Engineering applications of thermodynamics

Prepared By:- Nisarg Amin

Topic : Engineering Applications Of

Thermodynamics

Basic component of steam power cycle:

1.Steam boiler : convert water in to steam2.Steam turbine : convert kinetic energy of

steam in to mechanical energy3.Condenser : heat transfer device4.Feed pump : increase the preasure of

condansate steam.

Rankine cyclcle:

Process 2-3 in boiler : heat supplied (Qi)=(h3-h2) (since work done is zero)

Process 3-4 in turbine: turbine work (Wr)=(h3-h4) (since heat transfer is zero)

Process 4-1 in condenser : heat rejected to cooling water,(Qr)=(h4-h1) (since work done is zero)

Process 1-2 in feed pump:pump work (Wp)=(h2-h1) (since heat transfer is zero)

Flow diagram of rankine cycle

P-V ,T-S ,and h-s diagram of rankine cycle

Thermal efficiency of rankine cycle

Efficiency(ή)=shaft work/heat supplied =[(h3-h4)-(h2-h1)]/(h3-h2) =[(h3-h4)-(h2-h1)]/[(h3-h1)-(h2-h1)] if pump work is neglected than,

Efficiency(ή)=(h3-h4)/(h3-h4)

Steam rate(S.R):=3600/shaft speed

Flow diagram of reheat cycle

T-s and h-s diagram of reheat cycle

Analysis of reheat cycleThe thermal efficiency of reheat cycle is given by,

Efficiency(ή)=shaft work/heat supplied eqn-1………. shaft speed (Ws)=(Wt for L.P. +Wt for H.P.)-Wp =(h3-h4)+(h5-h6)-(h2-h1)Heat supplied(Qi)=heat supplied in boiler +heat supplied in reheater =(h3-h2)+(h5-h4) put the value of Ws and Qi in eqn-1….than we get

Efficiency(ή)=[(h3-h4)+(h5-h6)-(h2-h1)]/[(h3-h2)+(h5-h4) ]

Advantages of reheat cycle

Improves thermal efficiency the plant since the additional heat is supplied at higher mean temperature.It increases the network output of the turbine.It reduces the steam rate per KWh.It improves the condition of the steam at exhaust of the L.P. turbine so that tendency of blade erosion caused by the liquid particles in the L.P. turbine is reduced. The desirable maximum moisture is steam is considered to be about 10 to 12%.

Disadvantages of reheat cycle

To increase the cost and size of plant due to inclusion of reheater and its long piping.

Increase the size of condenser based on unit mass flow of steam due to improved quality of steam of exhaust from L.P. turbine.

Flow diagram of regenration cylce

T-s diagram analysis of regeneration cycle

It is obvious that the efficiency of regenerative cycle will more than rankine cycle because of the increased mean effective temperature during heat addition process , while the mean temperature of heat rejection process remain same,

Advantages of regeneration cycle

It increases the thermal efficiency of the plant.

The temperature stresses in the boiler are reduced due to decreased range of working temperatures.

Disadvantages of regeneration cycle

Steam rate increases due to reduced work done per kg of steam flow from boiler . Therefore ,for a given capacity of the power plant output the boiler size increases.Though the heat rejected in the condenser reduces for unit flow of steam , however , the size of condenser almost remains the same for a given capacity of power plant.The cost of the plant increases.

Mollier diagrams

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you