Air cooler

Air cooler

Product Overview
Air-cooled heat exchangers, commonly referred to as air coolers, use air as the cooling medium and can serve as both a cooler and a condenser. They are primarily composed of tube bundles, supports, and fans. In air coolers, the hot fluid flows inside the tubes while air blows over the tube bundles externally. Due to the large volume of ventilation required for heat exchange and the relatively low wind pressure, axial flow ventilators are commonly used (see fluid conveyance machinery).
The type and material of the fins greatly affect the performance of air-cooled heat exchangers. Due to the low heat transfer coefficient on the air side, fins are often added to the outside of the tubes to increase the heat transfer area and fluid turbulence, reducing thermal resistance. Air-cooled heat exchangers generally use tubes with an outer diameter of 25mm, low finned tubes with a fin height of 12.5mm, and high finned tubes with a fin height of 16mm. The fins are typically made from materials with high thermal conductivity (commonly aluminum) and are wrapped or embedded onto the tubes. To enhance the heat transfer efficiency of the air-cooled heat exchanger, water can be sprayed into the inlet air to increase humidity. This not only lowers the air temperature but also increases the heat transfer coefficient. Using air-cooled heat exchangers can save a significant amount of industrial water, reduce environmental pollution, and lower construction costs. Especially in water-scarce areas, replacing water-cooling with air-cooling can alleviate the contradiction of insufficient water resources.

Air-cooling unit structure
The air cooler is primarily composed of three parts: tube bundles, a fan, and a framework. The tube bundles include heat transfer tubes, tube boxes, side beams, and crossbeams. It can be arranged in three basic forms: horizontal, vertical, and slanting roof (chevron). The horizontal arrangement offers a large heat transfer area with even air distribution and good heat transfer performance. In the slanting roof setup, the fan is installed in the central chevron space, occupying less area and having a compact structure. To counteract the lower heat transfer coefficient on the air side, tubes with fins mounted on the outer surface of the smooth tube are typically used. Fins tubes, as heat transfer tubes, can expand the heat transfer area. Fins tubes are arranged in layers and connected at both ends to the tube box using welding or胀接 methods. The number of rows for the tube arrangement usually ranges from 3 to 8. The tube bundle series can extend up to 12 meters in length. The outer diameter of the smooth tubes is commonly 25mm and 38mm, with the fin height generally between 12 to 15mm, and the tube bundle width ranging from 100 to 3000mm. Fins tubes are the core component of the air cooler, and their form and material directly affect the equipment's performance. The tubes can be made from carbon steel, copper, aluminum, and stainless steel; the fin material is determined by the application environment and manufacturing process, usually industrial pure aluminum, but copper or stainless steel may also be used in high corrosion resistance requirements or special manufacturing conditions. Fins can be arranged horizontally or vertically. The basic forms of fins tubes include: coiled, inserted, rolled, sleeve, welded, elliptical tube, and turbulent (including radial, grooved, and wavy shapes). The tube box structure mainly includes flanged, plug, and manifold types. The flanged type is generally used for medium and low pressure, while the latter two are for high pressure. To accommodate the thermal expansion of the tube bundles, one end of the tube box is not fixed, allowing displacement along the tube length. The fan usually employs an axial flow fan.

Ventilation Method
Ventilation is available in two methods: blowing and suction. ①Blowing type: Air flows through the fan first before entering the bundle. ②Suction type: Air flows through the bundle first before entering the fan. The former is more economical in operation costs, generates beneficial turbulence for heat transfer, and is more widely used. The latter ensures uniform air flow distribution,有利于accurate temperature control, produces less noise, and represents the direction of development. The outlet temperature of the hot fluid mainly depends on controlling the air volume passing through the bundle, i.e., adjusting the angle of the blades, the fan speed, and the opening degree of the louvers. For fluids that are prone to condensation and freezing in winter, methods such as hot air recirculation or steam heating can be used to regulate the outlet temperature of the fluid.