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Analysis of Power Plant : A Scientific Engineering. P M V Subbarao Professor Mechanical Engineering Department. An Exclusive Engineering Science for Extrasomatic Needs ……. The Family of Steam Engines. A Direct Hardware Creations to the Essential Need ….
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Analysis of Power Plant : A Scientific Engineering P M V Subbarao Professor Mechanical Engineering Department An Exclusive Engineering Science for Extrasomatic Needs ……..
The Family of Steam Engines A Direct Hardware Creations to the Essential Need …..
James Watt Engine in Human Development • Watt's Double-Acting Engine, 1784. • The Watt Hammer, 1784. • John Fitch, 1788 • Trevithick's Locomotive, 1804 • The " Atlantlc," 1832. • Steam Engine Reached its pinnacle in size when it was called to drive 5 MW electric generator.
James Watt Engine • Watt's Double-Acting Engine, 1784. • The Watt Hammer, 1784. • Trevithick's Locomotive, 1804 • The " Atlantlc," 1832. • Steam Engine Reached its pinnacle in size when it was called to drive 5 MW electric generator. Steam Engine As an Alternate to Horse or Cattle…..
Definition of Thermodynamics • Thermodynamics is defined as the science of energy. • The name Thermodynamics stems from the Greek words therme (Heat) and dynamics (Power). • Clearly depicting the early efforts to convert heat into power. Steam power already had many uses - draining water from mines, excavating ports and rivers, forging iron, grinding grain, and spinning and weaving cloth - but it was inefficient.
The Family of Steam Engines A Direct Hardware Creations to the Essential Need …..
Pearl Street Station Thomas Edison in September 1882 achieved his vision of a full-scale central power station
Steam Tractors • The first steam tractors that were designed specifically for agricultural uses were portable engines built on skids or on wheels and transported to the work area using horses. • Later models used the power of the steam engine itself to power a drive train to move the machine and were first known as "traction drive" engines. • This was which eventually was shortened to "tractor".
Steam Wagon/Tractor : Last decade of 19th Century • By 1921, steam tractors had demonstrated clear economic advantages over horse power for heavy hauling and short journeys. • London market roads were free of Horse faeces….
Sadi Nicolas Léonard Carnot • 1814: After graduating, Carnot went to the École du Génie at Metz to take the two year course in military engineering. • 1819: Carnot began to attend courses at various institutions in Paris. • 1821: Carnot began the work which led to the mathematical theory of heat and helped start the modern theory of thermodynamics. • The problem occupying Carnot was how to design good steam engines. • Steam power already had many uses - draining water from mines, excavating ports and rivers, forging iron, grinding grain, and spinning and weaving cloth - but it was inefficient.
Carnot’s Thinking • It irked Carnot particularly that the British had progressed so far through the genius of a few engineers who lacked formal scientific education. • British engineers had also accumulated and published reliable data about the efficiency of many types of engines under actual running conditions. • They vigorously argued the merits of low- and high-pressure engines and of single-cylinder and multi-cylinder engines. • 1822 – 1823 : Carnot attempted to find a mathematical expression for the work produced by one kilogram of steam.
The Quintessential Novelty • Carnot's work is distinguished for his careful, clear analysis of the units and concepts employed and for his use of both an adiabatic working stage and an isothermal stage in which work is consumed. • 1824 : Réflexions sur la puissance motrice du feu et sur les machines propres à développer cette puissance which includes his description of the; • “ Mathematical Model for Carnot cycle". Thought experiment is in any case a necessary precondition for physical experiment. Every experimenter and inventor must have the planned arrangement in his head before translating it into fact. — Ernst Mach
The Thermodynamic Cycle Coal (Resource) Ability to Perform The power (Need) Ecological Nuisance
The Thermodynamic Cycle Burn Coal (to add Heat slowly) Ability to Perform The Work (Move piston slowly) Ecological Nuisance
The Carnot Cycle T x
Impact of Heat & Work Transfers on Steam • How to quantify the changes in steam due to work and heat transfer? • Humans depended on their senses to define these changes. • Out of Five senses, Three senses could not quantify/recognize these changes. • Only two senses could quantify these changes: • Vision : Volume (m3) • Touch : Pressure (kPa) and Temperature (C or K) • None of the above are equivalent to heat or work. • There must be a relation between these properties and heat & work.
Carnot Model for Engine • Maximum Power : 17BHP@8500 RPM • Maximum Torque :15Nm@7500 rpm
Cost to Benefit Ratio of Carnot Model • Work/power developed by the engine is the benefit. • Fuel mining, transportation, processing incur cost. • It is essential to develop a cost to benefit ration. • The scientific version of this ratio is named as efficiency.
Perpetual Power Plant • Any power plant which violates first law is called as PPP. • A PPP is a hardware which works continuously in cycle and • generates work only or • consumes work only or • accepts heat only or • rejects heat only. It is impossible to construct A Perpetual Motion Machine of first kind (PPP – 1).
The Carnot Cycle T x
All Substance Give the Same Efficiency • Engines had been proposed and constructed using working substances other than water, with no dramatic improvement in efficiency. • Carnot reasoning implies that : to the extent that is it possible to eliminate frictional losses and other sources of inefficient operation, all substances will do the same work for the same temperatures of operation. • All these situations led to the development of Ideal model for engine using Adiabatic and isothermal processes. • He could get an expression for efficiency independent of substance only through this model.
The Microscopic View • When a liquid evaporates to a gas in a closed container, the molecules cannot escape. • Some of the gas molecules will eventually strike the condensed phase and condense back into it. • When the rate of condensation of the gas becomes equal to the rate of evaporation of the liquid or solid, the amount of gas, liquid and/or solid no longer changes. • The gas in the container is in equilibrium with the liquid or solid.
Starting from Liquid State Let's consider the results of heating liquid from 20°C For Ammonia Pressure must be greater than 857.5kPa For Ammonia Pressure must be greater than 2.339 kPa 20C
State 1 Liquid Ammonia @ 1 MPa Liquid Water @ 100 kPa 20C • In the compressed liquid region, the properties of the liquid are approximately equal to the properties of the saturated liquid state at the temperature.
State 2 : Saturated Liquid • Process 1-2: • The temperature and specific volume will increase from the compressed liquid, or subcooled liquid, state 1, to the saturated liquid state 2. Saturated Liquid Ammonia @ 1 MPa &24.9C Saturated Liquid Water @ 100 kPa & 99.62C state 2
State 3 : Equilibrium Mixture of Saturated Liquid Vapour • Process 2-3: • At state 2 the liquid has reached the temperature at which it begins to boil, called the saturation temperature, and is said to exist as a saturated liquid. • Properties at the saturated liquid state are noted by the subscript fand v2 = vf. • During the phase change both the temperature and pressure remain constant. • Water boils at 99.62°C when the pressure is 100kPa . • Ammonia boils at 24.99°C when the pressure is 1000 kPa ). • At state 3 the liquid and vapor phase are in equilibrium and any point on the line between states 2 and 3 has the same temperature and pressure.
State 4 : Saturated Vapour • Process 3-4: • At state 4 a saturated vapor exists and vaporization is complete. • The subscript g will always denote a saturated vapor state. • Note : v4 = vg.
State 5 : Superheated Vapour • Process 4-5: • If the constant pressure heating is continued, the temperature will begin to increase above the saturation temperature. • State 5 is called a superheated state because T5 is greater than the saturation temperature for the pressure. Superheated Ammonia @ 1 MPa &300C Superheated Water @ 100 kPa & 300C
The Theory of Producing Steam • Water and steam can be easily used as heat carriers in heating systems. • Water boils and evaporates at 100°C under atmospheric pressure. • By higher pressure, water evaporates at higher temperature - e.g. a pressure of 10 bar equals an evaporation temperature of ~179.90C. • At a constant pressure of 10 MPa the saturation temperature is 311.10C.
Wet Vapour • Wet vapour is a mixture of vapour and liquid water at same temperature and pressure. • Saturation pressure is the pressure at which the liquid and vapor phases are in equilibrium at a given temperature. • Saturation temperature is the temperature at which the liquid and vapor phases are in equilibrium at a given pressure. • Saturation Pressure is function of temperature or vice versa. T = F(p) The Wagner-Ambrose equation
Equations for Saturation Conditions of Water Saturation Properties of Water :
Many Constant Pressure Processes • If all of the saturated vapor states are connected, the saturated vapor line is established. • If all of the saturated liquid states are connected, the saturated liquid line is established. • These two lines intersect at the critical point and form what is often called the “steam dome.” The critical point of water is 374.14oC, 22.09 MPa The critical point of ammonia is 132.3oC, 11.33 MPa
The Vapour Dome • The region between the saturated liquid line and the saturated vapor line is called by these terms: • Saturated liquid-vapor mixture region, • Wet region, • Two-phase region, and just • The saturation region. • The trend of the temperature following a constant pressure line is to increase with increasing volume. • The trend of the pressure following a constant temperature line is to decrease with increasing volume.
Peculiar Nature of Wet Vapour • Pressure and temperature are not independent properties. • Either p & Vor T& Vare independent pair. • P & v or T & v can also be considered. • A new property is to be defined for steam for ease of design. • This is called Quality or dryness fraction of wet steam.
Quality and Saturated Liquid-Vapor (Wet) Mixture • Now, let’s review the constant pressure heat addition process for water shown in Figure. • The state 3 is a mixture of saturated liquid and saturated vapor. • How do we locate it on the T-v diagram? • To establish the location of state 3 a new parameter called the quality x is defined as
The quality is zero for the saturated liquid and one for the saturated vapor (0x 1). • The average specific volume at any state 3 is given in terms of the quality as follows. • Consider a mixture of saturated liquid and saturated vapor. • The liquid has a mass mfand occupies a volume Vf. • The vapor has a mass mg and occupies a volume Vg.
Critical Point • The region to the left of the saturated liquid line and below the critical temperature is called the compressed liquid region. • The region to the right of the saturated vapor line and above the critical temperature is called the supercritical region. • At temperatures and pressures above the critical point, the phase transition from liquid to vapor is no longer discrete.
