WO2013068989A1

WO2013068989A1 - Heating radiator element made of die-cast aluminium

Info

Publication number: WO2013068989A1
Application number: PCT/IB2012/056308
Authority: WO
Inventors: Orlando NIBOLI; Maurizio BOLOGNA; Fabio Sassi; Francesco Franzoni
Original assignee: Fondital S.P.A.
Priority date: 2011-11-09
Filing date: 2012-11-09
Publication date: 2013-05-16
Also published as: EA201490943A1; CN104024785A; ITMI20112027A1; EP2776777B1; CN104024785B; EP2776777A1

Abstract

A heating radiator element (1) made of die-cast aluminium extends along a longitudinal axis (A) and has a monolithic aluminium structure (15), comprising a tubular body (2) and connections (7) which protrude from opposite sides of the body (2); the structure (15) is internally provided with a water circuit (16) for the circulation, in use, of a stream of water, while the volumes available for passage of the air around the structure (15) define an air circuit (17); the aluminium structure (15) and the water circuit (16) define heat exchange means such as to increase the aluminium/air heat exchange with respect to the water/aluminium heat exchange, increasing the volume of the air circuit (17) with respect to the volume generically available and specifically with respect to the volume of the water circuit (16).

Description

"HEATING RADIATOR ELEMENT MADE OF DIE -CAST ALUMINIUM"

TECHNICAL FIELD

The present invention concerns a heating radiator element made of die-cast aluminium.

BACKGROUND ART

In general, a radiator for heating buildings consists of a battery of radiator elements positioned side by side, normally (although not necessarily) produced separately and then assembled to form a radiator of appropriate dimensions . Typically, each radiator element has a main body which is essentially tubular and provided with an inner chamber in which a hot fluid circulates (commonly, water) . Some main types of radiator element are particularly widespread, which are characterised essentially by the component material ^• and by some structural features due to the production technology. In fact, the manufacturing technologies and materials directly affect the structure of the radiator elements and their heat exchange mechanisms.

Performance requirements actually have to be reconciled with production requirements . For these reasons, solutions adopted on radiator elements of a certain type cannot be immediately reproduced on radiators of other types .

Radiators made of die-cast aluminium (in which the radiator element consists of a monolithic body made of aluminium or aluminium alloy obtained by die-casting) are characterised with respect to other types, for example aluminium radiators produced by extrusion (consisting of an extruded central body to which two end headers are subsequently fixed) or radiators made of cast iron or other metallic materials or bimetallic radiators (having components of different coupled materials) , not only by the production technologies but also by some structural characteristics, which are due to the materials used and the production techniques. In the specific sector of die-cast aluminium radiators, the general configuration of the single radiator element is substantially consolidated and consists essentially of a tubular body provided with inner water chamber and hydraulic connections arranged at the opposite ends of the element ; from the water chamber, along a centreline plane of the element, two opposite aluminium partitions branch off, supporting a front plate and a rear plate respectively; a plurality of heat exchange fins protrude from the tubular body. One of the reference parameters commonly used to characterise a radiator element is the specific power per unit of weight, i.e. the ratio between the thermal power emitted by the radiator element and transferred to the environment (measured according to specific standards, for example EN 442) and the weight of the element (which is the fundamental parameter directly affecting production costs) .

It is a common belief in the sector that the die-cast aluminium radiator elements currently available have now reached the limits of their performance and can be improved no further, or only minimally.

Furthermore, all solutions potentially capable of improving the efficiency of a radiator element must be compatible with the overall dimensions of the radiator elements, which are generally restricted, since consolidated market standards have to be complied with, in particular in terms of width (maximum width of the element, normally defined by the distance between the free ends of the hydraulic connections arranged at the same end of the element) , depth (distance between the front and rear plates) and centre distance (distance between the centres of the hydraulic connections) .

The current design criteria for die-cast aluminium radiator elements have resulted in products with specific powers considered at the moment to be satisfactory and practically non- improvable .

The technicians of the Applicant, however, have ascertained that the known solutions still have significant margins for improvement, which can be achieved by completely changing the approach to the problem of the increase in specific power.

DISCLOSURE OF INVENTION

One object of the present invention is to provide a die-cast aluminium heating radiator element which has a high thermal performance, superior to that of a traditional radiator element of comparable dimensions, at the same time maintaining a high mechanical resistance and resistance to internal pressure and in any case complying with the market dimensional standards . The present invention therefore relates to a die-cast aluminium heating radiator element as essentially defined in the attached claim 1 and, in its preferred embodiments, in the dependent claims . Compared to known radiator elements, the radiator element of the invention has decidedly superior performance, with the same footprint and dimensions, and specifically a superior specific power. The improvement in performance is obtained by appropriate heat exchange means which favour heat exchange between the aluminium structure of the radiator element and the surrounding air; according to the invention, the heat exchange between the aluminium and the air is given priority over the heat exchange between the water (circulating inside the radiator element) and the aluminium, as in the known art which considers the water/aluminium exchange the critical aspect to be improved in order to improve the performance of the radiator element .

In a radiator element, the heat is transferred to the environment to be heated in three successive stages: first, the heat is transferred by the water that circulates inside the radiator element (namely in the water chamber) to the walls of the water chamber by forced convection; therefore the heat is transferred by conduction to the inside of the aluminium structure of the radiator element, passing from the walls of the water chamber to the other parts of the element (fins, partitions, plates) ; lastly, the heat is transferred from the aluminium to the air of the environment in which the radiator element is installed essentially by natural convection (in addition to radiation but to a significantly lesser and substantially negligible extent) .

The radiator element therefore includes a water circuit, defined by the water chamber and by the hydraulic connections that connect the element to adjacent elements and/or to an external hydraulic system, and an air circuit, defined by the volumes available for passage of the air around the aluminium structure of the element. According to the current common knowledge of the phenomena of heat exchange in a radiator element, and specifically a die-cast aluminium radiator element, the most effective heat exchange part is considered the high temperature part between the water and the aluminium. The known art consequently prescribes an increase in the temperature and the dimensions of the water/aluminium exchange surfaces.

Since the heat comes mainly from the water at high temperature circulating in the water chamber, the known solutions for increasing the specific power therefore consist essentially in: - using large-dimension hydraulic connections, and relatively large water chambers;

- reducing the thickness of the aluminium parts (water chamber wall, fins, partitions, etc.);

- developing the fins directly on the water chamber to increase the temperature of the fins and therefore promote heat exchange between the water and the fins.

This approach is overall unfavourable to the heat exchange between the aluminium structure of the radiator element and the surrounding air, since it limits the space available and therefore the speed and efficiency of the aluminium/air heat exchange .

Actually, the technicians of the Applicant have realised that the critical aspect for increasing the efficiency of the radiator element (its specific power) is the heat exchange between the aluminium and the air, and not the heat exchange between the water and the aluminium. According to the invention, therefore, the transmission of heat is increased between the aluminium of the radiator element and the air that laps its surfaces, enlarging the space available for the air inside the reference volume of the radiator element (i.e. the volume defined by the overall dimensions of the element) .

The increase in space available for the aluminium/air heat exchange is not achieved simply by increasing the dimensions of the radiator element, since it is necessary to comply with market requirements, which establish standard dimensions of the elements .

The invention therefore consists of a radiator element comprising heat exchange means configured so as to promote heat exchange between the aluminium parts and the air that laps the surfaces of said parts, with respect to the heat exchange between the water circulating in the radiator element and the aluminium structure of the element, observing the dimensional constraints of the element . In short, given that the radiator element has a pre-defined reference volume, comprising a portion of volume occupied by- aluminium, a portion of volume occupied by water and a portion of volume occupied by air, according to the invention the portion of volume occupied by the air is increased, reducing the portions of volume occupied by the aluminium and the water.

In this way, numerous advantages are obtained in terms of heat exchange performance and efficiency, confirmed by experimental data.

A greater specific power is obtained, substantially maintaining the thermal power and reducing the weight of the element; the air circulation speed is improved, thus improving the aluminium/air exchange efficiency (a particularly significant result obtained by intervening on the sections of the air circuit with smaller air passage section) ; the space for development of the finned surfaces, which are very high- performance in terms of heat emission, is increased; the impact in terms of weight of the water circuit is reduced, thus reducing the overall weight of the element.

To summarise, according to the invention the specific power per unit of weight of the radiator element is increased by increasing the volume of the air circuit and reducing the volume of the water circuit.

It has been seen that reducing the space for the water and consequently increasing the space available for the air (in compliance with the dimensional limits imposed by the market) results in higher air flow rates. - -

The best result is obtained by applying the concept on the entire water circuit and therefore reducing the dimensions of both the hydraulic connections and the water chamber. The reduction in the dimensions of the water chamber also allows an increase in the space available for the fins and therefore an increase in the surface of the fins.

In general, reducing the overall dimensions of the water circuit with respect to the overall volume of the radiator element significantly increases the efficiency of the element .

The water circuit consists essentially of the water chamber and the hydraulic connections and has a volume V which is therefore the internal volume of the water chamber and the hydraulic connections .

The overall volume of the radiator element can be appropriately replaced by a reference volume V_ref defined by the nominal dimensions of the element, namely by width, depth and centre distance (which are generally market standards) :

V_ref = L x P x .1

where L, P, I are the width, depth and centre distance of the element respectively.

According to the invention, the ratio between the volume V of the water circuit and the reference volume V_ref of the radiator element is less than or equal to a maximum limit, given by the following formula, to one decimal place:

(I) k+k'-I + k"- I •100 + 0,1

L-P-I where

k = -0.1856679

k' = - 0.02474 - -

k" = +0.2417

L = Width [dm]

P = Depth [dm]

I = Centre distance [dm]

In other words, the radiator element has dimensions (width, depth, centre distance) and a volume of the water circuit (volume occupied in use by the water inside the radiator element and by the hydraulic interconnection systems arranged inside the hydraulic connections of the element) which satisfy the following relation:

10

v L-P-I

•100 <

L-P-I 10

where:

k = -0.1856679

k' = -0.02474

k" = +0.2417

L = Width [dm]

P = Depth [dm]

I = Centre distance [dm]

V = Water circuit volume [dm3]

(the symbol containing all the terms in the numerator of the right-hand side of the relation indicates the rounding-off to the first decimal place of the expression contained) .

Having established that the performance of the radiator element improves if the aluminium/air heat exchange is given priority over the water/aluminium exchange, therefore increasing the volume of the air circuit with respect to the volume generically available and specifically with respect to the volume of the water circuit, the heat exchange means according to the invention can take various configurations . In one embodiment, since the volume of the air circuit has been identified as a critical parameter, i.e. the space available to -

the air within the standard dimensions of the radiator element, the invention intervenes specifically on the sections for passage of the air. In a generic cross section of the radiator element, i.e. on a plane perpendicular to the longitudinal axis (vertical in use) of the radiator element, the overall space available is given by a reference area defined by the overall dimensions of the element, namely as a product of the nominal width and depth of the radiator element.

Having defined a reference area S_REF of the cross section of the radiator element (section on a plane perpendicular to the longitudinal axis, vertical in use, of the element) as a product of the nominal width and depth of the radiator element, the area S_A available for the convective motion of the air in every cross section is only a portion of the reference area S_REF, the rest being occupied by water and aluminium. According to the invention, the sections for passage of the air are increased with respect to the section generically available (again, subject to compatibility with the dimensional constraints dictated by the market standards) : more precisely, the ratio between the section for the air and the section available overall, in every cross section between the axes of the hydraulic connections, including the extremes, is higher than a pre-established minimum value, defined by the following formula :

where :

z = 120 [mm2]

z' = 38.5 [mm]

L = Width [mm] P = Depth [mm]

The relation is satisfied in every cross section plane (horizontal) between the hydraulic connections, extremes included (i.e. also in the cross sections passing through the axes of the hydraulic connections) .

In this way, an enlargement of the air passages is obtained in the areas of the hydraulic connections: consequently, in these critical areas a higher air speed, a greater air flow, an increase in the aluminium/air heat exchange coefficients and an overall increase in specific power are obtained.

The increase in the air passage section in the areas of the hydraulic connections entails, in some embodiments of the invention, a reduction in the dimensions of the hydraulic connections.

According to the teachings of the known art, a reduced hydraulic connection would not allow adequate heat emission, because it would have a smaller exchange surface at high temperature, a criterion preferred in the traditional approach; a larger hydraulic connection allows higher temperatures to be obtained in the end area of the radiator element .

However, according to the innovative approach of the present invention, a surface with higher temperature does not always correspond to a greater heat exchange. It has been ascertained that the high temperatures encountered in the area of the hydraulic connections with traditional dimensions are due to the low air flow rate around said hydraulic connections; but a low air flow rate means low thermal power transmitted to the air and therefore poor heat exchange efficiency. According to the invention, around the hydraulic connections (arranged at the upper end and/or at the lower end of the radiator element) an air duct is provided which has a horizontal dimension (measured in the direction of the depth of the radiator element on a plane perpendicular to the longitudinal axis of the element and passing through the central axis of the hydraulic connection) , preferably on both sides of the connections, such as to increase the air flow around said hydraulic connections.

In particular, the difference between:

- the distance of the central axis of the hydraulic connection from the front or rear surface of the radiator element (measured perpendicular to the axis of the radiator element and to the central axis of the connection) ; and

the minimum distance between the outer surface of the connection and the front or rear surface of the radiator element (also measured perpendicular to the axis of the radiator element and to the central axis of the connection) ,

is less than or equal to approximately 18 mm (subject to the usual working tolerances) .

According to another embodiment of the invention, to further increase the specific power of the radiator element the aluminium-air exchange surface is also modified, specifically increasing the interface surface between the aluminium and the air, without jeopardising the desired increase in air flow.

The component that simultaneously guarantees lower resistance to the passage of the air and greater increase^" in the interface surface is the lateral finning (fins that protrude from the sides of the radiator element) .

It has been ascertained that the fins do not seriously impact on the air speed, and in any case they have significantly less influence on the air speed than the hydraulic connections . Since the fins are components with a high specific power per unit of weight, it is expedient to increase the space available for the finned surfaces. The area generically available for applying the lateral fins is subject to geometrical constraints due to market requirements; in general, the centre distance and the depth of the radiator element indirectly determine the space available for the finned surface .

According to the invention, in order to increase the space available in the vertical direction for the finned surfaces, the radiator element is characterised by the fact that the difference between the centre distance of the radiator element and the distance between the hydraulic connections measured parallel to the longitudinal axis of the element is less than or equal to approximately 36 mm (subject to the usual working tolerances) .

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will appear clear from the following description of a non- limiting embodiment example, with reference to the figures of the accompanying drawings, in which:

figure 1 is a perspective schematic view of a heating radiator element made of die-cast aluminium in accordance with the invention;

figure 2 is a schematic view in cross section of the radiator element of figure 1;

- figure 3 is a schematic view in longitudinal section of the radiator element of figure 1;

- figures 4A-4D are enlarged schematic views of respective details of the element of figure 1;

- figure 5 is a lateral schematic view of the element of figure 1, with parts removed for the sake of clarity.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to figures 1 and 2, a heating radiator element 1 made of die-cast aluminium comprises a substantially tubular monolithic body 2 made of aluminium (said term also comprising aluminium alloys) by means of a die-casting process. The element 1 and the body 2 extend substantially along a longitudinal axis A (in use, substantially vertical) between two axially opposed ends 3, 4; the body 2 is provided with a main inner water chamber 5 for passage of the water, radially delimited by a lateral wall 6 arranged around the axis A and closed axially at respective opposite longitudinal ends; advantageously, but not necessarily, the body 2 has a cross ^* section (perpendicular to the axis A) substantially oval, elliptic or in any case elongated along an axis, and the lateral wall 6 of the body 2 which delimits the chamber 5 is tapered towards one of the ends 3 , 4.

The ends 3, 4 of the element 1 are provided with respective pairs of connections 7 which protrude from opposite sides of the body 2 along respective central axes X parallel to each other and substantially perpendicular to the axis A to connect the element 1 to other similar elements and/or to an external hydraulic system; the connections 7 are shaped for example (but not necessarily) like cylindrical sleeves with circular section and are internally provided with transverse through ducts 8, communicating with the chamber 5.

The element 1 comprises a system 10 of heat exchange fins.

In particular, the system 10 comprises: a pair of partitions 11 which protrude diametrically opposite from the lateral wall 6 along a longitudinal centreline plane of the element 1; a front plate .12 and a rear plate 13 , arranged at respective ends of the partitions 11 and substantially perpendicular to the partitions 11 and parallel to the axis A, optionally formed of several sectors or portions of plate separated by slits and/or apertures; a plurality of lateral fins 14 that protrude from the - -

body 2 , namely from the lateral wall 6 and/or from the partitions 11.

The element 1 has a width L (maximum width of the element 1, given by the distance between the opposite free ends of each pair of connections 7 aligned along an axis X) , a depth P (distance between the plates 12, 13) and a centre distance I (distance between the central axes X of the connections 7) . The body 2, including the connections 7, and the system 10 define as a whole an aluminium structure 15 of the element 1. The entire structure 15 constitutes a monolithic piece produced by die-casting. As schematically shown in figure 3, the element 1 includes a water circuit 16, defined by the main chamber 5 delimited by the wall 6 and by the ducts 8 of the connections 7 ; and an air circuit 17, defined by the volumes available for passage of the air around the structure 15.

The water circuit 16 has a volume V which is the internal volume of the chamber 5 and of the connections 7.

The ratio between the volume V of the water circuit 16 and the reference volume V_ref of the element 1, defined as:

V_ref = L x P x I

where L, P, I are the width, depth and centre distance of the element 1 respectively, is less than or equal to a maximum limit, given by the following formula, to the first decimal place:

where

k = - 0.1856679

k' = - 0.02474 k" = +0.2417

L = Width [dm]

P = Depth [dm]

I = Centre distance [dm]

The air circuit 17 is configured so that the ratio between the section for the air and the overall section available, in every cross section between the axes X of the connections 7 , including the extremes (i.e. including the sections that contain the axes X) , is higher than a pre-established minimum value, defined by the following formula:

where :

S_A is the area available for the convective motion of the air in the cross section considered;

S_REP is the reference area of the cross section considered (section on a plane perpendicular to the axis A) , given by the product of the width L and depth P of the element 1,

z = 120 [mm2]

z' = 38.5 [mm]

L = Width [mm]

P = Depth [mm]

With reference also to figures 4A-4D, the connections 7 are shaped so that the following relation is satisfied (preferably, for each connection 7 ) , subj ect to the usual working tolerances : (VI) a - b < 18 mm

where :

"a" is the distance (in mm) between the central axis X of the connection 7 and a front or rear surface 18 of the element 1, in particular of the plates 12 and/or 13, measured perpendicular to the axis A of the element 1 and to the central axis X of the connection 7; - 1 -

^wb" is the distance (in mm) between an outer surface 19 of the connection 7 and the front or rear surface 18 of the element 1, again measured perpendicular to the axis A and to the axis X. With reference to figure 5, the connections 7 are also shaped so that the difference between the centre distance I of the element 1 and the distance d between the connections 7 , measured parallel to the axis A of the element 1, is less than or equal to approximately 36 mm (subject to the usual working tolerances), i.e. so that the following relation is satisfied (preferably, for each connection 7) :

(VII) I - d≤ 36 mm

It is understood that the individual configurations described can also be applied separately to the element 1.

It is also understood that further modifications and variations can be made to the radiator element described and illustrated here which do not depart from the scope of the attached claims .

Claims

1. A heating radiator element (1) made of die-cast aluminium, extending along a longitudinal axis (A) and having a monolithic structure (15) made of aluminium by die-casting, comprising a tubular body (2) and connections (7) that extend from opposite sides of the body (2) along respective central axes (X) for connecting the element (1) to other similar elements and/or to an outer plumbing system; the structure (15) being internally provided with a water circuit (16) for circulation, in use, of a water stream; the element being characterized in that the aluminium structure (15) and the water circuit (16) define heat exchange means that increase the aluminium/air heat exchange so as:

where :

V is the volume of the water circuit (16), expressed in dm3 ; L, P, I are width, depth and centre distance respectively of the element (1) , expressed in dm;

k = -0,1856679;

k' = -0,02474;

k" = +0,2417.

2. The element according to claim 1, wherein the heat exchange means defined by the aluminium structure (15) and by the water circuit (16) are configured so as, in each cross section defined on a plane perpendicular to the axis (A) and set between the central axes (X) of the connections (7) , including extremes :

z

>1-

REF L-P P where :

SREF is the area of the cross section, calculated as the product of the width (L) and the depth . (P) of the element (1) , expressed in mm2;

S_A is the area of the cross section available for air passage, expressed in mm2 ;

L, P are width and depth respectively of the element (1) , expressed in mm;

z = 120 [mm2] ;

z ' = 38, 5 [mm] .

3. The element according to claim 1 or 2 , wherein at least one connection (7) is shaped so as:

a - b ≤ 18 mm

where:

"a" is the distance, expressed in mm, between the central axis (X) of the connection (7) and a front or rear surface (18) of the element (1) , measured perpendicular to the axis (A) of the element (1) and to the central axis (X) of the connection (7) ; "b" is the distance, expressed in mm, between an external surface (19) of the connection (7) and the front or rear surface (18) of the element (1) , measured perpendicular to the axis (A) of the element (1) and to the central axis (X) of the connection (7) .

4. The element according to one of the preceding claims, wherein at least one connection (7) is shaped so as the difference between the centre distance (I) of the element (1) and the distance (d) between two connections (7) set on the same side of the element (1), measured parallel to the axis (A) of the element (1) , is lower than or equal to about 36 mm.