Effect Of Spectral Absorption Of Solar Energy On Evaporation Of Still Water

Water evaporation can be widely found in nature, agricultutre and various industrial fields.It is important to analyse the characteristics and mechanism of water evaporation. In this thesis, the heat and mass transfer in evaporation of still water were investigated by experiment and numerical simulation, and the effects of solar radiation and airflow on water evaporation were analysed. The main contents included are as follows:(1) The steady state model was built for the evaporation of still water under solar irradiation and airflow convection, in which the spectral absorption of solar energy inside water was considerd. The Monte Carlo method (MCM) combined with the Finite Volume method (FVM) and the spectral band model was employed to simulate the heat and mass tranfer, and a computer code was developed. By comparing with results in references, the reliability of computer code is verified. The effects of solar irradition and airflow parameters on the evaporation and interior temperature were analysed.(2) The convective heat transfer of turbulent airflow on large surface was simulated by Fluent software.The effect of natural convection, wall condition and turbulence intensity were investigated.The characteristics of convective heat transfer coefficients were also discussed on the long measurement ,which supplies the basis for calculating coefficients between airflow and large water surface.(3) The outdoor experiment devices containing three round ponds for evaporation were built.The baffle at night,day and night were utilized to construct three conditions of solar irradiation and infrared radiation loss in the same airflow condition.The data of evaporation,interior temperature of three ponds was obtained in several days continuously.The effects of solar irradiation,radiation loss,airflow velocity,temperature and humidity were investigated by the comparison of the three ponds.Further more, aimed at the experiment process,the physical and mathematical model on unsteady state was built to compare with the experiment results.(4) The effect of porous material on evaporation by changing the performance of solar spectral absorption was discussed in experiment.The effect of its position in water on evaporation and temperature was also compared.The experiment data of water evaporation was accumulated by research. The rule of solar radiation and airflow convective parameter on evaporation was also obtained.At the same time,the solar spectral absorption ability of water was understood,which provides reference for the related applications and studies.