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What Is A Ammonia Dx Evaporator?
Jan 09, 2018

Liquid ammonia DX evaporator refrigeration is a very important part of the four components, low temperature condensate liquid through the evaporator, with the outside air heat exchange, gasification heat absorption, to achieve the cooling effect. 

Evaporator: The refrigerant evaporates at a lower temperature (evaporating temperature) at a lower pressure (evaporating pressure), absorbs the heat of the substance to be cooled, and is a device that delivers cooling to the outside.

Liquid ammonia DX evaporator principle

Ammonia from the liquid ammonia evaporator, low-temperature and low-pressure vapor is sucked into the compressor, compressed into high-pressure high-temperature superheated vapor, and then into the condenser. As the high temperature and high temperature overheated ammonia gas temperature higher than the temperature of its environment medium, and its pressure so that ammonia can be condensed into liquid state at room temperature, thus discharged to the condenser, cooled, condensed into high pressure ammonia solution. Ammonia liquid under high pressure and normal temperature passes through the expansion valve and depressurizes due to throttling. At the same time when the pressure is reduced, the ammonia liquid absorbs heat due to boiling to decrease its temperature correspondingly, thereby becoming a low pressure and low temperature ammonia liquid. The low-pressure low-temperature ammonia solution into the evaporator endothermic evaporation, you can make the surrounding air and material temperature drop to achieve the purpose of refrigeration. The low-pressure and low-temperature ammonia coming out of the evaporator re-enters the compressor to complete a refrigeration cycle. Then repeat the process. Cooling water is taken away from the condenser heat, and then recycled water cooling tower, cooled and recycled. Chilled water in the evaporator was cooled, chilled water pump to the use of cold equipment, heat exchange back to the evaporator cycle

Liquid ammonia DX evaporator classification

Liquid ammonia evaporator operating pressure sub-pressure, pressure and decompression 3 kinds. According to the movement of the solution in the evaporator points:

 ① cycle type. Boiling solution in the heating chamber several times by heating the surface, such as the Central circulation tube, hanging baskets, external heat, Columnar and forced circulation and so on. 

② one-way type. Boiling solution in the heating chamber through a heated surface, not circulating flow, the row discharge concentrate, such as rising film, falling film, stirring film and centrifugal film and so on.

 ③ direct contact type. Heating medium and solution in direct contact with heat transfer, such as submerged combustion evaporator. Evaporator in the operation process, to consume a lot of heating steam, in order to save heating steam, you can use multi-effect evaporation unit and steam recompression evaporator. Evaporation is widely used in chemical, light industry and other departments.

Liquid ammonia DX evaporator operation characteristics

Engineering, the evaporation process is only part of the solvent isolated from the solution, and solute remained in solution, therefore, liquid ammonia evaporator evaporation operation is a solution of volatile solvents and non-volatile solute separation process. Since the vaporization rate of the solvent depends on the heat transfer rate, the evaporation operation is a heat transfer process. The evaporation device is a heat transfer device. However, the evaporation operation is compared with the heat transfer process in general and has the following features:

1. The boiling point of the solution increases

Since the solution contains a non-volatile solute, the vapor pressure of the solution is lower than that of the pure solvent at the same temperature. That is, at the same pressure, the boiling point of the solution is higher than that of the pure solvent and the concentration of the solution is higher The more significant the impact.

2. Material and process characteristics

Materials in the concentration process, solutes or impurities often deposited on the heating surface, the precipitation of crystallization and the formation of scale layer, affecting heat transfer; some solute is heat-sensitive, high temperature residence time is too long and easy to degenerate; Some materials have greater corrosive Or higher viscosity and so on

3. Energy recovery

Evaporation process is a solvent evaporation process, due to the large latent heat of solvent vaporization, evaporation process is a large energy unit operation. Therefore, energy saving is an important issue that should be considered in the evaporation operation.

Liquid ammonia evaporator layout

The evaporation area of the ice bank evaporator is calculated in the same way as the other cold-room evaporators. Also available in accordance with the ice pool net area to match, generally according to a square meter area with 0.6 ~ 0.7m2 evaporation area. The temperature of the ice bank should be determined according to the type of ice stored. The temperature of the ice bank for storing brine ice should be -4 ° C. The ice bank temperature for storing ice should be -18 to -15 ° C. Refrigeration system in the design of the pipeline, it should be considered when the ice machine does not produce ice can still cool. Evaporator defrost mode can be used to mine manually.

In the setting of the evaporator for the building with a net height below 6m in the ice bank may not set the wall of the row of pipes, but the top row of pipes must be dispersed, building height of 6m or above 6m of the ice bank should be set up wall drain shall not be used wings Tube to prevent stacking ice crushing damage.