VENTILATION OF WIND-PERMEABLE CLOTHED CYLINDER SUBJECT TO PERIODIC SWINGING MOTION

摘要

A theoretical and experimental study has been performed to determine ventilation induced by swinging motion and external wind for a fabric-covered cylinder of finite length representing a limb. The estimated ventilation rates are used in determining the sensible heat loss form a clothed cylinder using a simplified resistance model. A model is developed to estimate the external pressure distribution resulting from the relative, wind around the swinging clothed cylinder. A mass balance equation of the microclimate air layer is reduced to a pressure equation assuming laminar flow in axial and angular directions and that the air layer is lumped in the radial direction. The ventilation model predicted the total renewal rate during the swinging cycle. A good agreement was found between the predicted ventilation rates at swing frequencies between 40 and 60 rpm and measured values from experiments conducted in a controlled environmental chamber (air velocity is less than 0.05 m/s) and used the tracer gas method to measure the total ventilation rate induced by the swinging motion of a cylinder covered with cotton fabric for both closed and open aperture cases. A parametric study using the current model is performed on cotton fabric to study the effect of wind on ventilation rates for a non-moving clothed limb at wind speeds ranging from 0.5-8 m/s, the effect of a swinging limb in stagnant air at frequencies up to 80 rpm, and the combined effect of wind and swinging motion on the ventilation rate. For a non-moving limb, ventilation rate increases with external wind. In absence of wind, the ventilation rate increases with increased swinging frequency. The combined effect of wind and swing is not additive of the single effects at high wind speed while at low frequency it can be assumed additive for wind speeds below 2 m/s and frequencies below 40 rpm. The heat transfer by ventilation is more than 50% of total heat loss from a clothed cylinder at f=80 rpm in abs cense and presence of wind.