Calculations of pressure equilibration underneath loose-laid, flow permeable roof insulation boards
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文摘
The flow underneath a loosely laid insulation board or a paver is approximated by a two-dimensional laminar flow in a very shallow channel having a porous upper roof. The momentum theorem and flow continuity are used to determine a set of non-linear differential equations which are solved numerically to obtain the pressure distribution underneath the paver for a given outer pressure distribution on a roof top. The important parameters that influence the flow and pressure equilibration are identified. Considering the critical case where the separated flow reattaches within the length of the paver it is found that the pressure distribution underneath a flow impermeable paver is linear and depends on the ratio of the flow resistance in the joints of adjacent pavers to the resistance underneath the paver. The flow rate underneath the paver is, however, directly proportional to the inverse of the sum of the resistances. For a flow permeable paver the additional influencing parameters are the flow resistance within the porous medium of the paver and the ratio of the effective flow area of the paver to the cross-sectional flow area underneath the paver. Two cases of outer pressure distribution, sinusoidal and uniform distributions, are investigated. The results presented are also applicable to flow permeable building claddings.