Percepción del riesgo por parte del trabajador: la realidad ecuatoriana

El presente estudio demuestra la reducción del nivel de riesgo biológico por inoculación percutánea con material corto-punzante en la actividad de toma de muestras sanguíneas en el laboratorio de un centro médico de atención primaria de salud de Ecuador aplicando medidas higiénicas y de bioseguridad. Material y métodos: se aplicó la metodología BIOGAVAL de evaluación de riesgo biológico considerando; la identificación de los agentes biológicos principales, daños a la salud, mecanismos de transmisión, porcentaje de trabajadores vacunados, frecuencia de exposición y aplicación de medidas higiénicas. El presente estudio es de carácter descriptivo y longitudinal. Resultados: De los resultados obtenidos en la Fase 1, tras la aplicación del Método Biogaval, se evidenció que el nivel de riesgo biológico para la exposición a VHB, VHC y VIH superaba los niveles LEB y NAB, siendo el porcentaje de cumplimiento del cuestionario (medidas higiénicas) del 21%. Estableciendo un plan de corrección de las medidas higiénicas y de bioseguridad se cumplimentó hasta el 93% el cuestionario propuesto por el método, Fase 2, reduciendo de este modo, el nivel de riesgo para los agentes biológicos a niveles aceptables. Conclusiones: El método de cuantificación del nivel de riesgo por exposición a agentes biológicos empleado permite establecer las medidas higiénicas y de bioseguridad apropiadas para reducir el nivel de riesgo en la actividad de toma de muestras hasta condiciones no peligrosas en los trabajadores de laboratorio

Numerical performance of a water source transcritical CO2 heat pump with mechanical subcooling

In order to improve their efficiency, transcritical CO2 heat pumps need to resort to the use of a subcooling method. Among the different subcooling methods, dedicated mechanical subcooling (DMS) systems and internal heat exchangers (IHX) are currently the more promising technologies. This paper presents a numerical study of a transcritical water source CO2 heat pump during hot water generation using different subcooling methods. Ten different configurations, including both, IHX and DMS, separately and combined in different layouts, some of them not studied previously, are analyzed numerically under the same operating conditions in order to compare their performance. A description of the numerical model is presented: compressors are modeled using the performance curves provided by their manufacturers, expansion valves are modeled as isenthalpic, and heat exchangers are modeled by deriving correlations for the evaporation/condensation pressure and heat transfer rate obtained using a 1D cell-by-cell discretization method previously applied to all heat exchangers. Results are presented for different water heating conditions and show that in most configurations analyzed, the use of a DMS does not improve the performance of the system compared to the base system with IHX. There is only an improvement in the efficiency for two of the configurations analyzed, those in which the main CO2 cycle and the DMS cycle are coupled by the water flowing first through the evaporator of the auxiliary cycle and then through the gas cooler of the main cycle. Specifically, compared to the base cycle with IHX, the configuration that provides the best results (Conf. F* according to the nomenclature used in this work) gives average improvements of around 26% in efficiency and almost 160% in the heating capacity, while the optimum gas cooler pressure is reduced by an average of 12%. Even more, compared to the best performance system previously studied by other authors (indirect DMS without IHX, Conf. F in this work) this configuration improves the efficiency by almost 8.5%, with a decrease in the total capacity lower than 1% and similar gas cooler pressure. The results also show that the auxiliary compressor capacity and the way in which the water is distributed among the main and the auxiliary cycle have an important influence on the efficiency of the system, although that influence depends on the configuration studied. For the configuration that provides the best efficiency (Conf. F*), the optimum efficiency is obtained when the auxiliary compressor capacity is similar to the capacity of the main compressor (55% of the total heating capacity comes from the auxiliary cycle), and the water is mostly heated in the auxiliary cycle (85% of the water flow heated in the condenser of the auxiliary cycle, 15% heated in the gas cooler of the main cycle).This research was funded by the Spanish Ministry of Science and Innovation under Project TED2021-131173B-I00 and the NextGenerationEU recovery plan

Numerical assessment of the use of a dedicated mechanical subcooling system during hot water generation in a water to water transcritical CO2 heat pump

This paper presents a numerical study of the use of a dedicated mechanical subcooling (DMS) system using R1234yf, for hot water generation in a water-to-water CO2 heat pump. Compressor mass flow rates and power consumptions were modeled using the manufacturer’s correlations, expansion valves were modeled as isenthalpic, and heat exchangers were modeled by deriving correlations for the evaporation/condensation pressure and heat transfer rate. In the condenser, IMST-ART was used to obtain condensation pressure and heat transfer rate. A cell-by- cell discretization model was used for the evaporator, which was a transcritical CO2, subcritical R1234yf heat exchanger. Three different systems were compared for the transcritical CO2 cycle: with internal heat exchanger (IHX), with DMS, and with IHX+DMS. Results showed that, for the conditions studied (hot water generation up to 60 ºC and evaporator water inlet temperature from 5- 25 ºC), the use of a DMS does not improve the performance of the system.The authors wish to acknowledge the financial support of the Spanish Ministry of Economy, Industry, and Competitiveness and the European Regional Development Fund through project ENE2017-83665-C2-2-P

A comparative study of the thermal behavior of three different 3D printer liquefiers

The expansion of 3D printing systems as mechatronic devices able to localize manufacturing activities has attracted the attention in academic and professional labs worldwide. However, little is known from a formal point of view about the actual possibilities of optimization in terms of hardware and software. This paper proposes alternative geometrical designs of RepRap 3D printer liquefiers, and offers an evaluation of their thermal performance by analyzing the temperature profiles derived from their functioning in a steady state regime. For that purpose, finite element calculation and experimental techniques are combined and compared. A detachable model of liquefier, used in numerous RepRap 3D printers, has been taken as a reference to design and manufacture two new variations. As the objective of the liquefier is to heat the plastic material while limiting the temperature at its top, heat conduction must be prevented by means of a refrigerating fan faced at the liquefier body. The effect of that fan has been introduced in the system of study, by evaluating the influence of five different fan velocities on the final temperature profile. All combinations of fan speed and liquefier geometry have been calculated through a finite elements model. Then, they have been reproduced experimentally, measuring discrete temperatures at different heights of the liquefier by a group of thermocouples installed on the surface of the fins composing the liquefier heat sink. Results showed that the defined FEM model reproduces acceptably the final temperature profiles obtained by experimental measures. Furthermore, the new proposed design provided with thick fins shows its good performance when the 3D printing process is performed with a fan speed higher than 10% (defined according to a PWM function programmed at the 3D printer's firmware), while its design presents a much lower manufacturing time with regards to the present available design. It is also concluded that refrigerating the liquefier during a standard 3D printing process with an airflow higher than PWM¿=¿20% is not recommended, due to a fall in efficiency and not remarkable refrigerating effect obtained through it.Postprint (author's final draft

Building customer loyalty: The effect of experimental state, the value of shopping, trust and perceived value of service on online clothes shoping.

Copyright de los autores.Based on consumer behavior theories, the aim of this study is to provide a model supported by empirical evidence in order to improve knowledge of the antecedents of loyalty to online clothing retailers. The model has been verified through partial least squares analysis of the data obtained from a survey of a sample of 412 online clothing shoppers. The results show that, firstly, the affective and cognitive experiences have a positive effect on the degree of satisfaction, and the affective experiences also have a positive impact on trust. Secondly, it has been demonstrated that consumer satisfaction with online clothing retailers can be increased by both the hedonic and utilitarian values of shopping. Thirdly, an indirect relationship has been established between satisfaction and loyalty through trust and perceived value of service. These findings can improve our understanding of the determinants of online consumer loyalty. Discussion and implications are provided.Plan Andaluz de Investigación Desarrollo e Innovación (Convocatoria 2017) Grupo SEJ-567 (Spain)

Impact of an internal heat exchanger on a transcritical CO2 heat pump under optimal pressure conditions: Optimal-pressure performance of CO2 heat pump with IHX

Transcritical R744 (CO2) heat pumps are a low-GWP high-efficiency alternative for domestic hot water generation and space heating. For high set-point temperatures, however, the COP drops and the optimum operating pressure increases. For this reason, the effect on system performance achieved by the inclusion of an Intermediate Heat Exchanger (IHX) is analyzed in depth. This is carried out by means of a numerical-experimental approach in which the effectiveness of the IHX and other characteristic parameters of the heat pump cycle are studied as a function of the IHX heat transfer area. The numerical modeling of the heat pump components is implemented for transient simulations of system heating-up process. Experimental tests with and without IHX are carried out with a water-to-water heat pump that feeds an accumulator tank, to assess its influence on the system’s COP and the electrical consumption. Simulations reveal that improving the efficiency of the IHX, by increasing the exchange area, improves the system’s performance. For the cases with higher IHX exchange area, the optimum pressure in the system is lower. For the heating experiments, the resulting thermodynamic COP is 7.55 % higher in the case with IHX, while the effective COP increases by 4.26 %. In consequence, the use of the IHX is recommended for the conditions analyzed.This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness and the European Regional Development Fund through project ENE2017-83665-C2-2-P

Efecto 2020 en la siniestralidad laboral de la República del Ecuador: un año atípico por COVID-19

La pandemia por el SARS-CoV-2 (enfermedad de la COVID-19), ha generado un cambio en el estilo de vida y convivencia para la sociedad ecuatoriana en general y, con ello, una adaptación del trabajo en la que se ha reducido la presencialidad en algunas actividades laborales y que hasta ahora se mantiene desde comienzos de la crisis sanitaria de marzo de 2020

Diferencias de edad en los accidentes de trabajo: Estudio transversal en asalariados del Ecuador

Los accidentes de trabajo son un problema de salud laboral y pueden estar asociados a la edad. Este artículo tiene como objetivo principal comparar las diferencias en los accidentes de trabajo entre jóvenes y adultos en una submuestra representativa en la República del Ecuador. Se trata de un estudio analítico de corte transversal basado en la Encuesta Nacional de Empleo, Desempleo y Subempleo (n = 4.562) de 2018. El análisis consistió en el cálculo de prevalencias y Odds Ratio (IC95%) por características sociodemográficas, laborales y de empleo, considerando a los adultos como grupo de referencia. En general, se encontraron importantes diferencias en los accidentes de trabajo entre jóvenes y adultos. La prevalencia en adultos (4%) fue mayor que en jóvenes (2,4%). Por el contrario, los jóvenes indígenas (9,2%; OR = 2,527 [2,271-2,812]) y en áreas rurales (6,4%; OR = 1,776 [1,696-1,859]) presentaron mayor prevalencia y riesgo en comparación con los adultos. Los resultados no apoyan la hipótesis de que los trabajadores jóvenes tienen más accidentes de trabajo frente a los adultos. Se concluye que se necesitan más investigaciones para ampliar estos hallazgos y buscar otros factores que puedan estar asociados a los accidentes de trabajo

Ball-burnishing effect on deep residual stress on AISI 1038 and AA2017-T4

Ball-burnishing induces compressive residual stresses on treated materials by the effect of plastic deformation. The result is an increase in the fatigue life of the treated part, retarding the initiation of cracks on the surface. Compressive residual stresses have been previously measured by X-ray diffraction near the surface, revealing considerably high values at the maximum analyzed depth, in relation to other finishing processes such as shot peening. However, the maximum analyzed depth is very limited by using this technique. In this paper, the incremental hole drilling (IHD) technique is tested to measure residual stresses, being able to reach a 2-mm measuring depth. To that objective, a commercial strain gage is used and calibrated using finite element model simulations. A second Finite Element Model based on material removal rate is developed to obtain the equations to calculate the strain release through IHD. Finally, residual stresses are measured experimentally with that technique on two different materials, confirming that ball-burnishing increases the compressive residual stresses in layers up to 0.5¿mm deep for the testing conditions, which is a good response to industrial needs. The method proves to be suitable, simple and inexpensive way to measure the value of these tensions.Preprin