Study of air flow in hollow bricks using holographic interferometry

Natural convection is a topic of considerable interest in many engineering applications. To improve the thermal insulation of walls, hollow bricks in which this kind of convection occurs could be used. Thus a good understanding of the free convection of the air inside this type of bricks is valuable. Theoretical studies consisting of computer simulation have already been carried out and give a good understanding of the flow movement, velocity, and temperature variation in different types of fluids.1-2 The aim of our study was to perfect a good holographic interferometric method to visualise the isothermal lines of a free air flow convection inside a hollow brick. By viewing and understanding the heat transfer inside, it will be possible to define a cavity shape that reduces heat exchange between the cold outdoor and the hot indoor surface (and vice versa). The hollow brick cavity dimensions were 180 × 60 × 60 mm, two walls were in aluminium, two in Tuffnal and the two windows were in a Plexiglas. Temperature differences, ΔT, of 7 to 30°C were obtained with the heater on the vertical side. The temperature was measured with four thermocouples inside the two aluminium walls.