Abstract
Thermal management is a key technology to desterilize unused energy sources for building sustainable societies. However, conventional temperature measurement methods such as infrared thermography can detect only the surface temperature of objects because they use infrared light. We thus present a novel three-dimensional X-ray thermography using a phase-contrast X-ray imaging technique, which enables non-destructive observations of the inner thermal distribution of samples. The sensitivity of phase-contrast X-ray imaging is about 1000 times higher than that of conventional X-ray imaging. Therefore, temperature changes can be detected by using density changes caused by thermal expansion. We applied X-ray interferometric imaging (XI) that detects phase-shift by using a crystal X-ray interferometer. The highest sensitivity of XI was utilized to successfully obtain the first three-dimensional image that visualizes the thermal distribution in heated water nondestructively. Additionally, projection images visualizing the dynamic thermal flow in heated water were also obtained, and their distribution and diffusion velocity agreed well with those of the calculated images obtained by computational fluid dynamics analysis. These results show that the novel thermography enables nondestructive observations of inner temperature and thermal flow and can provide solutions for optimum thermal design of electrical devices, motors, and engines.
Highlights
Along with length and weight, temperature is one of the basic physical values of materials, which expresses the thermal energy generated by the vibration of atoms and molecules
X-ray interferometric (XI) phase-contrast imaging[1], which detects phase-shift using a crystal X-ray interferometer, has the highest sensitivity compared with that of other phase-sensitive methods such as diffraction-enhanced imaging and the Talbot interferometric method[8,9], because it detects the phase-shift directly from the superposition of X-rays. This high-sensitivity was utilized to clearly visualise, β-amyloid plaques in brains taken from Alzheimer disease mice models[10], cancerous tissues in rat livers[11], and air hydrates in old ice cores mined from Antarctica[12] without any contrast agents or harmful X-ray doses
A density resolution of 0.5 mg/cm[3] was attained for an XI imaging system using feasibility observations with a 1-hour measurement time[14,15] and monochromated synchrotron radiation X-rays emitted from a vertical wiggler at the beamline BL-14C of the Photon Factory in Japan
Summary
The coefficient of the thermal linear expansion of water and iron are 70 and 12 × 10−6/K, respectively, and the high sensitivity of XI enables us to observe two- and three-dimensional temperature maps (spatial distribution) of a sample by means of density changes. As shown in equation (6) in the supplemental method, the temperature changes can be obtained from the measured phase-shift directly, and the thermal detection limit (temperature resolution) is estimated as 2 and 6 degrees for water and iron, respectively, from the density resolution. The density of the bottom of the cell changes indicating that the cell is heated and the temperature is increased These results show that the novel X-ray thermography is a powerful tool for the non-destructive detection and visualization of inner temperatures and thermal flows. The exposure times for obtaining one interference pattern were 0.2 and 1 s for two- and three-dimensional observation
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