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Application of internal thread low fin tubes in condensers
Fin tubes are used to improve heat exchange efficiency. Usually, fins are added to the surface of the heat exchange tube to increase the outer surface area (or inner surface area) of the heat exchange tube, thereby achieving the purpose of improving heat exchange efficiency.
There are many types of fin tubes, which are classified according to processing technology, fin shape, material, purpose and other aspects.
In condensers, the commonly used fin tubes are in the following forms.
1) Internal threaded tubes
2) Integral spiral fin tubes
3) Spiral groove tubes
Threaded fin tubes, sleeve fin tubes, corrugated tubes, spiral twisted tubes, spiral wound tubes and other high-efficiency heat transfer elements have been widely used in condensers, and the heat transfer effect has been significantly improved. In addition, new toothed heat transfer tubes are constantly emerging.
Compared with bare tubes, finned tubes have the following common characteristics:
(1) Fins of different shapes can make the heat transfer wall surface rough, thereby destroying the static laminar boundary layer, improving the convective heat transfer coefficient, and enhancing the heat transfer to varying degrees;
(2) Under certain load conditions, the required area of the condenser can be greatly reduced;
(3) According to common sense of most people, the rough surface of finned tubes is prone to scaling;
Because the turbulence caused by the rough surface of low-finned tubes destroys the static boundary layer, it will make it difficult for dirt to adhere; even if there is dirt attached, the dirt will appear in discrete scales. The temperature change during the operation of the heat exchanger equipment causes the tube to expand and contract, which will cause peeling due to the huge expansion difference between the dirt and the tube wall material, and fall off by itself under the impact of the medium. The scale layer of bare tubes is cylindrical and has no self-detachment force. Therefore, the scaling of finned tubes is not much more serious than that of bare tubes.
The application range of condensers is very wide, 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 enhancement of the heat transfer process of the condenser has received more and more attention. In order to improve the overall performance of the condensing equipment, the heat transfer process is enhanced by modifying the shape or surface properties of the low-fin tube to improve the efficiency of the condenser.
The compact elliptical finned tube used in the finned tube heat exchanger is a new type of high-efficiency heat transfer element. Its unique sheet structure and processing process make the air cooler product have a more compact size, higher heat transfer efficiency and lighter weight.
The condenser is a component of the air conditioning system that can transfer the heat in the tube to the air near the tube in a very fast way. Most cars are placed in front of the water tank.
A device that converts gas or steam into liquid
Power plants use condensers to condense the steam discharged from the turbine;
In refrigeration plants, condensers are used to condense refrigeration vapors such as ammonia and Freon.
In the petrochemical industry, condensers are used to condense hydrocarbons and other chemical vapors.
>In the distillation process, the device that converts steam into liquid is called a condenser.
All condensers operate by taking away the heat of gas or steam
1. Common types and characteristics of condensers
Condensers, also known as “liquefiers”, are heat exchangers that allow steam to release heat and liquefy. According to the cooling medium and cooling method, condensers can be divided into three types: water-cooled, air-cooled, and evaporative.
1) Water-cooled condensers
Water-cooled condensers use water as a cooling medium and rely on the temperature rise of water to take away the condensation heat. Water-cooled condensers have the characteristics of 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. Its main disadvantage is that a special cooling water circulation system needs to be set up, with high initial investment and high water treatment costs. Commonly used water-cooled condensers include horizontal shell and tube, vertical shell and tube, and sleeve types.
Water-cooled condensers are generally used in large and medium-sized air-conditioning refrigeration devices and industrial refrigeration, among which shell and tube condensers are the most commonly used. In shell and tube condensers, the refrigerant usually condenses outside the tube and water flows inside the tube.
Currently used shell and tube condensers are of two types: bare tube bundles and rolled low-fin tubes (i.e. spiral tubes). Generally, horizontal shell and tube condensers for ammonia mostly use bare tube bundles, and Freon condensers mostly use rolled low-fin tubes.
2) Air-cooled condensers
Air-cooled condensers are also called air-cooled condensers. The refrigerant condenses in the tubes, and the heat released by the refrigerant is taken away by the air. Among these condensers, there are natural convection air-cooled condensers and forced convection air-cooled condensers.
Due to the low convection heat transfer coefficient of air (25-35 W/m·2K), the heat transfer efficiency of air-cooled condensers is not as good as that of water-cooled condensers, and the condensation temperature and condensation pressure are both higher.
Under the condition of constant heat exchange load, the required heat transfer area of air-cooled condenser is larger than that of water-cooled condenser, so the equipment volume and mass are both large and occupy a large area. However, it can be used for both cooling and heating, with low initial investment and relatively simple system maintenance and management.
Air-cooled condensers are widely used in engineering practice. They can be used in refrigeration systems as well as air-conditioning systems. Its biggest advantage is that it does not require cooling water, so it is particularly suitable for water-scarce areas or occasions with difficult water supply, and is particularly widely used in the field of small refrigeration and air conditioning.
3) Evaporative condenser
The evaporative condenser is based on evaporative condensation and sensible heat exchange. The heat released by the refrigerant is taken away by cooling water and air at the same time. The refrigerant flows in the tube, and the cooling water absorbs the latent heat of vaporization when it sprays and evaporates outside the tube, so that the refrigerant in the tube is cooled and condensed.
In the evaporative condenser, the sensible heat transfer stage of cooling water in the condenser is omitted, making the condensation temperature closer to the wet bulb temperature of the air, which can be 3 to 5°C lower than the water-cooled condenser system, thereby greatly reducing the power consumption of the compressor, and the water consumption is only about 1/3 of that of the water-cooled condenser system.
For those refrigeration and air-conditioning systems that need to be controlled and occasions with harsh operating environments, evaporative condensers are more likely to meet process control requirements.
2. Commonly used low-fin tubes for enhanced heat transfer in condensers
The heat transfer process of low-fin tubes is the process of heat transfer from one fluid to another fluid through the solid wall. In engineering practice, the heat transfer performance of the heat exchanger is mainly enhanced by strengthening the convective heat transfer process between the media on both sides and the inner and outer walls of the heat exchange tube.
Commonly used heat transfer enhancement technologies include:
(1) Surface coating;
(2) Rough surface;
(3) Extended surface;
(4) Various internal and external threaded tubes;
(5) Turbine elements;
(6) Additives;
(7) Impact heat transfer.
Among various heat transfer enhancement technologies, adding fins to the wall is widely used in engineering as a major means of enhancing heat transfer.
Finned tube heat exchangers have the characteristics of efficient heat transfer and compact structure, and have been widely used in various fields such as refrigeration and air conditioning equipment, aerospace equipment, solar collectors and electronic equipment. They are particularly common in condensers.
