Mejora en el desarrollo de sistemas de refrigeración aplicados al transporte

Los procesos de almacenamiento y transporte de frutas encontramos riesgos que pueden producir un daño en la salud el consumidor. La adecuada manipulación de los productos durante su transporte es crucial para la seguridad de sus productos. Los consumidores de frutas y vegetales son cada vez más exigentes por lo la calidad de estos productos, no solo la que tienen al ser empacados en origen, sino la que presentan en el momento de ser comprados, y más aún, al consumirse.Fundación Séneca. Ministerio de Educación y Ciencia. Fondo Social Europeo

Esquemas numéricos conservativos para flujo bifásico 1D no estacionario

[SPA] Esta tesis está dedicada al modelado de mezclas bifásicas no estacionarias de líquido y vapor. Esta motivada por la gran cantidad de aplicaciones industriales en las que podemos encontrar estos fenómenos. Los transitorios en flujo bifásico son un aspecto muy importante en diferentes aplicaciones químicas, nucleares e industriales. En el caso de la industria nuclear, el estudio de transitorios en flujo bifásico es fundamental, debido a la importancia que tiene prevenir accidentes con pérdida de refrigerante (LOCA), as como garantizar un buen funcionamiento del circuito del refrigerante. Mediante la introducción de algunos de los códigos más importantes desarrollados en las dos últimas décadas, así como las técnicas de mallado que utilizan justificamos el presente desarrollo que se ha centrado en la extensión de algunos esquemas explícitos conservativos para obtener soluciones aproximadas del sistema de ecuaciones en flujo bifásico unidimensional. Estos han sido esquemas centrados y "upwind" para resolver problemas con flujo multifásico, muchos de ellos basados en la solución exacta o aproximada de problemas de Riemann usando métodos tipo Godunov tales como "Approximate Riemann Solvers" o métodos "Flux Vector Splitting". Fundamentalmente hemos estudiado los esquemas TVD, TVD Adaptados y la familia de esquemas AUSM. [ENG]The thesis is devoted to the modelization of non steady two phase mixtures of liquid and vapour. It has been motivated by the great amount of industrial applications in which we nd these phenomena. Transient two phase ow is a very important issue in nuclear, chemical and industrial applications. In the case of the nuclear industry due to the importance of preventing loss of coolant accidents (LOCA) and guarranteing a good perfomance of the coolant system in power plants. By means of the introduction of the most important codes developed during the last two decades and their associated mesh techniques we justify the present development which is centred on the extension of some conservative and explicit schemes to obtain approximate solutions of the system of equations in one dimensional one pressure two phase ow. They have been Centred and Upwind Schemes to solve multiphase ow problems, most of them based on the exact or approximate solution of Riemann problems using Godunov's like methods such as Approximate Riemann Solvers or Flux Splitting methods. We have studied mainly TVD schemes, Adapted TVD schemes (ATVD) and the AUSM family of schemes.Universidad Politécnica de Valenci

Modelado, diseño y ensayo de sistemas solares térmicos

El grupo de investigación ha estado participando en el modelado de un gran número de sistemas térmicos. En concreto y a través de una serie de contratos con la Agencia de Gestión de la Energía de la Región de Murcia, ARGEM se ha participado en la realización de un mapa de radiación solar de la Región de Murcia, se dispone de un banco de ensayo de colectores y también se ha participado en el estudio los parámetros de diseño del circuito primario de una instalación solar térmica

R32 Heat Transfer Coefficient During Condensation In A Mini-Channel Multiport Tube

The use of micro- and mini-channels in heat exchanger has increased in recent decades. They contribute to increasing efficiency and reducing refrigerant charge and compactness of heat exchangers. The aim of this study is to experimentally determine the heat transfer coefficient in mini-channels of two-phase flow processes with the low GWP refrigerant R32 and compare it with the values provided by some of the correlations developed by other researchers. In the existing literature there are a few publications studying the refrigerant R32. R32 has medium flammability, classified as A2 by ASHRAE. European air conditioning manufactures point to use R32 instead of R410A. R32 has lower global warming potential (GWP = 675) than R410a (GWP = 2088). Environmental improvements must also be considered. R32 is a single component refrigerant so recycling is easier than R410A process; also R32 is safer than R410A according to NFPA classification, although R410A flammability is lower than R32 because of the addition of R125. An installation for the study of condensation processes has been constructed at the “Technical University of Cartagena”. The more relevant results of heat transfer coefficient will be presented in this paper. The analysed data have been measured for R32 flowing through aluminium square multiport tubes with a hydraulic diameter of 1.17 mm and compared with R410A. The influence of saturation temperature (or pressure), flow velocity, and vapour quality in heat transfer coefficient have been studied. The values considered for these variables are: saturation pressure corresponding to 30, 35, 40, 45, and 50ºC; flow velocities from 100 to 700 kg/(s•m2); vapour quality from 0.05 to 0.9

Atlas de irradiación solar y temperatura ambiente de la Comunidad Autonoma de la Región de Murcia

El presente documento es el informe final de resultados del contrato entre la Universidad Politécnica de Cartagena y la Agencia de Gestión de la Energía de la Región de Murcia (ARGEM) para actividades de asesoramiento y asistencia técnica. El contrato lleva por título: “REALIZACIÓN DE UN MAPA DE IRRADIACIÓN SOLAR DE LA REGIÓN DE MURCIA” El objetivo global de este trabajo es la elaboración de un mapa de irradiación solar media recibida sobre plano horizontal e inclinado, específico para la Región de Murcia. En el desarrollo del trabajo se desarrollarán técnicas de búsqueda, tratamiento e interpretación de los datos disponibles de irradiación solar y temperatura ambiente de las diferentes estaciones meteorológicas instaladas en la Comunidad Autónoma de la Región de Murcia.Agencia de Gestión de la Energía de la Región de Murcia (ARGEM

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

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

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

Experimental characterization of the coupling and heating performance of a CO2 water-to-water heat pump and a water storage tank for domestic hot water production system

This work presents an experimental study of the dynamic performance of a CO2 water-to-water heat pump in a domestic hot water production system. A facility was developed and used to characterize the time evolution of the COP of this heat pump, the heating and stratification processes of the hot-water storage tank, and the global COP of the system. Results showed that, when heating the water storage tank, strategies based on promoting stratification to reach Ri ∼40, such as the use of vertical tank filling velocities ∼ 10-4 m·s−1 with low water flow rates between the tank and the heat pump gas cooler, permits an increase of ∼12.4% in the system global COP and a reduction of ∼16% of the compressor energy consumption compared to other strategies. However, strategies based on considering higher water flow rates (i.e. Ri ∼1) increase the thermal energy available in the tank (∼6% when flow rate and increases a factor 3.6) but enhance the water mixing and extend the heating time which reduces the global COP of the system. Besides, an increase of the evaporator inlet water temperature from 5 °C to 20 °C increases the system global COP by 59% and reduces the heating time ∼40%.This work has been performed in the context of the project in the project “Maximisation of the efficiency and minimisation of the environmental impact of heap pumps for the decarbonisation of heating and domestic hot water production in nearly zero energy buildings” ENE2017- 83665-C2-2-P, Funded by the Ministry of Economy and Competitiveness, Spain and the support of the European Regional Development Fund. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper

A discretization method for the characterization of a plate heat exchanger working as evaporator during transient conditions

In this work, a method for the characterization of a plate heat exchanger working as evaporator is presented. It is based on a one-dimensional discretization of the exchanger, which solves the heat transfer balance equations by means of an iterative methodology based on a heat transfer area converging method. The inputs of the method are the flow rates of the fluids, the inlet enthalpy of the refrigerant, the superheating, and the inlet temperature and pressure of the secondary fluid. Once the inlet pressure of the refrigerant is assumed, pressure drop is calculated in each cell and then enthalpy. The consideration of the proper heat transfer coefficient (HTC) correlations allows the calculation of the heat transfer area, which is after compared to the actual one. The method has been validated by means of a database of 366 experimental data obtained for eight plate heat exchangers working as evaporators by using six different refrigerants, namely R134a, R1234yf, R513A, R744, R290, and R507A. As the method requires suitable correlations for the calculation of the HTC and pressure drop, several correlations for the HTC and Δp found in the literature are studied and the results obtained by using them are presented in terms of the maximum absolute relative deviation (MARD). The results corresponding to the correlation which yields the best results are graphically represented. Finally, the method is used to predict the evaporator performance operating in transient conditions. The results obtained show an excellent agreement with the experimental results collected during the transient operation of a transcritical CO2 water heater coupled to a storage tank.The work in this paper has been financed by the Spanish Ministry of Science and Innovation under Project TED2021-131173B–I00 and the NextGenerationEU recovery plan