Complex sentence: Steam goes through the tube side in one way and back passes in a tube bundle in this type of reboiler and the material from the bottom of the tower to be heated, commonly called the "bottoms", goes through the shell side.
Split into simpler sentences: Steam goes through the tube side in one way and back passes in a tube bundle in this type of reboiler. Material from the bottom of the tower to be heated, commonly called the bottoms, goes through the shell side.