paraffin wax deposition and fouling

0
w
2 °c)
shear stress of 30.4 per cent. As shown by Walker the Dittus—
rerresents a change in diameter of 6.4 per cent resulting in an
1. k = 0.42 mm. For a tube having i.d. 13.1 mm this
— 66 —
plane of weakness will devalor. Time is often an important factor
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Using the thermal conductivity of a typical wax given in Appendix 1
resistances will be as follows:
as k = 0.0002387 (kW/m °c) the average deposit thickness was
evaluated as fl
Using the new fouling resistance the deposit thickness was evaluated
value, a cohesive faalure within it is likely to occur. The strength
regalar pattern being sustained is reduced so that eventually a
increase in average velocity of 1.2 per cent and an increase in
of the wax layer will depend upon a close and regalar pattern of wax
as 0.45 mm. The resulting increase in shear stress will therefore
Boelter equation gives heat transfer coefficient values constantly
7.5 Remova.. of eosi:s
below those xperimentaliy obtained in commerciai tubes. Substract—
and fouling.
ing therefore 30 per cent, as recommended by Walker, the various
be about 32.9 per cent.
by over 30 per cent during deposition. These increases and the
contributing to the asymptotic behaviour of paraffin wax deposition
decreases in heat flux will therefore be the major factors
Outside tube resistance R = 0.024’
IT
Wall resistance 2 = 0.0023
U
Inside tube resistance R. = 0.4742 (kW/m
Fouling resistance = 1.8978
II
2en a wax deposit has increased its thickness to some critical
The shear stresses acting on deposits may therefore increase
2 = 2.3987