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

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

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Process Equipment and Plant Design
In a shell and tube heat exchanger, the clearance of the tube is generally

More in case of triangular pitch as compared to the square pitch tube layout
Equal to the tube diameter
More than the tube diameter
Not less than one-fourth of the tube diameter or 3/16"

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