Latent Heat Energy Storage in a Household Refrigerator Powered by Photovoltaic Electricity – Heat Transfer Design and Technical Viability

In remote rural areas without access to the electrical grid, the use of a stand-alone photovoltaic (PV) installation to drive a domestic refrigerator can be a viable option for adequate food preservation. In this application, energy storage, probably in electric batteries, is required to guarantee refrigeration conditions during periods without solar energy availability. However, electric batteries are still costly, have limited lifespan and use materials with restricted availability. Latent heat thermal energy storage (LHTES) can be an alternative to electric batteries with reduced cost and lower environmental impact. The current study presents general design guidelines for a system with a household refrigerator driven by PV power and with LHTES units. The LHTES units consist of finned panels filled with phase change material (PCM) that are placed on the vertical walls of the compartments, and are passively discharged by free convection. A thermodynamic model is used to size the system components and assess the technical viability of the proposed configuration. Special attention is paid to the heat transfer considerations involved in the design of the LHTES units to guarantee the required charge and discharge powers. The analysis is applied to a 400 L sample commercial refrigerator operating in Medellín, Colombia. It is concluded that the refrigerator necessitates moderate modifications to achieve the technical viability of the proposed configuration

Operación integrada de redes de distribución de energía y gas natural: un análisis de confiabilidad

Currently the world faces a great challenge, to achieve a sustainable production of energy, which allows the adequate development of humanity but at the same time does not irreversibly affect the environment. For this, it is absolutely necessary to make optimal and effective use of the available energy resources, in order to aim for energy transition objectives that result in the rational and efficient use of energy, the penetration of renewable resources, and social development. This requires that at a technical level, methodologies be proposed that allow for a holistic analysis of the different interactions and synergies present in the energy system. Therefore, it is essential to delve into the knowledge associated with the interaction between the electricity and natural gas networks, since natural gas is expected to be the energy source that supports the increase in generation from intermittent renewable energy sources. It is for the above that this research work analyzes the reliability of the electric power distribution network based on the impact associated with a contingency in the natural gas distribution network, when both networks are coupled through natural gas-based distributed power generators. A novel non-supplied energy index and a single contingency criterion are used for estimation purposes, considering failure rates and repair times of the natural gas network to obtain a more accurate in the estimation. Numerical results show that significant penetration of natural gas-based distributed generation can compromise the reliability of the power distribution network if the natural gas network is of low reliability.Actualmente, el mundo enfrenta un gran desafío y es lograr una producción sustentable de energía que permita el adecuado desarrollo de la humanidad pero que al mismo tiempo no afecte irreversiblemente al medio ambiente. Para ello, es absolutamente necesario hacer un uso óptimo y efectivo de los recursos energéticos disponibles, con el fin de apuntar a objetivos de una transición energética que resulten en un uso racional y eficiente de la energía, la penetración de los recursos renovables y el desarrollo social. Esto requiere que a nivel técnico se propongan metodologías que permitan un análisis holístico de las diferentes interacciones y sinergias presentes en el sistema energético. Por ello, es fundamental profundizar en el conocimiento asociado a la interacción entre las redes de electricidad y gas natural, ya que se espera que el gas natural sea la fuente energética que sustente el incremento de la generación a partir de fuentes renovables intermitentes. Por lo anterior, en este trabajo de investigación se analiza la confiabilidad de la red de distribución de energía eléctrica a partir del impacto asociado a una contingencia en la red de distribución de gas natural, cuando ambas redes se acoplan a través de generadores de energía distribuida a base de gas natural. Para su estimación se utiliza un novedoso índice de energía no suministrada y un criterio de contingencia sencilla, considerando tasas de falla y tiempos de reparación de la red de gas natural para obtener una mayor precisión en la estimación. Los resultados numéricos muestran que una penetración significativa de la generación distribuida basada en gas natural puede comprometer la confiabilidad de la red de distribución de energía si la red de gas natural es de baja confiabilidad

Planificación óptima de sistemas secundarios de distribución considerando fuentes renovables y de almacenamiento: un enfoque de gestión energética

This study focuses on the optimal planning of secondary power distribution systems considering distributed renewable generators (DG) and energy storage systems (ESS) to minimize expansion costs. The methodology solves a mixed integer non-linear mathematical model that describes the planning problem, including the operating and technical aspects of the secondary power distribution system. Such methodology uses an iterated local search algorithm and a two-stage load flow decomposition method to solve said problem. The two-stage load flow decomposition method finds the optimal operation of the storage devices and the low-voltage distribution system for each solution proposed by the iterated local search algorithm; thus, optimal energy management is achieved for the best solution. The proposed methodology was tested on a real medium-sized secondary power distribution system to establish its effectiveness. The results obtained show a reduction of 51.97 % in the total energy purchase cost of the system and a decrease of 3.02 % in the installation costs of the secondary circuits and distribution transformers when DG and ESS are considered. In conclusion, the results show that the integration of these distributed energy resources into the distribution system planning problem increases the profits of distribution companies from energy purchase and sale and reduces their fixed costs.Esta investigación se centró en la planificación óptima de los sistemas de distribución secundaria teniendo en cuenta los generadores renovables distribuidos (DG) y los sistemas de almacenamiento de energía (ESS) para minimizar los costos de expansión del proyecto. La metodología resuelve un modelo matemático no lineal entero mixto que describe el problema de planificación, incluyendo los aspectos operativos y técnicos del sistema de distribución secundario. Esta metodología utiliza un algoritmo de búsqueda local iterada y un flujo de carga de descomposición en dos etapas para resolver el problema. El flujo de carga de descomposición en dos etapas encuentra el funcionamiento óptimo de los dispositivos de almacenamiento y del sistema de distribución de baja tensión para cada solución propuesta por el algoritmo de búsqueda local iterada; así, se consigue una gestión óptima de la energía para la mejor solución. La metodología propuesta se probó en un sistema de distribución de dimensiones reales para verificar su efectividad. Los resultados obtenidos mostraron una reducción del 51.97 % en el coste total de compra de energía del sistema, y una disminución del 3.02 % en los de instalación de los circuitos secundarios y transformadores de distribución cuando se consideran los DG y los ESS. En conclusión, los resultados evidencian que la integración de estos recursos energéticos distribuidos en el problema de planificación de los sistemas de distribución aumenta los beneficios de las empresas de distribución por la compra y venta de energía, además de reducir sus costos fijos

A Soft Sensor for Biomass in a Batch Process with Delayed Measurements

This paper presents a soft sensor to estimate the biomass concentration in a batch bioprocess used in production of δ-endotoxins of Bacillus thuringiensis, subject to delayed measurements. The soft sensor proposed is based on a cascade observer-predictor algorithm. The observer stage is based on a class of second order sliding mode algorithms, allowing a fixed time estimation of the biomass. Additionally, the prediction stage offsets the effect of the delay in measurements. Simulations show the feasibility of the proposed observer.Universidad Nacional de ColombiaCINVESTAV-IPNITESO, A.C

An Equivalent Control Based Observer for Biomass in a Batch Process

In this paper a sliding-mode observer for a batch bioprocess, the d-endotoxins production of bacillus thuringiensis (BT), is presented. The proposed observer is based on the equivalent control method and a class of second-order sliding mode operators. The use of these operators in the observer design allows the fixed-time convergence of the measured variables, while the unmeasured variables converge exponentially. This structure allows to estimate the biomass in the d-endotoxins production of BT, even, under noisy measurement conditions. Simulations show the feasibility of the proposed observer. Convergence proofs are also presented

Imantodes inornatus (Boulenger, 1886) (Squamata: Dipsadidae): expansión del rango de la distribución conocida y primeros registros del valle del río Magdalena, Colombia

The first report of the Speckled Blunt-headed Tree Snake (Imantodes inornatus) is presented for the Magdalena River valley, from the departments of Antioquia, Bolívar, Boyacá and Caldas in Colombia. Since these records correspond to the biogeographic Magdalena province, the known range for the species is expanded. In Colombia, this is a trans-Andean species found from the Pacific rainforests of the Chocó region, through the northern portion of the Western and Central Andean ranges, to the middle Magdalena River valley.Se registra por primera vez la serpiente de árbol cabeza moteada (Imantodes inornatus) en el valle del río Magdalena en los departamentos de Antioquia, Bolívar, Boyacá y Caldas, en Colombia. Estos registros corresponden a la provincia biogeográfica del Magdalena, lo que aumenta el área de distribución conocida. En Colombia, esta especie es un elemento transandino que cruza las selvas tropicales del Pacífico de la región chocoana, a través de la porción septentrional de las cordilleras Occidental y Central hasta el valle medio del río Magdalena

Maternal vitamin D deficiency associated with neonatal hypocalcaemic convulsions

Maternal vitamin D insufficiency is not uncommon. Infants born to mothers who are deficient in vitamin D and or calcium, usually due to cultural modifications in their diets or clothing habits, and in addition are breastfed, are at risk of developing vitamin D deficiency and hypocalcaemia. We present a case of neonatal hypocalcaemic seizures secondary to vitamin D deficiency

Effectiveness-NTU Relationships of Parallel-Plate Moving Bed Heat Exchangers

Paper presented at 2018 Canadian Society of Mechanical Engineers International Congress, 27-30 May 2018.Moving bed heat exchangers (MBHEs) are used in various industrial processes. Recently, analytical solutions to several MBHE heat transfer problems have been presented in the literature. In this work, the mathematical procedure by which these new solutions are used to construct effectiveness-NTU relationships is presented, for parallel-plate configurations. Expressions for both co- and counter-current orientations are outlined. Effectiveness-NTU plots are then generated, and contrasted with those of fluid-fluid systems. As expected, a functionality with respect to the Number-of-Transfer-Units and the Capacity Ratio is observed. A novel dependency with respect to the Biot number is also demonstrated, whereby effectiveness decreases with increasing Biot number, due to the increasing resistance imparted by the diffusion of energy through the solids bulk. These effectiveness-NTU plots can serve as a design platform, which engineers can use to size and rate MBHEs

Energy Consumption Analysis Of Machining Centers Using Bayesian Analysis And Genetic Optimization

Responding to the current urgent need for low carbon emissions and high efficiency in manufacturing processes, the relationships between three different machining factors (depth of cut, feed rate, and spindle rate) on power consumption and surface finish (roughness) were analysed by applying a Bayesian seemingly unrelated regressions (SUR) model. For the analysis, an optimization criterion was established and minimized by using an optimization algorithm that combines evolutionary algorithm methods with a derivative-based (quasi-Newton) method to find the optimal conditions for energy consumption that obtains a good surface finish quality. A Bayesian ANOVA was also performed to identify the most important factors in terms of variance explanation of the observed outcomes. The data were obtained from a factorial experimental design performed in two computerized numerical control (CNC) vertical machining centers (Haas UMC-750 and Leadwell V-40iT). Some results from this study show that the feed rate is the most influential factor in power consumption, and the depth of cut is the factor with the stronger influence on roughness values. An optimal operational point is found for the three factors with a predictive error of less than 0.01% and 0.03% for the Leadwell V-40iT machine and the Haas UMC-750 machine, respectively