A model was developed to predict the ratio of air entrainment into mechanical smoke vent on ceiling in two-layer environment where upper part is occupied by hot smoke, while lower part is occupied by cold air. Prediction model was developed for both cases that streamline of entrained air is visible (direct entrainment) and that lower air is mixed with smoke before entrained into vent (mixing entrainment). Direct entrainment takes place when actual smoke layer thickness is smaller than critical thickness for the onset of entrainment developed in part 1 of research. Mixing entrainment takes place when actual smoke layer is larger than critical thickness. In case of direct entrainment, flow pattern was approximated by either plane, line or point sink according to the scale of vent opening relative to the scale of flow field below opening. Air entrainment ratio is calculated by the fraction of surface area of control volume that is below smoke-air interface over the entire control volume surface. In case of mixing entrainment, interface is lifted towards the opening. It was assumed that the degree of mixing is proportional to the surface area of lifted interface. Varying the combination of smoke layer temperature, thickness and venting rate, experimental measurements was repeated for 88 times. In case of direct entrainment, it was demonstrated that the streamline for smoke-air interface outside control volume was lifted upwards when smoke layer thickness was close to critical thickness. The degree of lifting would be expressed by a linear function of the ratio of actual smoke layer thickness to critical thickness. In case of mixing entrainment, it was found that air entrainment ratio is inversely proportional to 2 power of ratio of actual smoke layer thickness to critical thickness. Predicted results are in good agreement with experimental results.
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