计算圆管内部层流对流换热系数 强迫

Forced Convection Heat Transfer Coefficient Correlations (S.I. units)

2. Laminar Flow Inside a Circular Tube

Inputs Calculations

Fluid = water Reynolds Number, Re =472

Ave. Fluid Temp, T b =30o C Prandtl Number, Pr = 5.7

Pipe Diam., D =12.5mm Correlations #1, Fully Developed Flow ( Le<< L )

Pipe Diam., D =0.013m Const. T wall Nu o = 3.66

(calculated)

h o =611

Ave. Velocity, V =0.03m/s

Const. heat flux Nu o = 4.36

Fluid Density, r =995kg/m3

h o =728

Fluid viscosity, m =0.00079N-s/m2202.30

Correlation #2 ( Pr > 5 ; Le > L ):

Fluid Sp. Heat, C p = 4.19kJ/kg-K

Nu o =5

Fluid Sp. Heat, C p =0.58W/m-K

(calculated)h o =

Fluid Thermal

Conductivity, k =0.00058kJ/s-m-K

Correlation #3 ( 0.6 < Pr < 5 ; Le > L )

Pipe Length, L = 1.8m

Nu o =5

Entrance Length, Le =0.354m

(calculated)h o =825

229.151948

Correction for Temperature Variation: ( h = h o(m b/m w)0.14

Inputs Calculations

Ave. Fluid Temp, T b =30o C Correlations #1, Fully Developed Flow Fluid Visc. at T b, m b =0.000785N-s/m2Const. T wall h =639

Ave. Wall Temp, T w =50o C Const. heat flux h =762

Fluid Visc. at T w, m w =0.00057N-s/m2Correlation #2 ( Pr > 5 ):

h =858

Correlation #3 ( 0.6 < Pr < 5 ):

h =863

NOTE: The spreadsheet calculates the forced convection heat transfer coefficient, h, for each of

the three correlations. You need to choose the correct one to use. In this case, Correlation #2 is the correct one, because Le > L and Pr > 5.

Equations for Forced Convection Flow inside Pipes

Correlations #1: Fully Developed Laminar Flow ( L >> Le ) ow ( Le<< L )

kJ/hr-m2-K

w/m2-K Correlation #2: ( Le > L )

kJ/hr-m2-K

w/m2-K

kJ/hr-m2-K

w/m2-K Correlation #3: ( Le > L )

r < 5 ; Le > L ):

kJ/hr-m2-K

w/m2-K

veloped Flow

kJ/hr-m2-K177.6063w/m2-K

kJ/hr-m2-K211.5747w/m2-K

kJ/hr-m2-K238.2843w/m2-K

kJ/hr-m2-K239.653w/m2-K , Correlation #2