Although Attyub194 is known for his constructive, experienced, and accurate posts, I have to correct the following statement:
“Therefore, it will be difficult to put a dirty fluid i.e. fluid containing solids or substances which can be accumulated on shell side with U tube bundle.”
ALL U-tube construction heat exchangers are capable of having their U-tube bundle removed. Otherwise, they couldn’t be practically and economically fabricated. Because of this inherent U-tube bundle feature, it is possible to remove the bundle from the shell and clean it mechanically out in the open and not treat the bundle with chemical solutions while it is inside the shell. If fouling is expected or anticipated for the service it is always wise to specify square pitch for the tubes – which allows for external mechanical cleaning.
However, having said the above, it is also important to bear in mind WHAT type of fouling is anticipated. For example: in a prior 1985 U-tube heat exchanger installation that I inherited, the outlet cooling water on the exchanger shell side was specified to be 125 oF. At this outlet temperature, the cooling water solids – mostly carbonates – precipitated out and formed a solid block. It was virtually impossible to physically pull the U-tube bundle out of the shell and I had to cut the shell in sections to salvage the U-tube bundle. I welded on a new shell later, after mechanical cleaning. The point here is that cooling water should not be allowed to heat up above 120 oF – especially where the cooling water has dissolved solids.
It is the responsibility of the designer (and NEVER the responsibility of the Computer program – even HTRI) to ensure that the heat exchanger complies with all of the project scope – especially the characteristics of both fluids and their properties. In doing so, it becomes common place to be able to select the proper, best heat exchanger selection and orientation.