Shell and Tube Heat Exchangers

Elite’s manufactured shell and tube heat exchangers for a wide range of applications. Our heat exchangers are used in a variety of industries including petroleum, utility, paper, chemical, rendering and metals. Applications are as diverse and demanding as the oil fields of Alaska, off-shore platforms from the Gulf of Mexico to the South China Sea, refineries in Canada and fermentation plants in Mexico. Kennedy heat exchangers are operating in applications as exotic as dual condenser / reboilers for uranium fuel enrichment processes and as common as product coolers and glycol to glycol exchangers.

Basic Structure:

1. Shell: The outer cylindrical casing that houses the tube bundle. The shell typically contains one of the fluids (either the hot or cold fluid).
2. Tube Bundle: A collection of tubes that are placed inside the shell. One fluid flows inside the tubes, while the other fluid flows over the tube surface within the shell.
3. Tubes: The tubes allow one fluid (either the hot or cold fluid) to pass through them while the other fluid flows over the outside of the tubes in the shell. The fluids can flow in various configurations, such as parallel, countercurrent, or cross-flow.
4. Baffles: These are placed inside the shell to direct the flow of the fluid, increasing the heat transfer efficiency by forcing the shell-side fluid to flow across the tube bundle in a controlled manner.
5. Heads: The end components of the heat exchanger that contain the tube sheet, where the tubes are fixed, and allow the fluid to enter and exit.
6. Nozzles: The inlet and outlet connections on both the shell and the tube side for the fluids.

Working Principle:

The basic principle of a shell and tube heat exchanger is heat transfer through the tube walls between two fluids of different temperatures. Here’s how it works:

• One fluid flows through the tubes, while the other fluid flows over the tubes inside the shell.
• Heat is transferred from the hot fluid to the cold fluid through the tube walls via conduction.
• The heat transfer efficiency depends on the fluid temperatures, flow configuration (counterflow, parallel flow, or crossflow), material of the tubes, and flow rates of the fluids.

Types of Shell and Tube Heat Exchangers:

1. Single-Pass Heat Exchanger: The fluid flows through the tubes only once.
2. Multi-Pass Heat Exchanger: The fluid is passed through the tubes multiple times to increase the heat transfer by lengthening the flow path.
3. Fixed Tube Sheet Heat Exchanger: The tube sheets are fixed and the tubes are secured at both ends. This type is simpler but may be harder to clean or maintain.
4. U-Tube Heat Exchanger: The tubes are bent in a U-shape, allowing for thermal expansion, making this type ideal for high-temperature applications.
5. Floating Head Heat Exchanger: The tube bundle is not fixed at one end, allowing for thermal expansion and easier cleaning.
6. Plate-Fin Heat Exchanger: A variant where plates or fins are used to increase the surface area for heat transfer, often found in compact designs.

Flow Configurations:

1. Counter flow: The two fluids flow in opposite directions. This configuration is the most efficient in terms of heat transfer, as it maintains the highest temperature difference along the length of the heat exchanger.
2. Parallel Flow: The fluids flow in the same direction. This is less efficient than counterflow because the temperature difference between the fluids decreases as they flow.
3. Crossflow: One fluid flows parallel to the tubes while the other flows perpendicular to the tubes. This is common in applications where space is limited.

Heat Transfer and Pressure Drop:

• The heat transfer rate depends on factors like the temperature difference between the fluids, flow rates, fluid properties (e.g., viscosity, thermal conductivity), and the geometry of the heat exchanger.
• The pressure drop (the difference in pressure between the inlet and outlet of the fluids) is a critical design parameter. Too high a pressure drop can result in excessive pumping power requirements.

Applications:

Shell and tube heat exchangers are used in a wide range of industries due to their versatility and reliability:

• Power Plants: For cooling systems and heat recovery.
• Chemical and Petrochemical: Used in distillation, condensation, and cooling processes.
• Oil Refineries: In the heat exchange of crude oil, gas, and water.
• HVAC Systems: For heating and cooling buildings.
• Food Processing: To cool or heat liquids such as milk or fruit juices.

Advantages:

• High heat transfer efficiency, especially in counter flow arrangements.
• Compact design with the ability to handle large temperature differences.
• Versatility in handling a wide range of fluids and operating conditions.
• Scalability to accommodate high flow rates.
• Easy maintenance due to removable tube bundles (in many configurations).

Disadvantages:

• Higher initial cost compared to simpler heat exchangers.
• Potential for fouling: Over time, fluids can deposit solids inside the tubes, reducing heat transfer efficiency and requiring regular cleaning.
• Pressure drop: The design must balance the heat transfer efficiency and the pressure drop.