The classification of low fin tubes is mainly based on their structural parameters, manufacturing process, and fin shape and material.
Low Fin Tube Structural Parameters
These include fin height, spacing, thickness, and finning ratio (the ratio of the total surface area of the finned tube to the surface area of the base tube). The finning ratio is usually 2-3, which directly affects the extent of heat transfer area expansion; fin efficiency decreases with increasing fin height, while fin spacing needs to be optimized according to fluid characteristics (such as liquid surface tension). Excessive spacing will weaken the heat transfer effect.
The structural parameters of low fin tubes mainly include fin height, spacing, thickness, and finning ratio. These parameters directly affect their heat transfer performance and applicable scenarios.
1. Fin Height
Fin height is the vertical distance that the fin extends from the surface of the base tube. Increasing the fin height expands the heat transfer area, but also leads to a decrease in fin efficiency (because the temperature gradually decreases as heat is transferred along the fin height direction). The choice of fin height needs to balance the heat transfer effect and pressure drop according to specific application requirements.
2. Fin Spacing
Fin spacing is the distance between adjacent fins. Fin spacing has a significant impact on heat transfer performance and pressure drop:
Heat transfer performance: When the fin spacing is within 1-2 mm, the heat transfer performance increases with increasing spacing; beyond 2 mm, the heat transfer performance decreases with increasing spacing.
Pressure drop: As the fin spacing increases, the pressure drop also increases. Therefore, the fin spacing needs to be optimized according to fluid characteristics (such as flow rate and viscosity) to balance the heat transfer effect and pressure drop.
3. Fin Thickness
Fin thickness is the dimension of the fin perpendicular to the fin height. Fin thickness has a relatively small impact on heat transfer performance and pressure drop, but overly thin fins may lead to insufficient mechanical strength, while overly thick fins may increase material costs and weight. The choice of fin thickness needs to consider heat transfer performance, mechanical strength, and cost.
4. Fin Ratio
The fin ratio is the ratio of the total surface area of the finned tube to the surface area of the base tube. It is an important parameter for measuring the enhanced heat transfer effect of finned tubes. A larger fin ratio indicates a greater increase in the heat transfer area of the finned tube, and consequently, enhanced heat transfer performance. The fin ratio of low-finned tubes is typically 2-3.
5. Fin Efficiency
Fin efficiency is the ratio of the actual heat transfer of the fin to the ideal heat transfer. Fin efficiency decreases with increasing fin height because the temperature gradually decreases as heat is transferred along the fin height direction, leading to a decrease in the heat transfer per unit area of the fin. Optimizing fin efficiency requires considering parameters such as fin height, spacing, and thickness.
6. Influence of Structural Parameters on Heat Transfer Performance
The heat transfer performance of low-finned tubes is affected by fin spacing, fin height, and fin thickness, with fin spacing having the most significant impact. When the fin spacing is between 1 and 2 mm, the heat transfer performance increases with increasing spacing; beyond 2 mm, the heat transfer performance decreases with increasing spacing. Increasing the fin height expands the heat transfer area, but also leads to a decrease in fin efficiency. The influence of fin thickness on heat transfer performance is relatively small, but mechanical strength and cost need to be considered.
7. Parameter Selection in Practical Applications
In practical applications, the structural parameters of low-finned tubes need to be optimized according to specific operating conditions (such as fluid type, flow rate, temperature, etc.). For example, in applications such as boilers, greenhouses, metallurgy, and chemical industries, the selection of fin spacing, fin height, and fin thickness needs to consider heat transfer effect, pressure drop, and cost. In waste heat recovery in the power, metallurgical, and cement industries, as well as in the petrochemical industry, the structural parameters of finned tubes need to be optimized based on flue gas volume, temperature range, etc.
Low Fin Tube Processing Technology
The main method is the three-roll oblique rolling method, which forms the fins on the outer surface of the plain tube through mechanical rolling, creating an integral structure to avoid contact thermal resistance;
Mandrel insertion: A mandrel is inserted into the plain tube to act as a forming support.
Spiral motion: The tube material moves in a spiral linear motion driven by the rolling mill blades, and the fins are gradually processed through the die formed by the rolling mill groove and the mandrel.
Three-stage forming:
Biting: The metal undergoes initial deformation, forming the fin prototype.
Rolling: The metal flows radially and axially, and the fins gradually take shape.
Shaping: The fins are complete, smooth, and regular, ensuring heat transfer efficiency.
Process advantages:
Integral structure: The base tube and outer fins are an organic whole, without contact thermal resistance loss and electrochemical corrosion problems.
High heat transfer efficiency: The fins increase the outer surface area, achieving higher heat exchange efficiency with the same material consumption.
Strong deformation resistance: The integral structure enhances mechanical strength.
Low Fin Tube Fin Shapes
Regarding fin shapes, common types include spiral fin tubes and longitudinal fin tubes. Spiral fin tubes are made by continuously winding and welding or hot-dip galvanizing steel strips, while longitudinal fin tubes are formed by integral rolling or welding.
Structural Features: The steel strip is spirally wound and welded, forming a continuous “ribbed” structure. The fin height and pitch are adjustable.
Performance Advantages:
Heat transfer area is increased by 3-8 times, and the heat transfer coefficient is 20%-40% higher than traditional fin tubes.
The spiral structure reduces fluid resistance, lowers energy consumption, and is suitable for confined spaces.
Typical Applications: Air preheaters in power plant boilers, high-temperature heat exchange in chemical reactors.
Low Fin Tube Materials
In terms of materials, low fin tubes can be made of stainless steel 304/316, carbon steel, duplex stainless steel 2205, or titanium tubes to suit different corrosive environments. The choice of material affects corrosion resistance, thermal conductivity, and mechanical strength.
1. Stainless Steel 304/316 Low Fin Tubes
Features: Strong corrosion resistance, suitable for corrosive environments such as chemical plants and power plants.
Applications: 304 stainless steel is less expensive, while 316 stainless steel has stronger resistance to chloride ion corrosion.
2. Carbon Steel Low Fin Tubes
Features: Good thermal conductivity and high mechanical strength, but prone to corrosion.
Applications: Commonly used in non-corrosive environments such as industrial drying rooms and greenhouses.
3. Duplex Stainless Steel 2205 Low Fin Tubes
Features: Combines the advantages of austenitic and ferritic steel, with high corrosion resistance and mechanical strength.
Applications: Suitable for high-temperature and high-pressure chemical and petroleum industries.
4. Titanium Tube Low Fin Tubes
Features: Extremely strong corrosion resistance and good thermal conductivity, but higher cost.
Applications: Suitable for extreme corrosive environments such as seawater desalination and chemical industries.
5. Other Materials for Low Fin Tubes
Copper tubes: Excellent thermal conductivity, commonly used in air conditioning condensers and evaporators.
Aluminum alloy tubes: Lightweight, good thermal conductivity, but lower mechanical strength.
6. Material Selection Suggestions
Corrosive environment: Prioritize stainless steel 316, duplex stainless steel 2205, or titanium tubes.
Non-corrosive environment: Carbon steel or copper tubes are economical and efficient choices.
Cost considerations: Titanium tubes are more expensive, while carbon steel is the least expensive.