The turbine nozzle

The turbine nozzle performs two functions:

1. It transforms a portion of the energy of the fluid, acquired in the heat exchanger and evidenced by a high pressure and temperature, into kinetic energy.

2. a) In the impulse turbine it directs the high-velocity fluid jet against blades which are free to move in order to convert the kinetic energy into shaft work; b) In the reaction turbine the nozzles, which are free to move, discharge high-velocity fluid. The reactive force of the fluid against the nozzle produces motion, and work is done.

For the first function to be performed efficiently, the nozzle walls must be smooth, streamlined, and so proportioned as to satisfy the changing conditions of the steam or gas flowing through the nozzle.

НАУЧНО-ИНФОРМАЦИОННЫЙ ЦЕНТР САНКТ-ПЕТЕРБУРГСКОГО ГОСУДАРСТВЕННОГО ТЕХНОЛОГИЧЕСКОГО УНИВЕРСИТЕТА РАСТИТЕЛЬНЫХ ПОЛИМЕРОВ

For the second function the nozzle should discharge the fluid at the correct angle with the direction of blade motion to allow a maximum conversion of kinetic energy into work.

The main consideration in nozzle design is o provide a nozzle of proper wall contour. The contour of the walls depends upon the conditions of the fluid required by the turbine and upon certain properties of the fluid which are influenced by these established conditions. For nozzle design the engineer has at his disposal four fundamental tools or relations. They are: 1) the first law of termodynamics; 2) the equation of continuity of flow; 3) the characteristic equation of state of the fluid; 4) the equation of the process.

CHAPTER V

Pumps, draft; fans, blowers, compressors

One of the most important problems of the engineer is the efficient and controlled transfer of fluids from one point to another. This transfer may be opposed by gravitational force, by some other external force, or by friction. Under certain conditions the gravitational force and other forces may it to aid the transfer, but friction always exists as a force opposing motion. The engineer attempts to reduce the effect of friction and at the same time takes advantage of useful forces to produce a motion of the fluids under conditions that can be controlled.

As previously defined, a fluid is a substance in a liquid, gaseous, or vapor state which offers little resistance to deformation. Common examples of the three states of a fluid are water as a liquid, air as a gas, and steam as a vapor. All these types of fluids have a tendency to move because of natural forces acting on them. A city may be supplied with water flowing by gravity from high ground. Air may circulate in an auditorium because of its own temperature difference. Steam rises through the water in a boiler owing to the difference in density or specific weight of steam and water. In many cases, however, the circulation is inadequate, and mechanical equipment must be built to supplement the natural circulation. Often mechanical circulation is the only means of obtaining the desired fluid flow. The equipment for producing this fluid flow is divided into two major classes: pumps for handling liquids, and fans, blowers, and compressors for handling gases or vapors.

Both classes of equipment in various forms may be found in the modern stationary power plant or small mobile power plants such as the aircraft engine, Diesel locomotive, or automobile engine.