This application claims the benefit of an priority to Italian patent application number MI2014A002208, filed on Dec. 12, 2014, the entirety of which is hereby incorporated by reference
The present invention relates to a transportable air heater, in particular to a transportable combustion heater which can be used in very different ambient conditions, for example in work sites, mines, industrial warehouses, and also in temporary or permanent civil and military installations.
Transportable liquid or gas fuel heaters are known for heating air, with a combustion chamber, a fuel supply device which dispenses a liquid fuel into the combustion chamber, a first air conveyor which introduces combustion air into the combustion chamber, an annular thermal exchange chamber formed in relation to thermal exchange around the combustion chamber, and a second air conveyor which conveys the ambient air through the thermal exchange chamber to heat the ambient air. In order to allow the installation and transport of the heater, it is also known to mount all the components thereof on a transportable supporting structure, for example a carriage that can be towed on the road.
The nature of the typical applications (work sites, mines, large areas in remote locations and in difficult climate and ambient conditions, high production of heat) of these heaters has favored the aspects of reliability and structural sturdiness to the detriment of other functional features to date considered secondary and not deserving of particular attention, such as in particular the overall heat efficiency of combustion and thermal exchange, the noisiness, vibrations and accordingly, the weight, dimensions and operating costs.
With the ever increasing attention paid to operating in an economically and ecologically sustainable manner, there is a need for improving large-sized and high thermal power heaters, also with reference to the aforesaid “secondary” functional aspects, while obviously ensuring the reliability and sturdiness thereof.
It is therefore the object of the present invention to improve a heater of the type specified above, with reference to the energy efficiency of combustion and thermal exchange and, secondarily, also concerning the operating costs, noisiness, vibrations, weight and dimensions.
According to an approach of the invention, at least part of the objects of the invention can be achieved by modifying the fluid-dynamic behavior, with particular reference to the flow of the combustion fumes, and the conditions of thermal exchange between the combustion fumes and the ambient air, so as to increase the time, the pathway and the surface of the thermal exchange without however generating an excessive counterpressure when the fumes are exhausted, which would jeopardize the stability of the combustion.
According to a further approach of the invention, at least a part of the objects can be achieved by isolating the combustion and thermal exchange unit from the outer housing in an effective and space-saving manner.
At least part of the objects of the invention is achieved by means of a heater according to claim 1. The dependent claims relate to advantageous and preferred embodiments of the invention.
The features and advantages of the present invention will become apparent from the description of preferred embodiments thereof, given only by way of non-limiting, indicative example, with reference to the drawings, in which:
With reference to the drawings, a transportable combustion air heater 1 comprises:
A) a transportable supporting frame 2 (possibly equipped with wheels),
B) a housing 3 made of steel sheet fixed to frame 2 and having:
C) a cylindrical combustion chamber 14 made of steel sheet fixedly arranged in housing 3 and internally defining a combustion space 15, said combustion chamber 14 having:
D) a cylindrical annular thermal exchange channel 24 formed around the combustion space 15 and defined by the side wall 16 of the combustion chamber 14 and by a first cylindrical wall 28 outwardly extended around the side wall 16 of the combustion chamber 14, the thermal exchange channel 24 having:
E) an external heating chamber 26 made of steel sheet fixedly arranged in the housing 3, in which said external heating chamber 26 forms a cylindrical annular fume channel 27 around the thermal exchange channel 24 and comprises:
E) an exhaust fume pipe 35 extended from the exhaust fume opening 32 of the external heating chamber 26 up to or through the third pathway 11 of housing 3 for exhausting the exhausted fumes from the annular fume channel 27 to the outside of heater 1,
F) an air distribution space 36 defined by housing 3 and by the front walls 20, 30 of the combustion chamber 14 and of the external heating chamber 26,
According to an aspect of the invention, the fume inlet openings 31 lead into a first end portion 41 of the annular fume channel 27 and the exhaust fume opening 32 is formed in a second end portion 42 of the annular fume channel 27, opposite to the first end portion 41, in which the first end portion 41 has a longitudinal extension L41 which is less than one third of the whole longitudinal length L27 of the annular fume channel 27 and the second end portion 42 has a longitudinal extension L42 which is less than half of the whole longitudinal length L27 of the annular fume channel 27. Moreover, one or more guide walls 43 are arranged in the external heating chamber, which guide walls 43 are transversal to the first and second cylindrical walls 28, 29, which lengthen the fume flow paths 12 in the annular fume channel 27 from the fume inlet openings 31 to the exhaust fume opening 32.
Heater 1 thus configured allows a thermal exchange between the combustion fumes 12 and the air to be heated 10 in two cylindrical interfaces (side wall 16 of the combustion chamber 14 and first cylindrical wall 28) and with a better distribution and increased permanence of the still hot fumes along the outer thermal exchange interface formed by the first cylindrical wall 28.
In accordance with an embodiment, the guide walls 43 can comprise windows 44, for example narrow, elongated slots, to cause a portion of the fumes 12 to flow directly through the guide walls 43 rather than guiding them along it, to avoid the occurrence of excessive counterpressures (resistance to the flow) in particular operating conditions of heater 1, for example having reduced thermal power with reduced flow rate of fuel 45 and combustion air 8.
According to an embodiment, the guide walls 43 comprise a first group of (preferably two) guide walls spaced from each other in circumferential direction (relative to the longitudinal axis 17) and running in longitudinal direction (parallel to the longitudinal axis 17) from a front end of the annular fume channel 27 towards an opposite rear end thereof, and a second group of (preferably two) guide walls spaced from each other in a circumferential direction (relative to the longitudinal axis 17) and running in a longitudinal direction (parallel to the longitudinal axis 17) from the rear end of the annular fume channel 27 towards the front end thereof, in which the guide walls 43 of the first group overlap or alternate with the guide walls 43 of the second group, thus defining a fume flow path having an undulated shape from the fume inlet openings 31 to the exhaust fume opening 32. Preferably, the guide walls 43 lie on planes radial to the longitudinal axis 17 and have an axial length L43 ranging from 60% to 80%, preferably of about 70%, of the total axial length L27 of the fume channel 27, thus ensuring a distribution of the hot fumes along the whole thermal exchange area of the first cylindrical wall 28.
The windows 44 are formed in the guide walls 43 of the second group at the position of the fume inlet openings 31 and extend in axial direction along the whole region of the first cylindrical wall 28 in which the fume inlet openings 31 are formed. Preferably, the axial length L44 (parallel to the longitudinal axis 17) of the windows 44 ranges from 40% to 60%, preferably is about 50% of the axial length L43 of the corresponding guide wall 43.
Advantageously, the fume inlet openings 31 are formed in an area circumferentially opposite (and preferably, but not necessarily, also axially opposite) to the area where the exhaust fume opening 32 is formed and the guide walls 43 are positioned between the fume inlet 31 and the exhaust fume 32 openings in such a manner as to define a complete wave path, i.e. with two opposed bends, between such openings 31, 32 (
According to a further aspect of the invention, the sum of the areas of opening section of the fume outlet openings 23 ranges between 1/40 (=2.5%) and 1/60 (=1.67%), preferably between 1/50 (=2%) and 1/60 (=1.67%), even more preferably approximately 1/54 (=1.85%) of the total area of the cylindrical side wall 16 (including the area of the fume outlet openings 23) of the combustion chamber 14, while the opening section area of the single fume outlet opening 23, considered individually, can be advantageously less than 100 cm2, preferably less than 75 cm2, even more preferably approximately 45 . . . 55 cm2.
Thus, the fume outlet openings 23 result in a constriction of the flow outlet from the combustion chamber 14 which creates a counterpressure such as to promote a complete distribution and sufficient permanence of the hot fumes along the whole side wall 16 of the combustion chamber 14, i.e. on the inner thermal exchange interface. Moreover, the total pathway area of the fume outlet openings 23 ensures both the stability and reliability of combustion and a sufficient heating of the first cylindrical wall 28 which forms the outer thermal exchange interface.
In accordance with a further aspect of the invention, heater 1 comprises a layer 46 of heat-reflecting material, in particular an aluminized sheet, formed around the second cylindrical wall 29 of the external heating chamber 26 such as to provide a first thermal isolation barrier with respect to housing 3. The layer 46 of heat- reflecting material is preferably circular cylindrical and coaxial with the longitudinal axis 17 of heater 1. The aluminized sheet can comprise a base metal layer, e.g. steel, and an aluminum coating which automatically forms an outer layer of aluminum oxide (Al2O3) called alumina and is very heat-resistant but also heat-reflecting. The aluminized sheet forms the aforesaid heat-reflecting layer 46 with the surface of the alumina facing radially inwards.
Alternatively or additionally, an annular interstice 47 can be provided, which is formed:
The first barrier reduces heat losses by means of thermal isolation and heat retro-reflection, while the second barrier disperses residual heat to obviate the overheating of housing 3, and brings the extracted heat back into the flow of heated air.
This solution of thermal isolation is less cumbersome and more long-lasting than a thermal isolation for example by means of a layer of mineral fibers.
In an advantageous embodiment, the fume pipes 33 extend in a direction radial to the longitudinal axis 17 and have an elongated transversal section shape in a heater 1 longitudinal direction (direction of the air flow 10 to be heated in the thermal exchange channel 24), in particular a prismatic shape, for example hexagonal, with front and rear corners aligned in longitudinal direction which corresponds to the direction of the air flow 10.
This reduces the resistance to the air flow 10 to be heated on the one hand and compensates for and increases the thermal exchange area at the fume pipes 33 on the other.
According to a preferred embodiment, the ratio between the total area of thermal exchange, intended as the sum of the areas of the side wall 16 of the combustion chamber 14 and of the first cylindrical wall 28 of the external heating chamber 26, and the sum of the areas of the combustion space 15 and of the annular fume channel 27 in section perpendicular to the longitudinal axis 17, is greater than 10:1, preferably ranges between 10:1 and 14:1, even more preferably is approximately 12:1, while the ratio between the total area of thermal exchange and the area of the thermal exchange channel 24 in section perpendicular to the longitudinal axis 17 is greater than 25:1, preferably ranges between 30:1 and 40:1, even more preferably is about 37:1.
The aforesaid geometrical ranges are particularly advantageous from a fluid-dynamic and energy efficiency (reduction of noise and of vibrations, combustion stability, thermal exchange efficiency) point of view for configurations of heater 1 in which the cylindrical walls 16, 28, 29 of the combustion chamber 14 of the external heating chamber 26 are coaxial.
Looking in even greater geometrical detail of the preferred embodiment, tests and numeric simulations point out a high energy efficiency (combustion and thermal exchange) with reduced vibrations and noise, when:
By way of non-limiting example, the aforesaid geometrical parameters can be chosen as follows (approximate values of example ranges, preferred values being underlined):
Axial length L16 of the combustion chamber 14=725 mm . . . 825 mm . . . 875 mm,
Diameter D16 of the combustion chamber 14=400 mm . . . 423 mm . . . 450 mm,
Diameter D28 of the first cylindrical wall 28=490 mm . . . 513 mm . . . 540 mm,
Diameter D29 of the second cylindrical wall 29=560 mm . . . 581 mm . . . 600 mm,
When provided, diameter D46 of the heat-reflecting layer 46=590 mm . . . 611 mm . . . 630 mm,
Diameter D4 of the side wall 4 of housing 3=605 mm . . . 621 mm . . . 635 mm.
According to an embodiment, the side wall 4 of housing 3 comprises two semi-cylindrical half-shells 53 removably screwed to each other, preferably in a substantially vertical (to reduce the side dimensions) or horizontal (to facilitate the opening of housing 3 for maintenance operations or the replacement of the burner-heat exchanger unit) screwing plane. In any case, forming the side wall 4 by means of two half-shells 53 reduces the transport and handling costs of the semi-finished sheets and the manufacturing of heater 1.
According to a further embodiment, the external heating chamber 26 comprises one or more cleaning windows 49 possibly formed in the annular front wall 30 and accessible through the fourth pathway 13 of housing 3, and being openable/closable by means of lids 50 removably fixed (e.g. by means of screws) to the external heating chamber 26 (
In accordance with a further embodiment, the side wall 16 of the combustion chamber 14 and the first cylindrical wall 28 of the external heating chamber 26 each form a plurality of bosses 52 protruding radially outwards and adapted to further promote the thermal exchange in the inner and outer thermal exchange interfaces.
Those skilled in the art may make several changes and adaptations to the above-described embodiments of the heater, and may replace elements with others which are functionally equivalent in order to meet contingent needs, without thereby departing from the scope of the following claims. Each of the features described as belonging to a possible embodiment can be embodied independently of the other embodiments described.
Number | Date | Country | Kind |
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MI2014A002208 | Dec 2014 | IT | national |