Decreasing the condenser pressure. The effect of lowering the condenser pressure on the Rankine cycle efficiency is illustrated on a T-s diagram on the left. … Superheating the steam to a high temperature. … Increasing the boiler pressure.

Which of the following increases the efficiency of Rankine cycle?

The thermal efficiency of the Rankine cycle can also be increased by: Increasing the average temperature of the working fluid at which heat is added to the cycle. Decreasing the average temperature of the working fluid at which heat is rejected by the cycle.

Does reheating increase efficiency in Rankine cycle?

The Rankine cycle performance and efficiency can be improved with the reheat cycle as well as by regenerative cycle. It can be improved by increasing the thermodynamic properties of the steam entering into the turbine. At the initial stage, increased pressure results in increased expansion ratio.

Which factors affect the efficiency of a Rankine cycle engine?

The ability of a Rankine engine to harness energy depends on the relative temperature difference between the heat source and heat sink. The greater the differential, the more mechanical power can be efficiently extracted out of heat energy, as per Carnot’s theorem.

What is the efficiency of Rankine cycle?

In modern nuclear power plants, which operate the Rankine cycle, the overall thermal efficiency is about one-third (33%), so 3000 MWth of thermal power from the fission reaction is needed to generate 1000 MWe of electrical power.

Why efficiency of Rankine cycle is less than Carnot cycle?

The thermal efficiency of a Rankine cycle is lower then that of a Carnot cycle operating between the same temperature levels. This is primarily because of the fact that the energy transfer as heat in the boiler does not take place at constant temperature in the Rankine cycle.

How can the efficiency of Rankine cycle be improved Mcq?

The thermal efficiency of the Rankine cycle can be increased by the use of a regenerative heat exchanger. … In this way, the amount of heat added at the low temperatures is reduced and the mean effective temperature of heat addition is increased, thus cycle efficiency is increased.

Where is energy lost in a Rankine cycle?

The thermal energy lost through the exhaust is used to heat a fluid in an interchanger. The steam produced powers a turbine, which aids the engine to propel the car. Steam is further condensed to continue the Rankine cycle.

What is regeneration in Rankine cycle?

Regeneration: Regeneration, a process during which heat is transferred to a thermal energy storage device (called a regenerator) during one part of the cycle and is transferred back to the working fluid during another part of the cycle.

How does reheat increase efficiency?

Once reheated, the steam is sent to the low-pressure boiler. This improves power generation efficiency by effectively reusing the steam while reducing the percentage losses associated with condensing the steam.

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How can the efficiency of the reheat cycle be improved?

In case of two reheats, steam is super-heated twice at different constant temperatures. A high reheat pressure increases the the moisture content at turbine exhaust which results in scaling and it should be optimised. Thus the work produced is increased ,thereby efficiency increases.

What is the most preferable dryness fraction of the exhaust steam?

What is the most preferable dryness fraction of the exhaust steam? Explanation: The dryness fraction of the exhaust steam is in the range of 0.86-0.88 for modern turbines.

How is Rankine efficiency calculated?

1. The thermal efficiency, ηth, represents the fraction of heat, QH, converted to work. …
2. dH = dQ → Q = H2 – H1 …
3. dH = Vdp → W = H2 – H1 …
4. The enthalpy can be made into an intensive or specific variable by dividing by the mass.

How can you increase the efficiency of a steam power plant?

At present, the most popular approaches to improve the total efficiency of a steam turbine include increasing the initial steam parameters, decreasing final steam parameters, installing a feed-water heater, and applying combined-cycle technology.

What are the processes that make up the ideal Rankine cycle?

The ideal Rankine cycle consists of the following four processes, as shown on the T-s diagram on the left: 1-2: Isentropic compression in a pump. 2-3: Constant pressure heat addition in a boiler. 3-4: Isentropic expansion in a turbine.

Which one of the following modifications to a Rankine cycle would upgrade enhance its efficiency so as to approach that of Carnot cycle co2 *?

Explanation: Area under P-V curve for Rankine will be more as compared to Carnot cycle. Explanation: In winters, the temperature of cooling water is low, which increases Condenser’s efficiency.

Which of the following station is least efficiency?

Steam engine has the least thermal efficiency as some of the heat is lost in warming the vessel.

What is typical efficiency of cogeneration system?

The overall energy efficiency of a cogeneration system is the percent of the fuel converted to both electricity and useful thermal energy. Typical cogeneration systems have overall efficiencies ranging from 65% to 90%.

Which is more efficient Carnot cycle or Rankine cycle?

In carnot cycle all heat is added at higher temp whereas in rankine cycle it is at constt pressure ie at variable temp, so why work output of carnot cycle is more and hence more efficient. As the other friend has mentioned the heat addition and heat rejection in Carnot cycle is very high.

Which cycle has lowest thermal efficiency?

The Diesel cycle is less efficient than the Otto cycle when using the same compression ratio. However, practical Diesel engines are 30% – 35% more efficient than gasoline engines.

Is it possible theoretically to achieve the efficiency of Rankine cycle with that of Carnot state the conditions for this?

Carnot is theoretical and ideal and its efficiency is hardly achieved by any working cycles. hence, rankine must be less compared to carnot due to losses.

How does regeneration increase efficiency?

Advantages of Regeneration cycle: Thermal efficiency is increased since the average temperature of heat addition to the cycle is increased. Due to bleeding in the turbine, erosion of turbine due to moisture is reduced.

How can you increase the efficiency of the Brayton cycle?

The efficiency of a Brayton engine can be improved by: Increasing pressure ratio, as Figure 1 above shows, increasing the pressure ratio increases the efficiency of the Brayton cycle. This is analogous to the increase of efficiency seen in the Otto cycle when the compression ratio is increased.

What is the efficiency of an ideal regenerative Rankine cycle?

Cycle EfficienciesUnmodified Rankine CycleRankine Cycle with RegenerationCarnot efficiency52.6%52.6%Thermal efficiency36.2%38.4%% Increase in Power Generation0%6.1%mean temperature of heat addition226.7 C251.5 C

Why is the Rankine cycle modified?

This cycle is known as modified Rankine cycle. The reason for the early release is that at the lower pressure the specific volume of steam is high. In order to accommodate such rapidly expanding steam, large cylinder volume is necessary and the extra work obtained is very small.

Why do you need a condenser in a Rankine cycle?

Originally Answered: Why is a condenser used in a Rankin cycle? A condenser is used to convert the steam from the exit of the turbine to saturated liquid. This is done so that we can use a pump to pressurize the liquid. There is no mechanical device till date which can work on steam+liquid mixture.

Which is more efficient reheat cycle or the regenerative cycle?

Analysis shows that regenerative cycle is more efficient compare to reheat cycle for a given set of operating conditions.

What is ideal Reheat Rankine cycle?

A steam power plant operates on the ideal reheat Rankine cycle. Steam enters the high-pressure turbine at 8 MPa and 500°C and leaves at 3 MPa. Steam is then reheated at constant pressure to 500°C before it expands to 20 kPa in the low-pressure turbine.

Which of the following improves of efficiency of Rankine cycle in a thermal power plant?

Thermal efficiency of Rankine cycle can be improved by increasing the mean temperature of heat addition, by using of high pressure steam. The mean temperature of heat addition can be increased by using super heat, reheat and regeneration.

Can dryness fraction be more than 1?

Explanation: Dryness fraction is defined as the ratio of mass of dry steam (vapour) to combined mass of dry steam (vapour) & mass of liquid in mixture. It is denoted by x. The value of dryness fraction lies between 0 and 1.

Which steam will have least enthalpy?

Wet steam, the dryness fraction and enthalpy The actual enthalpy of evaporated wet steam is the product of the dryness fraction – ζ – and the specific enthalpy – hs – from the steam tables. Wet steam has less usable heat energy than dry saturated steam.