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Thermodynamics

Thermodynamics. Laws & Properties Temperature & Pressure Scales Thermodynamic Cycles. Thermodynamics. Branch of science dealing with the interchange of thermal & mechanical energy 2 Laws 6 Properties 3 Phases 3 Modes of Heat Transfer 2 Effects of Heat Transfer. WORK IN. HEAT IN.

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Thermodynamics

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  1. Thermodynamics Laws & Properties Temperature & Pressure Scales Thermodynamic Cycles

  2. Thermodynamics Branch of science dealing with the interchange of thermal & mechanical energy • 2 Laws • 6 Properties • 3 Phases • 3 Modes of Heat Transfer • 2 Effects of Heat Transfer

  3. WORKIN HEATIN HEATOUT WORKOUT Thermodynamic Laws • 1st Law:Conservation of Energy (you can’t win—the best you can do is tie) SYSTEM with stored, internal energy U HEATIN – HEATOUT = WORKOUT – WORKIN + DU

  4. The 1st Law is an accounting rule 1 BTU = 778 lb-ft = 1055 joules = 252 calories

  5. WORKIN HEATIN HEATOUT WORKOUT Thermodynamic Laws • 2st Law:Not all processes are reversible (sometimes you can’t even tie) SYSTEM with stored, internal energy U HEATOUT = WORKIN (can happen) HEATIN = WORKOUT (cannot happen)

  6. Thermodynamics • 2 Laws • 6 Properties • 3 Phases • 3 Modes of Heat Transfer • 2 Effects of Heat Transfer

  7. Thermodynamic Properties Define the “state” of a system • Temperature, T (oF, oC, oR, oK) • Pressure, P (psi, bar, in. Hg) • Internal Energy, u (BTU/lb) • Specific Volume, v (cu.in./lb) • Enthalpy, h (BTU/lb) • Entropy, s (BTU/lb)

  8. Thermodynamic Properties • 6 properties linked—measure any two  calculate (or look up) other 4 v h v P h s P T s v T h P s T u u u • Which two are you probably going to observe (measure)?

  9. Temperature Scales • Relative scales:Fahrenheit & Celsius • Absolute scales:Rankine & Kelvin TSES Boiler 961 oR 672 oR 492 oR 0 oR 494 oF 257 oC 530 oK 373 ok 273 oK 0 oK Boiling (Atmos) 100 oC 212 oF 100o 180o Body Temp 98.6 oF 37 oC Room Temp 72 oF 22 oC 32 oF 0 oC Freezing 0 oF Absolute Zero -273 oC -460 oF

  10. Pressure Scales • Relative scales: psig, inches (Hg) of Vacuum TSES Boiler 614.7 psiA 600 psig “gage pressure” Standard Atmosphere 14.7 psiA 29.92 “Hg 0 “Hg “inches of vacuum” Perfect Vacuum 0 “Hg 0 psiA 29.92 “Hg

  11. Vacuum measure Perfect Vacuum 29.92 “Hg Atmospheric Pressure A Barometer is used to measure atmospheric pressure via comparison to a (very nearly) perfect vacuum

  12. Vacuum measure 0 psia 5 psia 10 psia 14.7 psia Evacuated Space 29.92 “Hg Atmospheric Pressure 20.0 “Hg A Vacuum Gage is used to measure the pressure in an evacuated space via comparison to atmospheric pressure 10.0 “Hg 0.0 “Hg

  13. Thermodynamics • 2 Laws • 6 Properties • 3 Phases • 3 Modes of Heat Transfer • 2 Effects of Heat Transfer

  14. 3 Phases of matter • Solid – maintains shape • Liquid – lower surface & sides conform to shape of container; upper surface flat & horizontal • Vapor (Gas) – conforms to shape of container A Fluidis either a liquid or vapor which flows and can be pumped

  15. Thermodynamics • 2 Laws • 6 Properties • 3 Phases • 3 Modes of Heat Transfer • 2 Effects of Heat Transfer

  16. 3 Modes of heat transfer • Radiation– transfer through space viaelectromagnetic waves; travel in a straight line (may reflect off surfaces) • Conduction– transfer through solids (molecule vibration) • Convection– transfer via movement of a fluid Note: Heat is thermal energy in transition from a high temperature area to a lower temperature area

  17. Heat transfer BOILER TUBE • Transfer from FURNACE to Boiler Tube by radiation and convection • Transfer through Boiler Tube wall by conduction • Transfer to Steam Drum via circulation of fluid (convection)

  18. Thermodynamics • 2 Laws • 6 Properties • 3 Phases • 3 Modes of Heat Transfer • 2 Effects of Heat Transfer

  19. 2 Effects of heat transfer When heat is transferred to/from a substance, one of two effects may be realized • Temperature change–a rise or fall in temperature is a sensible heateffect • Phase change– (liquid-vapor, vapor-liquid, solid-liquid, liquid-solid) is a latent heateffect • But not both simultaneously

  20. at least not in the same space 300o steam SUPERHEATER SENSIBLE heat 212o vapor 88o of SUPERHEAT 212o liquid BOILER Saturation Conditions SENSIBLE heat LATENT heat

  21. Transferring heat to 1 lb of H2O(at atmospheric pressure) Temp (oF) VAPOR LIQUID-VAPOR MIX SOLID-LIQUID MIX 212 LIQUID SOLID Sensible Latent 32 Heat (BTU) 0

  22. Transferring heat to 1 lb of H2O(at atmospheric pressure) Temp (oF) “wet” steam Superheated VAPOR 0% “quality”(100% liquid) 50% “quality”(50% liquid() 100% “quality”(0% liquid() Sensible Heat0.5 BTU/oF LIQUID-VAPOR MIX Saturation Conditions: 0 psig; 212oF 212 BOILING Sub-cooled LIQUID CONDENSING Latent Heat *of vaporization)970 BTU/lb Sensible Heat1.0 BTU/oF Heat (BTU) 0

  23. 1 Atm 0 psia 1 Atm (14.7 psia) 0 psia Boiling (saturation) Temperature linked to pressure Pressure Cooker 162o vapor 20”Hg (VAC) 162o liquid 10”Hg (bar) 5 psig 230o vapor Mt. Everest 230o liquid

  24. STEAM DOME 490 92 570 212 Saturation Temperatures & Pressures Temp (oF) 1200 psig 610 BTU/lb 600 psig 728 BTU/lb 1 Atm (14.7 psia, 0 psig) 970 BTU/lb 28.5 “Hg (VAC) 1040 BTU/lb Heat (BTU) 0

  25. Thermodynamic CYCLES • 5 components: • Heat source • Heat sink • Engine • Pump • Working Fluid • Closed Cycle: working fluid reused • Open Cycle: working fluid discarded

  26. ENGINE W HEAT SOURCE HEAT SINK W PUMP H H Closed Cycle WORKING FLUID

  27. ENGINE W HEAT SOURCE HEAT SINK W PUMP H H Open Cycle WORKING FLUID

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