X-ray image analysis and ultramicroscope study of magnetic fluids used as working liquid in heat transfer experiments

Boiling characteristics of water-based and ionic magnetic fluid have been v isualized using x-ray microfocus. During magnetic fluid boiling, large vapo r bubbles nucleated around the vicinity of the heating surface and particle s that came into contact with the heating element formed agglomerates large enough to be seen in real time x-ray images. This caused irreversible dama ge to the magnetic fluid heated to temperatures higher than 373 K. However, application of the magnetic field showed improvements in heat transfer cha racteristics and ionic magnetic fluid performed better over the water-based magnetic fluid. Ultramicroscope observations of ionic and water-based magn etic fluids heated only up to 353 K in vacuum for ten consecutive days and were found stable. However, ionic magnetic fluid heated in a vacuum glass c ell at 373 K burst suggesting the accumulation of noncondense gas. (C) 1999 American Institute of Physics. [S0021-8979(99)43708-9].