Effect of wind on drying from wet porous building materials surfaces - A simple model in steady state

The effect of wind on drying of wet porous building materials was studied. A model that assumes that evaporation from a material can be expressed by a surface resistance B was used. B gives the maximum drying capacity of a su rface. B can be measured assuming that evaporation from the material is pro portional to the evaporation from a free water surface, the material porosi ty and a material constant, K. Experiments were performed to verify the mod el and to provide material data on B using a wind tunnel. Steady state flow was measured through thin building material specimens mounted in "wet cup" specimen holders. Water was absorbed from the lower side and evaporated fr om the upper side of the specimens during exposure to wind. Six building ma terials with large variations in porosity and sorptivity were tested. K was quite constant for each material for wind velocities of 0.15 - 10 m/s, ver ifying the model. Wind affected flow more the higher the material sorptivit y. Calculation of B at 50% relative humidity and wind velocities 0.15 - 10 m/s for the six materials is shown in the paper. B = J(h).K.epsilon/(H-surf ace - H-environment) with Jh = evaporation rate from free water, epsilon = material porosity and H = humidity. For concrete with w/c = 0,75 at 10 m/s wind velocity, B = 0.003 m/day.