Pump Performance Improvement Using AxSTREAM ION

As pumps have numerous uses, they constitute a significant part of energy consuming equipment.  Therefore, pump efficiency plays a significant role in energy savings and operating cost. The design of a centrifugal pump is more challenging to reduce overall cost of the pump and increasing demand for higher performance.

Redesign Pump with Smooth Beta and Theta Distributions
Figure 1. Centrifugal Pump in AxSTREAM

There are two traditional approaches to design a pump for new requirements. One approach is to redesign or modify an existing impeller of centrifugal pump for increasing flow rate/head and efficiency. The modification will also involve selection of different geometric parameters and then optimizing them with the goal of performance improvement in terms of efficiency, increase the head, reduce cross flow and secondary incidence flows. The other approach is to design a pump from the preliminary stage to meet the desired design objectives. Most of the time, the designer knows what they need to achieve (performance target) but the challenge is in how to achieve this target within the given constraints (geometry, cost, manufacturability etc.).
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Series on Micro Gas Turbines And How They Can Make the World Greener

If you’re familiar with turbomachinery, then you probably know the pivotal role they play in our lives. If you’re not, no biggie! Have a look at this blog where I discuss a world without turbomachinery. But where do microturbines fit in? I can’t speak for anyone else, but my mind immediately jumps to turbochargers in small-displacement car engines. There is, however, a whole slew of information, history, and applications for microturbines beyond being a component in your car.

The best place to start, is to establish just what a microturbine is and isn’t. Granted the prefix in the word is a dead giveaway, but just how small is a micro gas turbine?  In terms of power output, a micro gas turbine puts out between 25 and 500 kW. The size of these machines varies; some systems can be the size of a refrigerator, while others can fit on your desk. For reference, some of these machines are smaller than your average corgi!

Micro Gas Turbine and Corgi
Figure 1: A micro gas turbine with a pencil for scale (left) and your average corgi (right). Not very aerodynamic, but awfully cute. Source

In terms of components, microturbines typically consist of a compressor, combustor, turbine, alternator, generator, and in most machines, a recuperator. While incorporating a recuperator into a microturbine system comes with its own set of challenges, the benefits are often well worth it as efficiency when recuperated hovers around 25-30% (with a waste heat recovery/cogeneration system, efficiency levels can reach up to 85% though).

Figure 3: A commercial airliner's turbofan engine the common image that is conjured when one thinks of turbines in transportation
Figure 3: A commercial airliner’s turbofan engine; the common image that is conjured when one thinks of turbines in transportation.
History

When and how did the concept of micro gas turbines come about? After the advent of the jet engine in World War II and the prominence of turbochargers being used on piston-driven propeller planes during the war, companies started to see where else gas turbine technology could be utilized. Starting in the 1950’s automotive companies attempted to offer scaled down gas turbines for use in personal cars, and you can read our blog covering that more in-depth here. You can probably guess by the number of gas turbine-powered cars on the road today, that it wasn’t very successful.

Fast forward to the 1970s, companies started to take an interest in micro turbines for stationary power generation on a small, portable scale. Allison developed microturbine-powered generators for the military that showed substantially lower fuel consumption in initial testing. In the 80’s, GRI supported the AES program where they attempted to develop a 50kW turbine for aviation applications, using a heat recovery system to improve efficiency through a cogeneration system. More recently, companies like Capstone have worked with GRI on new projects to introduce microturbines to different industries where they could be useful, using the latest advancements in technology to ensure higher efficiencies and reliability of designs past. To discuss the current state of affairs for microturbines however, it might be good to list some of their present advantages and drawbacks, and then explore where in the world they could be most useful.

Micro Turbine Compressor
Figure 4: A micro turbine compressor model.

 

Advantages and Disadvantages of Microturbines

As with just about any other type of technology, microturbines have their own set of advantages and disadvantages as a result of their design that are seen in their different applications.

Advantages: 

  • – Lower emissions
  • – Lower noise level than comparable reciprocating engines
  • – Fewer moving parts with results in less maintenance needs
  • – Lower vibration levels
  • – Ligherweight, compact systems
  • – Diverse fuel selection (jet fuel, kerosene, diesel, natural gas)

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Disadvantages:

  • – Very low efficiency without recuperator/waste heat recovery system
  • – High work requires high speeds (30-120 krpm) for small diameters
  • – Poor throttle response
  • – Expensive materials required for manufacturing
  • – More sensitive to adverse operating conditions

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A Micro Gas Turbine
Figure 5: A Microturbine
Potential Transportation Industry Applications

There are a number of different industries which microturbines can be found both in and outside of the transportation. Throughout the upcoming months, we’ll be taking a closer look at:

  • – The Aviation Industry
  • – The Automotive Industry
  • – The Marine Industry
  • – The Rail Industry

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Each of these industries has at least one application where micro gas turbine technology has the potential to conserve fuel and lower emissions without compromising power. In the next entry, we’ll look at the current state of the aerospace industry and where/how micro gas turbines can improve upon existing technology.

If you want to learn more about designing a micro gas turbine, or about the tools our engineers and thousands of others around the world rely on for their turbomachinery designs, reach out to us at info@softinway.com

Choosing the Right Turbomachinery Component

Traditionally the engineering process starts with Front End Engineering Design (FEED) which is essentially the conceptual design to realize the feasibility of the project and to get an estimate of the investments required. This step is also a precursor to defining the scope for Engineering Procurement and Construction Activities (EPC). Choosing the right EPC consultant is crucial as this shapes the final selection of the equipment in the plant including turbomachinery.

Large thermal power machine

Choosing the right component for the right application is not an easy task. Too many times, one ends up choosing a component that is not the best choice by far. This is quite true when we look at component selections in the process industries compared to those in a power plant where the operating conditions are more or less constant. This improper selection of components is due to multiple reasons such as: insufficient research and studies; limitation of time, resources, budget etc. Read More

Thermal Management in Aerospace Electric Propulsion Systems

The growing interest towards electric propulsion system for various applications in aerospace industry is driven first by the ambitious carbon emissions and external noise reduction targets. An electric propulsion (EP) system not only helps reduce the carbon emissions and external noise, but also helps reduce operating cost, fuel consumption and increases safety levels, performance and efficiency of the overall propulsion system. However, the introduction of electric propulsion system leads engineers to account for certain key challenges such as electric energy storage capabilities, electric system weight, heat generated by the electric components, safety, and reliability, etc. The available electric power capacity on board may be one of the major limitations of EP, when compared with a conventional propulsion system. This may be the reason electric propulsion is not the default propulsion system. Now, let’s consider how electric propulsion is used in the aerospace industry. Following the hybridization or complete electrification strategy of the electric drive pursued on terrestrial vehicles, the aerospace industry is giving great attention to the application of electrical technology and power electronics for aircrafts.

Figure 1 Aircraft Electric Propulsion Architectures
Figure 1. Aircraft Electric Propulsion Architectures. SOURCE: [1]
Electric Propulsion in aircrafts may be able to reduce carbon emissions, but only if new technologies attain the specific power, weight, and reliability required for a successful flight. Six different aircraft electric propulsion architectures are shown in Figure 1, above, one is all-electric, three are hybrid electric, and two are turbo-electric.  These architectures, rely on different electric technologies (batteries, motors, generators, etc.).

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An Introduction to Thermal Management in Electric Propulsion Systems

Reduction in CO2 emissions is driving the development of different electric, turbo-electric and hybrid electric propulsion systems for various applications and industries including space, aviation, automotive and marine. Electric propulsion (EP) is not a new concept, having been studied in parallel with chemical propulsion for many years. EP is a generic name encompassing all the ways of accelerating a propellant using electric power by different possible electric and/or magnetic means. The simplest way to achieve electric propulsion is to replace the heat generated by combustion in conventional chemical engines with electrical heating.

Electric propulsion systems offer several advantages compared to other conventional propulsion systems. It not only helps reduce the environmental emissions but also helps reduce fuel consumption and increases safety levels. Electric propulsion has become a cost effective and sound engineering solutions for many applications. Electric propulsion engines are also more efficient than others. It is proven to be one of the most energy saving technologies as we can use more renewable sources of energy (due to the versatility of electricity generation) instead of non-renewable sources of energy like gasoline. The major limitation of electric propulsion, when compared with conventional propulsion is limited by the available electric power capacity on board, this may be the reason, it is not the default propulsion system.

Electric Propulsion Architectures
Figure 1. Electric Propulsion Architectures. SOURCE: [4]
Generally, electric propulsion architectures vary depending on the application. Figure 1, above, shows the EP architectures for an aviation application. These architectures rely on different electric technologies (batteries, motors, generators, and so on). Typical aircrafts use gas turbine engines as the source of propulsion power, but all electric aircraft systems use batteries as the only source of propulsion power as shown in Figure 1 on the right. The hybrid systems use gas turbine engines for propulsion and to charge batteries which also provide energy for propulsion and accessories during one or more phases of flight as shown in Figure 1 on the left. Read More

Gas Turbine Lubrication Systems

Gas turbines have had a presence in many industries for more than a century. They are a unique technology for either producing an energy or propelling a vehicle and the efficiency of modern gas turbines is being improved continuously. One of them, a cooling system, has been described in earlier blogs. Another is the lubrication system of a gas turbine which we will cover in this blog. This  system, similar to that of a piston engine or a steam turbine, provides lubrication to decrease mechanical losses and prevent of wear on friction surfaces. Another function is the removal of heat released during friction by high rotational part and transmitted from the hot part of a turbine.  The basic units which need lubrication are the bearings supporting a shaft of a gas turbine 2.

Modern Dual Journal
Figure 1. The construction of modern dual journal4
Elements for lubrication

In a common case, gas turbine installation contains three main journal bearings used to support the gas turbine rotor 3. Additionally, thrust bearings are also maintained at the rotor-to-stator axial position 4. Click here for additional information about optimization of journal bearings. The bearing has important elements in its construction to prevent leakages from a lubrication system. The work, design and analysis of labyrinth seals is describe here.

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Preventing Choke and Surge in a Compressor

Turbo Compressors are used to increase the pressure of a gas, which are required in propulsion systems like a gas turbine, as well as many production processes in the energy sectors, and various other important industries such as the oil and gas, chemical industries, and many more.

Such compressors are highly specific to the working fluid used (gas) and the specific operating conditions of the processes for which they are designed. This makes them very expensive. Thus, such turbo compressors should be designed and operate with high level of care and accuracy to avoid any failure and to extract the best performance possible from the machine.

Axial Compressor and Centrifugal Compressor in AxSTREAM
Figure 1 (A) Axial Compressor (B) Centrifugal Compressor in AxSTREAM®

Turbo Compressor Characteristic Curves

The characteristic curves of any turbo compressor define the operating zone for the compressor at different speed lines and is limited by the two phenomenon called choke and surge. These two opposing constraints can be seen in Figure 2.

Choke conditions occurs when a compressor operates at the maximum mass flow rate. Maximum flow happens as the Mach number reaches to unity at some part of the compressor, i.e. as it reaches sonic velocity, the flow is said to be choked. In other words, the maximum volume flow rate in compressor passage is limited by limited size of the throat region.  Generally, this calculation is important for applications where high molecular weight fluids are involved in the compression process.

Surge is the characteristic behavior of a turbo compressor at low flow rate conditions where a complete breakdown of steady flow occurs. Due to a surge, the outlet pressure of the compressor is reduced drastically, and results in flow reversal from discharge to suction. It is an undesirable phenomenon that can create high vibrations, damage the rotor bearings, rotor seals, compressor driver and affect the entire cycle operation.

Compressor Performance Curve
Figure 2 Compressor Performance Curve

Preventing Choke and Surge Conditions

Both choke conditions and surge conditions are undesirable for optimal operation of a turbo compressor.  Each condition must be considered during design to ensure these conditions are prevented. Read More

The Role of Turbomachinery in Modern Hypersonic Cycles

In the coming age of hypersonics, a variety of engine types and cycles are being innovated and worked on. Yet turbomachinery remains unique in its ability to use a single airbreathing engine cycle to carry an aircraft from static conditions to high speeds. One of the largest limitations of turbomachinery at hypersonic speeds (Mach 5+) is the stagnation temperature, or the amount of heat in the air as it is brought to a standstill. While material improvements for turbomachinery are made over time which increases the effective range of temperatures steadily (Figure 1), this steady rate means that the ability of these materials to allow use at stagnation temperatures of more than 1600K remains unlikely any time soon.

Figure 1 Material Improvements Over Time
Figure 1 Material Improvements Over Time

This is the limiting point for traditional turbojet cycles, as Mach 5+ speeds result in temperatures far exceeding these limitations, even for the compressor. However, improvements in cryogenic storage of liquid hydrogen has allowed the concept of precooling, using the extremely low liquid temperature of hydrogen to cool the air enough to push this Mach number range, as well as improve compressor efficiency. To drive the turbine, the exhaust gas and combustion chamber can used, heating the hydrogen and reducing the nozzle temperature for given combustion properties. This has the added effect of separating the turbine inlet temperature from the combustion temperature, reducing limitations on combustion temperatures.  This type of cycle can reduce the inlet temperatures underneath material limits. Read More

Optimization of the Closed Supercritical CO2 Brayton Cycle with the Detailed Simulation of Heat Exchangers

Recently scientists and engineers have turned their attention again to carbon dioxide as a working fluid to increase the efficiency of the Brayton cycle. But why has this become such a focus all of a sudden?

The first reason is the economical benefit. The higher the efficiency of the cycle is, the less fuel must be burned to obtain the same power generation. Additionally, the smaller the amount of fuel burned, the fewer emission. Therefore, the increase in efficiency also positively affects the environmental situation. Also, by lowering the temperature of the discharged gases, it is possible to install additional equipment to clean exhaust gases further reducing pollution.

So how does all of this come together? Figure 1 demonstrates a Supercritical CO2 power cycle with heating by flue gases modeled in AxCYCLE™. This installation is designed to utilize waste heat after some kind of technological process. The thermal potential of the exhaust gases is quite high (temperature 800° C). Therefore, at the exit from the technological installation, a Supercritical CO2 cycle was added to generate electrical energy. It should be noted: if the thermal potential of waste gases is much lower, HRSG can be used. More information on HRSG here: http://blog.softinway.com/en/introduction-to-heat-recovery-steam-generated-hrsg-technology/

Any cycle of a power turbine installation should consist of at least 4 elements : 2 elements for changing the pressure of the working fluid (turbine and compressor) and 2 elements for changing the temperature of the body (heater and cooler). The cycle demonstrated in Figure 1 has an additional regenerator, which makes it possible to use a part of the heat of the stream after the turbine (which should be removed in the cooler) to heat the stream after the compressor. Thus, part of the heat is returned to the cycle. This increases the efficiency of the cycle, but it requires the introduction of an additional heat exchanger.

The heat exchangers used in the sCO2 cycle are of three basic types: heaters, recuperators, and coolers. Typical closed Brayton cycles using sCO2 as the working fluid require a high degree of heat recuperation.

Supercritical CO2 Power Cycle with Heating by Flue Gases
Figure 1 – Supercritical CO2 Power Cycle with Heating by Flue Gases

Having examined this scheme and examined the process in detail, we can draw the following conclusions about the advantages of this cycle which is demonstrated in Figure 2: Read More

Digital Engineering Modern Turbomachinery Design Platforms

Automatic Turbocharger Compressor Design 

In the age of green energy and increased efforts to minimize our carbon footprint,  the design of a turbocharger plays an important role in reducing engine fuel consumption and emissions while increasing the performance.  When developing an engine with a turbocharger, the general approach is to select a turbocharger design from a product list. The primary issue with this approach is that it does not cover 100% of the requirements of engine characteristics, i.e. it has non-optimal construction for the engine being developed. The operational characteristics of an engine directly depends on the interactions between the system components. This non-optimal construction will always lead to a decrease in the engine’s performance. In addition, the iteration process of turbocharger selection is time and resource consuming.

That is why the most optimal way to develop an engine with turbocharging is to design a turbocharger from scratch; wherein the operational points of compressor needed to satisfy the engine’s optimal operation are known, i.e. compressor map (Figure 1). But how do we quickly get a compressor map? Even at the preliminary design level, the design of turbocharger flow path requires dozens of hours for high-level engineers. And what about less experienced engineers?

Figure 1 Compressor Map Generated in AxSTREAM
Figure 1 Compressor Map Generated in AxSTREAM®

Incorporating a digital engineering approach with a turbomachinery design platform such as  AxSTREAM® allows designers to find the compressor design with all the required constraints which correspond to the specified compressor map needed. The design process is presented in Figure 2. Read More