High-Precision and High-Resolution Measurements of Thermal Diffusivity and Infrared Emissivity of Water–Methanol Mixtures Using a Pyroelectric Thermal Wave Resonator Cavity: Frequency-Scan Approach

Abstract

The thermal diffusivity and effective infrared emissivity of water-methanol mixtures were measured at atmospheric pressure and ambient temperature using a pyroelectric thermal-wave resonator cavity. The applied frequency-scan method allows keeping the cavity length fixed, which eliminates instrumental errors and substantially improves the precision and accuracy of the measurements. A theoretical model describing conduction and radiation heat transfer in the cavity was developed. The model predictions and the frequency-scan experimental data were compared, showing excellent agreement. The measurements were performed for methanol volume fractions of 0, 0.5, 1, 2, 5, 10, 20, 40, 75, and 100%. The fitted thermal diffusivity and effective emissivity vs. concentration results of the mixtures were compared to literature theoretical and experimental data. The maximum resolution of 0.5% by volume of methanol in water by means of the thermal-wave cavity method is the highest reported to date using thermophysical techniques. Semi-empirical expressions for the mixture thermal diffusivity and infrared emissivity as functions of methanol concentration have been introduced. The expression for infrared emissivity is consistent with the physical principle of detailed balance (Kirchhoff's law). The expression for thermal diffusivity was found to describe the data satisfactorily over the entire methanol volume-fraction range.

Diffusive-to-ballistic transition of the modulated heat transport in a rarefied air chamber

“…[22][23][24] Note that, for large enough cavity lengths, the amplitude tends to a constant value, as a result of the dominant radiation contribution, which agrees with previous theoretical and experimental investigations. [17][18][19][20] The cavity length at which this radiative effect shows up, increases as the pressure decreases, due to the increasing thermal diffusion length of the thermal-waves. The amplitude signal in (a) has been plotted in logarithmic scale to compare in detail our experimental data with the available theoretical predictions for the viscous regime.…”

“…[12][13][14][15][16][17][18][19][20][21][22][23][24][25] The thermal-wave resonant cavity (TWRC) has demonstrated to be a simple, reliable, and accurate technique to study the heat transport in a large variety of fluids. [12][13][14] This photothermal technique involves the use a lock-in amplifiers and filters that allow us measuring very low signals even in highly noisy environments.…”

“…These two signals have been theoretically modeled taking into account not only the pure heat diffusion, 15,16 but also the contribution of heat radiation from the heater to the detector. [17][18][19][20] Previous experimental works [22][23][24] (conductivity) of the air inside the TWRC increases (remains nearly constant) as the intra-cavity pressures reduces, as predicted by the kinetic theory of ideal gases. This has been done in a relatively short range of pressures involving the viscous and transitional regimes, but not so much attention has been put in the free molecular regime occurring at very low pressures, which are considered in present work.…”

A novel on-chip three-dimensional micromachined calorimeter with fully enclosed and suspended thin-film chamber for thermal characterization of liquid samples

“…To determine the time the temperature changes arrives at the sensor, the maximum of the second derivative of the temperature profile is used as shown in Figure 8(b). Although the thickness of the sample is approximately the thickness of the wafer, which is 300 6 5 lm, we used DI-water with a known diffusivity 47 at 25 C to calibrate the thickness of our device. The time delay, t 0 , can be expressed as…”

Perspective: Photopyroelectric effects and pyroelectric measurements: “Invited Review Article: Photopyroelectric calorimeter for the simultaneous thermal, optical, and structural characterization of samples over phase transitions” [Rev. Sci. Instrum. 82, 121101 (2011)]

“…19 and 22) have been explored in the review by Matvienko and Mandelis. 12 Besides accurate and precise measurements of thermophysical properties of non-solid matter, PPE thermalwave cavities have been used for studies of equations of state, 23 thermal infrared emissivity of fluids in simple instrumental configurations 24 and other thermophysical properties such as thermal effusivity. 25 PPE TWC detection holds a strong promise for measuring infrared emissivity values of liquids.…”