Investigations on Determining the Overall Heat Transfer Co-efficient of Building Materials

Abstract

A Guarded Hot Box (GHB) may be applied to investigate the heat transmission through the walls of building. A GHB is an instrument in which an environment is developed to simulate condition on the two sides of a test specimen by means of two (cold and hot) compartments (called boxes). For creating forced convection conditions, an air circulating fan may be placed in the boxes and baffles are provided to direct the air flow inside the box. In the standards related to the construction of GHB, ASTM C1363 - 11 and ISO 8990, the optimum position of fan to create forced convection condition and optimum position of baffle to direct flow inside the guarded hot box is not provided. The present study relates to the optimized positioning of the air circulating fan in the GHB along with the baffle position by applying Taguchi Method. For applying Taguchi's method, there are three position parameters i.e. Y position, Z position and the baffle position. Numerical experiments are carried out by changing one factor and keeping other two stationary, so that the maximum value of each factor is achieved. Taguchi orthogonal array is planned with two levels of position factors and one level of baffle factor with the help of software Minitab 16.Taguchi method gives the importance of studying the response variation using the signal–to–noise (S/N) ratio, resulting in minimization of quality characteristic variation due to uncontrollable parameter. The velocity analysis is done considering over the specimen as the quality characteristic with the concept of "the nominal-the-better”. The S/N ratio values are calculated by the help of software Minitab 16.

In the present CFD work, a simulation fan placed the inside guarded hot box is carried out by using FLUENT®6.3.26. A fan boundary condition and standard k-ε turbulence model is applied to model the problem. The main objective of this project is to develop a CFD (Computational Fluid Dynamics) model that could be used as a flexible modelling tool, in addition with experimental procedures, for the study, design and improvement of the guarded hot box. A model of the guarded hot box (GHB) is developed in PRO-E and after meshing using GAMBIT, the CFD study is done using FLUENT while the optimization of fan is done using Minitab 16 software. The CFD results match well with experimental results available from the literature review.