Nonsteady condensation and evaporation waves

We study motion of a phase transition front at a constant temperature between stable and metastable states in fluids with the universal Van der Waals equation of state (which is valid sufficiently close to the fluid's critical point). We focus on a case of relatively large metastability and low viscosity, when it can be shown analytically that no steadily moving phase-transition front exists. Numerically simulating a system of the one-dimensional Navier-Stokes and continuity equations, we find that, in this case, the nonsteady phase-transition front emits acoustic shocks in forward and backward directions. Through this mechanism, the front drops its velocity and eventually comes to a halt. The acoustic shock wave may shuttle, bouncing elastically from the system's edge and strongly inelastically from the phase transition front. Nonsteady rarefaction shock waves appear in the shuttle process, despite the fact that the model does not admit steady rarefaction waves propagating between stationary states. If the viscosity is below a certain threshold, an instability sets in, driving the system into a turbulent state. This work was supported by the Japan Society for Promotion of Science.Comment: revtex text file and four eps files with figures. Physical Review Letters, in pres

Compact Source of Electron Beam for Facility of Electron-Beam Welding with the Location of the Electron Gun and the Source of High Voltage in a Single Monoblock. Concept and Bench Tests of the Monoblok Prototype

Представлен прототип компактного источника электронного пучка для установок электронно-лучевой сварки с расположением электронной пушки и источника высоковольтного напряжения в едином моноблоке. Размещение электронной пушки, источника высоковольтного напряжения, электроники управления пучком и питания накала катода источника электронного пучка для электронно-лучевой сварки в едином корпусе-моноблоке снижает вес и стоимость (за счёт уменьшения количества используемых материалов), объём и занимаемые производственные площади. Это существенно расширяет возможности применения представляемого типа источников электронного пучка в разнообразных областях деятельности человека, в том числе в космических технологиях в открытом пространстве космоса. Цель работы – показать целесообразность концепции компоновки источника электронного пучка в едином корпусе-моноблоке на примере стендовых испытаний прототипа источника-моноблока. Спроектирован и изготовлен прототип источника-моноблока. Проведены его предварительные стендовые испытания с лазерным подогревом катода. Обсуждаются возможные применения. Получен электронный ток источника до 70 мА с энергией 90 кэВ. Данный результат демонстрирует возможность практической реализации нового способа компоновки источника электронного пучкаA prototype of an electron beam compact source for electron-beam welding is presented. The electron gun and a high-voltage source are united in a single monoblock. The placement of the electron gun, the high-voltage source, the beam control electronics and the power supply of the cathode heating of the electron beam source for electron beam welding in a single monoblock housing reduces weight and cost by reducing the amount of materials used, volume and occupied production areas. This significantly expands the possibilities of using the presented type of electron beam sources in various fields of human activity, including space technologies in the open space of space. The purpose of the work is to show the expediency of the concept of arranging the electron beam source in the single monoblock housing as the example of bench tests of the source prototype. The prototype of the monoblock was designed and manufactured. Its preliminary bench tests with laser cathode heating were carried out. Its possible applications are discussed. An electron source current up to 70 mA with an energy of 90 keV was obtained. The result obtained demonstrates the possibility of practical implementation of a new method of arranging an electron beam sourc