One is emerging from perhaps the most deliberate and least colourful engineering fields of all: gas turbine engineering. Gas turbines are internal combustion engines, like the ones that drive cars, except that they use a rotating shaft or rotor instead of pistons “reciprocating” in cylinders. This makes their operation smooth and steady, which lowers maintenance costs and increases reliability. Though they became practical only sixty years ago, today gas turbines are one of the keystone technologies of the civilization. As jet engines, they deliver most of our air transport, while stationary gas turbines are responsible for an increasing fraction of our electrical power generation.Partly because of this critical role, gas turbine engineers tend to innovate one tiny step at a time. In a field where liability exposures and development costs both can run into nine and ten figures, any kind of sweeping enthusiasm makes people nervous. Still, that doesn’t mean engineers can’t dream on their own time. In the spring of 1994, when a MIT turbine engineer named Alan Epstein found himself sitting in a jury pool, he started to think about what it would take to build the smallest possible jet engine. He concluded that in theory the device could be shrunk a lot, perhaps to the size of a collar button.
If you attached a microgenerator to the turbine, essentially creating a tiny power plant, the combination would act like a battery, making power at twenty to fifty times the rate of anything you could get at the hardware store. (Because there is much more energy per gram in burning hydrocarbons than in the electrochemicals that usually go in batteries.) Depending on how much fuel came with the turbine, a laptop might run for months on a single charge; a cellphone, for half a year. Given the insatiable appetite our portable gizmos have for batteries, the microturbine project suddenly became very interesting. The U.S. Army, which badly wants to reduce the weight carried by their “soldier systems”, agreed to write the checks.
There are many thermodynamic and architectural design choices in a device as complex as a gas turbine engine. These involve trade-offs among fabrication difficulty, structural design, heat transfer, fluid mechanics, and electrical performance. Given that the primary goal is to demonstrate – that a high power density MEMS heat engine physically reliable, the design philosophy adopted is that the first engine will be as simple as possible, trading performance for simplicity. For Example, the addition of a heat exchanger transferring heat from the turbine exhaust to the compressor discharge fluid (a recuperated cycle) offers many benefits including reduced fuel consumption and relaxed turbo machinery performance requirements, but it introduces additional design and fabrication complexity. Thus, the baseline design is a simple cycle gas turbine generator. While this engine is the simplest of gas turbines, it is an extremely complex and sophisticated MEMS device. Arriving at a satisfactory design requires heavy dependence on simulation of the mechanical, thermo fluid, and electrical behavior to achieve the required levels of component performance and integration .The baseline engine design is illustrated in Figure 1.The engine consists of a supersonic radial flow compressor and turbine connected by a hollow shaft. Gaseous H2 fuel is injected at the compressor exit and mixes with air as it flows radially outward to the flame holders. The combustor discharges radially inward to the turbine whose exhaust turns 90 degrees to exit the engine nozzle. A thin film electric induction starter-generator is mounted on a shroud over the compressor blades and is cooled by compressor discharge air. Cooling air is also used to thermally isolate the compressor from the combustion and turbine. The rotor is supported on air bearings. The following sections briefly discuss component design considerations.
APPLICATIONS OF MICRO TURBINE
Microturbines are suited to meet the energy needs of small users such as schools, apartments, restaurants, offices and small businesses. The Microturbine coupled with solid oxide fuel cell can be used in supermarkets, factories, and military developing nations. This can be applied for heating, drying, cooling, desalination and several others. They include space vehicles, electronic devices, unmanned aircrafts. The microturbines can be used in remote areas. This is because of small size. Microturbines are used when a high quality, energy density energy is needed.
Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.
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