ABSTRACT
This research proposes designing and implementing a system to produce hydrogen, utilizing the thermal energy from the exhaust gases in a natural gas engine. For the construction of the system, a thermoelectric generator was used to convert the thermal energy from the exhaust gases into electrical power and an electrolyzer bank to produce hydrogen. The system was evaluated using a natural gas engine, which operated at a constant speed (2400 rpm) and six load conditions (20 %, 40 %, 60 %, 80 %, and 100 %). The effect of hydrogen on the engine was evaluated with fuel mixtures (NG + 10 % HEF and NG + 15 % HEF). The results demonstrate that the NG + 10 % HEF and NG + 15 % HEF mixtures allow for a decrease of 1.84 % and 2.33 % in BSFC and an increase of 1.88 % and 2.38 % in BTE. Through the NG + 15 % HEF mixture, the engine achieved an energy efficiency of 34.15 % and an exergetic efficiency of 32.84 %. Additionally, the NG + 15 % HEF mixture reduces annual CO, CO2, and HC emissions by 9.52 %, 15.48 %, and 13.39 %, respectively. The addition of hydrogen positively impacts the engine's economic cost, allowing for a decrease of 1.56 % in the cost of useful work and a reduction of 3.32 % in the cost of exergy loss. In general, the proposed system for hydrogen production represents an alternative for utilizing the residual energy from exhaust gases, resulting in better performance parameters, reduced annual pollutant emissions, and lower economic costs.
ABSTRACT
The education sector was considerably affected by the COVID-19 pandemic, risking the learning process and forcing governments to pull out contingency actions to ensure the students' development of generic and specific skills and guarantee education quality. These actions include the shift to online and hybrid (i.e., online and in-person) classes. This work assesses the pandemic effect on the generic skills of undergraduate students in a Colombian university. The study aims to determine the effect of COVID- 19 on the development of generic skills quantitatively. Two datasets were retrieved: i) A dataset with the scores obtained by the students in an institutional Generic Skills test and in the midterm tests; ii) A dataset with the students' scores in the Colombian standardized test for undergraduate students, called the Saber Pro test. Three analysis stages were performed: i) Univariate exploratory analysis; ii) Differential analysis to compare the No COVID vs. COVID scenarios; iii) A correlation analysis. Results showed that the scores of the Generic Skills and the Midterm tests increased significantly when comparing the two scenarios, except for the Written Communication. As for the Saber Pro test, only the scores for Written Comprehension, Quantitative Reasoning, and the global scores increased significantly. On the other hand, the correlation analysis showed a strong correlation only between the scores obtained at the Generic Skills and the Saber Pro tests for the English Proficiency skill. In addition, the analysis elucidated a weak correlation between the Generic Skills test's average and the Saber Pro's global score. Finally, the results prove that online education is a feasible alternative that offers students more flexibility to ensure the development of generic and specific skills.
ABSTRACT
Heavy metals have become a subject of special concern worldwide, mainly due to high persistence in the environment, toxicity, biogeochemical recycling and ecological risk. Therefore, the objective of this investigation was to analyze the spatial-temporal distribution of heavy metals in water and sediments to determine the environmental status of El Guájaro Reservoir, where such studies have not been developed. Two measurement campaigns (dry and wet period) were carried out and eight sampling stations were selected. A comparison of water and sediment quality parameters with existing national and international regulations was done. Also, heavy metal distribution maps were generated, and the geoaccumulation index was calculated to identify sources and sediments contamination level. Based on the obtained results, agriculture and mining activities are the main causes of the reservoir contamination. This metals levels could be a potential risk for the aquatic life and the populations that are supplied from this water body.
