The Optimization Challenge in the Development of Turbomachinery

Optimization (or parametric studies) of a twin spool bypass turbofan engine with mixed exhaust and a cooled turbine can be considered one of the most complex problem formulations. For engine selection, determining the thrust specific fuel consumption and specific thrust is necessary against variables such as design limitations (Inlet temp, etc.), design choices (fan pressure ration, etc.) and operating conditions (speed & altitude). The task involves cycle level studies following machine, module, stage and component level optimization. This calls for an integrated environment (IE) and it is desirable to have such an IE operating on a “single” platform.

Historically IE was developed for the design of axial turbines (mainly steam). Later, it was expanded for gas turbines (especially blade cooling calculations) and axial compressors via plug-in modules. The new challenge designers face today is developing mixed flow machinery. An effective system for modern turbomachinery design needs to do the following:

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Alternative Refrigerants to R-22

Gas tanks
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The majority of HVAC installations dating back to the 1990s have R-22 as their main working fluid. However, recent studies have proven that R-22 or as we commonly known as “Freon” (brand type) is not as environmentally friendly as we once thought it was. Ergo the use of this refrigeration type has been banned by the Environmental Protection Agency along with other substances which contributes to ozone depletion. With phasing out of R-22, HVAC manufacturers and end-users are forced to look into other comparable refrigerants which won’t negatively impact the environment as much.

R-410A offers a few benefits when compared to the traditional R-22 fluid – one of which is greater energy efficiency which translates into lower operational costs. This hydro-fluorocarbon has been approved for use in new systems and is classified as a non-ozone-depleting HFC. One note that has to be taken into consideration is that R-410A operates on roughly a 50% higher pressure than R-22, thus can only work with high pressure limit equipment.

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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.

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Factors in your HVAC Selection

HVAC

A few decades ago, opening and closing a window was enough air temperature control. In modern days though, the standard bar of comfortable living has become higher and the occurrence of global warming, which raises the world’s temperature to the extremes, is abundant.  With all this in mind, temperature control becomes a major necessities. During this post, we will be exploring factors which should be considered for a new installation of a HVAC system either to modern or conventional homes.

Regardless of the size of property, ductwork that is balanced and well designed must be installed to make sure that the air and temperature circulation is optimal –especially for locations with extreme weather conditions. Externally insulated round ducts are found to be the most efficient. Installation of balance dampers in the ductworks should also be important to regulate airflow.

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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.

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Rerates, Upgrades, and Modifications to Steam Turbine

Steam Turbine DesignSteam turbines are designed to have long, useful lives of 20 to 50 years. Often, many parts of steam turbine are custom designed for each particular application, however, standardized components are also used. It is therefore inherently possible to effectively redesign a steam turbine several times during its useful life while keeping the basic structure (foot print, bearing span , casing etc) of these turbines unchanged! Indeed this is also true for many turbomachines. These redesigns are usually referred to as rerates and upgrades, depending on the reasons for doing them. The need for changes to hardware in an existing turbine may be required for (a) efficiency upgrades, (b) reliability upgrade (including life extension), (c) rerating due to a change in process (Process HMDB, use in combined cycle etc), and (d) modification for a use different from that of its original design. Typical changes include hardware components such as buckets/blades, control system,  thrust bearing , journal bearing , brush and laby seals, nozzle/diaphragm , casing modification,  exhaust end condensing bucket valves, tip seals and coatings.

Performance and Efficiency Upgrade The basic power and/or speed requirements of a steam turbine may change after commissioning for various reasons. The most common reason is an increase (or decrease) in the power required by the driven machine due to a plant expansion or de-bottlenecking. Other reasons include a search for increased efficiency, a change in the plant steam balance, or a change in steam pressure or temperature. Because steam turbines are periodically refurbished, an opportunity exists to update the design for the current operating environment. Turbine OEM’s , services companies and end users often face a challenge of undertaking engineering work within the very tight  time frame available for maintenance.  The AxSTREAM® software suite provides users with an automated capability of rerate, upgrade and modifications for performance and efficiency objectives. A summary of such features highlighting the capabilities is presented below:

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Compressor Types in Air Conditioning Systems

Compressor for HVAC
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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.

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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:

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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].

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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.

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