Thermal conductivity of refractory glass fibres

In the present study, the current international standards and corresponding apparatus for measuring the thermal conductivity of refractory glass fibre products have been reviewed. Refractory glass fibres are normally produced in the form of low-density needled mats. A major issue with thermal conductivity measurements of these materials is lack of reproducibility in the test results due to transformation of the test material during the test. Also needled mats are inherently inhomogeneous, and this poses additional problems. To be able to compare the various methods of thermal conductivity measurement, a refractory reference material was designed which is capable of withstanding maximum test temperatures (1673 K) with minimum transformation. The thermal conductivity of this reference material was then measured using various methods according to the different standards surveyed. In order to compare different materials, samples have been acquired from major refractory glass fibre manufacturers and the results have been compared against the newly introduced reference material. Materials manufactured by melt spinning, melt blowing and sol–gel have been studied, and results compared with literature values

Laminar axisymmetric multicomponent buoyant plumes in a thermally stratified medium

This paper presents the results of a numerical study of laminar axisymmetric plumes that emanate from a source of combined buoyancy due to simultaneous heat and mass diffusion. The ambient is considered to be stably stratified through a linear temperature increase with height. Boundary layer and Boussinesq approximations are incorporated in the governing equations of mass, momentum, energy and species conservation. These equations are solved using an explicit finite-difference numerical scheme. Velocity, temperature and concentration fields are obtained for a range of Pr and SC. The basic physical mechanisms that underlie these flows are described. The results indicate a complex interaction between buoyancy ratio, thermal stratification, and Prandtl and Schmidt numbers

Natural Convection Heat Transfer From an Isothermal Vertical Surface to a Stable Thermally Stratified Fluid

Natural convection from an isothermal vertical surface to a thermally stratified fluid is studied numerically. A wide range of stratification levels is considered. It is shown that at high levels of ambient thermal stratification, a portion at the top of the plate absorbs heat, while a horizontal plume forms around a location where the plate temperature equals the ambient temperature. The plume is shown to be inherently unsteady, and its transient nature is investigated in detail. The effect of the temperature defect in striating the plume is discussed. Average Nusselt number data are presented for Pr = 6.0 and 0.7

Natural convection flows due to the combined buoyancy of heat and mass diffusion in a thermally stratified medium

This paper presents a numerical study of laminar doubly diffusive free convection flows adjacent to a vertical surface in a stable thermally stratified medium. The two buoyant mechanisms are thermal diffusion and species diffusion. The species concentration is assumed to be small. Boussinesq approximations are incorporated and the governing conservation equations of mass, momentum, energy, and species are nondimensionalized. These equations are solved using a finite-difference method. The results are explained in terms of the basic physical mechanisms that govern these flows. It is observed that the ambient thermal stratification has a profound influence on the transport characteristics. The results show many interesting aspects of the complex interaction of the two buoyant mechanisms

A numerical study of laminar axisymmetric plumes due to the combined buoyancy of heat and mass diffusion

This paper presents the results of a computational study of laminar axisymmetric plumes generated by the simultaneous diffusion of thermal energy and chemical species. Species concentrations are assumed small. The plume is treated as a boundary layer. Boussinesq approximations are incorporated and the governing conservation equations of mass, momentum, energy and species are suitably non-dimensionalised. These equations are solved using one time-step-forward explicit finite-difference method. Upwind differencing is employed for convective terms. The results thus obtained are explained in terms of the basic physical mechanisms that govern these flows. They show many interesting aspects of the complex interaction of the two buoyant mechanisms

Numerical study of double-diffusive free convection from a vertical surface

The double-diffusive free convective flow from a vertical surface has been studied numerically. The mass, momentum, energy and species conservation equations have been solved by a finite-difference method using an explicit scheme. Boundary layer and Boussinesq approximations have been incorporated. The velocity, temperature and concentration profiles indicate complex interaction between temperature and concentration driven buoyancy flows. The effects of Schmidt number and buoyancy ratio on the temperature profile have been discussed. The role of temperature stratification in the ambient has been highlighted