The defrosting of the cold storage is mainly due to the frost on the surface of the evaporator in the cold storage, which reduces the humidity in the cold storage, hinders the heat conduction of the pipeline, and affects the cooling effect. The cold storage defrosting measures mainly include:
hot gas defrosting
Directly passing hot gaseous condensing agent into the evaporator and flowing through the evaporator. When the cold storage temperature rises to 1 °C, the compressor is turned off. The temperature of the evaporator rises, which causes the surface frost layer to melt or peel off; the hot air melting is economical and reliable, and the maintenance and management is convenient, and its investment and construction are not difficult. However, there are many options for hot air defrosting. The usual method is to send the high pressure and high temperature gas discharged from the compressor into an evaporator to release the heat and defrosting, and let the condensed liquid enter another evaporator to absorb the heat and evaporate into a low temperature and low pressure gas. Go back to the compressor suction to complete a cycle.
Water spray defrosting
Regularly spray the water to cool the evaporator to prevent the formation of the frost layer; although the defrosting effect of the water spray defrosting is good, it is more suitable for the air cooler, which is difficult to operate for the evaporation coil. There is also a solution with a higher freezing point temperature, such as 5%—8% concentrated brine, to prevent frost formation.
Electrical defrost Electric heaters are heated to defrost.
Although it is simple and easy, according to the actual structure of the cold storage base and the use of the bottom, the construction difficulty of installing the heating wire is not small, and the failure rate is relatively high in the future, the maintenance management is difficult, and the economy is also poor.
There are many other cold storage defrosting methods, in addition to electrical defrosting, water defrosting and hot air defrosting, there are mechanical defrosting, etc. Mechanical defrosting is mainly using tools to manually defrost, the frost layer on the cold storage evaporating coil When it is necessary to remove, since the design cold storage has no automatic defrosting device, only manual defrosting can be performed, but there are many inconveniences.
Hot Fluoride Defrosting Device (Manual): This device is a simple defrost device developed according to the principle of hot fluorine defrost. It is now widely used in the refrigeration industry such as the ice industry and refrigeration. No solenoid valves are required. Scope Independent circulation system for single compressor and single evaporator. Not suitable for parallel, multi-stage, cascade units.
Advantages: the connection is simple, the installation operation is simple, the power supply is not required, the safety is not required, the storage is not required, the goods are not stored, the storage temperature is not frozen, and the inventory is cold and cold. The application of the refrigeration and refrigeration industry is 20 square meters to 800 square meters, and the small and medium-sized cold storage tube is defrosted. The effect of ice industrial equipment combined with two fin aluminum rows.
the best features of defrosting effect
1.manual control one-button switch, simple, reliable, safe, no equipment failure caused by misoperation.
2. Heating from the inside, the combination of the frost layer and the pipe wall can be melted, and the heat source is highly efficient.
3. the defrosting is clean and thorough, more than 80% of the frost layer is solid, and the effect is better with the 2-fin aluminum discharge evaporator.
4. according to the diagram directly installed on the condensing unit, simple pipe connection, no other special accessories.
5. according to the actual thickness of the thickness of the frost layer, generally used 30 to 150 minutes.
6. Compared with electric heating cream: high safety factor, low negative impact on cold temperature, and little impact on inventory and packaging.
The evaporator of the cold storage system should pay attention to maintenance. If the evaporator frosting will affect the normal use of the cold storage, how to defrost in time? Our cold storage installation expert overnight cooling tips you should pay attention to the points of the evaporator frosting will lead to increased thermal resistance, heat transfer coefficient decreased. For the chiller, the cross-sectional area of the air flow is reduced, the flow resistance is increased, and the power consumption is increased. Therefore, it should be defrosted in time.
The current cold storage schemes are as follows:
1. Manual frosting is simple and easy, and has little impact on the storage temperature, but the labor intensity is large, the defrosting is not thorough, and there are limitations.
2. The water is flushed, and the frost water is sprayed to the surface of the evaporator through the spraying device to melt the double layer, and then discharged by the drainage pipe. The scheme has high efficiency, simple operation procedure and small fluctuation of the storage temperature. From the energy point of view, the cooling capacity per square meter of evaporation area can reach 250-400kj. Water flushing also makes it easy to fog the interior of the warehouse, causing dripping water in the cold roof, which reduces the service life.
3. Hot air defrosting, using the heat released by the superheated steam discharged from the compressor to melt the double layer on the surface of the evaporator. Its characteristics are strong applicability and reasonable in energy utilization. For ammonia refrigeration system, the defrosting can also rush out the oil in the evaporator, but the defrosting time is longer, which has a certain influence on the storage temperature. The refrigeration system is complex.
4, electric heating and defrosting, using the heating element to heat the cold storage to defrost. The system is simple, easy to operate, easy to automate, but consumes a lot of power.
When the actual plan is determined, sometimes a defrosting scheme is used, and sometimes different schemes are combined. Such as cold storage shelf pipe, wall, top smooth pipe, you can use artificial combination of hot gas method, usually manual frosting, regular hot air defrost, to thoroughly understand the artificially sweeping frost is not easy to remove the frost and discharge the oil in the pipeline . The air blower is flushed with water and hot air. For more frosting, frequent defrost can be performed by hot air combined with water defrosting. When the refrigeration system of the cold storage is working, the surface temperature of the evaporator is usually below zero. Therefore, the evaporator is subject to frosting, and the frost layer has a large thermal resistance, so the necessary defrosting treatment is required when the frost is thick.
The evaporator of the cold storage is divided into wall-pipe type and fin type according to its structure, the wall-displacement type is natural convection heat transfer, the fin type is forced convection heat transfer, and the defrosting method wall-row tube type is generally manually manualized. Frost, fin type with electric heating cream.
Manual defrosting is more troublesome. It is necessary to manually defrost, clean the frost, and move the contents of the library. Usually, the user has to go to the defrosting for a long time or even a few months. When the defrosting, the frost layer is already thick. The thermal resistance of the layer has made the evaporator far from achieving refrigeration. Electric heating defrosting is one step further than manual manual defrosting, but limited to finned evaporators, wall-and-tube evaporators cannot be used.
The electric heating type should be inserted into the electric heating tube in the fin-type evaporator, and the electric heating tube should be placed in the water receiving tray. In order to remove the frost as soon as possible, the power of the electric heating tube cannot be selected too small, usually It is going to be a few kilowatts. The control method for the operation of the electric heating tube generally adopts the timing heating control. When heating, the electric heating tube transfers heat to the evaporator, and a part of the frost on the evaporation coil and the fin dissolves, and a part of the frost does not completely dissolve the falling water tray, and is heated and melted by the electric heating tube in the water receiving tray. This is a waste of electricity, and the cooling effect is very poor. Because the evaporator is full of frost, the heat exchange coefficient is extremely low.
Unusual cold storage defrosting method
1. For hot gas defrosting of small systems, the system and control method are simple, the defrosting speed is fast, uniform and safe, and the application range should be further expanded.
2. Pneumatic defrosting is especially suitable for refrigeration systems that require frequent defrosting. Although it is necessary to add special air source and air treatment equipment, as long as the utilization rate is high, the economy will be very good.
3. Ultrasonic defrosting is an obvious method of defrosting energy saving. The layout of ultrasonic generators should be further studied to improve the thoroughness of defrosting for engineering applications.
4, liquid refrigerant defrosting, cooling process and defrosting process at the same time, there is no additional energy consumption during defrosting, frost cooling is used for liquid refrigerant before the supercooling expansion valve, improve cooling efficiency so that the library temperature can be basically maintained The temperature of the liquid refrigerant is within the normal temperature range, and the temperature rise of the evaporator during the defrost is small, which has little effect on the deterioration of the heat transfer of the evaporator. The disadvantage is that the complicated control of the system is cumbersome.
During the defrosting time, it is generally regardless of temperature. The defrosting time is over, and then to the dripping time, the fan starts again. Your defrosting time should not be set too long, and the electric heating cream should not exceed 25 minutes. Try to achieve a reasonable defrosting. (The defrosting cycle is generally based on the power transmission time or the compressor startup time.) Some electronic temperature control also supports the defrosting end temperature. It ends the defrosting in two modes, 1 is time and 2 is kuwen. This generally uses 2 temperature probes.
In the daily use of the cold storage, it is necessary to regularly remove the frost on the cold storage. The excessive frost on the cold storage is not conducive to the normal use of the cold storage. In the paper, the details of the frost on the cold storage should be taken. Method to remove it? What are the common techniques?
1. Check the refrigerant and check if there is any bubble in the sight glass. If there is a bubble indicating insufficient, add refrigerant from the low pressure pipe.
2. Check if there is a gap in the cold storage plate near the frost exhaust pipe, resulting in leakage of cold. If there is a gap, seal it directly with glass glue or foaming agent.
3. Check the copper pipe for leaks, spray leak detection or soapy water to check for air bubbles.
4. the cause of the compressor itself, for example, high and low pressure gas, need to replace the valve, sent to the compressor repair shop for repair.
5. to see if it is close to the return to the place to pull, if it is, then leak detection, add refrigerant. In this case, the pipe is generally not placed horizontally. It is recommended to level with a level. Then there is not enough refrigerant charge, it may be that the refrigerant is added, or there is ice block in the pipeline.
Post time: Sep-26-2024