Macroscopic flow numbers relating to the jet momentum of air diffusion terminal devices are studied in this paper. Diffuser jet momentum, jet momentum number and jet momentum ratio are reviewed in the literature. New expressions for jet momentum ratios and jet volume numbers are proposed for specifying the mean room air speed in mechanically ventilated enclosures. The proposal is validated against experimental data from seven sites under fifteen operating flow conditions. Two macroscopic flow numbers correlate with the measured mean air speed in the room.
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