° from nose 0 30 60 90 120 180 240
H 0 (m) 1.40 01.85 02.30 02.75 003.20 004.10 005.00
Knowing that r 1 (H 0 h 0 )/r 0 , equation (12.19) gives the spiral
radius for angle , and the results are tabulated below:
° from nose0 30 60 90 120 180 240H 0 (m) 1.40 1.85 2.30 2.75 3.20 0 4.10 0 5.00
r 1 (m) 2.62 2.68 2.71 2.81 2.87 0 2.99 0 3.10
R(m) 2.62 4.57 6.55 8.25 9.75 12.52 14.52
The maximum width of the spiral is R 60 R 240 6.5514.5221.07 m.
Practical widths are within the range (2.7 3)Dand hence let us adopt a
maximum width of 2.7D9.45 m. Therefore the reduced maximum radius
R 240 is obtained as
R 240 9.4514.52/21.076.52 m.This reduction increases the vorticity of the flow which can be obtained
through equation (12.19). Thus the new vortex strength, K10.55 m^2 s^1.
Using this new Kvalue the spiral radii for all angles can be recomputed
and the results shown as in the following table:
° from nose 0 30 60 90 120 180 240
R(m) 2.62 03.53 04.18 04.82 005.22 006.02 006.52
The maximum scroll case width is now 4.186.5210.70 m.DRAFT TUBE SETTING
Using Thoma’s criterion,
YsB H.Using a value c1.15
Ys 10 1.15 10 1.5 m below TWL,i.e. the unit is to be submerged.
The sectional details through the unit are shown in Fig. 12.26.