Who knows why the impellers on turbines go from small to large
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Who knows why the impellers on turbines go from small to large
Steam expands to do work, and the pressure decreases sequentially.
As the pressure decreases, the specific volume of the steam increases. To ensure there is sufficient flow area and to keep the gas velocity within a certain range, the blades become longer
To ensure that the work done is roughly the same, it’s necessary to make up for the power lost earlier!
Well, the steam pressure decreases while the volume increases. So at first the blades are smaller; later on, longer blades are needed to provide a larger surface area for applying sufficient force in order to generate enough work. Also, do you think that if the front part is larger and the back part is smaller, it will be possible to push air towards the back?
The same principle applies to compressors, from large to small
An impulse turbine discharges steam at high speed through nozzles, causing the impulse impeller to do work. Typically, the first and second stages are at high speed levels with high steam pressure; the pressure decreases gradually in subsequent stages. Therefore, it is necessary to increase the size of the blades in order to enhance the force exerted and ensure sufficient work output.
As the steam does work, its pressure decreases and its volume increases; therefore, the impeller moves from large to small.
Those who work with thermodynamics all have a little \"Bible\"——the gas law of state: pV=nRT. Since turbines produce work through expansion, the change in pressure (decrease) is much greater than the change in temperature (decrease), and since n and R remain essentially constant, it is easy to see that V will increase, causing the impeller to grow larger step by step.
I agree with what was said above: steam expansion does work, and as the volumetric flow rate increases, the flow area between stages must also increase accordingly.