Experimental study on a solar-powered cogeneration system for freshwater and electricity production.

In this study, a photovoltaic/thermal (PVT) collector and a stepped solar still system were constructed and integrated. The PVT collector was used to improve the performance of a stepped solar still device. Saltwater enters into the PV-T system and the temperature of the solar panel declines, and then ultimately the efficiency of the PV-T collector increases. After leaving the PVT collector, the temperature of the saltwater increased and was used as a pre-heater for further evaporation in the solar still, which ultimately caused an increase in its efficiency. The more tremendous temperature difference generated between the stepped surface and the glass increases efficiency and produces more freshwater. A flow rate of 7.5 L/hour of saline water was used to study the efficiency of the solar still device and the PVT collector. The value of productivity of solar still system with photovoltaic/thermal collector was 0.76 kg/m2 more than that of conventional solar still. Despite the PVT collector, the daily efficiency of the solar still system increased to 34.8%, which shows an increase of 13.9% compared to the passive solar still device. Also, by cooling the PV-T system, the average electrical efficiency has increased from 13.1 to 13.7%. Production power reached 72.46 W from 65.96 W in two consecutive days at 11:15.

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.

Performance analysis of a parabolic trough collector using partial metal foam inside an absorber tube: an experimental study.

This paper offers an experimental investigation of the effect of metal foam on the thermal and hydrodynamic performance of a parabolic trough collector (PTC). Metal foams play a crucial role in heat transfer improvement due to their high thermal conductivity. Three different arrangements of metal foams are applied inside the absorber tube of the PTC. The flow regime in the absorber tube is laminar at different Reynolds numbers of 422, 844, 1267, and 1689. Experimental tests are designed with Design-Expert software in which the response surface method is utilized. Experimental results revealed that maximum enhancement in thermal efficiency is related to the periodic array arrangement of the metal foam inside the tube. This arrangement leads to a 14% increase in thermal efficiency. However, in this arrangement, the friction factor increases considerably compared to a plain receiver tube.

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.

An experimental study on a cylindrical-conical cavity receiver for the parabolic dish collector.

Solar thermal energy is a promising solution to the environmental and energy demands issues which the world is faced with them. Among all the solar thermal collectors and solar towers used in this field, parabolic dish collectors are one of the preferable options for researchers due to their high working temperature range and high thermal performance. It has been proved that cavity receivers in solar dish collectors are the best way to achieve the best thermal performance. The main concern in the cavity receivers is their thermal efficiency enhancement by employing different geometries. The hybrid geometry of cylindrical-conical can be used to achieve the high pressure drop and low thermal efficiency of conventional cylindrical and conical cavity receivers, respectively. Furthermore, using proper insulation for the cavity receiver helps to performance enhancement of the dish collector. Ceramic fiber insulation can be suitable for this purpose due to its good thermal properties and fewer environmental issues. Hence, in this study, the objective of efficiency enhancement of parabolic dish collector is followed by utilizing a cylindrical-conical cavity receiver equipped with the fiber ceramic insulation. The results show that ceramic fiber is better insulation than the common mineral wool insulation and can enhance thermal performance by 5.03% on average. In addition, the maximum, average, and minimum thermal efficiencies of the cylindrical-conical cavity receiver by using the ceramic fiber insulation and water as the working fluid were obtained up to 38.77%, 35.19%, and 32.66%, respectively.

Capacity and strategies of energy production from renewable sources in Arab countries until 2030: a review from renewable energy potentials to environmental issues.

Slowing and reversing climate change and keeping energy prices at affordable levels are the main important achievements of the use of renewable energy. About 210% increase in energy consumption from 1990 to 2018, reduction in fossil fuel reserves, and high capacity of renewable energy in Arab countries encourage them to increase the use of renewable and sustainable energy sources as a key way to supply the energy in future and have a sustainable economy. There is no a comprehensive review study to focus on the capacity and strategies of renewable energy in Arab countries at the transnational level until 2030. To fill this gap, this article investigates the current and future capacities and strategies of renewable energy production by 22 Arab countries, which are the center of fossil energy production in the world, until 2030. Indeed, it provides a roadmap for advancement towards energy production from renewable sources in these countries. It is observed that Egypt and Morocco with an installed capacity of 5980 and 3447 MW, respectively, had the highest installed renewable energy capacity among the Arab countries in 2020. The results also showed that most ambitious goal is related to Djibouti, where it is targeted to supply 100% of energy from renewable resource by 2035. Finally, it should be mentioned that most Arab countries focus on solar and wind energy, and very little attention is paid to geothermal, biomass, and hydroelectric energy.

A review on solar-powered cooling systems coupled with parabolic dish collector and linear Fresnel reflector.

Solar energy is the most sustainable and free source to manage the world energy demand. One aspect of solar-driven energy supply can be observed in cooling systems. Recently, solar energy-based cooling systems have received many attentions. Solar cooling systems utilizing solar collectors, as the renewable and sustainable-based solution, have the good potentials to overcome the challenges associated with consumption of fossil fuels. In this study, the recent advances about the potentials of dish collectors and linear Fresnel reflectors for the usage in the cooling systems are reviewed. In addition, the solar-powered conventional absorption chiller and cryogenic systems are investigated. Hybrid cooling solar systems and solar-based combined cooling, heating, and power systems are also studied. The hydrogen production in cooling integrated systems and cold thermal energy storage are discussed. In each section, in addition to general description of the system, some explanations about the thermodynamic and economic aspects of the systems are provided. Finally, the main results of the review are summarized and based on the available gaps between the literatures, some suggestions are provided for the future studies. It was found that using solar dish collectors in a hybrid system, designed for the freshwater and LNG production, causes carbon dioxide emissions reduction by 40%, and also increases freshwater and LNG production by 95% and 4.7%, respectively. In the hybrid trigeneration solar-biomass power plants, using the linear Fresnel reflector leads to 29% save in biomass and land.

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.

Impact of a Ration Negative in Dietary Cation-Anion Difference and Varying Calcium Supply Fed before Calving on Colostrum Quality of the Dams and Health Status and Growth Performance of the Calves.

This study investigated the effect of diets negative in dietary cation-anion difference (DCAD) or restricted in Ca fed prepartum to dairy cows for three weeks on colostrum yield and composition, and the health and growth performance of their calves. Thirty-six pregnant non-lactating Holstein-Friesian cows were randomly assigned to three isoenergetic diets: (1) low Ca: 0.24% Ca, DCAD: +86 mEq/kg; (2) high Ca: 1.23% Ca, DCAD: +95 mEq/kg; and (3) low DCAD: 1.28% Ca, DCAD: -115 mEq/kg (all dry matter (DM) basis). While colostrum quality was not affected, low Ca supply prepartum tended to increase the colostrum yield compared to high Ca (low Ca = 8.81 vs. high Ca = 5.39 kg). However, calves from cows fed low DCAD showed higher serum concentrations of K, lower body weight (BW), starter feed intake and average daily weight gain before weaning compared to low Ca and high Ca calves (53.12 vs. 57.68 and 57.32 kg) but BW was similar postweaning (d 70). In addition, calves from dams fed low DCAD were more likely to develop diarrhea and had increased number of days with abnormal fecal scores. Consequently, calves from low DCAD dams had to be treated more frequently.

Entropy generation analysis of different solar thermal systems.

The entropy generation analysis is an approach to optimize the performance of different thermal systems by investigating the related irreversibilities of the system. This paper provides a concise review of the entropy generation analysis performed for different solar thermal energy systems including solar collectors, solar heaters, solar heat exchangers, and solar stills. The mathematical formulation and the equations for calculating the entropy generation are briefly presented. Moreover, main passive techniques including the usage of nanofluids, porous materials, and inserts which are used to improve the efficiency of different solar systems are discussed. It is shown that using entropy generation minimization method is an efficient tool to find the optimal design of solar systems. The current review aims to motivate researchers in the field of solar energy for using entropy generation analysis to reduce the lost work and consequently improving the system performance.

Modelling Study on Internal Energy Loss Due to Entropy Generation for Non-Darcy Poiseuille Flow of Silver-Water Nanofluid: An Application of Purification.

In this paper, an analytical study of internal energy losses for the non-Darcy Poiseuille flow of silver-water nanofluid due to entropy generation in porous media is investigated. Spherical-shaped silver (Ag) nanosize particles with volume fraction 0.3%, 0.6%, and 0.9% are utilized. Four illustrative models are considered: (i) heat transfer irreversibility (HTI), (ii) fluid friction irreversibility (FFI), (iii) Joule dissipation irreversibility (JDI), and (iv) non-Darcy porous media irreversibility (NDI). The governing equations of continuity, momentum, energy, and entropy generation are simplified by taking long wavelength approximations on the channel walls. The results represent highly nonlinear coupled ordinary differential equations that are solved analytically with the help of the homotopy analysis method. It is shown that for minimum and maximum averaged entropy generation, 0.3% by vol and 0.9% by vol of nanoparticles, respectively, are observed. Also, a rise in entropy is evident due to an increase in pressure gradient. The current analysis provides an adequate theoretical estimate for low-cost purification of drinking water by silver nanoparticles in an industrial process.