Analytical simulation of energy behavior of solar stills and experimental validation

A simple and efficient method for the behavior description of solar stills, developed on the basis of extensive testing, is theoretically and experimentally evaluated. The method relates the main climatic data and operating conditions of the still with distilled water output in daily and night base with linear equations using characteristic coefficients. Evaluation of the method is performed in three steps, the first being experimental determination of the coefficients and successive prediction of output, the second being calculation of coefficient values through analytical relations and the third being the use of the model in a continuous way. The agreement between the predicted and experimental water output and also between experimental and theoretical values of the characteristic parameters reveals the validity and suitability of the developed method. The results of the investigation show that this method is a valuable tool used not only for the optimization of the still in the design phase but also for evaluation of test results of an existing installation in order to further improve it.

The “input-output” method for the description of the behavior of a solar still has been evaluated in three steps on the basis of experimental data. The model uses coefficients, which are characteristic of each specific solar still and are expressed by equations containing all technical and operation data of the still. The validity of the model has been shown at the first stage by fitting experimental data on the model, by which the values of the characteristic coefficients are determined. Using the experimentally determined values, the model has been found to be capable of predicting the water output of the still for the whole period considered very accurately compared to the real output. Moreover, the values of the characteristic coefficients have been calculated by their relations using the still data and it has been found that they lie within the range of the values as determined experimentally, taken also into account the variations or uncertainties of the still data. Finally, the continuous use of the model has shown that it is able to predict the longterm output of the still with an accuracy of about 1% compared with the real output, knowing only the initial state and the basic operation levels of the still. Through the model, cover transmittance and basin surface absorbance mainly and insulation of the still secondly have been shown to be the most important parameters affecting the still output. In addition to this, it has been found that the wind speed affects the still output, however this influence is revealed to be stronger during the night operation periods. The results of the investigation show that the developed model proved to be valid and very suitable for the description of the behavior of solar stills. It can be a valuable tool for the still optimization, used, on the one hand, in the stage of the solar still design and, on the other hand, in the stage of evaluation of an existing solar still through testing.