Simulation of the control of a salt gradient solar pond in the south of Tunisia

摘要

We are interested in the modeling and control of a salt gradient solar pond (SGSP) in the south of Tunisia. We developed a model of a closed cycle salt gradient solar pond (CCSGSP) that ensures successful year round operation. This model was used to study the response of the solar pond (SP) to various control techniques. It takes into account heat and salt diffusion within the pond and simulates the transient behavior of a SGSP. Furthermore, we investigated the dynamic process, which involves internal gradient stability, boundary behavior between the gradient zone and the convective zones. We thus incorporated the double diffusive processes into the SP model by using the one dimensional stability criterion produced by linear theory. The governing differential equations are solved numerically by using a control-volume scheme. The results show that successful operation of a SP requires three things: the maintenance of the storage zone temperature through heat extraction and brine injection, the use of surface washing to control the deepening of the upper mixed layer and a well designed initial salt stratification to prevent the formation of instability within the gradient. Using linear salinity profile as an initial condition, three round year simulations were run using average meteorological data with the result that adequate stability (R_ρ > 2 throughout the gradient and R_ρ ≈ 10 at the interfaces) was maintained. Numerical results show also that 10-30% efficiency could have been reached if heat extraction is performed routinely especially when one considers that the storage temperature is within 40-80℃. The model is validated against data taken from the operation of the UTEP SP. Close correlation between computed and measured data was obtained.