Solar and geothermal energies are considered cleaner and more useful energy sources that can be used to avoid the negative environmental impacts caused by burning fossil fuels. Several works have reported airconditioning systems that use solar energy coupled to geothermal renewable energy as a thermal source. In this study, an Absorption AirConditioning System (AACS) used sodium hydroxide-water (NaOH-H 2 O) instead of lithium bromide-water to reduce the cost. Low enthalpy geothermal heat was derived from two shallow wells, 50 and 55 m deep. These wells are of interest due to the thermal recovery (temperature vs. time) of 56.2 • C that was possible at the maximum depth, which can be used for the first stage of the process. These wells were coupled with solar energy as a geothermal energy application for direct uses such as airconditioning systems. We studied the performance of an absorption cooling system operating with a NaOH-H 2 O mixture and using a parabolic trough plant coupled with a low enthalpy geothermal heat system as a hybrid heat source, as an alternative process that can help reduce operating costs and carbon dioxide emissions. The numerical heat transfer results showed the maximum convective heat transfer coefficient, as function of fluid velocity, and maximum temperature for a depth higher than 40 m. The results showed that the highest temperatures occur at low fluid velocities of less than or equal to 5.0 m/s. Under these conditions, reaching temperatures between 51.0 and 56.2 • C in the well was possible, which is required of the geothermal energy for the solar energy process. A water stream was used as the working fluid in the parabolic trough collector field. During the evaluation stage, the average experimental storage tank temperature achieved by the parabolic trough plant was
The WO3/W redox pair is proposed as an alternative option for the production of solar fuels due to high reactivity and selectivity in two‐step thermochemical redox cycles. This study addresses the high‐temperature solar step involving the use of carbonaceous materials (carbon or methane) as reducing agents to lower the temperature of the reduction step in the WO3/W cycle, which makes the process compatible with the use of concentrated solar energy as the source of process heat. The carbothermal reduction of tungsten trioxide to tungsten by using carbon in the form of graphite, carbon black, and activated carbon was investigated with a thermobalance and a packed‐bed tubular reactor, whereas methanothermal reduction was studied by using a solar‐driven thermogravimetric reactor. The WO3/C powder reactivity was analyzed as a function of temperature, carbon type, and stoichiometry of the reactant mixture. The reaction was complete upon heating to 1280 °C when using excess carbon in the mixture, with metallic tungsten and carbon monoxide as the main products. A high specific surface area of carbon favored the solid–gas reaction mechanism, whereas a small carbon nanoparticle size favored the solid–solid mechanism, along with the formation of carbides. Methanothermal reduction of WO3 started from 850 °C and yielded mainly W and WC at 1000 °C with WO3 conversion above 80 %. This study thus indicates that carbo‐ and methanothermal reduction of tungsten trioxide can be used to produce metallic tungsten powder efficiently.
Potentiodynamic polarization analysis and electrochemical impedance spectroscopy, were used to determine the corrosion rate AISI 316L stainless steel (316L) in a NaOH-H 2 O working airconditioning mixture. The aqueous concentrations were 40% and 50% (w/w), temperature was set at 35°C and 90°C (similar to the conditions of the absorber and generator in an absorption airconditioning system). The results showed that the material exhibited a passivation region in all cases, and the corrosion mechanism was dominated by charge transfer. Additionally, at 35°C and 90°C the corrosion process was mainly influenced by the concentration and temperature of the solution. The results were attributed to the steel chemical composition, the chemical stability of the corrosion products, the structural state of the passive film, and the ability to prevent the diffusion of metal ions. According to the results, the NaOH-H 2 O mixture possesses electrochemical characteristics that permit its application as a working fluid for air-conditioning absorption processes.
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