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 %

Boiling process assessment for absorption heat pumps: A review

Absorption technology becomes an attractive option for cooling or heating when driven by solar thermal energy, residual heat from different processes, or geothermal energy. Further development of this technology could help to cover current cooling or heating requirements and have a much lower impact on the environment than mechanical compression cooling and heat pumps systems. Moreover, the rising cost of electrical energy added to the issue of climate change are reasons to move towards the development of environmental and sustainable energy technologies. The desorbers are key components of absorption heat pump technologies. Studies in the open literature on desorbers show advances in new design concepts to enhance heat and mass transfer with different working fluids. Therefore, the objective of this review is to identify, summarise, and discuss the experimental studies that deal with the boiling process in desorbers and boiling correlations specifically for use in absorption heat pump technologies. It includes a comprehensive scrutiny on the boiling phenomenon in pool desorbers, falling-film desorbers, and forced flow desorbers for conventional and promising working fluids, and details the experimental techniques and the latest advances in desorber design concepts. Finally, the review contains proposals for future studies to be carried out so as to contribute to the further development of absorption heat pump technologies

Energy Performance Analysis of a Solar Refrigerator Using Ecological Refrigerants

The development of sustainable energy technologies must be a priority given the rising global energy demand and global warming gases emission. In this work, the energy evaluation of a small-capacity direct-current refrigerator with internal heat exchange using R600a, R290, R717, and R134a as a base case, for autonomous solar refrigeration, is discussed. A thermodynamic model was developed to assess a 200 W refrigerator performance at evaporation temperatures of -32/-10°C, condensation temperatures of 35/46 °C, and different internal heat exchanger effectiveness values while considering the environmental conditions in the city of Barranquilla whose metropolitan and urban area presents a great potential for solar refrigeration. Results showed that the R290 system coefficient of performance was up to 2.6% higher than that of the R134a. The R600a system coefficient of performance was up to 2.7% higher than that of the R134a, but only under the most favourable conditions. The R717 system surpassed the compressor discharge temperature limits so it was found unsuitable for the present application. Moreover, the internal heat exchanger was found beneficial to reduce the exergy destruction in the compressor and expansion valve but increased that in the condenser for R134a, R600a, and R290. The internal heat exchanger recommended effectiveness should be around 0.4 for R600a or 0.3 for R290 at an evaporation temperature of -32 °C. For an evaporation temperature of -10 °C, the IHX effectiveness can be up to 0.5 for both R600a and R290. Finally, the maximum power consumption of the solar R290 refrigeration system was estimated around 4.08 kWh and 2.28 kWh at evaporation temperatures of -32 °C and -10 °C, respectively, which could be covered by a solar panel area of 3.76 m2 y 2.10 m2, respectively, while similar values were obtained for the solar R600a refrigeration system

Experimental thermal performance and modelling of a waste heat recovery unit in an energy cogeneration system

In this paper, the performance of a gas/oil heat recovery unit is assessed experimentally and by the development of an Aspen model and artificial neural networks. The heat recovery unit is a cross-flow heat exchanger used to recover the residual heat of the exhaust gases coming from a microturbine to drive an absorption chiller. The test facility consists mainly of a microturbine, a heat recovery unit, and an air-cooled absorption chiller. The experiments were conducted at partial power loads and different thermal oil mass flows. Regarding the models, the Aspen model depends on inlet conditions, the mechanical description of the heat recovery unit, and the fluids thermophysical properties, whereas the ANN model consists of 3 trained artificial neurons, 4 inputs (inlet flows and temperatures), and 2 outputs (thermal load and overall heat transfer coefficient). The experimental tests show that the recovery unit recovers from 18.8 kW to 8.1 kW when the microturbine power output is varied from 23 kWe to 4 kWe. Results also show that the overall heat transfer coefficient ranges between 243 W.m−2.K−1 and 89 W.m−2.K−1, while they evidence that the overall heat transfer resistance is controlled by the exhaust gases heat transfer resistance. Furthermore, simulation results show that the Aspen model predicts the heat recovery unit thermal load and overall heat transfer coefficient with average relative differences of 0.93% and 11.27%, respectively, to the experiments. The ANN model evidences average relative differences of 0.51% and 3.48% for the thermal load and overall heat transfer coefficient, respectively

Estudios fisiológicos y heteróticos en poblaciones heterogéneas de maíz.

Maíz-Zea maysMaestría en CienciasMaestrí

Actividades del Programa de Maíz en la EE. Tulio Ospina durante 1989.

Maíz-Zea may

Prácticas del cultivo en maíz

Maíz-Zea may

Corpoica V. 306 :variedad forrajera del maíz (Zea mays L.) para las regiones con clima medio en Colombia.

La agricultura colombiana localizada en el piso térmico medio (1200-1800 m.s.n.m.). se caracteriza por tener suelos quebrados de baja fertilidad e irregular distribución de lluvias durante el segundo semestre. Los principales cultivos de este clima son café. plátano. maíz. frijol y frutales. La mayor parte de los suelos están dedicados principalmente a la ganadería extensiva. con gramas naturales y pastos como el Puntero y Braquiaria y en menor proporción el pasto Estrella (Cynodon nienfuenses) y las leguminosas nativas. También se encuentran productores que utilizan pastos de corte como los imperiales (Axonopus scopartus) y elefantes (Pennisetum sp).Maíz-Zea may

División del llenado del grano en un híbrido varietal de maíz (progenitores y generación F)*

En La Estaciôn Experimental "La Selva", ubicada en un clima frio moderado de Colombia (2.040 m.s. n.m. , 16° C de temperatura media y 1.600 mm de precipitación anual) se realizó un estudio con los progenitores y la generación F del híbrido varietal amarillo de maiz, ICA H 401, con elfin de estimar la acumulación de la materia seca en el grano, durante el perIodo de Ilenado de los mismos, para lo cual se dividió dicho perIodo en tres partes. Los resultados obtenidos indican lo siguiente Es posible que la superioridad en producción de grano del híbrido varietal amarillo de maiz ICA H 401 sobre sus padres, se deba a un mayor crecimiento de la planta durante el periodo reproductivo, mayor cantidad de reservas fotosintéticas en la planta durante el primer perfodo del Ilenado del grano, menor cantidad de fotosintatos en la planta durante el dltimo perIodo, tasa o velocidad de crecimiento del grano más rápida, traslocación de mayor cantidad de nutrientes al grano durante el tercer perIodo (87 g/planta contra 34 y 37 g de sus padres) y mayor eficiencia fisiológica con base en la retraslocación de nutrientes al grano (55% contra 36%y 51%de los progenitores). ANT. 439 fue el padre ms pobre en eficiencia (variedad criolla con 36% de retraslocación al grano), posiblemente por las siguientes razones: menor cantidad de reservas nutritivas en la planta durante el primer perIodo de Ilenado del grano (26 g/planta contra 33 y 36 del otro padre y el hibrido, respectivamente), menor acumulación de materia seca en el grano durante el tercer perIodo (37 g/planta contra 54 y 87 de DiacolV. ETO e ICA H 401, respectivamente), deja mayor cantidad de materia seca en la planta al finalizar el lienado de los granos (30 g/planta contra 19 y 17 de los otros maIces). Posiblemente este maiz no mejorado posee algün impedimento en el Ilenado de los granos entre el segundo y tercer perIodo, que puede estar relacionado con la ausencia de más mazorcas hacia dónde enviar los nutrimentos, los cuales se quedan en la planta. Las razones anteriores podrfan explicar el porqué los maIces no mejorados son ineficientes fisiolágicamente para la obtención de altas producciones en granos. DiacolV. ETO, a pesar de no estar en su zona de adaptación, muestra una gran eficiencia fisiológica, por su rendimiento en grano prácticamente similar al de la variedad ANT. 439 (98 y 104 g/planta, respectivamente) y por el alto porcentaje de retraslocación al grano (519o' ). Estos resultados muestran el efecto del mejoramiento sobre los sistemas fisiológicos responsables de la producción en grano de esta variedad.Crop growth rate and grain growth rate of the yellow varietal hybrid corn ICA H 401. This study was conducted at the Experimental Station "La Selva", located at 2.040 in of altitude, with an average temperature of 16° C and 1.600 mm of annual precipitation corresponding to the colombian cold moderate climate. This study dealt with crop growth rate (all plant without the grain) and grain growth rate, during seven periods of the plant vital cicle (seed to physiological maturity), using the parents and the F I generation of the yellow varietal hybrid corn, ICA H 401. Furthermore, the grain filling period was divided into three periods, in order to know the physiological processes involved in the reproductive growth of this maize. The results of this research allow to conclude the following: The higher yield in grain of the varietal hybrid, ICA H 401, over its parents may be due to the following reasons: larger growth of crop during the reproductive period; larger amount of storage during the grain filling period; less amount of assimilates during the third period; faster increases in grain growth rate; translocation of a greater amount of nutrients to grain during the third period (87 g per plant against 34 and 37 g of parents) and greater physiological efficiency based on the re-translocation of materials to the grain (55% vs. 36%and 51%of the progenitors). ANT. 439 was the poorest patent in efficiency (native variety with 36% of re-translocation to the grain), perhaps due to the following reasons: less amount of nutrient storaged in crop during the grain filling period (26 g per plant vs. 33 and 36 of the other parent and the hybrid, respectively); less accumulation of dry matter in grain during the third period (37 g per plant against 54 and 87 in Diacol V. ETO and ICA H 401, respectively; a larger amount of dry matter remains in the crop when the grain filling period is completed (30 g per plant vs. 19 and 17 of the other maizes); it is possible that this nonimproved corn, has an impediment in the grain filling between the second and third period which may be due to the absence of more ears to store the nutrients remaining in the plant. These rationals could explain why the non-improved maizes are physiologically limited to obtain high er yields. DiacolV. ETO, corn genotype non adapted to the colombian conditions of cold moderate clirnats shows a large physiological efficiency because of its yield almost similar to ANT. 439 variety (98 and 104 g per plant, respectively) and the large percentage of re-translocation of grain (5511o). These results show the effects of plant breeding upon the physiological system responsible of grain yield in this varietyMaíz-Zea may