Steam and Gas for Power Generation

Nowadays, gas and steam turbines are contributing to more than 80% of the electricity generated worldwide. If we add the contribution from hydro turbines too, then we reach 98% of total production.

The improvement of the flow path is crucial, and an advanced design can be achieved through several strategies. The aerodynamic optimization of gas and steam turbines can lead to enhanced efficiency. In addition to that, the minimization of secondary losses is possible by introducing advanced endwall shaping and clearance control. Moreover, further increase of efficiency can be achieved by decreasing the losses of kinetic energy at the outlet from the last stage of the turbine. This can be done using longer last-stage blades as well as improving the diffuser recovery and stability.

Flow Path
                     Flow Path of a Gas Turbine

Moreover, increased gas turbine performance is very much related to an increase of the turbine inlet temperature. However, the coolant mass flows will need to be minimized at the same time to achieve the highest performance benefits possible [1]. Therefore, effort must be put on the development of advanced cooling system concepts for the engine’s first stage components. New cooling surfaces as well as new cooling schemes should be studied by CFD modelling to use the coolant in the best possible way before it leaves the component.

A phenomenon that must be further addressed in this context is hot gas ingestion which can cause unacceptably high rotor temperatures. We need to develop more advanced technologies that will handle hot gas ingestion to make sure that the hot gases will be confined in the cavity without reaching the rotor itself. To use new sophisticated cooling methods based on porous structures a new method of thinking is necessary. Analysis methods, design concepts, and criteria must be developed and tested for such structures in order to optimize the design for components with porous structures. High temperature materials in gas turbines have properties that change significantly during the expected life of the component due to thermal exposure, mechanical load and the combination of the two. Issues that affect lifting and reliability and can cause serious problems are, for example, crack propagation usually due to creep or fatigue. In many components, early TBC (Thermal Barrier Coating) spallation will increase the material temperature of the component and reduce the safe life for which the component can be used [1].

Considerations for any power system, new or existing, include not only efficiency and optimization, but also cost, longer life-cycle of components, and keeping pace with current environmental restrictions. Given the scale of some of these projects, accurate early-stage design is critical for project success, whether it’s a new construction or retrofit.

At SoftInWay we have built our reputation on creating accurate preliminary design models for such projects. Our strength in engineering and power plant consulting combined with our AxCYCLE® heat balance calculation software are core offerings of success for turbomachinery design in the power generation sector.

References:

[1]http://www.euturbines.eu/cms/upload/publictaions/documents/EUTurbines_Roadmap_on_Turbomachinery_Research-final.pdf

 

SuperTruck II Program and Waste Heat Recovery Systems

Familiar to many, the 2011 SuperTruck program was a five-year challenge set by the U.S. Department of Energy to create a Class-8 truck that improves fuel efficiency by 50 percent.  Hoping for even more groundbreaking achievements this time around, the Department of Energy has initiated a second five-year program to bring further fuel-efficiency advancements and near closer to eventual commercialization.  Cummins, Peterbilt, Daimler Trucks North America, Navistar, and Volvo Group remain the five teams involved in this R&D endeavor.  Michael Berube, head of the Energy Department’s vehicle technology office mentioned “SuperTruck II has set goals beyond where the companies think they can be.”  SuperTruck II is looking for a 100 percent increase in freight-hauling efficiency and a new engine efficiency standard of 55 percent.  With such lofty goals, the SuperTruck II development teams will need to tackle improvements in freight efficiencies from all sides.

Figure 1 - Daimler SuperTruck
Figure 1 – Daimler SuperTruck

Material considerations, body aerodynamics, low-resistance tires, predictive torque management using GPS and terrain information, combustion efficiency, and several other improvements methods on the first iteration have demonstrated how the SuperTruck II will require a multi-phase and integrated systems approach to achieve equally successful numbers. However, with an engine efficiency target that is 31 percent above the SuperTruck’s first go around, special attention will be required on engine advancement to achieve an efficiency standard of 55 percent.

One of the main methods apart from auxiliary load and friction reduction is a comprehensive waste heat recovery (WHR) system dedicated to the engine.  From the existing works devoted to waste heat recovery, the following methods of efficiency increase can be highlighted:

  1. Addition of the internal heat recuperation to a WHR cycle
  2. Appropriate working fluid selection
  3. Increment of initial parameters of bottoming cycle up to supercritical values
  4. Maximize waste heat utilization due to the usage of low temperature heat sources
  5. Bottoming cycle complexification or usage of several bottoming cycles with different fluids

Figure 2 - AxSTREAM Platform for Radial Turbine Design
Figure 2 – AxSTREAM Platform for Radial Turbine Design

With regards to fluid selection, no universal organic fluid exists that is suitable for a wide range of ORC applications.  For this reason, each WHR project requires an extensive fluid selection analysis as one of the main design steps.  In general, working fluids are selected based on their thermodynamic properties, thermal stability, and environmental impact/safety.  Amongst the most popular options are water, ethanol, R245fa, and R134a.  Once the proper design range it set for the waste heat cycle, the designer can successfully set which fluid may be the best for its given application.

Later in the design process, the engineer must consider how to design a turbine that will create the optimal amount of power for the selected fluid type and operating ranges.  With high efficiency targets on the SuperTruck II, the proper experience and resources are required to create high-efficiency ORC turbines that can achieve these targets.  It is will be interesting to see what kind of engine advancements and technologies will be utilized from each design team throughout the outset and final completion of the SuperTruck II.  If you would like to learn more about SoftInWay’s AxSTREAM platform for design ORC Turbines in WHR cycles, please visit: http://www.softinway.com/software-applications/heat-balance-design-analysis/ 

References:

http://www.softinway.com/wp-content/uploads/2015/10/whr-based-on-SORC-10-2015.pdf

https://energy.gov/articles/energy-department-announces-137-million-investment-commercial-and-passenger-vehicle

https://www.trucks.com/2016/10/31/supertruck-program-5-year-phase/

https://energy.gov/sites/prod/files/2014/03/f8/deer12_sisken.pdf

 

Compressor Types in Air Conditioning Systems

Compressor for HVAC
Source

A compressor unit is an important component in an air conditioning system used to remove the heat laden vapor refrigerant from the evaporator. The compressor raises the temperature and pressure of the working refrigerant fluid and transforms it to a high temperature and high pressure gas. Since the compressor is one of the most vital parts of a cooling system, to be able to have an efficient working cycle, an appropriate and optimum compressor design must be installed.

Generally, there are 5 types of compressor that can be used in HVAC installations, the most common  of which being reciprocating compressors used within a smaller scale conditioning system. Reciprocating compressors utilize pistons and cylinders to compress the refrigerant and an electric motor is used to provide a rotary motion.

In recent application, scroll compressors are found to be increasingly popular as an alternative to reciprocating compressors in HVAC installation. This type of compressor outstands in the reliability and efficiency sector when compared to reciprocating compressors. Scroll compressors consist of one stationary scroll and a second moving scroll which compresses the refrigerant – giving this type of compressor fewer moving parts and thus, higher reliability and efficiency. At a smaller size, scroll compressors can achieve similar flow rates and outlet pressure when compared to reciprocating compressors.

There are different kinds of rotary compressors, the most common ones being rotary screw and rotary vane. Rotary vane compressors are known to be smaller, quieter and more reliable and are commonly used in smaller residential split system applications. The application works with a rotating shaft as the blades move around the cylinder. The other rotary compressor consists of stationary blades which are attached to the housing, used for larger applications in comparison to rotary vane compressors.

Last but not least is the centrifugal compressor. Centrifugal compressors are mostly used in industrial installations due to the ability to cool large capacity of air. No piston, valve or cylinder is incorporated in the design and it relies on centrifugal force enabling it to have very few moving parts leading to higher efficiency and reliability.

Interested in learning more! Check out AxSTREAM for your compressor design!

References: 

  1. http://www.airconditioning-systems.com/air-conditioner-compressor.html 
  2. https://www.artplumbingandac.com/air-conditioning/different-types-of-air-conditioning-compressors/ 

Thermo-Physical Properties of Fluids for Simulation of Turbomachinery

Computer simulation and use of CAE/CAD are well-established tools used to understand the critical aspects of energetics (various losses), kinematics (velocities, mach no. etc.) and thermodynamics (pressures, temperatures, enthalpy etc) in thermodynamic cycles and turbomachinery. Computational models are now enabling the design and manufacture of machines that are more economical, have higher efficiency and are more reliable. Accuracy of complex processes that are simulated depends on thermos-physical properties of the working fluid used as input data. The importance of such properties was recognized when it became evident that a steam turbine cycle can have efficiency variance by a few percentage points depending on the chosen set of fluid properties.

Today the thermo-physical properties data is represented in the form of a set of combined theoretical and empirical predictive algorithms that rest on evaluated data. These techniques have been tested and incorporated into interactive computer programs that generate a large variety of properties based upon the specified composition and the appropriate state variables. Equations of state, correlations, or empirical models are used to calculate thermos-physical properties of fluids or mixtures. Examples of this include Helmholtz energy based equations, cubic equation of state, BWR pressure explicit equations, corresponding states models, transport models, vapor pressure correlations, spline interpolations, estimation models or calculation methods for vapor-liquid equilibrium or solubility, and surface tension correlations. Further fitting techniques, and group contribution methods are incorporated. The following broad level properties are often used in simulation tools:

  1. Thermodynamic properties including equation of state, phase equilibria, p-V-T behavior, heat capacity, enthalpy, thermal expansion, sound speed, and critical phenomena.
  2. Transport properties including thermal and electrical conductivity, viscosity, mass diffusion, thermal diffusion, non-Newtonian behavior, and thermal, thermoacoustic, and other diffusion waves.
  3. Optical and thermal radiative properties including dielectric constant, refractive index, emissivity, reflectivity, and absorptivity.
  4. Interfacial properties including solid-solid interfaces, surface tension, interfacial profiles, interfacial transport, and wetting.



Databases are now available for hydrocarbon mixtures, including natural gas, as well as a number of pure and mixed fluids of industrial importance. IAPWS, NIST and Coolprop are a few examples of such resources that provide valuable tools for turbomachinery and refrigeration engineers, and chemical and equipment manufacturers. One example is the IAPWS-IF97 that divides water and steam properties into five distinct regions.

Another example is properties of R134a expressed as 32 term, modified Benedict-Webb-Rubin (MBWR) equation of state, the accuracy of equation of state is estimated to be ± 0.2 % in density, ± 1 % in constant volume heat capacity and ± 0.6 % in sound velocity. The thermos-physical property databases provide core information for process modeling and development. The completeness, correctness, currency and reliability of the data as well as the integrity and management of the database itself are important factors in the ultimate reliability of the modeled process.

Micro Gas Turbines – Addressing the Challenges with AxSTREAM

During the last decade the development and extensive use of unmanned air vehicles (UAV) has accelerated the need for high performing micro gas turbines. In fact, their large energy density (Whr/kg) makes them attractive not only for UAV application, but also for portable power units, as well as for distributed power generation in applications where heat and power generation can be combined.
Micro gas turbines have the same basic operation principle as open cycle gas turbines (Brayton open cycle). In this cycle, the air is compressed by the compressor, going through the combustion chamber, where it receives energy from the fuel and thus raises in temperature. Leaving the combustion chamber, the high temperature working fluid is directed to the turbine, where it is expanded by supplying power to the compressor and for the electric generator or other equipment available [1].

Regarding the design of micro gas turbines, there are several challenges that need to be overcome. First, scaling is a common technique to define larger or smaller geometries with similar characteristics. However, a simple scaling of a high performance large gas turbine is not the right way to go for a good micro gas turbine design. One of the main reasons is the big change of the Reynolds number, as well as the heat transfer between the hot and cold components, which is not negligible [2].

Moreover, the high rotational speed that is needed to obtain the enthalpy and pressure changes prescribed by the gas turbine cycle constitutes a major mechanical problem. As far as geometrical constraints are concerned, material and manufacturing technique selection is crucial in order to lower the cost of the production, since micro gas turbines need to compete with heavier but cheaper batteries in many cases (i.e. for UAV applications). Finally, another major issue in micro gas turbines is the decrease of compressor and turbine efficiency with decreasing dimensions.

To address the above challenges and ensure a robust design, powerful tools are needed. AxCYCLE allows the user to design, analyse and optimize the thermodynamic cycles of the micro gas turbines and export the boundary conditions to AxSTREAM software platform for design and optimization of the components. The integration of preliminary design, CFD, FEA, and rotordynamic modules along with the simulation of cooling and secondary system flows under one common platform gives the power of controlling the overall design process while decreasing significantly the engineering time. Request now for a demonstration of AxSTREAM and speak to our engineers for additional details on the design process.

References:

[1] http://dx.doi.org/10.5772/54444

[2] “Micro Gas Turbines – A Short Survey of Design Problems”, R.A. Van den Braembussche, von Kármán Institute for Fluid Dynamics

Upcoming Webinar: Design and Optimization of Axial and Mixed Flow Fans for High Efficiency and Low Noise

Thursday, May 18 | 10:00 – 11:00 AM EST

Axial Fan CAD Image
Registration is now open for our May webinar demonstrating best practices for the development of competitive, high efficiency, and low noise axial and mixed flow fans for different aerodynamic loadings.

Axial and mixed flow fans have been in high demand for a number of years. The application of these machines span many different industries including HVAC, automotive, appliance, military equipment, and much more. Like many other types of turbomachinery, changing industry standards and market trends have resulted in fierce rivalry to compete on lifespan, efficiency, environmental and user friendliness, and overall quality. With this in mind, it goes without saying that companies are looking for tools needed to develop highly efficient equipment while minimizing noise as quiet fans are typically more desirable which results in higher demand and marketability.

Over the course of the last few years our company has experienced a number of clients coming to us requesting help with axial fan redesign. This is due to many factors including flawed code during the initial design. Often what would happen is the original design code would have issues with matching meanline/streamline simulations and CFD. This resulted in an insufficient design which, given the increased competition in the market, is less than ideal. Currently, we support different clients in these industries through the use and application of AxSTREAM®. By utilizing our software platform clients can develop competitive, high efficiency, and low noise axial and mixed flow fans the first time around or redesign existing models to meet their full potential.

Due to our experience, we wanted to share our expertise in our upcoming complementary webinar. Topics covered include:

Axial Fan CAD Front

  1. An overview of axial and mixed flow fans and their practical application
  2. Requirements of axial and mixed flow fans
  3. Noise estimation techniques
  4. Axial fan design using the AxSTREAM® software platform
  5. Fan blade design and optimization
  6. Fan aerodynamic blade loadings and performance simulation

 

The webinar also consists of a live software demonstration and a Q&A session with the presenter at the end of the presentation. Register below or follow this link for more information!

Register Here!

Turbomachinery Software for Education

Turbomachinery design has significantly evolved over the last two decades, as supporting education and training methods and techniques remains a challenge. Diversity of technologies covered in the varying courses and extensive use of software by industry designers makes the task of delivering the course curriculum that meets expectations of industry and students difficult. Many educational institutes and business use generic CAE tools for the purpose of learning turbomachinery through student projects. While generic tools have proven their value in research and design, the comprehensiveness of these tools to tackle real life turbomachinery situations is far from desired. The inexperience of fresh graduates from universities and colleges in their inability to perceive a 4D machinAxSTREAM EDUe (3D plus time), traditionally taught using a 2D blackboard, is evident. A student is not only required to have a very good understanding of underlying fundamentals, but is also required to address multitude of design, analysis and optimization problems within the limited time available for education. Coupling of theoretical and computer aided design knowledge to augment the capability of students to contribute to the industrial endeavor is necessary. Such a solution provides students with implicit understanding of the level of detail required by final designs, such as mean line design to the specification of a blade profile varying from hub to tip of a blade, and further complexities of iteration due to an aerodynamically correct blade profile being unsuitable because of stress levels or excitation frequencies and much more. AxSTREAM® EDU introduces multiple dimensions of design required by turbomachinery very early in the instruction process which, by using,  the students are able to develop insights that traditionally are difficult to attain in the same time frame. The use of AxSTREAM® EDU as a design software has been proven to multiply the skills of the students, enabling broad 3-D design considerations and visualization seldom possible otherwise.

AxSTREAM® EDU provides the user with the ability to design many different types of turbomachinery from scratch, such as axial turbines and compressors, radial compressors and turbines, axial fans, integrally geared compressors, mixed flow turbines and compressors and more. The moot question is how important is preliminary design? The efficiency gain possible to achieve in the preliminary design is of the order of 5-10 %, as compared to 0.5 % using 3D optimization (blade profiling, stress and CFD). One has an option of spending several weeks running  full 3D CFD calculations in generic software to try to optimize 0.5% of design, or spending much less time and resources using AxSTREAM® to figure out the best flow path design, followed by use integrated stress, CFD and rotor dynamic solvers!

Expander Configurations and Torsional Analysis

Lateral rotor-dynamic behavior is often discussed as one the critical aspects in determining the reliability and operability of rotating equipment. However, as multiple equipment are coupled together to form trains for centrifugal pumps, fans/blowers, compressors, steam or gas turbines and motors or generators, torsional behavior requires a thorough analysis. As per industry standards, torsional response is sought only for train units comprising of three or more coupled machines (excluding any gears).Blog 6

The configurations of the expanders used in the oil and gas industry makes it not only ideal but mandatory to perform train torsional analysis.  Expander trains are commonly used in CCU and FCU units and in the production of nitric acid. Serving the purpose of energy recovery, various arrangement for power recovery train are illustrated to the left:

As part of torsional analysis, the drive-train critical speeds (rotor lateral, system torsional, blading modes, and the like) need to be established to ensure they will not excite any critical speed of the machinery and the entire train is suitable for the rated speed and starting-speed hold-point requirements of the train. Finding frequency margins (torsional natural frequencies and torsional excitations) and if necessary undertaking stress analysis is mandated to demonstrate that resonances do not have  an adverse effect.RD

Such analysis requires modelling complexities of flexible supports, foundation, rotor seal interaction, instabilities etc. of the entire train and their interaction. SoftInWay’s CAE tool AxSTREAM® RotorDynamics is comprehensive, user friendly, and fully integrated with modules for flowpath and blade design making it unique to undertake train torsional analysis. Further information about the software is available by following the link

Air Conditioning in Automotive

Car AC
                          Source

While the term of air conditioning in relation to automotive might instantly correlate to a system which provides passenger with a comfortable air temperature/environment, HVAC systems also are used for heating and cooling of batteries in such application as well as cooling of the vehicle fuel systems. Thermal management for automotive application isn’t easy though. Many factors have to be accounted for in order to build a dependable cooling system.

While talking about HVAC concerns and challenges which arise in automotive application, the biggest inconvenience commonly comes down to the lack of cold air produces. Mobile refrigeration/air conditioning systems come with quite a few concerns from two sides: the refrigeration side, where it removes heat and injects cold air, and from the electrical side which provides control. From the system, the most common challenges are found in moisture –which would fail the cooling system if present in the air, soiled condenser which would block air flow, and various other mechanical complications which might occurs.

While diagnosing an air conditioning issue, especially if environment temperature seems higher than it should be, there are few conditions that can be looked into including freon leak, failed blower, damaged or failed motor, damaged condenser to the most common problem usually arises from the compressor. Compressor, compressor clutch switch, fuses, wires, fan belt and seal are at the top of the list to be check for functional adequacy. Consequently, with many concerns arising from the compressor side of the system, a good and reliable compressor design must be implemented to avoid unwanted challenges during operation. Design your automotive turbomachinery with SoftInWay! Ask us about the projects that we’ve done in this field and how our turbomachinery development code will be helpful for your automotive and HVAC design, analysis and optimization activities.

References:

http://www.doityourself.com/stry/5-common-car-air-conditioning-system-problems

http://www.aa1car.com/library/ac98.htm 

http://www.agcoauto.com/content/news/p2_articleid/256

http://blog.firestonecompleteautocare.com/ 

Foil Air Bearings for High-Temperature Turbocharger Applications

Within the realm of turbocharging, there are a number of different design challenges that influence the design process on both large-scale marine applications and smaller-scale commercial automobile applications.  From aerodynamic loads to dynamic control systems to rotor dynamics and bearing challenges, turbochargers represent a special subset of turbomachinery that requires complex and integrated solutions.  Turbocharger rotors specifically, have unique characteristics due to the dynamics of having a heavy turbine and compressor wheel located at the overhang ends of the rotor. The majority of turbocharger rotors are supported within a couple floating-ring oil film bearings.  In general, these bearings provide the damping necessary to support the high gyroscopic moments of the impeller wheels.  However, there are several disadvantages of working with these oil systems that have allowed different technologies to start to surface for these turbomachines.  With the floating-ring oil models, varying ring speed ratios and oil viscosity changes significantly influence the performance of the rotor dynamic model.

Dan blog bearing for turbochargers
Figure 1 – Floating-Ring Bearing Model for a Turbocharger

The application of oil-free bearings have started to emanate due to the overall consistency of their performance and the minimized heat loss associated with air as the damping fluid. Studies on these bearing types for turbomachinery applications are neither trivial nor unique, as they have seen plenty of exposure within the commercial and military aircraft industries within turbo compressors and turboexpanders. However, the success of these specific applications are due to the fact that these turbomachines operate with light loads and relatively low temperatures. The main design challenges with foil air bearings are a result of poor rotor dynamic performance, material capabilities, and inadequate load capacities at high temperature/high load applications.

Foil Air Bearing
Figure 2 – Foil Air Bearing

Foil air bearings operate based on a self-acting hydrodynamic air film layer during normal operation, but they exhibit serious wear on start up and shut down if not properly attended to. Prior to developing a gas film on start up, these bearings must handle the sliding that occurs between the rotor and the inner surface of the bearings. For this reason, solid lubricants like polymer foil coatings were considered for these bearings. Polymer coatings have a serious temperature restriction which do not allow them to be considered for high-temperature applications above 300 °C. Different chrome oxide based coatings have shown greater performance at higher temperatures. Initial testing of these coatings showed significantly poor performance at lower temperatures of 25 °C and difficulties with adhesion through repeated thermal cycles. However, NASA has developed a new high temperature PS400 formulation of this coating that performs well under different load conditions and between the temperature range of 25 °C and 650 °C. Essentially, the viability of these bearings within the automotive market has become a reality with individualized bearing designs. The question now becomes whether the foil gas bearing manufacturers can penetrate the market from a larger-scale and create a standard for these turbocharger setups to run free of oil altogether. To learn more about the simulation of both floating-ring oil film bearings and foil air bearings using the SoftInWay platform, please visit: http://www.softinway.com/software-applications/bearing-design/

References:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20000004303.pdf

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090033769.pdf