Estimation Of Effective Thermal Conductivity For Hollow Air-Pocketed Building Material

Abstract

The heat transfer through the building elements such as hollow ceramic bricks plays an important role in building energy consumpti on by reducing the effective thermal conductivity of the brick such that the heat transfer through the building walls is reduced. Numerical thermal analysis has become one of the powerful tools for predicting the performance of various building structures including hollow brick design which concern the energy saving issue in buildings. Since thermal conductivity of ceramic brick is comparatively low and when combined with the air pockets, the effective thermal conductivity of the brick can be further reduced thereby reducing the heat flux through the brick. The present study analyses the effect of hollow air pockets in bricks by considering a hollow brick (300×300×27) mm with 5, 9,13,16 and 25 number of cylindrical air pockets with varying diameter of air pockets, with different orientation, size and location of the air pockets in the brick. The thermal performance of the all the bricks are analysed by using general computational fluid dynamics (CFD) software package ANSYS FLUENT 16.1. The results obtained using CFD are validated by theoretically solving the problem using Fourier’s law of heat transfer and also with the experimental set-up of Guarded Hot Plate (ASTM C 177 Test Method). The effective thermal conductivity (ETC) of brick with 5 cylindrical air pocket of 20mm diameter is 0.25323 W/mK whereas ETC of brick with 25 cylindrical air pocket of 20 mm diameter is 0.23696 W/mK, From the simulation studies, it is observed that as the number of air pocket increases, the effective thermal conductivity of the brick decreases hence the effective thermal conductivity of brick is inversely proportional to number of air pockets in the brick. The optimization of the brick geometry is done on the basis of the lowest effective thermal conductivity and higher strength based on maximum cross-sectional area along the line of failure.