1、 Types and characteristics of condenser
According to the different cooling media, condensers can be divided into water-cooled, air-cooled and evaporative.
A. Water cooled condenser
Water cooled condenser uses water as the cooling medium and takes away the condensing heat by the temperature rise of water. Generally, cooling water is recycled, but cooling tower or cooling pool should be set in the system. According to its structure, the water-cooled condenser can be divided into shell and tube condenser and tube condenser, and the shell and tube condenser is the common one.
Vertical shell and tube condenser
The main features of vertical condenser are as follows:
Due to the large cooling flow rate and high flow rate, the heat transfer coefficient is high, generally k = 600-700 (kcal / m2? H? ℃).
Vertical installation covers a small area and can be installed outdoors.
The cooling water flows straight through and has a high flow rate, so the water quality is not high, and the general water source can be used as cooling water.
The scale in the tube is easy to remove, and the refrigeration system does not have to stop working.
However, the temperature rise of cooling water in vertical condenser is only 2-4 ℃, and the logarithmic average temperature difference is generally about 5-6 ℃, so the water consumption is large. Because the equipment is placed in the air, the pipe is easy to be corroded, and the leakage is easy to be found.
B. Horizontal shell and tube condenser
It is similar to the vertical condenser shell structure, the main difference lies in the horizontal placement of the shell and the multi-channel flow of water.
Horizontal condenser is not only widely used in ammonia refrigeration system, but also in freon refrigeration system, but its structure is slightly different.
The cooling pipe of ammonia horizontal condenser is smooth seamless steel pipe, while that of Freon horizontal condenser is generally low rib copper tube. This is due to the low heat release coefficient of Freon.
It should be noted that some freon refrigeration units generally do not have liquid storage tanks, only use a few rows of tubes at the bottom of the condenser, which are also used as liquid storage tanks.
C. Tubular condenser
The vapor of refrigerant enters the cavity between the inner and outer tubes from the top, condenses on the outer surface of the inner tube, and the liquid flows down successively at the bottom of the outer tube, and flows into the liquid reservoir from the lower end. The cooling water enters from the lower part of the condenser, and flows out from the upper part through the inner pipes in turn, and is countercurrent with the refrigerant.
The advantages of this kind of condenser are simple structure, easy to manufacture, and because of the single tube condensation, the medium flow direction is opposite, so the heat transfer effect is good. When the water flow rate is 1 ~ 2m / s, the heat transfer coefficient can reach 800 kcal / (M2? H? ℃).
The disadvantage is that the metal consumption is large, and when the number of longitudinal tubes is large, the lower tube is filled with more liquid, so that 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 required. Therefore, this kind of condenser has been rarely used in ammonia refrigeration plant.
The tubular condenser is still widely used in small Freon air conditioning units.
2， Air cooled condenser
Air cooled condenser takes air as the cooling medium and takes away the condensing heat by the temperature rise of air. This kind of condenser is suitable for the situation of extreme water shortage or no water supply, and is commonly used in small freon refrigeration units. According to the different ways of air flow, it can be divided into natural convection type and forced convection type.
3， Evaporative condenser
The heat transfer of evaporative condenser mainly depends on the evaporation of cooling water in the air to absorb the latent heat of gasification. According to the air flow mode can be divided into suction type and pressure type, as shown in the figure.
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 bending and installed in a rectangular box made of thin steel plate. Fans are set on both sides or top of the box body, and the bottom of the box is also used as a cooling water circulating pool.
Parallel connection of evaporative and shell and tube condensers:
4， Spray condenser
The main advantages of the spray type condenser are as follows:
- 1. The structure is simple and the manufacture is convenient;
- 2. Ammonia leakage is easy to find and maintain;
- 3. Easy to clean;
- 4. The requirements for water quality are low.
Its main disadvantages are as follows:
- 1. The heat transfer coefficient is low;
- 2. High metal consumption;
- 3. It covers a large area.
The water spraying condenser takes away the condensation heat by the temperature rise of water and the evaporation of water in the air. The condenser is mainly used in large and Medium-sized Ammonia refrigeration systems.
It can be installed in the open air or under the cooling tower, but should be protected from direct sunlight.