What is the heat transfer efficiency of a tubular heat exchanger
The overall heat transfer efficiency of tubular heat exchangers is at a medium to high level, and the efficiency of different types of tubular heat exchangers varies greatly. Their efficiency performance depends on structural design, heat transfer medium characteristics, and operating conditions. The specific analysis is as follows:
The overall heat transfer efficiency of tubular heat exchangers is at a medium to high level, and the efficiency of different types of tubular heat exchangers varies greatly. Their efficiency performance depends on structural design, heat transfer medium characteristics, and operating conditions. The specific analysis is as follows:
1. Core influencing factor: Structure type determines basic efficiency
Tube and tube heat exchangers are mainly divided into three categories: shell and tube, jacket and tube, and spiral tube. The efficiency is ranked in descending order: spiral tube>jacket and tube>conventional shell and tube.
Spiral tube heat exchanger: The heat transfer tube is wound in a spiral shape, and the medium flows in turbulent flow inside the tube. The degree of turbulence is high, which can effectively destroy the thermal resistance of the tube wall boundary layer. The heat transfer coefficient can reach 1000-3000 W/(㎡·℃), and the efficiency is high. Meanwhile, the spiral structure has a compact heat transfer area, making it suitable for heat transfer in small spaces and high viscosity media such as heavy oil and syrup.
Sleeve type heat exchanger: adopting a concentric structure of "tube sleeve", two media flow in opposite directions inside the tube and the annular gap, and the temperature difference driving force of reverse flow heat transfer is large. The heat transfer coefficient is about 800-2000 W/(㎡·℃), and the efficiency is better than conventional shell and tube type. It is suitable for small and medium flow, high temperature and high pressure conditions (such as steam condensation and heat transfer oil heating).
Conventional shell and tube heat exchanger: The structure consists of multiple straight tubes arranged inside the shell, and the media on both the tube and shell sides are often cross or folded. The turbulence level is lower than that of spiral tubes, and the heat transfer coefficient is about 500-1500 W/(㎡·℃). But the turbulence level of the shell side medium can be improved by installing baffles (such as bow shaped baffles), thereby enhancing heat transfer efficiency.
2. The impact of operating conditions on efficiency
Medium flow state: The heat transfer efficiency of turbulent flow is much higher than that of laminar flow. When the flow velocity of the medium increases, the degree of turbulence increases, the thermal resistance of the boundary layer decreases, and the heat transfer efficiency significantly improves; On the contrary, low flow rate and high viscosity media are prone to form laminar flow, resulting in a decrease in efficiency.
Heat exchange temperature difference: Adopting a tube heat exchanger with counter current heat exchange, the average logarithmic temperature difference is larger, the heat transfer is more complete, and the efficiency is 10% -30% higher than that of co current heat exchange.
Scaling situation: If the tube wall of a tubular heat exchanger is attached with scale, oil, and other dirt, additional thermal resistance will be formed, leading to a decrease in heat transfer efficiency. For example, cooling water with harder water quality is prone to scaling, and the heat transfer efficiency may decrease by 20% -40% after long-term operation. Smooth stainless steel or titanium alloy pipe walls, as well as regular cleaning (such as chemical cleaning, mechanical cleaning), can alleviate the impact of scaling.
3. Efficiency comparison with other heat exchangers
Compared to plate heat exchangers (with a heat transfer coefficient of 2000-6000 W/(㎡·℃)), tube heat exchangers have slightly lower efficiency, but they are superior in high temperature resistance, high pressure resistance, and corrosion resistance. They are suitable for heat transfer scenarios in corrosive media (such as strong acids and alkalis) or particulate media (such as slurry and sewage); Compared to immersive serpentine heat exchangers, tubular heat exchangers have higher medium flow rates, 3-5 times higher efficiency, and a more compact structure.
4. Common methods to improve heat transfer efficiency
Strengthening treatment of heat exchange tubes: such as using threaded tubes and finned tubes to increase the heat exchange area while enhancing turbulence effects;
Optimize the shell structure: Install baffles and guide vanes to avoid dead zones in the shell medium;
Control the flow rate of the medium: keep the medium on the tube side and shell side in a turbulent state (Reynolds number Re>4000);
Regular maintenance and cleaning: remove dirt from the pipe wall and restore heat transfer performance.
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