Development and Application of Fiber Optic-Based Thermal Wave Resonant Cavity Technique for Measurement of Thermal Diffusivity of Liquids

In the study a thermal wave resonant cavity technique (TWRC) was set up and was used to measure thermal diffusivity of various types of liquids. In this technique the thermal diffusivity was determined by scanning the cavity length, instead of frequency, that has a high signal-to-noise ratio in thermally thick case. By using metal foil that attached to a tube as the thermal wave (TW) generator the calibration of the conventional TWRC set up was done on distilled water and the thermal diffusivity value, i.e. 1.44×10-3 cm2/s, agrees with literature value. Further, a few liquids thermal diffusivity, including crude palm (0.988×10-3 cm2/s), soy bean (1.06×10-3 cm2/s), corn oil (0.934×10-3 cm2/s), were determine by using this set up. In this set up the TW is enough to be regarded as rays reflecting and transmitting in cavity. Later the metalized optical fiber tip was used to generate TW instead of metal foil attached to a tube as in the case of conventional TWRC technique. A polymer optical fiber tip or free end coated with silver conductive paint was used to generate TW, by moving this tip with respect to detector and the liquid thermal diffusivity was obtained in a thermally thick region. The thermal diffusivity of distilled water, glycerol, and five different types of cooking oil used which are sunflower, soy bean, olive, corn and palm oils were determined with four-significant-figure at room temperature. These values are in good agreement to the values reported in literatures. The TW field was calculated in a three-dimensional approach. The calculations show that the dimensionality of the TW field in the cavity depends on the lateral (radial) heat transfer boundary conditions and the relation between the laser beam spot size and TW generator diameter. The three-dimensional treatment of the metalised fiber tip was reduced to one-dimensional treatment by using a relatively bigger TW generator diameter compared to laser beam spot size. The set up using optical fiber end also was used to determine thermal diffusivity of a two-layer which is normally difficult to achieve in the conventional large area metal foil due to contact problem. In order to check the validity of the proposed model, the method was experimentally tested for distilled water and glycerol; the values obtained were close to the literature values. A good linear relation of the amplitude with respect to cavity length in thermally thick region of both media was observed. In other TWRC methods the thermal diffusivity values can be obtained by measuring the relative distance of two adjacent extrema. The thermal diffusivity values were obtained by this method compare with “fitting data” method

Measuring Nanofluid Thermal Diffusivity and Thermal Effusivity: The Reliability of the Photopyroelectric Technique

It is important to study nanofluids to understand their extraordinary thermal properties and how the size, concentration and agglomeration of the nanoparticles affect those properties. Photopyroelectric (PPE) technique has been well established in the use of non-destructive measurement of thermal diffusivity and thermal effusivity, by using polyvinylidene fluoride (PVDF) films as sensitive pyroelectric sensors in thermally thick conditions instead of using very thick ceramic sensors. There have been two proposed practical configurations for the PPE technique, the back and the front PPE configurations, to obtain both the thermal diffusivity and effusivity, which are suitable thermal parameters of materials. This PPE technique involves the measurement of thermal waves in the sample due to absorption of optical radiation, by placing a pyroelectric sensor in thermal contact with the sample. This chapter provides a review of the back and the front PPE configurations to determine the thermal diffusivity and effusivity of nanofluids, sample preparation techniques using high-amplitude ultrasonic dispersion and data analysis for metal oxide-based nanofluid materials

The reliability of optical fiber-TWRC technique in liquids thermal diffusivity measurement

The conventional thermal-wave resonator cavity (TWRC) technique was modified by using an optical fiber as both to transmit light beam and to produce thermal wave. This technique also known shortly as OF-TWRC was used to measure liquid thermal diffusivity in a thermally thick condition. The stability of the pyroelectric signal amplitude was good over long time duration. The thermal diffusivity values of various liquids obtained by this technique are in agreement with those of literature indicating this technique is reliable as compared to the conventional TWRC technique

Photothermal effect of modulating laser irradiation on the thermal diffusivity of Al2O3 nanofluids

Modulated continuous wave (CW) lasers cause photothermal effect that leads to rapid optical absorption and generation of thermal waves around the irradiated nanostructures. In this work, we examined the effect of modulated CW laser irradiation on the particle fragmentation process to enhance the thermal diffusivity of nanofluids. A facile and cost-effective diode laser was applied to reduce the agglomerated size of Al2O3 nanoparticles in deionized water. The thermal wave generation, which was determined by the modulated frequency of the laser beam and the optical and thermal properties of the nanofluid, is also briefly discussed and summarized. The influence of laser irradiation time on nanoparticle sizes and their size distribution was determined by dynamic light scattering and transmission electron microscopy. The thermal diffusivity of the nanofluid was measured using the photopyroelectric method. The data obtained showed that the modulated laser irradiation caused the partial fragmentation of some agglomerated particles in the colloids, with an average diameter close to the original particle size, as indicated by a narrow distribution size. The reduction in the agglomerated size of the particles also resulted in an enhancement of the thermal diffusivity values, from 1.444 × 10ˉ³ to 1.498 × 10ˉ³ cm2/s in 0 to 30 min of irradiation time. This work brings new possibilities and insight into the fragmentation of agglomerated nanomaterials based on the photothermal study

Thermal diffusivity determination of liquid trough thermal diffusion length measurement

A new Optical Fiber Thermal Wave Resonance Cavity (OF-TWRC) technique was used to determine thermal diffusivity of liquids from the thermal diffusion length obtained from the curve of pyroelectric amplitude exponential decay with respect to cavity length and compared with the linear fitting of pyroelectric phase signal. The average thermal diffusivity of water obtained by this calculated method gives the value for water as 1.4723210cms−×. The thermal parameters for water and for other liquids agree with reported values in the literature

Thermal wave interferometry of gas-liquid using optical fibre thermal wave resonator cavity

The optical fibre thermal wave resonator cavity (OF-TWRC) technique was used to measure thermal diffusivity of a two-layer sample; air-liquid. The thermal waves were generated by transmitting the modulated laser beam through one end of optical fibre and illuminating the other fibre end surface that metalised with silver paint. The cavity length scan was done by moving the fibre end surface towards the pyroelectric detector continuously through air and then into the liquid. A good linear relationship of pyroelectric amplitude with respect to cavity length was obtained in thermally thick region in both media; air and liquid. The thermal diffusivity of air, glycerol and water obtained were closed to the literature values

Measuring thermal parameter by thermal diffusion length measurement using OF-TWRC technique

The newly developed Optical Fiber TWRC technique or shortly as OF-TWRC was used to determined the thermal diffusivity of liquids from the thermal diffusion length obtained from the curve of pyroelectric amplitude exponential decay with respect to cavity length and compared with the linear fitting of pyroelectric phase signal. The average thermal diffusivity of water obtained by this calculated method gives the value for water as 1.472 x 10 -3 cm2/s. The thermal parameters for water and for other liquids agree with reported values in the literature

Characterization of nanostructured CdS film deposited at low growth rate using CBD technique

Cds film was deposited by chemical bath deposition (CBD) on commercial glass substrate at the constant bath temperature 72 o C. The deposition time was varied from 1 to 4 hours. The film growth rate varies from 0.89 nm to 0.26 nm. It was found that the adhesion was very good for all film deposition times. Film thickness was measured by ellipsometer and ranges from 52.7 to 56 nm for all deposition times. XRD analyses show that the film was cubic with crystallite size from 38 to 45 nm. The optical energy band gap (E g), Urbach energy (E oo) and absorption coefficient (α) was calculated from the transmission spectral data

Simple TWRC technique by using optical fiber

The metalized optical fiber tip was used to generate thermal wave instead of metal foil attached to a tube as in the case of conventional thermal wave resonance cavity (TWRC) technique. The liquid thermal diffusivity was obtained through scanning the cavity length by moving this tip with respect to pyroelectric detector in liquid media, in a thermally thick region. Three-dimensional treatment of the metalized fiber tip was reduced to one-dimensional treatment using diameter of thermal wave generator relatively bigger than that of laser spot size. This applicability can be seen in two diameter size of optical fiber where the thermal diffusivity value of water obtained by this technique agrees with the values obtained by the conventional TWRC technique. This technique has a potential to be used in measuring thermal diffusivity of small liquid volume

Characterization of CdS nanocrystalline thin films grown by CBD technique at very low solution concentrations

CdS films were deposited on glass substrate by chemical bath deposition (CBD) from a bath containing very low concentrations of CdCl2 and (NH2)2CS. The adhesion of the deposited films was very good for all solution concentrations. The films were thermally annealed in air at the temperature 240 °C for 1 hour. The maximum and minimum film thickness 75.6 nm, 33 nm was observed, respectively. XRD analyses show that the films were cubic along with few feeble peaks of hexagonal phase at lower solution concentrations. The crystallite size was increased from 17 to 51 nm with the increase of the solution concentration. The optical energy band gap (Eg), Urbach energy (Eoo) and absorption coefficient (a) was calculated from the transmission spectral data. The best transmission (> 94 %) was obtained in this experiment