Application of Fin Tubes in Condensers

Fin tube is to improve the heat exchange efficiency, usually by adding fins on the surface of the heat exchange tube, increase the outer area (or internal surface area) of the heat exchange tube, so as to achieve the purpose of improving the heat exchange efficiency, such a heat exchange tube. The condenser is a part of the air conditioning system that can transfer the heat in the tube to the air near the tube in a very fast way.

1. Common condenser types and features

Condenser, also known as “liquefier”, is a heat exchanger in which the vapour is liquefied by releasing heat. According to the cooling medium and cooling method. Condenser can be divided into water-cooled, air-cooled, evaporative three types.

(1) Water-cooled condenser

The water-cooled condenser uses water as the cooling medium and relies on the temperature rise of water to take away the condensation heat. Water-cooled condensers are characterised by high heat transfer efficiency and compact structure. At present, due to the shortage of water resources, the cooling water used in water-cooled condensers is generally recycled, and its main disadvantage is the need to set up a special cooling water recycling system, the initial investment is high, and the cost of water treatment is large. Commonly used water-cooled condenser has horizontal shell and tube, vertical shell and tube and casing type.

In large and medium-sized air-conditioning and refrigeration units and industrial refrigeration are generally water-cooled condensers, which are most commonly used in shell-and-tube condensers. In the shell and tube condenser, the refrigerant is usually condensed outside the tube, the water flows in the tube. Currently used shell and tube condenser with light tube bundle and rolling low finned tube (i.e. spiral tube) two kinds. Generally, horizontal shell-and-tube condensers for ammonia tend to use light tube bundles, and Freon condensers tend to use rolled low-fin tubes.

(2) Air-cooled condenser

Air-cooled condenser, also known as air-cooled condenser, the refrigerant is condensed in the tube, and the heat released by the refrigerant is taken away by the air. There are natural convection air-cooled condenser and forced convection air-cooled condenser in this type of condenser. Due to the low convection heat transfer coefficient of air (25-35 W/m2.K), the heat transfer efficiency of air-cooled condenser is not as good as water-cooled type, and the condensing temperature and condensing pressure are higher.

In addition, in the case of a certain heat transfer load, the air-cooled condenser requires a larger heat transfer area than the water-cooled condenser, so the volume and quality of the equipment are huge, covering a large area. However, it can be used for both hot and cold, with low initial investment and relatively simple system maintenance and management. Air-cooled condenser is widely used in engineering practice, both for refrigeration systems, also widely used in air conditioning systems. Its biggest advantage is that it does not need cooling water, so it is especially suitable for water-scarce areas or water supply difficulties in the field of small refrigeration and air-conditioning applications are particularly widespread.

2. Enhanced Heat Transfer Fin Tubes Commonly Used in Condensers

Heat transfer process is heat from a fluid through the solid wall to another fluid process. In engineering practice, to strengthen the heat transfer performance of the heat exchanger is mainly from the strengthening of the two sides of the medium and the heat transfer tube between the inner and outer walls of the convection heat transfer process.

The commonly used enhanced heat transfer techniques are:

(1) surface coatings; (2) rough surfaces; (3) extended surfaces; (4) various internally and externally threaded tubes; (5) spoiler elements; (6) additions; and (7) shock heat transfer.

Among the various enhanced heat transfer technologies, the addition of fin tubes on the wall surface, as a major means of enhancing heat transfer, is widely used in engineering. Fin tube heat exchangers, which are characterised by high efficiency heat transfer and compactness, have been widely used in various fields such as refrigeration and air-conditioning units, aerospace equipment, solar collectors and electronic equipment. Applications in condensers are particularly common.

There are many types of fin tube, and new varieties are still emerging, and more research has been done in this area. Broadly speaking, fin tubes can be classified according to several aspects, such as processing technology, fin shape, material and use.

In condensers, the following forms of fin tubes are commonly used

Internal threaded tube

Integral spiral finned tube

Spiral groove tube

Threaded finned tubes, sleeve finned tubes, corrugated tubes, spiral twisted tubes, spiral wound tubes and other highly efficient heat transfer elements have been widely used in condensers, and the heat transfer effect has been significantly improved. In addition, new tooth-shaped heat transfer tubes are still emerging.

Compared with the light pipe, they have the following common features

(1) Different shapes of fin tubes can make the heat transfer wall surface become rough, thus destroying the static laminar boundary layer, improve the convection heat transfer coefficient, so that the heat transfer is strengthened to different degrees;

(2) under certain conditions of load, the condenser area required can be greatly reduced

(3) According to most people’s common sense, the rough surface of the finned tube is easy to cause scaling; in fact, due to the turbulence caused by the rough surface destroys the static surface layer, which makes it difficult for dirt to adhere; even if there is dirt adherence, dirt is also presented as discrete scales, the temperature change in the operation of the equipment makes the tube expansion and contraction, which will be due to the dirt and the tube wall material between the expansion of the difference between the huge stripping caused by the impact in the medium. Under the impact of the medium to fall off by itself. The light tube scale layer for the cylinder, without any self-dehiscence force. Therefore, the finned tube fouling situation is not much more serious than the light tube.

Condensers have a wide range of applications, especially in refrigeration and air conditioning systems. As one of the main heat transfer equipment, the performance of the condenser directly affects the overall working performance of the device. Therefore, the strengthening of the heat transfer process of the condenser has received more and more extensive attention.

In order to improve the overall performance of condensing equipment, it has become a trend in the development of condensers at home and abroad to strengthen the heat transfer process by modifying the shape of the tubes or the nature of the surfaces to improve the efficiency of the condenser.