SIMPLIFIED ANALYTICAL MODEL FOR THERMAL TRANSFER IN VERTICAL HOLLOW BRICK

A modern building envelope has a lot of little cavities. Most of them are vertical with a high height to thickness ratio. We present here th e conception of a software to determine heat transfer through terra-co tta bricks full of large vertical cavities. After a bibliographic stud y on convective heat transfer in such cavities, we made an analytical model based on Karman-Polhausen's method for convection and on the rad iosity method for radiative heat transfer. We used a test apparatus of a single cavity to determine the temperature field inside the cavity. Using these experimental results, we showed that the exchange was two -dimensional. We also realised heat flux measurements. Then we expose our theoretical study: we propose relations between central core tempe ratures and active face temperatures, then between outside and inside active face temperatures. We calculate convective superficial heat tra nsfer because we noticed we have boundary layers along the active face s. We realise a heat flux balance between convective plus radiative he at transfer and conductive heat transfer, so we propose an algorithm t o calculate global heat transfer through a single cavity. Finally, we extend our model to a whole hollow brick with lined-up cavities and pr opose an algorithm to calculate heat flux and thermal resistance with a good accuracy (approximate to 7.5%) compared to previous experimenta l results.