What are Elliptical Finned Tubes?
Elliptical finned tubes are heat exchange elements consisting of an elliptical base tube and external fins. Common types include elliptical rectangular finned tubes, elliptical elliptical finned tubes, elliptical circular finned tubes, spiral elliptical flat tubes, and elliptical H-shaped finned tubes.
Owing to their superior performance compared to circular finned tubes, elliptical finned tubes are gaining popularity and are widely used in industries such as ethylene and oil refining.
Elliptical finned tubes are used in heat exchange equipment as high-efficiency heat exchange elements. Their low external flow resistance and high heat transfer efficiency make heat exchange equipment more compact, lightweight, efficient, and miniaturized.
Introduction to Elliptical Finned Tubes
Heat exchange equipment is becoming increasingly compact, lightweight, efficient, and miniaturized, but conventional heat exchangers cannot meet these requirements. This has prompted research into high-efficiency heat exchangers. Consequently, fin-and-tube heat exchangers have gained widespread application as a high-efficiency heat exchanger.
Fin-and-tube heat exchangers are widely used in industrial fields such as refrigeration and air conditioning. The core component is the tube bundle within the heat exchanger. Adding fins to the base tube surface is a very effective way to enhance heat transfer performance. Compared to plain tubes, finned tubes offer advantages such as compact structure, flexible material selection (the base tube and fin materials can be different), and high heat transfer efficiency.
Types of Finned Tubes
Depending on the fin installation position, finned tubes are divided into internally finned tubes and externally finned tubes, with externally finned tubes being the most commonly used.
Depending on the fin arrangement, finned tubes are divided into longitudinally finned tubes and transversely finned tubes.
Depending on the base tube shape, finned tubes can be divided into circular finned tubes, elliptical finned tubes, and flat finned tubes.
Circular finned tube heat exchangers play a leading role in the heat exchange industry. Compared with circular finned tubes, the back-flow area and windward area of elliptical tubes are much smaller, which effectively reduces the flow resistance on the air side and reduces energy consumption. When the number of tube bundles is the same, elliptical tubes and flat tubes are more compact than circular tubes, and the volume of the heat exchanger is smaller, which reduces the cost. Therefore, elliptical tube fin heat exchangers are also widely used in many places.
Characteristics of elliptical finned tubes
(1) Compared with circular finned tubes, elliptical finned tubes are easier to achieve compact arrangement, which reduces the overall volume of the heat exchanger and thus reduces the floor space.
(2) Due to the shape characteristics of elliptical finned tubes, the air side resistance is small and the heat transfer coefficient between fluids is increased; the thermal resistance inside the tube is relatively small, which increases the heat transfer of the fluid inside the tube.
(3) The heat transfer area of elliptical finned tubes is larger than that of circular tubes with the same cross-sectional area. This is because the heat transfer perimeter of elliptical tubes is longer under the same cross-sectional area.
(4) The most commonly used elliptical finned tubes are rectangular steel fins, which have high strength, are not prone to freezing and cracking in winter, and have a long service life.
(5) Since elliptical finned tubes can be arranged more compactly, the front row of tubes has a greater impact on the rear row. The outer flow resistance of the tube can be reduced by increasing the fin spacing of the rear row of tubes, but the number of tube rows should not be too large.
Elliptical finned tubes
The heat release and resistance performance of the elliptical rectangular finned tube bundle are determined. The optimal transverse tube spacing and longitudinal tube spacing of the elliptical rectangular finned tube bundle under the minimum volume and minimum frontal area standards are determined.
The effect of the elliptical tube fin spacing with different elliptical major and minor axis ratios (a/b) on heat release is studied, and the heat release of the rectangular finned elliptical tube with four turbulent holes in the cross-flow gas is studied. Testing of the heat transfer and flow resistance characteristics of three elliptical finned tube air coolers and one circular finned tube air cooler revealed that, at equal windward flow velocities, the air-side heat transfer coefficient of the elliptical finned tubes was approximately 3 to 7 times greater than that of the circular finned tubes. At equal heat transfer coefficients, the elliptical finned tubes also exhibited a lower pressure drop than the circular finned tubes. Furthermore, the elliptical finned tube heat exchanger required less induced draft fan energy and heat transfer surface area.
Tests of the heat transfer and flow resistance characteristics of a rolled elliptical aluminum-fin steel tube heat exchanger revealed that the pressure drop gradually increased with increasing wind speed on the finned tube side, while increasing the number of tube rows weakened the finned tube’s heat transfer. Manufactured using a unique process, rolled elliptical aluminum-fin steel tubes exhibit excellent heat transfer and flow resistance performance, as well as sufficient structural strength, and therefore have broad application prospects.
The heat transfer and resistance performance of finned tube radiators with unequal fin spacing in a staggered tube arrangement were tested. A steel tube and steel fin elliptical tube radiator was used. The heat exchanger has two rows of tubes. The second row’s fin spacing is larger than the first row’s. This arrangement reduces air resistance outside the second row’s tubes and increases heat transfer.
Calculation Method for Elliptical Finned Tube Fin Efficiency
Elliptical finned tubes consist of an elliptical base tube and external fins. Common types include elliptical rectangular finned tubes, elliptical elliptical finned tubes, elliptical circular finned tubes, spiral elliptical flat tubes, and elliptical H-shaped finned tubes. Elliptical finned tubes are gaining popularity due to their superior performance compared to circular finned tubes and are widely used in industries such as ethylene and oil refining.
When calculating the fin efficiency of elliptical tube-finned heat exchangers, elliptical finned tubes are often treated as equivalent to circular finned tubes, and the calculation and analysis are based on these. There are two methods for selecting an equivalent circular tube. One is to make the cross-sectional area of the equivalent circular tube equal to the cross-sectional area of the elliptical tube, and the other is to make the circumference of the equivalent circular tube equal to the circumference of the elliptical tube.
Elliptical finned tubes are used as high-efficiency heat exchange elements in heat exchange equipment. The external flow resistance of the tube is small and the heat transfer efficiency is high, which makes the heat exchange equipment compact, lightweight, efficient and miniaturized.
(1) Elliptical finned tubes have many advantages, but research is relatively scarce.
(2) Fin efficiency plays a key role in heat transfer calculations.
(3) The air side resistance of elliptical finned tubes is relatively small and the heat transfer coefficient is high, but its internal fluid resistance is relatively large and the refrigerant charge is relatively small, which limits the application of elliptical finned tubes in heat exchangers.