Doping directed at the oxygen sites in Y1Ba2Cu3O7−δ: The effect of sulfur,fluorine, and chlorine

We have investigated the effect of three dopants directed at the oxygen sites in Y₁Ba₂Cu₃O_7?δ : sulfur, fluorine, and chlorine. Single-phase material has been obtained up to a (nominal) replacement of ～1% of the oxygen. Although the lattice parameters are unchanged, all dopants raiseT _c (very slightly), sharpen the resistive transition, reduce the normal state resistivity, and very substantially increase the (magnetically determined) fraction of the material that is superconducting. All of these results differ qualitatively from those obtained with dopants directed at other locations in the 123 structure, and it is suggested that small additions of sulfur, fluorine, or chlorine may help to stabilize the ideal 123 stoichiometry.     

Analysis of a black liquid flat plate solar collector

In this paper we present a theoretical model of the black liquid flat plate solar energy collector. Numerical calculations have been performed corresponding to the experiments of Minardi and Chuang (1975). The present model has a good agreement with the experiments of Minardi and Chuang. A study of the effects of varying parameters, such as the liquid flow rate, radius and length of the tube has been made corresponding to the average solar intensity and ambient temperature data of 20 June 1974 in Ohio, U.S.A. The system's performance has also been studied for tropical climates.     

Performance of collector/storage solar water heaters: Arbitrary demand pattern

This paper presents a simple transient model for predicting the thermal performance of two novel water heaters which combine both collection and storage of solar energy in a single configuration. The proposed model is applicable for demand patterns, characteristic of various domestic and industrial applications. The model takes into account the appropriate heat transfer processes during sunshine and off-sunshine hours and predicts, for a particular case, the time dependence of water temperature which is in close agreement with experimental observations. The model also predicts the variation of water temperature for the withdrawal of hot water at constant flow rate. Furthermore, it determines the time dependence of flow rate corresponding to extraction of hot water at constant temperature; this is a desirable situation in process heating and other applications.     

Diurnal response of solar air heaters

A time-dependent heat transfer model has been developed to predict the diurnal performance of a conventional solar air heater which consists of a flat passage between two metallic plates through which the heating fluid (air) is made to pass. The effect of various parameters such as the heat capacities of the glass cover, the absorbing plate and the air streams, as well as the heat transfer coefficient from the absorbing plate to the air stream, have been investigated. It is found that the heat capacities of the glass cover and the absorber do not alter the performance characteristics of the solar air heater while the heat capacity of the air stream significantly influences both the rise in temperature of the fluid and the shift in phase. However, the effective heat transfer coefficient from the absorbing plate to the air stream significantly affects the diurnal response of a solar air heater.     

Analysis of a non-porous double-flow solar air heater

In this paper, we present the theory of a non-porous air heater in which the air is blown both below and above the absorbing surface. Explicit expressions for the outlet air temperature and useful heat flux have been obtained in terms of mass flow rate of the air, distance along the direction of air flow and other relevant parameters. The double-flow air heater is found to perform more efficiently than a single-flow air heater.     

Periodic analysis of a transwall: A passive heating concept

A periodic analysis of the novel ‘transwall’ for passive heating is described and the thermal flux entering an air-conditioned space through the ‘transwall’ is evaluated. Numerical calculations have been performed corresponding to the meteorological data of the 11th of January at Boulder, Colorado, USA, i.e. for a harsh North American winter's day.     

On the response of a critical point reactor to inherent reactivity noise input

It is shown that the use of linearization and/or quasistatic approximation leads to general methods for assessing the influence of reactivity noise on a power reactor. Exact time dependent expressions have been found for the moments of state variables for the case of an uncontrolled critical point reactor. For the special case of an initial equilibrium between neutrons and precursors, it is found that the normalized centred covariances of neutrons and precursors increase linearly with time exactly at the same rate.     

Alternating current chronopotentiometry—III. Electroreduction of silver(I), cadmium(II), and thallium(I) in calcium nitrate tetrahydrate melt

The electroreduction of silver(I) on a platinum electrode and of cadmium(II) and thallium(I) on a mercury electrode has been studied by alternating current chronopotentiometry. Expected relations for the diffusion controlled, one-electron deposition of an insoluble substance are obeyed for silver(I); but reduction of cadmium(II) on mercury is more complex. Nucleation of metallic thallium is the rate controlling process during the early stages of the reduction of thallium(I).