Thermal analysis and optimization of a heat regenerator composed of two coupled moving bed heat exchangers

This work presents a study to optimize the performance of a heat regenerator composed by two coupled moving bed heat exchangers (MBHE). A MBHE is used to recover heat, from a hot gas stream, and the other one is used to preheat an air stream. A direct application might be a gasifier. The heat exchangers performance was studied in two cases, considering or not the conduction heat transfer in the solid phase. When the solid conduction is taken into account, a numerical solution is obtained, while an analytical solution is possible when the conduction terms are neglected. In both cases, the optimum values of bed length (in the air flow direction) and particle diameter were obtained from an exergy point of view. Finally, an energy optimization of the heat regenerator was carried out, obtaining the optimal heat regenerator dimensions as a function of gas velocity and gas flow rate.Publicad

Exergy optimization in a steady moving bed heat exchanger

Proceedings of: Interdisciplinary Transport Phenomena V: Fluid, Thermal, Biological, Materials and Space Sciences (ITP 2007), 14-19 of October, 2007, Bansko, Bulgaria (Oral paper nº 70)This work provides an exergy analysis of a moving bed heat exchanger to obtain for a range of incoming fluid flow rates the operational optimum and the incidence on it of the relevant parameters such as the dimensions of the exchanger, the particle diameter and the flow rate of the fluid. The MBHE proposed can be analyzed as a cross flow heat exchanger where one of the phases is a moving granular medium. In the present work the exergy analysis of the MBHE is carried out over operation data of the exchanger obtained in two ways: a numerical simulation of the steady state problem and the analytical solution of the simplified (avoiding conduction terms) equations. The numerical simulation is carried over the two steady energy equations (fluid and solid), involving for the solid the convection heat transfer to the fluid and the diffusion term in both directions, and for the fluid only the convection heat transfer to the solid. The analytical solution is the wellknown solution of the simplified problem neglecting conduction effects.Publicad

Coherent structures and bubble-particle velocity in 2-D fluidized beds

This work presents an experimental study to characterize ascending bubbles and granular velocity in the dense phase of a 2-D fluidized bed. Three different non-intrusive techniques based on images obtained with a high speed camera are developed, and applied to the images. First the bubble paths are characterized with time-average concentration maps and the bubble velocities are obtained, using a tracking algorithm over the mass centers of the bubbles. Finally, a PIV (particle image velocimetry) method is used to characterize the particle velocity vectors. This procedure is repeated for different bed aspect ratios, and different superficial gas velocities. This study analyzes the superficial gas velocity influence on the bed behavior, and how the bubble path configuration depends on the bed aspect ratio. The PIV measurements give us information on the location of the recirculation regions and the influence of the superficial gas velocity.Publicad

Performance of a LiBr water absorption chiller operating with plate heat exchangers

This paper studies the performance of a lithium bromide water absorption chiller operating with plate heat exchangers (PHE). The overall heat transfer coefficients in the desorber, the condenser and the solution heat recoverer are calculated using the correlations provided in the literature for evaporation, condensation and liquid to liquid heat transfer in PHEs. The variable parameters are the external driving temperatures. In the desorber, the inlet temperature of the hot fluid ranges from 75°C to 105°C. In the condenser and the absorber, the inlet temperature of the cooling water goes from 20°C to 40°C. The coefficient of performance (COP) obtained ranges from 0.5 to 0.8 for cooling duties ranging from 2 kW to 12 kW. The chiller response to different hot fluid temperatures and circulated mass flow rates is also presented. The performance and the internal parameters of the chiller at part load are, therefore, calculated. A higher efficiency results when the solution pumped from the absorber to the desorber decreases. The heat transfer analysis of the PHEs is also presented. The overall heat transfer coefficient in the desorber, equal to 790 W/m²K at the design conditions, is also analysed at part load. The condenser performance can be represented by a similar relationship found in conventional air cooled condensersThis work was partially funded by CICYT Ministerio de Ciencia y Tecnología (CLIMABCAR project no. DPI 2003-01567)Publicad

¿Influye la gestión de los empleados en su decisión de seguir utilizando el teletrabajo después de la pandemia?

[ENG] This paper analyses the intention of Spanish companies to continue using telework after the end of the COVID-19 pandemic. With this aim, we consider the influence that the management of several variables related to one of the key stakeholders, employees, has on this intention. This line of study is of great interest, given the implications not only for the management of companies, but also for key aspects such as the goals of the 2030 Agenda for Sustainable Development. To this end, we start with a review of the relevant literatura on this topic, which allows us to raise various research hypotheses. This is followed by an analysis of a sample of 1,879 Spanish SMEs though a binary logistic regression model, which shows the positive influence of managers’ university education and companies’ orientation towards innovation on the use of telework after the pandemic. [SPA] Este trabajo analiza la intención de las empresas españolas de seguir utilizando el teletrabajo tras el fin de la pandemia del COVID-19. Con este objetivo, consideramos la influencia que tiene en esta intención la gestión de diversas variables relacionadas con uno de los principales grupos de interés, los empleados. Esta línea de estudio es de gran interés dada las implicaciones no solo para la gestión de las empresas, sino también para aspectos clave como los objetivos de la Agenda 2030 para el Desarrollo Sostenible. Para ello, partimos de una revisión de la literatura relevante sobre este tema, lo que nos permite plantear diversas hipótesis de investigación. A continuación, se analiza una muestra de 1.879 pymes españolas mediante un modelo de regresión logística binaria, que muestra la influencia positiva de la formación universitaria de los directivos y la orientación a la innovación de las empresas en el uso del teletrabajo tras la pandemiaThis research was supported by the Universidad Internacional de La Rioja - UNIR (Funder Identifier: http://dx.doi.org/10.13039/100017407) through the Observatorio Competitividad Pequeña y Mediana Empresa UNIR-FAEDPYME programme (Proyecto B0036)

Solid conduction effects and design criteria in moving bed heat exchangers

This work presents a theoretical study of the energetic performance of a moving bed heat exchanger (MBHE), which consists of a flow of solid particles moving down that recovers heat from a gas flow percolating the solids in cross-flow. In order to define the solid conduction effects, two solutions for the MBHE energy equations have been studied: an analytical solution considering only convection heat transfer (and neglecting solid conduction) and a numerical solution with the solid conductivity retained in the equations. In a second part, the power requirements of a MBHE (to pump the gas and to raise the down-flowing particles) are confronted with the heat transferred considering the variation of design parameters, such as gas and solids’ velocities, solids particle diameter or MBHE dimensions. The numerical results show that solid conductivity reduces the global efficiency of the heat exchanger. Therefore, a selection criterion for the solids can be established, in which their thermal conductivity should be minimized to avoid conduction through the solid phase, but to a limit in order to ensure that temperature differences inside an individual solid particle remain small. Regarding the other energy interactions involved in the system, these are at least one order of magnitude lower than the heat exchanged. Nevertheless, for a proper analysis of the system the efficiency of the devices used to pump the gas and to raise the particles and the relative costs of the different energy forms present in the system should be taken into account.Publicad

Exergy Optimization of a Moving Bed Heat Exchanger

The MBHE proposed can be analyzed as a crossflow heat exchanger where one of the phases is a moving granular medium. In the present work the exergy analysis of the MBHE is carried out over operation data of the exchanger obtained in two ways: a numerical simulation of the stationary problem and a simplified analysis. The numerical simulation is carried over the two steady state energy equations (fluid and solid), involving (for the fluid) the convection heat transfer to the solid and the diffusion term in the flow direction, and (for the solid) only the convection heat transfer to the fluid. The simplified analysis followed the well-known e-NTU method, taking the equipment as a crossflow heat exchanger with both fluids unmixed.Publicad

The Effects of Melatonin Supplementation on Professional Football Player Performance: A Systematic Review

This study was funded by the High Council for Sports (CSD), Spanish Ministry of Culture and Sport, through the NESA NETWORK “Spanish Network of Sports Care at Altitude (RADA)” Ref. 19/UPB/23. This research was supported by an FPU grant from the Spanish University Ministry to Alejandro Lopez-Moro (FPU20/00210). The authors thank FSI (Football Science Institute) for their support.Background: Melatonin is a hormone that has shown anti-inflammatory actions, reduced oxidative stress, and has effects on physical performance, so the aim of this study was to review the effects of melatonin supplementation on the performance of professional soccer players. Methods: Critical and systematic review. Data were obtained by performing searches in the following bibliographic databases: Web of Science, MEDLINE (via PubMed), Embase, Cochrane Library, and Scopus. The terms used were “Soccer Athlete”, “Melatonin”, and “Soccer Performance”, using “Humans” as a filter. The search update was in May 2023. Results: Having applied the inclusion and exclusion criteria, eight articles were selected out of 59 retrieved references. The dose of melatonin administered in the studies ranged between 5 and 8 mg. The outcomes showed a decrease in oxidative stress, muscle damage, and inflammatory markers in the melatonin-treated group. Conclusions: Exogenously administered melatonin seems to attenuate some of the effects derived from physical exercise, such as oxidative stress, inflammation, and muscle damage, in professional football players, and since it has no potential adverse effects, it could be interesting to apply it in this population. However, the direct effects of melatonin supplementation on physical performance have not been demonstrated, so more research is needed on the intervention period and effective dose and with larger participant populations.High Council for Sports (CSD)Spanish Ministry of Culture and Sport Ref. 19/UPB/23Spanish University Ministry FPU20/00210FSI (Football Science Institute

On the pressure drop in plate heat exchangers used as desorbers in absorption chillers

The influence of the pressure drop in Plate Heat Exchangers (PHE) in the boiling temperature of LiBr H₂O and NH₃ H₂O solutions is studied. For the NH₃H₂O solution, the pressure drop-temperature saturation relationship estates that high pressure drops can be allowed in the solution with negligible changes in the saturation temperature, and in the PHE performance. Besides, in the case of the LiBr H₂O solution, as the working pressure is usually very low, the analysis of the pressure drop must be taken as a main limiting parameter for the use of Plate Heat Exchangers as vapour generators. In this case, the pressure drop may considerably change the boiling temperature of the solution entering the heat exchanger and therefore a higher heating fluid temperature may be required. A guideline to design these systems is proposedThis work has been partly supported by the ‘‘Ayuda a grupos” of CAM under the project numbers CCG07 UC3M/AMB 3412 and CCG08 UC3M/AMB 4227Publicad

Aging Impairs Reverse Remodeling and Recovery of Ventricular Function after Isoproterenol-Induced Cardiomyopathy

Abstract: Information about heart failure with reduced ejection fraction (HFrEF) in women and the potential effects of aging in the female heart is scarce. We investigated the vulnerability to develop HFrEF in female elderly mice compared to young animals, as well as potential differences in reverse remodeling. First, HF was induced by isoproterenol infusion (30 mg/kg/day, 28 days) in young (10-week-old) and elderly (22-month-old) female mice. In a second set of animals, mice underwent isoproterenol infusion followed by no treatment during 28 additional days. Cardiac remodeling was assessed by echocardiography, histology and gene expression of collagen-I and collagen-III. Following isoproterenol infusion, elderly mice developed similar HFrEF features compared to young animals, except for greater cell hypertrophy and tissue fibrosis. After beta-adrenergic withdrawal, young female mice experienced complete reversal of the HFrEF phenotype. Conversely, reversed remodeling was impaired in elderly animals, with no significant recovery of LV ejection fraction, cardiomyocyte hypertrophy and collagen deposition. In conclusion, chronic isoproterenol infusion is a valid HF model for elderly and young female mice and induces a similar HF phenotype in both. Elderly animals, unlike young, show impaired reverse remodeling, with persistent tissue fibrosis and cardiac dysfunction even after beta-adrenergic withdrawal