C14_Nonisothermal_Interphase_Trasnport

C14_Nonisothermal_Interphase_Trasnport - Nonisothermal...

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1 Nonisothermal Interphase Transport Definitions of heat transfer coefficients General definition Qh A T = Δ Overall heat transfer coefficients between two fluid streams separated by one or more solid layers 1 1 01 , Recall that 11 1 n ii i i j n xx hh k h = ⎛⎞ =+ + ⎜⎟ ⎝⎠
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2 Nonisothermal Interphase Transport Definitions of heat transfer coefficients Heat transfer coefficients for circular tubes ( )( ) ( ) 10 1 1 1 1 b Qh D L T T h D L T ππ =− Δ - Heat transfer coefficient based on the inlet temperature With constant physical properties
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3 Nonisothermal Interphase Transport Definitions of heat transfer coefficients Heat transfer coefficients for circular tubes - Heat transfer coefficient based on arithmetic mean T () ( ) ( ) 01 1 02 2 2 bb aa a TT Qh D L h D L T ππ −−− ⎛⎞ =≡ Δ ⎜⎟ ⎝⎠ - Heat transfer coefficient based on logarithmic mean ( ) ( ) ( ) 01 1 02 2 ln ln 01 1 02 2 ln ln a D L h D L T Δ −− - Heat transfer coefficient defined locally ( )( ) 0 loc b dQ h Ddz T T hD d z T π =− ≡Δ
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4 Nonisothermal Interphase Transport Definitions of heat transfer coefficients Heat transfer coefficients for circular tubes With temperature-dependent physical properties -The above definitions of heat transfer coefficient are the same, but all the physical properties such as density, viscosity, thermal conductivity, and heat capacity should be taken at the film temperature defined as ( for tubes, slits, and ducts ) -Further, Re should be written in the following form to account the temperature dependence () 1 2 01 02 11 1 22 2 fb b TT T T T =+ + + Re Du Dw S ρ μ ==
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5 Nonisothermal Interphase Transport Definitions of heat transfer coefficients Heat transfer coefficients for submerged objects With constant physical properties () ( ) 2 0 4 m Qh R T T π =− - Mean heat transfer coefficient - Heat transfer coefficient defined locally With temperature-dependent physical properties ( )( ) 0 loc dQ h dA T T T 0 and T are the temperature at the object’s surface and of the fluid approaching the object 0 1 2 f TT T =+ - The above definitions of heat transfer coefficient are the same, but all the physical properties such as density, viscosity, thermal conductivity, and heat capacity should be evaluated at Temperature T
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6 Nonisothermal Interphase Transport
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7 Nonisothermal Interphase Transport Heat transfer coefficients for forced convection
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This note was uploaded on 09/01/2011 for the course PGE 312 taught by Professor Peters during the Fall '08 term at University of Texas at Austin.

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C14_Nonisothermal_Interphase_Trasnport - Nonisothermal...

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