Basic Theory of Rapid-Transit Tunnel Ventilation

Abstract

An analysis has been carried out for the basic mechanism of rapid-transit tunnel ventilation due to train piston action and for the temperatures resulting in the system. Theory is in general agreement with experimental results, indicating air velocities in tunnels of the order of 1/5 of the train velocity even though trains occupy only 1/4 to 1/3 of the cross-sectional area of the tunnel. Little of the heat load owing to trains, brakes, passengers, and machinery is conducted through the ground about the tunnel, but the ground serves as a heat reservoir, causing the amplitude of the diurnal subway temperature variation to be about half that of the ambient air temperature and causing a phase shift of several hours. With the help of a partly empirical theory combined with experiment, it was possible to indicate approximately the temperatures to be expected in a tunnel under differing climate conditions. The effect of train scheduling on ventilation rate is discussed, as is the possibility of using models to obtain more precise design data.