WO1982001935A1

WO1982001935A1 - A method and equipment for defrosting the vaporiser of compressor refrigeration machinery

Info

Publication number: WO1982001935A1
Application number: PCT/FI1981/000087
Authority: WO
Inventors: Oy Huurre; Veijo Tuominen; Juha Mentula; Raimo Makkonen; Rauno Savolainen
Original assignee: Oy Huurre
Priority date: 1980-11-26
Filing date: 1981-11-18
Publication date: 1982-06-10
Also published as: IT8149769A0; FI803668L; IT1172102B; FR2494822A1; FI68314B; FI68314C

Abstract

A method and an equipment is used for defrosting the vaporiser of compressor refrigerating machinery. The invention is intended for use in connection with so-called hot gas defrosting, in which frost and ice accumulated in the vaporiser (4) of the freezing machinery are periodically melted. In the first phase of the method a highly superheated refrigerant is led direct from the compressor (1) to the vaporiser (4). In the second phase the refrigerant which has given up its heat of superheat to the vaporiser (4) is removed from the vaporiser (4) in a superheated state close to the vapour saturation boundary curve so that the refrigerant does not condense in the vaporiser (4). In the next phase the refrigerant vapour pressure in the superheated area is reduced suitably at the compressor (1). Then the possible liquefied drops of refrigerant in the hot gas are vaporised and thus the passage of cold liquid material to the compressor (1) suction valve is eliminated. Defrosting is terminated, when ice formed on the surface of the vaporiser (4) has melted. Equipment comprises a by-pass pipe (8), through which the superheated refrigerant is led past the condenser (2) and pressure reducing means (3) direct to the vaporiser (4), and by a by-pass line (5) through which the refrigerant vapour is led from the vaporiser (4) to the compressor (1), in which the main suction line is closed. In addition the equipment comprises a possible control equipment (16) which terminates the defrosting period directly after the ice formed on the surface of the vaporiser (4) has melted. A pressure reducing device has been arranged to the by-pass line (5) the said device being preferably a fusion capillary (7) or the like.

Description

A method and equipment for defrosting the vapouriser of compressor refrigeration machinery

The invention relates to a method, particularly described in patent claim 1, for the defrosting of the vapouriser of compressor freezing machinery. In addition the invention relates to equipment for the realisation or application of the method. In particular the method and equipment are intended for use in connection with so-called hot gas defrosting, in which frost and ice accumulated in the vapouriser of the freezing machinery are periodically melted.

For defrosting a cold room vapouriser there are in accordance with known technique mostly used one or other of the following: 1) electric defrosting and 2) defrosting by hot refrigerant vapour.

In known electric defrosting equipment the melting device in an electric resistance separate from the ref rig era t ing machinery, the heating elements of which electric resistance are placed between the pipes of the vapouriser. The resistance develops a known quantity of heat for melting the ice accumulated in the vapouriser. Defrosting equipment of this type has the disadvantage that defrosting time is lengthy and a considerable amount of electrical energy is required, since the heating elements are placed between the vapouriser pipes. In this case in addition the refrigerated space warms up during defrosting, since part of the heat energy produced by the electric resistance is transmitted to the aforementioned space. The invention described herein belongs more nearly to the group of so-called hot gas defrosting methods. The most commonly used of these is a so-called reversed system, in which during defrosting the flow of refrigerant is arranged to take place in the opposite direction compared with its flow during refrigeration.

Thus the vapouriser acts during defrosting as a condenser and correspondingly the condenser acts during defrosting as a vapouriser. A system using this kind of hot gas defrosting is in itself quick and powerful. The disadvantage of the reversed system is, however, the constructional changes required in the equipment feeding the vapouriser and condenser, from which it follows that vapourisers and condensers of fixed construction are hot suitable for use. In addition the special valves required are expensive and liable to faults.

In known hot gas defrosting methods, in which the superheat and latent heat of vapourisation of the hot gas is used for defrosting, the partly liquefied circulating medium removed from the vapouriser must be vapourised before being led to the compressor. It is possible to carry out this re-vapourisation in many ways, as by means of a heat exchanger, electrically, of by using the other cooling vapouriser surface or by using the heat of a separate heat store, the liquid in which store is heated during the refrigeration circulation. The disadvantage of these vapourising methods is the expense and space requirements of the components required for defrosting.

In addition a hot gas defrosting method is known in which defrosting is accomplished using the superheat of the hot gas alone without condensing the vapour itself. The disadvantage of the method mentioned is the expense of the current flow control valve required to prevent condensat ion.

The object of the invention described herein is to present a method and equipment for defrosting the vapouriser of compressor refrigerating machinery, in which the disadvantages of known methods are obviated or eliminated. According to the invention the refrigerant is superheated during the whole derfosting time thus using only the superheat of the gas.

The method and equipment according to the invention are characterised in that which is presented in the appended patent claim characteristics section.

An embodiment of the invention with the method and equipment according to the patent claim results in a powerful and speedy defrosting method with low constructional costs and without comlicated and expensive control equipment.

The invention will now be described in the following by way of example with reference to the accompanying drawings, in which

Fig. 1 is a schematic representation of compressor refrigerating machinery in which are empodied according to the invention the defrosting method and equipment and

Fig. 2 shows the melting circulation in a refrigerant p-h diagram.

The diagram of Fig. 1 shows the four parts of the compressor cooling machinery, namely compressor 1, condenser 2 , pressure reducing device 3, and, situated in the cold space, the vapouriser 4, in which the cold material refrigerant circulation takes place according to arrow J.

Periodic defrosting of the vapouriser of the refrigerating machinery is effected by means of the defrosting circulation (arrow S) associated with the refrigerant circulation J . Defrosting circulation is accomplished by means of the strongly superheated vapour (refrigerant change of state 9-10 in Fig. 2) which is led through the by-pass pipe 8 past the condenser 2 and the pressure reducing device 3 direct to the vapouriser 4. The refrigerant line is closed by the valve 17 so as to lead the refrigerant to the defrosting line through the valve 18 which is simultaneously opened at the commencement of defrosting. The superheated vapour flowing through the vapouriser piping gives up its superheat, which melts the ice accumulated on the pipes in layers powerfully and quickly, for all the heat is transferred from the interior of the pipe to the layer of frost and ice on the outside. The heat load imposed on the cold space remains small since the defrosting heat is used almost entirely for melting the frost and ice. Hence the refrigerated products are not subjected to a disturbing increase of temperature.

Refrigerant change of state in the vapouriser is shown in Fig. 2 by line 10-11, from which it will be observed that the final state of the refrigerant after the vapouriser is in the superheated area close to the saturated vapour boundary curve 15.

The main suction line between the vapouriser 4 and the compressor 1 is provided with a bypass line 5. which is connected to the suction side of the compressor 1. The main suction line is closed by the valve 6 during defrosting, so that the refrigerant which has given up its superheat is led from the vapouriser 4 along the bypass line 5 to the compressor 1. The maine part of the by-pass line is formed by the fusion capillary tube 7, the function of which is to vapourise a possible liquefied part of the current of refrigerant and to reduce the pressure of the current suitably for the suction side of the compressor. Change of state of the refrigerant taking place in the by-pass line 5 and the capillary tube 7 is shown in Fig. 2 line 11-12. As will be seen from Fig. 2 the refrigerant is at point 12 or the compressor suction side clearly in the superheated area, so that a flow of liquid cold material to the compressor inlet valve is prevented. In this embodiment the control element 7 formed in the by-pass line 5 is a capillary tube, but it can also be any other control element whatever that accomplishes the change of state, being suitable dimensioned with regard to the rest of the equipment and the operational conditions.

The heat requirement for defrosting is obtained principally from the work done by the compressor during compression. The vapour is warmed at the beginning of the defrosting cycle in the suction channel of the compressor due to the heat dissipated in the motor winding (change of state 12-9 in Fig. 3) and the compression work of the compression cylinder greatly increases the superheat of the vapour. Because of the operating principle of the system there is no danger of drops of liquid reaching the compressor suction valve. The arrangement of the equipment thus eliminates so-called compressor liquid impact risk. In addition to simplified equipment an advantage is that there is no need for an extra external source of heat to produce the heat required for defrosting, nor is it necessary to store heat during cooling circulation.

Automatic termination of the defrost ing period is easily associated with the defrosting system. When the ice formed on the surface of the vapouriser has melted, the hot gas is no longer cooled and thus the pressure and temperature of the current of refrigerant leaving the vapouriser increase. This situation is shown diagrammatically in Fig. 2 by the change of state curve depicted by means of a broken line. The impulse for terminating the defrosting period may be taken either from the compressor suction side or the compressor pressure side to the pressure switch 16 or from points 13 and 14. in Fig. 2. Correspondingly the increase of temperature at the corresponding refrigerant state points may be used to provide the required impulse to a temperature switch, which terminates the defrosting period. The control methods are thus alternatives,

The embodiments of the invention may vary within the appended patent claims.

Claims

Patent claims:

1. A method for defrosting the vapouriser of compressor refrigerating machinery, in which the refrigerating machinery comprises a compressor (1), condenser (2), pressure reducing means (3) and vapouriser (4) and in which there is employed for defrosting so-called hot gas defrosting in which the refrigerant is led in a highly superheated condition direct from the compressor (1) (state change 12-9-10 Fig. 2.) to the vapouriser (4) and in which defrosting is terminated, when ice formed on the surface of the vapouriser has melted, such termination of defrosting being accomplished for example by means of an impulse given by increase of refrigerant temperature and/or pressure, the method being c h ar a c t e r i s e d i n the following phases:

- the refrigerant which has given up its heat of superheat to the vapouriser (4) is removed from the vapouriser (4) in a superheat state close to the vapour saturation boundary curve (change of state 10-11 Fig.2) so that the refrigerant does not condense in the vapouriser.

- the refrigerant vapour pressure in the superheated area is reduced suitably at the compressor (1) (state change 11-12, Fig. 2) so that possible liquefied drops of refrigerant in the hot gas are vapourised and thus the passage of cold liquid material to the compressor suction valve is eliminated.

2. Equipment for utilising the method of patent claim 1, comprising a by-pass pipe (8), through which the superheated refrigerant is led past the condenser (2) and pressure reducing means (3) direct to the vapouriser (4) c h a r a c t e r i s e d b y a by-pass line (5) through which the refrigerant vapour is led from the vapouriser (4) to the compressor (1), in which the main suction line is closed for example by means of a valve (6) and possible control equipment (16) which terminates the defrosting period directly after the ice formed on the surface of the vapouriser has melted.

3. Equipment according to patent claim 2, c h a r a c t e r i s e d i n t h a t, the by-pass line (5) is equipped with a fusion capillary (7) or corresponding simple pressure reducing device.