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Formulas Thermo


Enviado por   •  30 de Enero de 2014  •  422 Palabras (2 Páginas)  •  242 Visitas

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Closed Systems First Law

Sign convention first law

Work by system positive

Heat to system positive

Mass entering system positive

Function Restriction Process Boundary work Boundary work per unit mass

P = f(V) none Prescribed function

PV0 = c n = 0 Constant pressure

PV1 = c

n = 1 Constant temperature

= c

Constant volume Wb = 0 wb = 0

= c

Polytropic

= c

Polytropic

= c

Polytropic

= c

Polytropic

= c

Adiabatic

n = k Isentropic

Work Type Work Work rate Work per unit mass

Potential

Kinetic

Shaft Wsh =2nT

Electrical

Transfer of mass and energy across a system boundary

Open system Closed system Isolated system

Heat Yes Yes No

Work Yes Yes No

Mass Yes No No

Mixed region

Saturated vapour

v = vf + x vfg vg= vf + vfg

u = uf + x ufg ug= uf + ufg

h = hf + x hfg hg= hf + hfg

Subcooled region Mixed region Superheated region

v < vf vf < v < vg v > vg

h < hf hf < h < hg h > hg

u < uf uf < u < ug u > ug

solid liquid Ideal gas

du = Cv dT du = Cv dT du = Cv dT

dh = Cp dT dh = Cp dT dh = Cp dT

Cp = Cv = C

h = u + Pv Cp = Cv = C

h = u + Pv Cp = Cv + R

h = u + Pv

k = Cp/Cv

No restriction No restriction Ideal gas

Variable Symbol Unit Alternative Used in

Acceleration a m/s2 F = ma

Area A m2 V = A ds

Velocity

m/s

Flow rate

kg/s

Force F N kg m/s2 P = F/A

Internal Energy/unit mass u kJ/kg e = u + ke + pe

Internal Energy U kJ kN s E = U + KE + PE

Temperature T K oC Pv=RT

Pressure P kPa kN/m2

Density

kg/m3

Specific volume

m3/kg

Heat Capacity Cv, Cp, C kJ/kgoC dh = u + Pv

Gravity g m/s2 g = 9.81 m/s2

Mass fraction x x = mv/m

Mass m kg w=W/m

Enthalpy H kJ H

...

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