P M V Subbarao Professor Mechanical Engineering Department Thermodynamics of High Temperature Steam Generation in an Open System (Control Volume) P M V Subbarao Professor Mechanical Engineering Department Economy of Creation of High Temperature in a Cycle…..

Steam Generation : Closed System Vs Open System

Energy transport by Moving fluid Amount of energy transport by a moving fluid of mass m is defined as methalpy and denoted by: Q = mθ = m ( h + ½V2 + gz ) Rate of Energy Transport:

Clues to Generate High Economy and Eco-friendly Steam

Economics of Flow Steam generation

Constant Pressure Steam Generation Process Theory of flowing Steam Generation

Creation of High Temperature @Constant Pressure Steam Generation Process

Economics of Flow Steam generation Supercritical Steam Generation Subcritical Flow Boiling Pump Exit

Selection of Steam Generation Pressure in A Rankine Cycle T C v, m3/kg

Entropy, x=s : A Measure of State of Matter So (J/K•mol) H2O(liq) 69.95 H2O(gas) 188.8 For a given substance S (gaseous state) > S (liquid state) > S (solid state)

Entropy and Order of Molecules of Matter S˚(Br2 liq) < S˚(Br2 gas) S˚(H2O solid) < S˚(H2O liquid)

Entropy, S : Molecular Complexity Increase in molecular complexity generally leads to increase in S.

Standard Molar Entropies

Entropy and Temperature S increases slightly with T S increases a large amount with phase changes

Entropy Change during a Reversible Process From the definition of the entropy, it is known that Q=TdS during a reversible process. The total heat transfer during this process is given by Qreversible =  TdS Therefore, it is useful to consider the T-S diagram for a reversible process involving heat transfer T S On a T-S diagram, the area under the process curve represents the heat transfer for a reversible process A reversible adiabatic process

Process : h-s Diagram : Mollier Diagram Enthalpy-entropy diagram, h-s diagram: it is valuable in analyzing steady-flow devices such as turbines, compressors, etc. Dh: change of enthalpy from energy balance (from the first law of thermodynamics) Ds: change of entropy from the second law. A measure of the irreversibilities during an adiabatic process. Ds Dh h s

Enthalpy Vs Entropy Diagram

Constant Pressure Steam Generation Process Theory of flowing Steam Generation Constant Pressure Steam Generation: A clue to get high temperature with same amount of burnt fuel

Steam Generation : Expenditure vs Wastage Vapour h mfuel Liquid +Vapour Liquid x

Steam Generation At High Pressure x=s

Analysis of Steam Generation at Various Pressures Specific Pressure Enthalpy Entropy Temp MPa kJ/kg kJ/kg/K C 1 3500 7.79 509.9 2 5 7.06 528.4 3 10 6.755 549.6 4 15 6.582 569 20 6.461 586.7 6 25 6.37 602.9 7 30 6.297 617.7 8 35 6.235 631.3

Fuel Savings during Steam Generation   Specific Temp Pressure Enthalpy Entropy C MPa kJ/kg kJ/kg/K 575 5 3608 7.191 10 3563 6.831 12.5 3540 6.707 15 3516 6.601 17.5 3492 6.507 20 3467 6.422 22.5 3441 6.344 25 3415 6.271 30 3362 6.138 35 3307 6.015

Law of Nature Behavior of Vapour at Increasing Pressures Reversible nature of substance at a given temperature All these show that the irreversible behavior of a fluid decreased with increasing pressure.

Reduction of Wastage

Less Fuel for Creation of Same Temperature

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