Drag reduction within radial turbine rotor passages using riblets

In this paper, reducing the friction losses in a radial inflow turbine rotor surface by adding engineered features (riblets) is explored. Initially, computational fluid dynamics analysis was used to study the operating mechanism of riblets and to test their ability to reduce drag within the rotor passage when running the turbine at the design point. Thereafter, riblets with different heights and spacing have been implemented at the rotor hub to study the effect of riblets geometry and arrangement on the drag reduction, which leads to determine the riblet geometry where the maximum benefit on turbine performance can be achieved. The effect of riblets on boundary layer development and on the secondary flow generation within the rotor passage has been examined. It was found that the introduction of riblets could reduce the wall shear stress at the hub surface, and on the other hand, they contribute to increasing the stream-wise vorticity within the rotor passage. The maximum wall shear reduction was achieved with riblet with relative height hrel = 2.5% equivalent to 19.3 wall units, while the maximum performance happens when using riblets with hrel = 1.5% equivalent to 11.8 wall units as the later contributes less in secondary flow generation within the passage. For riblets with height more than 19.3 wall units, the overall effect is negative, as they cause an increase in drag and give rise to secondary flow leading to lower turbine performance

Thermal conductivity of heterogeneous mixtures and lunar soils

The theoretical evaluation of the effective thermal conductivity of granular materials is discussed with emphasis upon the heat transport properties of lunar soil. The following types of models are compared: probabilistic, parallel isotherm, stochastic, lunar, and a model based on nonlinear heat flow system synthesis

Mean-Line Design of a Supercritical CO2 Micro Axial Turbine

Supercritical carbon dioxide (sCO 2 ) power cycles are promising candidates for concentrated-solar power and waste-heat recovery applications, having advantages of compact turbomachinery and high cycle efficiencies at heat-source temperature in the range of 400 to 800 ∘ C. However, for distributed-scale systems (0.1–1.0 MW) the choice of turbomachinery type is unclear. Radial turbines are known to be an effective machine for micro-scale applications. Alternatively, feasible single-stage axial turbine designs could be achieved allowing for better heat transfer control and improved bearing life. Thus, the aim of this study is to investigate the design of a single-stage 100 kW sCO 2 axial turbine through the identification of optimal turbine design parameters from both mechanical and aerodynamic performance perspectives. For this purpose, a preliminary design tool has been developed and refined by accounting for passage losses using loss models that are widely used for the design of turbomachinery operating with fluids such as air or steam. The designs were assessed for a turbine that runs at inlet conditions of 923 K, 170 bar, expansion ratio of 3 and shaft speeds of 150k, 200k and 250k RPM respectively. It was found that feasible single-stage designs could be achieved if the turbine is designed with a high loading coefficient and low flow coefficient. Moreover, a turbine with the lowest degree of reaction, over a specified range from 0 to 0.5, was found to achieve the highest efficiency and highest inlet rotor angles

Multi-Objective Optimisation of A Centrifugal Compressor for a Micro Gas Turbine Operated by Concentrated Solar Power

Solar powered micro-gas turbines (MGTs) are required to work over a wide range of operating conditions due to the fluctuations in the solar insulation. This means that the compressor has to perform efficiently over a wider range than in conventional MGTs. To be able to extend the efficient operating range of a compressor at the design stage, both impeller blades and diffuser passage need to be optimised. Vaneless diffusers could offer more flexibility to extend the operating range than typical diffuser vanes. This paper presents a methodology for the design and optimisation of a centrifugal compressor for a 6 kW micro-gas turbine intended for operation using a Concentrated Solar Power (CSP) system using a parabolic dish concentrator. Preliminary design parameters were obtained from the overall system specifications and detailed cycle analysis combined with practical constraints. The compressor’s geometry optimisation has been performed using a fast and computationally efficient method, which involves the Latin hypercube Design of Experiment (DoE) technique coupled with the response surface method (RSM) in order to build a regression model through CFD simulations. Three different RSM techniques were compared with the aim to choose the most suitable technique for this specific application and then a genetic algorithm was applied. The CFD analysis for the optimised compressor showed that the high efficiency operating range has increased compared to the baseline design. Cycle analysis for the plant has been performed in order to evaluate the effect of the new compressor design on the system performance. The simulations demonstrated that the operating range of the plant was increased by over 30%

L’exstrophie vésicale chez l’adulte: A propos de 5 cas

RésuméButle but de cette étude est d’analyser les particularités de l’exstrophie vésicale chez l’adulte, sur les plans psycho-social et chirurgical.Patients et méthodesil s’agit d’une étude rétrospective de 5 patients, âgés entre 18 et 25ans, hospitalisés pour prise en charge d’une exstrophie vésicale. Les scores ICIQ-SF et MCS-SF36 ont été utilisés pour évaluer respectivement la continence urinaire et la qualité de vie avant et après réalisation d’une urostomie de type de vessie iléo-coecale continente VICC.Résultatsune amélioration significative a été notée sur les plans de continence et qualité de vie: l’ICIQ-SF après 6 mois était de 4,2+- 4,02 contre 18,8+- 2,28 avant chirurgie (p=0,0003), et le MCS-SF à 6 mois était de 57,15+/-13,37 contre 37,2+/-13,22 avant chirurgie (p=0,045). Des complications stomiales à long terme ont été enregistrées.Conclusionl’urostomie continente à type de VICC améliore la qualité de vie et la continence des patients adultes ayant une exstrophie vésicale, mais au prix de complications stomiales à long terme.AbstractObjectivethe aim of this study is to analyze sexual, psycho-social and surgical particularities of bladder exstrophy in adulthood.Patients and methodsa retrospective study was performed including 5 patients, from 18 to 25 years old, admitted for management of bladder exstrophy. ICIQ-SF and MCS-SF36 scores were used to assess respectively urinary continence and quality of life before and after continent ileo-coecal bladder.Resultsa significant improvement was noted in both urinary continence and quality of life: the ICIQ-SF after 6 months was 4.2+/- 4.02 against 18.8+/- 2.28 before surgery (p=0.0003), and MCS-SF at 6 months was 57.15+/-13.37 against 37.2+/-13.22 before surgery (p=0.045). Stomal complications were recorded in the long term.Conclusionthe continent ileocoecal bladder improves the quality of life and urinary continence in adult patients with bladder exstrophy, but at the cost of long-term stomal complications

PROCEEDINGS AND PHOTO ALBUM FROM THE OFFICIAL PRESENTATION OF THE RELIGIOUS STUDIES LABORATORY (RELIGLAB) OF THE NATIONAL AND KAPODISTRIAN UNIVERSITY OF ATHENS

A special issue by Theophany Journal (Proceedings 1)A special issue by Theophany Journal (Proceedings 1

One year prognosis of young Middle Eastern patients undergoing percutaneous coronary interventions

Background: There is scarcity of data about the outcome in young Middle Eastern patients who undergo percutaneous coronary intervention (PCI). We sought to assess clinical and coronary angiographic features and one year outcome of young compared with older patients following PCI.Methods: Baseline clinical and coronary angiographic features and major cardiovascular events from hospital admission to one year were assessed in young patients (45 years of age).Results: Of 2426 patients; 308 (12.7%) were young. Young and older patients were predominantly males (76.3% vs. 79.8%; p=0.18) and had similar prevalence of hypertension, diabetes, dyslipidemia, and cigarette smoking. There were no differences between young and older patients in the rates of acute coronary syndrome as an indication for PCI (75.6% vs. 76.1%; p=0.90). The two groups had similar prevalence of one-vessel coronary artery disease (55.2% vs. 58.1%; p=0.37) and intervention for one vessel (74.0% vs. 72.1%; p=0.53). No significant differences were observed in the incidence of in-hospital adverse events in young compared with older patients. Incidence of adverse events in young patients at one year were not different from those in older patients, including cardiac death (3.63% vs. 2.11%), stent thrombosis (3.63% vs. 2.08%), major bleeding (1.30% vs. 1.18%), and coronary revascularization (3.65% vs. 3.24%); all p=NS.Conclusions: Among Middle Eastern patients undergoing coronary intervention; 13% were 45 years of age or younger. No favourable risk profile, coronary angiographic features or cardiovascular outcome were observed in young compared with older patients

Sensitivity of transcritical cycle and turbine design to dopant fraction in CO2-based working fluids

Supercritical CO2 (sCO2) power cycles have gained prominence for their expected excellent performance and compactness. Among their benefits, they may potentially reduce the cost of Concentrated Solar Power (CSP) plants. Because the critical temperature of CO2 is close to ambient temperatures in areas with good solar irradiation, dry cooling may penalise the efficiency of sCO2 power cycles in CSP plants. Recent research has investigated doping CO2 with different materials to increase its critical temperature, enhance its thermodynamic cycle performance, and adapt it to dry cooling in arid climates. This paper investigates the use of CO2/TiCl4, CO2/NOD (an unnamed Non-Organic Dopant), and CO2/C6F6 mixtures as working fluids in a transcritical Rankine cycle implemented in a 100 MWe power plant. Specific focus is given to the effect of dopant type and fraction on optimal cycle operating conditions and on key parameters that influence the expansion process. Thermodynamic modelling of a simple recuperated cycle is employed to identify the optimal turbine pressure ratio and recuperator effectiveness that achieve the highest cycle efficiency for each assumed dopant molar fraction. A turbine design model is then used to define the turbine geometry based on optimal cycle conditions. It was found that doping CO2 with any of the three dopants (TiCl4, NOD, or C6F6) increases the cycle’s thermal efficiency. The greatest increase in efficiency is achieved with TiCl4 (up to 49.5%). The specific work, on the other hand, decreases with TiCl4 and C6F6, but increases with NOD. Moreover, unlike the other two dopants, NOD does not alleviate recuperator irreversibility. In terms of turbine design sensitivity, the addition of any of the three dopants increases the pressure, temperature, and expansion ratios across the turbine. The fluid’s density at turbine inlet increases with all dopants as well. Conversely, the speed of sound at turbine inlet decreases with all dopants, yet higher Mach numbers are expected in CO2/C6F6 turbines

Heat Transfer Effect on Micro Gas Turbine Performance for Solar Power Applications

This paper presents an experimentally validated computational study of heat transfer within a compact recuperated Brayton cycle microturbine. Compact microturbine designs are necessary for certain applications, such as solar dish concentrated power systems, to ensure a robust rotodynamic behaviour over the wide operating envelope. This study aims at studying the heat transfer within a 6 kWe micro gas turbine to provide a better understanding of the effect of heat transfer on its components’ performance. This paper also investigates the effect of thermal losses on the gas turbine performance as a part of a solar dish micro gas turbine system and its implications on increasing the size and the cost of such system. Steady-state conjugate heat transfer analyses were performed at different speeds and expansion ratios to include a wide range of operating conditions. The analyses were extended to examine the effects of insulating the microturbine on its thermodynamic cycle efficiency and rated power output. The results show that insulating the microturbine reduces the thermal losses from the turbine side by approximately 11% without affecting the compressor’s performance. Nonetheless, the heat losses still impose a significant impact on the microturbine performance, where these losses lead to an efficiency drop of 7.1% and a net output power drop of 6.6% at the design point conditions

Residential Micro-CHP system with integrated Phase change material thermal energy storage

This paper presents an analysis and experimental investigation of the effect of integrating Phase Change Material (PCM) within a heat exchanger within a Micro Combined Heat and Power (Micro-CHP) system intended for residential applications. A commonly used Micro-CHP layout is replicated in a test rig to characterise the performance of two alternative heat exchanger arrangements. The first is a conventional arrangement where the exhaust gas produced by the prime mover is directed to an air-to-water heat exchanger to heat water and store it in a tank. In the second arrangement, PCM material is encapsulated within specially designed compartments in a heat exchanger to store part of the exhaust thermal energy from the prime mover while heating the water in the storage tank. The time needed to heat the water and discharge heat is compared for both cases, as well as the amount of thermal energy stored during the same operating period. The study also explored the potential to improve the designed unit by using different PCM materials. The test results show that adding 4.7 L capacity paraffin compartments within the heat exchanger extended the discharge time of the hot water by over 400 %, which reflects a marked improvement in the heat storage capacity of the system. This would result in a significant increase in the viable operating period of a CHP system. The one-dimensional analysis revealed that replacing the paraffin with ClimSel C58 PCM can reduce the charging time of the water tank by around 54 % improve the heat storage capacity by factor of 2.35 comparing to Paraffin. The proposed heat exchanger with encapsulated PCM has a potential in other applications such as storage of excess renewable energy or integration with heat pumps to improve matching of supply and demand and thus flexibility of an energy system with integrated intermittent renewables