A theoretical study of heat transfer in a flat-flate solar collector

The thermal boundary layer problems associated with flat-plate solar collectors has been analysed using fourth degree polynomials for temperature profiles that obviates the shortcomings of results hitherto available using lower degree polynomials. The equations giving the heat flux distribution and hence temperature distribution in the collector have been solved by assuming the heat losses to be proportional to any non-dimensional power of the temperature difference. Three particular cases of practical interest have been studied. In the case of no heat loss, it is found that the Nusselt number for the heat transfer in the fully developed region agrees completely with the exact value. Confirmation of fully developed exact solutions, by the fourth degree polynomial, lends confidence to the results derived in this paper.     

Influence of intermolecular interactions on the melt rheology of a propylene–acrylic acid copolymer and its salts

Ionomers based on propylene–acrylic acid copolymer have been prepared and their rheological behavior studied. With different cations the melt viscosity at any shear rate increases as tributylamine salt < acid < zinc salt < sodium salt. Similarly, the activation energies for viscous flow follow the order polypropylene ～ tributylamine salt < acid ～ zinc salt < sodium salt. These results are a consequence of intermolecular interactions between salt groups for the metal acrylate derivatives and hydrogen bonding for the acid derivatives. Strong ionic interactions are absent in the tributylamine salt because of steric hindrance of the bulky amine substituents. The glass transition temperatures for these materials were equivalent. The elastic properties of these polymers follow a similar trend as does the viscosity.     

Solubility characteristics of R22-DMF refrigerant-absorbent combinationCaractéristiques de solubilité du mélange frigorigéne-absorbant R22-diméthylformamide

This Paper presents the solubility data of Refrigerant 22 (R22) - dimethyl formamide (DMF) measured over a wide range of temperature (?25°C to 120°C) and over a complete range of composition. The mixtures show large negative deviation from Raoult's law and there is large difference in normal boiling point its components. Thus this combination is suited for vapour absorption refrigerant systems. The In P-1/T diagram and temperature-composition diagram for the mixtures of R22-DMF have also been plotted for use in the analysis of vapour absorption systems.     

Multiplierless Implementations of MF/DTMF Receivers

The ever-increasing use of VLSI in telecommunications systems is leavening the search of new algorithms for task realizations suited to VLSI implementations of systems. Toward this search, the paper presents implementations for MF/DTMF receivers, which are based on multiplierless basic filters or primitive VLSI cells such as(1 + z^{-n}),(1 - z^{-n}), and(1 pm z^{-n} + z^{-2n}). These implementations require parallel processing and are designed to meet the requirements of a switching system.     

Buckling of cylindrical panels under axial compression

This paper investigates the effects of boundary conditions and panel width on the axially compressive buckling behavior of unstiffened, isotropic, circular cylindrical panels. Numerical results are presented for eight different sets of boundary conditions along the straight edges of the panels. For all sets of boundary conditions except one (SSI), the results show that the panel buckling loads monotonically approach the complete cylinder buckling load from above as the panel width is increased. Low buckling loads, sometimes less than half the complete cylinder buckling load, are found for simply supported panels with free in-plane edge displacements (SSI). The SSI buckling loads are below the complete cylinder load even for ‘360° panels’. It is also observed that the prevention of circumferential edge displacement is the most important in-plane boundary condition from the point of view of increasing the buckling load, and that the prevention of edge rotation (i.e. clamping) in the circumferential direction also significantly increases the buckling load. Parametric studies are also performed to determine the effects of variations in panel length and thickness on the buckling loads.     

Theory of susceptibility of a-Ge and a-Si

We propose a model of the thin films of a-Ge and a-Si with microvoids as frustrated spin glasses. Within this model the various qualitative aspects of the experimental results can be reasonably explained.     

Pressure loss in a spiral solar energy collector

A knowledge of the magnitude of pressure loss in a spiral solar collector for different flow rates is important not only because of its influence upon the power required to circulate a given fluid, but also becouse of its effect upon the efficiency of the collector. Experiments have been performed to determine the pressure losses in spiral solar collectors of different lengths for different flow rates. Three spirals—A, B and C—of different lengths but identical in nature were prepared from a polythene tube. Corroboration of theoretical predictions occurs for Re ≤ 3000. For higher values of Reynold's number (Re ≤ 10,000), excellent agreement between theory and experiment ensues.     

Statistically optimal null filter based on instantaneous matched processing

A novel approach is proposed for solving the problem of enhancement/suppression of narrowband signals of short-record length based on combining the maximum signal-to-noise ratio (SNR _o) and the least-squares (LS) optimization criteria. This two-fold optimization is implemented by scaling the output of an instantaneous matched filter used for the maximization of theSNR _o, over a variable-time observation interval, with the locally generated function (t) whose gain is optimized through the LS procedure. The intrinsic property of the proposed statistically optimal null filter (SONF) is its ability to track rapidly, leading to a more practical processing of short duration signals (transients). The theoretical analysis and simulation studies show that the SONF, based on this proposed two-fold optimization procedure, is closely related to the Kalman filter. On the other hand, the design of the SONF does not require the solution of a nonlinear equation of the Ricatti type that is necessary in finding the gains of the Kalman filter. Consequently, the proposed algorithm may be considered as an alternate approach to Kalman filtering. The paper also presents some simulation results illustrating the application of the proposed SONF.This work was partially supported by Micronet, a Candidan Network of Centre of Excellence, by the Natural Sciences and Engineering Research Council of Canada (NSERC) and by Fonds Pour la Formation de Chercheurs et L'Aide a la Recherche (FCAR) of Province of Quebec, Canada.     

Radiation from a waveguide-backed aperture in an infinite ground plane in the presence of a thin conducting plate

Coupled integrodifferential equations are formulated for the general problem of radiation from a waveguide-backed aperture in an infinite conducting plane when a thin, finite, and arbitrarily oriented conducting plate is located in its proximity. The general equations are particularized for the special case of a rectangular aperture and a rectangular plate and solved numerically using the method of moments. Detailed data are presented and discussed for various quantities of interest.