Heat exchange – Thermosyphonic flue type – Flue formed between facing second fluid containing conduits
Patent
1988-04-05
1989-08-15
Kamen, Noah P.
Heat exchange
Thermosyphonic flue type
Flue formed between facing second fluid containing conduits
165 78, 165177, 165180, 165905, 285156, 285361, 285396, F24H 300
Patent
active
048565814
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat exchanger apparatus and a method for its manufacture.
The invention more particularly relates to a heat exchanger modular unit, the assembly of which together with similar modular units forms a heat exchanger apparatus.
The apparatus according to the invention is particularly useful as a radiator in hot water or steam heating plants for buildings. Consequently, for the sake of brevity in the following description, the term "radiator" will be used as a synonym for a heat exchange apparatus. However, this apparatus can be efficiently used also in a reverse mode for the cooling of rooms.
Still more particularly, the invention relates to a radiator manufactured from a material of extruded or die-cast anticorodal aluminium alloy which can be passivated in electrolytic bath.
2. Description of the Prior Art
Pig iron and steel radiators have been known for some time. These largely widespread radiators show the drawback of having a relatively low heat transfer coefficient (heat conduction coefficient 40 calories/m.sup.2 hour 0.degree. C.), so that they show a certain inertia in their heat transfer function and moreover they make a transfer by forced ventilation difficult, in that in such a case the low heat transfer coefficient becomes a controlling and restrictive factor.
Also known are the drawbacks due to difficulties in their transportation, assembly and installation in view of the excessive weight.
Aluminium is an ideal material due to the manufacturing of radiators for its high heat transfer capacity (heat conduction coefficient 175 calories/m.sup.2, hour 0.degree. C.).
Several approaches have been made in the prior art for manufacturing radiators of aluminium and alloys thereof.
The technical problem to be solved in this case is the difficulty of obtaining structural aluminium pieces suitable for radiators, by means of conventional methods of aluminium fabrication.
A further important problem is that in the operating conditions of the radiators, in contact with flowing water at a relatively high temperature, problems of corrosion arise in that the aluminium alloy structure and the various other metals in the plant with a different electric potential, produce electrode couples. These couples in the presence of hot water form a cell, the anode of which is aluminium. A process of corrosion is thus initiated, which is destined to produce holes.
Some prior art methods of manufacturing aluminium radiators, use aluminium alloy plates made by die-casting.
In order to be able to carry out die-casting, the prior art methods use an aluminium alloy containing considerable amounts of silicium (10 to 20%), as well as copper, iron, magnesium, and so on. Such silicium amounts are needed to obtain a sufficient fluidification of the melt which has to be cast in very thin thicknesses and into particularly large and complicated moulds.
A typical alloy used for this purpose is an alloy type UNI 5076. This is an aluminium-silicium-copper-iron alloy for die-casting (Si 12%, Cu 2%, Fe 0.7%). This alloy, however, due to such a high silicium content is particularly susceptible to corrosion, cannot be passivated in an electrolytic bath and consequently, not being electrically insulated, it is liable to form electrolytic couples, so that the initiation of the corrosion process is only a matter of time and unavoidable.
Moreover the heat conduction coefficient is considerably lower than that of pure aluminium, being known that silicium is the most efficient thermic insulator.
These characteristics led to the consequence that this type of aluminium alloy radiator has not met with success.
In British Pat. No. 1292767 a radiator is described having the radiant elements made of extrudates of aluminium alloy. The structure of this radiator comprises, however, pieces of different materials, such as an inner copper coating, headers, the material of which is not specified, and tie rods of steel for connecting the headers and the radiant elements. This
REFERENCES:
patent: 2800343 (1957-07-01), Ulrich
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