fenom transp anot aula 2015
DESCRIPTION
Material sobre fenomenos de transporte bem detalhado e de fácil compreensãoTRANSCRIPT
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9$=2(9(/2&,'$'(1) VAZO VOLUMTRICA Vazo volumtrica definida como sendo o volume de fluido que passa por uma determinada seo por unidade de tempo.
Q
Q =
V t
vazo volumtrica
volume
tempo
E tambm: Q= v . A, onde: v= velocidade; A= rea As unidades mais usuais so: m3/h; l/s; m3/s; GPM (gales por minuto). 2) VAZO MSSICA Vazo mssica a massa de fluido que passa por determinada seo , por unidade de tempo.
Qm=
Qm vazo mssica
m massa
t tempo E tambm: Qm= . v . A, onde: v= velocidade; A= rea ; = massa especfica As unidades mais usuais so: kg/h; kg/s; t/h; lb/h.. 3) VAZO EM PESO Vazo em peso o peso do fluido que passa por determinada seo, por unidade de tempo.
Qp=
Qp vazo em peso
G peso t tempo
E tambm: Qp = . v . A, onde: v= velocidade; A= rea ; = peso especfico As unidades mais usuais so: kgf/h; kgf/s; tf/h; lbf/h. 4) VELOCIDADE Existe uma importante relao entre vazo, velocidade e rea da seo transversal de uma tubulao:
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Com a relao entre vazo e velocidade, Q = v . A (v=velocidade e A=rea), podemos escrever: Q1 = v1 . A1 = Q2 = v2 . A2 Se o fluido incompressvel a vazo em volume a mesma em qualquer seo. Essa equao valida para qualquer seo do escoamento, resultando assim uma expresso geral que a Equao da Continuidade para fluidos incompressveis. Q1 = Q2 = constante Pela equao acima, pode-se obter a relao de velocidades em qualquer seo da tubulao. Nota-se que para uma determinada vazo escoando atravs de uma tubulao, uma reduo de rea acarretar um aumento de velocidade e vice-versa.
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.REGIME LAMINAR: .REGIME TRANSITRIO:.REGIME TURBULENTO:Reynolds aps sua investigaes, concluiu que o melhor critrio para determinar estes regimes so, atravs da equao:
Re Nmero de Reynolds (n sem dimenso)
Re = v x D v velocidade de escoamento do fluido (m/s) D dimetro interno da tubulao(m)
viscosidade cinemtica do fluido(m2/s)
.LIMITES DO NMERO DE REYNOLDS PARA TUBOS
Re 2000 escoamento laminar
2000 Re 4000 escoamento transitrio
Re 4000 escoamento turbulento
Notar que o nmero de Reynolds um nmero adimensional, independendo portanto do sistema de unidades adotado, desde que coerente. No geral, na prtica, o escoamento da gua em canalizaes se d em regime turbulento. Exceo feita quando as velocidades so muito baixas ou fluidos tem alta viscosidade.
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Equao de Bernoulli para Fluido Real e Presena de uma Mquina no Escoamento.
a) Sem Mquina Perda de energia
(1) H1 > H2 (2)
H1 > H2
H1 = H2 + H
H
= Perda de energia de 1 para 2 por unidade de peso.
H
= Perda de carga (m, cm, mm)
Observao Importante: Havendo o escoamento e devido HP, temos por exemplo:
(Trecho onde no existe mquina)
(1) (2)
Escoamento de (1) para (2): H1 > H2 Escoamento de (2) para (1): H2 > H1
b) Com Mquina
M
H1 + Hm = H2 + HP12 (1) (2)
H2H1
H2H1
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c) Resumo:
Fluido Perfeito Fluido Real
a) sem mquina: H1 = H2 a) sem mquina: H1 = H2 + HP12 b) c/ mquina H1 + Hm = H2 b) com mquina H1 + Hm = H2 + HP12Potncia (P0) Fornecida ou Retirada do Fluido na Passagem pela Mquina e Rendimento
.Potncia (P0) RXSRWrQFLDKLGUiXOLFDIRUQHFLGDRXUHWLUDGDGHSHQGHGRWLSRGHPiTXLQD
: Peso especfico do fluido que atravessa a mquina.
Q: Vazo volumtrica do fluido na passagem pela Mquina.
Hm : Energia fornecida ou retirada do fluido pela mquina por unidade de peso.
P0 = QHm
- M.K*.S -
kgf/m3 Q m3/s P0 = kgf . m/s (kgm/s) Hm m
- S.I.
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s s
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1C.V. = 75 kgf .m/s
1C.V. = 736 W = 0,736 kW
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