What Are Advantages and Disadvantage 2 Pass Flow and 4 Flow Pass Heat Exchanger?

4 pass coolers are compact as compared to 2 pass coolers but cooling achieved in 2 pass cooler is more then 4 pass cooler.

In 4 pass cooler, media pass velocity reduces considerably so more chances of silt formation.

4 pass coolers are suitable for small requirements and cooling water requirement is less as compared to 2 pass coolers.

The number of passes depends primarily on the desired velocity and pressure drop through the heat exchanger. Greater velocity ordinarily leads to higher K factor, but also to greater pressure drop. There may be some minimum and maximum desired velocities, for example to avoid sedimentation or erosion, respectively.

Size is important _{- especially if you want your wallpaper to stay up.}

There is good presentation on heat exchanger. This may help you understand.