(1) water-cooled condenser
Water-cooled condenser takes water as cooling medium, and the temperature rise of water takes away the condensation heat. Generally speaking, cooling water is recycled, but a cooling tower or cooling pool is needed in the system. Water-cooled condensers can be divided into vertical shell-and-tube condensers and horizontal shell-and-tube condensers according to their different structural types, and can also be divided into vertical shell-and-tube condensers, horizontal shell-and-tube condensers, among which shell-and-tube condensers are common.
1, vertical shell-and-tube condenser
Vertical shell-and-tube condenser, also known as vertical condenser, is a water-cooled condenser widely used in ammonia refrigeration system at present. Vertical condenser is mainly composed of shell (cylinder), tube sheet and tube bundle.
Refrigerant vapor enters the gap between tube bundles from the vapor inlet at the height of 2/3 of the cylinder, and the cooling water in the tube and the high-temperature refrigerant vapor outside the tube exchange heat through the tube wall, so that the refrigerant vapor condenses into liquid, gradually flows down to the bottom of the condenser and flows into the liquid receiver through the liquid outlet tube. The absorbed water is discharged into the lower concrete pool, cooled and pumped into the cooling tower for recycling.
In order to distribute the cooling water evenly to each nozzle, a water distribution plate is installed on the water distribution tank at the top of the condenser, and a guide plate with a chute is installed on each nozzle at the upper part of the tube bundle, so that the cooling water flows downward along the inner wall of the tube in a film-like water layer, which not only improves the heat transfer effect, but also saves water. In addition, the shell of the vertical condenser is also provided with a pressure equalizing pipe, a pressure gauge, a safety valve and an exhaust pipe, so as to be connected with corresponding pipelines and equipment.
The main features of vertical condenser are:
1. Because of the large cooling flow, high flow rate and high heat transfer coefficient.
2. Vertical installation occupies a small area and can be installed outdoors.
3. The cooling water flows directly and has a large flow rate, so the requirements for water quality are not high, and general water sources can be used as cooling water.
4. The scale in the tube is easy to remove, and it is not necessary to stop the refrigeration system.
5. However, the temperature rise of cooling water in vertical condenser is generally only 2 ~ 4℃, and the logarithmic average temperature difference is generally around 5 ~ 6℃, which requires a lot of water. And because the equipment is placed in the air, the pipeline is easy to be corroded and the leakage rate is easy to be found.
2. Horizontal shell-and-tube condenser
Horizontal condenser and vertical condenser have similar shell structures, but there are many differences in general. The main difference lies in the horizontal placement of the shell and the multi-channel flow of water. The outer surfaces of the tube plates at both ends of the horizontal condenser are closed by end caps, and the end caps are cast with designed water distribution ribs which cooperate with each other to divide the whole tube bundle into several tube groups. So that the cooling water enters from the lower part of an end cover, flows through each tube group in turn, and finally flows out from the upper part of the same end cover, with 4- 10 round trips. This can not only improve the flow rate of cooling water in the tube, thus improving the heat transfer coefficient, but also make high-temperature refrigerant vapor enter the tube bundle from the air inlet pipe at the upper part of the shell, and fully exchange heat with the cooling water in the tube.
The condensed liquid flows into the liquid storage barrel from the lower liquid outlet pipe. On the other end cover of the condenser, there is also a drain valve and a drain cock. The exhaust valve is at the upper part. When the condenser is put into operation, it is opened to exhaust the air in the cooling water pipe and make the cooling water flow smoothly. Remember not to confuse it with the exhaust valve to avoid accidents. When the condenser is out of service, drain the faucet to avoid freezing and cracking the condenser due to water freezing in winter. The shell of the horizontal condenser is also provided with a plurality of pipe joints connected with other equipment in the system, such as air inlet, liquid outlet, pressure equalizing pipe, exhaust pipe, safety valve, pressure gauge connector and oil discharge pipe.
Horizontal condenser is widely used not only in ammonia refrigeration system, but also in Freon refrigeration system, but its structure is slightly different. The cooling pipe of ammonia horizontal condenser adopts smooth seamless steel pipe, and the cooling pipe of Freon horizontal condenser generally adopts low-ribbed copper pipe. This is due to the low exothermic coefficient of freon. It is worth noting that some Freon refrigeration units generally do not have a liquid storage tank, only a few rows of tubes are arranged at the bottom of the condenser, and the condenser is also used as a liquid storage tank.
The water temperature rise and water consumption of horizontal and vertical condensers are different except for their installation positions and water distribution methods. The cooling water of the vertical condenser flows down along the inner wall of the pipe by gravity, which can only be a single stroke, so a large amount of water must be used to get a large enough heat transfer coefficient K. The horizontal condenser pumps the cooling water into the cooling pipe, so it can be made into a multi-stroke condenser, and the cooling water can get enough flow and temperature rise (? T=4~6℃). Therefore, the horizontal condenser can obtain a large enough K value with a small amount of cooling water.
However, if the flow rate increases too much, the heat transfer coefficient K will not increase too much, but the power consumption of the cooling water pump will increase obviously. Therefore, the cooling water flow rate of ammonia horizontal condenser is generally about 1m/s, and that of Freon horizontal condenser is mostly1.5 ~ 2m/s. Horizontal condenser has high heat transfer coefficient, small cooling water consumption, compact structure and convenient operation and management. However, the quality of cooling water is required to be good, and the scale is inconvenient to clean, and it is not easy to find if it leaks.
The vapor of the refrigerant enters the cavity between the inner tube and the outer tube from above, condenses on the outer surface of the inner tube, and the liquid sequentially flows downward at the bottom of the outer tube and flows into the liquid reservoir from the lower end. Cooling water enters from the lower part of the condenser and flows out from the upper part through each row of inner tubes in turn, which is counter-current to the refrigerant.
The advantages of this condenser are simple structure and easy manufacture. Because it is a single tube condensation, the medium flows in the opposite direction and the heat transfer effect is good. When the water velocity is 1 ~ 2m/s, the heat transfer coefficient can reach 800kcal/(m2h℃). Its disadvantages are large metal consumption, too many longitudinal tubes, too much liquid in the lower tubes, and the heat transfer area can not be fully utilized. In addition, the compactness is poor, cleaning is difficult, and a large number of connecting elbows are needed. Therefore, this kind of condenser has been rarely used in ammonia refrigeration equipment.
(2) Evaporative condenser
The heat exchange of evaporative condenser is mainly carried out by absorbing the latent heat of gasification through the evaporation of cooling water in the air. According to the air flow mode, it can be divided into suction type and pressure type. In this condenser, the refrigerant vapor on the other side of the heat transfer partition wall is cooled by the cold effect produced by the evaporation of refrigerant in another refrigeration system, and the latter is condensed and liquefied. The evaporative condenser is composed of cooling pipe group, water supply equipment, fan, water baffle and box. The cooling pipe group is a serpentine coil group made of seamless steel pipe, which is installed in a rectangular box made of thin steel plate.
Ventilators are installed on both sides or at the top of the box, and the bottom of the box is also used as a cooling water circulation pool. When the evaporative condenser works, the refrigerant vapor enters the serpentine tube group from the upper part, condenses and releases heat in the tube, and flows into the accumulator from the lower liquid outlet pipe. The cooling water is pumped by the circulating water pump to the sprinkler, sprayed from the surface of the steering wheel tube group directly above the serpentine coil group, and evaporated by absorbing the condensation heat in the tube through the tube wall. The fan installed on the side or top of the box forces the air to sweep the coil from bottom to top, which promotes the evaporation of water and takes away the evaporated water.
Among them, the fan is installed at the top of the box, and when the serpentine tube group is located at the suction side of the fan, it is called suction evaporative condenser, while the fan is installed at both sides of the box, and when the serpentine tube group is located at the outlet side of the fan, it is called pressure delivery evaporative condenser. The inhaled air can pass through the serpentine tube group evenly, so the heat transfer effect is good, but the fan is prone to failure when it runs under high temperature and high humidity. Although the air passing through the serpentine tube group is uneven, the fan motor works well.
Characteristics of evaporative condenser:
1. Compared with the water-cooled condenser with DC water supply, it saves about 95% water. But compared with the combination of water-cooled condenser and cooling tower, the water consumption is similar.
2. Compared with the combined system of water-cooled condenser and cooling tower, the condensation temperature of the two systems is similar, but the evaporative condenser is more compact. Compared with air-cooled condenser or water-cooled condenser with DC water supply, its size is relatively large.
3. Compared with air-cooled condenser, its condensation temperature is lower. Especially in arid areas. When running all year round, it can be air-cooled in winter. Compared with the water-cooled condenser with DC water supply, its condensation temperature is higher.
4. The condenser coil is easy to corrode, and the outside of the condenser coil is easy to scale, making it difficult to maintain.
Generally speaking, the main advantage of evaporative condenser is less water consumption, but the circulating water temperature is high, the condensation pressure is high, the scale is not easy to clean, and the water quality is strict. Especially suitable for dry and water-deficient areas, it should be installed in an open place with good ventilation or on the roof, not indoors.
(3) Air-cooled condenser
Air-cooled condenser takes air as cooling medium, and the temperature rise of air takes away the condensation heat. This kind of condenser is suitable for the situation of extreme water shortage or water supply, and is often used in small Freon refrigeration units. In this condenser, the heat released by the refrigerant is taken away by the air. Air can be natural convection or forced flow by fans. This condenser is used for freon refrigeration equipment in places where water supply is inconvenient or difficult.
(4) Water drenching condenser
It mainly consists of a heat exchange coil and a spray tank. Refrigerant vapor enters from the steam inlet at the lower part of the heat exchange coil, while cooling water flows from the gap of the shower tank to the top of the heat exchange coil, and flows downwards in the form of a film, so that water absorbs condensation heat, and under the natural convection of air, part of condensation heat is taken away by evaporation of water. The heated cooling water flows into the pool, and then it is cooled and recycled by the cooling tower, or a part of water is discharged and a part of fresh water is added to the shower pool. The condensed liquid refrigerant flows into the receiver. Water-drenched condenser means that the temperature of water rises, and the moisture in the air evaporates to take away the condensation heat. This condenser is mainly used in large and medium-sized ammonia refrigeration systems. Can be installed in the open air or under a cooling tower, but direct sunlight should be avoided. The main advantages of the drenching condenser are as follows:
1, simple structure and convenient manufacture.
2. Ammonia gas leakage is easy to find and easy to maintain.
3, easy to clean.
4. Low requirements for water quality.
Disadvantages are:
1, low heat transfer coefficient.
2. High metal consumption
3, covers an area of large
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