Applications of Plate Heat Exchanger in Different Refrigeration System

                                The Flow Chart For Refrigeration System

Hofmann heat exchanger

Plate heat exchanger is efficient and compact heat exchanger equipment, has been widely used in the refrigeration system, and is indispensable refrigeration system equipment that can be used as a condenser, evaporator, regenerator and intercooler for change thermal equipment. Compared with the traditional shell and tube heat exchanger, with high heat transfer efficiency (2 to 4 times of the traditional shell and tube heat exchanger), energy saving, economical, compact structure, easy to disassemble and so on. So it is widely used in refrigeration systems. However, if the plate heat exchanger in different refrigeration systems cannot get the correct use and maintenance, it cannot play its role and use normally, which is not only diseconomy, but influence production to bring economic losses to the enterprises.

1 plate heat exchanger in ammonia refrigeration system applications

1.1 working conditions

1.2 Problems and Improvements

(1) Dirty block.

In the ammonia refrigeration system the main reason caused by plate evaporator dirty block is due to the plate evaporator flow section is small, easy to plug, the second is the use of cold ~: l JCaCL. Solution added in the additional impurities into the system, impurities gathered in the plate evaporator, which cause blockage of the plate evaporator. In order to solve the problem about the slugging of the plate evaporator, it is necessary to reconstruct the CaCl2 solution system. Through establishing a special salt pool, after the initial precipitation of the impurities, then added to the system by the filter, most of the impurities are precipitated in the salt tank, regularly clean the salt pool and filter. Add a filter before the plate evaporator; further filter the impurities in the system to ensure the cleanliness of the CaCl2 solution.

(2) Ice blocking.

To the thermal physical properties of CaCl2 solution, a certain concentration of CaCl2 solution corresponds to a certain crystallization point and precipitation point, as the CaCl2 solution crystallization and precipitation, which cause evaporator blockage. The CaCl2 salt water density is 1.23 × 10kg / m at 25 ℃, so the CaCl2 solution must be in the range of 1.22 ~ 1.24 × 10kg / m in order to ensure the CaCl2 brine temperature is 22 ℃ ~28 ℃ with no crystallization and precipitation phenomenon, no blocking plate evaporator, so as to affect the heat transfer effect. Therefore, through strengthening the management, measuring the CaCl2 solution density regularly, recording CaCl2 solution density, it is not only to control the salt water density, but also to ensure that the temperature does not exceed the standard.

(3) Oil discharge difficulties, poor cooling effect.

The lubricating oil in the refrigeration compressor is separated more than 99% after the ammonia refrigerant passed through the oil separator, and the rest is accumulated in the refrigeration system with the condensation, throttling, evaporation and other processes, floated on the surface of the heat exchanger, to form oil film whose thermal resistance is too large to reduce transfer effect, increase energy consumption to affect the normal work of the system, so in the run after a period of time the cooling system should let out oil. However, because the plate evaporator is a low-temperature and low-pressure heat transfer equipment, and the unit flow section is very small, oil viscosity is high, difficult to let out, it must take ways of dripping water and heating for the evaporator of the oil-filled package and increase the number of oil drainage, generally 3 to 5 days and other effective measures to ensure the oil release effect of the evaporator, to improve the efficiency of evaporator heat transfer.

2 Plate heat exchangers in Freon 22 ~ 1J cold system applications

2.1 Working conditions

2.2 Existing problems and improvement measures

The main problem with the presence of plate evaporators in the Freon 2251.1 cold system is frost block. The main thing is that the system work normal under normal higher temperature, while in low temperature conditions (water inlet temperature is about 5 ℃, the unit is about to stop) it will be easy to have freeze blocking. When the plate evaporator is freeze blocking, the operating condition is rapid fluctuation, in a very short period of time it can froze the inside of the entire evaporator, to influence the cooling operation production.

The main reasons for the freezing the plate evaporators are as follows:

(1) Plate evaporator has a high heat transfer coefficient, the heat transfer temperature difference is generally 2 ~ 3 ℃, smaller than the shell and tube heat exchanger generally 5 ~ C. But because the long operation, evaporator internal fouling, dirty block, oil film, air and other causes, the plate evaporator heat exchange capacity is reduced, the heat transfer temperature increases, the actual operation of the process the evaporation temperature is low, evaporation temperature is lower than cold water. It is necessary to clean plate evaporator regularly to improve the heat transfer efficiency, and add the temperature control antifreeze blocking device, and strictly control the cold water outlet temperature, to ensure that the evaporation temperature is not lower than the cold water freezing point. Manage the relationship correctly among evaporation temperature, cold water freezing point, and cold water temperature. Appropriately increase the cold water flow and water exit temperature, to further reduce the possibility of frozen block.

(2) Plate heat exchanger is composed of very narrow cell channels, in each unit, cold water or refrigerant flow is very small, heat exchanger plate is very thin, heat exchange capacity is very strong. Due to the improper maintenance of the equipments, have no timely detection of the refrigeration system, the refrigerant reduced in the refrigeration system, or because the refrigerant supply is not normal. When the system refrigerant or refrigerant supply is not normal, the refrigerant distribution is uneven in the unit channel, at the same, the evaporation pressure is very low, and the limited number of units as the intense heat transfer will be blocked, and then the adjacent cell channel will get blocked, causing a chain reaction, until the whole evaporator is completely frozen. Therefore, to strengthen the daily maintenance of the refrigeration system, establish a sound equipment leak detection system, take the responsibility to the people to ensure that the refrigerant supply normal, and then increase drying protection devices of the plate evaporator. Once the cold pump outage or failure, resulting in insufficient water, the cutoff flow protection device do action, refrigeration compressor stopped, to avoid frozen blocking to ensure that the evaporator intact.

3 Plate heat exchanger in Freon 13 $ ~ J cold system applications

3.1 working conditions

3.2 Problems and Improvements

In the Freon 13 refrigeration system, the problems are:

(1) Oil return difficulties, cause unstable operation of the refrigeration compressor, having low oil pressure alarm, low suction pressure alarm and other failures. Cooling effect decreased, cooling difficulties, leading to serious damage to the compressor, they all impact the production seriously.

(2) Prone to leakage.

Main causes and improvement measures:

1) In the Freon 13 ~ lJ cold system, although more than 99% of the oil through the oil separator is separated, but there are still a small amount of lubricants with Freon l3 into the evaporator. Plate evaporator belongs to low temperature and low pressure heat transfer equipment, with small unit flow section, high oil viscosity, poor mobility, and because the Freon l3 and lubricants are basically insoluble, cannot use recycled. In the evaporator will accumulate more lubricants, affecting the evaporator heat transfer effect, while at the same time due to the lack of oil the compressor working conditions deteriorate, which will damage to the rotation. Therefore, it is necessary to increase the oil return device of the plate evaporator, carry out the oil return treatment on the evaporator regularly, and add a small amount of Freon 12 (usually not more than 5% of the Freon l3 filling amount) in the Freon l3 refrigeration system. In the refrigeration system equipment configuration should be made reasonable, to ensure that the height of the plate evaporator is above the compressor so as to increase the oil back effect.

2) The pressure capacity of the plate evaporator is relatively low. In the Freon 135U cold system, the evaporative pressure of the Freon l3 is low, and if the refrigerant in the system is not pumped out or pressed into the accumulator in time, Freon l3 in the gaseous state in the refrigeration system, and if the pressure relief valve failure, cannot be depressed in time, or the system added Freon l3 too much, they are all likely to cause high system pressure, more than the pressure capacity of the evaporator. If the Freon 11 is not pure, water content exceeded, it will produce hydrofluoric acid, hydrochloric acid to corrode the evaporator, and the evaporator is leakage. So in the Freon ll cycle system increase the dry filter device to remove water in the Freon 11.

In short, as long as in the practical application of the process we fully take into account the characteristics of the plate heat exchanger, to avoid weaknesses, and to strengthen the use of plate heat exchanger maintenance, with the improvement of technology, plate heat exchanger performance improvement, and its superior characteristics in the refrigeration system, their applications in the refrigeration industry will be more and more extensive.