X-ray vision.
Recent correspondence initiated by Dr. Cochrane Shanks' account of the sensation of light experienced during a CAT scan recalls an article on vision by X rays by R. R. Newell (1948).
SI units in radiotherapy.
We note with concern recent correspondence advocating the use of the centigray as a unit of dose (Halnan 1978, Martin-Smith 1978). Considering the reasoning and history behind the introduction of the SI system, it would be a retrograde step to introduce a unit such as the centigray. As the Australian Metric Conversion Board recommended that Australians adopt the SI units in radiotherapy by January 1978, the Cancer Institute, Melbourne changed to these units (rad to gray and centimetre to millimetre) on October 3, 1977.
Effect of superficial gas velocity on the particle temperature distribution in a fluidized bed with heat production
The heat transfer behavior of particles and gas in an olefin polymerization fluidized bed was numerically analyzed using an in-house developed 3-D computational fluid dynamics discrete element model (CFD-DEM). First the implementation of the model was verified by comparing simulation results with analytical results. A constant volumetric heat production rate was implemented in the particle energy equation to mimic the heat production due to the polymerization reaction. It was found that the probability density function (PDF) of the particle temperature becomes more homogeneous with increasing superficial gas velocity. Furthermore, instantaneous snapshots of the thermal driving force (the difference between the single particle temperature and bed-average gas temperature, Tp− ) for different heat production rates provide detailed insight in the particle temperature distribution inside the fluidized bed. The time- and bed-averaged particle convective heat transfer coefficient, which was calculated by Gunn׳s correlation, was found to be independent of the superficial gas velocity. This is explained by the fact that the relative velocity of gas and particles in the emulsion phase, where most of the particles and gas interact, is hardly influenced when increasing the gas superficial velocity. From the spatial distribution of Nusselt number, it becomes apparent that the high heat transfer regions are found in the wake of rising bubbles, whereas low heat transfer rates are found in the clouds of the bubbles.