Recently a new class of superconducting compounds with remakable superconducting properties has been found. These compounds are ternary molybdenum chalcogenides of the type MxMo6X8[Mx=Pb, Cu… X=S, Se, Te] and the first system of ternary superconductors. It seems that the discovery of these compounds is a beginning to produce new improved superconductors. This paper describes the superconducting and normal properties of these compounds.
At present, method of transient cooldown is widely used for studying boiling process. This method was successfully applied to studies of film boiling of cryogenic liquids. The aim of the present work is to determine temperature of heat exchange surface while investigating heat transfer by the method of transient cooldown. For this purpose it is proposed to approximate temperature curve cooldown with the help of continued smooth function.
Forced convection boiling of liquid nitrogen flowing in a horizontal annulus has been studied. The heat transfer test section consists of an electrically heated core tube 0.85cm O.D.×50cm long and an insulated outer tube. Three sizes of outer tube having inner diameter of 1.24, 1.45 and 2.23cm were used to investigate the effect of diameter ratio on heat transfer coefficient. The temperature of the heated tube were measured by eight copper-constantan thermo-couples immersed along the heated length. The experiment was carried out at an atmospheric pressure and in low quality range and the mass flow rate was varied from 45.8 to 208 grams per second. The flow pattern in a horizontal annulus is more complicated than in a horizontal tube, therefore visual studies were made of the flow pattern of the fluid boiling in horizontal annulus. Experimental data were well correlated by Lockhart-Martinelli parameter, Reynolds number and diameter ratio in convective region. The maximum heat flux in the horizontal annulus was well correlated with mass flow rate for the present study.
It is well known how to measure the level of liquid helium surface by using a superconducting wire. However, there are two difficulties in this method. One is due to the electrical resistivity change which depends on self-heating of the wire. Another is due to the change of the plateau region in current-voltage curve of this wire when the helium bath temperature has changed or the evaporation rate of helium gas has changed. These difficulties have been surmounted by using the new method of two steps pulse current measurement, which makes use of the properties of return curve in current-voltage hysteresis loop.
Seven electronic circuits, which are simple and very convenient for the use in low temperature experiments, are presented. The working principle, some important notes for construction, and performances of them are also described.