EP2690374A1

EP2690374A1 - Resistive structure for the uniform heating of fluids

Info

Publication number: EP2690374A1
Application number: EP12425128.1A
Authority: EP
Inventors: Costante Dall'anese
Original assignee: HT SpA
Current assignee: HT SpA
Priority date: 2012-07-25
Filing date: 2012-07-25
Publication date: 2014-01-29
Anticipated expiration: 2032-07-25
Also published as: EP2690374B1

Abstract

A resistive structure for the uniform and homogeneous heating of fluids, comprising a resistor (10) formed by at least one perforated tubular element (13) made of conductive material, inside which there are inserted, in order, starting from the external edge and proceeding towards the center of the resistor (10), at least a first tubular element (11) made of conductive material, an insulating layer (14) within which a wire or ring-shaped resistive layer (12) is embedded, at least a second tubular element (15) made of conductive material and an inner central portion (16) made of conductive material.

Description

The present invention generally relates to a resistive structure for uniformly heating fluids.
More particularly, the invention relates to a resistor device which is made so as to have a remarkable surface able to exchange heat with the fluid, in order to obtain a homogeneous and instantaneous heating of the fluid passing within the resistive structure, thus maximizing the pressure drop and also saving space and/or encumbrance.
Hot water for sanitary use is normally obtained by passing cold water through a plates heat exchanger, inside which a hot fluid is sent through a secondary circuit of the heat exchanger, in order to have a substantially constant temperature of the outgoing fluid.
In fact, for sanitary uses, it is preferable to maintain a constant temperature of the outgoing water, which is usually between 55°C and 60°C, and, for many applications, it is preferable to directly heat the outgoing fluid flow, so as to avoid the use of holding tanks.
As previously mentioned, the use of plates heat exchangers makes it possible to obtain a heat exchange which is rather efficient and also allows to provide enough hot water, however by employing a minimum amount of fluid stored inside the heat exchanger.
However, a main drawback of the known heat exchangers for providing hot fluids and, in particular, for supplying hot water is that for each new opening of the tap the water comes out, for a certain period of time, at a temperature value which is substantially higher than a predetermined value and this can constitute a real danger for the user.
This occurs since the heating fluid which is sent inside the heat exchanger must have a temperature of about 10-20°C higher than the predetermined temperature of the fluid outgoing from the tap and since, when the tap is closed, the water which is contained in the heat exchanger is brought to the temperature value of the heating fluid, while, when the tap is again opened, the outgoing water has, for a certain time, a temperature of 10-20°C higher with respect to the predetermined temperature of 55-60°C.
This drawback can be bound by using a hot water tank or container (i.e. a pipeline) placed between the heat exchanger and the tap; however, using a pipeline causes remarkable overall dimensions and production costs, which is advisable to reduce or completely eliminate. Moreover, by using said tank or pipeline, the water coming to the tap when said tap is opened will be substantially cold after a certain time period since the last drawing of hot water.
The present invention therefore overcomes the above mentioned prior art drawbacks and, in particular, the main object of the invention is to provide a resistive structure for heating fluids in a uniform or homogeneous way, which is able to instantly provide a uniformly heated water flow to one or more supplies, said water flow having a predetermined, controlled and substantially homogeneous temperature.
Another object of the present invention is to provide a resistive structure for the homogeneous heating of fluids, which may be used together with a heat exchanger, in order to obtain an extremely efficient and compact device, which is suitable for delivering an almost instantaneous water flow that is always uniformly heated.
Another object of the present invention is to provide a resistive structure for the homogeneous heating of fluids, which allows to obtain a total heat exchange, without using tanks and/or fluid containers and/or connecting pipelines between the resistive structure and the heat exchanger, thus limiting the overall dimensions and saving time, costs and/or water.
A further object of the present invention is to provide a resistive structure for the homogeneous heating of fluids, which is particularly effective, reliable, convenient and cheap, with respect to the prior art, and which may be used for any new or already existing water supply.
These and other objects are achieved by a resistive structure for uniformly heating fluids according to the enclosed claim 1.
Further technical features of the resistive structure which is the object of the invention are given in the dependent claims.
Advantageously, the resistive structure according to the invention allows to quickly heat a fluid and to instantly obtain a fluid flow having a homogeneous and controlled temperature, simply by using a labyrinth resistor that works as a heat exchanger within a total heat exchanging device.
The heat exchange takes place instantly and therefore subsequent and remarkable savings of water and time are obtained for heating a prefixed quantity of fluid (water), with respect to the prior art.
Furthermore, it is not necessary to use tanks and/or containers for storing the fluid to be heated, nor pipelines which are particularly long and/or bulky. Finally, the resistive structure which is the object of the invention can be particularly used for supplying domestic hot water, but can be similarly used for any other private and/or industrial use (for example, as a heat exchanger for plastics molding machines) and when it is necessary to have a continuous fluid flow at a homogeneous and controlled value of temperature. Further objects and advantages of the present invention will become more clear from the description which follows, relating to a preferred embodiment of the resistive structure for the homogeneous heating of fluids, according to the invention, and from the appended drawings, which are also provided purely by way of preferred and not limitative example, in which:

figure 1 is a side view of the resistive structure for the uniform or homogeneous heating of fluids, according to the present invention;
figure 2 is a sectional view taken along the line II-II of figure 1, according to the present invention;
figure 3 is a sectional view taken along the line III-III of figure 1, according to the invention;
figure 4 is a perspective and cross-section view of the resistive structure for the homogeneous heating of fluids, according to the invention.

Referring to the above mentioned figures, the resistive structure according to the invention is substantially composed of a resistor 10 formed by a perforated tubular element 13, which is made of conductive material and preferably of aluminum, inside which there are inserted, starting from the external edge and proceeding towards the center of the resistor 10, a tubular element 11, made of conductive material and preferably made of stainless steel, an insulating layer 14, made preferably of compressed magnesium oxide, within which a wire or ring-shaped resistive layer 12 is embedded, a tubular element 15 made of conductive material, such as stainless steel, and a central internal portion 16 made of conductive material, such as aluminum.
The resistor 10 is connected to a pipe section, by means of a fitting ring nut and/or by a special flange, for connecting the grounded cables, the three-phase power cables 21 of the resistor 10 and the cables for connecting a possible insulation thermocouple (if any). Furthermore, said resistor 10 is associated with a fluids distribution connector, for example of the T-shaped type, and/or to a base for connecting a possible thermostat.
In particular, as shown in detail in the enclosed figures 2 and 4, the resistor 10 has internally a labyrinth structure, in such a way that the flow of the fluid incoming from the inlet 25 (arrow F), which passes inside the space 17 between the outer casing and the tubular element 13 and from here inside the openings or holes 22 made on the tubular element 13 (according to the direction and the direction of the arrows F1, F2, F3), indirectly contacts the wire or ring-shaped resistive layer 12 and is again centrally conveyed (arrows F4), passing again above the wire or resistive layer 12, inside the tubular element 15 (arrows F5) and from here, through the inner central portion 16, toward the end terminal 23 (arrow F6), before exiting from the resistive structure (arrow F8), through the lateral duct 24 (arrow F7) and the outlet 26.
Therefore, by using the wire or resistive layer 12 which is placed inside the tubular element 13, which is inserted in turn in a labyrinth-shaped resistive structure, and by passing the fluid laterally into the tubular element 13 and then centrally with respect to the resistive structure, as described, it is possible to have a suitable passage of the fluid within the wire or resistive layer 12, since the above mentioned fluid is forced to make at least three revolutions in the labyrinth structure and is forced to lap, inside and outside, at least three different surfaces.
The result is a heat exchange surface which is considerably large, thus maximizing the pressure drop and maintaining a compact size of the resistive structure and avoiding, at the same time, a direct contact between the fluid and the wire or resistive layer 12.
This allows to bring the entire quantity of incoming fluid, almost instantly, to a predetermined temperature value (which is determined by the power of the resistive wire 12 and which is homogeneous and controlled) and to obtain an output fluid flow which is always uniformly heated.
The resistor device is therefore a temperature "calibrator" and is able to give time savings (so that the fluid can reach a given and controlled temperature value) and fluid (water) savings, because it is not necessary to have a containment tank for collecting the fluid to be heated.
Moreover, using a single tubular element 13, it is possible to provide a three-phase power to the resistor 10 and it is possible to insert one or more probes for detecting and controlling the temperature of the fluid (the incoming and the internal fluid) in the tubular element 13 and in the wire or resistive layer 12. Finally, the above mentioned resistive structure allows to avoid the complete destruction of the resistor also when an interruption of the fluid flow inside the tubular element 13 occurs, since the metal mass of the external structure is intimately attached to the wire or resistive layer 12.
The resistive structure thus obtained can also be advantageously combined with a suitable heat exchanger for applications which require an electric heating combined with an effective heat dissipation (such as, for example, the temperature control units in the molding of plastics); in fact, the resistor 10 is placed inside a container or shaped casing, preferably made of stainless steel, with the interposition of a prismatic block and a mounting flange 20.
The characteristics of the resistive structure for a uniform and homogeneous heating of fluids, which is the object of the present invention, as well as the advantages thereof, become clearly apparent from the above description.
In particular, the resistive structure of the invention can be used in the following conditions:

three-phase power without star-shaped electrical connection + grounded connector;
closed immersion circuits with fluid and liquid forced circulation, such as water for sanitary uses and/or for industrial uses;
maximum pressure value equal to approximately 20 Bar;
maximum value of fluid temperature of 140°C;
using at least two probes for temperature control;
power density of about 40 W/cm².

Anyway, it is clear that several variations can be made to the resistive structure of the invention, without thereby departing from the scope of the invention, and that, when practically carrying out the invention, the materials, shapes and dimensions of the illustrated details can vary according to the user's needs and be changed with other technically equivalent ones.
Where the technical features mentioned in the subsequent claims are followed by reference numbers or signs, those reference signs have been introduced with the sole aim of increasing the intelligibility of the claims themselves and, consequently, they have no limiting effect on the interpretation of each element which is therefore identified only by way of example with said reference signs.

Claims

Resistive structure for a uniform and homogeneous heating of fluids, characterized in that it comprises a resistor (10) formed by at least one perforated tubular element (13) made of conductive material, inside which there are inserted, in order, starting from an external edge and proceeding towards the center of the resistor (10), at least one first tubular element (11) made of conductive material, an insulating layer (14) within which a wire or ring-shaped resistive layer (12) is embedded, at least one second tubular element (15) made of conductive material and an inner central portion (16) made of conductive material.
Resistive structure according to claim 1, characterized in that said resistor (10) is connected to a pipe section for connecting the grounded cables, the three-phase power cables (21) and the cables for connecting a possible insulation thermocouple.
Resistive structure according to at least one of the previous claims, characterized in that said resistor (10) is connected with a fluids distribution base and/or with at least one terminal plate for the connection of a possible thermostat.
Resistive structure according to at least one of the previous claims, characterized in that said resistor (10) has internally a labyrinth structure, so that a fluid flow (F) incoming the resistive structure and passing within a space (17) provided between an outer casing and said perforated tubular element (13) goes (F1, F2, F3) towards openings or holes (22) made on said tubular element (13), thus indirectly contacting said wire or resistive layer (12), before being again conveyed (F4), by lapping said wire or resistive layer (12), in (F5) said second tubular element (15), and from here, through said inner central portion (16), towards (F6) a terminal end (23) and towards (F7, F8) a side duct (24) and an outlet (26) of the resistive structure.
Resistive structure according to at least one of the previous claims, characterized in that said fluid makes at least three turns inside said labyrinth structure, thus lapping, inside and outside, at least three different surfaces of said structure, thus obtaining a large heat exchanging surface, maximizing the pressure drop, maintaining a compact size of the structure and avoiding, at the same time, a direct contact between the fluid and said wire or resistive layer (12).
Resistive structure according to at least one of the previous claims, characterized in that one or more probes for detecting and controlling the temperature of said fluid are placed inside said first tubular element (13) and/or said wire or resistive layer (12).
Resistive structure according to at least one of the previous claims, characterized in that said structure is combined with at least one heat exchanger and said resistor (10) is inserted inside a container or shaped casing, made of conductive material, through the interposition of a prismatic block and/or a fixing flange (20).