Potential assessment of using dry cooling mode in two different solar thermal power plants.

Most of Concentrating Solar Power (CSP) plants are usually installed in desert regions where water resource availability is a critical limitation due to the lack of water required for the exploitation of these systems in these regions. Therefore, the aim of this study is to investigate the techno-economic competitiveness of deploying both modes of cooling (wet and dry) in two different parabolic trough solar thermal power plants integrated with thermal energy storage and fuel backup system; the first one is using thermic oil, while the other is working using molten salt. The obtained results show that the dry cooling mode can decrease the yields of the two power plants down to 8.7 % and 9.3 % for oil and salt configurations respectively. On the other hand, the levelized cost of electricity can increase by using this cooling option up to 9.3 % for oil plant, and 10.0 % for salt one. However, the main advantage of using dry cooling option is reducing water consumption which has been decreased by more than 94 % for both plants. The application of our methodology to other two sites worldwide, confirms the viability of the obtained results. The importance of this results is to show the effect of working fluids on the cooling system of solar power plants

The effect of zeitgeber (fasting and exercise) on phase advance blood glucose circadian rhythms in endurance athletes

Fasting is usually associated with changes in the metabolic, psychological and physiological responses of athletes; advancing and/or delaying their biological clock and therefore, affecting their sport performance. The aim of this study was to assess the effect of Ramadan fasting on blood glucose level, mean arterial pressure (MAP), heart rate (HR) and skin temperature in 11 experienced endurance athletes. Blood finger-pricking, blood pressure (BP), HR and skin temperature samples were taken every 2 hours over a 24-hr period during the 3 rd or 4 th weeks of Ramadan. A clear within-day variation was revealed in blood glucose concentrations and HR (

Diurnal variation in physiological, psychological and immune responses to running 10 km time trials performed in hot and cold environments

Purpose: To investigate the physiological, immunological and psychological response to an intense bout of exercise performed by highly trained individuals at 09:00 hs and 16:00 hs (Chapter 5) and at 09:00 hs and 18:00 hs (Chapter 6). Methods: Using a crossover randomized design, 7 and 13 well trained runners (range V̇O2max 61-79 ml.kg-1min-1) performed a 10 km time trial run, in two contrasting environments: cold (6°C) and hot (28°C and 70% relative humidity), at 2 different times of day (09:00 hs and 18:00 hs or 16:00 hs). Lung function tests and blood samples were taken immediately pre-, post- and 1h post-trial to determine, total WBC counts, WBC variables, total RBC counts, RBC variables, IL-6, CC16 and HSP70 levels. Nasal lavage procedure for the analysis of upper respiratory airway was conducted pre-, post- and 1h post-trial. Core body temperature, heart rate, power, strength and flexibility as well as RPE, mood, arousal and alertness were measured pre-, post-trial and 1h post- trial at both times of the day. Results: The time taken to complete the trial was not significantly different in both studies but was faster at 09:00 hs under hot environmental conditions. During the time trial, core body temperature was significantly higher at 18:00 hs (P < 0.05) under hot and humid conditions, whereas, heart rate and core body temperature were higher at 09:00 hs in the cold environment. A significant diurnal difference (P < 0.05) was found for total WBC, neutrophil and lymphocyte counts with higher values at the evening in both studies. Plasma CC16 and total RBC and RBC variable counts were not affected by the time of the day in the cold condition. Resting IL-6 and CC16 as well as HSP70 at 1 h post-trial were significantly higher in the morning, whereas, HSP70, total RBC and RBC variables counts were not affected by the time of the day in hot and humid conditions. Similarly no significant differences were observed in power, strength or flexibility in these conditions. Most psychological measures were not affected by the time of the day in either environmental condition. However, recovery arousal at 09:00 hs was significantly higher (P < 0.05) in the hot and humid condition. Conclusion: a 10 km time trial run, in both environmental conditions, can cause different physiological and immunological responses dependent on the time-of-day in which it is performed. Nevertheless in highly trained runners this variation was not enough to impact on their performance. Despite no statistically significant difference in diurnal running performance in the hot and humid condition a 19 second mean difference in completion time would decide the race winner or even new records

Numerical study of a hybrid photovoltaic/thermal PVT solar collector using three different fluids

Hybrid photovoltaic and thermal (PV/T) systems have been widely used for the combination of PV modules and solar thermal collectors to generate both electrical energy and heat at the same time. In the present work, a numerical model has been developed to simulate the performances of a hybrid photovoltaic/thermal (PV/T) solar collector. Furthermore, a comparative study has been performed between the hybrid PV/T working with three conventional working fluids; air, water, and specified nanofluid (AL2O3+ water). The obtained results show that the use of the Alumina nanofluid is the best choice to increase the heat removal, and to improve the performances of the collector with the values of 73.28%, 10.37% and 99.21% for the thermal, the electrical and the global efficiency respectively. On the other hand, the PVT collector working with air as the primary fluid is the worst in terms of electrical, thermal, and global performances with the lowest values of 9.506 %, 41.55%, and 65.315% respectively

4E (Energy-Exergy-Economic-Environmental) performances assessment of different configurations of power cycles

Steam power plants are alimented by different sources of energy including fossil fuels or renewable ones such as solar thermal, biomass or geothermal. Thus, thermodynamic, economic and environmental analyses of different steam power cycles are highly required for identification and choice of the most effective and viable layout to be adopted in the installation. Consequently, the main aim of the present paper is to compare five different configurations of power cycles in terms of energy and exergy efficiencies, fuel and cooling water consumptions, CO2 emissions rate, as well as investment and operating costs, and net present value (NPV). The obtained results present relevant differences; the energy and exergy efficiencies of the fifth configuration similar to the one of Achouat power station are the highest with 41.9% and 39.5% respectively. On the other hand, this configuration shows better environmental performances represented by CO2 emission (46.12 kg/s), and water consumption for cooling (7.42 m3/s). Economically, there is a clear convergence in the NPV values for configurations with Reheating and Regeneration processes. Moreover, the fourth configuration is the best in terms of net present value (NPV) of 103.1(M€)

Potential for N pollution swapping from riparian buffer strips and an instream wetland

Diffuse agricultural pollution is a major contributor to poor water quality in many parts of the world. Consequently agri-environment policy promotes the use of riparian buffer strips and/or denitrifying wetlands to intercept and remove diffuse NO3--N pollution. However, these methods have the potential to cause ‘pollution swapping’: the exchange of one form of pollution as a result of measures implemented to reduce another. Thus the benefits of intercepting NO3--N could be offset by enhanced emissions of the potent greenhouse gases, nitrous oxide (N2O) and methane (CH4), from buffer strips and wetlands. This research aimed to: (1) quantify the direct N2O emissions from an irrigated buffer strip (IBS), using nitrate-rich agricultural drainage water, compared to a non-irrigated control (CP); (2) improve the understanding of N2O production and consumption within soils using controlled soil monolith experiments; (3) assess the effectiveness of a small (60 m2) instream wetland at intercepting and removing diffuse NO3--N pollution, and quantify pollution swapping in the form of CH4 and N2O emissions; (4) assess the production of CH4 and N2O within the sediment, and their emissions as well as inorganic-N concentrations in the overlying water column in response to temperature and turbulence, using intact wetland sediment and membrane inlet mass spectrometry (MIMS). The research focused on mitigating diffuse NO3--N pollution from grazed pasture at a farm in north-east England. Annual N2O-N emissions from the IBS and CP were not statistically different (P > 0.05): 509 and 263 g N2O-N ha-1, respectively, in 2007 and 375 and 500 g N2O-N ha- 1 year-1, respectively, in 2008. Irrigation of the IBS increased spatial variability in flux and generated hotspots of denitrification compared to the CP. However, these changes were short-lived. Direct N2O emission factors (EF1) calculated using the available NO3--loading data (September 2007 - December 2008) for the IBS were lower (c.0.1%) than those calculated for the CP assuming N input from biological N fixation only (<1.9%). Soil monolith experiments under a variety of irrigation and NO3--N loading regimes confirmed low direct and indirect (of dissolved N2O-N in leachate) emissions (<3.1 and <2.3% of applied NO3--N emitted as N2O-N, respectively), similar to the IPCC default emission factors. However, N loss in leachate was high, up to 82% of added NO3--N with concentrations reaching 24 mg NO3--N L-1. Therefore even though no pollution swapping occurred the high leachate losses indicate irrigation of buffer strips are not effective mitigation methods. Monitoring for 2 years of the instream wetland that received median NO3--N concentrations of c. 6 mg N L-1, but up to c. 20 mg N L-1, showed it to be ineffective at intercepting diffuse NO3- pollution: likely a result of the relatively high discharge and short water residence time, as well as the direct input of NO3--N to the wetland from secondary sources: field drains and/or overland flow. The wetland was a net source of NH4+-N in both 2007 and 2008, and a net sink of NO3--N in 2007 only. Annual wetland CH4 and N2O emissions were 713 and 237 mg CH4 m-2 year-1, and 3.5 and 1.9 mg N2O-N m-2 year-1, for 2007 and 2008, respectively and were highly variable between seasons. N pollution swapping was minimal from either direct or indirect emissions, but CH4 emissions were found to be of greater importance at a net cost of ~ £600 ha-1 over the study period (2007 to 2008), compared to N2O emissions (~ £60 ha-1) and low NO3--N interception savings (~ £24 ha-1). Incubation experiments suggest that spatially variable microsites of nitrifying, denitrifying or methanogenic activity and CH4 oxidation occur within the wetland sediment. Therefore off-line, larger wetland systems offer the best prospects of enhanced NO3--N interception and potentially reduced CH4 emissions by maintaining shallow water depths (increased CH4 oxidation) and long residence times (increased opportunity for denitrification), within the wetland or wetland cells

Diurnal Variation in Physiological and Immune Responses to Endurance Sport in Highly Trained Runners in a Hot and Humid Environment

Purpose. The purpose of this study was to investigate the physiological and immunological response of highly trained runners to an intense bout of exercise performed at two different times of day, in a hot, humid environment. Methods. Using a crossover randomized design, 13 highly trained runners (range VO 2 max 64–79 ml·kg −1 min −1) performed a 10 km time trial run in hot (28 ° C) and humid conditions (70%), at 2 different times of day (09:00 hs and 18:00 hs). Venous blood samples were taken to determine WBCs (white blood cells), IL-6 (interleukin-6), CC16 (club cell protein 16), and HSP70 (heat shock protein-70) concentrations. Upper respiratory tract inflammation was additionally assessed using a nasal lavage procedure. Results. A significant diurnal difference (p < 0 05) was found for core body temperature, total WBC, and neutrophil and lymphocyte concentrations with higher values at 18:00 hs. A phase response in IL-6, HSP70, WBC, neutrophil, lymphocyte, and CC16 was noted, being more pronounced at 18:00 hs, whilst core body temperature and HR phase responses were more pronounced at 09:00 hs. Conclusion. In hot and humid conditions, athletes may wish to consider, when possible, racing and particularly training in the morning where the least homeostatic perturbation occurs

Diurnal physiological and immunological responses to a 10-km run in highly trained athletes in an environmentally controlled condition of 6 °C

PurposeThe Clara cell protein CC16, secreted from Clara cells in the lung, is discussed as a potential biomarker for toxic effects on the airways. An increased concentration of CC16 in serum may be caused by increased permeability of the lungs. To investigate the changes in P-CC16 in response to an intense exercise bout performed at different times of day (9 am and 4 pm) of highly trained individuals.MethodUsing a crossover randomized design, 8 runners (mean VO2max 71 ml kg−1 min−1, SD 6) performed a 10-km time trial run, at 9 am and 4 pm, in an environmental chamber set at 6 °C. Lung function tests and blood sampling occurred at baseline, immediately post and 1 h post time trial.ResultDiurnal differences (P < 0.05) were found for blood neutrophil and lymphocyte counts; with higher values at 4 pm. P-CC16 was higher at the pre- and post-trial time point at 9 am compared to 4 pm. Lung function was not different between or within trials.ConclusionMorning trial in cold condition caused more physiological strain compared to the same trial in the evening. However, this extra stress caused by zeitgebers could be a useful strategy for athletes, coaches, and general population to improve their running performance and protect their health in cold conditions in the long-term plan

Modélisations physique et numérique des géostructures énergétiques

Energy geostructures are civil engineering structures equipped with energy exchanger elements in order to store heat seasonally. The aim of this study is the use of compacted soil to store energy through installation of horizontal exchangers in an embankment. During the soil compaction, two parameters were controlled: the water content w and the dry density ρd. This parameters as well as the soil nature, the mechanical load path and the cyclic temperature variation may affect the storage capacity and the system stability. This work includes an experimental part and a modeling part. In the experimental part, the impact of the temperature variation is studied on the thermal and mechanical properties of the compacted soil. The Plaisir loam (PL) extracted from the Paris region was investigated through laboratory tests at a temperatures range of 20 to 50°C. The results showed that the thermal properties of the compacted soils increased on the dry side of the compaction curve. This evolution was clearly confirmed for higher temperatures. The application of cyclic temperature variations showed reversible evolutions in the thermal properties after one cycle. The results of unconfined compressive tests and pressuremeter tests showed that heating induces a softening of the material whereas several temperature cycles induce a stiffening of the material. Thereafter, a coupled thermo-hydraulic modeling of an embankment made of the compacted Plaisir loam is performed in order to optimize the storage system. The comparison of different modelling results, fixed the temperature sensors spacing that minimizes the interactions between them, and the optimal distance between the last sensors and the bottom of the slope. It is shown that if an appropriate thermal program is chosen, the heat storage in the embankment could be possible. A better efficiency of the storage capacity can be reached by introducing 3 temperature sensors rows in the storage and by covering the storage with a thermal insulation. The simulation of this scenario over 10 years including temperature cycles shows a heating of the embankment for several years, until to reach an equilibrium state after the 7th yearLes géostructures énergétiques sont des ouvrages de génie civil qui intègrent un circuit de fluide caloporteur. Dans cette étude l’installation de circuits géothermiques dans des remblais est envisagé afin d’injecter ou d’extraire de la chaleur. Lors de la construction de ces remblais, deux paramètres sont à contrôler : la teneur en eau w (%) et la masse volumique sèche rd (Mg/m3). Ces deux paramètres ainsi que la nature du sol, le chargement appliqué et la variation cyclique de la température pourraient influencer la capacité de stockage et la stabilité du système. Après une partie synthétisant l’état de l’art sur ces thématiques, cette thèse comprend une partie expérimentale puis une partie numérique appliquée à un cas test de stockage. Dans la partie expérimentale, l’influence de la variation de température induite par l’échange thermique sur les propriétés thermiques et mécaniques du sol est étudiée. Pour cela des essais sont réalisés en laboratoire sur un limon du bassin parisien compacté et soumis à une gamme de variation de température de 20° à 50°C. Les effets de ces variations sur les paramètres mécaniques et les paramètres thermiques sont mesurés. Les résultats obtenus montrent une évolution des paramètres thermiques du matériau du côté sec de la courbe de compactage, particulièrement visible pour les températures importantes. La réversibilité de l’effet du chauffage est obtenue après plusieurs cycles de chauffage-refroidissement. Les propriétés mécaniques mesurées sont la résistance à la compression simple et les paramètres pressiométriques. Pour cela, des essais en laboratoire, à l’échelle métrique, sont réalisés. Un ramollissement du sol sous l’effet du chauffage et une rigidification sous l’effet des cycles thermiques sont constatés. Pour optimiser le système du stockage, une modélisation thermo-hydrique d’un remblai modèle réalisé avec le limon de Plaisir compacté légèrement du côté humide de l’optimum Proctor est effectuée. La comparaison des cas tests a permis de déterminer l’entraxe qui minimise l’interaction entre les sondes thermiques, ainsi que la distance optimale entre les dernières sondes et le pied de remblai. Les scenarii d’injection/extraction étudiés ont montré que le stockage de chaleur dans le remblai est faisable en choisissant un programme thermique adéquat pour l’exploitation du stockage. La mise en place de plusieurs lits de sondes thermiques et d’une isolation thermique sur la partie supérieure du remblai de stockage permet d’augmenter la capacité du remblai à accumuler de la chaleur dans le noyau à la fin de la période de relaxation. La simulation de ce scénario sur 10 ans avec la prise en compte des cycles de température, montre un réchauffement du remblai sur plusieurs années jusqu’à atteindre une évolution équilibrée au bout de la 7 ème année. Arrivé à cet état d’équilibre, l’évolution des températures est reproductible d’une année sur l’autr