K. Badari Narayana

Heat transfer correlations for multilayer insulation systems

Multilayer insulation (MLI) blankets are extensively used in spacecrafts as lightweight thermal protection systems. Heat transfer analysis of MLI is sometimes too complex to use in practical design applications. Hence, for practical engineering design purposes, it is necessary to have simpler procedures to evaluate the heat transfer rate through MLI. In this paper, four different empirical models for heat transfer are evaluated by fitting against experimentally observed heat flux through MLI blankets of various configurations, and the results are discussed.

A general procedure for modified crack closure integral in 3D problems with cracks

In linear elastic fracture mechanics (LEFM), Irwins crack closure integral (CCI) is one of the signficant concepts for the estimation of strain energy release rates (SERR) G, in individual as well as mixed-mode configurations. For effective utilization of this concept in conjunction with the finite element method (FEM), Rybicki and Kanninen [Engng Fracture Mech. 9, 931 938 (1977)] have proposed simple and direct estimations of the CCI in terms of nodal forces and displacements in the elements forming the crack tip from a single finite element analysis instead of the conventional two configuration analyses. These modified CCI (MCCI) expressions are basically element dependent. A systematic derivation of these expressions using element stress and displacement distributions is required. In the present work, a general procedure is given for the derivation of MCCI expressions in 3D problems with cracks. Further, a concept of sub-area integration is proposed which facilitates evaluation of SERR at a large number of points along the crack front without refining the finite element mesh. Numerical data are presented for two standard problems, a thick centre-cracked tension specimen and a semi-elliptical surface crack in a thick slab. Estimates for the stress intensity factor based on MCCI expressions corresponding to eight-noded brick elements are obtained and compared with available results in the literature.

Cracks emanating from pin-loaded lugs

Pin-loaded lugs were analysed in the presence of cracks emanating from circular holes. The analysis presents a unified treatment of interference, push or clearance fit pins. Both metallic (isotropic) and composite (orthotropic) plates were dealt with. The finite element model used special singular six-noded quadrilateral elements at the crack tip. The non-linear load contact behaviour at the pin-hole interface was dealt with by an inverse technique. A modified crack closure integral (MCCI) technique was used to evaluate the strain energy release rates (SERRs) and stress intensity factors (SIFs) at the crack tips. Numerical results are presented showing the non-linear variation of SIF with applied stress, and the influence of the amount of interference or clearance and the interfacial friction on SIF.

Combined conduction and radiation heat transfer in a gray anisotropically scattering planar medium with diffuse-specular boundaries

Coupled conduction and radiation heat transfer in a gray planar nonlinearly anisotropic scattering medium bounded between two plane parallel surfaces reflecting both diffusely and specularly is analyzed. The governing integrodifferential equations are solved by a numerical iterative method consisting of Numerovs method to solve the energy equation and Chandarsekhars discrete ordinates method in conjunction with the Crank-Nicolson method to solve the radiative transfer equation. Convergence of the solution is enhanced by Ng-acceleration. The numerical algorithm described is found to be fast and reliable. Numerical results based on

Heat transfer analysis of mutually irradiating fins

S_{32}

USE OF GCG METHODS FOR THE EFFICIENT SOLUTION OF MATRIX PROBLEMS ARISING FROM THE FVM FORMULATION OF RADIATIVE TRANSFER

method indicate that anisotropy plays an important role, and difference between the diffuse and specular reflections is found to be insignificant.

View factors for parallel rectangular plates

Abstract Apparent emittance of a longitudinal rectangular fin system with an opening angle, accounting fin-to-fin radiation interaction and also with surfaces that reflect radiation in both diffuse and specular regimes has been evaluated. The governing equation of the problem is a complicated integro-differential equation. This equation has been solved with the Gauss–Jacobi orthogonal collocation method, which possesses the quality of exceptional accuracy with a few numbers of nodes. Finally, the minimum mass design of the fin has been arrived at.

Two-dimensional heat transfer analysis of radiating plates

Preconditioned generalized conjugate gradient (GCG) iterative methods are applied to the solution of large, sparse, and unsymmetric linear algebraic equations resulting from the application of the finite-volume method to the problem of radiative heat transfer in an absorbing, emitting, and scattering gray medium, with the boundary surfaces reflecting radiation in both diffuse and specular regimes. The governing radiative transfer equation, which is a complicated integro-differential equation, has been discretized using the S N finite-volume method (FVM). Different variants of GCG methods have been tested on a problem of 2-D radiation in a cylinder, and efficiencies of the methods have been compared. Numerical results indicate that preconditioning suggested in the article dramatically improves the performance of the GCG methods. Results on test problems based on S 8 FVM agree well with exact results reported in the literature.Preconditioned generalized conjugate gradient (GCG) iterative methods are applied to the solution of large, sparse, and unsymmetric linear algebraic equations resulting from the application of the finite-volume method to the problem of radiative heat transfer in an absorbing, emitting, and scattering gray medium, with the boundary surfaces reflecting radiation in both diffuse and specular regimes. The governing radiative transfer equation, which is a complicated integro-differential equation, has been discretized using the S N finite-volume method (FVM). Different variants of GCG methods have been tested on a problem of 2-D radiation in a cylinder, and efficiencies of the methods have been compared. Numerical results indicate that preconditioning suggested in the article dramatically improves the performance of the GCG methods. Results on test problems based on S 8 FVM agree well with exact results reported in the literature.

Heat and Mass Transfer Characteristics and the Evaluation of Thermal Properties of Moist Food Materials

This article provides closed-form equations for computing view factors for parallel rectangular plates. View factor algebra is used in the derivation of these equations. Results of nine cases of parallel rectangular plates are given. Some results presented are taken from the literature and reproduced here for the sake of completeness. The equations given are easy to use for computation.

Determination of thermal properties of food materials theory and experiments

Abstract The strongly implicit procedure is used to solve non-linear elliptical two-dimensional heat conduction in radiating plates. A uniform heat flux is applied at one end of the plate which dissipates heat by radiation from one end into a vacuum at 0 K and into an ambient at temperature T i from the other. The results are presented with reference to four non-dimensional parameters.