DE3224385A1 - Lossless oil return for flooded evaporator - Google Patents

Abstract

The invention makes it possible to operate the evaporator in a flooded condition in combination with a level controller in any refrigeration system with oil-lubricated compressor and oil-soluble refrigerant, and periodically to perform the indispensable oil return without loss. For the purpose of oil return, the evaporator is taken out of operation by shutting off the refrigerant feed. The compressor continues to run and sucks refrigerant vapour from the evaporator until the refrigerant filling of the evaporator has been evaporated. At the end of the process of sucking empty, the compressor is switched off by a pressure regulator. The refrigerator oil displaced during normal operation into the evaporator collects during the process of sucking dry in the lowest place of the evaporator as pure oil or as an oil-refrigerant mixture and after the end of the process of sucking dry is fed back from there via a valve with a natural gradient to the oil sump of the compressor or to the oil collector. Since the evaporation of the refrigerant filling during the process of sucking dry occurs with entirely normal cold production in the evaporator, this kind of oil return takes place losslessly.

Description

Prof. Jürgen Lettner * /
Kropbacher Weg 41
6300 casting

To the

German Patent Office

Zweibrückenstrasse 12

8000 Munich

Re .; Patent application

Applicant; Prof. Jürgen Lettner, Kropbacher Weg 41, 6300 Giessen

Lossless oil return when the evaporator is flooded

The invention relates to the lossless return of the in the
Flooded evaporator relocated refrigerating machine oil to the oil sump of the compressor or to the oil collector.

In the case of oil-lubricated refrigeration compressors, despite the downstream oil separators, it is impossible to prevent the constant flow of oil
from the compressor to the evaporator. This oil must be returned from there by special measures continuously or periodically to the oil sump of the compressor or to the oil collector, otherwise the compressor would suffer from a lack of oil due to the shifting of oil and would suffer mechanical damage. In refrigeration technology, the dry evaporator or forced flow evaporator is very often used, in which the refrigerant is throttled in the thermostatic expansion valve (TEV)

predominantly liquid enters the evaporator and after one time Run-through at the end as superheated steam escapes.

Appropriate refrigerant conduction in the evaporator ensures that the oil displaced into the evaporator reaches the evaporator outlet and, if the suction line is laid correctly, is continuously returned to the oil sump of the compressor. The overheating of the refrigerant vapor at the end of the evaporator is unavoidable as a control variable of the TEV and can be up to 12 ^° C. This results in the disadvantage that the evaporator has to be operated with a relatively large temperature difference (At) because of its control loop and that this temperature difference (t) is largely retained, even if the cooling capacity approaches 0 in partial load operation. In the case of a flooded evaporator with refrigerant feed via a level controller, the disadvantage of the excessive temperature difference (At) is avoided, because in this operating mode the smallest possible temperature difference (At) is always set depending on the current operating conditions. If the cooling capacity approaches 0 in partial load operation, then the temperature difference (At) also approaches 0. However, according to the state of the art, this evaporator operation is subject to the considerable deficiency that the oil shifted into the evaporator cannot be returned to the compressor without losses. because it is dissolved from the liquid refrigerant in the evaporator and / or as undissolved oil floats on the liquid refrigerant. In order to be able to return the oil from the evaporator to the compressor, a partial flow of liquid refrigerant (up to 10% of the refrigerant throughput) with oil is constantly diverted from the area of the evaporator with the greatest oil enrichment. The refrigerant is evaporated from this partial flow by means of a special heat supply, and the remaining oil is returned to the compressor. Since the branched off partial flow is not involved in the generation of cold, it represents a pure loss: In this case, the advantages of flooded evaporator operation are bought with a reduction in cooling capacity of up to 10%.

The invention is based on the object, the extremely advantageous Operation of the flooded evaporator with a loss

allow loose oil return.

According to the invention, this object is achieved as follows: The evaporator is operated with the aid of a level regulator flooded and for the purpose of oil return by blocking the refrigerant feed decommissioned. The compressor continues to run and sucks refrigerant vapor from the evaporator until the entire refrigerant charge of the evaporator has evaporated. At the end of this evacuation process, the pressure in the evaporator drops sharply and the compressor is switched off pressostatically. The refrigeration machine oil shifted into the evaporator during normal operation During the evacuation process, it collects at the lowest point of the evaporator as pure oil or as an oil-refrigerant mixture and becomes vo "there after the end of the vacuum process returned via a valve with a natural gradient to the oil sump of the compressor or to the oil collector. Because the evaporation the refrigerant charge during the evacuation process with a completely normal or beneficial refrigeration in the Is connected to the evaporator, this type of oil return takes place lossless.

The advantages achieved with the invention are in particular that in every refrigeration system with an oil-lubricated compressor and oil-soluble refrigerant the evaporator is operated in combination with a flooded level regulator and the indispensable oil return can be carried out periodically without losses. As opposed to the flooded operated evaporator the dry evaporator only offers advantages, this invention is of particular importance in terms of energy management.

Claims (1)

Patent to sayings Lossless oil return when the evaporator is flooded, characterized in that after blocking the refrigerant feed and evacuating the evaporator in vapor form by the compressor that collected at the lowest point in the evaporator oil or oil-refrigerant mixture via a valve to the oil sump of the Compressor or to the oil collector. 2. Lossless oil return after flooded evaporator Claim 1, characterized in that the evaporator has several deepest points and the oil is returned from all the deepest points via a collecting line and a common valve or via several Single valves. 3. Lossless oil return after flooded evaporator Claims 1 and 2, characterized in that the valves mentioned in claims 1 and 2 are closed during normal operation of the evaporator and are only opened for the oil return. 4. Lossless oil return after flooded evaporator Claims 1 to 3, characterized in that the oil return takes place when the evaporator is locked in the context of the refrigeration capacity control the refrigerant supply has been taken out of operation and evacuated in vapor form by the compressor. 5. Lossless oil return after flooded evaporator Claims 1 to 4, - £ - " characterized in that during prolonged operation or in continuous operation of the evaporator, the oil return will then take place at the latest must if the maximum permissible amount of oil has been shifted from the compressor to the evaporator. For this purpose the vaporizer is used temporarily shut down by blocking the refrigerant feed and sucked empty in vapor form by the compressor. 6. Lossless oil return after flooded evaporator Claims 1 to 5, characterized in that the evaporator can only be put back into operation by appropriate locking when the oil return has ended. 7. Lossless oil return after flooded evaporator Claims 1 to 6, characterized in that the oil return is manual or in automatic switching. 8. Lossless oil return after flooded evaporator Claims 1 to 7, characterized in that the evaporator with standing refrigerant charge and natural vapor bubble buoyancy, with natural circulation of the refrigerant or with forced circulation of the refrigerant. 9. Lossless oil return after flooded evaporator Claims 1 to 8, characterized in that the evaporator has the smallest possible volume on the refrigerant side with regard to the evacuation process having. 0O. Lossless oil return after flooded evaporator Claims 1 to 9, characterized in that the oil return in the same Type occurs when several evaporators and / or several compressors belong to the refrigeration system. 11. Lossless oil return after flooded evaporator Claims 1 to 10, characterized in that the evaporator (s) are not in a refrigeration system but in another system - e.g. a heat pump - is (are) used and the working medium in this system may not be called refrigerant but a different name leads.