The rate at which evaporation can occur from a surface is limited by the rate of heat flow into the surface. Because of this limitation when a liquid at its boiling point commences to flow, the proportion of vapour which forms as a result of the Bernoulli fall in pressure is less than is calculated from adiabatic expansion. A theory for the actual amount of vapour which will form is given, together with an analysis of its effect upon the velocity of flow and the quantity of fluid passed by a

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... zle. It is found that although the system consists of a central core of liquid and an envelope of vapour, the calculated limiting velocity of flow, which is the velocity of pressure propagation in the system, is low. The order of magnitude is 20 m./sec. as compared with 400 and 1500 m./sec. for vapour alone and liquid alone respectively. There is a corresponding critical pressure, analogous to that in a gas nozzle, but in contrast to the gas case, both the critical pressure and the limiting velocity itself are functions of the diameter and length of nozzle. Experiments are described which confirm these theoretical deductions in all respects, and which also show good quantitative agreement with calculated velocities, critical pressures, and amount of discharge and of evaporation. On the basis of this experimental verification general phenomena to be expected in pressure propagation through liquids near saturation temperature are discussed. Temperature and pressure phenomena in flow of saturated liquids 465 Vol. 194. A. 30