末廣型ノズルを有する油鑛散眞空ポンフの硏究(第1報)

Abstract

We designed pump with a long divergent nozzle with expansion ratio of 100 and divergent angle of 10°. This expansion ratio, 100, was greater than those given by W.W. Crawford in 1917 for the mercury diffusion pump and by M. J. Copley in 1935 for mercury and oil diffusion pump. The expansion ratios adopted in their experiments were 30 and 64 respectively. Our horizontal pump was similer to that designed by Crawford, but had a covering tube around the nozzle. Further, in our case, an exhaust tube for the fore pump was connected to the main body horizontally to avoid the disturbance of the molocular flow from the ejector. Within a suitable range, the relation between the final pressure P and the boiling oil vapour pressure H in cm. oil was found to be expressed empirically P=F exp {--0.880 (H--0.32)}, (1) where F was the pressure of the fore pump. At the pressure H higher 4.8 cm. the final pressure obtained was the order of one hundredth of the fore vacuum. The value γ of the vapour was obtained by measuring its temperatures before and after the expansion through the divergent nozzle, and was estimated to be 1.042, being smaller than that of mercury, 1.666. On the other hand, according to (1), the back diffusion coefficient should be very much larger than the value calculated by Dayton on the basis of Matricon's formula. In conclusion, to operate the pump effectively, one must use the diffusion oils of greater γ, or use the nozzle designed to diminish the back diffusion.