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Computational fluid dynamics (CFD) predictions of film cooling performance for gas turbine airfoils are an important part of the design process for turbine cooling. Typically, industry relies on the approach based on Reynolds Averaged Navier Stokes equations, together with a two-equation turbulence model. The realizable k-ɛ (RKE) model and the shear stress transport k-ω (SST) model are recognized as the most reliable. Their accuracy is generally assessed by comparing to experimentally measured adiabatic effectiveness. In this study, the performances of the RKE and SST models were evaluated by comparing predicted and measured thermal fields in a turbine blade leading edge with three rows of cooling holes, positioned along the stagnation line and at ±25 deg. Predictions and measurements were done with high thermal conductivity models which simulated the conjugate heat transfer effects between the coolant flow and the solid. Particular attention was placed on the thermal fields along the stagnation line, and immediately downstream of the off-stagnation line row of holes. Conventional evaluations in terms of adiabatic effectiveness were also carried out. Predictions of coolant flows at the stagnation line were significantly different when using the two different turbulence models. For a blowing ratio of M = 2.0, the predictions with the SST model showed coolant jet separation at the stagnation line, while the RKE predictions showed no separation. Experimental measurements showed that there was coolant jet separation at the stagnation line, but the actual thermal fields obtained from experimental measurements were significantly different from that predicted by either turbulence model. Similar results were seen for predicted and measured thermal fields downstream of the off-stagnation row of holes.

Tests on a specifically designed linear nozzle guide vane cascade with trailing edge coolant ejection were carried out to investigate the influence of trailing edge bleeding on both aerodynamic and thermal performance. The cascade is composed of six vanes with a profile typical of a high pressure turbine stage. The trailing edge cooling features a pressure side cutback with film cooling slots, stiffened by evenly spaced ribs in an inline configuration. Cooling air is ejected not only through the slots but also through two rows of cooling holes placed on the pressure side, upstream of the cutback. The cascade was tested for different isentropic exit Mach numbers, ranging from M2is = 0.2 to M2is = 0.6, while varying the coolant to mainstream mass flow ratio MFR up to 2.8%. The momentum boundary layer behavior at a location close to the trailing edge, on the pressure side, was assessed by means of laser Doppler measurements. Cases with and without coolant ejection allowed us to identify the contribution of the coolant to the off the wall velocity profile. Thermochromic liquid crystals (TLC) were used to map the adiabatic film cooling effectiveness on the pressure side cooled region. As expected, the cutback effect on cooling effectiveness, compared to the other cooling rows, was dominant.

This study investigated the clinical application of a magnetic-resonance (MR)-guided breast biopsy (MRBB) system consisting of a nonmagnetic coaxial needle and a ferromagnetic core biopsy needle.MRBB was performed on 70 breast lesions. The biopsy device consisted of a nonmagnetic 14- to 16-gauge coaxial needle and a ferromagnetic 16- to 18-gauge biopsy needle.Of the 70 lesions, 29 were malignant and 41 nonmalignant. All 29 malignant lesions underwent surgery and were confirmed as malignant at final histology. Of the 41 nonmalignant lesions, 35 underwent follow-up breast MR imaging (mean, 26 ± 19 months), which demonstrated no lesions changes; six lesions underwent surgery because of poor radiological-pathological correlation; of these 6 lesions, 3 were nonmalignant, one was borderline (lobular carcinoma in situ) and two were malignant (well-differentiated tubular carcinoma and infiltrating ductal carcinoma). Sensitivity, specificity, positive and negative predictive values and diagnostic accuracy were, respectively, 93.5%, 100%, 100%, 95.1% and 97.1% if the lobular carcinoma in situ was considered a nonmalignant histological result, and 90.6%, 100%, 100%, 92.7% and 95.7% if the lobular carcinoma in situ was considered malignant.MRBB with a ferromagnetic-nonmagnetic coaxial system represented an easy way to perform a biopsy procedure and was easily applicable in the routine clinical setting.

The present work focuses on a modelling procedure to simulate the operation of a solar hybrid gas turbine. The method is applied to a power generation system including an heliostat field, a receiver and a 36 MW commercial gas turbine. Heat is provided by concentrated solar power and integrated by fossil fuel. A detailed modelling of the gas turbine (GT) is proposed to predict the performance of commercial GT models in actual operating conditions. Advanced software tools were combined together to predict design and off-design performance of the whole system: TRNSYS® was used to model the solar field and the receiver while the gas turbine simulation was performed by means of Thermoflex®. A detailed comparison between the solarized and the conventional gas turbine is reported, taking into account GT electric power, efficiency and shaft speed. All thermodynamic parameters such pressure ratio, air flow and fuel consumption were compared. The main advantage of solarization is the fossil fuel saving, but it is balanced by a relevant penalty in power output and efficiency.

In this study computational fluid dynamic simulations of a turbine blade with endwall film cooling were compared to measurements of both aerodynamic and thermal performance. The experimental data were collected at low Mach number (Ma2is = 0.3) in a linear cascade arrangement with 7 blades which geometry is typical of first stage high pressure turbine. A junction between the blade hub and the platform is provided by a 3D fillet. Coolant is injected through ten cylindrical holes distributed along the blade pressure side. Coolant to mainstream mass flow ratio was set to assure an inlet blowing ratio of M1 = 2.4 and M1 = 3.2. The simulations were carried out using the Shear Stress Transport (SST) k-ω turbulence model. Numerical predictions were compared against experimentally measured secondary flows and endwall film cooling effectiveness, at different injection conditions. Simulation results agreed with the experiments for what concerns the general shape and the location of secondary flows. However, some limitations in the modeling were highlighted when going into the details of loss computation and vortex structure. Predictions overestimated both secondary and midspan blade wake losses. Moreover, the effect of the fillet on the aerodynamic flow features was not fully captured. Predicted film cooling results showed the sweeping of coolant across the passage in agreement with experiments even though jets persistency was higher than that measured. Levels of adiabatic effectiveness were generally well simulated.

A modeling procedure was developed to simulate design and off-design operation of hybrid solar gas turbines in a combined cycle (CC) configuration. The system includes a heliostat field, a receiver, and a commercial gas turbine (GT) interfaced with a conventional steam Rankine cycle. Solar power input is integrated in the GT combustor by natural gas. Advanced commercial software tools were combined together to get design and off-design performance prediction: TRNSYS® was used to model the solar field and the receiver while the gas turbine and steam cycle simulations were performed by means of Thermoflex®. Three GT models were considered, in the 35–45 MW range: a single shaft engine (Siemens SGT-800) and two two-shaft engines (the heavy-duty GT Siemens SGT-750 and the aero derivative GE LM6000 PF). This was in order to assess the influence of different GT spool arrangements and control strategies on GT solarization. The simulation method provided an accurate modeling of the daily solar hybrid CC behavior to be compared against the standard CC. The effects of solarization were estimated in terms of electric power and efficiency reduction, fossil fuel savings, and solar energy-to-electricity conversion efficiency.

OBJECTIVE. Gadobutrol is an extracellular macrocyclic gadolinium chelate recently introduced in MRI, and it has already been used for cardiac late enhancement imaging; however, until now it has never been compared with gadopentetate dimeglumine. The purpose of our study was to compare 0.1 mmol/kg gadobutrol to 0.2 mmol/kg gadopentetate dimeglumine for the detection of myocardial late enhancement in the same group of patients. SUBJECTS AND METHODS. This was an exploratory single-blind parallel group study comparing gadobutrol (0.1 mmol/kg) to gadopentetate dimeglumine (0.2 mmol/kg) in 20 adult patients scheduled for cardiac late enhancement MRI with gadopentetate dimeglumine and whose MR images showed late enhancement. MR images were acquired at 10, 15, and 20 minutes after peripheral injection of gadobutrol by using a 3D turbo field echo inversion recovery T1-weighted sequence. Volume and percentage of late enhancement, number of involved segments, late enhancement localization and pattern, and late enhancement signal-tonoise ratio (SNR) and contrast-to-noise ratio (CNR) were compared between contrast agents. RESULTS. Late enhancement was not significantly different with gadobutrol and gadopentetate dimeglumine both in terms of total volume of myocardium (mean ± SD, 37.8 ± 56.1 and 35.1 ± 46.7 cm 3, respectively; p = 0.33) and percentage of myocardial wall involvement (22.5% ± 19.1% and 22.0% ± 17.2%, respectively; p = 0.67). The number of segments involved was not different (138 with gadobutrol vs 134 with gadopentetate dimeglumine). Furthermore, SNR and CNR were not different (gadopentetate dimeglumine, 123.8 ± 82.9 and gadobutrol, 117.2 ± 88.6, p = 0.58 and gadopentetate dimeglumine, 96.2 ± 68.9 and gadobutrol, 88.4 ± 72.9, p = 0.53, respectively). CONCLUSION. A single dose of gadobutrol seems to be as effective as a double dose of gadopentetate dimeglumine for the detection of late enhancement. © American Roentgen Ray Society

The present paper investigates the effects of the application of trenched holes in the front part of a contoured film cooled endwall. Two trench configurations were tested, changing the trench depth. Tests have been carried out at low speed (M2is=0.2) and low inlet turbulence intensity level, with coolant mass flow rate ratio varied within the 0.5–2.5% range. Pressure probe traverses were performed downstream of the vane trailing edge to show the secondary flow field modifications and to evaluate trench additional losses. Endwall distributions of film cooling effectiveness have been obtained by the thermochromic liquid crystal (TLC) technique. For each injection condition, energy loss coefficient and film cooling effectiveness distributions were analyzed and compared with the ones obtained from rows of cylindrical holes. Laterally and area averaged effectiveness as well as pitch and mass averaged kinetic energy loss coefficients were computed to enlighten any change induced by the introduction of trenched holes. A uniform and high thermal coverage was obtained in the region just downstream of the trench, but it quickly decayed because of enforced mixing of coolant with main flow. Compared with the cylindrical hole configuration, trenches are able to provide a higher global cooling effectiveness, but a larger amount of coolant injection is required. The introduction of both trenches is responsible for a secondary thermodynamic loss increase of about 0.7% at low coolant injection rates. Increasing the blowing rates, the additional loss vanishes.

In Brescia, Italy, heat is delivered to 70% of 200.000 city inhabitants by means of a district heating system, mainly supplied by a waste to energy plant, utilizing the non recyclable fraction of municipal and industrial solid waste (800,000 tons/year, otherwise landfilled), thus saving annually over 150,000 tons of oil equivalent and over 400,000 tons of CO2 emissions. This study shows how the performance of the waste-to-energy cogeneration plant can be improved by optimising the condensation system, with particular focus on the combination of wet and dry cooling systems. The analysis has been carried out using two subsequent steps: in the first one a schematic model of the steam cycle was accomplished in order to acquire a knowledge base about the variables that would be most influential on the performance. In the second step the electric power output for different operating conditions was predicted and optimized in a homemade program. In more details, a thermodynamic analysis of the steam cycle, according to the design operating condition, was performed by means of a commercial code (Thermoflex©) dedicated to power plant modelling. Then the off-design behaviour was investigated by varying not only the ambient conditions but also several parameters connected to the heat rejection rate, like the heat required from district heating and the auxiliaries load. Each of these parameters has been addressed and considered in determining the overall performance of the thermal cycle. After that, a complete prediction of the cycle behaviour was performed by simultaneously varying different operating conditions. Finally, a Matlab© computer code was developed in order to optimize the net electric power as a function of the way in which the condensation is operated. The result is an optimum set of variables allowing the wet and dry cooling system to be regulated in such a way that the maximum power is achieved. The best strategy consists in using the maximum amount of heat rejection in the wet cooling system to reduce the operational cost of the dry one.

Non-invasive imaging techniques have now completely replaced invasive angiography in the diagnosis of aortic disease. Among the non-invasive cardiovascular diagnostic methods, magnetic resonance imaging (MRI) holds a central role, beside ultrasonography and computed tomography. The main strengths of MRI in the setting of aortic disease lie in the large spectrum of techniques available, which give the possibility of studying any single aspect of the patient’s aortic disease, ranging from characterization of an aortic wall thickening, to precise measurements of the vessel diameter, as well as functional and quantitative evaluation of the vessel flow. Moreover, the recent technological advances have improved magnetic resonance performance and have further expanded the techniques available, making MRI more suitable also for application in the emergency setting.

The main goal of this work was to evaluate the influence of impingement cooling on the cooling performance on a film cooled turbine blade leading edge. Cooling performance was quantified in terms of overall effectiveness, i.e. the normalized external surface temperature. Numerical simulations, using the commercial code FLUENT, were carried out for a leading edge model corresponding to an experimental model tested previously. The leading edge geometry consisted of three rows of holes positioned along the stagnation line and at ±25°. Three different impingement plate configurations were investigated. Two impingement plate configurations had a single row of holes along the center so that the impingement jets were directed on the stagnation line in between coolant hole entrances. These configurations had varying hole diameters such that impingement jet velocity varied by a factor of two. The third impingement plate configuration had two rows of holes with each row was placed in between the coolant hole entrances along the off stagnation lines. A configuration with no impingement plate was also investigated. For these simulations the realizable k-e turbulence model was used. All experimental conditions were matched including the density ratio of 1.5 and blowing ratios of 1.0 and 2.0. The numerical simulations were consistent with experiments in showing that the overall effectiveness was only slightly improved by the impingement cooling. This small effect on overall effectiveness was shown to be due to conjugate effects including a reduction of convective cooling within the coolant holes when impingement cooling was used.Copyright © 2010 by ASME

This paper focuses on the legitimacy of using conventional predictions, based on adiabatic wall temperature (Taw ) and heat transfer coefficient (HTC) augmentation, of heat flux into a film cooled leading edge. To answer this question, the heat flux predicted using Taw was compared to the heat flux into a conducting leading edge. The study used numerical simulations with the k-e turbulence model of FLUENT. The model simulated was a three-row leading edge with one row of holes on the stagnation line and two additional rows located at ±25°, which has been experimentally studied extensively. The adiabatic wall temperature was obtained from an adiabatic simulation. External heat transfer coefficients were determined from a constant heat flux simulation using a density ratio of DR = 1.0, as is commonly done experimentally. A conjugate heat transfer simulation was also run to give the surface temperature and heat flux into the conducting leading edge. Overall, the heat transfer was well predicted with the use of Taw and HTC augmentation. However, between the holes, conventional predictions of heat transfer were poor, with disparity up to 30% when compared with the conducting wall heat flux obtained from the conjugate heat transfer simulation. Thermal boundary layer profiles were used to understand the disparity between the heat fluxes obtained from the conventional prediction and the conducting wall simulation.Copyright © 2010 by ASME

The present paper shows the results of an experimental investigation into a nozzle vane cascade with endwall contouring and film cooling. In a film cooled endwall the front area, especially close to the leading edge, is one of the most critical regions to be cooled; in case of a contoured endwall the thermal protection becomes even more difficult because of the endwall curvature effect. Two film cooling hole geometries with four rows of holes were tested: cylindrical holes and conical expanded holes. Tests were performed at low speed (M2is = 0.2) and low inlet turbulence intensity level, with coolant to main stream mass flow ratio varied within the 0.5–2.5% range. Aerodynamic and thermal performances were evaluated in every injection condition. Compared to cylindrical holes, results showed that shaped film cooling holes generate slightly higher secondary losses and provide a better thermal coverage, at the expense of a higher coolant flow injection.

Il cuore e una pompa muscolare che crea un flusso pulsato unidirezionale grazie alla sequenza ritmica di rilasciamento (riempimento) e contrazione (svuotamento), governata dall’eccitazione elettrica che si propaga lungo il sistema di conduzione. Da un punto di vista fisiologico, il ciclo cardiaco puo essere schematicamente suddiviso in diverse fasi: una fase di contrazione isovolumetrica (la pressione all’interno dei ventricoli aumenta rapidamente, il volume rimane costante, entrambe le valvole sono chiuse), la fase di eiezione (la valvola aortica si apre, il volume ventricolare si riduce prima rapidamente poi lentamente; la pressione ventricolare aumenta lentamente per poi ridursi), una seconda fase isovolumetrica (chiusura della valvola aortica, il miocardio ventricolare si rilassa comportando una rapida riduzione della pressione a volume costante) ed infine una fase di riempimento con progressivo aumento volumetrico a pressione costante (la valvola atrioventricolare si apre, il volume aumenta prima in modo rapido e poi piu lentamente e, infine, si ha un ultimo piccolo contributo al riempimento ventricolare, dato dalla contrazione atriale).

Waste Management 2006 Third International Conference on Waste Management and the Environment 21 - 23 June 2006 Malta

The integration of a Concentrated Solar Power (CSP) plant with cooling energy production is investigated in the present paper. The power block is based on a steam Rankine cycle fully driven by two types of solar concentration devices: i) Parabolic Trough Collector (PTC) solar field and ii) Heliostat field with Central Receiver (HCR). Storage tanks allow the plant to operate also during nighttime hours. Cooling production is carried out by steam-driven double-effect absorption chillers feeding a district cooling network. The system was designed to operate in “island mode” to cover both the electrical and the cooling demand for a town of about 50,000 inhabitants. A typical location in the desert region of the Saudi Arabia Kingdom was selected as a case study. Commercial software and in-house computer codes were combined together to predict annual CSP plant performance. Results of annual plant operation on a one hour basis are presented and discussed. CSP plant showed a good capability of load-following operation, providing at the same time a relevant fossil fuel saving.

Hot streak migration in a linear vane cascade with showerhead film cooling was experimentally and numerically investigated at isentropic exit Mach number of Ma2is = 0.40, with an inlet turbulence intensity level of Tu1 = 9%. Two tangential positions of the hot streak center were taken into account: 0% of pitch (hot streak is aligned with the vane leading edge) and 45% of pitch. After demonstrating that computations correctly predict hot streak attenuation through the vane passage with no showerhead blowing, the numerical method was used to investigate hot streak interaction with showerhead film cooling, at blowing ratio of BR = 3.0, corresponding to a coolant-to-mainstream mass flow ratio of MFR = 1.15%. The effects of mixing and coolant interaction on the hot streak reduction were interpreted under the light of the superposition principle, whose accuracy was within 12% on the leading edge region, in the central section of the vane span.