Increased permeability of clothing material can reduce the heat load caused by Nuclear-Biological-Chemical (NBC) protective clothing, but implies reduced protection. The goal of the present work is to study the influence of the air permeability on human comfort and safety. A numerical study is presented of the air flow with heat and mass transfer around a cylinder, mimicking a human limb, placed in a turbulent external air flow and surrounded by protective clothing. The problem is described in terms of the relevant dimensionless numbers. The dependence of the flow field underneath the clothing and the heat and mass transfer to the limb are studied as a function of the Reynolds, Darcy and Damkoehler numbers, which are a measure for the wind speed, clothing permeability and adsorptivity of the poisonous gas, respectively. The air flow simulations are validated with experiments, in which the flow field around a bare cylinder and in the space between a cylinder and its porous cover, is measured with LDA. Scaling rules for heat and mass transfer are presented.
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