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

An Energetic Model for Detonation of Granulated Solid Propellants

Unexpected detonation of granular solid energetic materials is a key safety issue in the propellants manufacturing industry. In this work, a model developed for the characterization of the early stages of the detonation process of granular solid energetic materials is presented. The model relies on a two-phase approach which considers the conservation equations of mass, momentum, and energy and constitutive relations for mass generation, gas-solid particle interaction, interphase heat transfer, and particle-particle stress. The work considers an extension of approximated Riemann solvers and Total Variation Diminishing (TVD) schemes to the solid phase for the numerical integration of the problem. The results obtained with this model show a good agreement with data available in the literature and confirm the potential of the numerical schemes applied to this type of model. The results also permit to assess the effectiveness of different numerical schemes to predict the early stages of this transient combustion process.The research was performed thanks to the financial support of the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund throughout project RTC-2016-5194-8

Modelización numérica de la movilización de partículas en gases

En el presente artículo se presenta una descripción de la problemática relacionada con la presencia de partículas de polvo en el proyecto internacional del reactor experimental de fusión nuclear, ITER, frente a posibles accidentes que podrían llegar a darse. Uno de estos sucesos hipotéticos consiste en la movilización y combustión de partículas por la presurización repentina del reactor. Para el análisis de este problema, como paso previo a la realización del proyecto, se describe el modelo matemático de mezclas altamente diluidas, que se ha planteado para la modelización numérica del problema y para su posterior resolución mediante diferentes esquemas de discretización.Asociación de Jóvenes Investigadores de Cartagena, (AJICT). Universidad Politécnica de Cartagena. Escuela Técnica Superior de Ingeniería Industrial UPCT, (ETSII). Escuela Técnica Superior de Ingeniería Agronómica, (ETSIA), Escuela Técnica Superior de Ingeniería de Telecomunicación (ETSIT). Escuela de Ingeniería de Caminos, Canales, y Puertos y de Ingeniería de Minas, (EICM). Fundación Séneca, Agencia Regional de Ciencia y Tecnología. Parque Tecnológico de Fuente Álamo. Grupo Aquilin

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

Modelado de la combustión de propulsante para problemas de balística interior

Se presenta un modelo para el estudio de problemas de balística interior que implican el análisis de una mezcla bifásica de sólidos (pólvora/propulsante) y gases (productos de la combustión). Dicho modelo está basado en una aproximación unidimensional por Volúmenes Finitos de un conjunto de ecuaciones adaptadas del modelo no conservativo de Gough. El cálculo de los flujos numéricos en la interfase se hace mediante solvers aproximados de Riemann, en concreto los esquemas numéricos aplicados son el esquema de Rusanov y el AUSM+. En este trabajo se introducen las ecuaciones correspondientes al modelo y las relaciones de cierre necesarias para caracterizar los fenómenos físicos que ocurren durante la combustión y como consecuencia de la interacción entre las fases: velocidad de combustión, fricción, tensión interfacial y transferencia de calor interfacial. Además, se realiza la validación del código desarrollado. Para ello se presenta un test experimental, las condiciones del mismo y los resultados experimentales se comparan con los obtenidos con el modelo implementado. También se contrastan los resultados obtenidos con los de otros programas que utilizan aproximaciones 0D (Balint) o aproximaciones unidimensionales (FNGun). Para finalizar, se expondrán algunas conclusiones de los resultados obtenidos con este modelo.Este trabajo ha sido financiado mediante un proyecto de investigación del “Ministerio de Industria, Energía y Turismo” a través de la convocatoria INNPACTO denominado “Smart Propellants” (IPT-2011-0712-020000) que involucra a EXPAL Systems S.A. y a la Universidad Politécnica de Cartagena (UPCT). Parte de esta ayuda ha sido financiada con fondos FEDER

Avances en Ciencias y Técnicas del Frío - 11

Este año 2022 se han cumplido 20 años desde la fundación de la Sociedad Española de Ciencias y Técnicas del Frío (SECYTEF; http://secytef.upct.es/), que tuvo lugar precisamente en la Universidad Politécnica de Cartagena, durante la celebración en esta Universidad del primer congreso CYTEF en 2002. Fue el Primer Congreso Español de Ciencias y Técnicas del Frío de esta serie de congresos CYTEF. Posteriormente, los congresos CYTEF han tenido lugar cada 2 años, y de su organización se ha encargado especialmente la SECYTEF, ya que es su principal cometido Los trabajos de investigación presentados en los Congresos CYTEF han sido publicados en los libros de actas correspondientes que constituyen una serie denominada Avances en Ciencias y Técnicas del Frío. Contando con este libro de Actas del CYTEF 2022, ya son 11 números de esta serie de libros los publicados. Representan una valiosa fuente de información científico-técnica para los investigadores, técnicos y profesionales interesados en las Ciencias y Técnicas del Frío, tanto en lo que se refiere a tecnologías de producción de frío, como a las tecnologías de su aplicación en los distintos sectores

Games-Based Learning Framework

This work presents the authors’ experience in the field of mobile technologies, from which several initiatives have emerged. As result of this, a games-based framework for learning has been developed in these last years. This framework is composed by a competition called Mobigame, which has as main aim to stimulate the participation of the students. By participating in this competition participants learn to develop for mobile devices. A game to practice Japanese is also presented in this article, which was presented in the above mentioned competition. This game has been developed for mobile phones or PDAs (Personal Digital Assistants) based on the JME (Java Mobile Edition) technology. Finally, another initiative is also presented: A free download platform of digital contents for mobile devices based on info-educational games

Modelado de problemas de combustión de propulsantes

[ESP] Se presenta una revisión del estado del arte en el que se identifican modelos bifásicos para analizar problemas que implican la combustión de propulsantes. En estos problemas coexisten una fase sólida, pólvora o propulsante, y una fase gaseosa que corresponde a los gases que resultan de la combustión de la primera. En este estudio se detallan aquellos modelos en los cuales el sistema de ecuaciones se completa con las ecuaciones de cierre necesarias para caracterizar físicamente el problema. [ENG] A review of the state-of-the-art two-phase models for solid propellants combustion is presented. A solid phase, solid propellant, and a gas phase, as a result of propellant combustion, coexist in these problems. In this study the models detailed are those in which the governing equations system is completed by the necessary constitutive relations to solve the problem.Escuela Técnica Superior de Ingeniería de Telecomunicación (ETSIT), Escuela Técnica Superior de Ingeniería Agronómica (ETSIA), Escuela Técnica Superior de Ingeniería Industrial (ETSII), Escuela Técnica Superior de Arquitectura y Edificación (ETSAE), Escuela Técnica Superior de Ingeniería de Caminos, Canales y Puertos y de Ingeniería de Minas (ETSICCPIM), Facultad de Ciencias de la Empresa (FCCE), Parque Tecnológico de Fuente Álamo (PTFA), Vicerrectorado de Estudiantes y Extensión de la UPCT, Vicerrectorado de Investigación e Innovación de la UPCT, y Vicerrectorado de Internacionalización y Cooperación al Desarrollo de la UPCT

Modelado tridimensional de la combustión de gases con turbulencia Large Eddy Simulation

[ESP] La mecánica de fluidos computacional permite la resolución numérica de problemas cada vez más complejos. En el presente trabajo se presenta un ejemplo de aplicación de esta técnica mediante el modelado de una cámara de combustión de gases en el que se incluye turbulencia “Large Eddy Simulation” y modelo de radiación “Finite Volume Discrete Ordinates Model” (fvDOM) mediante la herramienta de código abierto OpenFOAM. [ENG] Computational Fluid Dynamics achieves numerical resolutions of more and more complex problems. In this work it is presented an application of this branch, which consists of modelling a gas combustion chamber including “Large Eddy Simulation” and “Finite Volume Discrete Ordinates Model” (fvDOM) as turbulence and radiation models. For this purpose, the open-source CFD toolbox OpenFOAM has been used.Escuela Técnica Superior de Ingeniería de Telecomunicación (ETSIT), Escuela Técnica Superior de Ingeniería Agronómica (ETSIA), Escuela Técnica Superior de Ingeniería Industrial (ETSII), Escuela Técnica Superior de Arquitectura y Edificación (ETSAE), Escuela Técnica Superior de Ingeniería de Caminos, Canales y Puertos y de Ingeniería de Minas (ETSICCPIM), Facultad de Ciencias de la Empresa (FCCE), Parque Tecnológico de Fuente Álamo (PTFA), Vicerrectorado de Estudiantes y Extensión de la UPCT, Vicerrectorado de Investigación e Innovación de la UPCT, y Vicerrectorado de Internacionalización y Cooperación al Desarrollo de la UPCT