What are the common condensers and evaporators in refrigeration systems?

Condensers can be divided into three types according to their cooling media: water-cooled, air-cooled and evaporative.

1. water-cooled condenser

Water-cooled condenser takes water as cooling medium and takes away condensation heat through the temperature rise of water. 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 shell-and-tube condensers according to their structural forms, and shell-and-tube condensers are common.

The main features of vertical shell-and-tube condenser are:

(1) Because of the large cooling flow and high flow rate, the heat transfer coefficient is high.

(2) Vertical installation occupies a small area and can be installed outdoors.

(3) The cooling water flows directly with high speed, 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 unnecessary 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℃, so the water consumption is large. Moreover, because the equipment is placed in the air, the pipeline is easily corroded and easily found when it leaks.

2. Horizontal shell-and-tube condenser:

It has a similar shell structure to the vertical condenser, and the main difference lies in the horizontal placement of the shell and the multi-channel flow of water. Low-ribbed copper tubes are generally used for cooling tubes of Freon horizontal condensers. 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.

3. Sleeve condenser:

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 800 kcal/(m2 h℃). 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.

4. Air-cooled condenser

Air-cooled condenser takes air as cooling medium and takes away condensation heat through the temperature rise of air. 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. According to the different air flow modes, it can be divided into natural convection and forced convection.

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, it can be divided into suction type and pressure type, as shown in the figure. 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. It is a parallel device based on evaporative condenser and shell-and-tube condenser.

5. Air-cooled condenser

Air-cooled condenser takes air as cooling medium and takes away condensation heat through the temperature rise of air. 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. According to the different air flow modes, it can be divided into natural convection and forced convection.

I. Plate evaporator

Plate evaporator is a kind of equipment that heats the mixture to evaporate and separate it, which has the characteristics of high efficiency and energy saving. It consists of a plurality of parallel plates. After the mixture enters the plate group, a film is formed on the plate, and then the mixture is evaporated and separated by the boiling of steam or heat medium on the heating surface. The evaporator is suitable for handling viscous, easily crystallized and easily polluted materials.

Second, the coil evaporator

Coil evaporator is the most common type of evaporator, including natural circulation and forced circulation. It consists of one or more coils. The mixture evaporates in the heated coil and flows out of the coil with steam or heat medium, and then the pure substance is obtained in the separation chamber. This evaporator is suitable for treating materials with low crystallinity.

Thirdly, the rotary evaporator.

Rotary evaporator is a kind of evaporator with simple structure and convenient operation, which is suitable for drying, concentrating and separating materials. It consists of a rotating conical container and a heater. The mixture forms a film in the container, evaporates and separates under the action of the heater, and the rotating container drives the mixture to flow downwards and is recycled for many times, thus achieving the effect of high efficiency and energy saving.

In addition, there are multi-effect evaporators, thin-film evaporators, low-temperature evaporators and other types of evaporators.