Mathematical Simulation Analysis of Concrete Perforated Bricks with Three-dimension Conjugate Heat Transfer

3-D heat transfer behaviors in two types of concrete perforated bricks used in external walls were numerically simulated. Air density was modeled both with Boussinesq assumption and ideal gas model, and air thermal properties were calculated alternatively with constant and polynomial parameters. Results of four different inputs shown us that there had little difference between them and they agreed well with Guard hot box tests. The effective conductivity of bricks decreased with increase of the air interlayer thickness at first and then increased as it continued to increase, which meant that thickness of the air interlayer was crucial to insulation effect of bricks. This was because of the cooperation of the conduction and natural convection. Under the same condition, effective conductivity is proportional to concrete conductivity.