Volume 80, Issue 5, May 2009
Index of content:
- THERMOMETRY; THERMAL DIFFUSIVITY; ACOUSTIC; PHOTOTHERMAL AND PHOTOACOUSTIC
80(2009); http://dx.doi.org/10.1063/1.3125625View Description Hide Description
The beam profiles of pulsed lasers are currently measured using either complementary metal oxide semiconductor(CMOS) or charge coupled device(CCD) cameras. Despite providing high-resolution beam profiles, these devices cannot work with high power lasers. If additional optical attenuators are used, beam distortions may occur. In this paper we demonstrate a high-resolution photoacoustic technique capable of measuring the beam profile of pulsed lasers. The beam profiles of a pulsed neodymium-doped yttrium aluminium garnet(Nd:YAG) laser and a pulsed optical parametric oscillator(OPO) laser system were measured using a polydimethylsiloxane film and a single element high-frequency ultrasonic transducer. The advantages and limitations of the developed photoacoustic technique are discussed.
Quantification of unsteady heat transfer and phase changing process inside small icing water droplets80(2009); http://dx.doi.org/10.1063/1.3139005View Description Hide Description
We report progress made in our recent effort to develop and implement a novel, lifetime-based molecular tagging thermometry (MTT) technique to quantify unsteady heat transfer and phase changing process inside small icingwaterdroplets pertinent to wind turbineicing phenomena. The lifetime-based MTT technique was used to achieve temporally and spatially resolved temperature distribution measurements within small, convectively cooled waterdroplets to quantify unsteady heat transfer within the small waterdroplets in the course of convective cooling process. The transient behavior of phase changing process within small icingwaterdroplets was also revealed clearly by using the MTT technique. Such measurements are highly desirable to elucidate underlying physics to improve our understanding about important microphysical phenomena pertinent to ice formation and accreting process as waterdroplets impinging onto wind turbine blades.
Coupled analysis of high and low frequency resonant ultrasound spectroscopy: Application to the detection of defects in ceramic balls80(2009); http://dx.doi.org/10.1063/1.3142462View Description Hide Description
A coupled analysis of high and low frequency resonant ultrasound spectroscopy of spheroidal modes is presented in this paper. Experimentally, by using an ultrasonic probe for the excitation (piezoelectric transducer) and a heterodyne optic probe for the receiver (interferometer), it was possible to take spectroscopic measurements of spheroidal vibrations over a large frequency range of 100 kHz–45 MHz in a continuous regime. This wide analysis range enabled variations in velocity due to the presence of defects to be differentiated from the inherent characteristics of the balls and consequently, it offers the possibility of detecting cracks independently of production variations. This kind of defect is difficult to detect because the C-shaped surface crack is very small and narrow , and its depth does not exceed . The proposed methodology can excite spheroidal vibrations in the ceramic balls and detect such vibrations over a large frequency range. On the one hand, low frequency resonances are used in order to estimate the elastic coefficients of the balls according to various inspection depths. This method has the advantage of providing highly accurate evaluations of the elastic coefficients over a wide frequency range. On the other hand, high frequency vibrations are considered because they are similar to the surface waves propagating in the surface zone of the ceramic balls and consequently can be used to detect C-crack defects.
High accuracy, self-calibrating photopyroelectric device for the absolute determination of thermal conductivity and thermal effusivity of liquids80(2009); http://dx.doi.org/10.1063/1.3131625View Description Hide Description
An improved photopyroelectric approach to simultaneously determine the thermal conductivity and thermal effusivity of minute quantities of liquids, which is based on a combined scan of the modulation frequency and the piston-sensor distance, is presented. A thorough sensitivity analysis and statistical analysis of the fitting uncertainties show that the method is a very accurate tool for the simultaneous determination of the thermal conductivity and thermal effusivity of liquid samples.