An aniline-alcohol solution is flowing at a velocity of 3 m/s through a long, 2.5 cm-ID thin-wall tube. Steam is condensing at atmospheric pressure, on the outer surface of the tube, and the tube-wall temperature is 100°C. The tube is clean, and there is no thermal resistance due to a scale deposit on the inner surface. Using the physical properties tabulated below, estimate the heat transfer coefficient between the fluid and the pipe using and compare the results. Assume that the bulk temperature of the aniline solution is 20°C and neglect entrance effects.

Question

GIVEN

• An aniline-alcohol solution flowing through a thin-walled tube

• Tube is clean with no scaling on inner surface

• Velocity (V) =3 m/s

• Inside diameter of tube (D) = 2.5 cm = 0.025 m

• Tube wall surface temperature (Ts) = 100°C

• Solution has the properties listed above

• Solution bulk temperature (Tb)= 20°C FIND

• The heat transfer coefficient ( ch ) using: (a) Equation (7.61) (b) Equation (7.66)

ASSUMPTIONS

• Steady state

• Entrance effects are negligible

• Thermal resistance of the tube is negligible

• Tube wall temperature is constant and uniform

• Fully developed flow

SKETCH



PROPERTIES AND CONSTANTS

The density of water ? 1000 kg/m3

Answer 1

The kinematic viscosity (?) of the solution at the bulk temperature is



The Prandtl number is



The Reynolds number is



(a) Applying the Dittus-Boelter correlation



(b) Using the Sieder-Tate correlation



COMMENTS

These estimates vary by about 3% around an average value of 1828 W/(m2 K). But the Sieder-Tate

correlation is more applicable in this case because it takes the large variation of the viscosity with

temperature into account.

Note that the above correlations require that all properties (except ?s) be evaluated at the bulk

temperature.