Most of the condenser is placed in front of the car water tank, but the parts of the air conditioning system can transfer the heat in the pipe to the air near the pipe in a very fast way. In the distillation process, the device that converts the gas or vapor into a liquid state is called a condenser, but all condensers operate by taking away the heat of the gas or vapor. In the condenser of automobiles, the refrigerant enters the evaporator, the pressure is reduced, and the high-pressure gas becomes a low-pressure gas. This process absorbs heat, so the surface temperature of the evaporator is very low, and then the cold air can be blown out through the fan. Condensation The compressor is the high-pressure, high-temperature refrigerant from the compressor, which is cooled to high pressure and low temperature. Then it is vaporized by capillary tube and evaporated in the evaporator.
Condensers can be divided into four categories: water-cooled, evaporative, air-cooled, and water-sprayed condensers according to their different cooling media：
The water-cooled condenser uses water as the cooling medium, and the temperature rise of the water takes away the heat of condensation. Cooling water is generally used in circulation, but a cooling tower or a cold pool should be installed in the system. Water-cooled condensers can be divided into vertical shell-and-tube and horizontal shell-and-tube condensers according to their different structures. There are many kinds of tube type and casing type, the most common is shell and tube type condenser.
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 systems. Vertical condenser is mainly composed of shell (cylinder), tube sheet and tube bundle.
The refrigerant vapor enters the gap between the tube bundles from the steam inlet at 2/3 of the height of the cylinder, and the cooling water in the tube and the high-temperature refrigerant vapor outside the tube conduct heat exchange through the tube wall, so that the refrigerant vapor is condensed into liquid. It gradually flows down to the bottom of the condenser and flows into the liquid reservoir through the liquid outlet pipe. The heat-absorbing water is discharged into the lower concrete pool, and then pumped into the cooling water tower for cooling and recycling.
In order to distribute the cooling water evenly to each nozzle, the water distribution tank at the top of the condenser is provided with a water distribution plate, and each nozzle on the top of the tube bundle is equipped with a deflector with a chute, so that the cooling water can flow along the inside of the tube. The wall flows downward with a film-like water layer, which can improve heat transfer and save water. In addition, the shell of the vertical condenser is also provided with pipe joints such as pressure equalizing pipe, pressure gauge, safety valve and air discharge pipe, so as to be connected with corresponding pipelines and equipment.
The main features of vertical condensers are:
1. Due to the large cooling flow and high flow rate, the heat transfer coefficient is high.
2. The vertical installation occupies a small area and can be installed outdoors.
3. The cooling water flows straight and has a large flow rate, so the water quality is not high, and the general water source 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, because the temperature rise of the cooling water in the vertical condenser is generally only 2 to 4 °C, and the logarithmic average temperature difference is generally about 5 to 6 °C, the water consumption is relatively large. And because the equipment is placed in the air, the pipes are easily corroded, and the leakage is easier to find.
2. Horizontal shell and tube condenser
The horizontal condenser and the vertical condenser have a similar shell structure, but there are many differences in general. The main difference is the horizontal placement of the shell and the multi-channel flow of water. The outer surfaces of the tube sheets at both ends of the horizontal condenser are closed with an end cap, and the end caps are cast with water-dividing ribs designed to cooperate with each other, dividing the entire tube bundle into several tube groups. Therefore, the cooling water enters from the lower part of one end cover, flows through each tube group in sequence, and finally flows out from the upper part of the same end cover, which requires 4 to 10 round trips. This can not only increase the flow rate of the cooling water in the tube, thereby improving the heat transfer coefficient, but also make the high-temperature refrigerant vapor enter the tube bundle from the air inlet tube at the upper part of the shell to conduct sufficient heat exchange with the cooling water in the tube.
The condensed liquid flows into the liquid storage tank from the lower liquid outlet pipe. There is also a vent valve and a water drain cock on the other end cover of the condenser. The exhaust valve is on the upper part and is opened when the condenser is put into operation to discharge the air in the cooling water pipe and make the cooling water flow smoothly. Remember not to confuse it with the air release valve to avoid accidents. The drain cock is used to drain the water stored in the cooling water pipe when the condenser is out of use to avoid freezing and cracking of the condenser due to water freezing in winter. On the shell of the horizontal condenser, there are also several pipe joints such as air inlet, liquid outlet, pressure equalizing pipe, air discharge pipe, safety valve, pressure gauge joint and oil discharge pipe which are connected with other equipment in the system.
Horizontal condenser is not only widely used in ammonia refrigeration system, but also can be used in Freon refrigeration system, but its structure is slightly different. The cooling pipe of ammonia horizontal condenser adopts smooth seamless steel pipe, while 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, and only use a few rows of tubes at the bottom of the condenser to double as a liquid storage tank.
For horizontal and vertical condensers, in addition to the different placement positions and water distribution, the water temperature rise and water consumption are also different. The cooling water of the vertical condenser flows down the inner wall of the tube by gravity, and it can only be a single stroke. Therefore, to obtain a large enough heat transfer coefficient K, a large amount of water must be used. The horizontal condenser uses a pump to send the cooling water into the cooling pipe, so it can be made into a multi-stroke condenser, and the cooling water can obtain a sufficiently large flow rate and temperature rise (Δt=4～6℃). Therefore, the horizontal condenser can obtain a sufficiently large K value with a small amount of cooling water.
However, if the flow rate is excessively increased, the heat transfer coefficient K value does not increase much, but the power consumption of the cooling water pump increases significantly, so the cooling water flow rate of the ammonia horizontal condenser is generally about 1m/s. The cooling water flow rate of the device is mostly 1.5 ~ 2m/s. The horizontal condenser has high heat transfer coefficient, small cooling water consumption, compact structure and convenient operation and management. However, the quality of the cooling water is required to be good, and it is inconvenient to clean the scale, and it is not easy to find the leakage.
The vapor of the refrigerant enters the cavity between the inner and outer tubes from above, condenses on the outer surface of the inner tube, and the liquid flows down in sequence at the bottom of the outer tube, and flows into the liquid receiver from the lower end. The cooling water enters from the lower part of the condenser and flows out from the upper part through each row of inner pipes in turn, in a countercurrent manner with the refrigerant.
The advantages of this type of condenser are simple structure, easy to manufacture, and because it is a single-tube condensation, the medium flows in the opposite direction, so the heat transfer effect is good. When the water flow rate is 1 ~ 2m/s, the heat transfer coefficient can reach 800kcal/(m2h °C). The disadvantage is that the metal consumption is large, and when the number of longitudinal pipes is large, the lower pipes are filled with more liquid, so that the heat transfer area cannot be fully utilized. In addition, the compactness is poor, cleaning is difficult, and a large number of connecting elbows are required. Therefore, such condensers have been rarely used in ammonia refrigeration plants.
