Exhaust Gas Heat Recovery for an ORC: A Case Study

This work aims at developing a heat exchanger (HEX) sizing approach considering the need to maximize the heat recovery within the limitations of pressure drop and space. The application consists in the recovery of the energy contained in exhaust gases coming from an internal combustion engine (ICE). Two heat exchanger geometries are selected as case studies. The design approach involves the application of design of experiments (DOE) techniques and computational fluid dynamics (CFD) simulations. DOE techniques are used to observe the influence of some selected parameters (factors) in the design of the heat exchangers, and CFD simulations are carried out to determine the performance of the heat exchanger. The information obtained is used to determine local Nusselt number correlations that are used for the design of the heat exchangers

Sustainability

The use of an internal heat exchanger in vapor compression refrigeration systems of one stage is a common practice because it helps to increase the cooling capacity in the evaporator. Furthermore, the use of refrigerants with low global warming potential is becoming more frequent due to environmental regulations worldwide. Thus, this paper presents an evaluation of the improvement produced by the inclusion of an internal heat exchanger cycle (IHXC) in an experimental installation from the viewpoint of exergy, economic and environmental through to exergy, exergoeconomics, and Specific Life Cycle Climate Performance (SLCCP) studies. The tests were conducted using R1234ze(E) as a replacement alternative to R134a in three evaporating temperature conditions: 4 °C, 9 °C, and 14 °C. Comparisons were made considering R134a in BRC mode versus R1234ze(E) in BRC and IHXC modes. Results show that a lower environmental impact is produced by an evaporating temperature of 14 °C with a reduction in SLCCP of 13.3% using IHXC and R1234ze(E). Moreover, the highest increase in exergy efficiency was observed for an evaporating temperature of 4 °C, with this increase being 9%, while the lowest increase in the total cost rate was observed for the same evaporating temperature, being 12.3% and 21.2% for BRC and IHXC modes using R1234ze(E), respectivelyMDPI Academic Open Access Publishinghttps://www.mdpi.com/2071-1050/14/10/600

Desarrollo de un modelo físico para una instalación de producción de frío por compresión de vapor utilizando el refrigerante R134A. Validación experimental y aplicación para la simulación energética

Este trabajo doctoral esta enfocado al desarrollo de un modelo físico que permita simular el comportamiento de una instalación de producción de frío por compresión de vapor, partiendo de las condiciones y requerimientos de funcionamiento. El modelo tiene un grado alto de fiabilidad y puede ser usado en la simulación del comportamiento de la instalación, y de esta manera predecir un mejor funcionamiento encaminado a la operación energéticamente eficiente del sistema u otras aplicaciones. Por lo tanto, los objetivos generales planteados en esta tesis son: desarrollo y validación del modelo físico capaz de predecir el comportamiento estacionario de la instalación, y la aplicación del modelo para la simulación energética con el fin de ayudar a encontrar las condiciones de operación que optimicen el funcionamiento energético de la instalación

Applied Thermal Engineering

Several technologies are being researched to address the challenges of cryogenic heat transfer in liquefied natural gas (LNG) production. Single mixed refrigerant (SMR) or dual mixed refrigerant (DMR) systems have advantages vs. pure refrigerant-based systems (e.g., cascade or inverted Brayton cycle with nitrogen) due to compact design suitable for small-scale units. However, the selection of mixed refrigerant composition is a challenge. Several methods have been published, typically using heuristic and computational techniques; with power consumption, efficiency, and/or exergy as the figure of merit. This paper presents an alternative approach for the determination of optimum refrigerant mixture composition based on nonlinear thermodynamic equations relating heat exchanger composite curves and mass flow of LNG produced. Three case studies demonstrate the effectiveness of the approach, indicating that single mixed refrigerant systems can be used for cost-effective LNG production while improving LNG production per unit of refrigerant flow rate by as much as 6.5 % vs. conventional approaches. The research is applicable to current needs of the gas extraction industry because it helps increase LNG production in small-scale cryogenic systems, thereby enabling economic gas recovery and reducing flaring during fracking operation, as is typical in e.g., the Bakken formation of North Dakota.Sciencie Directhttps://www.sciencedirect.com/science/article/abs/pii/S1359431122014156#kg00

CO2 como refrigerante: del pasado al futuro CO2 as refrigerant: from the past to future

En años recientes y debido a la problemática que ha originado el calentamiento mundial, en el campo de la refrigeración y climatización se ha incrementado el interés por utilizar refrigerantes naturales e hidrocarburos con bajo potencial de calentamiento mundial, este es el caso de la utilización del CO2 como fluido frigorígeno que ha sido visto como una alter­nativa adecuada a los actuales refrigerantes en la comunidad científica. Hoy en día, el CO2 cada vez está retomando presencia en el campo de la refrigeración y climatización a nivel internacional, así pues, el presente trabajo tiene la finalidad de dar a conocer su potencial como refrigerante natural, las causas por las cuales este fluido fue relevado momentánea­mente por refrigerantes clorofluorocarbonados y su renacer en pleno siglo XXI. Además, se plantea su aplicación en la generación de frío en nuestro país mediante la tecnología de compresión de vapor basado en ciclo transcrítico.  In recent years, and due to problems resulting from global warming, interest has grown in the fields of refrigeration and air conditioning, specifically regarding the use of natural refrigerants and hydrocarbons with low potential for global warming. Such is the case of the use of CO2 as a cold fluid, which has been considered in the scientific community as an adequate alternative to common refrigerants. Nowadays, the use of CO2 in the areas of refrigeration and air conditioning has been recognized at international levels. Therefore, this work aims to show its potential as a natural refrigerant, the causes why this fluid was temporarily replaced by chlorofluorocarbon refrigerants, and its reappearance in the XXI century. It also proposes the use of CO2 in air conditioning in our country by using vapor compression technology, based on the transcritical cycle.</p

A Review of Small-Scale Vapor Compression Refrigeration Technologies

The study and development of miniature refrigeration and climate conditioning systems based on vapor compression for small-scale applications have received wide interest in recent years due to their advantages compared with other available technologies, both active and passive. This paper identifies different applications and areas of opportunity, including electronic components and personal cooling, where small-scale vapor compression refrigeration systems are anticipated to play a key role in technological development. This paper presents the current state of the art, including applications, component designs, operating conditions, experiments, published results, etc. to describe the current status of small-scale vapor compression refrigeration and illustrate a perspective for the future of this technology

SAGE Journals

n this paper, an Artificial Neural Network soft matrix correlation to estimate the pressure drop of air-water two-phase flow is developed. The applicability of the model is extended by using dimensionless physical numbers as inputs (Air-Reynolds number, Water-Reynolds number, and the ratio of Air Inertial Forces to Water Inertial Forces), so the model can be implemented for vertical pipes with the proper combination of diameter-velocity-density-viscosity allowing estimations of dimensional numbers within the range of: Air-Reynolds numbers (430–6100), Water-Reynolds number (2400–7200), and Air-Water-Inertial forces ratio (1.6–1834), including the diameter range from 3 to 28 mm. Experimental measurements of frictional pressure drop of water-air mixtures are determined at different conditions. A search of the most suitable density, viscosity, and friction models was conducted and used in the model. The performance of the proposed ANN correlation is compared against published expressions showing good approximation to experimental data; results indicate that the most used correlations are within a mean relative error (mre) of 23.9–30.7%, while the proposed ANN has a mre = 0.9%. Two additional features are discussed: i) the applicability and generality of the ANN using untrained data, ii) the applicability in laminar, transitional, and turbulent flow regimen. To take the approach beyond a robust performance mapping, the methodology to translate the ANN into a programmable equation is presented.Revista SAGE Journal on-linehttps://journals.sagepub.com/doi/10.1177/0954406221102032

Numerical Study on the Effect of Distribution Plates in the Manifolds on the Flow Distribution and Thermal Performance of a Flat Plate Solar Collector

Flow maldistribution represents a problem of particular interest in the engineering field for several thermal systems. In flat plate solar collectors, the thermal efficiency strongly depends on the flow distribution through the riser tubes, where a uniform distribution causes a uniform temperature distribution and therefore a higher efficiency. In this work, a Computational Fluid Dynamics (CFD) numerical analysis has been carried out using the commercial software FLUENT&reg;, in order to determine the flow distribution, pressure drop and hence the thermal efficiency of a solar collector with distribution flow plates inside the manifolds. The obtained numerical solution for this type of thermal systems has been validated with experimental results available in literature for laminar and turbulent flow. Four distribution plate configurations were analyzed. Results show that using two distribution plates in each of both manifolds improves the flow uniformity up to 40% under the same operating conditions when distribution plates are not used. Besides, it is shown that there exists an increase in the overall pressure drop which is practically negligible for the tilt angles commonly employed in the installation of flat plate solar collectors in Mexico. The use of closed end distribution plates on the dividing and combining manifolds allows the thermal efficiency to become close to the ideal thermal efficiency which is obtained with a uniform flow distribution

Thermal and energy evaluation of a novel polymer-ceramic composite as insulation for a household refrigerator

Este artículo presenta un estudio de viabilidad de un nuevo mat erial compuesto polímero-cerámico aplicado como aislante térmic o sobre una superficie de un refrigerador doméstico de pequeña capacida d volumétrica. Este trabajo describe de manera sucinta su manuf actura así como la comparación energética y térmica entre el refrigerador de referencia (cuando sale de fábrica) y el refrigerador con el composite instalado. Experimentalmente, c uando se usa el composite la tem peratura interna promedio del frigobar incrementa alrededor de 1°C, que para propósitos prácticos y de diseño, el refrigerador aún func iona por debajo de los 3°C. Además, para condiciones de operaci ón estables, la energía consumida usando el composite ahorra aproximadamente 1.5% en comparación con el refrigerador de referencia. A pesar de este ligero ahorro, la perlita pyro-expandida actúa como material ai slante. Este material puede exhibir mejor facilidad de uso y be neficios térmicos, energéticos y económic os, sin omitir las característi cas ambientales a su favor

Thermal and energy evaluation of a novel polymer-ceramic composite as insulation for a household refrigerator

Este artículo presenta un estudio de viabilidad de un nuevo material compuesto polímero-cerámico aplicado como aislante térmico sobre una superficie de un refrigerador doméstico de pequeña capacidad volumétrica. Este trabajo describe de manera sucinta su manufactura así como la comparación energética y térmica entre el refrigerador de referencia (cuando sale de fábrica) y el refrigerador con el composite instalado. Experimentalmente, cuando se usa el composite la temperatura interna promedio del frigobar incrementa alrededor de 1°C, que para propósitos prácticos y de diseño, el refrigerador aún funciona por debajo de los 3°C. Además, para condiciones de operación estables, la energía consumida usando el composite ahorra aproximadamente 1.5% en comparación con el refrigerador de referencia. A pesar de este ligero ahorro, la perlita pyro-expandida actúa como material aislante. Este material puede exhibir mejor facilidad de uso y beneficios térmicos, energéticos y económicos, sin omitir las características ambientales a su favor.This article presents a feasibility study of a new polymer-ceramic composite material applied as a thermal insulator on the surface of a low net volume household refrigerator. This paper describes its manufacture in a succinct manner, and a thermal and energy comparison between the factory refrigerator and the refrigerator with the composite installed. Based on the experiments, it is concluded that when using the composite, the average internal temperature of the fridge is increased by 1°C, for practical and design purposes, the refrigerator still functions below 3°C. It was also found that at stable operating conditions the energy consumption using the composite saves approximately 1.5%. Despite these slight savings,the pyro-expanded perlite composite acts as a thermal isolating material. This material may exhibit better ease of use and thermal, energetic and economic benefits, without omitting the environmental characteristics that they favor