ANS:B - 0.75 D

In a shell and tube heat exchanger, the height of 25 percent cut baffles is equal to 0.25 D, where D represents the inside diameter of the shell. Explanation:

1. Baffles in Shell and Tube Heat Exchangers: Baffles are internal structures within the shell of a shell and tube heat exchanger that are used to direct the flow of fluid and enhance heat transfer efficiency. They prevent tube vibration and ensure proper fluid distribution across the tube bundle.
2. Cut Baffles: Cut baffles are baffles with a portion removed to allow fluid flow through the shell. The height of the cut baffles is typically specified as a percentage of the shell diameter to achieve specific flow characteristics and turbulence promotion.
3. Height of 25 Percent Cut Baffles: When the baffles are referred to as "25 percent cut," it means that a quarter of the baffle's height is removed or cut. This removal facilitates fluid flow through the shell while still providing the necessary support and turbulence promotion.
4. Relation to Shell Diameter (D): The height of the 25 percent cut baffles is directly related to the inside diameter of the shell (D). Therefore, the height of the 25 percent cut baffles is equal to 0.25 times the diameter of the shell (0.25 D).