U.S. patent number 3,904,851 [Application Number 05/402,804] was granted by the patent office on 1975-09-09 for electric heater for heating a fluid medium.
This patent grant is currently assigned to Separex SA. Invention is credited to Karl Ake Sture Gustafson, Johan Eric Hayden Westbert.
United States Patent |
3,904,851 |
Gustafson , et al. |
September 9, 1975 |
Electric heater for heating a fluid medium
Abstract
An electric heater for heating flowing air comprises a sheet
support for a heater filament of non-circular cross-section and
twisted about its longitudinal axis. The heater filament is wound
about or attached in meander fashion to the support sheet in such a
manner that successive segments of it are parallel and extend
between opposed edges of the support sheet in contact with a face
of the latter. An insulating cover layer disposed in contact with
the heater filament segments defines together with these segments
and the support sheet a multiplicity of relatively narrow,
open-ended passages for the air to be heated. The support sheet may
be flat and rigid or flexible and convoluted on itself together
with the cover layer, or it may be tubular.
Inventors: |
Gustafson; Karl Ake Sture
(Chatel-St-Denis, CH), Westbert; Johan Eric Hayden
(Lidingo, SW) |
Assignee: |
Separex SA (CH)
|
Family
ID: |
20296368 |
Appl.
No.: |
05/402,804 |
Filed: |
October 2, 1973 |
Foreign Application Priority Data
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|
|
|
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Oct 5, 1972 [SW] |
|
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12823/72 |
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Current U.S.
Class: |
392/485; 219/546;
392/492; 219/542; 338/58; 338/320; 392/494 |
Current CPC
Class: |
H05B
3/16 (20130101); F24H 3/0405 (20130101); H05B
3/56 (20130101); H05B 3/565 (20130101) |
Current International
Class: |
F24H
3/04 (20060101); H05B 3/58 (20060101); H05B
3/54 (20060101); H05B 3/16 (20060101); H05b
003/10 (); F24h 003/04 (); H01c 003/00 () |
Field of
Search: |
;219/374-376,381,382,373,523,531,544,542,546,551,296-299,305-307,319,366-368,369
;338/57,58,282,286,297,287,320,315,321 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bartis; A.
Attorney, Agent or Firm: Hill, Gross, Simpson, Van Santen,
Steadman, Chiara & Simpson
Claims
What is claimed is:
1. An electrical heater for heating a fluid medium flowing
therethrough comprising:
a. an electrically insulating heating element support;
b. a filamentary heating element, twisted about the length of the
element, mounted on the heating element support and including a
plurality of parallel heating-current conducting segments extending
in spaced relations between opposed edges of the support and in
engagement with at least one face of the support, the length of
said segments being more than twice the spacing of adjacent
segments; and
c. an electrical insulating cover layer having one face thereof in
engagement with said segments and uniformly spaced from said face
of the heating element support;
the heating element segments defining between the heating element
support and the cover layer a plurality of helically walled
parallel passages for the passing of the fluid medium to be heated,
the passing being parallel to said walls from one of said edges of
the heating element support to the other, said passages having a
dimension transverse of said faces substantially equal to the
maximum cross-sectional dimension of the heating element
segments.
2. A heater according to claim 1 including:
a casing having a first opening defining a fluid inlet, a second
opening defining a fluid outlet, and an elongated flow path
extending between the inlet and the outlet in which said heating
element, said support, and said cover layer are disposed with said
passages extending substantially parallel to the longitudinal axis
of the flow path.
3. A heater according to claim 2 in which the heating element
support and the cover layer are held together as a unit fitting
snugly in the casing.
4. A heater according to claim 1 in which the filamentary heating
element comprises two wires twisted together.
5. A heater according to claim 1 in which the filamentary heating
element is a flat strip twisted about its longitudinal axis.
6. A heater according to claim 1 in which the heating element
support is a flexible strip,
the cover layer is flexible,
the heating element support and the cover layer are convoluted
longitudinally on themselves to an annular structure, and
inner and outer concentric annular casings are provided, which
define between them an annular space in which said annular
structure is disposed with a snug fit.
7. A heater according to claim 1 in which the heating element
support is a first tubular body, the filamentary heating element
segments are disposed on the outer surface of the tubular body and
extend between its ends, and the cover layer is a second tubular
body concentric with and enclosing the first tubular body.
8. A heater according to claim 7, including a second heating
element support formed by a third tubular body having additional
parallel heating element segments disposed on its outer surface and
extending between its ends, the second heating element support
being concentric with and disposed within the first tubular body
with said additional heating element segments engaging the inner
surface of the first tubular body.
Description
This invention relates to electric heaters, and more particularly
to electric heaters of the kind in which air or some other flowing
fluid medium contacts an electric heating element to be heated
thereby.
A common type of electric air heater comprises a heat-resistant
insulating support which carries a filamentary heating element and
is disposed in a flow passage for the air to be heated. In heaters
of this type, the transfer of the heat from the heating element is
often rather nonuniform and inefficient, because only a small
portion of the air flow contacts the heating element. In addition,
the electric insulation of the heating element from the walls of
the flow passage often renders the heater bulky and structurally
complicated.
A general object of this invention, therefore, is to provide an
electric heater for air or other fluid mediums which is simple and
inexpensive and ensures an efficient and uniform heating. A more
specific object is to provide an electric heater in accordance with
the foregoing general object which is compact so that it can be
used in applications where the available space is limited.
The above and other objects, features and advantages of the present
invention will be understood from the following detailed
descriptions of exemplary embodiments shown in the accompanying
drawings.
FIG. 1 is a longitudinal cross-sectional view along line I--I of
FIG. 2 of an air heater constructed in accordance with the
invention;
FIG. 2 is a cross-sectional view along line II--II of FIG. 1;
FIGS. 3 and 4 are cross-sectional views along line III--III of FIG.
4 and line IV--IV of FIG. 3, respectively, showing a modification
of the heater of FIGS. 1 and 2;
FIG. 5 is a developed view of an insulating support strip which is
provided with a helically wound heater filament and placed on an
insulating cover strip and which, in the finished heater, is
convoluted together with the cover strip to form an annular heater
body;
FIG. 6 is an end view showing the finished heater with the
convoluted heater body disposed in the annular space between two
concentric casing members;
FIG. 7 is a longitudinal cross-sectional view along line VII--VII
of FIG. 6;
FIG. 8 is a longitudinal cross-sectional view of a heater comprised
of three tubular, concentric heater bodies disposed in a tubular
outer casing;
FIG. 9 is a perspective view of one of the heater bodies in FIG.
8
In the drawings the flow of air to be heated is indicated by
arrows, but for simplicity of illustration, the means producing the
forced air flow through the heater are omitted.
As shown in FIGS. 1 and 2, the heater 10 includes a casing 11 of
rectangular cross-section (FIG. 2) and having a through opening 12
adapted to receive the air to be heated and discharge the heated
air. The two sidewalls of the opening 12 are each provided with an
electrically insulating, heat-resistant side plate 13 each of which
serves as a cover layer. Between the two side plates 13 and spaced
therefrom there is disposed another electrically insulating and
heat-resistant rigid plate 14 on which a filamentary resistance
heating element 15 of non-circular cross-section is supported. The
heating element 15 consists of two resistance wires 15' of circular
cross-section which are twisted together about their length and
have their ends connected to a pair of terminals 16 on the support
plate 14 the wires thus defining helical surfaces.
As best seen from FIG. 1, the heating element 15 is helically wound
about the support plate 14 in such a manner that the substantially
straight segments 17 of its convolutions are generally parallel to
the longitudinal axis of the opening 12 and substantially uniformly
distributed over both faces of the support plate 14. As seen from
FIG. 2 the segments 17 are covered and engaged by the side plates
13, whereby each side plate 13 defines together with the adjacent
face of the support 14 and the segments 17 a group of parallel and
substantially identical, open-ended air passages 18 extending
longitudinally of the opening 12. The side plates 13 sealingly
engage the side walls of the opening 12, and all air traversing the
opening 12 accordingly flows through the passages 18. A suitable
choice of the spacing of the segments 17 and the diameter of the
wires 15' (and thus the dimension of the air passages 18
transversely of the side and support plates 13,14,13, this
dimension being twice the wire diameter) ensures an efficient and
uniform heating of all air passing through the opening 12.
In assembling the heater 10 of FIGS. 1 and 2, the support plate 14
with the heating element 15 and the terminals 16 are slid as a unit
into the space between the side plates 13 in the opening 12. A
number of terminal posts 19 are then inserted through bores (not
shown) in the casing 11 and secured to the terminals 16.
Alternatively, the terminal posts 19 may be secured to the
terminals 16 before the unit is slid into the casing; notches in
the casing then receive the terminal posts.
In the heater 102 shown in FIGS. 3 and 4, the side plates 13 belong
to the aforesaid heater unit, which is adapted to be slid into the
opening 12 of the casing 11. To this end, the plates 13 and the
plate 14 are rigid and held together by a helically twisted and
helically wound wire 20 extending transversely of the heating
element 15a as shown in FIG. 3. The diameter of the wire 20 is
chosen such that the heater unit fits snugly in the casing opening
12. The wire 20 spaces the side plates 13 from the sidewalls of the
opening 12 but prevents the air from bypassing the air passages 18
between adjacent segments 17 of the heating element 15.
The resistance heating element 15a in FIG. 3 is a narrow strip
twisted about its longitudinal axis, and the dimension of the air
passages 18 transversely of the plates 13 and 14 thus is
approximately equal to the width of the strip. By varying the width
of the strip while maintaining a constant cross-sectional area,
different transverse dimensions of the air passages can be obtained
without changing the resistance value of the heating element.
In FIGS. 5 to 7, a resistance heating element 21 formed by a
helically twisted narrow strip is helically wound about an
elongated, electrically insulating support strip 22 with the
parallel, uniformly spaced segments 23 extending transversely of
and between the longitudinal support strip edges and in engagement
with the support strip faces. The ends of the heating element 21
are connected to a pair of terminals 24 adjacent the ends of the
support strip. The support strip 22 with the heating element 21 is
placed on an electrically insulating, flexible cover strip 25
slightly wider than the support strip 22 and having its end
portions 25A and 25B projecting from the ends of the support
strip.
FIGS. 6 and 7 show a complete heater 26, in which the support strip
22 and the cover strip 25 are convoluted longitudinally on
themselves to an annular heater body, the inner end of the
convoluted body being the right-hand end in FIG. 5. As seen in FIG.
6, the cover strip 25 engages and covers all of the heating element
segments 23.
The annular heater body is inserted and snugly fits in the annular
space defined between two concentric casing members, an inner
tubular member 27 and an outer tubular member 28 having an end wall
29. The air to be heated is passed through the several relatively
narrow air passages 30 defined by the strips 22 and 25 and the
heating element segments 23 and leaves the heater 26 through the
inner casing member 27 as shown in FIG. 7.
The heater 31 shown in FIGS. 8 and 9 comprises three tubular
concentric heater bodies 32, 33, 34 and a tubular casing body 35
concentrically surrounding the heater bodies. Apart from their
dimensions the three heater bodies are substantially identical, and
the outermost heater body 32 is shown in FIG. 9.
As shown in FIG. 9, the heater body 32 has a multiplicity of
notches 36 and intervening lips 37 at both ends. The lips serve to
hold a resistance heating element 38 formed by a twisted strip
which runs along a meandering path around the circumferential outer
surface of the body and has its ends connected to a pair of
terminals 39. The parallel segments 40 of the heating element
extending between the notched ends are slightly inclined relative
to the axis of the body 32 and define between them a large number
of correspondingly inclined open-ended air passages 41.
As shown in FIG. 8, the spacing between adjacent heater bodies and
between the outermost heater body 32 and the casing body 35 is
equal to the maximum cross-sectional dimension of the heating
element 38. That is, the circumferential inner surfaces of the
casing body 35 and the heater bodies 32 and 33 engage the heating
element segments 40 on, respectively, the outermost heater body 32,
the intermediate heater body 33, and the innermost heater body 34
and thus fulfil the function of the covering layers 13 and 25 in
FIGS. 1 to 4 and 5 to 7.
The three heating elements 38 of the heater 31 may be connected in
series or parallel or may be provided with with heating current
independently of each other. In order that unwanted
short-circuiting of the heating elements may be avoided, the three
heater bodies are of different lengths and staggered longitudinally
as shown in FIG. 8.
The air to be heated is directed into and discharged from the
heater 31 in the same direction, and bypassing of the air passages
41 is prevented by a transverse wall 42 in the innermost heater
body 34.
Since the air passages 41 are slightly inclined, the tubular stream
of heated air leaving the heater 31 has a rotational component of
motion, the magnitude of which of course depends on the degree of
inclination of the air passages.
The heater bodies 32, 33, 34 may be made from an elongated flexible
strip the ends of which are connected together after the heating
element 38 and the terminals 40 have been applied to the strip.
As shown in FIGS. 1, 3, 5, 9, the ratio of the length L of the air
passages to their width W is relatively high, namely, of the order
of ten to one. Although a high value of this ratio often is
advantageous, the value is not very critical and it may be
substantially smaller but should always be higher than about two to
one; if smaller it might be difficult to obtain the desired high
efficiency of the heat transfer.
Any suitable material may be selected for the heating element
support and the covering layers as long as it provides the desired
electrical insulation and is heat-resistant enough to withstand the
temperature of the heating element. As a nonlimiting example of a
suitable material for the heating element support, anodized sheet
aluminum may be taken.
* * * * *