Heat exchangers

The most corrosive fluid will be taken on tube side for ease of replacement on corrosion

in heat exchanger simply fluid which to be heat/cooled pass through tube and fluid is used to for a media for heating or cooing used in shell side .

More corrosive liquid enters tube
Tubes are meant for higher operating pressure
Tubes are meant for higher pressure drops
More viscous liquids should enter the shell side
Liquid with more fouling factor should enter the tube side.

Fluid having more corrosive nature and higher fouling factor is passed through tube side because we can easily replace the tube after maintenance but if the shell get corroded it will be more economical to replace or maintain it.

Fluid having high specific volume must go through the shell side.High temperature and pressure stream must go to the tube side and more viscous fluid must go to the shell side.so,that the baffles impart turbulence to the viscous fluid.