From Big Medical Encyclopedia

DEWAR VESSEL (J. Dewar, shotl. the chemist, 1842 — 1923) — the vessel with double walls (between to-rymi is created vacuum) intended for preservation for a long time of the easily evaporating liquefied gases and for cases when good heat insulation of substance is necessary. Of page use also for long-term storage fast-frozen (at t ° — 195 °) cultures of fabrics, plasma and bodies (see. Conservation of bodies and fabrics ). In life apply just arranged glass D. of the page known under the name a thermos, to maintenance of constancy of temperature of foodstuff.

Scheme of vessels of the Dewar (cross-section): glass (and and b); liquefied gas, metal for storage; 1 — vacuum; 2 — a layer of liquid nitrogen; 3 — liquid helium.

Of page happen generally cylindrical and spherical shape to a roundish bottom, various capacity. Pages make small D. of high-strength glass (fig., and and b); the vessels of bigger volume applied to transportation and storage of liquefied gases — from metal (fig., c).

D.'s heat exchange by the village can happen to the environment at the expense of three factors: convections, radiations and heat conductivity along walls. The heat transfer due to convection almost completely is eliminated with creation of a high vacuum between double walls (10 - 3 — 10 - 5 mm of mercury.); decrease in a heat transfer due to radiation is reached by a covering of internal walls of D. of page silver or copper or their polish.

Modern D. pages provide additional cooling with liquid nitrogen or a liquid air that provides a possibility of long-term storage of various liquefied gases.

Bibliography: Voskresensky P. I. Technology of laboratory works, M., 1973.

Yu. A. Zhukov.