EP0408152A1

EP0408152A1 - Humidifying cooling element

Info

Publication number: EP0408152A1
Application number: EP90201886A
Authority: EP
Inventors: Cornelis Johannes Simjouw; Robert Jans
Original assignee: Fri Jado BV
Current assignee: Fri Jado BV
Priority date: 1989-07-11
Filing date: 1990-07-10
Publication date: 1991-01-16
Also published as: NL8901785A

Abstract

The invention relates to a cooling element (8) to be applied in the field of refrigerated displays. According to the invention the cooling element (8) is provided with means (5) to control the flow of the evaporating liquid through the cooling element (8) such, that during periodical interruptions, the cooling element (8) is heated by heat being present in a part (9) of the cooling element. This avoids dehumidifying of the air flowing through the cooling element (8), so that said air keeps a substantial amount of its water contents and dehumidifying of the food stuffs to be cooled by said air is avoided. The present invention also provides a cooling element (8), in which deposition of ice on the cooling element (8) is substantially reduced. According to a preferred embodiment the cooling element (8) is divided in two parts (9, 10), wherein a control valve (16) has been connected between said two parts (9, 10), the control valve (16) controlling the amount of liquid fed towards the second part (10) of the cooling element (8) is such, that evaporation takes only part in the second part (10) of the cooling element (8).

Description

The present invention relates to a cooling element generally known, certainly in the field of refrigerated displays.
Such cooling elements are subject to the drawback that with such a cooling element mounted in a refrigerated display the moisture present in the air passing through the cooling element condenses onto the cooling element through the cooling of the air and freezes solidly thereon. Firstly the air is hereby dehumidified so that relatively dry, cool air is fed to the refrigerated display so that the foodstuffs present in the display are greatly subject to dehydration. Secondly, deposition of ice occurs on the cooling element whereby the operation thereof is greatly reduced.
It has therefore been usual to date to defrost the cooling element several times a day so that the deposited ice melts and is removed from the cooling element. However, such a heating takes a considerable amount of time, wherein no cooling of the refrigerated display takes place and the temperature inside the refrigerated display can reach unacceptably high values.
To avoid these drawbacks, US-A-2 539 813 proposes a cooling apparatus, comprising a cooling element comprising at least one continuous pipe, provided with fins; means for supplying evaporatable liquid; means for draining the evaporated liquid; control means for controlling the flow of liquid such, that this flow is interrupted periodically in dependance of the temperature present in the cooling element; a ventilator for conveying the gas to be conveyed towards the chamber to be cooled conveying through the cooling element; and means for heating the cooling element during the periods of interruption.
This known apparatus makes use of a separate heating element for heating the cooling element during the interruption period. This implies, that in said known apparatus a separate heating element has to be provided, which increases the costs, both in relation to the production costs of such a cooling apparatus, as in view of the energy use thereof. Often such a heating element will be electrical.
GB-A-820980 shows an apparatus for electrical heating a cooling element, in which an electric current flows through said cooling element to heat it.
The aim of the present invention is to provide such a cooling apparatus, in which said drawbacks are avoided.
This aim is reached in that the control means have been adapted for controling the flow of liquid such, that during the periods of interuption the cooling element is heated by heat being present in at least a part of the cooling element.
As a consequence of these features, the disadvantages, coupled with a separate heating element are avoided, so that a cooling apparatus is obtained, which is both in purchase as in exploitation relatively cheap.
Normally the cooling element is switched off when the lowest allowable temperature of the refrigerator display is reached. As soon as the highest allowable temperature is reached, the cooling element will be switched on again. These switching actions are executed by a thermostat, so that a switching cycle develops, in which the cooling element is switched in and switched off alternately. The frequency of the switching cycle is, in dependance of the qualities of the refrigerator display and the required temperature area several times per hour.
The invention makes use of this by heating the cooling element during the non-operational period thereof such that the ice deposited on the cooling element melts and evaporates so that it is carried back to the air. Accumulating ice deposition on the cooling element is hereby avoided while at the same time a decrease in the relative air humidity of the air passing through the cooling element is prevented. Dehydration of the foodstuffs present in the refrigerated display is prevented herewith.
The invention further makes use of the fact that the switching cycle is relatively frequent so that the quantity of ice for removal during each standstill period is small. The amount of heat to be supplied for causing the ice to melt and evaporate is therefore also small, while the period of time herefor is also short. Thus is prevented that the temperature in the refrigerated display reaches too high values during this period of interruption.
From DE-A-3128352 a heat pump is known, in which the evaporator comprises two separate parts, which are separated by a controllable valve. In this known apparatus evaporation only takes place in the second part of the evaporator. In the first part no evaporation takes place; only the passing air is heated, before this enters the second part of the evaporator. Consequently the air serving as heat source flows initially through the first part of the evaporator and subsequently through the second part thereof. One aims to preheat the air serving as heat source such, that no ice deposition takes place.
In the apparatus according to the present invention there is no question of a heat pump, instead there is question of a cooling apparatus. In the present invention the aim is to cool a gas flowing through an evaporator to make the temperature present in a chamber at a low level. The direction of flow of the gas through the evaporator is opposite to that in the case of the heat pump; in the evaporator according to the present invention the gas to be cooled down initially flows through the second part of the evaporator and subsequently through the first part, so that the well known principle of counter flow is applied. Further in the heat pump the useful effect of the partition of the evaporator takes place during the effective periods of the cycle, whereas in the apparatus according to the present invention the useful effect takes place during the interuption periods of the cycle.
The invention will be subsequently elucidated with reference to the annexed drawings, wherein:

fig. 1 shows a schematic view of a cooling device according to the present invention; and
fig. 2 shows a P-H (pressure-enthalpy) diagram in explanation of the invention.

The device comprises a liquid container 1 which is connected by means of a pipe 2 to a filter-dryer 3. This is connected in turn via a pipe 4 to a first magnetic valve 5. A sight glass 6 is arranged in this pipe 4. Further, a pipe 7 leads from the first magnetic valve 5 to a cooling element 8.
The cooling element is divided into two blocks, a first block 9 and a second block 10. The fins 12 of the first block 9 and the second block 10 are common; they extend over the first block 9 and the second block 10. The tube 13 extending through the first block 9 of the cooling element 8 is connected by means of a pipe 14 to the tube of the second block of the cooling element.
An expansion valve 16 is accommodated in the line 14. The expansion valve 16 aims to insure that at the end of the pipe 15 just all liquid has been evaporated.
Further, the tube 15 is connected by means of a pipe 18 to a compressor 19. Arranged in pipe 18 is a control member or valve 17 having as function to keep constant the pressure of the gas-liquid mixture flowing through the tube 15 of the second part 10 of the cooling block 8. Arranged in the pipe 18 is a second magnetic valve 5 as well as a valve 21 for isolating the compressor 19. The compressor 19 is further connected by means of a pipe 22 to a condenser 23. Finally, the condenser 23 is again connected via the pipe 24 to the container 1.
The liquid present in the container 1 is in the state indicated in fig. 2 by the point A. This liquid is then fed through the pipe 2, the dryer/filter 3, the sight glass 6 and the pipe 4 to the magnetic valve 5. The liquid subsequently runs through the pipe 7 and the tube 13 of the first block 9 of the evaporator 8. Lowering of the temperature of the liquid takes place herein. The point A′ is then reached, which indicates the supercooling of the liquid.
The liquid subsequently runs through the pipe 14 and the expansion valve 16 arranged therein where a throttling process takes place. The state is then reached which is indicated in fig. 2 with the letter B. It is noted here that as a result of the throttling process a mixture of cooling liquid and cooling gas occurs with the same temperatures, the value whereof is represented by the point B. The thus obtained liquid runs through the tube 15 of the second block 10 of the cooling element 8 and applies its cooling effect there. The dimensioning of the second block 10 is such that the gas contains no more liquid after passing through the cooling block 10. In this way the state C in fig. 2 is reached when the gas leaves the pipe 15.
The gas then runs through the pipe 18 wherein the control member 17, a magnetic valve 5 and a valve 21 are arranged and subsequently arrives in the compressor 19 wherein compression takes place to the point indicated in fig. 2 with the letter D.
The gas is compressed herein. It then passes through the pipe 22, the valve 21 and is guided to the condenser 23, wherein the gas condenses and again returns to the original state A and is carried back again to the container 1 as liquid.
The controlling action of the expansion valve 16 will be described subsequently in more detail. The expansion valve is accommodated in the pipe 14 and in this way controls the amount of liquid fed to the second evaporator block 10. The valve further senses the temperature of the gas leaving the second evaporator block 10 through the pipe 18. The valve 16 herein controls the amount of liquid fed to the second evaporator block such, that the overheating of the gas leaving evaporator block 10 amounts to approximately 10K. In this way a latent amount of cold is always present in the second evaporator block.
The process described above takes place during the closed state of the thermostat which measures the temperature of the space for cooling. As soon as this temperature reaches a determined minimum value the cooling process is terminated and the cooling element 8 is isolated using the magnetic valves 5. As a result of the heat present in the cooling element 8, in particular in the first block 9 thereof, the temperature of the cooling element will then increase so that ice deposition present melts and evaporates. The relative air humidity of the space for cooling will increase herewith so that danger of dehydration is avoided. After the temperature of the space for cooling has increased again, the cooling process is set into operation again and the valves 5 are opened again as soon as the switching point of the thermostat is reached.

Claims

1. Cooling apparatus, comprising:
- a cooling element comprising at least one continuous pipe, provided with fins;
- means for supplying evaporatable liquid;
- means for draining the evaporated liquid;
- control means for controlling the flow of liquid such, that this flow is interrupted periodically in dependance of the temperature present in the cooling element;
- a ventilator for conveying the gas to be conveyed towards the chamber to be cooled conveying through the cooling element; and
- means for heating the cooling element during the periods of interruption,
characterized in that the control means have been adapted for controling the flow of liquid such, that during the periods of interruption the cooling element is heated by heat being present in at least a part of the cooling element.

2. Cooling element according to claim 1, characterized in that the control means control the flow of liquid such, that in a first part of the cooling element no evaporation takes place.

3. Cooling element according to claim 2, characterized in that the cooling element has been divided in two parts, and that the control means comprise an expansion valve connected between the two parts of the cooling element, which expansion valve detects the temperature of the gas leaving the cooling element, and that controls the amount of liquid fed towards the second part of the cooling element in dependance of said temperature.

4. Cooling element according to one of the claims 1-3, characterized by valves for isolating the cooling element during the interruption period.

5. Cooling element according to one of the claims 3-5, characterized in that the fins stretch over both parts of the cooling element.

6. Cooling element according to one of the preceding claims, characterized in that the ventilator is driven in such a direction, that the flow of the gas to be cooled is opposite to the direction of flow of the liquid.