Thermal Energy Losses During Night, Warm-up and Full-Operation Periods of a CSP Solar Field Using Thermal Oil☆

Abstract In Concentrating Solar Power (CSP) systems, solar radiation allows to keep the Heat Transfer Fluid (HTF) at the design temperature (250-400 °C using thermal oil) during daylight. During night, the thermal losses of the receiver tubes lead to a fast reduction of this temperature. The very first hours of daily solar irradiance are used to warm-up the Solar Field to the nominal temperature. This work focuses on a detailed analysis of the thermal losses of a 8,400 m 2 Solar Field based on Linear Fresnel Collectors (LFC) using thermal oil as Heat Transfer Fluid. The proposed simulation model evaluates the performance of the Solar Field as a function of solar radiation, solar position, ambient temperature and wind speed for given values of the main geometrical and technical characteristics of the SF components (insulated piping and solar receivers), as well as for assigned thermodynamic properties of the Heat Transfer Fluid. The time-step considered (1 second) and the dense spatial discretization chosen allow the energy-balance-equation-based model to be suited to simulate night, warm-up and full-operation phases

Modelling, design and analysis of innovative thermal energy storage systems using PCM for industrial processes, heat and power generation

The topic of this PhD thesis is framed on the study and the analysis of thermal energy storage (TES) systems based on phase change materials (PCM) to be used as a back-up for intermediate temperature applications (up to 250 °C). The work is divided in two part: the first part presents the development of numerical models of the latent heat thermal energy storage (LHTES) devices. Different models are developed by means of a 2D and 3D numerical simulation codes specifically implemented in the COMSOL Multiphysics environment. Design of LHTES requires knowledge of the heat transfer process within them, as well as the phase change behaviour of the PCM used. For simulate the PCM, two approaches are used: the first approach takes only into account heat transfer by conduction during the entire process, also when the PCM is in the liquid phase. In the second, the energy equation considering both heat conduction and natural convection is solved to predict the behaviour of the PCM. Different PCM materials, geometries and configurations of the storage device are considered and tested in order to evaluate the effectiveness of the adopted numerical codes under different working conditions. Finally, the models are validated using experimental data obtained from tests carried out on a double tube heat exchanger with fins and with Rubitherm® RT35 paraffin as PCM. The tests are conducted in the laboratories of the University of Lleida (Spain) by the research group GREA Innovació Concurrent. The second part of this work concerns the design and implementation of a test rig, specifically built for experimental investigation of heat storage devices in the laboratory for TES technologies of the University of Cagliari. An accurate study and selection of both the test rig layout and all the needed equipment is carried out to perform experimental analysis. The test bench is composed of an electrical heater, which heats the HTF up to the operating temperature, an air cooler, which simulate the thermal demand during the discharge phase, a HTF circulating pump, two test sections for thermal energy storage systems, and a preliminary TES device which consists in a shell and tube heat exchanger, where the HTF flows in the tubes while the PCM is placed in the shell side. At this stage, the thermal energy storage system, the measuring devices and the data acquisition system are under implementation

STATEFUL METHOD FOR ACCESS POINT DISCOVERY OF WIRELESS LOCAL AREA NETWORK CONTROLLER

Access points (APs) for a wireless local area network (WLAN) can discover a wireless LAN controller (WLC) address (in order to establish a management session with the WLC) through a variety of mechanisms, such as Dynamic Host Configuration Protocol (DHCP) option 43 mechanisms, Domain Name System (DNS) server mechanisms, and Layer 2 (L2) broadcast discovery mechanisms. The DHCP discovery mechanism is the most commonly used mechanism for WLC discovery but is a laborious and manual task that may be prone to errors. Techniques proposed herein provide an easy to use, stateful, and reliable mechanism through which an AP can discover a WLC by leveraging a DHCP relay agent that can forward DHCP packets between clients and servers. The techniques involve various functionalities including, but not limited to, a stateful process that can be used to measure reachability and latency to each configured WLC Internet Protocol (IP) address, the creation of an updated priority list of WLC IP addresses based on network latency, and the inline insertion of the list of WLC IP addresses in the DHCP exchange between a server and AP

Numerical investigation on a packed-bed LHTES system integrated into a micro electrical and thermal grid

Currently, energy storage systems are considered a key solution when mismatch occurs between energy supply and demand, allowing a more ecient energy deployment and use. The present paper is focused on the study of a latent heat thermal energy storage (LHTES) system based on a packed bed of encapsulated phase change material (PCM) of spherical shape, conceived as an auxiliary component of a micro-grid to be built in a Research Center located in southwestern Sardinia (Italy). The main purpose of this work was to perform numerical simulations for predicting the performance of the TES system, designed to store the surplus thermal energy produced during the weekend by a heat pump fed by a photovoltaic (PV) plant. The stored energy would then be utilized during the weekdays to integrate the air-conditioning system supply. The numerical simulations were based on a one-dimensional (1-D) two-equation transient model, able to return the thermocline profile of the water and the PCM separately. The behavior of the LHTES device during charge and discharge phases was reproduced, as well as during the standby periods. Finally, two characteristic indexes of the PV system were evaluated, to investigate the eect of TES on grid interchanges, self-consumption, and self-suciency

Use of partial load operating conditions for latent thermal energy storage management

A proper management of thermal energy storage (TES) charging and discharging processes allows the final users to optimize the performance of TES systems. In this paper, an experimental research is carried out to study how the percentage of charge in a latent heat TES system (partial load operating conditions) influences the discharge process. Several charging and discharging processes were performed at a constant heat transfer fluid (HTF) mass flow rate of 0.5 kg/s and temperature of 155 °C and 105 °C, respectively. High density polyethylene (HDPE) with a total mass of 99.5 kg was used as phase change material (PCM) in a 0.154m3 storage tank based on the shelland-tube heat exchanger concept. Five different percentages of charge have been studied: 58 %, 73 %, 83 %, 92 %, and 97 % (baseline test). Results showed that by modifying the percentage of charge, the time required for the charging process was reduced between 97.2% and 68.8% in comparison to the baseline case. However, the energy accumulated was only reduced a maximum of 35.1% and a minimum of 5.2%, while the heat transfer rates during the first 60 min of discharge were reduced a maximum of 45.8% and a minimum of 6%. Therefore, partially charging the TES system not lower than 85% of its maximum energy capacity becomes a good option if the final application accepts a maximum decrease of discharging heat transfer rates of 10% if compared to the fully charged system.The work was partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER), ENE2015-64117-C5-3-R (MINECO/FEDER), and ULLE10-4E-1305). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. This project has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) under Grant agreement No. PIRSES-GA-2013-610692 (INNOSTORAGE) and from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 657466 (INPATH-TES). Jaume Gasia would like to thank the Departament d'Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya for his research fellowship (2017 FI_B1 00092). Alvaro de Gracia would like to thank Ministerio de Economia y Competitividad de España for Grant Juan de la Cierva, FJCI-2014-19940. Simone Arena would like to thank the Department of Mechanical, Chemical and Materials Engineering of the University of Cagliari for funding his research grant

Thermo-fluid Dynamic Analysis of a CSP Solar Field Line During Transient Operation

Abstract Concentrating Solar Power (CSP) technology allows to produce high temperature thermal energy from solar radiation. The thermal energy can be converted into electricity or it can be directly used for industrial processes. Most of the available simulation models of CSP plants evaluate the behavior of the solar field in stationary conditions, neglecting transient thermo-fluid-dynamic effects. Nevertheless, the study of the dynamic behavior of the solar field is a very challenging and interesting task and allows obtaining useful information for the design and the effective management strategies of CSP plants. This paper presents a thermo-fluid-dynamic analysis of asolar field line of the CSP plant currently under construction in Ottana, Sardinia (Italy), which uses thermal oil as heat transfer fluid. Dynamics of the system due to solar irradiance variations have been evaluated by using an axisymmetric unsteady 2D numerical model developed in Comsol® to evaluate the oil temperature distribution along the receiver tube for different operating conditions. The results have been compared with those obtained with a simpler, non-stationary one-dimensional model, developed in Matlab® environment. The comparative analysis show very similar results for the two models and demonstrate that the dynamic effects on the temperature distribution along the solar field line are not negligible

CFD Analysis and optimization of the DEMO WCLL central outboard segment bottom-Cap elementary cell

In the design of magnetic confinement nuclear fusion power plants, the Breeding Blanket (BB) plays a crucial role, since it must fulfil key functions such as tritium breeding, radiation-shielding and removing of the heat power generated by the plasma. The latter task is achieved by the First Wall (FW) and Breeding Zone (BZ) cooling systems, that in the Water-Cooled Lithium-Lead (WCLL) BB employs pressurized water. Different arrangements of BZ coolant conduits have been investigated in the recent past to identify an efficient layout, which could meet the structural materials operational temperature constraint and that could provide the optimal coolant outlet temperature. However, most of the Computational Fluid-Dynamic (CFD) analysis carried out until now have been focused on the equatorial WCLL elementary cell of the Central Outboard Segment (COB). The aim of this work is to broaden the analysis to other relevant locations in the blanket. An assessment of the design of the cooling system of the COB bottom-cap elementary BZ cell has been identified as the top design priority due to its different geometry and thermal loads. The cooling efficiency of the BZ and FW systems is investigated to assess if the coolant appropriate design conditions are matched and the temperature distribution in the cell is analyzed to identify the onset of hot spots. Different layouts of the FW systems are proposed and compared in terms of thermal-hydraulics reliability

Numerical analysis of a latent heat thermal energy storage system under partial load operating conditions

One of the features that should be considered when designing a thermal energy storage (TES) system is its behaviour when subjected to non-continuous (partial loads) operating conditions. Indeed, the system performance can be sensibly affected by the partial charging and discharging processes. This topic is analysed in the present study by means of a two-dimensional axisymmetric numerical model implemented in COMSOL Multiphysics. A latent heat TES system consisting of a vertical concentric tube heat exchanger is simulated to investigate the effect of different partial load operating conditions on the system behaviour. The effects of different heat transfer distributions and evolutions of the solid-liquid interface, are evaluated to identify the optimal management criteria of the TES systems. The results showed that partial load strategies allow to achieve a substantial reduction in the duration of the TES (up to 50%) process against a small decrease in stored energy (up 30%). The close correlation between the energy and the duration of the TES cycle is also evaluated during the discharge using detailed maps related to the melting fraction. These maps allow for the evaluation of the most efficient load conditions considering both charging and discharging processes to satisfy a specific energy demand.Simone Arena and Efisio Casti would like to thank the Department of Mechanical, Chemical and Materials Engineering of the University of Cagliari for their founding research grants. The work was partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER)). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. Jaume Gasia would like to thank the Departament d'Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya for his research fellowship (2017 FI_B1 00092)

Numerical simulation of a finned-tube LHTES system: influence of the mushy zone constant on the phase change behaviour

This work presents a numerical investigation on latent heat thermal energy storage (LHTES) systems during the phase change process. The numerical analysis, based on the apparent heat capacity formulation, was carried out through a two-dimensional axisymmetric numerical model developed by means of the COMSOL Multiphysics software. A thermal energy storage system based on the configuration of a double tube heat exchanger with finned surfaces was used as an experimental test case and the commercial paraffin RT35 was selected as phase change material (PCM). The influence of the heat transfer by convection, in particular the influence of the term describing the mushy zone in the momentum equation, was investigated during the whole charge and discharge processes. Three different values of the constant Amush, equals to 104, 106 and 108 were selected as well as two different values of the HTF volumetric flow rate were adopted in order to reproduce both laminar and turbulent flow regimes. The results are reported in terms of temperature, melting fraction and phases evolution during the whole melting and solidification processes, and compared to previous experimental tests carried out in the laboratories of the University of Lleida, Spain. A good agreement with the experimental results was obtained showing that the mushy zone constant has a significant influence on the interface shape and motion. The results show that large values of Amush determine an increase of the mushy region reducing the natural convection effects during the charge phase. Thus, the proper evaluation of the mushy zone constant allows providing a deeper understanding of the phase change behaviour, resulting in an important parameter for accurate modelling of LHTES systems.The work was partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER)). Jaume Gasia and Prof. Luisa F. Cabeza would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. This project has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) under Grant agreement Nº PIRSES-GA-2013-610692 (INNOSTORAGE) and from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 657466 (INPATH-TES). Jaume Gasia would like to thank the Departament d'Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya for his research fellowship (2017 FI_B1 00092)

Denture as an unexpected cause of obstructive jaundice

A 78-year-old woman who presented with jaundice and fever was referred from another hospital to our endoscopy unit. Her laboratory tests revealed a total bilirubin concentration of 11.7 µmol/L. Computed tomography (CT) scans revealed dilatation of the main biliary duct and the presence of a foreign body in the peripapillary area ([Fig. 1]). The appearance of the foreign body was suggestive of a denture, and the patient reported having involuntary ingested, 3 days previously, a denture that had been implanted many years ago. We performed an endoscopic retrograde cholangiopancreatography (ERCP), which revealed a protruding papilla with the appearance of an impacted stone. We started to perform a sphincterotomy using a precut needle-knife and completed it with a standard sphincterotome. After this, the denture was immediately expelled and allowed to pass into the duodenum ([Video 1]). In the following days, the patient’s total bilirubin level decreased and she was discharged home