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142 2 Mass transfer 0 60 45 30 15 0 0,07 0,14 0,21 Thickness in m Air pressure (Pa) Fig. 2.6 Airflow across a single-layer flat assembly, air pressure line and the inverse, 1/Wi=kai/di, the air conductance Kai of layer i. Air pressure in an interface is given by: Paj ˆ Pa1 ‡ Pj iˆ1 Wi WT Pa2 Pa1 … †ˆ Pa1 ‡ gaW1j (2.25) Graphically the assembly behaves as a single layer in the [W, Pa] plane. Transferring the intersections with all interfaces in the correct order to the [d, Pa] plane gives the air pressure course in the thicknesses (d) of the successive layers in the correctly drawn assembly (Figure 2.7). The air pressure difference over a layer thus is: ΔPaj ˆ Wj WT Pa2 Pa1 … † 60 45 30 15 0 0,0E+00 60 45 30 15 0 5,0E+04 1,0E+05 1,5E+05 2,0E+05 0 0,05 0,1 0,15 0,2 0,25 0,3 0,35 Air resistance (m/s) Air pressure (Pa) Air pressure (Pa) Thickness in m Fig. 2.7 Airflow across a composite flat assembly: air pressure in the [Wa, Pa] and [d, Pa] planes


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