Steam nozzle pdf

We refer to this as overexpanded flow because in this case the pressure at the nozzle exit is lower than that in the ambient the back pressure - i. A further lowering of the back pressure changes and weakens the wave pattern in the jet. Eventually we will have lowered the back pressure enough so that it is now equal to the pressure at the nozzle exit. In this case, the waves in the jet disappear altogether figure 3f , and the jet will be uniformly supersonic. This situation, since it is often desirable, is referred to as the 'design condition'.

Finally, if we lower the back pressure even further we will create a new imbalance between the exit and back pressures exit pressure greater than back pressure , figure 3g.

In this situation called 'underexpanded' what we call expansion waves that produce gradual turning and acceleration in the jet form at the nozzle exit, initially turning the flow at the jet edges outward in a plume and setting up a different type of complex wave pattern. Critical flow nozzles are also called sonic chokes.

By establishing a shock wave the sonic choke establish a fixed flow rate unaffected by the differential pressure, any fluctuations or changes in downstream pressure. A sonic choke may provide a simple way to regulate a gas flow. In large output turbines, the state path usually crosses the saturation line in the penultimate stages. The liquid phase in steam turbines is mainly created in the process of homogeneous and heterogeneous condensation. The part of the hetero-geneous condensation in liquid phase formation de-pends on steam purity.

For the purposes of the prob-lems considered in this paper it was assumed that the steam was perfectly pure. The flow in the low-pressure steam turbine is com-plicated and still requires thorough experimental and numerical analysis to increase energy conversion ef-ficiency. Low-pressure turbine blades are key com-ponents in overall steam turbine design. A fully de-veloped 3-D stage flow analysis can provide an op-timum blade profile, capable of minimizing losses from shock waves caused by supersonic flow and also from condensation shocks.

Figure 1: Steam tunnel with auxiliary devices: 1 Control valve, 2 By-pass, 3 Stop gate valve, 4 Stop gate valve at by-pass, 5 Inlet nozzle, 6 Test section, 7 Outlet elbow, 8 Water injec-tor, 9 Pipe, 10 Safety valve, 11 Condenser, 12 Suction line, 13 Throttle valve, 14 Desuperheater, 15 Condensate tank, 16 Control system of condensate level, 17 Condensate pump, 18 Discharge line, 19 Stop valve, 20 Water injector pump, 21 Cooling water pump, 22 Condensate pump, 23 Pump Construction of steam nozzle If great pressure differences exist in front and at the back of inlet nozzles of steam turbines a secure attachment of the nozzles is sometimes rather difficult.

The difficulties are eliminated by milling or otherwise machining the nozzles into a complete or undivided solid ring. An example is shown in the drawing affixed hereto. The single figure of the drawing shows a cross-section through one half of the nozzles. Referring to this figure it will be seen that the steam flows from the channel 6 in the casing 1 into the nozzles 7.

These nozzles are machined into a solid ring 2 which is inserted into the turbine casing 1. The turbine may work with full or partial steam admission. A particularly good attachment of the ring 2 within the casing 1 is attained by shrinking the nozzle ring into the casing without making use of a special guide wheel body.

The attachment of the ring 2 in the manner specified permits, however, of leaks as well relative displacements. According to a further development the nozzle ring is secured in position by a further locking ring. This ring is indicated in the drawing by the numeral 3, it is tightened up by cone head screws 8 and thereby forces a packing ring 5 against a shoulder on the ring 2 as well as on the easing 1. In order to make quite sure of a tight seal a ring 4; of soft metal is inserted between the adjacent surfaces of the casing 1 and the ring 2 by caulking.

It is particularly applicable to super-pressure turbines. Various modifications and changes may be made. In a steam turbine the combination of a casing, a nozzle carrier having nozzle grooves in its outer periphery and forming a complete solid ring located in the turbine casing, and having its outer periphery shrunk against the inner periphery of the turbine casing,which forms one of the nozzle sides, and a soft metal ring caulked between the inner ring surface and the casing so that the steam admitted to the nozzles can flow only substantially in the axial direction of the turbine.

Materials used for construction of a nozzle are : Brass , Stainless Steel , Zinc Aluminum Alloy, Hot Pressed Boron Carbide The construction of the nozzle was done with materials obtainable locally and the science of operation carried out in constructing the nozzle was; cleaning, marking out, cutting off, drilling, folding, centre punching, assembling, welding, filling, testing and painting.

The flow nozzle was constructed based on the following specifications and dimensions; Throat Diameter60mm The diameter of the duct pipe mm The length of the up stream pipe mm The thickness of the nozzle3. Most of the frictional losses occur between the throat and exit in nozzle, producing following effect.

This is due to the time lag in the condensation of steam and the steam remains in dry state instead of wet. Such a steam is called supersaturated steam. This time lag is caused due to the fact that, the converging part of the nozzle is too short and the steam velocity is too high that the molecules of steam have insufficient time to form droplets. Total views 12, On Slideshare 0.

From embeds 0. Number of embeds Downloads Shares 0. Comments 0. Likes The nozzle is so shaped that it will perform this conversion of energy with minimum loss. Types of Steam Nozzle: Convergent Nozzle: In a convergent nozzle , the nozzle cross-sectional area decreases continuously from its entrance to exit.

So for subsonic flow, a convergent portion becomes a nozzle and a divergent portion becomes a diffuser. So for supersonic flow, a convergent passage is a diffuser and a divergent portion is a nozzle. Get Started for Free Download App. Statement I : Mass flow through the convergent nozzle is maximum when the exit Mach number is 1.

Statement II : The divergent section is added to convergent nozzle to increase the exit Mach number and not to increase the mass flow rate. Statement I : Steady flow means that the rates of flow of mass and energy through the control volume are constant. Statement II : At the steady-state of a system, any thermodynamic property will have a fixed value at a particular location and will not alter with time. What is a diffuser? The major function of a steam nozzles is to:.

In a compressor, work is done by:. Select the most appropriate definition of a turbine from the following statements. A gas is following through an insulated nozzle. Assume air as a perfect gas. At exit, the velocity is negligibly small, but the pressure is high. Assuming zero heat transfer, the exit temperature is:.

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