Step #10: Calming zones and hole pitch (refer sections 7.6.2 & 7.6.4)

 

Perforated area ():

Where, = calming zone area (Figure 7.3).

            = area occupied by edge strip ( Figure 7.9)

            = 0.73; now, = 95° ( [3] page 573 )

           Angle subtended by the chord (edge plate), = 180°-95° = 85°

           The unperforrated edge strip (edge plate) mean length from the geometry:

            =( D_T -50×10^-3 )× =(2.4-50×10^-3 )× =3.49 m

            = 50×10^-3 × =0.175 m²

           Use 50 mm wide calming zones. The approximate mean length of zones:

            =Weir length ( + Width of unperfortaed edge strip

           =1.752+50×10^-3 =1.802 m

= 2(50×10^-3 × )= 0.18 m²

Therefore, perforation area per tray ( 3.616- 0.18-0.175= 3.26 m²

 

Take total hole area m²

m²                                  [ hole diameter 12 mm ]

Number of holes ()= 4326

. For equilateral triangular pitch:

This corresponds to hole-pitch to hole diameter ratio of ( . This is very close to the normal range of 2.5 to 4.0 times of hole diameter.

The estimated hole pitch (I_p)=is 29.5 mm.

Figure 7.9 . Angle subtended by the chord ( [3] page 583 ).