Air Fin Cooler | Air Cooled Heat Exchanger

Air fin cooler is referred to as air cooler or air cooled heat exchanger . It uses air as coolant and can be used as a cooler or a condenser. Air cooler is mainly composed of tube bundle, bracket and fan.

Air Fin Cooler Ventilation Method

Ventilation has two methods: forced draft and induced draft.

① Forced draft: air flows through the fan first and then flows into the tube bundle.

② Induced draft: air flows through the tube bundle first and then flows into the fan.

The former has a more economical operation cost and the turbulence generated is beneficial to heat transfer, so it is used more. The latter has uniform air flow distribution, which is conducive to precise temperature control and low noise, and is the direction of development. The outlet temperature of the hot fluid is mainly controlled by adjusting the air volume passing through the tube bundle, that is, adjusting the inclination angle of the blades, the speed of the fan and the opening degree of the shutters. For fluids that are easy to condense and freeze in winter, the outlet temperature of the fluid can be adjusted by hot air circulation or steam heating.

The hot fluid of the air cooler flows in the tube, and the air blows outside the tube bundle. Since the ventilation volume required for heat exchange is large, but the wind pressure is not high, axial flow fans are mostly used (see fluid conveying machinery). The type and material of the tube bundle have a great influence on the performance of the air cooler. Since the heat transfer coefficient on the air side is very small, fins are often added to the outside of the tube to increase the heat transfer area and fluid turbulence and reduce thermal resistance.

Most air coolers use radial fins. Air coolers usually use light tubes with an outer diameter of 25mm, low-fin tubes with a fin height of 12.5mm, and high-fin tubes with a fin height of 16mm. The fins are generally made of materials with high thermal conductivity (most commonly aluminum) and are wrapped or embedded on the light tubes. In order to enhance the heat transfer effect of the air cooler, water can be sprayed in the inlet air to increase humidity. This not only reduces the air temperature, but also increases the heat transfer coefficient.

The use of air coolers can save a lot of industrial water, reduce environmental pollution, and reduce infrastructure costs. Especially in water-scarce areas, replacing water cooling with air cooling can ease the contradiction of insufficient water sources.

High-quality air coolers are mainly composed of three parts: tube bundles, fans and frames (Figure 1). The tube bundle includes heat transfer tubes, tube boxes, side beams and cross beams. It can be arranged in three basic forms: horizontal, vertical and inclined top (herringbone).

Among them, the horizontal arrangement has a large heat transfer area, uniform air distribution and good heat transfer effect; when the inclined top is arranged, the fan is installed in the central space of the herringbone, which occupies a small area and has a compact structure. In order to offset the low heat transfer coefficient on the air side, tubes with fins on the outer wall of the bare tube are usually used.

Finned tubes are used as heat transfer tubes to expand the heat transfer area. The finned tubes are arranged in layers, and their two ends are connected to the tube box by welding or expansion. The row of tubes is generally 3 to 8 rows. The tube bundle series size is up to 12 meters. The outer diameter of the bare tube is usually 25 mm and 38 mm, the fin height is generally 12 to 15 mm, and the tube bundle width is 100 to 3000 mm.

Finned tubes are the core components of air coolers, and their form and material directly affect the performance of the equipment. The tubes can be made of carbon steel, copper, aluminum and stainless steel; the fin material is determined according to the use environment and manufacturing process. Most of them use industrial pure aluminum. Copper or stainless steel is also used when the corrosion resistance requirements are very high or the manufacturing process conditions are special. The fins can be arranged horizontally or vertically.

The basic forms of finned tubes are: winding type, inlay type, rolled type, sleeve type, welded type, elliptical tube type, turbulent type (including spoke type, slotted type and corrugated type, etc.). The structure of the tube box mainly includes flange type, pipe plug type and manifold type. Generally, the former is used for medium and low pressure, and the latter two are used for high pressure. In order to adapt to the thermal expansion of the tube bundle, the tube box at one end is not fixed, and displacement along the length of the tube is allowed. The fan usually uses an axial flow fan.