105A_synthesis

105A_synthesis - 105 A synthesis Conservation of Energy:...

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105 A synthesis
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Conservation of Energy: The 1 st Law of Thermodynamics K EP EU Q W ∆+ + = Change in amount of energy contained within the system during some time interval = Net amount of energy transferred in across the system boundary by heat transfer during the time interval - Net amount of energy transferred out across the system boundary by work during the time interval
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Alternative Forms of the Energy Balance • Differential Form: dE Q W δ = • Time Rate Form: dE QW dt =
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Simple compressible systems HU p V hu p v = + =+ Due to the frequent occurrence of the above combination of properties we construct a new property called enthalpy. dU Q pdV δ = 0 0 W pdV dKE dPE = = = Simple Compressible Systems
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Cycle Analysis Power Cycles Refrigeration & Heat Pump Cycles cycle cycle QW = cycle in W Q η= in cycle Q W β= out cycle Q W γ= 0 cycle E ∆= hence
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Quality For Saturated Mixture (Liquid-Vapor) Region Quality; x; an intensive property x gives fraction that is vapor (gas) (1-x) gives Moisture Content g fg m x mm + 0 x 1; x = 0 Saturated Liquid (subscript ‘f’) x = 1 Saturated Vapor (subscript ‘g’) ‘fg’ ‘g’-’f’ LET b = ANY INTENSIVE PROPERTY – (b = v, u, h, s, etc.) (1 ) f f gf f g ff g fg g f bb x b x b b bx b x b == =+ =− = ⋅+ −⋅
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• Using Saturated Liquid Data (‘Compressed Liquid Rule’) • Using ‘Incompressible Substance Model’ (, ) () ) ) ) f f f f vT p v T hT p h T uT p u T sT p s T 21 pv cc c uuc TT hhc v P P == −= + −≈ Specific Heats (Heat Capacities ) v v u c T = p p h c T = p v c k c =
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Properties for Ideal Gases P vn R T P vR T P Vm R T = = = The Ideal Gas Model: () uu T hh T u T R T = ==+ v p du cT dT dh = = Tables A-22(E) and A-23 (E) When specific heats are assumed constant Table A-20(E): 21 v p uuc TT hhc =− −= Requirements: 1 c c Z P P ± ² R R M =
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