steam engine sliding valve steam enters chamber from left, leaving from right both valves closed,...
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Steam Engine
Sliding valve
Steam enters chamber fromleft, leaving from right
both valves closed, piston moves to the right
Steam enters from right,leaving from leftpiston moves back to the left
Thermodynamics Properties
Thremo Porperties-1.ppt
Two independent properties are needed to define the state of a pure substance (Ch. 2, YAC)
Pure Substance: A homogeneous substance with a fixed chemical composition.Does not have to be a single element or in a single phase.
Helium, Nitrogen, Water, Sulfur-di-Oxide are pure substances.
Pressure (p), Temperature (T), specific volume (v) internal energy (u) andenthalpy (h) are among the most common thermodynamic properties.
The variation or behavior of properties of a pure substance and their relationshipto each other is most commonly and easily examined via property diagrams and property tables.
Property diagrams are also used to analyze the thermodynamic processes in thermal systems and thermodynamic cycles under which many systems operate.
Simple steam power plant cycle
Heat in
Work out
Condensing back to liquidfor easy transportation
Heat in
Work out
Heat out to cooling water
Work inby pump
Property Diagram
Superheated steam(or vapor)
Saturated waterliquid+vapor
Compressed(subcooled)liquid
Phase Change
Above critical point,there is no cleardistinction betweenliquid and vapor phases
Melting
vaporization
sublimation
Constant pressure process
Saturated (liquid+vapor)
p
v
p
T
T
v
Constanttemperaturelines
Constant pressureline
(a) P-v diagram: Along the constant temperature line, increasing vapor pressure will lead to higher density (lower specific volume) due to compression. After it reaches the saturation pressure at that temperature, the vapor will condense into liquid while the pressure remains constant until all vapor condense into liquid.
(b) T-v diagram: Along the constant pressure line, increasing liquid temperaturewill lead to lower density (higher specific volume) due to thermal expansion.At the saturation temperature, the liquid will vaporize into gaseous form at a constantpressure until all liquid vaporize.
p
T
(c)P-T phase diagram
solidliquid
vapor
Melting/freezing
Substances that contract on freezingSubstances that
expandon freezing ex. Water.Higher pressure makesit more difficult to freeze, thus requiring lower freezing temperature. The reverse is true for substances that contract on freezing
Critical point
Vaporization/condensation
Sublimation Triple point: all three phasescoexist in equilibrium
Critical point: A limiting state above which there is no clear distinction betweenliquid and vapor phases.
Vaporization: As pressure goes down, vaporization occurs at lower temps That’s why water boils at lower temperatures at higher elevations.