Shandong Zhilin Environmental Protection Technology Co., Ltd.

What kind of heat exchanger is a finned tube heat exchanger, and what is its working principle?

Release time:

2021-04-26 15:33

Source:

Finned tube heat exchangers are mainly used for air heating in drying systems and are the main equipment in hot air devices.

Finned tube heat exchangers are mainly used for air heating in drying systems and are the main equipment in hot air devices. The heat transfer medium used in the radiator can be steam or hot water, or it can also be thermal oil. The working pressure of steam generally does not exceed 0.8 MPa, and the temperature of hot air is below 170 ℃. It is the most widely used heat exchange equipment in gas-liquid heat exchangers. Finned tube heat exchangers are usually composed of partitions, fins, seals, and baffles. They achieve the purpose of enhanced heat transfer by adding fins to ordinary base tubes. The base tubes can be steel pipes; stainless steel pipes; copper pipes, etc. The fins can also be steel strips; stainless steel strips, copper strips, aluminum strips, etc.

Fins, baffles, and seals are placed between adjacent partitions to form a layer, which is called a channel. Such layers are stacked according to different fluid flow methods and brazed into a whole to form a plate bundle. The plate bundle is the core of the finned tube heat exchanger. With necessary end caps, nozzles, supports, etc., the finned tube heat exchanger is formed. The finned tube heat exchanger is mainly composed of three rows of parallel spiral finned tube bundles in the air flow direction. Because the finned heat exchanger uses mechanical winding, the contact area between the heat dissipation fins and the heat dissipation tubes is large and tight, the heat transfer performance is good and stable, the air resistance is small, and steam or hot water flows through the steel pipe. Heat is transferred from the tightly wound fins on the steel pipe to the air passing through the fins, achieving the effect of heating and cooling the air.

Working principle of finned tube heat exchanger

From the perspective of heat transfer mechanism, the finned tube heat exchanger still belongs to the shoulder-arm heat exchanger. Its main characteristic is that it has an extended secondary heat transfer surface (fin), so the heat transfer process is not only carried out on the primary heat transfer surface (partition), but also on the secondary heat transfer surface at the same time. The heat of the high-temperature medium is not only transferred to the low-temperature medium from the primary surface, but also partially transferred along the height direction of the fin surface, that is, along the height direction of the fin, heat is transferred from the partition, and then these heat is transferred to the low-temperature medium by convection.

Because the fin height is much larger than the fin thickness, the heat conduction process along the fin height direction is similar to the heat conduction of a homogeneous slender rod. At this time, the thermal resistance of the fin cannot be ignored. The temperature at both ends of the fin is the highest and equal to the partition temperature. As the fin and the medium convectively dissipate heat, the temperature continuously decreases until the medium temperature in the middle region of the fin. When the outside medium of the pipe is heated, a series of bubble nuclei will form in the tunnel. When the bubble nuclei are heated around the tunnel cavity, they rapidly expand and fill the cavity. Due to continuous heating, the pressure inside the bubbles increases rapidly, causing the bubbles to be ejected from the thin gap on the pipe surface. The bubbles are ejected with a great scouring force, creating a local negative pressure, which causes the surrounding low-temperature liquid to flow into the T-shaped tunnel, forming continuous boiling. This boiling method removes more heat per unit surface area per unit time than a bare tube, so this type of tube has a higher boiling heat transfer capacity.

Characteristics of finned-tube heat exchangers

Characteristics and features of plate heat exchangers