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Types and working principles of condensers

Condenser is one of the main heat exchange equipment in refrigeration plant. Its task is to discharge the compressor high pressure superheated refrigerant vapor, through its release heat to the environment medium and be cooled, condensed into saturated liquid, or even supercooled liquid.

According to the different cooling medium and cooling mode used by condenser, there are three kinds of water-cooled, air-cooled and water-air cooled.

Condenser according to cooling mode:

Air-cooled, water-cooled, evaporative cooled (water-air cooled)

According to the air flow mode outside the tube in the air-cooled condenser:

Natural convection air cooling condenser, forced convection air cooling condenser

 

Water-cooled condenser

 

This type of condenser uses water as the cooling medium to take away the heat released when the refrigerant condenses. Cooling water can be used once or recycled.

When circulating water is used, cooling towers or cold pools must be equipped to ensure that the water is constantly cooled. According to its different structure, there are mainly shell and tube type and tube type and now multi-purpose plate heat exchanger.

1. Shell and tube condenser:

Different refrigerants used in refrigeration units have different structural characteristics. Generally, vertical shell and tube condenser is suitable for large ammonia refrigeration units, while horizontal shell and tube condenser is generally used in large and medium ammonia or Freon refrigeration units. The fixed way of tube plate and heat transfer tube is generally expanded connection method, so as to facilitate the repair and replacement of heat transfer tube.

2. Features of horizontal shell and tube condenser:

High heat transfer coefficient, less cooling water consumption, easy operation and management; But the cooling water quality requirements are high. At present, this kind of device is widely used in large and medium refrigeration units.

 

Vertical shell and tube condenser

1 – liquid outlet pipe; 2 – pressure gauge connector; 3 – intake pipe; 4 – water distribution tank; 5 – safety valve joint; 6 – pressure tube; 7 – empty pipe; 8 – tubing

3. Tube condenser:

 

It is a water-cooled condenser made of pipes of different diameters which are set together and bent into a spiral or snake 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 bottom-up in the pipe with a small diameter, which is countercurrent with the refrigerant, so the heat transfer effect is better.

4. Plate condenser:

Plate condenser is composed of a group of stainless steel corrugated plates connected in series. Cold and hot fluid channels are formed on both sides of the heat transfer plate, and heat transfer is carried out through the plate wall in the flow process.

The thickness of the heat exchange plate is about 0.5mm, and the plate spacing is generally 2-5mm.

Plate heat exchanger has been widely used in recent years because of its small size, light weight, high heat transfer efficiency, low refrigerant charging amount and high reliability. But its internal volume is small, the condensed liquid refrigerant should be removed in time, the cooling water quality requirements are high, it is difficult to clean, the internal leakage is not easy to repair.

The cooling water goes up and down, the refrigerant vapor enters from above, and the liquid refrigerant flows out from below.

 

Air cooled condenser

 

This condenser uses air as the cooling medium. The refrigerant condenses in the tube, and the air flows outside the tube to absorb the heat released by the refrigerant vapor in the tube. Because the heat transfer coefficient of air is small, ribs are often set outside the tube (air side) to strengthen the 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 absorbs the heat emitted by the refrigerant when the air flows outside the tube. The density change causes the free flow of the air and constantly takes away the condensation heat of the refrigerant vapor. It does not need a fan, no noise, mostly used in small refrigeration units. As shown in the picture below:

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Air forced flow air-cooled condenser: As shown below, it consists of one or more sets of snake tubes with ribs. The refrigerant vapor enters the snake tube from the upper collector tube, and the outer ribs of the tube are used to strengthen the air side heat transfer and compensate for the low heat transfer coefficient on the air surface.

In terms of structure, the more the number of pipe rows along the direction of air flow, the smaller the heat transfer of the back pipe, so that the heat transfer capacity can not be fully utilized. In order to improve the utilization rate of heat transfer area, the number of pipe rows should be 4-6.

2. Comparison between air-cooled condenser and water-cooled condenser:

(1) In the place with sufficient cooling water, the initial investment and operation cost of water-cooled equipment are lower than that of air-cooled equipment;

(2) Due to the high outdoor air temperature in summer, the condensation temperature can generally reach 50, in order to obtain the same cooling capacity, the capacity of air-cooled equipment refrigeration compressor needs to increase by about 15%;

(3) The composition of the refrigeration equipment system using air-cooled condenser is simple, which can alleviate the tension of water supply;

 

Evaporative condenser

 

1. Evaporative condenser:

Water and air are used as the cooling medium. It uses water evaporation to absorb heat to condense the refrigerant vapor in the tube. The water is lifted by the pump and sprayed by the nozzle to the outer surface of the heat transfer tube, forming a water film, and part of the heat absorption evaporates into water vapor, and then is taken away by the air into the condenser.

The unevaporated droplets fall into the pool below. A water retaining grid is arranged above the box. It is used to prevent the loss of water droplets in the air. The structure principle of evaporative condenser is shown in the figure.

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2. Characteristics of evaporative condenser:

(1) When water is vaporized to take away the heat of condensation, the cooling water consumed is only the lost water of recharge, and the consumption of cooling water is less;

(2) The inlet air wet bulb temperature of evaporative condenser has a great influence on heat exchange. For the same condensation temperature and air volume, the smaller the inlet wet bulb temperature, the greater the evaporation of cooling water and the better the condensation effect;

(3) The water consumption of evaporative condenser is small, and the air required is less than 1/2 of the air-cooled type, so it is especially suitable for dry and water-scarce areas;


Post time: Oct-31-2022