Process Equipment and Plant Design
Triangular pitch tube layout as compared to square pitch in a shell and tube heat exchanger

Permits the use of less tubes in a given shell diameter
Facilitates comparatively easier external cleaning because of large clearance
Both B and C
Permits the use of more tubes in a given shell diameter

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Process Equipment and Plant Design
When one of the fluids is highly corrosive and has fouling tendency, it should

Perferably flow outside the tube
Preferably flow inside the tube for its easier internal cleaning
Flow outside the tube, when the flow is counter-current and inside the tube when the flow is co-current
Flow at a very slow velocity

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