ANS:B - tube diameter

In a shell and tube heat exchanger, the shell side fluid velocity can be affected by changing several parameters, including the tube layout, tube diameter, tube pitch, and the number of baffles. However, among the options provided, changing the tube diameter does not directly affect the shell side fluid velocity. Here's why:

• Tube Layout: The arrangement of tubes within the shell affects the flow distribution and resistance within the shell side. Different tube layouts can result in variations in fluid velocity and pressure drop.
• Tube Pitch: The tube pitch refers to the distance between adjacent tubes. Altering the tube pitch can change the flow area available for the shell side fluid, which in turn affects the fluid velocity.
• Number of Baffles: Baffles are plates or rods installed within the shell to promote turbulence and enhance heat transfer. Changing the number of baffles alters the flow pattern and can influence the shell side fluid velocity.

However, changing the tube diameter affects the flow area available for the fluid inside the tubes, not the fluid in the shell side. Therefore, it does not directly impact the shell side fluid velocity. So, among the options provided, the tube diameter is the parameter that cannot change the shell side fluid velocity in a shell and tube heat exchanger.