FI67951C - FOERFARANDE FOER AVFROSTNING AV IS PAO KYLANLAEGGNINGARS FOERAONGAREYTA OCH ANORDNING FOER UTFOERANDE AV DETSAMMA - Google Patents

Description

67951

Method of melting the ice formed on the surface of the evaporator of a refrigeration machinery and apparatus for carrying it out - Method for defrosting the ice formed on the surface of the evaporator of the refrigeration machinery

A refrigeration evaporator is a device that binds heat from an object to be cooled, causing the temperature in the object to drop below the ambient temperature or the temperature naturally present in the object. Heat binding is based on the fact that the temperature of the heat-binding surface of the evaporator is lower than the temperature of the object to be cooled.

If the evaporator absorbs heat from the air of the object to be cooled, as is the case, for example, in cold rooms, refrigerators, freezers, blast chillers and the like, water from the air to be cooled may condense on the surface of the evaporator. This is always the case when the temperature of the surface to be cooled is lower than the dew point of the air to be cooled. If the temperature of the cooling surface is then lower than 0 ° C, the moisture bound from the air will condense on the evaporator surface as ice (frost).

The ice accumulating on the evaporator surface reduces the heat-binding capacity of the evaporator and, as a result, causes a decrease in the power of the refrigeration machine. Therefore, the frost must be removed from the evaporator surface at suitable intervals. If the air temperature of the object to be cooled is slightly higher than 0 ° C, the plant can be dimensioned so that the ice left on the evaporator surface melts on its own during machine shutdown times. In this case, no special defrosting system is required at all.

Often, however, the air temperature of the object to be cooled is so low that it cannot be used as an aid to defrosting. In this case, the ice must be removed from the surface of the evaporator either by mechanical means or

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2 67951 using any suitable smelting method. Mechanical de-icing can be used e.g. in some household freezers and in freezer compartments with smooth-tube steam traps.

Various smelting methods are well known and their operating principles have been widely described in the refrigeration literature. The most common forms of smelting are electric smelting, hot gas smelting, water smelting and hot air smelting, and combinations thereof. What all these melting methods have in common is that during the melting the evaporator is heated by applying thermal energy to it, whereby the temperature of the evaporator rises so high that the ice accumulating on the surface of the evaporator melts.

In all the above-mentioned smelting forms, the energy required for smelting is taken from outside the machinery, with the exception of hot gas smelting and a form of water smelting. In all said smelting systems, the smelting energy is also transferred in the form of losses to the air of the object to be cooled during smelting, which is why all said smelting methods also increase the need for cooling capacity in the plant. None of the above-mentioned smelting methods reduces or increases the cooling capacity of the refrigeration machinery, except in some special cases of hot gas smelting.

The object of the present invention is to provide a defrosting method which reduces the amount of losses due to defrosting in the object to be cooled and further increases the cooling capacity of the refrigeration machinery during defrosting. The invention thus relates to a method and a device according to the features set out in claims 1 and 2. According to the method, the thermal energy required for defrosting is bound from the liquid refrigerant coming from the condenser 1 of the refrigeration machine through the liquid tank. which then subcools and, as a result, is able to bind a higher amount of heat per unit of circulating mass to be cooled than in a situation where the liquid refrigerant would not be subcooled.

The method is suitable for use in all refrigeration plants with at least two evaporators connected in parallel. The basic idea of the method is to change the piping of the machinery so that the liquid refrigerant is circulated through the piping of the evaporator to be melted at the condensing pressure before the liquid is fed to the expansion valves. The method resembles some hot-gas smelting methods in this respect, but differs substantially from them in the sense that, firstly, the load on the refrigeration unit 1 the time remains in the liquid state and its pressure is the same as the pressure in the liquid line.

The pipe connection of the defrosting system of the two evaporators is shown in Figure 1. The solenoid valves required for defrosting are (A), (B), (C), (D) and (E). The connection also includes non-return valves (T1) and (T2), the flow directions of which are marked with arrows. The fusible evaporators are (I) and (II).

During normal operation of the machine, the solenoid valves (A) and (C) are closed and the other solenoid valves are open. The refrigerant compressed by the compressor flows as high-pressure steam to the condenser and liquefies there. The liquid refrigerant flows through the tank into the liquid line and from there through the liquid pipe of the droplet separator-heat exchanger combination to the solenoid valve (B) and further through the evaporator valves (P1) and (P2) to the evaporators (I) and (II). In these, the refrigerant evaporates and binds heat from the object to be cooled. The refrigerant vapor formed flows further through the jacket of the droplet separator-heat exchanger combination to the suction line of the compressor. The evaporators thus operate in parallel.

To review defrosting, we assume that the evaporator (I) in Figure 1 must be defrosted. The defrost connection is performed as follows:

Solenoid valves (B) and (D) are closed and at the same time solenoid valve (A) is opened. The liquid refrigerant now flows after the hinge separator-heat exchanger combination through the solenoid valve (A) to the evaporator (I), filling it. The liquid, the inlet temperature of which is usually higher than + 25 ° C, cools when it encounters the cold structure of the evaporator (I) and, on cooling, transfers heat to the evaporator (I), the temperature of which begins to rise. At the same time, the pressure of the evaporator (I) rises to the pressure prevailing in the liquid line.

When the solenoid valve (B) is closed, the pressure in the inlet line of the expansion valves drops lower than the normal pressure in the liquid line. As a result, the non-return valve (T1) opens, allowing the liquid refrigerant to flow from the evaporator (I) to the expansion valve (P2) undercooling. As a result, the evaporator (ΙΪ) normally cools when the evaporator (I) is defrosted. Its cooling capacity only is higher than normal because the refrigerant is subcooled.

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As defrost approaches, the solenoid valve (A) closes under the control of either the defrost clock or the defrost protection thermostat. The other valves are connected as above. The evaporator (II) can then still receive the refrigerant only from the evaporator (I), the refrigerant charge of which is emptied because the solenoid valve (A) of the incoming refrigerant is closed. The result is a drop in pressure in the evaporator (I). When the pressure has dropped to the set value of the pressure switch (Kl), the solenoid valves (B) and (D) open, whereupon the plant starts to operate according to the normal cooling connection.

The melting of the evaporator (II) is carried out in a similar manner, taking into account that the coupling is symmetrical.

A small charge of liquid refrigerant remains in the molten evaporator, which, if it enters the compressor through the suction line, could cause damage to the compressor. To avoid this, the machinery has a droplet separator-heat exchanger combination which evaporates the liquid refrigerant from the suction line while pre-cooling the liquid refrigerant in the liquid line.

If there are more than 2 evaporators to be melted, the evaporators are melted alternately so that when each evaporator is melted, the solenoid valve in the suction line of the respective evaporator and the solenoid valve in the main fluid line are closed and the liquid in the evaporator liquid is opened. At the end of defrosting, always close the liquid inlet solenoid valve first and when the pressure has dropped sufficiently low, open the solenoid valve of the melted evaporator suction line! and main line solenoid valve !.

Claims (4)

5 67951 A method for melting ice accumulating in evaporators connected in parallel to a compressor refrigeration unit alternately from different evaporators, characterized in that the flow of liquefied refrigerant is led to the operating evaporators in operation via an evaporator to be melted, bypassing its expansion valve. Apparatus for carrying out the method according to claim 1 in an apparatus comprising two evaporators (I, II) with expansion valves (P 1, P 2) connected in parallel, a compressor, a condenser and an associated conventional gas (B) to shut off the liquid flow to the evaporators (I, II), to selectively close the suction lines of the evaporators from the valves (D, E), from the branch lines optionally openable by the valves (A, B) to conduct the refrigerant to the evaporators (I, II) . Apparatus according to claim 2, characterized in that it comprises a droplet separator heat exchanger, through which the liquid phase or the gas phase of the refrigerant is passed in heat transfer connection with one another. Apparatus according to Claim 2 or 3, characterized in that the expansion valves (P1 # P2) and the shut-off valve (B) are controlled by pressure switches which sense the pressure in the suction lines of the evaporators (I, II).