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Nickel hydroxide is widely used in supercapacitors, alkaline batteries, for the electrocatalytic oxidation of organic contaminants, etc. Due to their electrochemical activity, Ni(OH)2 (α+β) samples of a layer structure synthesized in a slit diaphragm electrolyzer are the most promising. The effect of the thermal field on the structural characteristics of layered (α+β) Ni(OH)2 was studied. The effect was assessed in two ways: 1) internal (in situ) cooling directly in the electrolyzer by cooling the cathode from the rear side; 2) external (ex situ) heating directly after the electrolyzer when passing through a spiral heat exchanger heated to 90 °C. The crystal structure of the samples was studied by X-ray phase analysis. It was shown that the base sample obtained without changing the thermal field was a monophase layered (α+β) structure with a high content of α-modification and a gradient transition from α to β through a number of intermediate structures. The crystallinity of the sample was not high. During the internal cooling of the cathode, the crystallinity decreased and the fraction of the α-modification increased. External heating of the nickel hydroxide suspension immediately after leaving the electrolyzer led to the recrystallization of the samples with the decomposition of the (α+β) layered structure and formation of β-Ni(OH)2 with high crystallinity. It was found that external 6-minute heating did not change the crystal structure. This is explained by the fact that the aging process of nickel hydroxide at an elevated temperature is a crystal-chemical transformation, which is characterized by an induction period, during which the rate of the process is minimal.As a result, the study has shown the possibility of controlling the type of forming crystalline modification of nickel hydroxide and its crystallinity by changing the internal (in situ) or external (ex situ) thermal field, Гидроксид никеля широко используется в суперконденсаторах, щелочных аккумуляторах, для электрокаталитического окисления органических загрязнений и т. д. Наиболее перспективными из-за электрохимической активности являются образцы Ni(OH)2 (α+β) слоевой структуры, синтезированные в щелевом диафрагменном электролизере. Изучено влияние теплового поля на структурные характеристики слоевого (α+β) Ni(OH)2. Оценку влияния проводили двумя путями: 1) внутреннее (in situ) охлаждение непосредственно в электролизере за счет охлаждения катода с тыльной стороны; 2) внешний (ex situ) нагрев непосредственно после электролизера при пропускании через спиральный теплообменник, нагреваемый до 90 °С. Кристаллическая структура образцов изучена методом рентгенофазового анализа. Показано, что базовый образец, полученный без изменения теплового поля, представляет собой монофазную слоистую (α+β) структуру с высоким содержанием α-модификации и градиентным переходом от α до β через ряд промежуточных структур. Кристалличность образца не высокая. При внутреннем охлаждении катода происходит снижение кристалличности и увеличение доли α-модификации. Внешний нагрев суспензии гидроксида никеля сразу после выхода из электролизера приводит к перекристаллизации образцов с распадом (α+β) слоистой структуры и формированием β-Ni(OH)2 с высокой кристалличностью. Выявлено, что при внешнем нагреве длительностью 6 минут не происходит изменения кристаллической структуры. Это поясняется тем, что процесс старения гидроксида никеля при повышенной температуре является кристаллохимическим превращением, для которого характерен индукционный период, в течение которого скорость процесса минимальна.Таким образом, исследованием показана возможность управления типом формирующейся кристаллической модификации гидроксида никеля и его кристалличностью путем изменения внутреннего (in situ) или внешнего (ex situ) теплового поля, Гідроксид нікелю широко використовується в суперконденсаторах, лужних акумуляторах, для електрокаталітичного окиснення органічних забруднювачів. Найбільш перспективними через високу електрохімічну активність є зразки Ni(OH)2 (α+β) шарової структури, синтезовані в щілинному діафрагмовому електролізері (ЩДЕ). Вивчено вплив теплового поля на структурні характеристики шарового (α+β) Ni(OH)2. Оцінку впливу проводили двома шляхами:1) внутрішнє (in situ) охолодження безпосередньо в електролізері за рахунок охолодження катоду з тильної сторони;2) зовнішнє (ex situ) нагрівання безпосередньо після електролізера при пропусканні через спіральний теплообмінник, нагрітий до 90 °С.Кристалічна структура зразків вивчена методом ренгенофазового аналізу. Показано, що базовий зразок, отриманий без зміни теплового поля, являє собою монофазну шарувату (α+β) структуру із високим вмістом α-модифікації та градієнтним переходом від α до β через ряд проміжних структур. Кристалічність зразка не висока. При внутрішньому охолодженні катоду відбувається зниження кристалічності та збільшення долі α-модифікації. Зовнішнє нагрівання суспензії гідроксиду нікелю відразу після виходу із електролізеру призводить до перекристалізації зразків з розпадом (α+β) шаруватої структури і формуванням β-Ni(OH)2 із високою кристалічністю. Виявлено, що при зовнішньому нагрівання протягом 6 хвилин не відбувається зміна кристалічної структури. Це пояснюється тим, що процес старіння гідроксиду нікелю при підвищеній температурі є кристалохімичним перетворенням, для якого характерна наявність індукціонного періоду, протягом якого швидкість процесу мінімальна.Таким чином, дослідження показана можливість управління типом кристалічної модифікації гидроксида никеля, що формується, та його кристалічністю шляхом зміни внутрішнього (in situ) чи зовнішнього (ex situ) теплового поля

The present thesis focuses on evaluating a conjugate heat transfer (CHT) simulation in a ribbed cooling passage with a fully developed flow assumption using LES with the immersed boundary method (IBM-LES-CHT). The IBM with the LES model (IBM-LES) and the IBM with CHT boundary condition (IBM-CHT) frameworks are validated prior to the main simulations by simulating purely convective heat transfer (iso-flux) in the ribbed duct, and a developing laminar boundary layer flow over a two-dimensional flat plate with heat conduction, respectively. For the main conjugate simulations, a ribbed duct geometry with a blockage ratio of 0.3 is simulated at a bulk Reynolds number of 10,000 with a conjugate boundary condition applied to the rib surface. The nominal Biot number is kept at 1, which is similar to the comparative experiment. As a means to overcome a large time scale disparity between the fluid and the solid regions, the use of a high artificial solid thermal diffusivity is compared to the physical diffusivity. It is shown that while the diffusivity impacts the instantaneous fluctuations in temperature, heat transfer and Nusselt numbers, it has an insignificantly small effect on the mean Nusselt number. The comparison between the IBM-LES-CHT and iso-flux simulations shows that the iso-flux case predicts higher local Nusselt numbers at the back face of the rib. Furthermore, the local Nusselt number augmentation ratio (EF) predicted by IBM-LES-CHT is compared to the body fitted grid (BFG) simulation, experiment and another LES conjugate simulation. Even though there is a mismatch between IBM-LES-CHT prediction and other studies at the front face of the rib, the area-averaged EF compares reasonably well in other regions between IBM-LES-CHT prediction and the comparative studies.

Forced convection is a phenomenon already widely investigated in literature. However, there remain potential important improvements on its understanding and numerical prediction. The classical RANS approaches, widely used in industry for the design of cooling systems, are based on a constant turbulent Prandtl number value and isotropic turbulence. This results in a limited fidelity for the prediction of the convective heat transfer coefficient (at best 10-15% of accuracy). The present investigation, therefore, aims at supporting the development of CFD codes by providing detailed and accurate experimental data. Unlike most of the investigations available in literature, which provide the wall heat transfer and/or the velocity fields, the present research addresses the flow temperature. This temperature information allows obtaining the turbulent heat transport term required for the determination of the turbulent Prandtl number value. Laser-Induced Fluorescence (LIF) has the advantage to provide a 2D temperature distribution by a non-intrusive optical approach. Gas-phase measurements, required for a consistent heat transfer investigation, were never applied before in internal flows as in the present application. First of all, the use of a fluorescent tracer is investigated regarding its impact on the Prandtl number value of the gas. After a detailed evaluation of the technique, including the image processing, the first experiments in a static cell show encouraging results of the first two-color measurements. A novel facility was designed and built at the von Karman Institute (VKI) to extend the study to the selected application. For simplicity, the test section is a smooth high aspect ratio duct to investigate a quasi 2D internal flow, as this configuration is closer to a cooling channel. The measurements performed with the one-color methodology and using toluene as the fluorescent tracer show a good agreement between the obtained mean temperature profile and the one re, (FSA - Sciences de l'ingénieur) -- UCL, 2018

Cooling of gas turbine blades is critical to long term durability. Accurate prediction of blade metal temperature is a key component in the design of the cooling system. In this design space, spatial distribution of heat transfer coefficients plays a significant role. Large-Eddy Simulation (LES) has been shown to be a robust method for predicting heat transfer. Because of the high computational cost of LES as Reynolds number (Re) increases, most investigations have been performed at low Re of O(104). In this paper, a two-pass duct with a 180° turn is simulated at Re = 100,000 for a stationary and a rotating duct at Ro = 0.2 and Bo = 0.5. The predicted mean and turbulent statistics compare well with experiments in the highly turbulent flow. Rotation-induced secondary flows have a large effect on heat transfer in the first pass. In the second pass, high turbulence intensities exiting the bend dominate heat transfer. Turbulent intensities are highest with the inclusion of centrifugal buoyancy and increase heat transfer. Centrifugal buoyancy increases the duct averaged heat transfer by 10% over a stationary duct while also reducing friction by 10% due to centrifugal pumping.

The heat transfer in the system piston - piston rod - crosshead of reciprocating compressors can be influenced by a fluid enclosed in an internal cavity. Thus, heat is transferred by the fluid flow inside the hollow parts utilizing the reciprocating motion. Subsequently, the high working frequency of such compressors can lead to an improved cooling of the high temperature compressor parts in comparison with conventional solid material designs.  For the experimental examination of this cooling concept a test rig has been set up at the Technische Universität Dresden which comprises a vertically oscillating hollow rod that is heated at its upper end and cooled at its lower end. Among other factors the heat transfer of this cooling concept is affected by the internal diameter of the piston rod. In order to quantify the influence of the internal diameter on the axial heat transfer three different hollow rods with varying internal diameters where investigated by means of temperature measurements.  The experimental results are presented and the influence of the size of the cavity is discussed. Furthermore, the measured temperatures are used for numerical simulations of the test rig in order to derive the axial heat flux of the fluid inside the cavity. Based on the resulting values the heat transfer capability of the investigated cooling concept can be examined with respect to the internal diameter and the benefit for the cooling of different compressor components can be estimated.

In the past few decades, the operating temperatures of gas turbine engines have increased significantly with a view towards increasing the overall thermal efficiency and specific power output. As a result of increased turbine inlet temperatures, the hot gas path components downstream of the combustor section are subjected to high heat loads. Though materials with improved temperature capabilities are used in the construction of the hot gas path components, in order to ensure safe and durable operation, the hot gas path components are additionally supplemented with thermal barrier coatings (TBCs) and sophisticated cooling techniques. The present study focusses on two aspects of gas turbine cooling, namely augmented internal cooling and external film cooling. One of the commonly used methods for cooling the vanes involves passing coolant air bled from the compressor through serpentine passages inside the airfoils. The walls of the internal cooling passages are usually roughened with turbulence promoters like ribs to enhance heat transfer. Though the ribs help in augmenting the heat transfer, they have an associated pressure penalty as well. Therefore, it is important to study the thermal-hydraulic performance of ribbed internal cooling passages. The first section of the thesis deals with the numerical investigation of flow and heat transfer characteristics in a ribbed two-pass channel. Four different rib shapes- 45° angled, V-shaped, W-shaped and M-shaped, were studied. This study further aims at exploring the performance of different rib-shapes at a large rib pitch-to-height ratio (p/e=16) which has potential applications in land-based gas turbines operating at high Reynolds numbers. Detailed flow and heat transfer analysis have been presented to illustrate how the innate flow physics associated with the bend region and the different rib shapes contribute to heat transfer enhancement in the two-pass channel. The bend-induced secondary flows were observed to significa

In the past few decades, the operating temperatures of gas turbine engines have increased significantly with a view towards increasing the overall thermal efficiency and specific power output. As a result of increased turbine inlet temperatures, the hot gas path components downstream of the combustor section are subjected to high heat loads. Though materials with improved temperature capabilities are used in the construction of the hot gas path components, in order to ensure safe and durable operation, the hot gas path components are additionally supplemented with thermal barrier coatings (TBCs) and sophisticated cooling techniques. The present study focusses on two aspects of gas turbine cooling, namely augmented internal cooling and external film cooling. One of the commonly used methods for cooling the vanes involves passing coolant air bled from the compressor through serpentine passages inside the airfoils. The walls of the internal cooling passages are usually roughened with turbulence promoters like ribs to enhance heat transfer. Though the ribs help in augmenting the heat transfer, they have an associated pressure penalty as well. Therefore, it is important to study the thermal-hydraulic performance of ribbed internal cooling passages. The first section of the thesis deals with the numerical investigation of flow and heat transfer characteristics in a ribbed two-pass channel. Four different rib shapes- 45° angled, V-shaped, W-shaped and M-shaped, were studied. This study further aims at exploring the performance of different rib-shapes at a large rib pitch-to-height ratio (p/e=16) which has potential applications in land-based gas turbines operating at high Reynolds numbers. Detailed flow and heat transfer analysis have been presented to illustrate how the innate flow physics associated with the bend region and the different rib shapes contribute to heat transfer enhancement in the two-pass channel. The bend-induced secondary flows were observed to significa

The heat transfer in the system piston - piston rod - crosshead of reciprocating compressors can be influenced by a fluid enclosed in an internal cavity. Thus, heat is transferred by the fluid flow inside the hollow parts utilizing the reciprocating motion. Subsequently, the high working frequency of such compressors can lead to an improved cooling of the high temperature compressor parts in comparison with conventional solid material designs.  For the experimental examination of this cooling concept a test rig has been set up at the Technische Universität Dresden which comprises a vertically oscillating hollow rod that is heated at its upper end and cooled at its lower end. Among other factors the heat transfer of this cooling concept is affected by the internal diameter of the piston rod. In order to quantify the influence of the internal diameter on the axial heat transfer three different hollow rods with varying internal diameters where investigated by means of temperature measurements.  The experimental results are presented and the influence of the size of the cavity is discussed. Furthermore, the measured temperatures are used for numerical simulations of the test rig in order to derive the axial heat flux of the fluid inside the cavity. Based on the resulting values the heat transfer capability of the investigated cooling concept can be examined with respect to the internal diameter and the benefit for the cooling of different compressor components can be estimated.

Jet engines often operate under dirty conditions where large amounts of particulate matter can be ingested, especially, sand, ash and dirt. Particulate matter in different engine components can lead to degradation in performance. The objective of this dissertation is to investigate sand transport and deposition in the internal cooling passages of turbine blades. A simplified rectangular geometry is simulated to mimic the flow field, heat transfer and particle transport in a two pass internal cooling geometry. Two major challenges are identified while trying to simulate particle deposition. First, no reliable particle-wall collision model is available to calculate energy losses during a particle wall interaction. Second, available deposition models for particle deposition do not take into consideration all the impact parameters like impact velocity, impact angle, and particle temperature. These challenges led to the development of particle wall collision and deposition models in the current study. First a preliminary simulation is carried out to investigate sand transport and impingement patterns in the two pass geometry by using an idealized elastic collision model with the walls of the duct without any deposition. Wall Modeled Large Eddy Simulations (WMLES) are carried to calculate the flow field and a Lagrangian approach is used for particle transport. The outcome of these simulations was to get a qualitative comparison with experimental visualizations of the impingement patterns in the two pass geometry. The results showed good agreement with experimental distributions and identified surfaces most prone to deposition in the two pass geometry. The initial study is followed by the development of a particle-wall collision model based on elastic-plastic deformation and adhesion forces by building on available theories of deformation and adhesion for a spherical contact with a flat surface. The model calculates deformation losses and adhesion losses from particle-wall

In non-lubricated piston compressors the wear of the piston rod packing rings is still a problem that needs to be considered. Due to the demands of high gas pressure and leak-tight sealing the frictional heat of the rings is causing high temperatures in the area of the piston rod packing. High temperatures are – among other factors – one reason for an increase of wear and thus for a lifetime reduction of the packing. To increase this lifetime – and so to increase the time between two technical services – the idea of an internal cooling of the piston rod with a phase changing medium was created. To investigate this new cooling method for non-lubricated piston compressors a research project between the EFRC R&D Working Group (European Forum for Reciprocating Compressors) and the Technical University of Dresden was initiated. Within this project a test bench with a full scale balanced opposed process gas compressor was set up and measurements shall be taken. The measured values will be used for a validation of a thermal simulation model based on the software ANSYS. Also a model test rig is investigated which allows the investigation of temperature along a hollow piston rod in a moving system.

In non-lubricated piston compressors the wear of the piston rod packing rings is still a problem that needs to be considered. Due to the demands of high gas pressure and leak-tight sealing the frictional heat of the rings is causing high temperatures in the area of the piston rod packing. High temperatures are – among other factors – one reason for an increase of wear and thus for a lifetime reduction of the packing. To increase this lifetime – and so to increase the time between two technical services – the idea of an internal cooling of the piston rod with a phase changing medium was created. To investigate this new cooling method for non-lubricated piston compressors a research project between the EFRC R&D Working Group (European Forum for Reciprocating Compressors) and the Technical University of Dresden was initiated. Within this project a test bench with a full scale balanced opposed process gas compressor was set up and measurements shall be taken. The measured values will be used for a validation of a thermal simulation model based on the software ANSYS. Also a model test rig is investigated which allows the investigation of temperature along a hollow piston rod in a moving system.

Whole-body precooling can improve endurance exercise performance, especially in the heat; however there are logistical considerations that restrict the use of various precooling strategies prior to actual competition. Precooling is proposed to collectively reduce deep skin and body temperature and in effect, increase the heat storage capacity of an athlete, thereby allowing a greater amount of work to be completed prior to attainment of a critical core temperature. While there is a sound theoretical basis for implementing precooling to improve cycling time trial performance in the heat, the practicalities of employing effective precooling strategies in the field warrant further investigation. The purpose of this thesis was to investigate the effectiveness of various practical precooling strategies for reducing core temperature and improving cycling time trial performance in hot (32-35ºC; 50-60% r.h.) and temperate (20-22 ºC; 50-60% r.h.) conditions. The first three studies of this thesis involved the manipulation of body temperature via a range of precooling strategies that were applied under hot and humid environmental conditions. In study 1, eight precooling strategies involving external application or internal ingestion of cold water and ice were evaluated for their effectiveness in lowering deep body temperature, with due consideration regarding their application in a practical setting. The novel strategy identified in this study, which involved the combined application of iced towels and ingestion of an ice-slurry (“slushie”) made from sports drink, was then compared with an established cooling strategy (Study 2). Both the new and established precooling strategies achieved noticeable cooling effects (moderate and very large, respectively) but only the new strategy enhanced mean power output (3%, 8W) during a 46.4 km laboratory-based cycling protocol, with performance improvements detected in the second half of the time trial. This strategy was also found to be

The rise in body core, skin and muscle temperatures associated with exercisein hot environments (~30°C and above) is known to impair performance over avariety of exercise modes and durations. Precooling has become a popular strategy tocombat this impairment, as evidence has shown it to be an effective method forlowering pre-exercise core temperature, increasing heat storage capacity andimproving exercise performance in the heat. To date, the majority of precoolingmanoeuvres are achieved via external means, such as cold water immersion and theapplication of cooling garments; methods which have been criticised for their lack ofpracticality for use in major sporting competitions. However, recent evidence hasshown that internal or endogenous cooling methods, such as drinking cold fluids, areable to lower core temperature and enhance endurance performance in the heat. Thismethod may be more advantageous than current forms of precooling, as ingestingcold fluids is easily implemented in the field and provides the additional benefit ofhydrating athletes. Based on the law of enthalphy of fusion, which states that asignificantly greater amount of heat absorption is required for water to change phasefrom solid to liquid (melt), the ingestion of an ice slurry mixture may be a morepowerful means for lowering pre-exercise core temperature. Therefore, the primaryfocus of this PhD thesis was to determine the effectiveness of ice slurry ingestion asa precooling manoeuvre for improving submaximal exercise performance in the heat,as well as investigate the potential mechanisms behind the improvements observed.

ROSS, M. L. R., L. A. GARVICAN, N. A. JEACOCKE, P. B. LAURSEN, C. R. ABBISS, D. T. MARTIN, and L. M. BURKE. Novel Precooling Strategy Enhances Time Trial Cycling in the Heat. Med. Sci. Sports Exerc., Vol. 43, No. 1, pp. 123–133, 2011. Purpose: To develop and investigate the efficacy of a new precooling strategy combining external and internal techniques on the performance of a cycling time trial (TT) in a hot and humid environment. Methods: Eleven well-trained male cyclists undertook three trials of a laboratory-based cycling TT simulating the course characteristics of the Beijing Olympic Games event in a controlled hot and humid environment (32-C–35-C at 50%–60% relative humidity). The trials, separated by 3–7 d, were undertaken in a randomized crossover design and consisted of the following: 1) CON—no treatment apart from the ad libitum consumption of cold water (4-C), 2) STD COOL—whole-body immersion in cold (10-C) water for 10 min followed by wearing a cooling jacket, or 3) NEW COOL—combination of consumption of 14 g of ice slurry (‘‘slushie’’) per kilogram body mass made from a commercial sports drink while applying iced towels. Results: There was an observable effect on rectal temperature (Trec) before the commencement of the TT after both precooling techniques (STD COOL G NEW COOL G CON, P G 0.05), but pacing of the TT resulted in similar Trec, HR, and RPE throughout the cycling protocol in all trials. NEW COOL was associated with a 3.0% increase in power (È8 W) and a 1.3% improvement in performance time (È1:06 min) compared with the CON trial, with the true likely effects ranging from a trivial to a large benefit. The effect of the STD COOL trial compared with the CON trial was ‘‘unclear.’’ Conclusions: This new precooling strategy represents a practical and effective technique that could be used by athletes in preparation for endurance events undertaken in hot and humid conditions.

The analysis of turbulent flows provides a unique scientific challenge whose solution remains central to unraveling the fundamental nature of all fluid dynamics. Measuring and predicting turbulent flows becomes even more difficult when considering a two-phase flow, which is a commonly encountered engineering problem across many disciplines. One such example, the ingestion of foreign debris into a gas turbine engine, provided the impetus for this study. Despite more than 40 years of research, operation with a particle-laden inlet flow remains a significant problem for modern turbomachines. The purpose, therefore, is to develop experimental methods for investigating multi-phase flows relevant to the cooling of gas turbine components. Initially, several generic components representing turbine cooling designs were evaluated with a particle-laden flow using a special high temperature test facility. The results of this investigation revealed that blockage was highly sensitive to the carrier flowfield as defined by the cooling geometry. A second group of experiments were conducted in one commonly used cooling design using a Time Resolved Digital Particle Image Velocimetry (TRDPIV) system that directly investigated both the carrier flowfield and particle trajectories. Traditional PIV processing algorithms, however, were unable to resolve the particle motions of the two-phase flow with sufficient fidelity. To address this issue, a new Particle Tracking Velocimetry (PTV) algorithm was developed and validated for both single-phase and two-phase flows. The newly developed PTV algorithm was shown to outperform other published algorithms as well as possessing a unique ability to handle particle laden two-phase flows. Overall, this work demonstrates several experimental methods that are well suited for the investigation of wall-bounded turbulent two-phase flows, with a special emphasis on a turbine cooling method. The studies contained herein provide valuable information regarding

ROSS, M. L. R., L. A. GARVICAN, N. A. JEACOCKE, P. B. LAURSEN, C. R. ABBISS, D. T. MARTIN, and L. M. BURKE. Novel Precooling Strategy Enhances Time Trial Cycling in the Heat. Med. Sci. Sports Exerc., Vol. 43, No. 1, pp. 123–133, 2011. Purpose: To develop and investigate the efficacy of a new precooling strategy combining external and internal techniques on the performance of a cycling time trial (TT) in a hot and humid environment. Methods: Eleven well-trained male cyclists undertook three trials of a laboratory-based cycling TT simulating the course characteristics of the Beijing Olympic Games event in a controlled hot and humid environment (32-C–35-C at 50%–60% relative humidity). The trials, separated by 3–7 d, were undertaken in a randomized crossover design and consisted of the following: 1) CON—no treatment apart from the ad libitum consumption of cold water (4-C), 2) STD COOL—whole-body immersion in cold (10-C) water for 10 min followed by wearing a cooling jacket, or 3) NEW COOL—combination of consumption of 14 g of ice slurry (‘‘slushie’’) per kilogram body mass made from a commercial sports drink while applying iced towels. Results: There was an observable effect on rectal temperature (Trec) before the commencement of the TT after both precooling techniques (STD COOL G NEW COOL G CON, P G 0.05), but pacing of the TT resulted in similar Trec, HR, and RPE throughout the cycling protocol in all trials. NEW COOL was associated with a 3.0% increase in power (È8 W) and a 1.3% improvement in performance time (È1:06 min) compared with the CON trial, with the true likely effects ranging from a trivial to a large benefit. The effect of the STD COOL trial compared with the CON trial was ‘‘unclear.’’ Conclusions: This new precooling strategy represents a practical and effective technique that could be used by athletes in preparation for endurance events undertaken in hot and humid conditions.

The present contribution describes the methodology and results of an experimental/numerical research program progressing at the von Karman Institute about the investigation of flow and heat transfer in a square section stationary duct equipped with high blockage ribs on one face. This geometry is representative of a high pressure turbine blade cooling channel. The purpose is to highlight the interaction and the synergy between experimental and simulation approaches. The paper shows how the experimental results lead to a conceptual model of the behavior and the topology of this flow. A numerical prediction of the flow over a single rib, obtained from a Large-Eddy Simulation, is able to validate this model, to provide additional information eventually not accessible by the experiments and to put in evidence the underlying structures driving the process. Simulations of a multi-rib domain put in evidence the possible existence of flow structures longer than one rib-pitch length and suggest possible avenues of futures experimental/numerical campaigns to gain a full understanding of this class of flows., Presented at the International Symposium on Integrating CFD and Experiments in Aerodynamics (3rd) held in Colorado Springs, CO on 20-21 Jun 2007. The original document contains color images.

The heat transfer characteristics through arrays of pin fins were studied for the further development of internal cooling methods for turbine airfoils. Low aspect ratio pin fin arrays were tested through a range of Reynolds numbers between 5000 and 30,000 to determine the effects of pin spacing as well as aspect ratio on pin and endwall heat transfer. Experiments were also conducted to determine the independent effects of pin spacing and aspect ratio on arrays with different flow incidence angles. The pin Nusselt numbers showed almost no dependence on pin spacing or flow incidence angle. Using an infrared thermogaphy technique, spatially-resolved Nusselt numbers were measured along the endwalls of each array. The endwall results showed that streamwise spacing had a larger effect than spanwise spacing on array-averaged Nusselt numbers. Endwall heat transfer patterns showed that arrays with flow incidence angles experienced less wake interaction between pins than arrays with perpendicular flow, which caused a slight decrease in heat transfer in arrays with flow incidence angles. The effect of flow incidence angle on array-average Nusselt number was greater at tighter pin spacings. Even though the pin Nusselt number was independent of pin spacing, the ratio of pin-to-endwall Nusselt number was dependent on flow conditions as well as pin spacing. The pin aspect ratio had little effect on the array-average Nusselt number for arrays with perpendicular flow; however, the effect of flow incidence angle on array-average Nusselt number increased as aspect ratio decreased.

The desire to achieve higher heat transfer augmentation for turbine blades is fueled by the increased power output and efficiency that is achievable with high turbine inlet temperatures. The use of internal cooling channels fitted with pin fin arrays serves as one method of accomplishing this goal. Consequently, the addition of pin fin arrays comes at the expense of increased pressure drop. Therefore the pin fin geometry must be judiciously chosen to achieve the required heat transfer rate while minimizing the associated pressure drop. This project culminates in the measurement of both pin fin force and array pressure drop as they related to changes in the array geometry. Specifically, the effects of Reynolds number, spanwise pin spacing, streamwise pin spacing, pin aspect ratio, and flow incidence angle. Direct two-component force measurement is achieved with a cantilever beam force sensor that uses highly sensitive piezoresistive strain gauges, relating the strain at the base of the beam to the applied force. With proper characterization, forces as small as one-tenth the weight of a paper clip are successfully measured. Additionally, array pressure drop measurements are achieved using static pressure taps. Experiments were conducted over a range of Reynolds numbers between 7,500 and 35,000. Changes in the spanwise pin spacing were shown to substantially alter the pin fin drag and array pressure drop, while changes in the streamwise pin spacing were less influential. The experimental results also showed a dramatic reduction in the pin fin drag and array pressure drop for an inline flow incidence angle. Finally, changes in the pin aspect ratio were shown to have little effect on the array pressure drop.

A first part of a ”Heat Transfer Handbook” about correlations for internal cooling of gas turbine vanes and blades has been created. The work is based on the cooling of vanes and blades 1 and 2 on different Siemens Gas Turbines. The cooling methods increase the heat transfer in the cooling channels by increasing the heat transfer coefficient and/or increasing the heat transfer surface area. The penalty paid for the increased heat transfer is higher pressure losses. Three cooling methods, called rib turbulated cooling, matrix cooling and impingement cooling were investigated. Rib turbulated cooling and impingement cooling are typically used in the leading edge or mid region of the airfoil and matrix cooling is mostly applied in the trailing edge region. Literature studies for each cooling method, covering both open literature and internal reports, were carried out in order to find correlations developed from tests. The correlations were compared and analyzed with focus on suitability for use in turbine conditions. The analysis resulted in recommendations about what correlations to use for each cooling method. For rib turbulated cooling in square or rectangular ducts, four correlations developed by Han and his co-workers [3.5], [3.8], [3.9] and [3.6] are recommended, each valid for different channel and rib geometries. For U-shaped channels, correlations of Nagoga [3.4] are recommended. Matrix cooling is relatively unknown in west, but has been used for many years in the former Soviet Union. Therefore available information in open literature is limited. Only one source of correlations was found. The correlations were developed by Nagoga [4.2] and are valid for closed matrixes. Siemens Gas Turbines are cooled with open matrixes, why further work with developing correlations is needed. For impingement cooling on a flat target plate, a correlation of Florschuetz et al. [5.7] is recommended for inline impingement arrays. For staggered arrays, both the correlations of Flor

The desire for smaller, faster, and more efficient products places a strain on thermal management in components ranging from gas turbine blades to computers. Heat exchangers that utilize internal cooling flows have shown promise in both of these industries. Although pin fins are often placed in the cooling channels to augment heat transfer, their addition comes at the expense of increased pressure drop. Consequently, the pin fin geometry must be judiciously chosen to achieve the desired heat transfer rate while minimizing the pressure drop and accompanying pumping requirements. This project culminates in the construction of a new test facility and the development of a unique force measurement methodology. Direct force measurement is achieved with a cantilever beam force sensor that uses sensitive piezoresistive strain gauges to simultaneously measure aerodynamic lift and drag forces on a pin fin. After eliminating the detrimental environmental influences, forces as small as one-tenth the weight of a paper clip are successfully measured. Although the drag of an infinitely long cylinder in uniform cross flow is well documented, the literature does not discuss the aerodynamic forces on a cylinder with an aspect ratio of unity in channel flow. Measured results indicate that the drag coefficient of a cylindrical pin in a single row array is greater than the drag coefficient of an infinite cylinder in cross flow. This phenomenon is believed to be caused by an augmentation of viscous drag on the pin fin induced by the increased viscous effects inherent in channel flow.

The desire for smaller, faster, and more efficient products places a strain on thermal management in components ranging from gas turbine blades to computers. Heat exchangers that utilize internal cooling flows have shown promise in both of these industries. Although pin fins are often placed in the cooling channels to augment heat transfer, their addition comes at the expense of increased pressure drop. Consequently, the pin fin geometry must be judiciously chosen to achieve the desired heat transfer rate while minimizing the pressure drop and accompanying pumping requirements. This project culminates in the construction of a new test facility and the development of a unique force measurement methodology. Direct force measurement is achieved with a cantilever beam force sensor that uses sensitive piezoresistive strain gauges to simultaneously measure aerodynamic lift and drag forces on a pin fin. After eliminating the detrimental environmental influences, forces as small as one-tenth the weight of a paper clip are successfully measured. Although the drag of an infinitely long cylinder in uniform cross flow is well documented, the literature does not discuss the aerodynamic forces on a cylinder with an aspect ratio of unity in channel flow. Measured results indicate that the drag coefficient of a cylindrical pin in a single row array is greater than the drag coefficient of an infinite cylinder in cross flow. This phenomenon is believed to be caused by an augmentation of viscous drag on the pin fin induced by the increased viscous effects inherent in channel flow.

The performance of many engineering devices from power electronics to gas turbines is limited by thermal management. Pin fins are commonly used to augment heat transfer by increasing surface area and increasing turbulence. The present research is focused on but not limited to internal cooling of turbine airfoils using pin fins. Although the pin fins are not limited to a single shape, circular cross-sections are most common. The present study examines heat transfer from a single row of circular pin fins with the row oriented perpendicular to the flow. The configurations studied have spanwise spacing to pin diameter ratios of two, four, and eight. Low aspect ratio pin fins were studied whereby the channel height to pin diameter was unity. The experiments are carried out for a Reynolds number range of 5000 to 30,000. Heat transfer measurements are taken on both the pin and on the endwall covering several pin diameters upstream and downstream of the pin row. The results show that the heat transfer augmentation relative to open channel flow is highest for the smallest spanwise spacing for the lowest Reynolds number flows. The results also indicate that the pin fin heat transfer is higher than on the endwall.

A first part of a ”Heat Transfer Handbook” about correlations for internal cooling of gas turbine vanes and blades has been created. The work is based on the cooling of vanes and blades 1 and 2 on different Siemens Gas Turbines. The cooling methods increase the heat transfer in the cooling channels by increasing the heat transfer coefficient and/or increasing the heat transfer surface area. The penalty paid for the increased heat transfer is higher pressure losses. Three cooling methods, called rib turbulated cooling, matrix cooling and impingement cooling were investigated. Rib turbulated cooling and impingement cooling are typically used in the leading edge or mid region of the airfoil and matrix cooling is mostly applied in the trailing edge region. Literature studies for each cooling method, covering both open literature and internal reports, were carried out in order to find correlations developed from tests. The correlations were compared and analyzed with focus on suitability for use in turbine conditions. The analysis resulted in recommendations about what correlations to use for each cooling method. For rib turbulated cooling in square or rectangular ducts, four correlations developed by Han and his co-workers [3.5], [3.8], [3.9] and [3.6] are recommended, each valid for different channel and rib geometries. For U-shaped channels, correlations of Nagoga [3.4] are recommended. Matrix cooling is relatively unknown in west, but has been used for many years in the former Soviet Union. Therefore available information in open literature is limited. Only one source of correlations was found. The correlations were developed by Nagoga [4.2] and are valid for closed matrixes. Siemens Gas Turbines are cooled with open matrixes, why further work with developing correlations is needed. For impingement cooling on a flat target plate, a correlation of Florschuetz et al. [5.7] is recommended for inline impingement arrays. For staggered arrays, both the correlations of Flor

Efficiency and power output of gas turbines improve with an increase in turbine inlet temperatures, and blade designers continually seek out new methods of increasing these temperatures. Increases in turbine inlet temperatures are achieved by utilizing a combination of internal convective cooling and external film-cooling. This study will evaluate several novel cooling schemes for turbine airfoils, called microcircuits. Microcircuits are placed inside the turbine blade wall, and the features turbulate the air and increase heat transfer surface area, thereby augmenting convective cooling. The coolant flow then exits internal cooling passages to the external side of the blade. Here the coolant forms a protective layer along the external surface of the blade to protect the blade from the heated mainstream flow. In the current study, a low-speed large-scale wind tunnel facility was developed to measure internal heat transfer coefficients and external adiabatic effectiveness, using thermal liquid crystallography and infrared thermography. This test facility is unique in that it can be used to test the effects of internal cooling features on external film cooling. Results show that the highest augmentations in internal heat transfer were seen at the lowest Reynolds numbers. Internal features affected the shapes of external film-cooling contours, but the magnitudes of the spanwise averaged values did not change significantly with changes in internal geometry.

Efficiency and power output of gas turbines improve with an increase in turbine inlet temperatures, and blade designers continually seek out new methods of increasing these temperatures. Increases in turbine inlet temperatures are achieved by utilizing a combination of internal convective cooling and external film-cooling. This study will evaluate several novel cooling schemes for turbine airfoils, called microcircuits. Microcircuits are placed inside the turbine blade wall, and the features turbulate the air and increase heat transfer surface area, thereby augmenting convective cooling. The coolant flow then exits internal cooling passages to the external side of the blade. Here the coolant forms a protective layer along the external surface of the blade to protect the blade from the heated mainstream flow. In the current study, a low-speed large-scale wind tunnel facility was developed to measure internal heat transfer coefficients and external adiabatic effectiveness, using thermal liquid crystallography and infrared thermography. This test facility is unique in that it can be used to test the effects of internal cooling features on external film cooling. Results show that the highest augmentations in internal heat transfer were seen at the lowest Reynolds numbers. Internal features affected the shapes of external film-cooling contours, but the magnitudes of the spanwise averaged values did not change significantly with changes in internal geometry.

Aircraft engine manufacturers strive for greater performance and efficiency by continually increasing the turbine inlet temperature. High turbine inlet temperatures significantly degrade the lifetime of components in the turbine. Modern gas turbines operate with turbine inlet temperatures well above the melting temperature of key turbine components. Without active cooling schemes, modern turbines would fail catastrophically. This study will evaluate a novel cooling scheme for turbine airfoils, called microcircuit cooling, in which small cooling channels are located extremely close to the surface of a turbine airfoil. Coolant bled from the compressor passes through the microcircuits and exits through film cooling slots. On further cooling benefit is that the microcircuit passages are filled with irregular pin fin features that serve to increase convective cooling through the channels. Results from this study indicate a strong interaction between the internal microcircuit features and the external film-cooling from the slot exit. Asymmetric cooling patterns downstream of the slot resulted from the asymmetric pin fin design within the microcircuit. Adiabatic effectiveness levels were found to be optimum for the slot design at a blowing ratio of 0.37. The pin fin arrangement along with the impingement cooling at the microcircuit entrance increased the area-averaged heat transfer by a factor of three, relative to an obstructed channel, over a Reynolds range of 5,000 to 15,000.

Aircraft engine manufacturers strive for greater performance and efficiency by continually increasing the turbine inlet temperature. High turbine inlet temperatures significantly degrade the lifetime of components in the turbine. Modern gas turbines operate with turbine inlet temperatures well above the melting temperature of key turbine components. Without active cooling schemes, modern turbines would fail catastrophically. This study will evaluate a novel cooling scheme for turbine airfoils, called microcircuit cooling, in which small cooling channels are located extremely close to the surface of a turbine airfoil. Coolant bled from the compressor passes through the microcircuits and exits through film cooling slots. On further cooling benefit is that the microcircuit passages are filled with irregular pin fin features that serve to increase convective cooling through the channels. Results from this study indicate a strong interaction between the internal microcircuit features and the external film-cooling from the slot exit. Asymmetric cooling patterns downstream of the slot resulted from the asymmetric pin fin design within the microcircuit. Adiabatic effectiveness levels were found to be optimum for the slot design at a blowing ratio of 0.37. The pin fin arrangement along with the impingement cooling at the microcircuit entrance increased the area-averaged heat transfer by a factor of three, relative to an obstructed channel, over a Reynolds range of 5,000 to 15,000.

For the past several years there has been great effort in the analysis of internal duct cooling. The steady increase in power output and thermal efficiency requirements for gas turbine engines has called for significant advancement in turbine blade internal duct cooling technology. Numerical analysis of turbulent duct flow has been largely limited to Reynolds Averaged Navier-Stokes (RANS) simulations. This is because of the low computational requirements of such calculations relative to Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS). However, the tides have started to turn in favor of LES, partly because of the exponential increase in computer hardware performance in recent years. Three conference papers make up the contents of this thesis. LES is performed for fully developed flow and heat transfer in a staggered 45º ribbed duct in the first paper. The rib pitch-toheight ratio P / e is 10 and a rib height to hydraulic diameter ratio h e / D is 0.1. The Reynolds numberbased on the bulk flow rate and hydraulic diameter is 47,300. The overall heat transfer enhancement obtained was a factor of 2.3, which matched experimental data within 2%. The surfaces of highest heat transfer enhancement were the ribbed walls and the outer wall. Results from LES of an orthogonally rotating 90º ribbed duct are presented in the second paper for rotation numbers: Ro = 0.18, 0.35 and 0.67. The Reynolds number is 20,000. The P / e and h e / D were the same as in the first paper. Turbulence and heat transfer are augmented on the trailing surface and reduced at the leading surface. Secondary flows induced by Coriolis forces, increase heat transfer augmentation on the smooth walls. Finally, the third paper studies the same flow conditions of the second paper and goes further by including effects of centrifugal buoyancy forces using LES. Two buoyancy numbers are studied: Bo = 0.12 and 0.29. Centrifugal buoyancy does not have a large effect on leading side augmentation ratio

An experimental study was made to obtain quantitative information on heat transfer, flow, and pressure distribution in a branched duct test section that had several significant features of an internal cooling passage of a turbine blade. The objective of this study was to generate a set of experimental data that could be used for validation of computer codes that would be used to model internal cooling. Surface heat transfer coefficients and entrance flow conditions were measured at nominal entrance Reynolds numbers of 45 000, 335 000, and 726 000. Heat transfer data were obtained by using a steady-state technique in which an Inconel heater sheet is attached to the surface and coated with liquid crystals. Visual and quantitative flow-field data from particle image velocimetry measurements for a plane at midchannel height for a Reynolds number of 45 000 were also obtained. The flow was seeded with polystyrene particles and illuminated by a laser light sheet. Pressure distribution measurements were made both on the surface with discrete holes and in the flow field with a total pressure probe. The flow-field measurements yielded flow-field velocities at selected locations. A relatively new method, pressure sensitive paint, was also used to measure surface pressure distribution. The pressure paint data obtained at Reynolds numbers of 335 000 and 726 000 compared well with the more standard method of measuring pressures by using discrete holes.

Bakalářská práce zaměřena na všeobecný přehled soustružení, dále na řezné nástroje s vnitřním chlazením. Popisuje výhody a nejnovější poznatky v oblasti řezných nástrojů s vnitřním chlazením u světových výrobců. V druhé části závěrečné práce je řešen návrh soustružnického nástroje s vnitřním chlazením a uvedeno jeho technologické a ekonomické zhodnocení., The bachelor´s thesis is partly focused on a general overview of turning and the turning tools with internal cooling. It describes the benefits and latest developments of this section at worldwide producers. There are a solution of a proposal of turning tools with internal cooling and its technological and economic evaluation in the second part of the thesis.

Bakalářská práce zaměřena na všeobecný přehled soustružení, dále na řezné nástroje s vnitřním chlazením. Popisuje výhody a nejnovější poznatky v oblasti řezných nástrojů s vnitřním chlazením u světových výrobců. V druhé části závěrečné práce je řešen návrh soustružnického nástroje s vnitřním chlazením a uvedeno jeho technologické a ekonomické zhodnocení., The bachelor´s thesis is partly focused on a general overview of turning and the turning tools with internal cooling. It describes the benefits and latest developments of this section at worldwide producers. There are a solution of a proposal of turning tools with internal cooling and its technological and economic evaluation in the second part of the thesis.

Bakalářská práce zaměřena na všeobecný přehled soustružení, dále na řezné nástroje s vnitřním chlazením. Popisuje výhody a nejnovější poznatky v oblasti řezných nástrojů s vnitřním chlazením u světových výrobců. V druhé části závěrečné práce je řešen návrh soustružnického nástroje s vnitřním chlazením a uvedeno jeho technologické a ekonomické zhodnocení., The bachelor´s thesis is partly focused on a general overview of turning and the turning tools with internal cooling. It describes the benefits and latest developments of this section at worldwide producers. There are a solution of a proposal of turning tools with internal cooling and its technological and economic evaluation in the second part of the thesis.

Bakalářská práce zaměřena na všeobecný přehled soustružení, dále na řezné nástroje s vnitřním chlazením. Popisuje výhody a nejnovější poznatky v oblasti řezných nástrojů s vnitřním chlazením u světových výrobců. V druhé části závěrečné práce je řešen návrh soustružnického nástroje s vnitřním chlazením a uvedeno jeho technologické a ekonomické zhodnocení., The bachelor´s thesis is partly focused on a general overview of turning and the turning tools with internal cooling. It describes the benefits and latest developments of this section at worldwide producers. There are a solution of a proposal of turning tools with internal cooling and its technological and economic evaluation in the second part of the thesis.