In a Superheat Rankine Cycle , the boiler produces superheated vapor. This helps maintain a high quality vapor-liquid mixture at the turbine effluent. Because the high pressure isobar slopes upward outside of the two-phase envelope , Q H increases by a larger percentage than Q C increases.
This is true as long as the turbine effluent is not superheated. The result is an increase in the thermal efficiency of the cycle and an increase in the quality of the turbine effluent! Lesson 9C Blog. Confused and have questions? We've got answers. With Chegg Study , you can get step-by-step solutions to your questions from an expert in the field. This requires the addition of another type of heat exchanger called a reheater.
The use of the reheater involves splitting the turbine, i. It was observed that more than two stages of reheating are unnecessary, since the next stage increases the cycle efficiency only half as much as the preceding stage.
High pressure and low pressure stages of the turbine are usually on the same shaft to drive a common generator, but they have separate cases. With a reheater , the flow is extracted after a partial expansion point D , run back through the heat exchanger to heat it back up to the peak temperature point E , and then passed to the low-pressure turbine.
The expansion is then completed in the low-pressure turbine from point E to point F. In the superheater , further heating at fixed pressure results in increases in both temperature and specific volume. The process of superheating of water vapor in the T-s diagram is provided in the figure between state E and saturation vapor curve.
As can be seen also wet steam turbines e. Typically most of nuclear power plants operates multi-stage condensing wet steam turbines the high pressure stage runs on saturated steam. The steam must be reheated or superheated in order to avoid damages that could be caused to blades of steam turbine by low quality steam.
High content of water droplets can cause the rapid impingement and erosion of the blades which occurs when condensed water is blasted onto the blades.
To prevent this, condensate drains are installed in the steam piping leading to the turbine. The reheater heats the steam point D and then the steam is directed to the low-pressure stage of steam turbine, where expands point E to F. For a constant pressure process ,. Hence, the energy addition during process ,. The energy rejection during the process ,. The thermal efficiency, h is given by. Since the process is isentropic,. Since the process is a constant volume process,. The processes and are isentropic.
For the constant pressure process,. Hence the efficiency becomes,. The mean effective pressure of an air standard diesel cycle is given by,. Dual cycle on a P-v diagram b T-s diagram.
Energy addition is in two stages: Part of energy is added at constant volume and part of the energy is added at constant pressure. Energy added, q 1. Energy rejected, q 2. Thermal efficiency, h. The efficiency can be expressed also in terms of,. Lowering the condenser Pressure :- Lowering the operating pressure of the condenser lowers the temperature at which heat is rejected. Superheating the steam to high temperatures :- The average temperature at which heat is added to the steam can be increased without increasing the boiler pressure by superheating the steam to high temperatures.
Increasing the Boiler pressure :- Increasing the operating pressure of the boiler, automatically raises the temperature at which boiling takes place.
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