Shell and tube heat exchangers are widely used devices for transferring heat between two fluids. They consist of a shell, which is a large outer pipe, and multiple tubes inside it. Baffles are essential components within the shell side of these heat exchangers.

Functions of Baffles in Heat Exchangers

Baffles are placed perpendicular to the tubes within the shell. They serve several important functions related to both the structural integrity of the heat exchanger and its thermal performance.

• Tube Support: Baffles act as support plates for the tubes, preventing them from vibrating excessively due to fluid flow or thermal expansion. This support is crucial for preventing tube damage or failure over time.
• Improved Heat Transfer: Baffles force the shell-side fluid to flow across the tube bundle rather than just parallel to the tubes. This cross-flow pattern increases turbulence in the shell-side fluid. Increased turbulence enhances the convective heat transfer coefficient, leading to better heat transfer between the shell-side fluid and the tube-side fluid.
• Preventing Stagnation: By directing the flow across the tubes, baffles ensure that the shell-side fluid flows through most of the shell volume. This prevents the formation of stagnant zones where fluid velocity is low, which could lead to temperature stratification or fouling.

Analyzing the Given Statements

Let's evaluate each statement provided in the options:

• "It is used to provide support for tubes." - This is a correct function of baffles.
• "It is used to improve heat transfer." - This is a correct function of baffles by inducing turbulence and cross-flow.
• "It is used to prevent stagnation of shell side fluid." - This is a correct function of baffles by ensuring flow distribution.
• "It is used to increase weight of the heat exchanger." - While adding baffles does add some weight to the heat exchanger, increasing weight is not a functional purpose or design objective of baffles. Their purpose is related to structural support and heat transfer performance, not mass addition. Therefore, stating that baffles are *used* to increase weight is incorrect regarding their primary function.

Based on the analysis of the primary functions of baffles, the statement that is INCORRECT is that they are used to increase the weight of the heat exchanger.