الفهرس 
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Abstract
The aim of this work is to improve the moving heat source method proposed theoretically by Roesnthal [ 15] and applied experimentally by AbdeL-Waked [ 19] to measure the thermal diffusivity of metals . The experiments were performed oil thin tubular specimens placed in quiescent air and the heat source was an electrically heated ring sliding axially oil the outside surface of the specimen . The moving heat source develops a temperature profile in the specimen , which seems invariant with time to an observer riding on the source and moving with the same velocity The thermal difYusivity and the heat transfer coefficient from the specimen can be determined from the closed form equations derived in [ 15] . In the analysis of [ 15] , the heat transfer coefficient between the specimen and the surrounding was assumed constant . In fact , the heat transfer by natural convection changes axially because the temperature is not
uniform Z”)
alon,, the tube . Moreover , the motion of the heat source produces air drafts which also influences the heat transfer from the specimen . Therefore , a modification oil the experiment of [19] seemed mandatory . The specimen with the heat source were laid in an air duct , where air is blown transversely on the tube . The modification has improved the experimental results considerably , but did not eliminate completely the effect of the motion of the heat source.