Working principle and characteristics of condenser

The condenser is one of the main heat exchange devices in refrigeration equipment. Its task is to cool and condense the high-pressure superheated refrigerant vapor discharged from the compressor into saturated or even supercooled liquid by releasing heat to the environmental medium.
According to the different cooling media and methods used in condensers, there are three types: water-cooled, air-cooled, and water air cooled.
Condenser cooling method:
Air cooled, water-cooled, evaporative cooling (water air cooling)
According to the airflow pattern outside the tube in the air-cooled condenser:
Natural convection air-cooled condenser, forced convection air-cooled condenser
1、 Water-cooled condenser
This type of condenser uses water as the cooling medium to remove the heat released during the condensation of the refrigerant. Cooling water can be used once or recycled.
When using circulating water, a cooling tower or cold water tank must be equipped to ensure that the water is continuously cooled. According to their different structures, there are mainly shell and tube type and sleeve type, as well as the commonly used plate heat exchangers nowadays.
closed shell and tube condenser
1. Shell and tube condenser:
The refrigerants used in refrigeration systems have different structural characteristics. Generally, vertical shell and tube condensers are suitable for large ammonia refrigeration units, while horizontal shell and tube condensers are commonly used in large and medium-sized ammonia or Freon refrigeration units. The fixing method between the tube plate and the heat transfer tube is generally the expansion joint method, which is convenient for repairing and replacing the heat transfer tube.
2. Characteristics of horizontal shell and tube condenser:
High heat transfer coefficient, low cooling water consumption, convenient operation and management; But high requirements are placed on the quality of cooling water. At present, this type of device is commonly used in large and medium-sized refrigeration systems.
Vertical shell and tube condenser
1- Liquid outlet pipe; 2- Pressure gauge connector; 3- Inlet pipe; 4- Water distribution tank; 5- Safety valve connector; 6- Pressure equalization tube; 7- Vent pipe; 8- Oil drain pipe
3. Sleeve condenser:
It is a water-cooled condenser consisting of tubes of different diameters that are fitted together and bent into a spiral or serpentine shape. As shown in the figure, the refrigerant vapor condenses between the sleeves, and the condensate is drawn out from below. The cooling water flows from bottom to top in the smaller diameter pipeline, forming a counterflow with the refrigerant, thus achieving better heat transfer effect.
double-pipe condenser
4. Plate condenser:
Plate condenser is composed of a set of stainless steel corrugated plates connected in series, forming cold and hot fluid channels on both sides of the heat transfer plate, and exchanging heat through the plate wall during the flow process.
The thickness of the heat exchange plate is about 0.5mm, and the plate spacing is generally 2-5mm.
Plate heat exchangers have been widely used in recent years due to their small volume, light weight, high heat transfer efficiency, low refrigerant charge required, and high reliability. But its content is small, and the condensed liquid refrigerant should be promptly discharged. It requires high cooling water quality, is difficult to clean, and internal leakage is not easy to repair.
Cooling water flows in and out, refrigerant vapor enters from above, and liquid refrigerant flows out from below.
2、 Air-cooled condenser
This condenser uses air as the cooling medium, with refrigerant condensing inside the tubes and air flowing outside the tubes, absorbing the heat released by the refrigerant vapor inside the tubes. Due to the small heat transfer coefficient of air, fins are often installed outside the tube (on the air side) to enhance heat transfer outside the tube. It is divided into two types: free air flow and forced air flow.
1. Air cooled condenser with free air flow:
The condenser utilizes the change in density caused by the absorption of heat emitted by the refrigerant when air flows outside the tube, resulting in the free flow of air and continuously carrying away the condensation heat of refrigerant vapor. It does not require a fan, has no noise, and is commonly used in small refrigeration units. As shown in the following figure:
Air forced flow air-cooled condenser: As shown in the figure below, it consists of one or several sets of finned coils. The refrigerant vapor enters the coil from the upper header, and its outer fins are used to enhance heat transfer on the air side and compensate for the low heat transfer coefficient on the air surface.
In terms of structure, the more rows of pipes along the direction of air flow, the smaller the heat transfer capacity of the pipes in the rear rows, which makes it difficult to fully utilize the heat transfer capacity. To improve the utilization rate of heat exchange area, it is better to have 4-6 rows of tubes.
2. Comparison between air-cooled condenser and water-cooled condenser:
(1) The initial investment and operating costs of water-cooled equipment are lower than those of air-cooled equipment in areas with sufficient cooling water;
(2) Due to the high outdoor air temperature in summer, the condensation temperature can generally reach 50 ℃. In order to achieve the same cooling capacity, the capacity of the air-cooled equipment refrigeration compressor needs to be increased by about 15%;
3、 Evaporative condenser
1. Evaporative condenser:
Using water and air as cooling media. It uses the heat absorbed during water evaporation to condense the refrigerant vapor inside the tube. The water is lifted by the water pump and sprayed onto the outer surface of the heat transfer tube through the nozzle, forming a water film. Part of it absorbs heat and evaporates into water vapor, which is then carried away by the air entering the condenser.
The unevaporated water droplets fall into the lower pool. There is a water barrier above the box. Used to prevent water droplets from dissipating in the air. The structural principle of the evaporative condenser is shown in the diagram.
2. Characteristics of evaporative condenser:
(1) By using water vaporization to remove condensation heat, the amount of cooling water consumed is only the amount of dissipated water supplied, resulting in less cooling water consumption;
(2) The wet bulb temperature of the inlet air of the evaporative condenser has a significant impact on heat transfer. At the same condensation temperature and air volume, the lower the inlet wet bulb temperature, the greater the evaporation of cooling water, and the better the condensation effect;