Ventilation rates of micro-climate air annulus of the clothing-skin system under periodic motion

A novel three-dimensional dynamic model is developed from first principles of mass and energy conservation of the modulated internal airflow in the variable annulus size between the clothing and the skin surface in presence of clothing apertures. The developed model solves for the flow and heat transfer problem in a finite length cylindrical annulus where the inner cylinder is oscillating within an outer fixed cylinder of porous fabric boundary. The changing annulus size induces pressure variations that cause air flow in the angular and the radial directions. In addition, axial airflow is present due to clothing open aperture to the atmosphere at one end of the annulus (sleeve or neck opening). The axial and angular flows in the trapped air layer are assumed locally governed by Womersley solution of time-periodic laminar flow in a plane channel in each direction. The 3-D model predicted the ventilation radial airflow through the fabric, the angular and axial airflow induced by the motion of the inner cylinder, and the sensible and latent heat losses from the skin due to ventilation with the presence of an open or closed aperture. Experiments were conducted using tracer gas method to measure time and space-averaged air ventilation rates induced by inner cylinder periodic motion within a fabric cylindrical sleeve at spacing amplitude ratio with respect to the mean of 0.8 for both closed and open aperture cases.