Finned Tube----Finned tubes in the condenser Application

Finned tubes to improve heat transfer efficiency, typically in the surface of the heat transfer tubes by the addition of fins to increase the area of heat transfer tubes of the outer (or inner surface ) , so as to improve heat transfer efficiency purposes, such a heat exchanger tube . Condenser is a mechanical air-conditioning system can heat the tube , a rapid manner , spread around the air tube , the tank is placed in front of the majority of automobiles . The gas or vapor into a liquid means . Many power plants use the turbine condenser exhaust steam is condensed ; refrigeration plant used in the condenser to condense the vapor of ammonia and freon refrigeration and the like . Petrochemical industry using the condenser so that hydrocarbons and other chemical vapor condensation . In the distillation process, the vapor into a liquid device called condenser. All the heat of the condenser is a gas or vapor and away operation .

1. A common type and characteristics of the condenser

Condenser known as " liquefaction " is that the vapor is liquefied therein releasing heat exchanger . Depending on the cooling medium and cooling methods, can be divided into water-cooled condensers , air-cooled , evaporative three types.

 1 ) water-cooled condenser

Water-cooled condenser is water as a cooling medium , taken away by the water temperature condensation heat. Water-cooled condenser has a high heat transfer efficiency , compact structure . Currently, due to the shortage of water resources , water-cooled condenser cooling water used widely recycled, its main drawback is the need to set up a dedicated cooling water systems, high initial investment, a large water treatment costs . Commonly used water-cooled shell and tube condensers are horizontal , vertical shell and tube type and tube type and other types .

Water-cooled condenser

In medium-sized industrial refrigeration and air conditioning and refrigeration equipment generally used in water-cooled condensers , among the most commonly used shell and tube condensers . In the shell and tube condenser , the refrigerant tube usually condensed water flowing in the pipe . Currently used shell and tube condenser tube bundle and roll down light finned tubes ( ie spiral ) two. In general, ammonia horizontal shell and tube condenser tube bundle to use more light , multi-use roll down freon condenser finned tubes .

2 ) air-cooled condenser

Also known as the air-cooled condenser air-cooled condenser , the refrigerant condensed in the tube , the refrigerant discharged air heat is taken away . This condenser has a natural convection air -cooled condenser and forced convection air-cooled condenser. Since the convective heat transfer coefficient of air is very low (25 ~ 35 W / m · 2K), air-cooled heat transfer efficiency is not as water-cooled condenser , the condensing temperature and the condensation pressure was high . In addition, the heat load under certain circumstances , the required air-cooled condenser heat transfer area larger than a water-cooled condenser, and therefore the device size and quality are huge , covering large . But be hot and cold dual-use, low initial investment, maintenance and management system is relatively simple. Air-cooled condensers used in engineering practice is very widespread , both for the cooling system, but also widely used in air conditioning systems. Its biggest advantage is that without cooling water , it is particularly suitable for dry areas or where the water supply difficulties in the field of small-scale refrigeration and air conditioning applications particularly extensive.

3 ) evaporative condensers

Evaporative condenser is condensed and evaporated to sensible heat exchange , based on the heat released while the refrigerant away from the cooling water and air. The refrigerant flowing in the pipe , the cooling water absorbs the latent heat of vaporization in the evaporator spray tube , the tube is cooled and condensed refrigerant . Evaporative condensers , cooling water was omitted in the condenser heat transfer stage , the closer to the condensation temperature of the wet bulb temperature of the air , water-cooled condenser system lower than 3 ~ 5 ℃, thereby greatly reducing the compressor power consumption, water consumption is only water-cooled condenser system about 1/3 . Development and application of evaporative condenser is lagging behind in the past and more used in large ammonia refrigeration system. In recent years , due to the scarcity of water and power resources strained , evaporative condensers as an energy -saving type of heat transfer equipment, which has been widely studied and applied importance to promote the maturation and further application of evaporative condenser technology products . Currently, there are a number of manufacturers in the structure of its perfect , making used in central air conditioning units .

For those who need to be harsh precisely controlled refrigeration and air conditioning systems and operating environment occasions , evaporative condensers easier to meet process control requirements. Engineering applications show that the product instead of the traditional " water-cooled condenser cooling tower + " mode , the increase is generally to recover the initial investment in about a year , the economic benefit.

2 , Commonly used in the condenser finned tube heat transfer enhancement

Heat from the heat transfer process is the process of a fluid to pass through the solid wall of another fluid. Engineering practice , and strengthen the performance of the main heat exchanger with tubes from the media on both sides to strengthen the convective heat transfer process between the starting wall . Heat transfer enhancement techniques commonly used are:

    ( 1 ) surface coating ;

    ( 2 ) a rough surface ;

    ( 3 ) Extended surface ;

    ( 4 ) a variety of internal and external threaded pipe ;

    ( 5 ) the mixing element ;

    ( 6 ) additives ;

    ( 7 ) the impact of heat . In a variety of enhanced heat transfer technology , the installation of the fin on the wall , as a primary means of enhancing heat transfer , has been widely used in engineering. Finned -tube heat exchanger with high efficiency , compact structure , etc. , have been widely used in refrigeration and air conditioning equipment , various fields of aerospace equipment, solar collector and electronic equipment and the like. Applications are particularly common in the condenser .

Many types of finned tubes , but also the emergence of new varieties, research in this area is greater [ 4-6 ] . Process according to several aspects of general , fin shape, material , and other uses of finned tubes classification. In the condenser, finned tubes commonly used are the following form .

1 ) Inner grooved pipe

The female is a common good and efficient heat transfer characteristics of tubes . Water-cooled condenser is generally used in air conditioning systems R22 , commonly used in the threaded tube , the heat transfer coefficient of up to 930 ~ 1 600 W / m · 2K, in turn, can reduce the condensation temperature , the cooling capacity of the unit energy consumption of the compressor chiller less. In addition, the water-cooled condenser, especially large chiller condenser cooling water is generally taken directly from the river water, sediment particles suspended in water and microbial fouling materials such as dirt is easy to form the inner wall of the tubes , so that the effect of the heat exchanger greatly weakened . Studies have shown that : condenser tube thread selection , the cooling water flow rate υ there is a critical threshold , when the flow rate υ <υ critical , no matter how long the unit operation , with respect to the light pipe can be realized in terms of economic operation ; If the cooling water flow rate υ> υ critical , then there must be a critical time t critical , when total running time t ≤ t the critical condenser still has the choice of the female economy . So long as the critical time for the regular cleaning of the condenser reference point , we can maintain the unit economy running .

2 ) the overall spiral finned tube

Overall shaped finned tube is shaped by special equipment --- overall disposable spiral finning molding equipment , spiral fins . Whole -fin tube can be divided into two bimetallic finned tube pipe and single metal fins . Bimetallic finned tubes made ​​of metal pipe composite of two different materials, rolling, there are aluminum composite pipe and steel and aluminum composite pipe ; single metal tube consists of a finned aluminum or copper rolling, because they do not contact resistance problems exist , can greatly improve the performance of finned tube heat exchangers . The basic structure of the overall shape of spiral finned tube shown in Figure 2 .

Overall shape finned tube heat exchange equipment as an important heat exchanger components , have been widely used in condenser heating and cooling systems , while also widely used in petroleum , chemical, electric power, metallurgy , baking, heat recovery , etc. a variety of industrial and agricultural production with heat exchange process , areas of life .

3 ) spiral grooved tube；spirally corrugated tube

Spiral groove tube that is threaded grooved tube is machined on a spiral groove from the base tube , shown in Figure 3 . Its mechanism of enhanced heat transfer boundary layer separation flow generated by the heat transfer boundary is destroyed. A single spiral groove tube head and long points, taking into account the combined effects of heat transfer and resistance factors engineering generally use a single head . Practice has proved that : the spiral groove tube of liquid - liquid, liquid - gas, gas - gas heat transfer process between both strengthening effect , compared with fluorescent tubes , the overall heat transfer coefficient can be increased by 20 % to 40 %, can be used in various forms heat exchangers , waste heat boilers.

Spiral groove tube,Thread class finned tube, plate finned tubes , bellows , spiral twisted tubes , spiral wound pipe pieces , such as efficient heat transfer components have been widely used in the condenser , the heat transfer effect has been improved significantly. In addition , the new tooth heat transfer tubes are still emerging. Compared with the light pipe , which has the following common characteristics :

    ( 1 ) can make different shapes of fin heat transfer wall becomes rough, thereby undermining the stationary laminar boundary layer , enhance the convective heat transfer coefficient , so that the heat exchanger to be strengthened to varying degrees ;

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

    ( 3 ) the knowledge of the majority of people , the rough surface of the finned tube prone to fouling ; Indeed , the turbulence caused by the destruction of the rough surface of the stationary boundary layer of dirt is difficult to make the attachment ; if dirt is attached , dirt also showed discrete scaly , equipment operation temperature changes occur so that the tube expansion and contraction due to differential expansion between the dirt and the wall material is huge and debonding, under the impact of the media off on their own . The light pipe scale layer of the cylinder , without any self- de-force . Therefore , fouling finned tube is not much serious than fluorescent tubes .

Condenser very broad range of applications , especially in the refrigeration and air conditioning systems. As one of the main condenser heat transfer equipment , and its performance has a direct impact on the overall job performance of the device . Therefore , strengthening the condenser heat transfer process has been more widely appreciated . In order to improve the overall performance of the condensing device , by modifying the shape or the surface properties of the tube to enhance the heat transfer process to improve the efficiency of the condenser , the condenser and abroad has become a developing trend . Compact series chip segment Byrne finned tube heat exchanger system used , it is a novel and efficient heat transfer components . Its unique structure and process flow sheet , making the air cooler products with more compact dimensions, higher heat transfer efficiency and lighter important.