modelling heat and mass transfer during convective drying of a building material

The purpose of this study is to characterize experimentally the behaviour of a cement mortar during its convective drying. The work presented here focuses on mortars with water-to cement ratios (w/C) of 0, 5. The drying tests are realized in a convective dryer designed for the drying of small samples (0 - 8g). Experiences are realized with different conditions of drying air temperature (60, 90 and 130 °C) and velocity (2, 3 and 5 m/s) the results show the influence of temperature and velocity on drying curve.

Mathematical models have been used for the description of drying curves. The exponential mathematical model seems the most adequate to describe the drying curves of cement mortars, with correlation coefficients changing with the air temperature and velocity and close to unity.

The convective mass and heat transfer coefficients are determined from the experimental data.

The results showed that both mass and heat transfer coefficients were affected by the air temperature and velocity.

The convective mass transfer coefficient changed from 0.0232m/s at V=2m/s to 0.045m/s at V=5m/s, and from 0.055 m/s at 60°c to 0.023 at 130°c. Heat transfer coefficient changed from 14.767 w/m2°c at V=2m/s to 28.64 w/m2°c at V=5m/s and from 7.71 at 60° c to 14.77 at 130°c

The temperature dependency of the two coefficients was expressed using an Arrhenius-type equation and related parameters were deduced