heat is
Since the heat flows out into the medium, the amount of heat flow per unit length can be determined by measuring the effective length of the thin wire. Q(
The thermal constant can be measured by the relationship between [) and ΔT.

As a supplement, the bridge is not limited to the Wheatstone Bridge, but bridges called by other names can be used as well.

[Brief explanation of drawings]

FIG. 1 shows an example of the measurement principle according to the present invention.
R1, R2, R3, R3, and RL are resistors forming a bridge. designated agent

Claims (1)

[Claims] A cylindrical heat conductor is placed in a medium in a state of thermal equilibrium, and from a certain time the temperature of the cylindrical heat conductor is instantaneously changed stepwise by a constant temperature amount ΔT to break the thermal equilibrium. A heat flow is caused to flow into the medium from then on, and the amount of heat is compensated so as to maintain the temperature of the cylindrical heat conductor at a constant value from then on.The amount of compensated heat Q(t) at this time is measured as a function of time t, and the temperature A method for measuring a thermal constant by temperature step thin wire heating, characterized in that the amount of increase ΔT and Q(t) is regressed to a function related to a known time t, and the thermal constant of the medium is determined from the regression coefficient.