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1. What are the characteristics of domestically produced refrigerated dryers compared to imported ones? At present, domestic cold dryers differ little from imported ones in terms of the hardware components; international renowned brands are widely used for refrigeration compressors, related accessories, and refrigerants. In terms of suitability for users, domestic models generally outperform imported ones. This is because domestic manufacturers have fully taken into account the characteristics of local users when designing and manufacturing refrigerated dryers, especially regarding climatic conditions and routine maintenance requirements. For example, the cooling compressors of domestically produced cold dryers generally have a higher power output than those of imported units of the same specification, which effectively suits China’s vast territory and the significant temperature differences across different regions and seasons. Furthermore, domestic machines are also highly competitive in terms of price, and they offer unparalleled advantages in after-sales service. Therefore, domestic cold dryers are quite popular in the domestic market. Currently, the gap between domestically produced and imported refrigerated dryers is mainly reflected in the level of manufacturing processes; in particular, there are significant differences in aspects such as the cleanliness of refrigerant system piping, assembly, and welding. Additionally, imports now commonly use the environmentally friendly refrigerant R134a, which does not harm the atmospheric ozone layer; this is still difficult to achieve in domestically produced refrigerated dryers for the time being. 2. What are the advantages of cold dryers compared to adsorption dryers? Compared to adsorption dryers, refrigerated dryers have the following characteristics: ① There is no consumption of compressed air; for most users of compressed air, using a refrigerated dryer is more energy-efficient than using an adsorption dryer ； ②No valve wear ； ③There is no need to regularly add or replace the adsorbent ； ④Low operating noise ； ⑤Daily maintenance is simple – just clean the filter of the automatic drainer on time ； ⑥There are no special requirements for the pre-treatment of the gas source or the accompanying air compressor; a standard oil-water separator is sufficient to meet the refrigerated dryer’s requirements regarding the quality of the incoming air ； ⑦The refrigerated dryer has a “self-cleaning” effect on the exhaust gas; that is, the amount of solid impurities in the discharged gas is relatively low ； ⑧While the condensed water is discharged, some oil vapor also condenses into liquid oil mist and is discharged along with the condensed water. Compared to adsorption dryers, cold dryers can only achieve a \"pressure dew point\" of around 10°C when processing compressed air; as a result, the degree of drying of the gas is much lower than that achieved by adsorption dryers. In many application areas, cold dryers are not capable of meeting the requirements regarding the dryness level of the gas supply specified by the process. In the technical industry, a selection convention has been established: when the required “pressure dew point” is above zero, refrigerated dryers are the first choice; when the required “pressure dew point” is below zero, adsorption dryers are the only option. 3. How to obtain compressed air with an extremely low dew point? The dew point of compressed air after being processed by a refrigerated dryer can be around -20°C (at atmospheric pressure); after treatment with a desiccant dryer, it can reach below -60°C. However, for certain industries with extremely high requirements regarding air dryness (such as the microelectronics industry, which requires a dew point of -80°C), this is obviously still insufficient. The current approach advocated in the technical community is to connect a refrigerated dryer and a desiccant dryer in series. The refrigerated dryer serves as a pre-treatment device for the desiccant dryer; this significantly reduces the moisture content of the compressed air before it enters the desiccant dryer, thereby producing compressed air with an extremely low dew point. Furthermore, the lower the temperature of the compressed air entering the adsorption dryer, the lower the dew point of the compressed air obtained in the end. According to foreign sources, when the inlet temperature of the adsorption dryer is 2°C and molecular sieves are used as adsorbents, the dew point of the compressed air can drop below -100°C. This method is also widely used in the country. 4. What should be noted when using a cold dryer in conjunction with a piston air compressor? Piston air compressors provide gas supply in a discontinuous manner, generating airflow pulses during operation. Air flow pulses exert a strong and prolonged impact on various components of the air dryer, leading to a series of mechanical damages. Therefore, when an air dryer is used in conjunction with a reciprocating piston air compressor, a buffer receiver tank should be installed downstream of the compressor. 5. What precautions should be taken when using a refrigerated dryer? When using a cold dryer, the following points should be noted: ① The flow rate, pressure, and temperature of the compressed air must remain within the ranges specified on the nameplate ； ②The installation location should be well-ventilated with low dust levels; there must be sufficient space around the machine for heat dissipation and maintenance, and it cannot be installed outdoors to avoid rain and direct sunlight ； ③Cold dryers can generally be installed without a foundation, but the floor must be level ； ④It should be located as close as possible to the user point to avoid excessively long pipelines ； ⑤There should be no detectable corrosive gases in the surrounding environment; in particular, it must not be located in the same room as ammonia refrigeration equipment ； ⑥The filtration precision of the pre-filter for the refrigerated dryer should be appropriate; excessively high precision is unnecessary for the refrigerated dryer ； ⑦The inlet and outlet pipes for cooling water should be set up separately; in particular, the outlet pipe must not be shared with other water-cooling equipment, to prevent drainage obstruction caused by pressure differences ； ⑧Ensure that the automatic drainer remains unobstructed at all times ； ⑨Do not start the cold dryer continuously ； ⑩For the parameters related to the actual processing of compressed air by the cold dryer, especially when the inlet temperature and operating pressure do not match the specified values, corrections should be made using the \"correction factors\" provided in the manual, in order to avoid overloading the device. 6. What impact does an excessively high oil mist content in compressed air have on the operation of a refrigerated dryer? The oil content in the exhaust gas of air compressors varies. For example, the oil content in the exhaust gas of domestically produced piston-type air compressors with oil lubrication is 65–220 mg/m3, while that of compressors with reduced oil lubrication is 30–40 mg/m3. Even in the case of domestically produced so-called oil-free air compressors (which are actually semi-oil-free), the oil content in their exhaust gas is still 6–15 mg/m3 ； Sometimes, due to damage or failure of the oil-gas separator in the air compressor, the oil content in the compressor’s exhaust gas **increases**. Compressed air with a high oil content enters the cold dryer, where it forms a thick layer of oil film on the surface of the copper tubes in the heat exchanger. Since the heat transfer resistance of this oil film is 40 to 70 times greater than that of the copper tubes, it **reduces the heat transfer efficiency of the pre-cooler and evaporator**; in severe cases, it can prevent the cold dryer from functioning properly. This is manifested as a decrease in evaporation pressure accompanied by an increase in dew point, an abnormally high oil content in the exhaust gas of the cold dryer, and frequent clogging of the automatic drain by oil residues. In this case, even continuously replacing the oil removal filters in the cold dryer’s pipeline system is of no use; the elements of the precision oil removal filters will soon become clogged with oil residues and cannot remain functional for long. The best approach is to repair the air compressor and replace the oil-gas separator filter element, so that the oil content in its exhaust meets the normal factory specifications. ) 7. How should filters be properly configured in a cold dryer? Compressed air from the air source contains large amounts of liquid water, solid dust particles of various sizes, as well as oil contaminants and oil vapors. If these impurities are allowed to enter the cold dryer directly, it will deteriorate the performance of the cold dryer. For example, oil contamination can pollute the heat exchange copper tubes in the pre-cooler and evaporator, affecting heat exchange ； Liquid water increases the workload on the cold dryer, while solid impurities can easily clog the drainage holes. Therefore, it is generally required to install a pre-filter upstream of the air inlet of the cold dryer, which serves to filter out impurities and separate oil from water, in order to prevent the aforementioned issues from occurring. The filtration precision of a pre-filter for solid impurities does not need to be very high; 10–25 μm is generally sufficient. However, it is better if it has a higher efficiency in separating liquid water from oils. Whether to install a post-filter on the cold dryer should be determined by the user’s requirements regarding the quality of compressed air. For general power gas use, a high-precision main pipeline filter is sufficient. When higher gas purity is required, corresponding oil mist filters or activated carbon filters should be installed. 8. What should be done to keep the exhaust temperature of a cold dryer very low? In certain specialized industries, not only is compressed air with a very low pressure dew point (i.e., low moisture content) required, but the temperature of the compressed air also needs to be low; in such cases, the cold dryer is used as a \"dehumidifying cooling fan\". The measures taken at this time are: ① eliminating the pre-cooler (air-air heat exchanger), so that the compressed air cooled by the evaporator cannot be reheated; ② simultaneously analyzing the refrigeration system, and if necessary, increasing the power of the compressor as well as the heat exchange areas of the evaporator and condenser. (A practical and simple approach is to use larger-sized cold dryers without pre-coolers to handle gases with lower flow rates.) 9. What measures should a cold dryer take when the intake air temperature is too high? Inlet temperature is an important technical parameter for cold dryers, and all manufacturers impose strict limits on the maximum inlet temperature for such devices. A high inlet temperature not only leads to an increase in sensible heat but also raises the water vapor content in the compressed air. JB/JQ209010-88 specifies that the inlet temperature of a refrigerated dryer should not exceed 38°C, and many well-known foreign manufacturers of refrigerated dryers have similar regulations. Normally, when the exhaust temperature of the air compressor exceeds 38°C, a rear cooler must be installed downstream of the compressor to reduce the temperature of the compressed air to the specified value before it enters the post-treatment equipment. The current situation regarding domestic cold dryers is that the allowable inlet temperature for these devices is continuously increasing. For ordinary cold dryers without pre-coolers, this temperature started to rise from 40°C in the early 1990s, and now there are already ordinary cold dryers with an inlet temperature of 50°C. Regardless of whether there is any element of commercial hype, from a technical perspective, an increase in intake temperature reflects not only a rise in the \"apparent temperature\" of the gas but also an increase in its moisture content; the resulting increase in the load on the refrigerated dryer does not follow a simple linear relationship. If the increase in load is compensated by raising the power of the refrigeration compressor, it is far too costly; since at normal temperatures, using a rear cooler to lower the temperature of the compressed air is the most economical approach. A high-temperature inlet type cold dryer incorporates the rear cooling unit into the cold dryer without altering the refrigeration system, and the effect is very significant. 10. What other environmental requirements does a cold dryer have besides temperature? The ambient temperature has a significant impact on the operation of cold dryers. In addition, refrigerated dryers also have the following requirements regarding their surrounding environment: ① Ventilation: This is particularly necessary for air-cooled refrigerated dryers ； ②There shouldn’t be too much dust ； ③There must be no direct sources of radiant heat at the location where the cold dryer is used ； ④The air should not contain corrosive gases, and in particular, no ammonia should be detected. Because ammonia is in a water-containing environment. It has a strong corrosive effect on copper metal. Therefore, cold dryers should not be installed together with ammonia refrigeration equipment.