Patent Publication Number: US-8122737-B2

Title: Refrigerating device comprising tubular evaporators

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a refrigerating device, in which an internal refrigerating compartment is cooled by a tubular evaporator through which coolant circulated by a compressor flows and which features a carrier plate and a tubular pipe arranged in contact with it so as to conduct heat. The tubular evaporator which is in close thermal contact with the internal refrigerating compartment is thermally screened from the environment by an insulation layer. The compressor is arranged outside the insulating layer and feeds compressed coolant to the evaporator at ambient temperature. As it passes a choke point of the evaporator the coolant is relaxed to a low pressure, which reduces the boiling temperature of the coolant to a value well below that of the ambient temperature. The vaporization of the coolant resulting from this causes the inner compartment to cool down. Gaseous coolant is sucked out of the compressor via a suction line. 
     With Rollbond evaporators which in general are constructed from two metal plates bonded together, of which in one there is embodied a serpentine coolant line, in general a collector is formed in the evaporator adjacent to the downstream end of the coolant line, which during an idle phase of the compressor traps unvaporized coolant and in this way prevents it being pushed out of the evaporator and into the suction line by coolant evaporating further upstream in the line. To also provide such a collector for a tubular evaporator is complex and expensive, since to do this it is necessary to tightly join together a number of tube sections with different internal widths. Instead of this, with conventional tubular evaporators an ascending outlet tube is frequently arranged directly upstream from the suction tube. While this outlet tube is not completely filled with liquid coolant, so that gaseous coolant can enter at the upstream, lower end of the outlet pipe, bubbles of the gaseous coolant can rise up through any liquid coolant which may possibly be present in the tube. If however the amount of coolant collected at the downstream end of the evaporator is greater than the ability of the outlet tube to accommodate it, liquid coolant gets into the suction line and cools this outside the insulation layer. On the one hand this results in a low thermal efficiency of the refrigerating device, on the other condensation water which precipitates on the outside of the suction line can result in damage to the appliance or can penetrate into the insulation layer and thereby adversely affect its insulation capabilities. To counter this danger, the amount of coolant in the refrigerating circuit of a refrigerating device is currently restricted in order to prevent sufficient liquid coolant from collecting so as to cause the outlet pipe to overflow. Such a restriction can however also adversely affect the efficiency of the refrigerating device. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the present invention is to create a refrigerating device with a tubular evaporator in which, despite more generous filling with coolant, the danger of overflow of the outlet tube is avoided. 
     The invention achieves this object by, with a refrigerating device with a tubular evaporator, which is connected via a suction line to a compressor and in which a coolant tube forms a plurality of serially-connected tubular loops and an ascending outlet tube connecting the loop of the tubular loops located furthest downstream to the suction line, instead of a conventional horizontal run of straight tube sections of the individual tubular loops, an ascending course of the tubular loops in the direction of flow of the coolant is provided over a predefined length, with the predefined length of the tubular loop in combination with its flow cross-section forming a buffer volume by which an overflow of liquid coolant into the outlet tube is prevented. Each tubular loop section with an ascending course is able to store liquid coolant and simultaneously to let gaseous coolant which is forcing its way in to sweep away over the liquid or to bubble through it, so that the liquid coolant remains trapped in the ascending section and does not reach the outlet tube. This significantly increases the storage capacity of the tubular evaporator for liquid coolant, and the danger of liquid coolant being expelled into the suction line is correspondingly reduced. 
     With the same throughflow cross section of the tubular loops and of the outlet tube it is especially advantageous for the tubular loops, over a least a length corresponding to the length of the outlet tube, to have an ascending course in the direction of flow of the coolant. 
     If each tubular loop, in a manner known per se, features two straight sections of tube joined by one curved section, in accordance with a first embodiment there can be provision for the straight sections of group of tubular loops situated furthest downstream to run in parallel with each other at an angle. This means that of the two parallel straight tube sections of each loop, one is in a position to store liquid coolant. 
     Preferably the section situated further downstream of the two straight sections of each tubular loop of the group has the course which ascends in the direction of flow of the coolant. 
     In accordance with a second embodiment in a group of tubular sections situated furthest downstream, both straight tube sections in each case ascend in the direction of flow of the coolant. Thus each straight tube section is in a position to trap liquid coolant and the amount which is allotted to an individual section is small. The smaller this amount is, the stronger the stream of gaseous coolant can be which can flow through the tube section without forcing out the liquid coolant. 
     In order to implement a high storage capacity the group should comprise a plurality of tubular loops embodied as described above; preferably all tubular loops of the evaporator belong to the group. 
     The difference in height between the two ends of each straight tube section preferably corresponds at most to half its average distance from adjacent straight tube sections. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the invention emerge from the description of exemplary embodiments given below which refers to the enclosed figures. The figures are as follows: 
         FIG. 1  a schematic view of an inventive refrigeration device; 
         FIG. 2  a section through a tubular evaporator in accordance with a first embodiment of the invention; and 
         FIG. 3  a fragment of a section through a tubular evaporator similar to that shown in  FIG. 2  in accordance with a second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
       FIG. 1  shows a schematic view of a refrigeration device, viewed from the rear of the device, with rear wall and insulation layer of a body  1  of the appliance omitted and the other outer surfaces of the body  1  shown as transparent in order to show an inner compartment  2  and a tubular evaporator  3  accommodated on the rear wall of the inner compartment. 
     In the lower rear area of the inner compartment  2  a niche is cut out in order to form a machinery area which accommodates a compressor  4  and a condenser  5 . The compressor  4 , the condenser  5  and the tubular evaporator  3  are interconnected to form a coolant circuit. 
     A suction line  6  extends from an upper right hand corner of the tubular evaporator  3  essentially vertically downwards to the compressor  4 . A pressure line  7  goes out from the condenser  5  and runs over a great part of its length within the suction line  6  up to the upper right hand corner of the evaporator  3 , where it exits from the suction line  6  again and comes out via choke point  8  into a coolant tube of the evaporator  3 . The coolant tube forms a plurality of vertically stepped, series-connected tubular loops  9 , each of which has two straight tube sections running in opposite directions connected by a tube bend  10 . The upstream tube section of each tubular loop  9  is labeled with the number  11 , the downstream section with the number  12 . The lowest tube section  12  is connected by an essentially vertical outlet pipe to the suction line  6  at the upper right hand corner of the evaporator. 
     As can be seen more clearly in the cross section through the tubular evaporator  3  depicted in  FIG. 2 , only the furthest upstream tubular loop  9  which directly adjoins the choke point  8  has horizontal straight tube sections  11 ′. In all other downstream tubular loops  9  the straight tube sections  11 ,  12  are parallel to each other sloping slightly down towards the side of the evaporator facing away from the suction line  6 . This means that a puddle  14  of liquid coolant can collect in each case in the lowest-lying area of each tubular loop  9 , at the start of its tube section  12 . 
     If it is assumed that the puddles  14  have a perfectly level liquid surface it can be easily seen that then amount of liquid, which each tube section  12  can hold, without the liquid entirely blocking its cross-section, must be at its greatest when the difference in height between the two ends of the section is slightly smaller than the diameter of the tube section  11 . Then the puddle  14  can extend over the entire length of the tube section  12  and fill just about half its volume. If the influence of surface tension on the shape of the liquid surface is negligible, be it as a result of a low surface tension of the coolant or of a large diameter of the coolant tube, it can thus be expedient to choose the difference in height between the ends of each tube section in this way. 
     If the liquid coolant tends, as a result of its surface tension, to block the free cross section, the falls in sections  11 ,  12  will sensibly be selected to be somewhat larger, in order to guarantee that the liquid coolant of puddle  14 , which would be expelled from the lowest point by the flow of gas onto it, provides sufficiently great resistance to this pressure so that in the course of the tube section  12  the gas can pass the liquid without forcing it downstream. The difference in height can amount here to a few multiples of the tube diameter. 
     In the one case, as in the other, the tubular loops can hold a significant amount of liquid coolant before the danger arises of this being pushed downstream during an idle phase of the compressor by coolant evaporating further upstream. The coolant circuit can thus be filled with a large amount of coolant without liquid coolant being able to fill the downstream tubular loops  9  to such an extent for it to fill the entire outlet tube  13  connecting the lowest tubular loop to the suction line and get into the suction line  6 . 
       FIG. 3  shows a tubular evaporator  3  as claimed in a second embodiment of the invention. The suction line  6 , the pressure line  7  and their course to the choke point  8  are the same as in the first embodiment and thus do not need to be described once again. In this embodiment the two straight tube sections  11 ,  12  of the tubular loops  9  are not parallel, but both run ascending the direction of flow of the coolant, with the incline being exaggerated in the figure to provide a clearer illustration. This enables the two tube sections  11 ,  12  of each tubular loop  9  to store liquid coolant, so that the amount of liquid coolant allotted to each tube section is small and the danger of the liquid coolant being forced downstream by evaporation occurring further upstream is reduced even further. 
     It is obvious that—depending on the filling of the coolant circuit with coolant—it may not be necessary to embody all tubular loops with ascending tube sections, in order to trap any liquid coolant which may arise in the idle phase of the compressor. Tubular loops with conventional horizontal tube sections and those with ascending tube sections can thus be combined in a evaporator, in which case the tubular loops with ascending tube sections should be provided in the downstream part of the evaporator, in order to be able to trap and to hold liquid coolant running out of upstream horizontal tube sections.