Nonsteady lamination of the flow of biphase helium in horizontal channels

Abstract

A distinguishing design feature of modern physical installations [i] cooled at the level of 4.2 K is the presence of horizontal channels for the reverse flow of biphase helium relative to the large diameter (up to some tens of millimeters) characterized by considerable local hydraulic resistance at the inlet which ensures the condition of constant flow rate of helium at the inlet to the channels with different cryostating regimes, and also characterized by constant pressure of the cryogenic agent at the outlet from these channels. The mass velocity of the cryogenic agent in such channels is not high, amounting to 10-30 kg/(m2"sec): this corresponds to laminated (stratified) flow of helium in channels [2, 3]. Besides that, a characteristic feature of systems for the cryostating of physical installations is a dynamic thermal regime of operation. Heat liberations are uniformly distributed over the length of the cryostating channels, their magnitude is much smaller than the critical density of the heat flow, and the length of the thermal pulse attains some tens of seconds. At the same time the permissible magnitude of change of the temperature of helium does not exceed several tenths of a centigrade, i.e., even with an imperceptible change of pressure in the reverseflow channels of biphase helium, the conditions of cryostabilization of the flow carrying elements may be infringed. The literature does not contain any data on investigations of the dynamic characteristics of horizontal channels with laminated flow of biphase helium.