A Simple Recuperated Ceramic Microturbine: Design Concept, Cycle Analysis, and Recuperator Component Prototype Tests

2016 ◽  
Author(s):  
Michael Vick ◽  
Trent Young ◽  
Matthew Kelly ◽  
Steven Tuttle ◽  
Katherine Hinnant
Keyword(s):  
Heat Transfer ◽  
Reverse Flow ◽  
Fuel Efficiency ◽  
Specific Power ◽  
Rotating Shaft ◽  
Axial Thrust ◽  
Design Concepts ◽  
Gas Leakage ◽  
Cfd Models ◽  
Flow Compressor

Ceramic recuperators could enable microturbines to achieve higher fuel efficiency and specific power. Challenges include finding a suitable ceramic fabrication process, minimizing stray heat transfer and gas leakage, mitigating thermal stress, and joining the ceramic parts to neighboring metal components. This paper describes engine and recuperator design concepts intended to address these obstacles. The engine is sized to produce twelve kilowatts of shaft power, and it has a reverse-flow compressor and turbine. Motivations for this layout are to balance axial thrust forces on the rotor assembly; to minimize gas leakage along the rotating shaft; to reduce heat transfer to the compressor diffuser; to enable the use of a simple, single-can combustor; and to provide room for lightweight ceramic insulation surrounding all hot section components. The recuperator is an annular, radial counterflow heat exchanger with the can combustor at the center. It is assembled from segmented wafers made by ceramic injection molding (CIM). These are housed in a pressure vessel to load the walls mainly in compression, and are joined together by flexible adhesives in the cool areas to accommodate thermal expansion. A representative wafer stack was built by laser-cutting, laminating, and sintering tapecast ceramic material. The prototype was tested at temperatures up to 675°C, and the results were used to validate analytical and computational fluid dynamics (CFD) models, which were then used to estimate the effectiveness of the actual design. Turbomachinery efficiencies were also calculated using CFD, and allowances were made for additional losses like bearing friction and gas leakage. Based on these component performance estimates, a cycle model indicates the engine could achieve a net fuel-to-electrical efficiency of 21%, at a core weight including the recuperator of 11 kg, or about 1 kg/kW electric output.

Experimental and Computational Analysis of Additive Manufactured Augmented Backside Liner Cooling Surfaces for Use in Micro Gas Turbines

2020 ◽  
Author(s):  
Adamos Adamou ◽  
Colin Copeland
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Gas Turbines ◽  
Conjugate Heat Transfer ◽  
Reverse Flow ◽  
Operating Conditions ◽  
Experimental Results ◽  
Gas Temperature ◽  
Cfd Models ◽  
High Heat Transfer

Abstract Augmented backside cooling refers to the enhancement of the backside convection of a combustor liner using extended heat transfer surfaces to fully utilise the cooling air by maximising the heat transfer to pumping ratio characteristic. Although film cooling has and still is widely used in the gas turbine industry, augmented backside cooling has been in development for decades now. The reason for this, is to reduce the amount of air used for liner cooling and to also reduce the emissions caused by using film cooling in the primary zones. In the case of micro gas turbines, emissions are of even greater importance, since the regulations for such engines will most likely become stricter in the following years due to a global effort to reduce emission. Furthermore, the liners investigated in this paper are for a 10 kWe micro turbine, destine for various potential markets, such as combine heat and power for houses, EV hybrids and even small UAVs. The majority of these markets require long service intervals, which in turn requires the combustor liners to be under the least amount of thermal stress possible. The desire to also increase combustor inlet temperatures with the use of recuperated exhaust gases, which in turn increase the overall system efficiency, limits the cooling effectiveness of the inlet air. Due to all these reasons, an advanced form of augmented backside cooling would be of substantial significance in such a system. Currently some very simple designs are used in the form of straight plain fins, transverse strips or other similar geometries, but the creation of high heat transfer efficiency surfaces in such small sizes becomes very difficult with traditional subtractive manufacturing methods. When using additive manufacturing though these types of surfaces are not an issue. This paper covers the comparison of experimental results with conjugate heat transfer CFD models and empirical heat balance models for two different AM liner cooling geometries and an AM blank liner. The two cooling fin geometries include a rotating plain fin and an offset strip fin. The liners were tested in an AM built reverse flow radial swirl stabilised combustion chamber at a variety of operating conditions. During the experiments the surfaces were compared using a thermal camera to record the outer liner temperature which was viewed through a quartz outer casing. The experimental results showed that the cooling surfaces were effective at reducing the liner temperatures with minimal pressure losses for multiple operating points. Those results were then compared against the conjugate heat transfer CFD models and the empirical calculations used to design the surfaces initially. From this comparison, it was noticed both the CFD and empirical calculations under predicted the wall temperatures. This is thought to be due to inaccuracies in the predicted flame temperatures and the assumed emissivity values used to calibrate the thermal imaging camera. Further uncertainties arise from the assumption of a constant air and hot gas temperature and mass flow along the cooling surfaces and the lack of data for the surface roughness of the parts.

Experimental and Computational Analysis of Additive Manufactured Augmented Backside Liner Cooling Surfaces for Use in Micro-Gas Turbines

2021 ◽  
Vol 143 (7) ◽  
Author(s):  
Adamos Adamou ◽  
Colin Copeland
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Gas Turbines ◽  
Conjugate Heat Transfer ◽  
Reverse Flow ◽  
Operating Conditions ◽  
Experimental Results ◽  
Gas Temperature ◽  
Cfd Models ◽  
High Heat Transfer

Abstract Augmented backside cooling refers to the enhancement of the backside convection of a combustor liner using extended heat transfer surfaces to fully utilize the cooling air by maximizing the heat transfer to pumping ratio characteristic. Although film cooling has and still is widely used in the gas turbine industry, augmented backside cooling has been in development for decades now. The reason for this is to reduce the amount of air used for liner cooling and to also reduce the emissions caused by using film cooling in the primary zones. In the case of micro-gas turbines, emissions are of even greater importance, since the regulations for such engines will most likely become stricter in the following years due to a global effort to reduce emissions. Furthermore, the liners investigated in this paper are for a 10 kWe micro-turbine, destine for various potential markets, such as combined heat and power for houses, electric vehicle hybrids and even small unmanned aerial vehicles. The majority of these markets require long service intervals, which in turn requires the combustor liners to be under the least amount of thermal stress possible. The desire to also increase combustor inlet temperatures with the use of recuperated exhaust gases, which in turn increase the overall system efficiency, limits the cooling effectiveness of the inlet air. Due to all these reasons, an advanced form of augmented backside cooling would be of substantial significance in such a system. Currently, some very simple designs are used in the form of straight plain fins, transverse strips, or other similar geometries, but the creation of high heat transfer efficiency surfaces in such small sizes becomes very difficult with traditional subtractive manufacturing methods. When using additive manufacturing though these types of surfaces are not an issue. This paper covers the comparison of experimental results with conjugate heat transfer computational fluid dynamics (CFD) models and empirical heat balance models for two different additively manufactured (AM) liner cooling geometries and an AM blank liner. The two cooling fin geometries include a rotating plain fin and an offset strip fin. The liners were tested in an AM-built reverse flow radial swirl stabilized combustion chamber at a variety of operating conditions. During the experiments, the surfaces were compared using a thermal camera to record the outer liner temperature, which was viewed through a quartz outer casing. The experimental results showed that the cooling surfaces were effective at reducing the liner temperatures with minimal pressure losses for multiple operating points. Those results were then compared against the conjugate heat transfer CFD models and the empirical calculations used to design the surfaces initially. From this comparison, it was noticed both the CFD and empirical calculations under-predicted the wall temperatures. This is thought to be due to inaccuracies in the predicted flame temperatures and the assumed emissivity values used to calibrate the thermal imaging camera. Further uncertainties arise from the assumption of a constant air and hot gas temperature and mass flow along the cooling surfaces and the lack of data for the surface roughness of the parts.

scholarly journals Uncertainties Analysis on the Prediction of Flow and Heat Transfer of Liquid Sodium with CFD Technology

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Zhanwei Liu ◽  
Xinyu Li ◽  
Tenglong Cong ◽  
Rui Zhang ◽  
Lingyun Zheng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Coefficient ◽  
Liquid Sodium ◽  
Heat Transfer Characteristics ◽  
Backward Facing Step ◽  
Heating Wall ◽  
Transfer Characteristics ◽  
Cfd Models ◽  
Flow And Heat Transfer

The prediction of flow and heat transfer characteristics of liquid sodium with CFD technology is of significant importance for the design and safety analysis of sodium-cooled fast reactor. The accuracies and uncertainties of the CFD models should be evaluated to improve the confidence of the numerical results. In this work, the uncertainties from the turbulent model, boundary conditions, and physical properties for the flow and heat transfer of liquid sodium were evaluated against the experimental data. The results of uncertainty quantization show that the maximum uncertainties of the Nusselt number and friction coefficient occurred in the transition zone from the inlet to the fully developed region in the circular tube, while they occurred near the reattachment point in the backward-facing step. Furthermore, in backward-facing step flow, the maximum uncertainty of temperature migrated from the heating wall to the geometric center of the channel, while the maximum uncertainty of velocity occurred near the vortex zone. The results of sensitivity analysis illustrate that the Nusselt number was negatively correlated with the thermal conductivity and turbulent Prandtl number, while the friction coefficient was positively correlated with the density and Von Karman constant. This work can be a reference to evaluate the accuracy of the standard k-ε model in predicting the flow and heat transfer characteristics of liquid sodium.

Transient Three-Dimensional Heat Transfer Model of a Solar Thermochemical Reactor for H2O and CO2 Splitting via Nonstoichiometric Ceria Redox Cycling

2013 ◽  
Author(s):  
Justin Lapp ◽  
Wojciech Lipiński
Keyword(s):  
Heat Transfer ◽  
Heat Recovery ◽  
Fuel Efficiency ◽  
Three Dimensional ◽  
Reactor Design ◽  
Heat Transfer Model ◽  
Heat Fluxes ◽  
Transfer Model ◽  
Rotating Cylinders ◽  
Solar Receiver

A transient heat transfer model is developed for a solar reactor prototype for H2O and CO2 splitting via two-step non-stoichiometric ceria cycling. Counter-rotating cylinders of reactive and inert materials cycling between high and low temperature zones permit continuous operation and heat recovery. To guide the reactor design a transient three-dimensional heat transfer model is developed based on transient energy conservation, accounting for conduction, convection, radiation, and chemical reactions. The model domain includes the rotating cylinders, a solar receiver cavity, and insulated reactor body. Radiative heat transfer is analyzed using a combination of the Monte Carlo method, Rosseland diffusion approximation, and the net radiation method. Quasi-steady state distributions of temperatures, heat fluxes, and the non-stoichiometric coefficient are reported. Ceria cycles between temperatures of 1708 K and 1376 K. A heat recovery effectiveness of 28% and solar-to-fuel efficiency of 5.2% are predicted for an unoptimized reactor design.

Turbine Split Rings Thermal Design Using Conjugate Numerical Simulation

2013 ◽  
Author(s):  
Aleksei S. Tikhonov ◽  
Andrey A. Shvyrev ◽  
Nikolay Yu. Samokhvalov
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Gas Turbine ◽  
Gas Dynamics ◽  
Thermal Condition ◽  
Fuel Efficiency ◽  
Thermal Design ◽  
Design Practice ◽  
Gas Temperature ◽  
Split Ring

One of the key factors ensuring gas turbine engines (GTE) competitiveness is improvement of life, reliability and fuel efficiency. However fuel efficiency improvement and the required increase of turbine inlet gas temperature (T*g) can result in gas turbine engine life reduction because of hot path components structural properties deterioration. Considering circumferential nonuniformity, local gas temperature T*g can reach 2500 K. Under these conditions the largest attention at designing is paid to reliable cooling of turbine vanes and blades. At present in design practice and scientific publications comparatively little attention is paid to detailed study of turbine split rings thermal condition. At the same time the experience of modern GTE operation shows high possibility of defects occurrence in turbine 1st stage split ring. This work objective is to perform conjugate numerical simulation (gas dynamics + heat transfer) of thermal condition for the turbine 1st stage split ring in a modern GTE. This research main task is to determine the split ring thermal condition by defining the conjugate gas dynamics and heat transfer result in ANSYS CFX 13.0 package. The research subject is the turbine 1st stage split ring. The split ring was simulated together with the cavity of cooling air supply from vanes through the case. Besides turbine 1st stage vanes and blades have been simulated. Patterns of total temperature (T*Max = 2000 °C) and pressure and turbulence level at vanes inlet (19.2 %) have been defined based on results of calculating the 1st stage vanes together with the combustor. The obtained results of numerical simulation are well coherent with various experimental studies (measurements of static pressure and temperature in supply cavity, metallography). Based on the obtained performance of the split ring cooling system and its thermal condition, the split ring design has been considerably modified (one supply cavity has been split into separate cavities, the number and arrangement of perforation holes have been changed etc.). All these made it possible to reduce considerably (by 40…50 °C) the split ring temperature comparing with the initial design. The design practice has been added with the methods which make it possible to define thermal condition of GTE turbine components by conjugating gas dynamics and heat transfer problems and this fact will allow to improve the designing level substantially and to consider the influence of different factors on aerodynamics and thermal state of turbine components in an integrated programming and computing suite.

scholarly journals Steady MHD Flow of Viscous Fluid between Two Parallel Porous Plates with Heat Transfer in an Inclined Magnetic Field

2015 ◽  
Vol 7 (3) ◽  
pp. 21-31 ◽  
Author(s):  
D. R. Kuiry ◽  
S. Bahadur
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Viscous Fluid ◽  
Pressure Gradient ◽  
Reverse Flow ◽  
Flow Behavior ◽  
Fluid Pressure ◽  
Mhd Flow ◽  
Fluid Viscosity ◽  
Temperature Dependent Viscosity

The steady flow behavior of a viscous, incompressible and electrically conducting fluid between two parallel infinite insulated horizontal porous plates with heat transfer is investigated along with the effect of an external uniform transverse magnetic field, the action of inflow normal to the plates, the pressure gradient on the flow and temperature. The fluid viscosity is supposed to vary exponentially with the temperature. A numerical solution for the governing equations for both the momentum transfer and energy transfer has been developed using the finite difference method. The velocity and temperature distribution graphs have been presented under the influence of different values of magnetic inclination, fluid pressure gradient, inflow acting perpendicularly on the plates, temperature dependent viscosity and the Hartmann number. In our study viscosity is shown to affect the velocity graph. The flow parameters such as viscosity, pressure and injection of fluid normal to the plate can cause reverse flow. For highly viscous fluid, reverse flow is observed. The effect of magnetic force helps to restrain this reverse flow.

Modeling and Control of the Electrical Actuation System of an Active Hydromagnetic Journal Bearing (AHJB)

2014 ◽  
Author(s):  
Michael G. Farmakopoulos ◽  
Eleftherios K. Loghis ◽  
Pantelis G. Nikolakopoulos ◽  
Nikolaos I. Xiros ◽  
Chris A. Papadopoulos
Keyword(s):  
Power Plants ◽  
Magnetic Hysteresis ◽  
Load Force ◽  
Specific Power ◽  
Data Series ◽  
Power Electronic ◽  
Sampled Data ◽  
Rotating Shaft ◽  
Electrical Actuation ◽  
Actuation System

The architecture of the electrical actuation module driving a magnetic-hydraulic bearing system is presented. The bearing is intended to be scaled for use in applications of all sizes in industries like shipboard for support of the engine-propeller shaft or in power-plants for the shaft through which the prime mover, e.g. steam or gas turbine, is driving the electric generator. The benefits of this new bearing is first and foremost its superb performance in terms of low down to practically no friction losses since there is no direct contact between the supporting bearing surface and the rotating shaft supported. Other benefits include the potential of active, inline, real-time balancing and alignment. To implement such concept of a magnetic-hydraulic bearing, the following tasks need to be carried out. First, identification of mechanical, electrodynamical and circuit properties of the bearing’s electromagnets in the system is necessary. Toward such identification, a series of experiments needed to be carried out. To be able to carry out these experiments, a specific power electronic converter is developed to drive each electromagnet. The power electronic drive is a quad MOSFET circuit based on full-bridge converter topology and outfitted with appropriate sensory instrumentation to collect and record measurements of all the physical variables of interest. Special care has been taken to compensate for magnetic hysteresis of the electromagnets, mitigate any induction heating effects and maintain operation within the material’s linear region i.e. without significant saturation occurring. The use of a power transistor bridge allows rapid changes to be applied on the electromagnet’s load force which could compensate disturbance or misalignment developed on the shaft supported. The data series from these experiments are useful for formulating a possibly nonlinear model of the electromagnetical and electromechanical processes involved in the bearing’s operation. Such a model can then be employed to help design a digital microcontroller system which could effectively drive the power electronics and electromagnets to perform their required tasks as part of the bearing. Besides, the model could also be used for the synthesis of the nonlinear, sampled-data (discrete-time) control law which will be programmed on the microcontroller system board.

Comparisons of Pins/Dimples/Protrusions Cooling Concepts for a Turbine Blade Tip-Wall at High Reynolds Numbers

2010 ◽  
Author(s):  
Gongnan Xie ◽  
Bengt Sunde´n ◽  
Weihong Zhang
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Computational Models ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Gas Leakage ◽  
Leakage Flows ◽  
Blade Tip ◽  
High Reynolds ◽  
The Cost

The blade tip region encounters high thermal loads because of the hot gas leakage flows, and it must therefore be cooled to ensure a long durability and safe operation. A common way to cool a blade tip is to design serpentine passages with 180° turn under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase blade tip lifetime. Pins, dimples and protrusions are well recognized as effective devices to augment heat transfer in various applications. In this paper, enhanced heat transfer of an internal blade tip-wall has been predicted numerically. The computational models consist of a two-pass channel with 180° turn and arrays of circular pins or hemispherical dimples or protrusions internally mounted on the tip-wall. Inlet Reynolds numbers are ranging from 100,000 to 600,000. The overall performance of the two-pass channels is evaluated. Numerical results show that the heat transfer enhancement of the pinned tip is up to a factor of 3.0 higher than that of a smooth tip while the dimpled-tip and protruded-tip provide about 2.0 times higher heat transfer. These augmentations are achieved at the cost of an increase of pressure drop by less than 10%. By comparing the present cooling concepts with pins, dimples and protrusions, it is shown that the pinned-tip exhibit best performance to improve the blade tip cooling. However, when disregarding the added active area and considering the added mechanical stress, it is suggested that the usage of dimples is more suitable to enhance blade tip cooling, especially at low Reynolds numbers.

scholarly journals Active magnetocaloric heat pipes provide enhanced specific power of caloric refrigeration

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Lena Maria Maier ◽  
Patrick Corhan ◽  
Alexander Barcza ◽  
Hugo A. Vieyra ◽  
Christian Vogel ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Pipes ◽  
Heat Transfer Fluid ◽  
Specific Power ◽  
Cooling Power ◽  
Cycle Frequency ◽  
Cooling Systems ◽  
Cooling Unit ◽  
Order Of Magnitude ◽  
Almost All

Abstract Today almost all refrigeration systems are based on compressors, which often require harmful refrigerants and typically reach 50% of the Carnot efficiency. Caloric cooling systems do not need any detrimental fluids and are expected to reach 60–70% of the Carnot limit. Current caloric systems utilise the active magnetocaloric regeneration principle and are quite cost-intensive, as it is challenging to achieve large cycle frequencies and thus high specific cooling powers with this principle. In this work, we present an alternative solution where the heat transfer from the heat exchangers to the caloric material is predicated on condensation and evaporation of a heat transfer fluid. Using thermal diodes, a directed heat flow is generated. Thereby we were able to build a cooling unit achieving a specific cooling power of 12.5 W g−1 at a cycle frequency of 20 Hz, which is one order of magnitude larger than the state-of-the-art.

Heat Transfer and Friction Studies in a Tilted and Rib-Roughened Trailing-Edge Cooling Cavity With and Without the Trailing-Edge Cooling Holes

2014 ◽  
Author(s):  
Mohammad Taslim ◽  
Joseph S. Halabi
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Flow Direction ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Cross Sectional ◽  
Heat Transfer Coefficients ◽  
Cfd Models ◽  
Cooling Cavity ◽  
Rib Roughened

Local and average heat transfer coefficients and friction factors were measured in a test section simulating the trailing edge cooling cavity of a turbine airfoil. The test rig with a trapezoidal cross sectional area was rib-roughened on two opposite sides of the trapezoid (airfoil pressure and suction sides) with tapered ribs to conform to the cooling cavity shape and had a 22-degree tilt in the flow direction upstream of the ribs that affected the heat transfer coefficients on the two rib-roughened surfaces. The radial cooling flow traveled from the airfoil root to the tip while exiting through 22 cooling holes along the airfoil trailing edge. Two rib geometries, with and without the presence of the trailing-edge cooling holes, were examined. The numerical model contained the entire trailing-edge channel, ribs and trailing-edge cooling holes to simulate exactly the tested geometry. A pressure-correction based, multi-block, multi-grid, unstructured/adaptive commercial software was used in this investigation. Realizable k–ε turbulence model in conjunction with enhanced wall treatment approach for the near wall regions, was used for turbulence closure. The applied thermal boundary conditions to the CFD models matched the test boundary conditions. Comparisons are made between the experimental and numerical results.

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