Application Analysis of Evaporator in Low Temperature Cold Storage

As one of the four major refrigeration components, the evaporator plays a vital role in the entire refrigeration system. Therefore, only when the compressor and the evaporator are reasonably matched can the entire refrigeration system play a better role. Therefore, the selection of the evaporator It is very important to match the whole refrigeration system. The two most common types of evaporators in low-temperature refrigerators are air coolers and exhaust pipes. The actual air coolers and exhaust pipes have their own advantages and disadvantages:

1. Enclosure structure

Whether the cold storage adopts civil construction or steel structure, the load-bearing of the top must be considered, which is called suspension load in design. When using seamless steel pipe to make the exhaust pipe, the design suspension load reference value is 70~80Kg/㎡; if using aluminum alloy pipe to make the top exhaust pipe, the design suspension load reference value is 40~50Kg/㎡; if the air cooler is used , only the suspension load of the cooling fan needs to be considered locally.

2. Refrigerant charge

The floor space of the air cooler is small, and the internal volume is relatively small, so the fluorine capacity of the air cooler does not account for a small proportion of the entire refrigeration system; the diameter of the exhaust pipes generally ranges from Φ22 to Φ38. The greater the increase in the fluorine capacity of the entire refrigeration system.

Generally, 2 to 4 times more Freon is added to the pipe warehouse than the fan warehouse. In the future, in the form of the rising price of Freon and the replacement of Freon, the cost of Freon is also a part that cannot be ignored.

3. Initial investment

From the evaporator selection alone, the initial investment of the aluminum exhaust pipe is generally larger than the initial investment of the air cooler. The overall cost of the system using the air cooler is about 15%~25% lower than that of the system using the aluminum exhaust pipe, and the larger the system, the more obvious the price difference between the two. Generally, the construction period of pipe production and hoisting is 3 to 4 times longer than that of installing air coolers. Therefore, the labor cost for pipe production and installation is much higher than that for air cooler installation. The low-temperature cold storage in developed countries uses air coolers to cool down, and this factor is also considered on the one hand (foreign labor costs are much higher than domestic ones).

4. Defrost method

At present, the common defrosting methods of cold storage air conditioners are: natural defrosting, water flushing, electric defrosting and hot fluorine defrosting. The automatic defrosting of the air cooler is relatively easy to achieve, and the defrosted water flows to the outside of the cold storage along with the defrosting downpipe of the air cooler. Aluminum alloy exhaust pipes are mostly used for hot fluorine defrosting, but when the exhaust pipes are distributed in the warehouse, the water droplets will fall down when defrosting. The cream is so flexible and convenient.

5. Power consumption later

Under the same other conditions, the forced convection of the air cooler relies on the motor-driven fan to work and the defrosting of the air cooler 1~2 times a day will generate a certain amount of power consumption; for the exhaust pipe, the exhaust pipe belongs to natural convection, and the general exhaust pipe Defrosting about twice a year, compared with the electricity consumption in the later period, the aluminum exhaust pipe is relatively less than the air cooler.

6. Cold storage capacity

The air cooler belongs to forced convection, and the cooling speed is fast; the aluminum exhaust pipe belongs to natural convection, and the cooling speed is relatively slow. Therefore, in the actual operation of the cold storage, if the matching of the main refrigeration equipment is basically the same, the start-up time of the compressor in the cooling fan storage and the exhaust pipe storage is similar.

The cold storage capacity of the aluminum exhaust pipes does not play much role in maintaining the overall storage temperature. The key role in maintaining the storage temperature is the storage envelope structure and thermal insulation practices, as well as the storage capacity of the stored goods. The low-temperature cold storage that adopts multi-layer, integral polyurethane foam spraying inside the civil frame will save much more electricity than the single-layer, steel structure, and polyurethane sandwich double-sided color steel plate assembled cold storage structure;

7. Dry consumption of goods

The main factors affecting the dry consumption of goods are: heat transfer temperature difference, wind speed, working time of evaporator and packaging method.

Generally speaking, the dry consumption of the goods stored in the cold storage using the air cooler is greater than that of the cold storage using the exhaust pipe. However, it should be noted that the main body of dry consumption refers to goods rather than cold storage or evaporator. Therefore, which evaporator is the most reasonable to use, the key question is what kind of goods are stored and how to pack them. Goods sealed in plastic bags do not need to consider dry consumption.

8. Utilization of funds

As mentioned earlier, the gap between the construction period of the air cooler and the exhaust pipe is long. The construction period of the exhaust pipe is long and the capital is occupied. The short construction period of the air cooler can be invested quickly, and the return on investment can be obtained earlier, leading the way. occupy the market. If the cold storage rent is about 3 yuan/day.㎡, the monthly rental return is not a small number.

9. Efficiency and quality stability

The air cooler is a mature product of stereotypes. It is assembled by the factory's specialized skilled workers and production lines, and the exhaust pipe is assembled on site. The assembly level of the workers has a great influence on the uniformity of the liquid supply of the exhaust pipe, and the uniformity of the liquid supply of the air cooler is relatively low. good.

The fault point of the air cooler is mainly the motor and electrical components as the running parts. As long as the well-known brand products are used, such as EBM, Xerox, Siemens, Schneider and other products, the failure rate is greatly reduced; and the exhaust pipe, especially the aluminum alloy exhaust pipe, Because the welding process requires high requirements and the rigidity is relatively poor, if the welding is not good, or if the force is uneven during hoisting, the probability of leakage of the exhaust pipe is very high. As more and more attention is paid to the safety of the refrigeration system, the quality control of equipment will become more and more standardized, and standardized production and management will become an insurmountable threshold for piping.

Note ①: Because the efficiency of the air cooler is higher than that of the exhaust pipe, and the compressors of the two systems start up at about the same time, the cold storage capacity can basically be ignored.