Mixed flow turbines
Mixed flow turbines are turbines in which the flow through the rotor is partially radial and partially axial. It combines the advantages of both the axial and radial types.[1]
Turbines are turbo machines that produce power by expanding the fluid to a lower pressure or head. They extract energy from the fluid. Depending upon the nature of the flow of the fluid through the rotor, there are three types of turbines: Axial Flow, Radial Flow and Mixed Flow.
Mixed flow type turbines are widely used in automotive turbochargers, mixed flow impeller fans and mixed flow compressors.[2]
History
By as early as 70 B.C. Romans were using waterwheels for grinding and milling, especially for grinding of corn. Around 700 A.D.
Persians were using windmills. Archimedes Screw was invented by the Greek scientist Archimedes. It was used for raising the water with much less effort than lifting buckets. Archimedes used a screw which was placed at an angle and rotated and water could be lifted with much less effort. So, the idea of using the fluid’s energy and using it to get some work done is an ancient one. Though a lot of advancements happened in the recent centuries.[2]
The Francis Turbine is a mixed flow turbine. It was developed in 1848 by James B. It was designed to cater to the need of medium head and medium discharge conditions.
Applications of mixed flow turbine
Automotive turbochargers
Forcing extra compressed air into the combustion chamber will proportionally force more fuel into the combustion chamber. Increase in the fuel amount will lead to an increase in the Internal Combustion engines’ efficiency and power output. A turbocharger is a device that caters to the need of forcing more compressed air into the combustion chamber.
There is a huge increase in the demands of improving fuel economy of passenger cars. To make this improvement possible, the design of the automotive turbocharger becomes a very important objective.[3]
For automobiles require turbines that can extract energy at high pressure ratio and low rotational speeds. As far as radial flow turbines are concerned, their efficiency is low at high pressure ratio and low rotational speeds. And experiments have shown that mixed flow turbines work at higher efficiency in such conditions.
Mixed flow impeller fan
Axial fans provide high volume flow rate at low pressure and centrifugal fans provide medium flow rate at high pressure. In case of axial fans, not enough pressure is generated and in case of centrifugal fans, not enough flow rate is available. Thus, something in the midway is needed that combine the benefits of both and avoid their disadvantages. Such one alternative is to use mixed flow fans that provide high flow rates just like axial fans and high pressure just like centrifugal fans. Thus, we can say that mixed flow fans fill the gap between the axial fans and the centrifugal fans.[4]
Mixed flow compressors
They combine the advantage of both the radial and axial compressors. In single stage, radial compressors can produce high pressure ratio but lead to lower efficiency. While axial compressors can produce higher efficiency but will then have lower pressure ratio for single stage. So, to overcome these problems, mixed flow compressors are chosen. They can provide high frequencies even with limited cross-sectional area. The only disadvantage occurs in case of bigger turbines, where the weight increases due to longer impellers.[5]
See also
References
- ↑ Yahya, S. M. (2005). Turbines Compressors and Fans. Tata McGraw-Hill. Search this book on
- ↑ 2.0 2.1 Landis and Budenholzer, Fred and Ronald (March 27, 2017). "Turbine". Encyclopædia Britannica. Unknown parameter
|url-status=ignored (help) - ↑ luddecke, Filsinger and Ehrhard, Bernhardt, Dietmar and Jan (August 16, 2012). "On Mixed Flow Turbines for Automotive Turbocharger Applications". International Journal of Rotating Machinery.
- ↑ Dan, FanMan. "fan types why choose an mixed flow diagonal fan". designspark. Unknown parameter
|url-status=ignored (help) - ↑ Kueffner, Daniel. "Feasibility of mixed flow compressors in aero engines". softinway. Unknown parameter
|url-status=ignored (help)
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