File Name: difference between carnot and rankine cycle .zip
You can download the paper by clicking the button above. Application of the First law of thermodynamics to the control volume pump, steam generator, turbine and condenser , gives.
- Definition: Rankine cycle
- 10 Difference Between Carnot Cycle And Rankine (With Diagram)
- Difference between Carnot Cycle and Rankine Cycle
- Rankine Cycle with Regeneration
In this article we will discuss about:- 1. Carnot Cycle 2. Rankine Cycle 3. Modified Rankine Cycle.
Definition: Rankine cycle
The basic Rankine cycle We will compare our regenerative cycle to a typical Rankine cycle. The Rankine cycle to which we will compare has the following parameters: The operating limits are heater pressure of 5 MPa heater exit temperature of C cooler pressure of 10 kPa and its efficiencies are Carnot efficiency: For reference, the Rankine cycle layout is shown below.
Figure 1: a Rankine cycle. The Rankine Cycle with Rengeration Improving cycle efficiencies Improving cycle efficiency almost always involves making a cycle more like a Carnot cycle operating between the same high and low temperature limits.
The Carnot cycle is maximally efficient, in part, because it receives all of its heat addition at the same temperature, which is the highest temperature in the cycle. Similarly, it rejects all of its heat at the same low temperature. The T-s diagram below details the working of a Carnot cycle operating between the same temperature limits as our Rankine cycle.
Figure 2: Carnot cycle T-s diagram. Figure 3: Rankine cycle T-s diagram. How regeneration works The idea behind regeneration is that we split the turbine into high-pressure and low-pressure stages and do the same for the pump.
Then, we can divert some of the heat in the fluid as it leaves the high-pressure turbine and add it to the cool fluid leaving the low-pressure pump, thereby sending fluid with a higher temperature to the heater. We'll look at this in more detail in a minute, but now we know enough to construct the Rankine cycle with regeneration. Figure 4: a Rankine cycle with regeneration. We don't know yet, so we'll choose kPa, which gives the two turbines pressure ratios of 25 and This makes them roughly equal and keeps either one from having an astronomically high pressure ratio.
The original Rankine cycle had a turbine PR equal to ! Later, when we have the cycle solved and we can let CyclePad do sensitivity analyses, we will see if another pressure works better.
The Splitter SPL1 The splitter is used to draw some of the working fluid from the high-pressure turbine stage and direct it towards the mixer. The assumption we make here is that the splitter is isoparametric. This means that the stuff exiting the splitter is the same as the stuff entering it. Quick Note The other assumption is that the splitter is not isoparametric. This simulates situations when we use a special splitter that allows us to separate the saturated mixture into two streams that each have different proportions of liquid and vapor.
This allows each stream to have different specific properties v , h , and so on , though they still have the same temperature and pressure. We might think that this would be advantageous to regeneration so that we could send only saturated vapor which has higher enthalpy to the low-pressure turbine and get more work out of it and send the low quality remainder down to heat the water entering the high-pressure pump. So why not do this? Let's try it. We can retract the isoparametric assumption and instead assume the stuff entering the low-pressure turbine is a saturated vapor.
Then when our other assumptions for this cycle have been made, we will see that the efficiency has changed by a few hundredths of a percent and we see that such an approach does not improve cycle efficiency by much. Our high-pressure pump condition S6 below requires that the total enthalpy H not h entering the high-pressure pump is constant, so the lower quality of the steam entering the mixer requires a higher mass flow into the mixer, nearly negating the benefit of the higher h steam that enters the low-pressure turbine.
That is, we could send lower h stuff to the pump, but we'd have to send more of it. Of course, any efficiency improvement is better than none, but it isn't always realistic to assume that we can use the special splitter than separates vapor from liquid, so we'll continue using the isoparametric splitter.
This water, which enters the pump at the cooler pressure, needs to be pumped up to the pressure of the water extracted from the high-pressure turbine. This is a matter of simple hydrostatics: if we make it lower, the higher pressure extract water will flow backward through the low-pressure pump and, if we make it higher, the low pressure pump water will flow backward through the splitter. We could just set this pressure at kPa, the pressure we set at the high-pressure turbine outlet. However, the better approach is to tell CyclePad to make the two pressures equal , using the "Equate T S5 to another parameter" option.
This way, when we need to experiment with different feedwater pressures, we don't need to make the change in two places. Another equivalent solution is to declare MXR1 to be isobaric. The High-Pressure Pump Inlet S6 Our whole purpose in adding heat to this water is to raise its temperature before it enters the heater and improve the cycle efficiency.
The water exiting the low-pressure pump is only at 46 C and the water entering the heater in the original Rankine cycle was at about the same temperature adding pressure to an incompressible fluid doesn't raise its temperature much. How high can we heat the water to improve this? The only limit we really need to consider is the practical use of the pump. We make sure the water entering the pump in a simple Rankine cycle is a saturated fluid because pumps cannot handle vapor very well.
We have the same consideration here. We want to heat this water up as much as we can, but not so much that some of it starts to vaporize again. We recall that this is the state of a saturated liquid. Examining regeneration efficiencies The Effect on Cycle Efficiency We now have made the changes needed to add a regeneration stage to our Rankine cycle.
Here are the new efficiencies and the ones of the plain Rankine cycle for comparison. Also shown is the percent gain in power output of the modified cycle when supplied with the same heat as the unmodified Rankine cycle and the mean temperatures of heat addition for both cycles. We made only one decision that was somewhat arbitrary in picking numbers, choosing the outlet pressure of the high-pressure turbine so that the two turbines would have similar and low pressure ratios. However, while that is a worthwhile choice considering the economics of turbine purchasing, it may not yield the optimal cycle efficiency.
We can examine the relationship between the thermal efficiency of our regenerative cycle and the feedwater pressure the pressure at S2.
The sensitivity analysis looks like this Figure 5: Effect of varying feedwater pressure on cycle efficiency of Rankine cycle with regeneration. Adding Further Regeneration Stages Of course, the limit on the improvement made by the regeneration stage seems to be that we can only add so much heat to the fluid entering the high-pressure pump before the fluid begins to evaporate, damaging the pump. At higher pressures, the working fluid can contain more heat before it begins to boil away.
So, we could repeat the process several times: add some heat until boiling almost occurs, then pump to a higher pressure, then add more heat, and so on. For instance, by adding another regeneration stage to the design above, and hunting a little to find good feedwater pressures, we can improve the cycle's thermal efficiency to about How far can this go? For a Rankine cycle where the steam enters the boiler as a superheated gas, we can never achieve the efficiency of the Carnot cycle, even with an infinite number of regeneration stages.
If the steam entered the turbine as a saturated vapor, we could, in theory, achieve Carnot efficiency with infinite regeneration stages, but such cycles are impractical for other reasons besides the need for infinite stages. The real limit is economic, since having the extra extraction stages and pumps adds to the cost of the plant.
At some point, the cost of the extra equipment outweighs the savings due to increased cycle efficiency. Practical plants seldom have more than five regeneration stages.
Download the CyclePad design of the Rankine cycle with one regeneration stage from here. Download the CyclePad design of the Rankine cycle with one regeneration stage at the optimal pressure from here. Download the CyclePad design of the Rankine cycle with two regeneration stages from here. Basic Engineering Thermodynamics. Oxford University Press. ISBN: Haywood, R. Analysis of Engineering Cycles. Pergamon Press. Go to or. Contributed by: M.
10 Difference Between Carnot Cycle And Rankine (With Diagram)
The basic Rankine cycle We will compare our regenerative cycle to a typical Rankine cycle. The Rankine cycle to which we will compare has the following parameters: The operating limits are heater pressure of 5 MPa heater exit temperature of C cooler pressure of 10 kPa and its efficiencies are Carnot efficiency: For reference, the Rankine cycle layout is shown below. Figure 1: a Rankine cycle. The Rankine Cycle with Rengeration Improving cycle efficiencies Improving cycle efficiency almost always involves making a cycle more like a Carnot cycle operating between the same high and low temperature limits.
Difference between Carnot Cycle and Rankine Cycle
Carnot vs Rankine cycle. Carnot cycle and Rankine cycle are two cycles discussed in thermodynamics. These are discussed under heat engines.
Introduction to Thermodynamics pp Cite as. To discuss the two performance criteria used in assessing steam power cycles: thermal efficiency specific work output. To discuss the use of superheating and two-stage expansion as means of improving the Rankine cycle operation.
It is an idealized cycle in which friction losses in each of the four components are neglected. To milk the advantage of higher efficiency Rankine Cycle has to operate on lower condenser pressure usually below atmospheric. And secondly, to study how this performance increase affect in fuel savings and CO2 emissions. The cycle is shown on -, -, and -coordinates in Figure 8.
Rankine Cycle with Regeneration
The Rankine cycle is the fundamental operating cycle of all power plants where an operating fluid is continuously evaporated and condensed. The selection of operating fluid depends mainly on the available temperature range. The Rankine cycle operates in the following steps:. High pressure liquid enters the boiler from the feed pump 1 and is heated to the saturation temperature 2.
Your email address will not be published. Skip to content. Thermal Engineering. Sharing is Caring : -. Today I am going to tell you difference between Carnot cycle and Rankine cycle. Both Carnot cycle and Rankine cycle are air standard cycles.
rankine cycle pdf
The Carnot cycle was first proposed by a French engineer in and was expanded upon by others in s and s. It is an ideal cycle in which, the working medium receives the heat energy from the high temperatures and rejects the heat at the lower temperature. This cycle laid the foundation for the second law of thermodynamics and introduced the concept of reversibility. Carnot cycle is an excellent yardstick to compare various thermodynamic cycles on theoretical basis. Nevertheless, all practical cycles, differ significantly from Carnot cycle. The Carnot cycle depends on the temperature of the heat source and heat sink only and is independent of the type of working fluid.
Rankine cycle is a theoretical cycle in which heat energy converts into work. Rankine cycle or vapor power cycle is the ideal thermodynamic cycle on which most of the thermal power plant works. Gas cycles :- In gas cycles the working fluid is gas. The steps in the Rankine Cycle as shown in Figure 1 and the corresponding steps in the pressure volume diagram figure 2 are outlined below:. It produces only small net power outputs for the plant size because dry saturated steam is used at inlet to the turbine. Rankine cycle for great powers, such as the Rankine cycle with reheat and regenerative Rankine cycle. The purpose of this project has two clear objectives: the first is to determine which parameters affect the cycle performance increase.