JPH059737B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for measuring thermophysical properties of a liquid material using AC calorimetry (adiabatic heating type thermal measurement).

(Prior Art) Conventionally, various liquid materials have been used for various purposes, and there is a measurement method that can measure thermal physical quantities such as thermal diffusivity and thermal conductivity with high accuracy when using liquid materials. development has become an important issue.

Conventionally, as a method for measuring the thermal constant of a liquid, there is a flash method in which the liquid sample to be measured is irradiated with light and the thermal constant of the liquid sample is determined from the amount of energy absorbed by the liquid sample and the temperature rise of the sample. There is a law. In addition, the unsteady thin wire method, step heating method, and Laplace transform method have been proposed.

A recently proposed measurement method has been reported that utilizes AC calorimetry to determine the √ (where c is the specific heat per unit volume and κ is the thermal conductivity) of a liquid sample. (Physical Review Letters Volume 54, 1985). This measurement method involves immersing a heater and a temperature sensor together in the liquid sample to be measured, applying power at a predetermined frequency to the heater to intermittently heat the liquid sample, and detecting temperature fluctuations on the heater to measure the liquid sample. We are looking for √ of Furthermore, the present inventor has proposed a method for measuring the thermal diffusivity of solid thin film samples using AC calorimetry (Review of Scientific Instruments, Vol. 56, p. 1643, published in 1985).
p. 1647). In this measurement method, a solid sample is irradiated with intermittent light of frequency f, a part of the sample is covered with a mask, and the thermal diffusivity is determined by analyzing the attenuation curve of the alternating current temperature of the sample under the mask. There is.

(Problems to be Solved by the Invention) When measuring a liquid sample, it is necessary to consider thermal diffusion between the liquid sample to be measured and surrounding members such as cells, which complicates analysis. At the same time, there was a problem that made it difficult to measure with high precision. For example, in the flash method, it is necessary to sufficiently absorb the emitted light energy in the liquid sample, and when measuring a transparent liquid sample, it is necessary to make a multilayer structure using a light absorbing material.
This has resulted in the inconvenience that the number of processing factors to be analyzed has increased, making the analysis even more complicated. Further, even when measuring by the step heating method and the Laplace transform method, the measurement must be carried out in a multilayered structure, which similarly has the drawback of complicating the analysis. Furthermore, the unsteady thin wire method cannot be easily applied to the measurement of electrical conductivity, and complex analysis is required even for the measurement of electrically insulating liquid samples.

On the other hand, the method using ac calorimetry has the advantage of being relatively easy to analyze and capable of highly accurate measurement. However, the measurement method described above detects the product of the specific heat and thermal conductivity of the liquid sample, and cannot measure the thermal diffusivity, thermal conductivity, and specific heat individually, and is established as a measurement of the thermal physical quantity of the liquid sample. has not been reached. Further, the measurement method using light irradiation proposed by the present inventor can also determine specific heat and thermal conductivity from the determined thermal diffusivity, and is extremely useful as a heat measurement method. However, the problem that only solid samples can be applied and is limited to solid samples still remains.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to eliminate the above-mentioned drawbacks and to provide a method for measuring thermophysical properties that can measure the thermal physical quantities of various liquid materials with a simple analytical method and with high accuracy.

(Means for Solving the Problems) In the method for measuring thermophysical properties of a liquid material of the present invention, when measuring the thermal physical quantity of a liquid material, a predetermined frequency f is applied from a heating source in the liquid material to be measured. An alternating current heat flow Q is supplied, an alternating current temperature amplitude of a temperature wave generated by the alternating current heat flow Q and propagating in the liquid material to be measured is measured by a temperature sensor, and the measurement of the alternating current temperature amplitude is performed at the heating source. The thermal wave number k is calculated based on the relationship between each distance d and the corresponding AC temperature amplitude. It is characterized by determining physical quantities.

(Function) FIGS. 1a and 1b are principle diagrams for explaining the principle of the method for measuring thermophysical properties of liquid materials according to the present invention. Figure 1a can be used both when the liquid sample to be measured is electrically conductive and insulating, and Figure 1b shows an example useful when the liquid sample is electrically insulating. First, the example shown in FIG. 1a will be explained. A liquid sample 2 to be measured is contained in a sample container 1 . A thermocouple 3 is placed immersed in this liquid sample 2, and a heater support 4 is placed above the thermocouple 3.
The heater 5 is mounted on the bottom surface 4a of the heater support base 4. The heater support base 4 is made of an electrically insulating material, and its bottom surface 4a is made thin so that the heat generated by the heater 5 is quickly propagated through the liquid sample 2. The heater 5 is a planar heater of electric power generation type, and is constructed by, for example, forming a metal thin film on the bottom surface 4a of the support base. For example, 0.5 to heater 5
When rectangular wave power of about Hz to 100 Hz is supplied, the heater 5 generates heat, and the generated heat propagates through the liquid sample 2 as an alternating current heat flow via the support base bottom 4a. When the amplitude of this AC heat flow is Q and the frequency is f, the thermal wave number k of the temperature wave propagating in the liquid sample 2 is given by the following equation.

k=√...(1) Here, D is the thermal diffusivity of the liquid sample 2. On the other hand, the number of heat fractions k _s propagating in the bottom surface 4a of the heater support base 4a
is given by the following equation.

k _s =√ _s (2) Here, D _s is the thermal diffusivity of the bottom surface 4a of the support base to which the heater 5 is attached. The temperature wave propagating in the liquid sample 2 is detected by a thermocouple 3,
The detected AC temperature amplitude T _ac is determined by the following equation.

T _ac = Q/κ ² k ² + (κ _s k _s +2πfC _s W) ²・e ^-kd ...(3) Here, R and κ are the thermal conductivities of the liquid sample and the bottom surface 4a of the heater support, respectively. where C _s is the specific heat per unit volume of the bottom surface 4a of the heater support, W is the thickness of the bottom surface 4a of the support, and d is the distance from the bottom of the support to the thermocouple. Expressing both sides of equation (3) using natural logarithms, the following equation is obtained.

InT _ac =A−k·d (4) Here, A is a constant.

Therefore, as is clear from equation (4), lnT _ac is expressed as a linear function of the distance from the bottom surface 4a of the support base 4a to the thermocouple 3. Therefore, the AC temperature amplitude T _ac is detected by a thermocouple while changing the distance d, and the horizontal axis shows the distance d.
The heat wave number k can be found from the slope of the curve obtained by plotting lnT _ac on the vertical axis. By substituting the obtained thermal wave number k into equation (1), the thermal diffusivity D can be obtained.

Next, a method for determining specific heat C and thermal conductivity κ will be explained. In equation (3), when d=0, that is, when the thermocouple 3 is in contact with the bottom surface 4a of the support base, k _s , k _s , f, C _s and W are known, so equation (3) is as follows. It is expressed as

Here, B is a known constant. In this case, if the AC heat flow Q is known, the product κ·k of the thermal conductivity κ and the thermal wave number k can be found by measuring T _ac at d=0. The AC heat flow Q is almost determined by the heater power and the thermal constant of the heater support and can be known, and even if it is unknown, the Q can be determined by measuring using a standard sample. Therefore, if Q is known, d=0
By measuring T _ac at , the value of κ·k can be found. Therefore, the heat wave number k obtained by the method described above
The thermal conductivity k is determined from the value of the product κ·k of the thermal conductivity κ measured at d=0 and the thermal wave number k. The following equation holds between thermal diffusivity D, specific heat C, and thermal conductivity k.

κ/C=D (6) By substituting D and κ into this equation (6), the specific heat C can also be determined. Therefore, by detecting the temperature amplitude T _ac while changing the distance d and further measuring the temperature amplitude T _ac at d=0, the thermal diffusivity D, specific heat C, and thermal conductivity κ can be determined in one measurement scan.
can be calculated automatically.

Next, FIG. 1b will be explained. This example is suitable for measuring electrically insulating liquid samples, and is shown in Figure 1a.
It is possible to measure with higher precision than the example shown in . In this example, a heater 5 mounted on a heater support base 4 is arranged to face the thermocouple 3, and the alternating current heat flow generated by the heater 5 is directly propagated in the liquid sample 2. In this case, the temperature amplitude T _ac of the AC temperature wave propagating in the liquid sample 2 and detected by the thermocouple 3 is given by the following equation.

T _ac =Q/√2(κk+ _κs k _s )−·e ^-kd (7) When both sides of equation (7) are expressed in natural logarithms, the following equation is obtained.

lnT _ac =A-k・d...(8) As is clear from equation (8), the distance from heater 5 to thermocouple 3 is plotted on the horizontal axis, and the distance from thermocouple 3 is plotted on the vertical axis, as in the previous example. Temperature amplitude detected by 3
By plotting the lnT _ac value of T _ac , the heat wave number k can be found from the slope of the resulting straight line. By using the method described above using the determined thermal wave number k, the thermal diffusivity D, specific heat C, and thermal conductivity κ of the liquid sample can be automatically determined.

(Example) FIG. 2 is a diagram showing the configuration of an example of a measuring device for carrying out the method for measuring thermophysical properties of a liquid material according to the present invention. A liquid sample 11 to be measured is contained in a container 10 . An X stage 12 that is driven stepwise at every minute distance in the x direction is arranged inside the container 10, and a thermocouple support stand 14 for supporting a thermocouple 13 is arranged on this X stage 12. thermocouple 13
It is desirable to use one with as small a heat capacity as possible in order to ensure responsiveness to the temperature waves to be detected. A heater 14 is placed above the thermocouple 13.
The heater support stand 15 on which is mounted is fixedly arranged. This heater 15 desirably has a small heat capacity in order to ensure thermal responsiveness, and a thin film heater in which a metal coating is formed on the surface of the electrically insulating heater support 15 can be used. In addition, the heater 14
It is desirable to use a planar heater with an area larger than the junction point of the thermocouple. For example, the heater support stand 15
is made of silicon carbide ceramic with a thickness of 100 μm, and allows the heat flow generated by the heater 14 to quickly propagate to the liquid sample 11. In this way, by arranging the heater above the thermocouple 13, the influence of convection can be reduced. Under the control of a central processing unit (CPU) 16, rectangular wave power of a predetermined frequency f is supplied to the heater 14 via a rectangular wave oscillator 17 and a power amplifier 18 to cause the heater to generate heat intermittently. This frequency f is, for example, 0.5Hz to 100
Hz. The alternating current heat flow Q released from the heater 14 propagates through the liquid sample 11. This AC heat flow Q generates an AC temperature wave, and the temperature amplitude T _ac of this AC temperature wave is detected by the thermocouple 13 . The output signal from the thermocouple 13 is supplied to the lock-in amplifier 19 via a lead wire, amplified, and then supplied to the CPU 16 for arithmetic processing. Since the thermocouple 13 performs temperature detection with high sensitivity, it detects noise as well as temperature waves based on heat generated by the heater. However, when rectangular wave power is supplied to the heater 14, an AC temperature wave in the form of an approximately triangular wave is detected, so the lock-in amplifier 17 is provided with a function to capture only the signal of the sine wave component of the triangular wave to avoid the influence of noise. do. Note that the shape of the AC temperature wave detected by the thermocouple 13 is the same as that of the heater 14.
Because it is determined by the heater power supplied to
The measurement accuracy can be further improved by determining the relationship between the heater power waveform and the AC temperature wave waveform in advance and capturing only the AC temperature wave having a predetermined waveform. Therefore, the power waveform supplied to the heater is not limited to a rectangular wave, and various forms of heater power can be supplied. The thermocouple 13 is connected to the zero contact 20 via another lead wire, and the output from the zero contact 20 is sent to the CPU 16 via a digital voltage measuring device 21.
The temperature is set as the reference temperature. A control signal for driving the X stage is supplied from the CPU 16 to an X stage drive control circuit 22, which generates a drive signal for driving the X stage, and supplies this drive signal to the X stage 12. The stage 12 moves intermittently one pitch at a time in the x direction (direction from below to above),
Therefore, the thermocouple 13 moves toward the heater 14 one pitch at a time. The amount of movement for 1 pitch is, for example, 1μ
m. Further, it is assumed that the distance d from the thermocouple 13 to the heater 14 is accurately controlled by the CPU 16. When measuring, CPU16
Under the control of , heater power of frequency f is intermittently supplied to the heater to generate an AC temperature wave, and the X stage 12 is moved one pitch at a time from below to above. Then, the AC temperature amplitude is detected by the thermocouple for each distance d between the thermocouple heaters and is supplied to the CPU 16 via the lock-in amplifier 19. The X stage is moved until the thermocouple 13 comes into contact with the heater surface. The CPU 16 uses the value of the detected AC temperature amplitude T _ac to calculate the heat wave number k by performing arithmetic processing based on the above-mentioned formula, and calculates the thermal diffusivity D, thermal conductivity κ, and specific heat based on the obtained heat wave number k. C is determined and displayed on the display device 23.

Figures 3a and 3b show the relationship of lnT _ac to distance d obtained by this measuring device. Here, the origin of the distance d is arbitrarily set. Figure 3a shows the lnT _ac dependence of pure water at 30°C, and Figure 3b shows the dependence of lnT ac at 30°C.
The lnT _ac dependence of glycerol at °C is shown.
As is clear from Figure 3 a and b, x≦150μm
However, when x>150μm
shows almost linearity. The thermal diffusivity of pure water calculated from the slope of this straight line is (1.41±
0.02)×10 ⁻³ cm ² /s, and the thermal diffusivity of glycerol is (0.91±0.03)×10 ⁻³ cm ² /s. When the thermal diffusivity was calculated using reliable specific heat and thermal conductivity obtained from known literature, the thermal diffusivity of pure water was 1.45×10 ^-3 cm ² /s, and that of glycerol.
0.93×10 ⁻³ cm ² /s was obtained. The thermal diffusivity obtained from these documents and the measured value obtained by the thermophysical property measuring device according to the present invention are almost in agreement.

The saturation of lnT _ac at x≦150μm indicates that the thermocouple is in contact with the heater support, and at this time
Specific heat and thermal conductivity can be determined from the T _ac reading and the thermal diffusivity determined above.

The present invention is not limited to the embodiments described above, and various modifications are possible. For example, in the embodiments described above, a thermocouple is used as the temperature detector, but the temperature sensor is not limited to a thermocouple, and various temperature sensors such as copper-constantan can be used.

(Effects of the Invention) The effects of the present invention described above are summarized as follows.

(1) AC heat flow is intermittently supplied from the heater, the AC temperature amplitude T _ac of the generated temperature wave is detected by a temperature sensor, and it corresponds to the distance between the heater temperature sensor.
Since the configuration is such that thermal physical quantities are determined based on the relationship lnT _ac , analysis can be made much simpler than with conventional measurement methods. As a result, a practical thermophysical property measuring device can be provided.

(2) The influence of external factors can be reduced;
Therefore, measurement accuracy can be further improved. In particular, since only the amplitude of the AC temperature corresponding to the amount of AC heat emitted from the heater is sampled, noise can be further reduced.

(3) Thermal diffusivity, specific heat, and thermal conductivity of a liquid material can be measured simultaneously in a single measurement operation, making the measurement work even easier.

[Brief explanation of the drawing]

1a and 1b are principle diagrams of the method for measuring thermophysical properties of liquid materials according to the present invention, FIG. 2 is a diagram showing the configuration of an example of an apparatus for carrying out the measuring method according to the present invention, and FIGS. b is a graph showing the relationship between the pure water and glycerol heaters and lnT _ac at 30° C. obtained according to the present invention. 10...Container, 11...Liquid sample, 12...X
Stage, 13...Thermocouple, 14...Thermocouple support stand, 15...Heater support stand, 16...CPU, 1
7... Square wave oscillator, 18... Power amplifier, 19
... Lock-in amplifier, 20 ... Zero contact, 21 ...
...Digital voltage measuring device, 22...X stage drive circuit, 23... Display device.

Claims (1)

[Claims] 1. In measuring the thermal physical quantity of a liquid material,
In the liquid material to be measured, an AC heat flow Q of a predetermined frequency f is supplied from a heating source, and the AC temperature amplitude of the temperature wave generated by this AC heat flow Q and propagated in the liquid material to be measured is calculated. The AC temperature amplitude is measured multiple times while changing the distance d between the heating source and the temperature sensor, and the thermal wave number is determined based on the relationship between each distance d and the corresponding AC temperature amplitude. 1. A method for measuring thermophysical properties of a liquid material, comprising determining the thermal wave number k, and determining a thermal physical quantity of the liquid material based on the determined thermal wave number k. 2. Claim 1, characterized in that when the thermal diffusivity of the liquid material to be measured is D, the thermal diffusivity D is determined based on the determined thermal wave number k and the formula k=√. Method for measuring thermophysical properties of liquid materials described in Section 1. 3 When C is the specific heat per unit volume of the liquid material to be measured and κ is the thermal conductivity, the product of the obtained thermal wave number k and the thermal conductivity κ and the thermal wave number k obtained at d=0. The method for measuring thermophysical properties of a liquid material according to claim 2, characterized in that the specific heat and thermal conductivity of the liquid material are determined based on the value of κ·k and the formula κ/C=D.