Results and discussions

2.1 Effect of temperature

Fig.3 shows the effect of temperature at 20C, 30C, 45C and 60C when the airflow velocity is 1.35m/s.

From Fig3a, it is seen from four curves that evaporation process is quickened rapidly with the increase of the temperature. Fig3b gives the result that the evaporation velocities fluctuate mainly between 0.40×10 kg sm and 1.27×10 kg sm at 20C, and reaching

0. 80-7.00×10-4kg s-1m-2 at 60C, which is approximately 7 times that at 20C. Since solar collector can heighten the temperature of seawater because of the greenhouse effects, and the results show that temperature is a very important factor to evaporation process, using solar chimney for drying is beneficial to the evaporation process.

2.2 Effect of airflow velocity

Fig.4. shows the effect of airflow velocity when the temperature is 30C. The velocities were 0.52m/s, 1.39m/s,1.60m/s and 1.78m/s.

Clearly, evaporation process increases with the higher wind velocity (From 0.52m/s to 1.60m/s), but it declines when wind velocity reaches 1.78m/s. During the experiments, we find that there is a layer of salt covered the surface of seawater, which hinders the mass transfer from the main body of seawater to the air because of the strong evaporation enhancement. So the design of solar chimney dryer should limit the wind velocity to a proper range. The drive for evaporation is humidity gradients between the body of seawater and the air just above the surface of seawater. So we can enhance the humidity grads by using solar chimney.