Effects of water and basin depths in single basin solar stills: an experimental and theoretical study

The effects of water depth in solar stills were studied in many earlier works. It was revealed that in the previous experimental works, the water surface-cover distance (WCD) was altered with the change of the water depth. However, in this research, the effects of water depth and WCD were investigated separately, and effects of water depth on the performance of solar stills with the same WCD were examined for the first time. In this way at first, some experiments were conducted in the summer and winter seasons using the stills with the same water depths, but different basin depths (i.e. different WCDs). It was found that WCD can affect the amount of distillate yield up to 26%. Thus, it was concluded that to study the effect of water depth accurately, different stills should be employed at the same time (to keep WCD constant). In the second step, some experiments were conducted using four stills in the summer, fall and winter seasons to examine the effects of water depth, while the WCD was constant. In addition, the stills with different water depths were modeled analytically and their performance was investigated. Moreover, an empirical relationship was obtained between the distillate yield and the water depth. By comparing the results of this empirical relation with previous studies, it was revealed that the past researches reported a lower dependency (in the average 15%) of the distillate yield on the water depth, since in their experimental works, WCD was changed along with the water depth

Theoretical and experimental investigation on internal reflectors in a single-slope solar still

This study investigated the effect of an internal reflector (IR) on the productivity of a single-slope solar still (during the summer and winter) experimentally and theoretically. A mathematical model was presented which took into account the effect of all walls (north, south, west and east) of the still on the amount of received solar radiation to brine, and the model was validated with the experimental data. The model can calculate the yield of the still with and without IR on various walls. The results show that the simultaneous use of IR on front and side walls enhances the still’s efficiency by 18%. However, installation of an IR on the back wall can increase the annual efficiency by 22%. The installation of IRs on all walls in comparison to a still without IR can increase the distillate production at winter, summer and the entire year by 65%, 22% and 34%, respectively. Furthermore, the effect of cloud factor on the installation of IRs on all walls was examined, and the results indicate that the increasing the cloud factor decreases the influence of IRs significantly

Optimization of operating parameters for efficient photocatalytic inactivation of Escherichia coli based on a statistical design of experiments

In this work, the individual and interaction effects of three key operating parameters of the photocatalytic disinfection process were evaluated and optimized using response surface methodology (RSM) for the first time. The chosen operating parameters were: reaction temperature, initial pH of the reaction mixture and TiO2 P-25 photocatalyst loading. Escherichia coli concentration, after 90 minutes irradiation of UV-A light, was selected as the response. Twenty sets of photocatalytic disinfection experiments were conducted by adjusting operating parameters at five levels using the central composite design. Based on the experimental data, a semi-empirical expression was established and applied to predict the response. Analysis of variance revealed a strong correlation between predicted and experimental values of the response. The optimum values of the reaction temperature, initial pH of the reaction mixture and photocatalyst loading were found to be 40.3°C, 5.9 g/L, and 1.0 g/L, respectively. Under the optimized conditions, E. coli concentration was observed to reduce from 107 to about 11 CFU/mL during the photocatalytic process. Moreover, all these results showed the great significance of the RSM in developing high performance processes for photocatalytic water disinfection

E. coli inactivation by visible light irradiation using a Fe–Cd/TiO2 photocatalyst: Statistical analysis and optimization of operating parameters

In this study, the antibacterial effect of a Fe and Cd co-doped TiO2 (Fe–Cd/TiO2) visible light sensitive photocatalyst was optimized by varying operating parameters and using a response surface methodology to evaluate the experimental data. Twenty sets of disinfection experiments were conducted by adjusting three operating parameters, i.e. initial pH of the solution, reaction temperature and catalyst loading, at five levels. Based on the experimental data, a semi-empirical model was established and subsequently applied to predict the final concentration of Escherichia coli after 45 min exposure to the catalyst and visible light irradiation. Using the accurate model (coefficient of determination R2 = 0.963), optimum values were found to be 40.1 °C, 6.3, and 1.0 g/L for reaction temperature, initial pH of solution and photocatalyst loading, respectively. Under the optimized conditions, the Fe–Cd/TiO2 catalyst achieved a bacterial inactivation efficiency of 99.9% after 45 min of visible light illuminatio

New correlations to estimate the rough fracture permeability using computational fluid dynamics simulation

Abstract In fractured reservoirs, the fracture network provides the main path for fluid flow. Appropriate estimation of the fracture permeability influences the precise prediction of the reservoir’s future performance. Commonly, for a known geometry of natural or induced fracture, the permeability is estimated by applying local cubic law. One major drawback of this approach is that the fracture surface roughness, which has a significant effect on fracture permeability, is not considered. Moreover, the knowledge about the impact of fracture surface roughness on fracture permeability is not currently sufficient. In this research, the fluid flow in fractures with rough-walled surfaces was studied using computational fluid dynamics. For this purpose, the fluid flow through fractures was simulated by applying appropriate roughness for fracture walls. Furthermore, two correlations, based on response surface methodology and power-law models, were proposed to predict fracture permeability as a function of four independent variables (surface roughness, fracture aperture, angle, and porosity). The results of the two presented correlations were validated, and the statistical analysis indicates that both models are appropriate to predict fracture permeability. The findings of this study will be of great assistance with understanding and characterization of the fluid flow in rough fractures and can be used in future works