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Freeze dryer parts and usage analysis

Technical Knowledge 2015-07-07 09:47:42
The freeze dryer consists of a refrigeration system, a vacuum system, a heating system, and an electrical instrument control system. The main components are drying ovens, condensers, refrigeration units, vacuum pumps, heating/cooling devices, etc. It works by freezing the dried item below the triple point temperature and then sublimating the solid water (ice) in the item to water vapor under vacuum conditions, removing it from the item and drying the item.

1. Compressor

Most of the refrigeration compressors used in the dryers are medium-high temperature type fully sealed reciprocating compressors, which are characterized by compact structure, small size, light weight, low vibration, low noise and high energy efficiency. Since the motor of the hermetic compressor and the main body of the compressor are sealed in a steel casing, the motor is operated in a gaseous environment of the refrigerant, and the cooling condition is good and the service life is long. A specified amount of lubricating oil is stored in the lower part of the casing, and when the compressor is in operation, the parts are automatically supplied with oil, and it is not necessary to add lubricating oil at ordinary times.

2. heat exchange, evaporator

The main function of heat exchange in the dryer is to use the cold volume carried by the compressed air cooled by the evaporator (for most users, this part of the cold is waste cold) and use this part of the cooling to cool and carry a large amount of The higher temperature compressed air of water vapor reduces the heat load of the refrigeration system of the cold dryer and saves energy. On the other hand, the temperature of the low-temperature compressed air in the heat exchanger is increased, so that the outer wall of the exhaust pipe does not cause dew condensation due to the low temperature.

3. condenser, secondary condenser (precooling regenerator)

In the cold dryer, the function of the condenser is to cool the high-pressure, superheated refrigerant vapor discharged from the refrigerant compressor into a liquid refrigerant, so that the refrigeration process can be continuously performed. The heat discharged from the condenser includes the heat that the refrigerant draws from the evaporator and the heat that is converted from the compression work. Therefore, the load of the condenser is larger than that of the evaporator. The condenser in the dryer is divided into an air-cooled (air-cooled condenser) and a water-cooled (water-cooled condenser).

4. cyclone separator (gas water separator)

The cyclone separator is also an inertial separator and is used more for gas-solid separation. After the compressed air enters the separator in the direction of the tangential direction of the cylinder wall, the rotation is generated therein, and the water droplets mixed in the gas also rotate together to generate centrifugal force. The centrifugal force generated by the large-sized water droplets is large, and the large water droplets move to the outer wall under the centrifugal force. After hitting the outer wall (also the baffle), it accumulates and grows up and separates from the gas.

5. hot gas bypass valve

When the compressed air is cooled in the evaporator, a large amount of condensed water is precipitated. In order to prevent this from happening, the evaporation temperature of the refrigerant must be controlled. The simple and effective measure is to add a hot gas bypass valve between the condenser and the evaporator, and the pressure pipe of the hot gas bypass valve is directly connected with the evaporation pressure. When the evaporation pressure is lower than a certain level, the hot gas bypass valve is automatically opened, and the high-temperature refrigerant vapor in the condenser directly enters the evaporator to raise the evaporation temperature and avoid the ice blockage phenomenon.

6, thermal expansion valve or capillary (throttle valve)

The expansion valve (capillary) is the throttling mechanism of the refrigeration system. In a cold dryer, the supply of evaporator refrigerant and its regulator are achieved by a throttling mechanism. The throttling mechanism causes refrigeration to enter the evaporator from the high temperature and high pressure liquid. Due to its simple structure and stable operation, the capillary tube has been widely used in small-sized cold dryers.

7. automatic drain valve

In the refrigerating dryer, the condensed condensed water should be discharged out of the equipment in time to avoid the increase of air moisture content due to the condensed water discharge. In order to facilitate the discharge of condensed water, the equipment is equipped with an automatic drain valve when the drain valve is stored. When the water level in the water cup does not reach a certain height, the pressure of the compressed air will press the float ball to close the drain hole, and no air leakage will occur.

8. drying filter

In the running refrigeration unit, due to impurities such as moisture, solid powder, and dirt in the refrigerant and the refrigerating oil, the throttle hole of the throttle structure may be dirty when the condition is severe. Therefore, a dry filter must be installed before the refrigerant supply pipe. In addition, trace moisture in the refrigerant is the most harmful to the refrigeration system. Drying of refrigerants, refrigeration oils and evaporators, condensers and piping is extremely important.

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