Exotic Turbomachinery – Viscous Disc Pumps

Turbomachinery can be divided into two main groups. Group one consists of machines that perform work on the fluid, requiring energy and increasing its pressure, such as compressors, pumps, and fans. Group two consists of those that extracts energy from the fluid flowing through it – for example, wind, hydro, steam, and gas turbines.

Pumps specifically are devices whose purpose is to move fluid at a constant density, increasing its kinetic energy and its pressure while consuming energy in the process. We are quite used to seeing centrifugal and axial pumps, as they are the most common configurations.  However, more exotic designs have been tested and developed throughout the history of fluid machinery.

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The Origin of Rotordynamics

Rotordynamics, the study of vibrational energy in rotors, has a rich history dating back to North America during the 1750’s. This branch of applied mechanics began with theories, but advanced quickly due to practices – starting with Mr. W.J.M Rankine in 1869 and his spinning shaft experiment. Now, decades later, we have strengthened our understanding of rotordynamics and created leading software tools, including AxSTREAM, that are able to simulate analyses to stabilize and increase the reliability of a turbomachinery.

W.J.M Rankine

Not only was W.J.M Rankine a prestigious theoretical scientist and educator, he was a main contributor in the development of rotordynamics and he contributed to thermodynamics and the development of heat engines throughout his lifetime. During his spinning shaft experiment, he concluded that beyond the shaft’s first critical speed, the shaft would be unstable simply because its shape had been bent. By not taking into consideration support damping and Coriolis force in his analysis, many engineers were left confused for almost two centuries, until Gustaf de Laval, a Swedish engineer, ran a steam turbine to supercritical speeds in the late 1880’s. Laval also introduced the use of bearings to oppose absolute motion in his machinery. As the years went by, many other engineers discovered and investigated additional phenomenons (FEM for example) that have an influence in today’s practices.
It is because of these previous innovators that companies like SoftInWay have been able to develop the advanced  rotodynamics modules that we use today.

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Working with Geothermal Heat Pumps

A geothermal heat pump utilizes earth’s thermal energy as a way to manipulate temperature. This is seemingly attractive toward HVAC utilization due to the relatively high efficiency as well as economic benefit. Temperature fluctuations below ground are relatively low as earth absorbs solar energy all year round and insulates the heat underground. Taking advantage of this event, geothermal energy heat pump application for residential and commercial building uses the “underground” as a heat source/sink.

geothermal heat pumps
Source: http://tidewatermechanical.com/geothermal-heat-pumps/

How does geothermal heat pump work?

A heat pump system mainly consists of a heat-pump unit, a pipeline loop functioning as a heat exchanger for a desired area (it can be horizontal, vertical or installed to an aquatic medium), and a duct – to deliver the controlled temperature flow to the consumer.

Fluid is pumped through an installed pipeline loop which transfers heat based on the season. During the hotter season (summer), heat will be absorbed from the air in the building, transferred into the ground and then cooler air will be circulated to the designated area. The contrary happens during the winter. In colder months, heat will be transferred into the fluid from the ground and collected heat will be distributed.

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Performance Effects of Axial Turbines & Compressors Due to Roughness Variations

As turbomachinery technology continues to advance in efficiency as well as overall power, many engineers want an estimate on how long these manufactured machines will operate.  Specifically, in high-temperature and high-flow turbomachinery applications, one of the main sources of performance degradation can be attributed to increases in surface roughness.  Gas turbine and compressor blades in particular experience a substantial amount of surface degradation over their lifetime.

gas turbine blade
Figure 1 – Gas Turbine Blade and Annulus Surface Wear (Source PowerMag)

There are many mechanisms that contribute to surface degradation in airfoils and annulus surfaces.  Foreign particles adhering to the material surface (or fouling) is generally caused by any increase in contaminants such as oils, salts, carbon, and dirt in the airflow.  Corrosion occurs when there is a chemical reaction between the material surface and the environment that causes further imperfections on the machine surfaces.  Additional mechanical factors such as erosion and abrasion will play a part in a machine’s surface degradation as well.

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Discussion – Alien Signal or Radio Noise: Leveraging Turbomachinery

The Internet practically exploded early yesterday morning with talk of an extraterrestrial discovery after a signal was detected by a Russian telescope. The star in question, HD 164595 located a vast 95 light years away, sent out a strong radio spike that was picked up and sparked a boom of excitement. According to an article published by National Geographic, however, this signal may not be what it was first interpreted as.

Astronomers have pointed their radio telescopes towards the stars for over half a century, hoping to catch a glimmer of life beyond this planet. Short of a futuristic rocket ship, these telescopes seem to be the best bet for catching a peak of something out of this world. That is a main causStarse as to why this discovery is so tantalizing to both scientists and the rest of us earthlings. However, after further investigation, neither the Allen Telescope Array, commanded by the SETI (the Search for Extra-Terrestrial Intelligence) Institute, nor the Green Bank Telescope, used by the Breakthrough Listen project, turned up additional signals or observations.

Another issue that has risen according to this article is that the signal did not repeat and could have been caused by something else. A source on Earth, such as a faulty power supply, military transmission, or arcing electrical fence for example. Another possible explanation could be that gravity from another object in space amplified a weaker signal. That being said, it would appear that HD 164595 is similar in many ways to our sun. It is composed of the same ingredients, is approximately the same age and has at least one planet in its orbit. This would suggest that theoretically, it would be plausible for life to exist within this system.

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Rotor Dynamics – Importance of Fundamental Understanding & Software tools

Rotor and bearings are the most critical components of any rotating machinery. Rotor lifetime and reliability depend, first of all, on the level of rotor vibrations. In order to meet highest requirements of reliability each step of the rotor design should be based on accurate Rotor Dynamics prediction.

Rotor dynamics is the branch of engineering that studies the lateral and torsional vibrations of rotating shafts, with the objective of predicting the rotor excessive vibrations. Rotor Dynamics is different from structural vibrations analysis because of gyroscopic moments, cross-coupled forces, critical speeds, whirling effect, etc. These difference makers are all due to the rotation of the rotor assembly.

Rotor-Dynamics

Understanding of basic rotor dynamics phenomena and the various types of problems is absolutely mandatory when designing and developing rotor-bearing systems for various applications. Fundamental approach for Rotor Dynamics analysis generally is based on the following steps:

  1.  Predict critical speeds.
  2. Determine design modifications to change critical speeds.
  3. Predict natural frequencies of torsional vibration.
  4. Predict amplitudes of synchronous vibration caused by rotor unbalance.
  5. Predict threshold speeds and vibration frequencies for dynamic instability.
  6. Determine design modifications to avoid dynamic instabilities.
  7. Calculate balance correction masses and locations from measured vibration data.

Another factor that determines accuracy of Rotor Dynamics calculation is rotor system simplification and the adequate modelling for rotor parts such as Impeller/disks, Sleeves, Balance pistons, Seals, Thrust collars, Couplings, Addition of Stiffening Due to Shrink Fits and Irregular Sections etc. (more…)

Product Development: Rescale existing turbomachine design vs full design process

When deciding on a new product line, manufacturers of turbomachines and their engineering teams must often decide whether to rescale a product that they already manufacture or to begin a full design process for a completely new machine. For example, a producer of 5 MW axial turbines wants to start manufacturing 10 MW turbines, does it make sense to create a brand new design from scratch or to simply scale up the 5 MW turbine they already produce to a similar 10 MW version? To answer this question, many considerations have to be taken into account, the general answer however is, that it is almost always a better idea to start a new design.

Improved Design Technology

Many manufacturers wrongly believe that by simply scaling their current product that they will save not only on design costs, but that they can leverage their existing manufacturing capabilities to stamp out a similar product. What is not factored in however is the progress of design technology and theory since their original machine was first conceptualized. The result from a simple scaling process will simply be a less optimized and efficient machine for any use as compared to a new configuration using the latest in design software. Increasing software sophistication and computing power are constantly pushing the boundaries of efficiency while minimizing operating costs. Simply put, your competitors will have designed a superior product compared to yours.

BladeProfiling-Turbomachinery-Design-Software

        AxSTREAM 3D Blade Design Software

Improved Materials

When was your current machine designed? Many older machines were created using materials that by today’s standards are simply not capable of operating at the extreme conditions  (mostly temperatures) required today to attain the energy efficiency requirements set up by ever increasing regulations. Depending on materials used, the optimal blading structure, bearings, etc. geometries would be significantly unique. If one were to simply scale up their current product, they would either be using old materials or have inefficiently designed machine components for a different material. In either case, their scaled machine will be inferior to a configuration that was conceptualized and optimized from scratch.

Scaling Factors

Another very significant aspect of machine resizing is that it is not a straight forward process; if you want to double your power generation in a turbine for example you are not going to be doubling the blade size or mean diameter, for example, even when considering the same boundary conditions (inlet pressure and temperature, as well as, outlet pressure, rotation speed, and so on). For each specific set of conditions, fluid, rotation speed, mass flow rate, etc. a unique flow occurs inside the different blades. Changing one parameter will lead to changes in the flow and therefore result in inefficiencies, as it is what happens in off-design conditions (the machine is not operating at its maximum performance). This is why flow similarity parameters become relevant.

Machine Purpose and Type

One of the obvious questions to ask is, what is the purpose of my new machine and how much larger (or smaller) will I need it to be? If the new machine is intended for use with a completely different fluid, a new design will be optimal as different fluids interact in unique ways with varied rotor and stator configurations.

The machine type that you are considering is also critical to the decision. Different turbomachines do not scale in similar fashion with increase in size. For instance, radial turbines are usually not as efficient as axial turbines when one starts to approach the 2 MW range. In this instance the ideal solution is for a complete redesign since a smaller scale version that the manufacturer may have had would not be configured to operate at higher power ranges efficiently.

 

Turbocharger Design and Industry Usage Discussion

An opportunity to discuss turbocharger usage and design with Softinway engineer Ursula Shannon in a question and answer format:

What are some of the major current turbocharger design challenges?

When it comes to turbocharger design, there are two challenges that engineers generally face. “Turbo lag” and turbo boost power at varying engine RPMs. “Turbo lag” is the time that it takes for the engine to produce enough exhaust to start the turbocharger “working”. This can vary greatly depending on engine size, turbocharger geometry, exhaust output etc. Ideally, engineers want to reduce this “Turbo lag” by as much as possible in any given situation, as during that time, the exhaust is “wasted” in a sense. Finding the most efficient configuration with all of the parameters in mind can be a very challenging scenario from a design perspective.

The turbo boost design challenge is one of efficiency at variable exhaust outputs. A smaller charger for example will start to boost at lower engine speeds while a larger one will start to boost at engine speeds. The trade off however is that a smaller turbo will start to create what is known as back pressure at higher speeds, and this results in a loss of potential power. A larger turbocharger, will be able to create more overall boost at higher speeds, however the “Turbo Lag” is more pronounced as more engine exhaust is required. Minimizing these trade offs is another key challenge in turbocharger design.

Finally, the process of turbocharger design process itself is complex, and requires highly specialized software such as our own here in Softinway (AxSTREAM).

Turbocharger blog 3

AxSTREAM Turbocharger Design Software ( Flowpath Design and Optimization )

turbocharger blog 2

AxSTREAM Turbocharger Design Software (Compressor 1D Design and Analysis)

What are some design changes do you see coming to turbochargers in the future?

As I mentioned some of the challenges engineers face in turbocharger design, currently many technologies and methods are being developed to alleviate some of the issues faced.

Two stage turbochargers are good example of trying to offer a solution to the boost powers at varying engine outputs, using a smaller turbocharger that operates at low RPMs and a larger turbocharger that operates at higher RPMs.

Electronic energy storage setups are currently being developed and used in European race cars which uses the output side of the turbocharger as a sort of generator which stores energy in a battery from turbocharger operations and acts as a boost during a turbocharger’s lag period.

(more…)

Improving Turbine and Compressor Design Matching

Compressor-Turbine-MatchingOne of the most prominent steps of complete gas turbine design is turbine-compressor matching. There are three major components to a gas turbine: compressor, combustor, and turbine. Although all of the components are designed individually, each of the components needs to correspond within the same operating condition range since all are integrated into one cycle. Consequently, an optimal design of each component must fit the requirement of other component’s optimal parameters. Corresponding operating points for each component must be found at equilibrium with the engine, thus the overall performance of gas turbine can be reached within the defined range of parameters.

The idea behind component “matching” process is to find flow and work compatibility between corresponding components. Based on the mechanical constraints, gas generator speed and firing temperature of a gas turbine have limitations depending on: ambient temperature, accessory load and engine geometry. The match temperature chosen should be the ambient temperature which reach both upper limits at the same time.  Pressure ratio needed to allow a certain gas flow is also one of the most prominent parameters that has to be taken into consideration. Designers need to make sure that the gas flow through the power turbine from gas generator satisfy the pressure ratio needed for compressor power requirements. Gas generator can easily show an altered match temperature due to some conditions i.e: reduction in compressor efficiency (due to fouling, etc), change of thermodynamic properties of combustion product, gas fuel with lower or higher hearing value, etc. Match parameters of an engine could also be altered by changing the flow characteristics on the first turbine nozzle.Turbine-Compressor

Using characteristic map/curve as well as thermodynamic relationships of turbine and compressor, calculations can be performed to identify the permitted operating range. It must be taken into consideration that all calculated value must match the value from map data.

Trying to find the fastest solution for this step? SoftInWay’s turbine-compressor matching feature in AxSTREAM could help you cut engineering time and simplify the process. Combining performance maps of turbine and compressor, making it easier for the user to determine points of joints operations.

Take a look into AxSTREAM’s to learn more about this.

Reference:

https://www.grc.nasa.gov/www/k-12/airplane/ctmatch.html
http://cset.mnsu.edu/engagethermo/components_gasturbine.html
http://turbolab.tamu.edu/proc/turboproc/T29/t29pg247.pdf
http://scholarcommons.sc.edu/cgi/viewcontent.cgi?article=3255&context=etd
Turbine Compressor Matching Compatibility Mode Document

The Economic Optimization of Renewable Energy

Global warming has been a very popular topic these days. With up-trend of clean technology and realization that strict climate policy should be implemented, demand of renewable energy sky-rocketed as conservative plants popularity falls. Number of coal power plants have significantly dropped since its peak era, being known as the largest pollutant contributor as it produces nitrogen oxide and carbon dioxide, the technology is valued less due to its impact on nature. Renewable energy comes from many sources: hydropower, wind power, geothermal energy, bio energy and many more. The ability to replenish and having no limit in usage and applications make renewable energy implementations seems attractive. Aside from that, they also produce low emission, sounds like a win-win solution for everyone. Theoretically, with the usage of renewable energy, human-kind should be able to meet their energy need with minimal environmental damage. With growth rate ranging from 10% to 60% annually, renewable energy are getting cheaper through the technology improvements as well as market competition. In the end, the main goal is still to generate profit, though these days taking impact on nature into the equation is just as important. Since the technology is relatively new, capital cost still considerable higher compared to some cases with more traditional (–and naturally harmful) implementations. So the question is: how to maximize the economic potential of a renewable energy power generation plant?

The Economic Optimization of Renewable Energy

Living up to the maximum potential of any power generation plant starts in the design process. Few examples for solar power plant: designers should take into consideration type and quality of panels, it’s important to see the economic-efficiency tradeoff before jumping into investment; looking into the power conversion is also one of the most important steps, one should take into consideration that it would be worthless to produce more energy than the capacity that are able to be transferred and put to use, though too low energy generation would mean less gross income.

Another example, for a geothermal power plant, many studies have shown that boundary conditions on each components play a big role in determining the plant’s capacity and efficiency. High efficiency is definitely desired to optimize the potential of a power plant and minimized the energy loss. Though, should also be compared to the economic sacrifice; regardless of how good the technology is, if it doesn’t make any economic profit, it would not make sense for one to invest in such technology. Low capital cost but high operating expenses would hurt the economic feasibility in the long run, whereas high capital cost and low operating expense could still be risky since that would mean a higher lump sum of investment upfront, which might or may not breakeven nor profitable depending on the fluctuation of energy market.

Modern technology allows investors and the engineering team to make this prediction based on models developed by the experts. SoftInWay just recently launched our economic module, check out AxCYCLE to optimize your power plant!

Reference:

[1] Optimal design of geothermal power plants 

[2] Strategies in tower solar power plant optimization