Sustainable freshwater production using novel cascade solar still with phase change material, serpentine water path, and copper fins

Heat losses in solar stills are high, which has led to a decrease in their thermal efficiency. Also, the production of these devices is limited to the presence of the sun, and their production stops during cloudy hours or at night. To solve these problems, in this experimental study, two cascade solar stills are examined under relatively similar conditions for sustainable freshwater production. One of these solar stills is modified with the phase change material and copper fins, and another one is a conventional cascade solar still without using the phase change material and copper fins. Paraffin was selected as a heat storage material to increase the time of desalination of water by the solar still. In addition, the copper fins are used to increase the conduction heat transfer in phase change material and provide better melting and solidification processes. To prolong the water path along the steps, the serpentine water path was considered. The results showed that at sunset hours, desalination efficiency with phase changing material and fins was increased. At 5 pm, the efficiency of the modified device was increased by 29% (on average) as compared to the conventional solar still without using phase changing material and fins. The rate of water production in conventional solar still in midday was higher compared to the modified solar still. However, in the sunset and night hours, the modified solar still has a higher production rate due to heat released from the thermal storage system.

Application of different Trombe wall solutions on the reduction of energy load and sustainable development in an eco-resort residential building in Binalood region with a cold and dry climate

Trombe wall is a passive strategy that reduces the energy consumption in buildings and helps for sustainable development of the residential sector. Applying these walls is very important in areas that need heating load in winter. This study evaluates a set of Trombe walls for the energy management of a residential building under real conditions in Binalood region with a cold and dry climate. In order to study the potentials of the Trombe wall, four different designs, including cubic Trombe wall with rectangular structure and three-sided glass, Trombe wall with trapezoidal structure and three-sided glass, Trombe wall with trapezoidal structure and four-sided glass, and Trombe wall with thicker storage wall, trapezoidal structure, and three-sided glass, for Trombe wall are considered. Trombe walls of all four suggested designs are exposed to outdoor conditions and installed at 17 places on the southern walls of the residential building. The results show that the most optimal design, i.e., Trombe wall with thicker storage wall, trapezoidal structure, and three-sided glass, leads to the greatest decrease (1637 kWh) in heating load in January. In addition, this design of the Trombe wall has the greatest effect in increasing the indoor air temperature among other Trombe walls investigated in this study. The Trombe wall with thicker storage wall, trapezoidal structure, and three-sided glass with a storage wall thickness of 40 cm is able to reduce the heating load of the building by 5.59 MWh in 5 months. This plan reduces the energy demand of the building by 8% more than the conventional structure of Trombe wall.

Progress and challenges of helical-shaped geothermal heat exchangers

Among various types of renewable energy, geothermal energy is recognized as an effective method for supplying thermal energy. Ground heat exchangers, as the main part of a geothermal energy system, are utilized for the extraction of the heat from the ground. Helical-shaped geothermal heat exchangers are very popular in this field as they need less land space compared to the other traditional straight ones. They have simple assembly and a high density of coils in their configuration. Considerable efforts have been done on the development of this type of geothermal heat exchanger. However, this topic has not been subject to a review. To address this issue, we present an overview of the potentials and challenges of helical-shaped geothermal heat exchangers in this study. The environmental and economic aspects, recent progress about the numerical simulations, soil features, different types and arrangements, and geometrical parameters for this type of heat exchangers are investigated. The installation cost is a critical challenge in the practical applications of these exchangers. However, the previous studies are mostly focused on the technical evaluation and optimization of the thermal performance of this type of heat exchanger, while little attention is paid to their installation costs. It is essential to understand the potential environmental impacts of each renewable energy technology to have a correct evaluation of the system. The life cycle assessment can be used as a proper method to assess the environmental issues of the helical-shaped geothermal heat exchanger in the studies.

Experimental Investigation of Water Droplet Impact on the Electrospun Superhydrophobic Cylindrical Glass: Contact Time, Maximum Spreading Factor, and Splash Threshold

The impinging of water droplets on superhydrophobic cylindrical glasses has been investigated experimentally by using a high-speed camera. The superhydrophobic cylindrical surfaces were fabricated by electrospinning technique combined with silane treatment. The effects of the diameter ratio of cylindrical glass and Weber number on the postimpact regime, contact time, maximum spreading factor, and splash threshold were investigated in the ranges 3.5-16 and 27-161, respectively. The results were compared with impact droplets on superhydrophobic flat glass and uncovered hydrophilic cylindrical glass. Three types of regimes were observed on hydrophilic and superhydrophobic cylindrical glasses including coating, splash, and splash-rebound. Results showed that contact time on the cylindrical surface is up to 50% less than the flat one. Moreover, the splash regime was started at the critical Weber number = 134 on high-diameter-ratio superhydrophobic cylindrical and flat surfaces while happening earlier when the diameter ratio is below D* < 4.

Investigation of airflow at different activity conditions in a realistic model of human upper respiratory tract

In the present study, the turbulent flows inside a realistic model of the upper respiratory tract were investigated numerically and experimentally. The airway model included the geometrical details of the oral cavity to the end of the trachea that was based on a series of CT-scan images. The topological data of the respiratory tract were used for generating the computational model as well as the 3D-printed model that was used in the experimental pressure drop measurement. Different airflow rates of 30, 45, and 60 L/min, which correspond to the light, semi-light, and heavy activity breathing conditions, were investigated numerically using turbulence and transition models, as well as experimentally. Simulation results for airflow properties, including velocity vectors, pressure drops, streamlines, eddy viscosity, and turbulent kinetic energy contours in the oral-trachea airway model, were presented. The simulated pressure drop was compared with the experimental data, and reasonable agreement was found. The obtained results showed that the maximum pressure drop occurs in the narrowest part of the larynx region. A comparison between the numerical results and experimental data showed that the transition (γ-Reθ) SST model predicts higher pressure losses, especially at higher breathing rates. Formations of the secondary flows in the oropharynx and trachea regions were also observed. In addition, the simulation results showed that in the trachea region, the secondary flow structures dissipated faster for the flow rate of 60 L/min compared to the lower breathing rates of 30 and 45 L/min.

Fabrication of Poly Vinyl Acetate (PVAc) Nanofibers Using DMAC Solvent: Effect of Molecular Weight, Optimization by Taguchi DoE

This study experimentally investigated the effect of different molecular weights of Poly vinyl acetate (PVAc) on electrospinning ability of PVAc/DMAC sol-gels. The influences of polymer solution concentration and electrospinning process parameters (needle tip to collector distance, flow rate, and applied voltage) on the mean diameters of electrospun PVAc nanofibers were examined by design of the experiments based on the Taguchi method. Three levels were considered for each process factor as inputs for the Taguchi DoE technique. To characterize and optimize the mentioned parameters, Taguchi's L9 orthogonal design (four parameters, three levels) was used. The “smaller-the-better” approach was used to utilize the optimum production conditions based on the signal-to-noise (S/N) ratios. The results indicated that the polymer solution concentration was the most important parameter on the mean diameter of the nanofibers. The minimum nanofiber diameter at the optimum conditions was measured about 52 nm. In conclusion, the Taguchi DoE method was identified as an efficient technique to characterize and optimize the electrospinning process parameters to increase the robustness of nanofiber fabrication.

A new modification of colpocleisis for treatment of total procidentia in old age

A new approach for treating uterine prolapse in old age is presented. Fiftten patients underwent this operation during our 5-year study. The procedure is simple and brief and can be performed, using a local anesthetic, on patients whose general condition is poor. The patients in our series had no immediate postoperative complications, and those who attended our follow-up clinic had no recurrence of the disease.