EVAPORATOR OF CONDENSED FLUIDS Field of the invention

The invention relates to an evaporator of condensed fluids in refrigerators or counters for displaying refrigerated food. State of the art

In refrigerated display counters or cabinets with condensing unit on board, commonly referred to as "plug-in counters", "plug-in refrigerated display cabinets", "self-contained display cabinets", etc., the intake of ambient air and relative humidity into the plant generates water which is to be eliminated. As it is well known, the formation of water in these refrigerated environments or containers derives from two phenomena.

The first one is the condensation of humidity included in the ambient air on the inner surfaces of the plant. This phenomenon is almost continuous and the amount of water deriving therefrom depends, other than on the working temperature of the counter, on the amount of ambient air which is input into the plant and on its relative humidity which is e.g. higher in "open" counters" than in those equipped with doors, therefore on the environmental conditions under which the "plug-in" operates. The second phenomenon consists in melting the frost formed on the evaporator of the refrigerating circuit by heating the same. The function of defrosting required to restore the ideal conditions of heat exchange of the evaporator may be performed by simply stopping the refrigerating cycle in plants having evaporating temperatures close to or higher than 0° C. Where defrosting is provided, the produced water "forms" in a relatively short time, typically from 10 to 45 minutes, and defrosting is cyclically implemented at intervals typically set between 6 and 12 hours.

Almost always, liquids, e.g. detergents, deriving from washing the display counter and from possible breaking of the packages of the displayed products, e.g. the breaking of a package of milk or soft drink, or meat blood, are also conveyed in conjunction with water and are to be eliminated. In case of using tanks for collecting such liquids, there are therefore formations of limestone and concentrations of "dirtiness" that make the liquid to be eliminated a "corrosive"

agent for metal parts.

Some solutions to this problem are known from the state of the art. There have been proposed collecting tanks with manual emptying of the condensed water. It is the simplest system but it assumes a manual operation by the end user and the sizing of the tank must be based on the most critical condition, i.e. the longest interval that may occur between a "draining" and the following one, typically during the week-ends. Its disadvantage is requiring a manual intervention and further posing limitations to the size of the tank. Solutions with a floor drain for the condensed fluid are known. This system is also very simple and effective but it provides the arrangement of drain pipes from the refrigerating counter, which is not always appreciated in small businesses and which restrains the possibilities of displacing the refrigerator. Basins arranged over the refrigerating circuit compressor have been proposed. It is the most used system in domestic refrigerators and in small sized "plug-ins". It is extremely simple and cost-effective since it provides a simple plastic tank, and its energy consumption is "zero" since it is based on the heat dissipated by the compressor for the operation thereof, the evaporating abilities of this system are restrained and linked to the compressor duty-cycle. These are solutions which only find their use in small size refrigerators for domestic use.

Another known solution provides a collecting tank with automatic evaporation by using heated gas. This system is currently very common especially in Europe and its success lies in the zero energy consumption, since the used power is the one that should be dissipated by the condenser anyway. It is formed by a tube serpentine arranged in a tank, which may be both in plastic and metal material, where the condensed or defrosting water is conveyed along with other liquids. The "hot" refrigerating gas passes within said serpentine before reaching at the condenser. In the plants using this solution, in order to restrain the possibility of perforating the serpentine by corrosion which would reflect on the reliability of the whole refrigerating plant, the typically copper-made tube is either protected by means of galvanic processes or with plastic/epoxy films or made of stronger materials, e.g. AISI 316 or Incoloy. Furthermore, such a system is essentially

"stationary" and, therefore, hardly extractable in order to allow the user to clean it in an ordinary manner. Furthermore, the increasing efficiency of the refrigerating plants and, in some cases, the use of refrigerating gases generating less energy available in the form of hot gas, make the amount of energy available in the form of hot gas smaller and smaller, thus making more and more often the integration of a resistive element necessary, in order to prevent the liquid from overflowing from the tank.

A solution is also known which uses an electrical tank having a PTC (Positive Thermal Coefficient) cartridge resistor. This solution is based on an electrical heater in which the resistor denotes a high PTC coefficient. It is mounted on a tank and develops its maximum power when it is hit by the condensed/defrosting water. Furthermore, the resistor keeps a high power value at the boiling temperature, in order to limit its absorption to much lower values under "dry" conditions. Level and safety controls are not required but it needs to be mounted on tanks made of materials able to stand auto-limitation temperatures under "dry" conditions, i.e. between 150° C and 220° C according to the used resistors. This solution suffers from a certain limitation in the output power and furthermore consumes energy even when there is no fluid to be evaporated. Another known solution consists in an electrical basin provided with a tubular resistor and equipped with a level sensor. The resistor is activated by a switch operated by the level sensor by means of float leverage. Due to the conditions of "dirtiness", high humidity and dust deposits accumulating within these basins, such a solution is less reliable. Indeed, the first cause of unreliability is the malfunction of the level sensor. Furthermore, this system is hard to be extracted by the end user for an ordinary cleanliness. In some cases, mainly in the developing markets, in these solutions no safety device is mounted and the resistor operates at high temperatures in exclusively steel-made tanks. Summary of the invention Therefore, it is an object of the present invention to obviate to the aforesaid problems by making an evaporator of condensed fluids collected in a container which, in accordance with claim 1 , comprises a heating element which may be placed in proximity of the container bottom, a level sensor arranged over the

heating element for detecting a predetermined minimum level and a predetermined maximum level of the fluid in the container, a casing containing said level sensor, wherein said casing can at least partially be lapped against by the fluid, thus preventing the fluid from contacting the level sensor. It is another object of the present invention to make a process for controlling the above mentioned evaporator of condensed fluids which, in accordance with claim 12, comprises the following steps:

- defining a predetermined minimum level and a predetermined maximum level of fluid in the container; - powering the heating element when said predetermined maximum level is detected by the level sensor so as to evaporate the fluid up to reach said predetermined minimum level.

The evaporator of the invention advantageously provides, instead of float level sensors which may jam and operate in an unreliable manner, the use of electronic sensors which "read" through the plastic and/or metal material of the container, e.g. a basin or tank, thus allowing the housing thereof in a zone protected against dirtiness, humidity and corrosive agents, thus intrinsically increasing the reliability thereof. The resistor with built-in thermal fuse and/or safety thermostat and the "protected" sensor allow a simpler solution with the advantage of also simplifying the cleanliness operations.

In an advantageous embodiment which also provides for the use of a resistor with a safety thermostat and/or thermal fuse incorporated in the tubular element sheath, the evaporator of the invention ensures the shut-down of powering to the heating resistor in case of malfunction of the level sensor. Brief description of the drawings

Further features and advantages of the invention will be more apparent in view of the detailed description of preferred, although not exclusive, embodiments of an evaporator of condensed fluids illustrated by way of non-limiting example, with the aid of the accompanying drawings, in which:

Fig. 1 schematically depicts the evaporator of the invention in a first embodiment; Fig. 2 depicts a diagram over time in which the fluid level pattern and the load

state of the evaporator in Fig. 1 are indicated;

Fig. 3 depicts a second embodiment of the evaporator according to the invention; Fig. 4 depicts a third embodiment of the evaporator according to the invention. Detailed description of preferred embodiments of the invention With reference to the mentioned figures, an evaporator 1 of fluids, especially of condensed liquids in refrigerating plants, is now described. In a first embodiment illustrated in Fig. 1 , the evaporator 1 comprises:

- a container 2, e.g. a basin or tank, made of plastic or metal material,

- a heating element 3, e.g. an electrical heating resistor, for example of the tubular or laminar type, preferably equipped with a thermal fuse and/or a safety thermostat

(not shown) inserted into the sheath of the resistor itself,

- a level sensor 4 having capacitive effect and suitable to detect a predetermined minimum level 6 and a predetermined maximum level 6', preferably placed on one side of the container 2, - an electronic board 5 comprising a set of control and command circuits controlling the activation of the heating element 3.

In advantageous variants of the inventions, the use of level sensors of other types, e.g. ultrasonic sensors, is provided. In the case of an ultrasonic sensor, container

2 is made of metallic material. The electrical connections and the electronic control and command board 5 are positioned on a same side of the container 2 and protected by a box or casing 10.

On the box 10 itself, a power connector 7 is placed which allows a simple and safe power shut-down of the heating element 3. A handle 8 is placed on the same side of the container 2 for easily extracting the evaporator. With reference to figure 1 , level sensor 4 is placed over the heating element 3. The distance between heating element 3 and level sensor 4 is such that it ensures the presence of the fluid across the whole surface of the heating element 3 even when the fluid reaches the predetermined minimum level 6.

Such a minimum level 6 is identified by sensor 4, of the capacitive type, by means of varying the capacitance of a condenser in which the dielectric between the armatures consists of the fluid to be evaporated.

The correct measurement of minimum level 6 allows a good operation of the

heating element 3 even when the fluid is boiling and the zone of sensor 4 is hit by a turbulent fluid.

Figure 2 depicts a diagram of the fluid level pattern and the load state of the heating element over time. Below the minimum level 6, the fluid no longer needs to be evaporated and the circuits of the control board 5, detecting this condition from the sensor 4, drive the heating element or resistor 3 to shut-down.

The subsequent powering of the heating element 3 occurs when the fluid exceeds the predetermined maximum level 6'. Therefore, during the operation period of the evaporator, there are steps of evaporating, in which the fluid level passes from a maximum or upper level to a minimum or lower level, alternating with steps of refilling, i.e. raising of the level, due to defrosting.

The container 2 is formed so that the relative position of sensor 4 and heating element 3 allows controlling the fluid level to be evaporated in order to allow the fluid level to never drop below a safety threshold which could lead to overheat the heating element 3.

The distance between maximum and minimum levels is determined by the construction of sensor 4 and determines the activation frequency of the heating element 3 and the time during which such a heating element remains active during the evaporating cycle. Such a distance must be characterized according to the shape and size of the basin 2 so as to prevent the heating resistor 3 from activating too frequently.

In order to define such a distance, the following parameters are taken into account:

• width between the maximum level and the minimum level of the collected fluid,

• distance between level sensor 4 and heating element 3,

• size and shape of the container 2. The electronic board 5 for commanding and controlling the evaporator can include activating programs of the heating resistor 3 which take into account factors such as the time periods in which heating starts, e.g. for taking into account variations in

the cost of power during the day, its continuation over time or other critical factors. The evaporator in accordance with the invention allows to use much higher powers than those used in known solutions, with a consequent possible reduction of the overall dimensions of the basin itself, and does not consume power when the fluid evaporation is not required.

It also allows to save energy for a better efficiency of the control process which may be implemented by the evaporator.

Such a control process comprises the following steps:

- defining predetermined minimum 6 and maximum 6' levels of fluid in the container 2;

- powering the heating element 3 when said maximum level 6' is detected by the level sensor 4 so as to evaporate the fluid up to reach said predetermined minimum level 6.

With reference to figure 3, a second preferred embodiment of the evaporator of the invention is depicted, in which sensor 4, electronic board 5 with the control and command circuits and the connection of the heating element 3 are included in a single casing 10. The so-constructed assembly may be placed within a collecting and/or evaporating container 2 of an existing evaporator which is activated, e.g. by a gas circulating in a serpentine 1 1 immersed in the fluid. This embodiment of the evaporator is thus especially useful when the improvement of the efficiency of evaporators equipped with hot-gas heating system only is desired, if it is deemed insufficient, since it may be easily inserted into pre-existing evaporating basins. Such an embodiment of the evaporator allows a great versatility as it may also be applied to current configurations in which evaporation occurs by means of hot gas. In this second embodiment, the evaporator of the invention may be employed to replace or integrate a hot gas system. In the case of replacement, the advantages are in:

• being able to ensure the elimination of water and other fluids apart from the refrigerating cycle; • being able to reduce the size of the basin by acting on the power of the electrical heater;

• allowing a much easy extraction of the basin in order to clean it;

• eliminating the possibility of perforating the serpentine, thus reflecting on the reliability of the refrigerating plant.

In the case of integration, only the first above-mentioned advantage remains essentially valid. In a third embodiment illustrated in Fig. 4, evaporator 1 comprises all components already described in the first variant of Fig. 1 and here indicated by the same reference numerals, and the operation thereof is the same as that previously described (Fig. 2).

In this case, the heating element 3 is an electrical resistor in the form of a heating foil or sheet. Such a foil 3 is placed outside the container 2 and adjacent to the bottom thereof.

By detecting that the minimum level has been reached at the end of a step of evaporating the condensed fluid, level sensor 4 allows to shut-down power to heating foil 3, so as to ensure that a determined amount of fluid always remains into the container 2. This amount of fluid allows the foil 3 to be cooled, thus preventing it from overheating.

In all of its constructional embodiments, the evaporator of the invention may also be provided with alarms which may be placed at various levels of the container in order to indicate for example when the fluid in the basin reaches the minimum level corresponding to the shut-down threshold of the energy powering the heating resistor. Another alarm signal may also be activated when the fluid reaches the allowed maximum level before outflowing from the basin.

A control signal may be sent from the electronic board 5 to the power unit managing the whole refrigerating plant in order to indicate when the load is active or should be active, in order to allow the power management of the whole plant

(e.g. absorbing peaks).