Energy balance_0829

Energy balance_0829 - Calculation of ∆H involving latent...

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Thermodynamics (con’d) 1 st Law of thermodynamics Energy can not be created or destroyed but energy does change form General form The total change in energy of a closed system is equal to the heat added to the system minus the work done by the system. = - = - ∆E Efinal Einitial Q W i.e. + + = - ∆Ei ∆EKE ∆EPE Q W In many situations where the potential energy and the kinetic energy of the system are constant = - ∆Ei Q W Energy balance for a closed system = + - ∆Ei Q Ef PdV ΔE i : change in internal energy; E f : work due to frictional force; PdV : work due to moving boundary If heating at constant volume = ∆Ei Q if heating under constant pressure = ∆H Q ∆H (change in enthalpy, J) is called heat content. Calculation of ∆H involving sensible heat: = - = = = ( - ) ∆H H2 H1 Q mT1T2CpdT mCp T2 T1 C p : specific heat capacity at constant pressure (J/Kg °C)
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Unformatted text preview: Calculation of ∆H involving latent heat: = ∆H mHlatent H latent : latent heat of phase change (J/Kg) Thermal energy balance (negligible work): + = + Qi MiHi Qe MeHe If well insulated at system boundary: = = Qi Qe 0 Energy balance for an open system For a steady flow system, energy of a process stream includes: • Internal E = E i • Potential E PE = mgz • Kinetic E KE =mu 2 /2 • Flow work (Pressure energy) E = PV Total energy: = + + + E Ei EKE EPE PV i.e. = + + + E Ei mu22 mgz PV Based on 1 st law of thermodynamics: = -=-ΔE Q W Eout Ein-= , + + +-( , + + + ) Q W Ei 2 m2u22 mgz2 P2V2 Ei 1 m2u12 mgz1 P1V1 When expressed on a basis of unit mass: = + +-+ + + ,-, + Qm u222 gz2 P2ρ2 u122 gz1 P1ρ1 Ei 2' Ei 1' Wm...
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This note was uploaded on 09/30/2011 for the course FDST 4050 taught by Professor Kong during the Fall '11 term at UGA.

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Energy balance_0829 - Calculation of ∆H involving latent...

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