Calculation of the three-dimensional boundary layer with solution of all three momentum equations

The paper describes the application of a calculation procedure to three flow situations which can be characterised as three-dimensional boundary layers. Unlike most of the published methods, the present procedure solves all momentum equations and takes full account of the pressure variation in directions normal to the main-flow direction. The applications demonstrate that, when the boundary conditions exhibit certain discontinuities, only the solution of all three momentum equations can give satisfactory accuracy. The results of the present calculations are compared with available similarity solutions wherever possible.     

Computer analysis of the three-dimensional flow and heat transfer in a steam generator

A calculation procedure is described for the class of flows in which the flow domain contains numerous dispersed solid objects such as tubes or rods. The central idea is to treat the solid objects as distributed resistances to flow and heat transfer. The calculation procedure is illustrated by an application to a steam generator of a nuclear power plant. The three-dimensional flow field and the enthalpy distribution are calculated. Since details of the thermal-hydraulic behaviour of the steam generator can thus be inexpensively predicted, the procedure can be useful to designers.     

A nonrenewable minimal-repair warranty policy with time-dependentcosts

Estimating warranty costs during the life cycle of a product is important to the manufacturer, who has to plan for creating a fund for warranty reserves. Replacement or repair costs associated with product-failure within the warranty period are drawn from this fund. This paper considers a policy where warranty is not renewed on product failure within the warranty period but the product is minimally repaired by the manufacturer. This implies that, on repair, the failure rate of the item remains the same as just prior to failure. Repair costs are assumed to depend on the product age. Such policies are suitable for complex and expensive products where repair typically involves a small part of the product. s-Expected warranty costs and amount of warranty reserves, based on a selected level of s-confidence, are derived. Applications of the results to various product market situations are considered. The results demonstrate how cost information can be used to decide and determine the warranty length     

Dielectric behaviour and a.c. conductivity in Cu x Fe3−x O4 ferrite

The dielectric properties (dielectric constant and loss) for the system Cu _x Fe_3−x O₄ with x = 1.0, 0.8, 0.6, 0.4 and 0.2, were studied in the temperature range 300 ∼ 800 K and also in the frequency range 1 kHz ∼ 1 MHz. A.c. conductivity was derived from dielectric constant and loss tangent data. The conduction in this system is interpreted as due to small polaron hopping. The dielectric relaxation was observed for the compositions with tetragonal structure whereas normal behaviour was observed for cubic structure.     

Effect of Dune Formation on Pressure Drop in Horizontal Pneumatic Conveying System

Pneumatic conveying is widely used in industries handling large amount of granular materials to transport the solid particles; however, the process is energy intensive as an instability of flow sets in the transportation line even in the dilute regime, causing large fluctuations in the line pressure drop, the reason of which is not clearly understood. Here, we investigate, both by experiments and by using numerical simulations, the instability transition regimes and identify the reasons of the fluctuations observed in the line pressure drop in a horizontal pneumatic transport system operating at near-saltation conditions. It is observed that the increase in the pressure drop (immediately after the saltation) is accompanied by the formation of distinct dunes. It is also observed that the line pressure drop depends on the axial location of the dune and shows large fluctuations in the regime where the dunes are unstable. Results obtained from the numerical simulations suggest that the increase in the line pressure drop in the presence of dunes is essentially due to the shear stresses at the dune surface which are larger than that for the flows in clean pipe.     

Laminar Heat Transfer in a Pipe Subjected to a Circumferentially Varying External Heat Transfer Coefficient

Abstract

Numerical techniques have been used to solve the thermally developed regime for a laminar pipe flow that exchanges heat with a fluid environment in the presence of a circumferentially varying external heat transfer coefficient. By making use of the fact that the temperature distributions have similar shapes at successive streamwise locations, the three-dimensional temperature field was scaled to two dimensions. The resulting two-dimensional eigenvalue problem was solved by a rapidly converging automated scheme that successively refines an initial guess. Solutions were obtained for two circumferential distributions of the external heat transfer coefficient respectively intended to model forced and natural convection cross flows. The circumferential average heat transfer coefficient was found to be quite insensitive to the imposed circumferential variations. The local wall heat flux is nearly circumferentially uniform when the mean value of the external coefficient is high. On the other hand, at low mean values of the external coefficient, the local wall heat flux tends to follow the imposed circumferential variations.     

Interface engineering via compatibilization in HDPE composite reinforced with sodium borosilicate hollow glass microspheres

In the present study dealing with hollow-sphere filled polymers, sodium borosilicate hollow glass microspheres (HGM) with the crushing strength of 30,000 psi were used as filler in high density polyethylene (HDPE). HGM remained intact in HDPE matrix with no sign of crushing during the compounding and injection molding operation. Polyethylene-graft-maleic anhydride (PE-g-MAH) used as compatibilizer resulted in nano sized needle like structure in the HGM HDPE interfacial region that resulted in enhanced mechanical properties of HDPE HGM composites.