JPH0465972B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention performs unsteady diffusion of heat into a medium by using a thin wire (cylindrical thermal conductor) that serves as a heat source element and a temperature setting element. It relates to a method of measuring. The feature of the present invention is that a cylindrical conductor is placed in a medium in a thermally equilibrium state, and the cylindrical conductor is instantaneously changed in steps by a constant temperature amount ΔT from a certain time to maintain thermal equilibrium. After that, the amount of heat is compensated so that the temperature of the cylindrical heat conductor is maintained at a constant value, the amount of compensated heat Q(t) at this time is measured as a function of time t, and the amount of temperature increase ΔT and Q(t ) is regressed on a function related to a known time t, and the thermal conductivity and thermal diffusivity, which are the thermal constants of the medium, are determined from the regression coefficients. When there is a non-uniform distribution of temperature in a medium, heat moves so that the entire system approaches an equilibrium state according to the magnitude of the temperature gradient, thermal conductivity, and thermal diffusivity. When a cylindrical conductor (thin wire) with radius a is placed in a medium in thermal equilibrium, from a certain time t = 0,
When the temperature of the thin wire is increased stepwise by ΔT by some kind of operation, a heat flow Q(t) expressed by the following equation flows out from the surface of the thin wire per unit length into the medium. Q(t)=4πλΔT _∞ 〓 〓 ⁿ⁼¹ {A _o /(logχt) ⁿ +1/2 4/σ ² χt B _o /(log
χt) ⁿ 1/32 (4/σ ² χt) ² C _o /(logχt) ⁿ +...
}(1) However, σ=e〓(γ=0.5772..., Euler's number), χ=4κ/a ² σ ² , λ, and κ are the thermal conductivity and thermal diffusivity, respectively, of the thermal constants. Coefficients A _o , B _o ,
C _o can be determined by strictly solving the equation, but Table 1 shows the range necessary for measurement.

【table】

[Table] Based on the above principle, a specific example of a method for determining a thermal constant will be described with reference to FIG. Figure 1 shows a state in which the output voltage of a Wheatstone bridge consisting of resistors R ₁ , R ₂ , R ₃ , R _S , and R _L is introduced into a servo amplifier, and the output voltage is fed back as a power source for the bridge. There is. R _S and R _L are the electrical resistances created by the thin wires mentioned above, and the subscripts S and L indicate the shortness and length of the thin wires. Use several thin wire resistors. R ₁ , R ₂ , and R ₃ are used to balance the bridge in the initial state. Generally, the resistivity of an electrical conductor depends on temperature, so the resistance values of R _S and R _L are a function of temperature. If we achieve bridge equilibrium by making the Joule heat generated in R _S and R _L negligible in the initial state, and then change the resistance of R ₁ , R ₂ , or R ₃ by a small amount from a certain moment, , the servo system operates so that the bridge output becomes zero again. When the bridge is in equilibrium again, the resistances R _S and R _L have increased by the temperature difference ΔT and have different values from their initial states. At this time, the Joule heat generated in R _S and R _L is the current value flowing in R _S and R _L ,
It can be easily calculated from the resistance value. Since this Joule 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. In this way, the thermal constant can be measured from the relationship between Q(t) and ΔT determined as a function of time. As a supplementary note, the bridge is not limited to the Wheatstone bridge, but bridges called by other names can be used as well.

[Brief explanation of the drawing]

FIG. 1 shows an example of the measurement principle according to the present invention, where R ₁ , R ₂ , R ₃ , R _S and _RL are resistances forming a bridge.

Claims (1)

[Claims] 1 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 in steps by a constant amount ΔT to break the thermal equilibrium and increase the cylindrical heat conduction. Flowing heat flow from the body into the medium, compensating the amount of heat so as to maintain the temperature of the cylindrical heat conductor at a constant value from then on, and measuring the compensated amount of heat Q(t) at this time as a function of time t, Temperature step heating by thin wire heating characterized by regressing the temperature increase ΔT and Q(t) on a function related to a known time t, and measuring the thermal constants of the medium, such as thermal conductivity and thermal diffusivity, from the regression coefficient. How to measure constants.