Carnot and renkine steam cycle

In summary, the vacuum pressure in a condenser helps to extract energy from the working fluid while keeping it in the gaseous phase.
  • #1
Micko
43
0
Hello to all,
this is my first post on this forum. I'm electrical engineer (technical informatics) but in my spare time I'm interested in thermodynamics especially about steam cycle in power plant.
I know that condenser is meant to convert steam to water and here we have pure losses of energy. Can anyone explaine why vakkum in condenser is needed?
Thanks
 
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  • #2
in the condenser, there is no loss in energy (look on the enthalpy/entropy diagram, the portion of the cycle from condenser to pump is a horizontal line). as far as why the condenser is at vacuum pressure (something like 1psi or 7kPa) it is to be able to extract as much energy from the working fluid while keeping it in the gaseous phase (water is still steam at 100F or 37C when the pressure is at 1psi) because obviously you can't have liquid in a turbine. hope that helps..
 
  • #3
Cycle efficiancy goes up when vacuum pressure goes down. Its that delta P between turbine inlet (steam P) and outlet (CD P) that determines power. In summer when the lake temperature goes up, the condensing cooling water is warmer, therefore the steam condenses at a higher pressure and we lose megawatts. You could exhaust the turbine to atmosphere theoetically but you'ld be losing a lot of power (and water!). There is something like 1000:1 reduction in volume as steam collapses, and this explains why the vessel is under vaccuum. Also note that there is no air or other non condensable gasses in the condensor, just water.
 
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  • #4
Okey, thanks guys, I'll try to understand your answers. I know that efficiency is something like (T1-T2)/T1 and at first I thought that condenser is there to reduce T2 and makes efficiency better, but then I know that this goes to air and not to turbine, so that is probably wrong conclusion.
Can you suggest me where to find out about difference between enthropy and enthalpy?
It seems that I'm confused about Work (Energy) and Heat. In condenser heat is rejected but no work energy. How to explain that?
 
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  • #5
It can be useful to think of temp and pressure as two parts of the same thing (indeed, for some other thermodynamic cycles, efficiency is expressed in terms of pressure ratio). If the pressure in a vessel goes down, the temperature will follow and if pressure is lower at a point in the cycle, the boiling point is also lower.
 
  • #6
russ_watters said:
It can be useful to think of temp and pressure as two parts of the same thing (indeed, for some other thermodynamic cycles, efficiency is expressed in terms of pressure ratio). If the pressure in a vessel goes down, the temperature will follow and if pressure is lower at a point in the cycle, the boiling point is also lower.
When you say: lower pressure, lower boiling point, is that conclusion from:
p*V/T = const?
 
  • #7
http://canteach.candu.org/library/20043706.pdf [Broken]

pretty late reply I know:zzz: , but check out the above... very related. esp. see pg's 8,9/13 which deal with thermo cycle of condenser a bit.
 
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What is the Carnot and Renkine steam cycle?

The Carnot and Renkine steam cycle is a thermodynamic cycle that is used to convert thermal energy into mechanical work. It operates on the principle of a heat engine, where heat is transferred from a high temperature source to a low temperature sink, resulting in the production of work.

Why is the Carnot and Renkine steam cycle important?

The Carnot and Renkine steam cycle is important because it provides a theoretical basis for the operation of steam engines, which were crucial in the Industrial Revolution. It also serves as a benchmark for the efficiency of real-world steam engines.

What are the components of the Carnot and Renkine steam cycle?

The Carnot and Renkine steam cycle consists of four main components: a boiler, a heat exchanger, a turbine, and a condenser. The boiler is where water is heated to produce steam, which then passes through the heat exchanger to transfer heat to the turbine. The turbine converts the thermal energy of the steam into mechanical work, and the remaining steam is condensed in the condenser.

How does the Carnot and Renkine steam cycle differ from the Carnot cycle?

The Carnot and Renkine steam cycle differs from the Carnot cycle in that it includes a heat exchanger and a condenser. This allows for a continuous flow of steam and a more efficient conversion of heat into work.

What are the limitations of the Carnot and Renkine steam cycle?

The Carnot and Renkine steam cycle is limited by the quality of the steam produced in the boiler and the efficiency of the turbine. It also operates under ideal conditions and does not account for the practical losses that occur in real-world steam engines.

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