A method for thermal diffusivity measurement in fluids

The laser flash method is a standard method for thermal diffusivity measurement. This paper reports the development of a method and theory that extends the standard laser flash method to measure thermal conductivity and thermal diffusivity simultaneously. By attaching a transparent reference layer with known thermal properties on the back of a sample, the thermal conductivity and thermal diffusivity of the sample can be extracted from the temperature response of the interface between the sample and the reference layer to a heating pulse on the front surface. The theory can be applied for sample and reference layer with different thermal properties and thickness, and the original analysis of the laser flash method becomes a limiting case of the current theory with an infinitely small thickness of the reference layer. The uncertainty analysis was performed and results indicated that the laser flash method can be used to extract the thermal conductivity and diffusivity of the sample. The results can be applied to, for instance, opaque liquid in a quartz dish with silicon infrared detector measuring the temperature of liquid-quartz interface through the quartz.

A new step-integration method for thermal diffusivity measurements in thin sheet materials by the converging thermal wave technique is considered. This method is based on an integration of the temperature evolution curve with respect to the current time during two consecutive intervals of time, the duration of the first one being set beforehand and the completion time of the second one being obtained from the equality of the first and the second integrals. The use of the integrating operations with the following equalization of the integrals minimizes errors caused by heat loss and signal noise while the error due to the pulse duration is negligible, since a part of the experimental temperature evolution curve is properly taken. This method is of importance to develop an automated system for thermal diffusivity measurement.

The specific absorption rate (SAR) is an indicator of the thermal effects caused by microwave exposure in biological tissues. Electric field probe scanning has been used as a practical SAR evaluation technology until now. A measurement standard is necessary for any physical quantity. In general, the existence of a standard constructed with a physically different procedure is important in uncertainty evaluation of the measurement standard. In this paper, a thermal SAR measurement method using an optical fiber thermal sensor is proposed. The thermal SAR measurement method is not suitable for dosimetric assessments for an actual cellular phone. Nevertheless, the proposed method is a simple measurement technique for measuring the temperature rise caused in an equivalent biological tissue (semisolid phantom) by electromagnetic energy absorption. A thermal sensor works independently of the frequency and is, therefore, suitable for primary testing of an electric field probe scanning system. The measurement utility of the proposed thermal SAR measurement method was verified in this paper. The results show that the proposed method is able to measure SAR within an error range of 1%-3% above 2 GHz.

Consideration has been given to the laser thermal-wave microscopy method of nondestructive inspection that relies upon thermal wave excitation with flying laser spot and IR-radiometry registration of thermal waves. The theoretical analysis disclosed that contrast and amplitude of thermal image depend heavily on the relative position of the thermal beam and observation point, as well as on scanning velocity. The location of the thermal wave recording point at a distance of 1 or 2 thermal beam diameters ahead of the moving laser beam is optimum. The use of laser-scanning heat source and thermal wave recording with IR detector array improves greatly the inspection efficiency over the point-by-point technique of thermal wave recording.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The application of optical-fiber thermal wave cavity (OF-TWC) technique was investigated to measure the thermal diffusivity of Ag nanofluids. The thermal diffusivity was obtained by measuring the thermal wavelength of sample in a cavity scan mode. The spherical Ag nanoparticles samples were prepared at various sizes using the microwave method. Applying the thermal wavelength measurement in a flexible OF-TWC technique requires only two experimental data sets. It can be used to estimate thermal diffusivity of a small amount of liquid samples (0.3 ml) in a brief period. UV-Vis spectroscopy and transmission electron microscopy were used to measure the characterization of the Ag nanoparticles. The thermal diffusivity of distilled water, glycerol, and two different types of cooking oil was measured and has an excellent agreement with the reported results in the literature (difference of only 0.3%–2.4%). The nanofluids showed that the highest value of thermal diffusivity was achieved for smaller sized nanoparticles. The results of this method confirmed that the thermal wavelength measurement method using the OF-TWC technique had potential as a tool to measure the thermal diffusivity of nanofluids with different variables such as the size, shape, and concentration of the nanoparticles.

The thermal conductivity and diffusivity of U 4O 9−y from 250 to 415 K

In the present study, the thermal diffusivities of the Al, Si and ITO films deposited on the SUS304 steel substrate are evaluated via the present technique. Before applying this technique, the temperature for the thin film of the multi-layered specimen is developed theoretically for the one- dimensional steady heat conduction in response to amplitude and frequency of the periodically oscillating temperature imposed by a peltier placed beneath the specimen's substrate. By the thermal-electrical data processing system excluding the lock-in amplifier, the temperature frequency a 3 has been proved first to be independent of the electrical voltage applied to the peltier and the contact position of the thermocouples. The experimental data of phase difference for three kinds of specimen are regressed well by a straight line with a slope. Then, the thermal diffusivity of the thin film is thus determined if the slope value and the film- thickness are available. In the present arrangements for the thermocouples, two thermal diffusivity values are quite close each other and valid for every kind of specimen. This technique can provide an efficient, low-cost method for the thermal diffusivity measurements of thin films.

A modified Angstrom's method for the measurement of thermal diffusivity in solid materials is presented, aimed at overcoming the limits of ordinary techniques with one-side measurements. The method requires a periodic thermal input to be supplied to the specimen, alternating heating and cooling stages. The thermal diffusivity is estimated by monitoring the temperature oscillations on the free surface of the specimen. The conditions at which a real 3D test- system can be studied by means of a 1D thermal model are investigated. Algorithms to estimate the thermal diffusivity are determined analytically and verified by numerical simulation. The method is finally validated by experimental measurements.

Clinical observation on edema based on the thermal sensitivity measurement method.

Electromagnetic energy is the backbone of wireless communication systems, and its progressive use is considered to have a low but measurable impact on a wide range of biological systems. Even though a growing amount of data has reported electromagnetic energy absorption in humans along with subsequent biological effects, the consequences of electromagnetic energy absorption on plants have been insufficiently addressed. The higher surface to volume ratio along with the enormous water-ion concentrations makes the plant an ideal model to interact with non-ionizing electromagnetic radiation. In this study, controlled and periodic electromagnetic exposure of 1837.50 MHz, 2.75 W/m2 for 6 h a day on a popular rice variety (var. Satabdi) reduced the seed germination rate. The same dose of periodic electromagnetic exposure upregulated phytochrome B and phytochrome C gene transcripts in 12-day-old seedlings, whereas, in 32-day-old plants, the dose upregulated calmodulin and phytochrome C while the bZIP1 gene showed repression. However, the transcript abundance of bZIP1, phytochrome B, and phytochrome C genes was enhanced even in 12-day-old Satabdi seedlings following instantaneous short-duration (2 h 30 min) controlled electromagnetic exposure to 1837.50 MHz, 2.75 W/m2 . The reported responses in rice were observed below the international electromagnetic regulatory limits. Thus, rice plants perceived electromagnetic energy emitted by the wireless communication system as abiotic stress as per its response by upregulation or repression of known stress-sensing genes. Bioelectromagnetics. © 2020 Bioelectromagnetics Society.

The application of microwaves has a demonstrated potential for the ultimate removal of water from fine coal. The electromagnetic energy absorption in coal during microwave drying is controlled by several factors, with dielectric properties being among the most important. In this paper, the measured dielectric properties of various ranks of coal are presented as a function of frequency and moisture content. A knowledge of the dielectric properties is essential in estimating the electromagnetic energy absorption in coal during microwave heating.

An empircal relationship is presented for the whole-body-average electromagnetic energy absorption in a 180-cell block model of man for near-field exposure conditions. Consideration is restricted to near fields with P polarization (no component of E directed arm-to-arm) in which the magnitude of the incident electric field is maximum immediately in front of the abdominal region. A highlight of this work is the considerably reduced whole-body average energy absorption for near-field partial-body exposures as compared to that obtained under plane-wave irradiation conditions.

PurposeThis paper aims to solve the typical thermal airflow sensor's high power consumption and integration difficulties, based on the FS5 thermal element and constant temperature measurement method, a flow sensor is developed with high measurement accuracy, low power consumption, small size, low cost and easy system integration.Design/methodology/approachA small wind tunnel was used to test and assess the sensor's measurement range, reaction time, stability, repeatability, measurement accuracy and multi-temperature calibration was performed in the temperature range of −10°C to 30°C. The effect of ambient temperature on the sensor's measurement data is investigated, and the coefficient correction method of power function was investigated to implement the sensor's software temperature compensation function.FindingsThe results show that the sensor is stable and repeatable, the output voltage has a power function relationship with the airflow rate, the flow rate measurement range is 0–18 m/s, the response time is less than 3 s, the measurement accuracy at high flow rates is within 0.4 m/s and the temperature-corrected airflow rate measurement error is less than 5%. Setting the temperature calibration interval to 2°C and 5°C has the same temperature compensation effect, reducing the sensor's calibration effort significantly.Originality/valueThis paper demonstrates that a thermostatic method is used to construct a thermal wind speed sensor that delivers accurate measurements in the wind speed measuring range of 0–18 m/s under test conditions. In addition, the sensor's performance is evaluated, and calibration tests for a wide range of temperatures are done. Finally, based on the power function correction method, a temperature compensation algorithm is proposed.

Friction wear of coatings analyzed by means of thermal wave excitation and modulated IR radiometry

The effects of sample surface treatments on laser flash thermal diffusivity measurements