Note: Descriptions are shown in the official language in which they were submitted.
~23~
F IELD OF THE IN~ENTI ON
The inYention relates to forced-air electric heaters, and
more particularly to improvements in the construction of electric
heaters incorporating semiconductor heating elements.
CACK~ROUND OF THE I N~ENT I ON
Electric heaters employing semiconductor heating
alements represent a msrked improYement over prior
resistance-wire type heaters. These new heaters include heating
elements which consists of a planar core of semiconductor material
10 formed with a multiplicity of apertures that permit passage of air
to draw heat from the core. Opposing faces of the core are coated
with electrically conductiYe coatings that produce a fairly eYen
distribution of current flow in the core when a Yoltage difference is
applied to the coatings. These heaters tend to be more durable than
15 prior resistance-wire type heaters, tend to be more compact for a
giYen heat requirement, and haYe the additional adYantage that Yery
hot air flows can be produced while the temperature of the
associated heating element remains below about 200 degrees
centigrade, thereby reducing the risk of fire, particularly where
20 thsre sre flammable materials in the heated environment. Such a
heater was proposed by me in my Canadian patent No. 1,190,579
i ssued on Jul y 1 6,1 9C5.
Heaters incorporating semiconductor heating elements of
the type described above are still relatively novel, and a number of
25 problems have arisen in the construction of such heaters. In
particular, a conYenient, inexpensiYe mechanism is required to hold
'" ;~`
~LZ3~
the heating elements. The ex~xct m~nner in which the heating
elements are held tends to be more critic~l in the new type he~ters
than in the old resistance-wire type~ as the heating elements tend
to ~e ~maller, ~nd sir flows from ~n ~ssoci~ted f,3n must
S consequently be more ti~htly constr~ined to achie~e the full ~enefit
of employlng SllCil he~ting elements. As well~ ~eoi3use of the size
~nd nature of the heatin~ elements~ considerable care must be taken
to ensure ~imultoneous electric31 an~ therm~l isolation of the
he~ting elements frorn ~ny assoc:ia~ed housing/ ~n~ proper electrical
10 contact with a supply of line ~olt3ge. Moero~er~ it is ~esir~ble to
impro~e ttle he3t transfer e~iciency of suctl a heater, and to pro~id~
~uieter oper~tion~ operation tending to be noi~y beoause of the
extent to whioh ~ir flows ~re ~ffected ~y the limited
cross-seotion~l sre~ of the new heoting elements.
Accordin~ly! it i~ one o~ject of the present in~,~ention to
pro~ide ~ he~ter oonstruction employin~q semioonduotor he~tin~q
elements of the type described ~bo~e which results in impro~ed he~t
tr~nsfer ond quiet oper3tion.
It is another o~ject o~ the in~ention to pro~ide ~
~0 GonYenient~ inexpensi~e meoh~nism tor holdin~ ~nd eleotric~lly
cont~oting semiconductor he~tin~ elements of the type descri~ed
3bo~e.
eRIEF SUMMAR'f OF TH IN~ENTION
The inYention provides ~n electric he~ter which includes
~5 ~ housin~ h~ing ~ rear ~ir inlet ~nd ~ ~orw~rd ~ir olltlet. A f~n is
mounted inside the housin~ intermedi3te of the reor ~ir inlet ~nd the
~23~
forward air inlet to produoe an air flow through the housing. The
fan is of a type whioh inoludes ~ fan Yenturi that. ~ireot.s air flows
generated ~y the fan frorll a re.ar Yenturi openin~ ~whioh i~ plaoed in
oommunioation with the rear air inlet of t.he hou~ing~ to a for,ward
5 ~enturi opening.
The fan air flows are heated ~y a multiplicity of
disk-shape~ heatin~ elements. Each heating element inolu~es a
~enerally planar eore with a pair of opposin~ forward and resr core
faoesl aleotrioally conduotiYe ooatin~s oo~ering eaoh of the
10 opposin~ faoesl and a multiplioity of apertures whioh permit air
flnw throu~h the oore. The oores are formed of a ~emioonduotor
materi~l with preferrably a positi~e re~i~tanoe-temperat~re
ooeffioientl the ~i~nifio~noe of whioh will ~e discussed ~elow in
oonneo~ion with a preferred em~odiment of ~he in~ention.
A heatin~ element holder formed of an electric~lly
insulatin~ and heat-insulating materi~l is mounted in the hou~in~
intermediate of the forw~rd f~n Yenturi openin~ and the forward air
outlet of the housin~. The holder includes holdin~ means whic.h
m~intoin the heating elements in ~ener~lly coplanar, spaced-apart
20 relationship relative to one ~nother. When the holder iSr in an
operati~e positionl the heating elements are oriented ~enerally
perpendicul~r to the longitudinal ~xis of the f3n venturi and spaced
forwardly therefroml ~,4fith each rear core fac.e facin~ ~ow~rds the
~orw~rd venturi openin~.
~5 The holder is adapted to direct air flows esGapin~ from
the forw~rd fan venturi opening through the cores. Aocordinglyr the
.,
~lVfl 3~Lt7~3
holder comprises ~ir flow reoei~in~ me~ns inoludinç~ a reoess
formed in 3 rear f~oe of the holder ~nd pnsitioned ~t. the fnrw~rd f~n
Yenturi openin~r whioh reoei~e su~st~ntislly ~11 air flow from the
forward ~enturi openin~ in t.he reoe~s. A niultiplioity of p~ss3ges in
S the holder ~ui~e air reoei-~ed in the reoess through the he~tin~
elements. E~oh pass~e extends ~etween ~ forw~rd f~oe ~nd the
re~r f~oe of the holderr ~nd e~oh p~ssage has ~ forw~rd openin~ in
the forward faoe of the holder ~nd ~ renr openin~ in the reoessl
~p~oed forwardly of the forw~rd f~n ~enturi openin~. E30h p~ssn~e
is ~ssooi~ted with ~ different one of the he~ting elements! the
assooi~ted he~tin~ element bein~ positioned intermedi3te of the
forw~rd ~nd re3r p~ss~e openillgsr ~nd positioned so th~t ~11 sir
flow in the pass~qe is oonstr~ined to flow throu~h the oore.
The p~s~r~e 3nd the recess ~re sh~ped or dimensioned to
proYide ~ smooth ~ir flow through the cores. In p~rticular, each of
~he p~ss~ges h~s ~ minimum cross-section~l area which
corresponds su~s~anti~lly to the cross-~ection~l area of the
~ooi~ted he~tin~ element. E~ch p~ss~ge is flared re~rw~rdly ~nd
r~di~lly outw~rdly from the rear faoe of the ~ssoci~ted heatin~
~0 element t.o gwide ~ir flow~ smoothly towards the he~ing element.
The recess is simil~rly fl~red~ radi~lly outwardly ~nd rearw~rdly,
from ~bbut the re~r p~s~ge openin~s to the re~r f~ce of the holder.
The fl~ring which may ~e either conYex or concaYe result in less
tur~ulent ~ir flows and cnnsequently quieter oper3tion.
Electric~l connection me~ns are proYided which extend
into the holder ~or placing the co3tin~qs of e~c:h he~tin~ element in
~3~7~8
oont3c.t with the source of electric. power/ ~nd also ser~e to pl~ce
the fan in contact with the so~lroe of power.
Other ~speets 3nd ~ nt~ges of the present inYention,
particlllarly a no~el heating element holderJ will be apparent from
5 the description below of a preferred em~odiment.
~OF THE ~RAWIN~S
The inltention will ~e better ~Inderstood with reference
to dr~wings illustr~tin~ a preferred embodimentr in which:
fi~. 1 is ~ perspecti~e ~iew of ~n eleotric he~ter
10 embodyin~ the in~ention;
fig. 2 is ~n explo~ed perspecti~e ~ieYY of the he3ter;
fig. 3 is ~ perspeeti~e ~iew of ~ he~tin~ elemen~ h~lder inc.orpor~ted
in the heater;
fi~. 4 is ~ cross-seotion~l ~iew alon~ the lines 4-4 of
15 f i ~ nd~
fi~. 5 is a schematic drawing 4f the electric;al control
oirouitry assooiated with the heater.
DE50RIPT ~N OF PREFERRED Et~BODIMENT
Fig. 1 illustrates the major components ~exo~ptin~
~O wirin~ of ~n electrio he~ter 10 embodyin~ the in~ention. The
heater 10 incll~des a housin~ constrwcte~ of sheet. metal. The
housin~ inGllldes 3 m~in housing member 1~ whose front face h~s a
forward air outlet 1~ ciroumscribed by abuttment flanges 1~ ~only
one spe~ifically indio~te~ in fig. ~. The housin~ ~lso includes ~
~5 re~r housin~ insert 1~ which fits ti~htly into the ~ack of the m3in
housin~ mernber 1~ and which is att30hed to the main ~-,ousing
3L23~7~
B
member 12 by mean~ of s~rews ~not illustr~ted~ thre~ded through
hole~ ~only one hole ~0 specifically indicated~ proYided in the
sidewalls of the main housing membe.r 17. The re~r housing insert
1 ~ has a rear ai r i nl et ~7 whi ch i ~ normal 1 y oo~ered by a remo~abl e
5 sheet ~4 of ~ppropriate air filterin~ material, retained by means of
br~ckets ~ ~two such ~r~ckets being illustrated in the
oross-sectional view of fi~. 4~. The construetion, tfunctiorl and
~s~em~ly of many of the oomponents will ~e readily apparent~ and
oonsequently only det~ils ot the Yariou~ components relating
10 specifio~lly to aspectC. of the inYention will be proYide~ in order to
better highlight the in~ention.
The ~e~ting function of the electric heater 10 i~ pro~ided
by four disk-shaped heating elements 2~.~ 30~ 4. The he~ting
elements are sub~t~ntially identical~ ~ncl c.onsequently only the
15 heating element ~8 will be desoribe~ in detail~ with particular
referenoe to tig. 5 where components of the he~ting element 2~
~etter illustrated. The heatin~ element ~ inelu~es ~ planar eore 40
of semioonduotor m~terial h~Y~ng 3 forYYard f~ee 4~, an opposing
rear f~e 44 ~nd ~ ~enerally eireul3r peripheral ed~e 4~. The
20 thiokness of the oore 40 is ~bout 1~4 ineh) ~nd the diameter ot the
peripheral ed~e 4~ i~ a~Gl~t 1 ~n~ 15~1~ inehe~. ~ondueti4~e sil~er
ooatings 4~, 50 are deposited on the forward ~nd rear eore f~oes 42,
44, and ser~e to produoe a distributed o~rrent flo~Y between the
opposing oore f~ces 4~, 44 ~YYhen a Yoltage differenoe is applied to
~5 the ooatin~s 4~, 50. A multiplioity of apertures ~not specifioally
indioated~ extending between the forw~rd and rear oore faoes 4~, 44
~LZ3~L7~8
permit ~ir flow throu~h the oore ~0 to dr~w heat from the oore 40
durin~ oper~tion. The rel~tiS~e orient~tion of the oore~; is th~t
illustr~teci in fig. ~, n~mely) ~ ~enerally copl~n~r~ sp~oe~ p~rt
rel~tionship.
The semioon~uotor m3teri~1 of the cores is preferr~ly
mixture of le~d titanate ~nd barillm tit~nate~ ~lthou~h ~ St~riety of
o~ler semioonduotor m~teri~ls may be used. The semioorlciuctor
m~teri~l has ~ relatiStely high resistsnGe-temper~ture coeffioient~
whioh is norm~lly ~bout 7.65 ohms~ciegrees oenti~r~e ~3S mes~ured
~etween the opposin~ faoes of ~11 oores ~nd oon~i~erin~ the oores ~s
p~r~llel resist~noe~s~. The rasistanoe as me~swred between tha
opposin~ f~oes of the cores ~onoe ag~in considerin~ the oores to ~e
resistanoes oonneoted in p~rallel~ tot~ls about ~ ohms ~t 1~5
~eQrees oenti~racie and about 161 ohms at 1~5 degrees oenti~rade.
With a line ~tolt~e of l 10 st. RMS ~pplied to the npposing faces of
the cores~ the cores will ha~e a nominal power oonsumption of about
1~500 W ~t ~n oper~tin~ temper~ture of 1~ degrees oenti~r~de~ ~nd
3 nomin~l power consump~ion of ~5 W at ~n operstin~ temper~ture
of 1~5 de~ree~ centigrade. It will ~e re3dily ~pp~rent th~t the
~0 power oonsumption of the cores drops m~rkedly 3s the oper~tin,q
temper~ture of the oores rises. Aooordin~lyJ in most
eircumst~noes, with no sir flow throu~h the oores to draw hest, the
cores m~y ~e expeoted to re~oh ~n equilibrium temper3ture below
~bout 200 de~rees centi~r~de.
2~ A fan 5~ is mounted inside the m~in housin~ member 1
intermediate of the rear ~ir inlet 1~ ~nd the forw~rd air outlet 14.
3~ 8
1~
The f~n 5~ has ~ fan rasin~ 54 whioh define~ ~ f~n ~enturi 56. The
f~n ~enturi 5~ h~s ~ forw~rd ~enturi opening 5~, ~ re~r ~enturi
opening ~0 Jnd ~ rentr~l longitlIdin~l ~xis 6~. The f~n 5~ h~s 3
rentr31 hub 64 mounted in the f~n ~enturi 5~ in gener~l ~lignment
S with the ~enturi ~xis 6~ ~y me~ns of ~ spider 6~ whioh h~s four 1Q9S
68 ~only one sperific~lly indio~ted~ oonneoting the hu~ ~4 to the f~n
casing 54. The hu~ 64 oontains ~n electrio motor ~not illustrsted~
~nd a f~n ~13de ~ssem~ly 70 whioh c~n ~e rot~ted oy the motor to
produoe ~n air flow forw~rdly throu~h the f~n ~enturi S~. Power to
10 oper~te the motor is oondurted through one of the legs of the ~pider
in ~ manner whioh will not ~e de~rri~ed. A suitable f~n is sold
~y Rotron Inc. of Woodstook~ llew ~ork, U.S.A. under the tr~de m~rk
11UFFIll.
The he~ter 10 ~lso includes ~ heating element holder
whir.h holds the heating elements 2~/ ~0. 3~1 ~4 in the generally
copl~nsr, spsred-spsrt rel~tionship referred to ~bove. The hestin~
element holder ~lso orients the cores of the he~ting elements
generally perpendicular to the longitudin~l ~xis ~2 of the lan
nturi 5~, spaced s~out 1 inch forw~rdly of the forw~r~ Yenturi
~0 openin~ 5~ with esch rear oore f~oe f~cin~ towards the forward
Yenturi opening 5~. The hol~er has ~ two-pieee sep~r~ble
construction in~ol~ing ~ forward holder member- 7~ ~nd 9 re3r holder
mem~er 74/ each of which is formed of 3 cersmic msteri~l. The
term "ceramic m~teri~l" ss used in this specific~tion is intended to
25 denote a clay-like m~terisl such ss fired ~reenware, porcel~in or
~ny other material that c~n ~e mol~ed in ~n initi~l condition ~nd
~L23~8
then fired to produoe a hard dur~le produot ~nd that is both
therm~lly ond electriG~lly insul3ting ~uch oer~mic m~teri~ls ~re
~ner~lly inexpensi~ ~nd e~sily mol~e~ into the e.h3pes required. It
will ~e ~ppreoi3ted~ howe~er, '~h~t the resùl'~nt produot tends to be
5 ~ry ~rittle.
The forw3r~ holder mem~er 72 defines 3 forward f~oe 7
of the holder ~nd h~s ~n opposing inner f~oe ~. The re~r holder
mem~er 74 defines ~ re~r f~oe ~0 of the holder ~n~ h~s ~n opposing
inner f~Ge ~2 which is positione~ ~dj~oent the inner f~oe 7~ when
10 the he~ting element hol~er is fully ~s~em~led.
The inner hnlder mem~er f~ces 7~ re oontoure~ to
define pooket~ ~two speoifio~lly indio~ted ~y referenoe numer~ls
~, 8& in the eross-see~ion~l ~iew of ~ig. 4~ in whioh the he3ting
elements arQ ret~ined. The oontourillg in this inst~nee oonsists of
15 ~ener~lly tri~n~ul~r projections ~only two projeotions 8~, 90
speoifio~lly indio~ted in fig. ~ where the oontouring is ~est shown~
and oentr~l oiroul~r projections 92, ~4, hest illustrated in the ~iew
of fi~. 3 where the holder mem~ers 7~, 76 ~re shown sep~r~ted.
When the holder is ~ssem~led, as in fi~. 4, the pookets oloe.ely
reoeive the he~ting elements, gripping the oppo~ing faoes of e~oh
hester el ement oore. Al thou~h ~he pookets ~ef i ned ~re rel ati ~el y
loose ~in r~di~l direGtions~, the ~rr3ngement has pro~en suffioient
for the purposes of the invention.
The heating element holder 31so has four p~ss~es, one
assooi sted wi th 3 di f f erent one of the f our hea~i n~ el ements, whi oh
direot ~ir flows through the heating elements. Eaoh p~ss~g~ extends
~231~
1~
between the forw3rd ~nd re3r holder faces 76/ ~0, ~nd h~s a forward
p~ss3ge openin~ ~not spec;ifioally irldioated~ in the forward holder
faoe ~6 and ~ re~r pass~e openin~ ~not speoific311y indioated~ in
the re~r holder f~ke ~0/ more speoifioally, in 3 reoess formed in the
. 5 rear holder f~oe ~0 and desoribed more fully below. Two suoh
pass3~es 96, Y~ are speoifioally indio3ted in the oross-seotion31
~iew of fig. 4. It will be apparent from fi~. 4 th3t eaoh of the
p3ss3ges g~, 9~ intersects the poeket in whioh the ~ssooiated
heating element ~ or ~, respeoti~ely, is oont~ined, and that eaoh
of the p~ssages 96; g~ h~s ~ minimum oross-seotion31 area
perpendioular to the ~enturi axis 6~ whioh is subst~nti~lly the s~me
as the oross-seotional 3rea of the assooiated heatin~ element,
there~y ensuring retention of the assooi~ted heatin~ elsment
without si~nifio3ntly impedin~ 3ir tlow throu~h the assooi~ted
heatin~ element. The he~tin~ elements ~re of oourse so positioned
in the ~ssooiate~ pass~ges th3t substanti~lly 911 ~ir flow in the
passa~es is constrained to flow throu~h the eores of the h~ating
elements.
The holdei- is also ~dapted t~ reoei~e su~stantially all air
flow from the forw~rd ~enturi openin~ 5~. In p3rtioular, the re3r
holder mem~er 74 h~s a reotan~ulsr oiroumf~renti~l lip 100
dimensioned to fit 3~cut ~ oorrespondin~ lip 10~ of the f~n cssin~
54. Air flow from the forward ~enturi opening 5~ is conse~w~ntly
directed ~inst the re~r holder f~ce ~0, 3nd ~ 13r~e r~cess 104 is
formed in the resr holder faoe ~0 ~djaoent to ~nd in ~ener31 3xisl
~lignment with the forward ~enturi openin~ 5~ to recei~e t.he 3ir
,
~Z3~7~8
flows. E~ch of the passa~es ~suGh as the pass3ges ~, 98~ in whioh
the heatin~ elements are positioned has its re~r p~s~e opening
looated within the recess 104/ spaced forw3rdly of the forward
~enturi opening 5~. As will ~e app~ren~ in fig Clr where the
5 orosg-seotional shape of the passages g6r g~ is shown, the passages
g~ flare radially outwardly an~ re~rwardly from the re~r faoe of
each assooiated heating element 2~ ~2 respeoti~ely to the
~ssoci3ted rear p~ss3~e opening. Simislrly/ the reoess 104 flares
radially outwar~ly and rearwardly from a~out the re3r pass~ge
10 openings to the re~r holder face B0. Aocordin~ly~ su~stantially all
~ir escaping from the forward venturi openin~ 5B is deli~ered in
relati~ely smooth fashion to the heatin~ elements.
The forw~rd holder member 7~ is identical to the rear
holder member ~ and is effeoti~ely the re~r holder mem~er 76
15 rot.~ted through 1~0 degrees a~ou~ a ~ertio31 axis. ~coordingly~ the
forw~r~ hol~er mem~er 72 defines a large recess 10~ in the forward
older face 76 into whioh eaoh of the forw~rd passage openin~qs
opens. Aocordin~qly, eaoh of the hol~er pass3~e~ ~UCh as ~he
pass~es g6, ~ whioh are exemplar~ and illustrated in fi~. 43 fl~res
~0 r~di~lly outw~r~ly and forw3rdly from the front faoes of e~ch
assooiated he~ting elernent~ ~nd the recess 106 fl~res radi~lly
outwardly and forwardly from a~out the forward passage openings
to the forw~rd holder f~ee 76. This arr~ngemsnt produoes ~
smoothin~q of the heated air flows escapin~ from the forward air
~5 outlet 14~ but is not striotl~ essential to o~t~ining improl/ed he~t
transfer effioienoy and quieter operation. The ~rrangement does~
~-~3~ 48
1~
howevet-, eliminste the need for ~n ~ditional distinot oomponent in
the hester 10.
Forw~rd and rear oon~uotive metal plates 10~, 110
proYide eleetrical oontaot with the forward sn~ rear faoes of the
he~tin~ element oores inside the holder. It will ~e ~pparerIt from
the view of fig. ~ th3t the forw~rd conduotive plate lOB seats in
reoess defined by the tri~n~ul~r projeetions on the inner f~ee 7B,
and h~s a een~ral ~perture 112 whioh permits olearanoe of the
oentr~l projeotion ~2. The plate 10~ oYerlsys the forward fsoe~ of
the he~ting element oores to proYide the required eleotrical cont~ot.
Four apertures 114 lonly one specifioslly indioated~ with ~ oiroular
periphery ~re forme~ in the pl~te 10~ ~n~ ~re po~itioned olY~er the
forwsrd fsee~ of the hester element cores to permit pas~e of ~ir.
The di~meter of the spertures on the pl~te 1 14 is m~rginally
sm~ller thsn th~t of the he~tin~ elements to ensure eleetrie~l
eontaot. A metal terminal strip 11~ is spot welded to the pl~te
10~, ~nd extends to points external of the he~ter element holder,
when assembled, to permit line ~olta~e to ~e convenientl~ applied to
the pl~te lQa To ~Gcommod~te the terminal strip 11~, 3 ~roove
2~ is formed in the inner faoe 7~ of the forward holder member 76,
~n~ is dimensioned to recei~te the terminal strip 11~ loosely. The
conducti~e pllte 110 provides electriosl contaot with the re~r faces
of the heating element Gores, ~nd seats sg3inst the inner f~ce ~ of
the resr holder member, in ~ msnner ~nalo~ous to the sestin~ of the
plate 10~. The struotllre and function of the two pl2tes 10~, 110 is
su~stantially i~entio~ nd consequently no further detail will ~e
~ 23~L~7
pro~ided reg3rdin~ the plate 110.
The hol~ler members 72, 74 ~re dr~wn to~ether ~o oont~in
the he~tin~ elements in the pockets ~y means of four fasteners.
~inee the fasteners are identie31, only one`f~tener 1~0 h~s ~een
speGifiGally illustrated 3nd indiosted, in fi~. ~. The fastener 1~0
oonsists ~sicslly of ~ ~olt 1~ nd ooil spring 124 ~nd a nut 12~.
The heatin~ element holder is first loosely assem~led, for ex~mple,
by seatin~ the plate 110 a~3inst the inner faoe ~ of the re~r holder
member 74, positienin~ the he3ter element~ ~ppr~pri3tely o~er the
lQ ~pertures in the pl~te 110, se~tin~ the pl~te lQ~ 3~inst the inner
f~oe 7~ of the forward holder mem~er 72, and then carefully
~ringing the hol~er mem~er 72, 7~ to~ether in ~n operatiS,~e
orientation. The holder mem~ers 72, 74 then h~e four p~irs of
31igned ~pertures, only the ~pertures 1~ 130 ~ein~ speoifio~lly
indioated, whioh extend fully ~etween the forward and re3r holder
faees J~, ~0. The ooil spring 124 is loo~ted a~out the ~h~ft 1~2 of
the ~olt 12~, 3nd the sh~ft extended fully throu~h the aligned
3pertures 12~, 13Q. The nut 1~6 i~ then threaded onto the re3r
sh3f~ en~ portion 1~4 until the nut 1~ abuts the rear holder faoe
~0. The ooil ~prin~ 124, which h3s a 13rger diameter than the
~pertures 1~ 0, locs~es in the process ~out ~ forward shaft
end portion 1~, and acts betY~een the bolt he3d and the forw~rd
holder face 76 to draw the holder mem~ers 7~, 74 together. To
ensure po~iti~e seatin~ of the coil spring 124 3g~in~t the for~3rd
~5 holder memher 7~, 3 ~hallow well 140 i~ located 3~0ut the ~per~ure
12~ in the forward holder face 7~ and dimensioned to recei~e a
~2~17~3
16
portion of the coil spring 124. In the preferred embod.iment
illustrated, a metal grill 141 is interposed between the
bolt head of each fastener and the associated coil spring to
fasten the grill directly to the forward holder member 72,
but the grill 141 could equally well be attached to the
abutment flanges 1~ of the main housing member 12.
The four fasteners being spring-loaded permit
separation of the holder members 72, 74 in response to
thermal expansion of the heating elements. This arrangement
is critical, as the ceramic holder members 72, 74 are very
brittle, and could otherwise be easily cracked during
operation of the heater 10.
The heating element holder and grill 141 when
assembled together are then attached to the fan casing 54.
This attachment is effected by passing the rear shaft
portions of the various fasteners through apertures in the
fan casing 54 and attaching additional nuts to the rear
shaft end portions. For example, with the fastener 120
illustrated, an aperture 142 in the fan casing 54 is aligned
20 with the previously aligned holder member apertures 128, 130
and the rear shaft end portion 134 passed through the
aperture 142. A nut 144 is then threaded onto the rear
shaft end portion 134 to complete connection to the fan
casing 54. The fan casing is in turn attached to the rear
2.5 housing insert 18 by means of four screws ~not illustrated)
which are threaded through aligned aperatures (only one pair
~..,~
17~31~74~3 1
16(a)
oE aligned apertures 146, 148 speciEically indicated) in the
fan casing 54 and rear housing insert 18. A strip of
insulating material 150 (fragmented) is wrapped around the
periphery of the heating
~3~8
element holder, and the entire assembly so forme~ ls inserted lnto
the mairl housing mem~er 1~ until th~ grill 14~ engages the
a~.utment flanges 1~. ~.eGurem0nt is completed ~.y threading screws
throu~h the holes ~0 in the main howsin~ mem~er 12 to secure the
5 rear hnusing insert t~ to the main housing mem~er t~, as mentioned
a~ove.
The electric31 wiring and control circwitry associ3ted
with the he3ter 10 is schematic~lly illustrated in fi~. 5. Line power
is deli~ered ~ia a power cord 5~ tthe two lines of the power cord
10 bein~ indicsted with the same reference numeral 5~,~ to the
conduotive plates 1O~J t 10. The electricsl connection so formed is
direct, invol~in~ no switchin~ GirGuitry to control the amount of
power delivered, except for a simple dou~le pole sinp,le throw
switGh t 54 which serves to turn the power to the heater 10 off and
15 on. The power consumed ~y the heating elements, 3nd the heat
conse~uently delivered is controlled entirely ~y varyino, fan speed
with a fan control 15~. The fan control 15~ includes ~s 3 primary
switching element a ~i~irection~l siliccn controlled rsctifier which
permits su~stantially continuous variation of fan speed. ~
~0 inereasing fan speed the temperatllre of the heatin~ elements
drops, ~.ut the resultsnt incre~se in conductivity of the hestin~
element Gores resul~s in ~ marked increase in power consumpti4n.
Thus, without effectively upw3rdly or downwardly scalinp, the line
volta~e applied to the heatino, element cores, the quantitu, ~If heat
~5 delivered c~n ~e varied. The re~uired control circuitry and switGhes
can ~e conveniently mounted to the rear housinp insert 18 with
~L23~7~8
1~
appropriate wirin~, as sohem~tio~lly illwstrated/ oonduct.ing power
to the fan 52 and heating element~. These matters will be readily
app~ren~ to one s~illed in the art.
A tesl: was performed to determine whether ~ he~ter
5 substanti~lly identioal to the preferred embodiment 10 exhibited
improYed he~t transfer effioiency and quieter operation. The test
inYol~e~l a oomparison with ~ prototype de~ioe that h~d an identio~l
housin~qJ identio~l heating elementsJ sn identioal f~nJ ~nd identioal
oontrol cirouitry. The prinoipal differenoe tletween the prelimin~ry
10 prototype ~nd the preferre~ Yersion of the heater resided in the
he~tin~ element holder. The four hestin~ elements were oontained
between t34o metal platesJ bolted to~etherJ e~ch of whioh was
apertured to permit pass~e of air throu~h the he~tin~ elements in
manner simil~r to that of the oonduotiYe pl3tes 108r 110. The
15 ~ssem~ly SQ formed was ~olted to the ~ssooi~ted fsn with the
- heatin~ elements positioned at a~out 1 inoh ~rom the forwsrd f3n
Yenturi opening. Power oorlsumption of the oores w~s monitore~ b~
mean~ of a watt nneter. With the protot~p~ ~ersi~n eoupled to a 1 lO
. ~MS lin~ souroeJ an am~iant temperature of ~out ~5 ~egrees
~O centigrade~ ~nd the fan operatin~ at full spee~J the heatin~ e.lements
h~d a to~al power oon~umption of about 1J~OO W h noti~le
le~k~ge of air baoksoattered throu~h the rear fan ~enturi openin~
was also noted. The preferred ~ersion substantially identical to the
preferred embodiment 10 wa~ operated under simil~r oonditionsJ
25 and a hea~ing element power consumption of a~out 1J3~0 ~ Wa~
noted with no apparent leakage of air throu~h the rear fan ~enturi
~23~L'7~8
1~
openin~. This represents about a 1S% impro~ement in energy
transf~r to f~n ~ir flows. Addition~lly~ on a purely qualit3ti~e
basis~ it w~s noted th~t the preferrsd ~ersion was oonsidera~ly
quiet~r in operation.
1~ will ~e appreoi~ted th~t a preferred embodimsnt of the
in~en~ion has ~een dssori~ed and that modifications may ~e macle
therein without dep3rting from the spirit of the in~ention and the
soope of the ~ppended ol~ims.
