ANS:B - Double pipe

A double pipe heat exchanger, also known as a tube-in-tube heat exchanger, is a simple and commonly used type of heat exchanger. It consists of two concentric pipes: an inner tube through which one fluid flows and an outer tube through which the other fluid flows. Here's how a double pipe heat exchanger works:

1. Flow Configuration: The two fluids flow in a counter-current or parallel flow configuration. In counter-current flow, the fluids flow in opposite directions, while in parallel flow, they flow in the same direction.
2. Heat Transfer: Heat transfer occurs between the fluids through the walls of the inner tube. One fluid gains heat while the other fluid loses heat, depending on the temperature difference between them.
3. Construction: The inner tube typically has a smaller diameter compared to the outer tube, allowing for a compact design. The tubes are often coiled or arranged in a helical pattern to increase the surface area available for heat transfer.
4. Applications: Double pipe heat exchangers are commonly used in various industrial applications where moderate heat transfer rates are sufficient. They are suitable for low to moderate pressure and temperature conditions and are often used in HVAC systems, refrigeration, chemical processing, and food processing industries.
5. Advantages: Double pipe heat exchangers are simple in design, easy to clean, and cost-effective to manufacture. They are also versatile and can handle a wide range of fluids and operating conditions.
6. Limitations: Despite their simplicity and versatility, double pipe heat exchangers may have limitations in terms of heat transfer efficiency compared to more complex heat exchanger designs such as shell and tube or plate heat exchangers. They may also have higher pressure drop characteristics due to their compact size.