Shell & Tube Heat Exchanger
A shell and tube heat exchanger (also known as a tube and shell heat exchanger) uses the walls of a tube bundle enclosed in a shell as the heat transfer surface. This type of heat exchanger has a simple structure, low cost, a wide flow cross-section, and is easy to clean against scale; however, it has a low heat transfer coefficient and occupies a large footprint. It can be manufactured from a variety of structural materials (primarily metal) and can operate under high temperatures and high pressures, making it the most widely used type.
Shell and tube heat exchangers include fixed tube sheet steam-water heat exchangers, shell and tube steam-water heat exchangers with expansion joints, floating head steam-water heat exchangers, U-shaped shell and tube steam-water heat exchangers, corrugated shell and tube steam-water heat exchangers, and segmented water-water heat exchangers. The main control parameters of shell and tube heat exchangers include heating area, hot water flow rate, heat transfer capacity, and heat medium parameters.
Shell-and-Tube Heat Exchanger Structure
A shell-and-tube heat exchanger consists of a shell, heat transfer tube bundle, tube sheet, baffles (baffles), and tube box. The shell is typically cylindrical, housing the tube bundle, which is fixed to the tube sheet at both ends. The hot and cold fluids involved in the heat exchange flow: one inside the tubes, known as the tube-side fluid; the other outside, known as the shell-side fluid.
To improve the heat transfer coefficient of the fluid outside the tubes, baffles are typically installed within the shell. These baffles increase the velocity of the shell-side fluid, forcing the fluid to pass through the tube bundle multiple times along a prescribed path, thereby increasing fluid turbulence. The heat exchange tubes can be arranged on the tube sheet in an equilateral triangle or square configuration. The equilateral triangle arrangement is more compact, resulting in higher turbulence and a higher heat transfer coefficient. The square arrangement facilitates cleaning of the tubes and is suitable for fluids prone to scaling.
Classification of Shell-and-Tube Heat Exchangers
Because the temperatures of the fluids inside and outside the tubes are different, the temperatures of the shell and tube bundle in a shell-and-tube heat exchanger also differ. If the temperature difference between the two is large, significant thermal stress will be generated within the heat exchanger, causing tubes to bend, break, or pull away from the tubesheet. Therefore, when the temperature difference between the tube bundle and the shell exceeds 50°C, appropriate compensation measures must be implemented to eliminate or reduce thermal stress. Shell-and-tube heat exchangers can be divided into the following main types based on the compensation measures used:
① Fixed-tube-sheet heat exchangers have the tubesheets at both ends of the tube bundle integrally connected to the shell. This simple structure is only suitable for heat exchange operations where the temperature difference between the cold and hot fluids is small and mechanical cleaning of the shell side is not required. When the temperature difference is slightly larger and the shell-side pressure is not too high, elastic compensation rings can be installed on the shell to reduce thermal stress.
② Floating-head heat exchangers have a tubesheet at one end of the tube bundle that floats freely, completely eliminating thermal stress. The entire tube bundle can also be withdrawn from the shell, facilitating mechanical cleaning and maintenance. Floating-head heat exchangers are widely used, but their structure is more complex and their cost is higher.
③ U-tube heat exchanger: Each heat exchange tube is bent into a U-shape, with its ends fixed to the upper and lower sections of a single tube sheet. A baffle within the tube box divides the tube into two chambers: the inlet and outlet. This type of heat exchanger completely eliminates thermal stress and is simpler in structure than a floating-head type, but the tubes are less easily cleaned.
④ Vortex heat film heat exchanger: Vortex heat film heat exchangers utilize the latest vortex heat film heat transfer technology, enhancing heat transfer efficiency by altering the fluid’s motion. As the medium passes through the vortex tube, it vigorously flushes the tube surface, improving heat transfer efficiency. Efficiency can reach up to 10,000 W/m²°C. This structure also offers corrosion resistance, high temperature resistance, high pressure resistance, and anti-scaling properties. Other types of heat exchangers use fixed-direction flow, creating vortex flow around the tube surface, reducing the convective heat transfer coefficient.
Performance comparison of various heat exchanger types:
| Item | Floating Coil Heat Exchanger | Threaded Tube Heat Exchanger | Vortex Heat Film Heat Exchanger |
|---|---|---|---|
| Applicable Media Types | Steam, Water | Steam, Water | Weakly corrosive chemical materials, Steam, Water |
| Media Parameter Range | Temperature: 0-150°C Pressure: 0-1.0 MPa |
Temperature: 0-150°C Pressure: 0-1.6 MPa |
Temperature: -40-400°C Pressure: 0-10.0 MPa |
| Heat Efficiency | 92% | 93% | 96% |
| Anti-fouling Performance | Automatic descaling2 | Manual descaling | Fouling-resistant function |
| Vibration Resistance & Noise | Severe vibration, Loud noise | Minor vibration, Low noise | Minimal vibration, Low noise |
| Service Life | About 10 years2 | About 10 years | About 20 years |
| Maintenance | Shutdown required, Tube bundle replacement | Shutdown required, Tube pulling and re-expansion | Maintenance-free |
Features of Shell and Tube Heat Exchangers
1. Highly efficient and energy-efficient, this heat exchanger has a heat transfer coefficient of 6000-8000 W/m².0°C.
2. Made entirely of stainless steel, it offers a long service life of over 20 years.
3. Shifts from laminar flow to turbulent flow, improving heat transfer efficiency and reducing thermal resistance.
4. High heat transfer speed, high temperature resistance (400°C) and high pressure resistance (2.5 MPa).
5. Compact structure, small footprint, lightweight, easy installation, and reduced construction investment.
6. Flexible design, comprehensive specifications, and practical, targeted solutions save money.
7. Widely applicable, suitable for a wide range of pressures and temperatures, and for heat exchange with a variety of media.
8. Low maintenance, easy operation, long cleaning cycles, and easy cleaning.
9. Utilizes nano-thermal film technology, significantly increasing the heat transfer coefficient.
10. Broad application areas, including thermal power, factories and mines, petrochemicals, urban centralized heating, food and pharmaceuticals, energy electronics, and machinery and light industry.
11. The heat transfer tubes utilize copper tubes with rolled fins on the outer surface, offering high thermal conductivity and a large heat transfer area.
12. The guide plates guide the shell-side fluid in a continuous, zigzag flow pattern within the heat exchanger. The guide plate spacing can be adjusted to optimize the flow rate. The robust structure accommodates high and even ultra-high flow rates and high pulsation rates.
13. When the shell-side fluid is oil, it is suitable for heat transfer with low-viscosity and relatively clean oils.