This is an excerpt from the Siemens Blog. You can read the full version here.
Originally written By Erik Munktell on January 14, 2021
Listening to the turbine experts: a review of 2020
Can a turbine simulation save the planet? One simulation alone is not enough. But one simulation with that intent can inspire other engineers and researchers to do the same. This butterfly effect is happening today in turbine design.
I live in Sweden, the same country as Greta Thunberg. Her message is that we must act now to save the planet. For a long time, Sweden’s electricity has come mainly from Hydropower and Nuclear power. But lately a lot of focus has still been on building wind and solar power plants. Here in Sweden we also have more trees being grown than being cut down. As a result we are close to being carbon negative, transportation and industry included.
With this country-wide energy focus friends often ask me why I work with gas turbines. Surely, they are not needed? I rarely get them to listen to my answer for more than a few minutes, as in my enthusiasm it quickly gets technical! But in short – I do it to save the planet. Or rather, we do it to save the planet. Because I am not alone in this effort. Many people work on making turbines run more efficiently, with fewer – or even no – polluting emissions. We can’t do everything by ourselves, but our work can inspire others and together we can create a clean energy future.
My small part in this plan is to make sure the actual makers of gas turbines have the best tools in the world for designing new and better electricity generating or flight enabling propulsion products. In this blog, I take a look at the many ways we saw in 2020 that turbine companies are using our simulation tools to do just that.
During industrial processes, an estimated 20 to 50% of the supplied energy is lost, i.e., by dumping the exhaust gas into the environment . The waste heat losses and the potential work output based on different processes including but not limited to the ones shown in Figure 1. Does it REALLY have to be thrown away? Sometimes yes, other times no. In this blog post, we will focus on the “no” through a process called “Waste Heat Recovery”.
Some well-known examples of waste heat recovery processes are found in turbochargers in cars or a heat recovery steam generator. One simple structure of application is when a heat exchanger is fed with the exhaust gas of a turbine, therefore being cooled down before being released into the air. This heat exchanger is part of a secondary (bottoming) cycle where another turbine provides additional power output without having to burn additional fuel. This heat exchanger is part of a secondary cycle where another turbine provides additional power output. Read More
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: https://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.
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
Vertical pump designs are similar to conventional pumps, with some unique differences in their applications. Pumps use centrifugal force to convert mechanical energy into kinetic energy and increase the pressure of the liquid. Vertical pumps move liquids in the vertical direction upwards through a pipe. All pumps pressurize liquids, which are mostly incompressible. Unlike compressible gases, it is impossible to compress liquids, therefore the volumetric flow rate can not be reduced. Therefore liquids are transported by pumping and the inlet volume flow rate is equal to the exit volume flow rate.
Vertical centrifugal pumps are simply designed machines, and have similarities to their horizontal counterparts. A casing called a volute contains an impeller mounted perpendicularly on an upright (vertical) rotating shaft. The electric drive motor uses its mechanical energy to turn the pump impeller with blades, and imparts kinetic energy to the liquid as it begins to rotate. These pumps can be single stage or multistage with several in-line stages mounted in series.
The centrifugal force through the impeller rotor causes the liquid and any particulates within the liquid to move radially outward, away from the impeller center of rotation at high tangential velocity. The swirling flow at the exit of the impeller is then channeled into a diffusion system which can be a volute or collector, which diffuses the high velocity flow and converts the velocity into high pressure. In vertical pumps, the high exit pressure enables the liquid to be pumped to high vertical locations. Thus the pump exit pressure force is utilized to lift the liquid to high levels, and usually at high residual pressure even at the pipe discharge.
Applications of Vertical Pumps
An “in line” vertical pump is illustrated in Figure 1 (Reference 1), where the flow enters horizontally and exits horizontally and can be mounted such that the center line of the inlet and discharge pipes are in line with each other. This is a centrifugal pump with a tangential scroll at the inlet that redirects the flow by 90 degrees and distributes it circumferentially and in the axial direction into the impeller eye. The discharge is a simple volute that collects the tangential flow from the impeller exit, and redirects it into the radial direction.
Figure 2 shows a vertical pump that has a vertical intake that directs the flow straight into the eye of the pump rotor. At the impeller exit, the tangential flow is collected by a volute and diffused in an exit cone. An elbow after the exit cone redirects the flow into the vertical direction to lift the liquid to the desired altitude. (Reference 2). Read More
Everyone is familiar with pumps, but how many people really think about how much depends on this ubiquitous invention? The scope of pump applications is wide: distribution and circulation of water in water supply and heat supply systems, irrigation in agriculture, in the oil industry, in fire extinguishing systems, etc.
A pump is a hydraulic machine designed to move fluid and impart energy to it. A schematic diagram of a simple pumping unit is presented below.
Positive Displacement and Dynamic Pumps
According to the principle of operation, pumps can be divided into two main groups: positive displacement and dynamic. In positive displacement pumps, a certain volume of the pumped liquid is cut off and moved from the inlet to the pressure head, where additional energy is supplied to it. In pumps with dynamic action, the increase in energy occurs due to the interaction of the liquid with a rotating working body.
The most widely used pumps are centrifugal pumps which are of the dynamic type. The principle of centrifugal pumps uses a rotating impeller to create a vacuum in order to move the fluid. The impeller rotates within the housing and reduces pressure at the inlet. This motion then drives fluid to the outside of the pump’s housing, which increases the pressure.
These pumps benefit from a simple design and lower maintenance requirements and costs. This makes them suited to applications where the pump is used often or continuously run.
In most cases, the pumps are electrically driven, but if the pump is of high power and high speed, then these pumps are driven by steam turbines. Read More
Due to concerns about air travel’s impact on climate change, research and development into electric aircraft has been ongoing for several years. Within the last decade several startups as well as larger corporations have been developing electric or hybrid electric aircraft (Ros, 2017). The ultimate goal is to Conduct long (>500 miles), full-electric commercial flights with large aircrafts capable of carrying 100’s of passengers, but this will require at least 5-10 more years of development. Luckily, smaller electric aircraft designed for short-range flights (<500 miles) with anywhere from 1-20 passengers have already been tested successfully utilizing electric batteries, a hybrid-electric system and even a hydrogen fuel cell. With these advances, emission-free air travel is closer than you think.
Examples of full-electric aircraft designs include the Airbus E-Fan 1.0 and E-Fan 1.1 (Airbus Group), shown in Figure 1. These two-person aircraft utilize two ducted, variable-pitch fans, shown in Figure 2. Each fan is powered by a 30-kW electric motor. The motors are powered by several lithium-ion battery packs stored in the wings. While the aircraft only provides an hour of flight time, the batteries can recharge in approximately one hour and can be easily be swapped in and out.
There are several reasons besides climate change why electric aircraft should be developed from a business perspective (Figure 3). Short and mid-range regional flights make up a significant portion of all flights around the world. The current flight range of electric aircraft is limited to these short and mid-range fights. Additionally, shorter flights spend relatively more time taking off and landing than cruising at high altitudes, which makes shorter trips less energy efficient. While short, regional flights are economically unattractive for large commercial aircraft, a smaller aircraft with less fuel consumption may provide a valuable alternative. Read More
The release of combustible gas during the interaction of metals and acids was observed as early as the 16th century. That is, during the formation of chemistry as a science. The famous English scientist Henry Cavendish had studied the substance since 1766, and gave it the name “combustible air”. When burned, this gas produced water. Unfortunately, the scientist’s adherence to the theory of phlogiston (the theory that suggested the existence of a fire-type element in materials) prevented him from coming to the correct conclusions.
In 1783 the French chemist and naturalist A. Lavoisier, together with the engineer J. Meunier, and with the help of special gas meters carried out the synthesis of water, and then its analysis by means of decomposition of water vapor with hot iron. Thus, scientists were able to come to the correct conclusions, and dismantle the phlogiston theory. They found that “combustible air” is not only a part of water but can also be obtained from it. In 1787, Lavoisier put forward the assumption that the gas under study is a simple substance and, accordingly, belongs to the number of primary chemical elements. He named it hydrogene (from the Greek words hydor – water + gennao – I give birth), that is, “giving birth to water”.
A Little About The Properties Of Hydrogen
In a free state and under normal conditions, hydrogen is a gas, and is colorless, odorless and tasteless. Hydrogen has almost 14.5 times mass less than air. It usually exists in combination with other elements, such as oxygen in water, carbon in methane, and organic compounds. Because hydrogen is chemically extremely active, it is rarely present as an unbound element. Read More
Ground source heat pumps (GSHP) are one of the fastest growing applications of renewable energy in the world, with annual increase of 10% in about 30 countries over the past 15 years. Its main advantage is that it uses normal ground or ground water temperatures to provide heating, cooling and domestic hot water for residential and commercial buildings. GSHP’s are proving to be one of the most reliable and cost-effective heating/cooling systems that are currently available on the market and have the potential of becoming the heating system of choice to many future consumers, because of its capacity for providing a variety of services such as heat generation, hot water, humidity control, and air cooling. Additionally, they have the potential to reduce primary energy consumption, and subsequently provide lower carbon emissions, as well as operate more quietly and have a longer life span than traditional HVAC systems. The costs associated with GSHP systems are gradually decreasing every year due to successive technological improvements, which makes them more appealing to new consumers.
The basic purpose of a GSHP is to transfer heat from the ground (or a body of water) to the inside of a building. The heat pump’s process can be reversed, in which case it will extract heat from the building and release it into the ground. Thus, the ground is the main heat source and sink. During winter, the ground will provide the heat whereas in the summer it will absorb the heat.
A GSHP comes in two basic configurations: ground-coupled (closed-loop) and groundwater (open loop) systems, which are installed horizontally and vertically, or in wells and lakes. The type chosen depends upon various factors such as the soil and rock type at the installation, the heating and cooling load required, the land available as well as the availability of a water well, or the feasibility of creating one. Figure 1 shows the diagrams of these systems.
In the ground-coupled system (Figure 1a), a closed loop of pipe, placed either horizontally (1 to 2 m deep) or vertically (50 to 100 m deep), is placed in the ground and a water-antifreeze solution is circulated through the plastic pipes to either collect heat from the ground in the winter or reject heat to the ground in the summer. The open loop system (Figure 1b), runs groundwater or lake water directly in the heat exchanger and then discharges it into another well, stream, lake, or on the ground depending upon local laws. Between the two, ground-coupled (closed loop) GSHP’s are more popular because they are very adaptable. Read More
An unsteady flow is one where the parameters change with respect to time. In general, any liquid flow is unsteady. But if a hydraulic system is working at constant boundary conditions, then the parameters of the fluid flow change slowly; thus this flow is considered steady. At the same time, if the parameters of the fluid flow oscillate over time relative to some constant value, then it called quasi-steady flow 1.
In practice, most fluid flows are steady or quasi-steady. Examples of the three flows are presented in Figure 1. Steady flow is presented by a simple pipe. The quasi-steady flow is represented by a sharpened edge channel. The unsteady flow is presented by an outflow from a reservoir.
Different Cases of Unsteady Flow
During operations, hydraulic systems act for long intervals at steady conditions which are called operating modes. Change between two different operating modes occurs over a short time interval (called a transient mode). If any hydraulic system works more than 95% of the time at these operating modes though, why is the unsteady flow is so important? Because the loads depend on time intervals. If the load is less, then the maximum system pressure is higher. Read More
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.
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