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.
This report presents a simplified computational model for combined air-, moisture and heat transport for one-dimensional cases. The model is based on finite difference technique with explicit forward differences in time. Analytical solutions for the coupling, the conductances, between the computational cells for a given air flow through the construction are used. Moisture is transferred by vapour diffusion and vapour convection. No liquid water transport occurs.
Forty subjects, 20 women and 20 men, were exposed to airflows from five different directions: horizontally towards the front, the back, and the left side and vertically upwards and downwards. The subjects were exposed to stepwise increased air velocities ranging from less than 0.10 m/s to 0.40 m/s at three temperature levels 20, 23 and 26°C. The results showed that airflow direction has an impact on perceived discomfort due to draught. At 20°C and 23°C, airflow from below was perceived as most uncomfortable followed by airflows towards the back and front.
A concept of mixing ratio of piston air is developed to evaluate the portion of the injecting air from tunnel mixed with the air in platform space of metro system. And a 3- dimensional turbulent model is used to simulate the airflow in metro platform resulted by the ventilation system and moving trains. Field measurement has been conducted to verify the 3-dimensional model. This experiment is performed during the normal operation time of a metro station with constant tracer-gas injection method. The results agree well with the numerical solution.
This paper presents a study of the dynamics of the turbulent mixing of a hot or cold air stream with the air in the interior of a building zone. Observations and CFO results of transient temperature behaviour in a fully developed jet flow field are presented. A simple model for the characteristic time-constant of the mixing process in a room is derived. The mixing of a turbulent jet, as a function of position inside the room, is also discussed. This mixing time-constant plays an important role in total system dynamic behaviour and stability.
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