Intensification of NH3 bubble absorption process using advanced surfaces and carbon nanotubes for NH3/LINO3 absorption chillers

En la presente tesis doctoral se realiza un estudio experimental de la intensificación del proceso de absorción de amoniaco por parte de la mezcla NH3/LiNO3 en absorbedores de burbuja por medio del uso de superficies avanzadas y nanotubos de carbono. Las condiciones de operación de los ensayos experimentales fueron obtenidas a partir de una simulación termodinámica de un ciclo de absorción de simple efecto con NH3/LiNO3 a las condiciones de operación de interés para una enfriadora por absorción activada por fuentes de energía a baja temperatura y enfriada por aire. Los experimentos se llevaron a cabo en un banco de prueba experimental diseñado para la evaluación del desempeño de absorbedores a las condiciones deseadas. El estudio del proceso de absorción se realizo en dos tipos de intercambiadores de calor trabajando como absorbedores; un intercambiador de calor de placas y un intercambiador de calor tubular. Los resultados experimentos en el absorbedor tubular muestran que las superficies avanzadas y nanotubos de carbono usados mejoran significativamente el proceso de absorción de amoniaco en el absorbedor de burbuja estudiado en comparación con un absorbedor de tubo liso con el fluido base. Las mejoras máximas alcanzadas fueron superiores al 50%.This thesis deals with an experimental study on intensification of the ammonia absorption process in the NH3/LiNO3 mixture in vertical bubble mode absorbers using advanced surfaces and nanoparticles of carbon nanotubes (CNTs). Operating conditions selected for the absorber test were obtained from a thermodynamic analysis of a single effect absorption cycle with NH3/LiNO3 driven by low temperature heat sources and head released by air. The experiments were conducted in an experimental test facility designed for evaluating the absorber performance at the desired operating conditions. Intensification of the ammonia absorption process was studied using two types of heat exchangers working as bubble absorbers; a plate heat exchanger and a tubular heat exchanger. Experimental results showed that the advanced surfaces and CNTs used significantly improve the ammonia absorption process in the tubular bubble absorber analyzed in comparison with results in the smooth tube absorber with the base fluid. The maximum improvements achieved were higher than 50 %

Enquête Sur Les Systèmes De Distribution D'air Et La Régulation De L'environnement Thermique Dans Les Installations De Traitement Des Aliments Réfrigérés

Air flow distribution in chilled food facilities plays a critical role not only in maintaining the required food products temperature but also because of its impact on the facility energy consumption and CO2 emissions. This paper presents an investigation of the thermal environment in existing food manufacturing facilities, with different air distribution systems including supply/return diffusers and fabric ducts, by means of both in-situ measurements and 3D CFD simulations. Measurements and CFD simulations showed that the fabric duct provides a better environment in the processing area in terms of even and low air flow if compared to that with the diffusers. Moreover, temperature stratification was identified as a key factor to be improved to reduce the energy use for the space cooling. Further modelling proved that air temperature stratification improves by relocating the fabric ducts at a medium level. This resulted in a temperature gradient increase up to 4.1 °C in the unoccupied zone

Numerical study of air temperature distribution and refrigeration systems coupling for chilled food processing facilities

This paper presents an air temperature distribution and refrigeration system dynamic coupling model to assess the performance of air distribution systems used in chilled food processing areas and its energy consumption impact. The coupling consists of a CFD air flow/temperature distribution system model and a compression refrigeration system model developed in EES integrated in the TRNSYS platform. The model was tested and validated using experimental data collected from a scaled air distribution test rig in an environmental chamber showing a good agreement with the measured data (an hourly energy consumption error up to 5.3 %). The CFD/EES coupling model can be used to design energy efficient cooled air distribution systems capable to maintain the required thermal environment in chilled food processing facilities

Experimental study and analysis of thermal comfort in a university campus building in tropical climate

This study presents the evaluation of the performance and acceptability of thermal comfort by students in the classrooms of a university building with minisplit-type air-conditioning systems, in a tropical climate. To carry out the study, temperature and humidity measurements were recorded, both outside and inside the selected classrooms, while the students were asked to complete thermal surveys on site. The survey model is based on the template proposed by Fanger and it was applied to a total number of 584 students. In each classroom, the Predicted Mean Vote (PMV) and the Predicted Percentage Dissatisfied (PPD) were estimated according to Fanger’s methodology, as well as the Thermal Sensation Vote (TSV) and the Actual Percentage Dissatisfied (APD), which were obtained from the measurements and the surveys. The results of this study showed that the PMV values, although they may vary with the insulation of the clothing, do not affect the TSV. Furthermore, comparing PMV vs. TSV scores, a 2 ◦C to 3 ◦C difference in operating temperature was found, whereby the thermal sensitivity for TSV was colder, so it could be assumed that the PMV model overestimates the thermal sensitivity of students in low-temperature conditions. In addition, an acceptability by 90% with thermal preferences between 23 ◦C and 24 ◦C were also found. These results indicate that it is possible to increase the temperature set point in minisplit-type air-conditioning system from 4 ◦C to 7 ◦C with respect to the currently set temperatures, without affecting the acceptability of the thermal environment to the students in the building

Evaluación del potencial de la refrigeración por absorción en el sector industrial de Barranquilla

La investigación doctoral pretende identificar el potencial de la refrigeración por absorción en el sector industrial de Barranquilla, considerando diferentes fuentes como energía solar y gas. Esto implica desarrollar una metodología que permita evaluar técnicoeconómicamente la refrigeración por absorción e identificar el escenario más adecuado para minimizar los costos y reducir los gases de efecto invernadero generados por las industrias. Con ello, se busca facilitar la implementación de la refrigeración por absorción y establecer el mejor escenario para su explotación en el sector industrial de Barranquill

Experimental Study and Analysis of Thermal Comfort in a University Campus Building in Tropical Climate

Producción CientíficaThis study presents the evaluation of the performance and acceptability of thermal comfort by students in the classrooms of a university building with minisplit-type air-conditioning systems, in a tropical climate. To carry out the study, temperature and humidity measurements were recorded, both outside and inside the selected classrooms, while the students were asked to complete thermal surveys on site. The survey model is based on the template proposed by Fanger and it was applied to a total number of 584 students. In each classroom, the Predicted Mean Vote (PMV) and the Predicted Percentage Dissatisfied (PPD) were estimated according to Fanger’s methodology, as well as the Thermal Sensation Vote (TSV) and the Actual Percentage Dissatisfied (APD), which were obtained from the measurements and the surveys. The results of this study showed that the PMV values, although they may vary with the insulation of the clothing, do not affect the TSV. Furthermore, comparing PMV vs. TSV scores, a 2 °C to 3 °C difference in operating temperature was found, whereby the thermal sensitivity for TSV was colder, so it could be assumed that the PMV model overestimates the thermal sensitivity of students in low-temperature conditions. In addition, an acceptability by 90% with thermal preferences between 23 °C and 24 °C were also found. These results indicate that it is possible to increase the temperature set point in minisplit-type air-conditioning system from 4 °C to 7 °C with respect to the currently set temperatures, without affecting the acceptability of the thermal environment to the students in the building