How the evaporator works

There are many types of evaporators, which can be divided into four categories. They work differently.

Here's a detailed description:

First, horizontal evaporator
1. Its structure is basically similar to that of horizontal shell and tube condenser. Can be divided into two categories: shell and tube evaporator and dry evaporator. Horizontal shell and tube evaporator is widely used in closed brine circulation system. Its main features are: compact structure, good contact between liquid and heat transfer surface, high heat transfer coefficient. However, it requires a large amount of refrigerant, and the liquid column has a certain effect on the evaporation temperature. When the salt water concentration is reduced or the salt pump is turned off, the salt water may be frozen in the test tube. If the refrigerant is freon, it is difficult to return to the compressor. In addition, the cleaning should stop working.
2, the main difference between dry freon evaporator is that the refrigerant flows in the pipe, and the refrigerant flows outside the pipe. The bottom of the throttled freon liquid side cap enters the evaporator, and after several processes the upper end cap, the refrigerant in the tube flows and evaporates, so the wall consists of a part of the steam, so the complete liquid type is better than its heat transfer effect. However, it has no liquid column to affect the evaporation temperature, and because of the high freon flow rate (greater than 4m/s), oil recovery is better. In addition, because the tube is filled with a large amount of refrigerant, the risk of freezing is reduced. The refrigerant filling amount of the evaporator is only 1/2 ~ l/3 or less, so it is called "dry evaporator".
Two, vertical tube evaporator.
The common feature of vertical tube and spiral tube evaporators is the refrigerant evaporation tube, the casing immersed in the evaporator tube is filled with refrigerant (or tank), in order to ensure that the load cooling circulates in the box at a certain speed, the longitudinal partition is welded in the cabinet and equipped with a spiral mixer. The coolant speed is generally 0.3 ~ 0.7m/s to enhance heat transfer.
These two evaporators can only be used in open circulation systems, so the refrigerant must be a non-volatile substance, usually used for salt water and water. For example, in salt water, the evaporator tube is easy to oxidize, and the salt water is easy to absorb water and reduce the concentration. These two evaporators can directly observe the flow of refrigerant and are widely used in brine refrigeration systems, with ammonia as the refrigerant.
Three, cooling discharge pipe.
Cooling drains are evaporators used to cool the air. It is widely used in cryogenic refrigeration, cooling pipes and evaporative coolants, and as a heat transfer medium for cooling air as natural convection.
The main advantages of cooling drainage tubes are simple structure, ease of manufacture, and less dry consumption of non-bagged food. However, the low heat transfer coefficient of the drainage tube and the difficulty of operation during defrosting are not conducive to automation. For the ammonia direct cooling system, seamless steel pipe welding is used. For freon systems, it is mainly used for coil or disc finned copper tube groups.
1. Coil.
Can be used to supply liquid or ammonia pumps. Single and double row wall tubes can be used to reduce the type of feed liquid inlet liquid ammonia pump system and gravity system, exhaust pipe and single snake tube can also be used for ammonia pump top-down hydraulic system and thermal expansion valve hydraulic system.
The advantages of coil tube are simple structure, convenient production, small liquid storage and strong applicability. The main disadvantage is that the steam generated in the lower part of the drainage tube cannot be extracted in time. It must be discharged after the entire length of the drain pipe, so the heat transfer coefficient is small, and the steam liquid flow resistance is large.
The U-shaped drainage tube commonly used in U-shaped drainage tube is composed of two or four smooth seamless steel tubes.
The advantages of U-shaped pipe top are uniform frost degree, convenient production and installation, small liquid amount, accounting for about 50% of its volume, suitable for gravity liquid supply system and ammonia pumping ammonia refrigeration system, and more widely used in cold storage. However, it has more efficient storage space, and the upper layer is not easy to thaw.
4. Cold fan (air cooler)

The chiller is mostly a complete set of equipment composed of axial fan and cooling pipe. It relies on the fan to force the air in the warehouse to flow through the cooling tube in the box for heat exchange, so that the air is cooled, so as to achieve the purpose of reducing the temperature of the warehouse.

According to the method used to cool the air, the chiller can be divided into dry type, wet type and dry and wet mixed type. Among them, the refrigerant or carrier refrigerant flows in the exhaust pipe and cools the air outside the pipe through the pipe wall. The spray refrigerant liquid is used for direct heat exchange with the air, which is called a wet chiller; In addition to the cooling pipe, the mixed chiller also has a spray device for carrying refrigerant. The following describes the dry air cooler widely used in cold storage at present.
Cold storage commonly used dry chiller according to its installation location can be divided into two types of ceiling type and floor type. They are composed of air cooling tubes, ventilation fans and defrosting devices, and the cooling tubes in the chiller are sleeve type. Large dry chillers are often floor type.