Question

What is the role of the baffles in a shell-and-tube heat exchanger? How does the presence of baffles affect the heat transfer and the pumping power requirements? Explain.

Short answer

Answer: The primary purposes of baffles in shell-and-tube heat exchangers are to support the tubes, prevent vibration, and enhance heat transfer by creating turbulence in the shell-side fluid. They improve heat transfer by reducing the thermal resistance of the fluid and increasing the overall heat transfer coefficient. However, baffles also result in a higher pressure drop, which requires additional pumping power to maintain the desired fluid flow rate. Optimizing baffle design can help minimize pressure drop and associated pumping power requirements.

Step-by-step solution

Definition of Shell-and-Tube Heat Exchanger

A shell-and-tube heat exchanger is a type of heat exchanger in which one fluid flows through a set of tubes enclosed in a cylindrical shell, while another fluid flows through the shell and around the tubes. The two fluids are separated by the tube walls, which allows heat to be transferred between them.

Function of Baffles in Shell-and-Tube Heat Exchangers

Baffles are plate-like structures placed in the shell side of a heat exchanger to create a more controlled flow of the shell-side fluid. They are installed perpendicular to the flow of the shell-side fluid and are used to support the tubes, prevent vibration, and enhance heat transfer. Baffles create turbulence in the shell-side fluid, which increases heat transfer by decreasing the thickness of the boundary layer and increasing the fluid's overall heat transfer coefficient.

Impact of Baffles on Heat Transfer

Baffles significantly improve heat transfer in a shell-and-tube heat exchanger by creating turbulence in the shell-side fluid. Turbulence disrupts the stagnant boundary layer formed around the tubes, which reduces the thermal resistance of the fluid and enhances heat transfer between the two fluids. Consequently, the presence of baffles enables a higher overall heat transfer coefficient and increased heat transfer efficiency compared to a heat exchanger without baffles.

Impact of Baffles on Pumping Power Requirements

The presence of baffles in a shell-and-tube heat exchanger also affects the pumping power requirements. Due to the pressure drop created by baffles, more pumping power is needed to maintain the desired fluid flow rate through the exchanger. More fluid turbulence results in a higher pressure drop across the baffles, which requires additional pumping power to overcome. However, this increase in pumping power is often justified by the improved heat transfer efficiency provided by the baffles. It should also be noted that optimizing the baffle design can help minimize pressure drop and associated pumping power requirements.