Q1: In a shell and tube heat exchanger, putting a longitudinal baffle across the shell, forces the shell side fluid to pass __________ through the heat exchanger.

ANS:B - twice

In a shell and tube heat exchanger, there are two primary fluid streams: the tube side fluid and the shell side fluid. The longitudinal baffle inside the shell of the heat exchanger serves to direct the flow of the shell side fluid. When the shell side fluid enters the heat exchanger, it encounters the baffle. The presence of the baffle forces the fluid to change its direction, typically causing it to flow parallel to the tubes. As the fluid flows along the length of the shell, it exchanges heat with the fluid inside the tubes. After reaching the end of the shell, the fluid encounters the baffle again. This time, it's redirected back towards the entrance of the heat exchanger. As a result, the shell side fluid passes through the heat exchanger twice: once in each direction. This arrangement increases the heat transfer efficiency of the heat exchanger by ensuring that the shell side fluid makes multiple passes over the tube bundle, maximizing the heat exchange between the two fluid streams.