[0001] The present invention relates to an infrared radiant heater having a high radiation
efficiency, which is defined as the ratio of the radiant energy to the applied energy
to the heater. This heater is mainly used for spot heating.
[0002] Various types of spot heating apparatus have been used. One such apparatus comprises
a heat generator provided with a flat surface having a comparatively large area which
surface is disposed substantially vertically. This heater is called a panel heater
and usually uses a metal body within which electric heating wires are arranged, said
electric heating wires being electrically insulated from said metal body. When said
metal body consists essentially of a metal such as Al with a low emissivity, an infrared
radiative layer comprising metal oxides with a high emissivity such as ZrO
2, SiO
2 or
Tio
2 is formed on the surface of said metal body. Needless to say, this fact indicates
that the infrared layer is not required to be formed when a heavily oxidized metal
is used as said metal body. There is also used another heater whose heat generator
comprises a metal plate, on whose surface a resistive film is formed instead of said
metal body described hereinbefore.
[0003] When electric power is applied to said electric wires or said resistive film, the
surface temperature of said metal body increases and is saturated at a higher temperature
than an atmospheric temperature. Then the infrared radiation emitted from the surface
is obtained. However, the convectional heater has the disadvantage that . the radiation
efficiency is low in the range of 40-50%. This low radiation efficiency is attributed
to the fact that the applied electric power is dissipated not only by radiation, but
also by convection. In the other words, more than half amounts of the applied electric
power are unavailably dissipated by convection. Accordingly, the conventional heater
has the another disadvantage that the unavailable thermal energy dissipated by convection
increases nearly linearly with an increase of the radiant energy, because higher radiant
energy can be obtained mainly by means of increasing the surface temperature when
said heat generator have a given emissive surface.
[0004] The heater has the further disadvantage that amounts of the radiant energy available
for heating is also low in comparison with that of the total radiant energy. When
occupants receive the radiant energy from the heater, the radiant energy available
for heating is considered to be usually limited to the radiant energy emitted for
the particular available space, which is defined as the space viewed from the heater
at the angle of elevation less than 20-30 degrees for the vertical direction and at
the wide angle for the horizontal direction.
[0005] However, since the infrared radiative layer has the nearly perfect diffused surface,
comparatively large amounts of the radiant energy are emitted for the unavailable
space for heating. This fact is attributed to the conventional radiation characteristic
that the radiant energy emitted from the nearly perfect diffused surface does not
decrease steeply with increase of the angle of elevation because the radiant energy
varies with the angle in accordance with Lambert's cosine law.
[0006] There has been also known an another type of heater which is possible to be used
as such a particular spot heating apparatus as described hereinafter.
[0007] This heater comprises a heat generator arranged horizontally with a flat surface
and a collimator arranged on the flat surface of said heat generator. Said collimator
consists of many plates which extend for the normal direction to the flat-surface
and are crossed each other in the form of a lattice and the like. Said plates are
preferably composed of metal plates having a highly reflective surface. This heater
was disclosed in West Germany Patent No. DE 2619622.
[0008] As described in the referenced Patent, this heater is availably used for industrial
applications such as firing organic materials with a small limited surface at a position
aparted slightly from the heater. When this heater is used as the infrared radiant
heater for heating occupants indoor, this heater is situated at a high position near
a ceiling and the radiant energy is emitted downward from near the ceiling. In this
heating process, the heater has the advantage of high radiation efficiency because
air is prevented from moving upward by said crossed plates and the resultant thermal
energy dissipated by convection decreases greatly. However, as for the radiant energy
emitted downward from near the ceiling, vertical radiant energy dencity decreases
steeply with the height, therefore, local warm discomfort occurres at the head, and/or
cold discomfort at the feet.
[0009] On the other hand, when said heat generator is arranged vertically, this heater has
the disadvantage that the radiation efficiency is lower than that of the conventional
panel heater. Since said collimator consisting highly reflective metal plates is highly
thermal conductive, said collimator increases the thermal energy dissipated by convection
and decreases that dissipated by radiation.
[0010] This heater has the further disadvantage that the radiant energy is limited to too
local space to be emitted over the available space for heating. Since said collimator
consists of many plates crossed each other in the form of the lattice and the like,
the radiant energy emitted for the normal direction to the flat surface of said heat
generator at the center position is high. However, the radiant energy emitted for
the different direction at the aparted position from the center decreases steeply.
This fact indicates that the radiant energy is emitted only for the normal direction
to said flat surface of said heat generator. Considering that the available space
for heating is spreaded widely for the horizontal direction, the too limited radiant
energy for the horizontal direction is not available for comfortable heating.
[0011] The other of the infrared radiant heating apparatus except for the panel heater comprises
a long and slender heat generator. One of this heater is called an electric stove.
Said long and slender heat generator is arranged horizontally or vertically. This
heater has the advantage of a high radiation efficiency by means of selecting the
suitable form of said heat generator. However, the heater has the disadvantage that
the more radiant energy is dissipated for the unavailable space for heating.
- SUMMARY OF THE INVENTION
[0012] An object of this invention is to provide an infrared radiant heater with a high
radiation efficiency when said radiant heater is situated vertically.
[0013] Another object of the present invention is to provide an infrared radiant heater
with a particular angular dependence of the radiant energy, which is characterized
in that the radiant energy for the space available for heating is higher than that
for the space unavailable for heating.
[0014] A further object of the present invention is to provide an infrared radiant heater
which can decrease hot discomfort when fingers or other human body touch the warmed
surface of said radiant heater.
[0015] Other objects of the present invention will be obvious from the contents of the detailed
description disclosed hereinafter.
[0016] According to one aspect of the present invention, there is provided an infrared radiant
heater comprising a heat generator with an infrared radiative surface standing for
the nearly vertical direction and both an infrared transparent and low thermal conductive
body arranged near the surface of said heat generator.
[0017] Infrared rays emitted from the surface of said infrared radiative surface pass through
said infrared transparent and low thermal conductive body almost without absorption
loss because of nearly perfect infrared transparency thereof and then infrared radiations
available for heating are obtained. On the other hand, since said infrared transparent
and low thermal conductive body is also a superior thermal insulator, the surface
temperature thereof is considerably lower than that of said infrared radiative surface.
This fact indicates that the heater
[0018] according to the present invention has a high radiation efficiency because convective
thermal energy owing to air flow decreases with decrease of temperature difference
between said infrared radiative surface temperature of the heater and a surrounding
temperature. Needless to say, the heater dissipates thermal energy almost only by
both convection and radiation, and heat transfer by conduction is possible to be neglected
because there exists no thermal conductive material except for electric wires for
applying electric power to the heater and the electric wires have a high heat resistance
owing to be small in section and long in length.
BRIEF DESCRIPTOIN OF THE DRAWINGS
[0019]
Fig. 1 is a cross-sectional view showing a fundamental construction of an infrared
radiant heater according to the present invention.
Fig. 2 is a cross-sectional view showing a construction of the infrared radiant heater
according to the present invention wherein an infrared
transparent and low thermal conductive body comprises both thin protruded plates and
spaces limited by said thin protruded plates and an infrared radiative surface of
the heater.
Fig. 3 shows schematically a measuring method of a radiant energy.
Fig. 4 shows vertical angular dependences of the radiant energy.
Fig. 5 shows horizontal angular dependences of the radiant energy.
Fig. 6 shows surface temperatures as a function of applied electric powers.
Fig. 7 is a cross-sectional view showing a construction of the infrared radiant heater
according to the invention wherein said thin protruded plates are inclined for the
downward direction to said infrared radiant layer.
Fig. 8 shows the vertical angular dependence of the radiant energy of the heater shown
in Fig. 7.
Fig. 9 is a cross-sectional view showing a construction of the heater according to
the invention wherein infrared reflective films are form on the surface of said thin
protruded plates.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] Referring now to Fig. 1, there is shown a fundamental construction of an infrared
radiant heater according to the invention. The heater according to the invention comprises
a heat generator ① with an infrared radiative surface

standing for the nearly vertical direction and an infrared transparent and low thermal
conductive body ② arranged near or on the surface

of said heat generator ①. A thermal insulating body ③ is arranged in order to decrease
the thermal energy dissipated from the other surface @ of said heat generator ①.
[0021] Infrared rays emitted from the infrared radiative surface

pass through said infrared transparent and low thermal conductive body almost without
absorption loss because of high infrared transparency thereof and infrared radiations
④ available for heating are obtained. On the other hand, since said infrared transparent
and low thermal conductive body ② is also a superior insulator in thermal conduction,
the surface

temperature thereof is considerably lower than the surface

temperatuer of said heat generator ①. Considering that an applied energy to said
heat generator ① is almost dissipated both convection ⑤ owing to air flow and infrared
radiations ④ if said thermal insulating body ③ is perfect, a high radiation efficiency
can be achieved because thermal energy dissipated by convection ⑤ decreases with decrease
of temperature difference between the surface

temperature and a surrounding temperature.
[0022] It is obvious from the contents described hereinbefore that the high radiation efficiency
can be achieved by two characteristics of said infrared transparent and low thermal
conductive body ② ; (1) high infrared transparency thereof which causes the infrared
radiations ④ to be emitted from the surface

of said heat generator ① to an outer space, and ② low thermal conductivity thereof
which causes the decrease of the surface

.temperature.
[0023] Needless to say, when said heat generator ① has the poor infrared radiative surface

, an infrared . radiative layer is formed on the surface

. A fired film comprising metal oxides such as ZrO
2, SiO
2, F
e203, Cr
20
3, TiO
2 and the like is frequently used as said infrared radiative layer.
[0024] Referring to Fig. 2, there is shown an embodiment of the heater according to the
invention. Said heat generator ① consisted essentially of a metal substrate ⑩, said
infrared radiative layer ⑪ formed on one surface

of said metal substrate ⑩, an electric insulating film ⑫ fixed to the another surface

of said metal substrate ⑩ and a planar resistive film 13 formed on said electric
insulating film ⑫. Al, Fe and the other metal plates were used as said metal substrate
⑩. A polymer film was used as said electric insulating film ⑫. A fired film of a mixture
of fine carbon particles and polymer was used as said planar resistive film ⑬. A fired
film of metal oxides described hereinbefore was used as said infrared radiative layer
⑪.
[0025] Said infrared transparent and low thermal conductive body ② consisted essentially
of both thin protruded plates ⑦ for the normal direction to the surface

of said infrared radiative layer said thin protruded plates ⑦ being arranged horizontally
near or on the surface

in such a way that said thin protruded plates ⑦ of H(cm) in height and t(cm) in thickness
were separated each other at a given interval P(cm), and spaces ⑧ limited by said
thin protruded plates ⑦ and said infrared radiative layer ⑪. Thin poly-ethylene terephthalate
films of 0.3 mm in thickness were typically used as said thin protruded plates ⑦.
[0026] Said thermal insulating body ③ is arranged on said planar resistive film ⑬. A polyurethane
foam of 15 mm in thickness da was typically used as said thermal insulating body ③.
Needless to say, said thermal insulating body is required when infrared radiations
from one surface

of the heater is available for heating. Accordingly, it is obvious that the same
construction as that including said infrared radiative layer ⑪ and said infrared transparent
and low thermal conductive body ② is arranged instead of said thermal insulating body
③ when infrared radiations from both the surface

of said infrared radiative layer ⑪ and the surface

of said planar resistive film ⑬ is required.
[0027] Said thin protruded plates ⑦ prevent air from flowing upward along said infrared
radiative layer ⑪ when the surface

temperature is increased by applying an electric power to said planar resistive film
⑬. In addition, air is an excellent thermal insulator. These facts indicate that thermal
energy dissipated by convection ⑤ owing to air flow is decreased by arranging said.thin
protruded plates ⑦. On the other hand, since air is also very transparent in the region
of infrared wavelengthes, infrared radiations ④ emitted from the heated surface

of said infrared radiative layer ⑪ passes through said 'spaces ⑧ almost without being
absorbed by said spaces ⑧ and then is radiated outside the heater. It is obvious from
the contents described hereinbefore that the construction comprising said thin protruded
plates ⑦ and said spaces ⑧ is an excellent infrared transparent and low thermal conductive
body ②.
[0028] In addition to say, it is obvious that the existence of an interval

between said infrared radiative layer ⑪ and all or parts of said-thin protruded plates
⑦ is not harmful to decrease of convective thermal dissipation under the conditions
that the interval

is less than several millimeters. This fact is due to an existence of a large resistance
to air flow when the interval

is small.
[0029] Radiation characteristics will be described in detail hereinafter when said planar
resistive film ⑬ has a very low positive temperature coefficient of resistance.
[0030] Referring to Fig. 3, there is schematically shown a measuring method of the radiant
energy. The radiant energy was detected by a radiation detector ⑨ along boundary lines
of a circle whereof the center agreed with the center of the heater. Two types of
an angular dependence of the radiant energy were typically measured. One angular dependence
was a vertical angular dependence, which showed a variation of the radiant energy
incident to said radiation detector ⑨as a function of a vertical angle 6 under the
conditions of a given radius r and a particular horizontal angle ϕ=0 degree. Another
angular dependence was a horizontal angular dependence, which showed a variation of
the radiant energy incident to said radiation detector ⑨as a function of a horizontal
angle φ under the conditions of the given radius r and the particular vertical angle
8=0 degree.
[0031] Since the radiant energy in a given and comparatively large solid angle (~2.5 radian)
around the normal - to a small sensing surface of said radiation detector ⑨ was incident
to said radiation detector ⑨, the incident radiant energy contained not only the radiant
energy emitted from the heater, but also a radiant energy emitted from a surrounding
under the particular conditions depending on the heater size (L
1, L
2) and the radius r. In the following description, when the measured total energy included
the radiant energy emitted from both the heater and the surrounding, the former radiant
energy was used. A hemispherical radiant energy, designating a whole radiant energy
emitted for all directions of the enclosing hemisphere, was determinded by integrating
the angular radiant energy over all directions.
[0032] In this experiment, the heater in the rectangular form of L
1=L
2=45 cm and dh=2 mm was used. The radiant energy was typically measured at the conditions
of the radius r=100 cm and the applied power of .630 W/m
2. As described hereinbefore, the thickness da of said thermal insulating body ③ was
typically 15 mm. However, the radiation efficiency varies with the thickness da because
the thermal energy dissipated from the surface of said thermal insulating body ③ varies
with the heat resistance determined by the thickness da. In order to evaluate exactly
the effect of said infrared transparent and low thermal conductive body comprising
said thin protruded plates ⑦ and spaces ⑧, the radiation, efficiency was also measured
under the conditions that the thickness da was thick enough for the thermal energy
dissipated from the surface of said thermal insulating body ④ to be neglected. The
radiation efficiency measured in such a way is defined as the elemental radiation
efficiency. On the other hand, the radiation efficiency measured under the conditions
of the suitable thickness da for practical uses is defined as the practical radiation
efficiency.
[0033] The elemental and practical radiation efficiencies of the conventional heater without
said thin protruded plates ⑦ and spaces ⑧ were about 50% and 42%, respectively. On
the other hand, the elemental and practical efficiencies of the heater having said
thin protruded plates ⑦ and spaces ⑧ increased greatly. Typical efficiencies in the
various forms of said thin protruded plates ⑦ and spaces ⑧ are shown in Tab. l.together
with those of the conventional heater.
[0034] Referring to Fig. 4, there are shown various vertical angular dependences of the
radiant energy. In Fig. 4, the ratios of the radiant energy emitted from the heater
according to the present invention with a given thickness da=15 mm and various values
of H and P to that emitted from the conventional heater whereof the size L
1' L
2 is the same as that of the present heater are shown when the radiant energy from the
conventional heater was measured at'the given conditions-of r=100 cm and θ=φ=0 degree.
The vertical angular dependences with regard to the conventional heater are also shown
in Fig. 4 by the same ratio as that described hereinbefore. The conventional heater
showed the vertical angular dependence of the radiant energy which decreased slowly
with the vertical angle φ, as shown by curve Al in Fig. 4. This characteristic agreed
nearly with Lambert's cosine law.
[0035] On the other hand, the heater according to the

present invention showed unique characteristics, as shown by curve Bl and Cl in Fig.
4, in that the radiant energy decreased very sharply with the vertical angle 0 in
comparison with that of the conventional heater, as shown by curve Al in Fig. 4. Curve
Bl and Cl were obtained with regard to the heater construction of t=0.3 mm, P=10 mm,
H=30 mm and t=0.3 mm, p=7.5 mm, H=15 mm, respectively. The radiant energy (curve Bl
and Cl) emitted for the direction of the vertical angle 6 less than about 20 degree
increased greatly in comparison with that of the conventional heater (curve Al). In
particular, heater wherein said thin protruded plates ⑦ of t=0.3 mm and H=30 mm were
arranged at the interval P=
10 mm emitted the radiant energy for the direction of the vertical angle 8=0 which
was about 1.3 times greater in intensity than that of the conventional heater. On
the contrary, the radiant energy emitted for the direction of the vertical angle 8
larger than about 20 degrees decreased greatly in comparison - with that of the convectional
heater.
[0036] Referring to Fig. 5, there are shown various horizontal angular dependences of the
radiant energy. The ratio, described in Fig. 4, is shown as a function of the horizontal
angle φ. These measurements were carried out at the same conditions as those in Fig.
4. The radiant energy (curve B2 and C2) of the heater according to the present invention
for all the directions of the measured horizontal angle ϕ increased greatly in comparison
with that of the conventional heater (curve A2).
[0037] As disclosed hereinbefore, the heater according to the present invention has a useful
angular dependence of the radiant energy in that the radiant energy for the directions
of both all the horizontal angle φ and the vertical angle 8 less than about 20 degree
increased greatly in comparison with that of the conventional heater. Since the available
space for heating by infrared radiations is considered to be the space viewed from
the heater at the angle of elevation less than 20~30 degree, this angular dependence
of the radiant energy indicates that the heater according to the present invention
is mostly suitable for heating by infrared radiations.
[0038] The reason why the useful angular dependence of the radiant was obtained is considered
as followings.
[0039] When the electric power was applied to said resistive film ⑬ , the surface temperature
Ts of said infrared radiative layer ⑪ at the center increased as shown in Fig. 6.
The surface temperature Ts (curve B3 and C3) of the heater according to the present
invention increased greatly in comparison with that of the conventional heater (curve
A3) under the conditions of a given applied electric power. Curve A3, B3 and C3 were
measured at the same conditions except for the applied electric power as those whereat
curve Al, Bl and Cl were measured in Fig. 4. The heater construction of t=
0.
3 mm, P=15 mm, H=
30 mm and t=
0.
3 mm, p=7.5 mm, H=15 mm showed the surface temperatures Ts which were about 30°C and
19°C higher than that of the conventional heater, respectively, when the electric
power of 630 W/m
2 was applied to the heater. The surface temperature Ts depended mainly on the height
H and the interval P. The higher the height H became, the higher the surface temperature
Ts became under the conditions of the given interval P. And the shorter the interval
P became, the higher the surface temperature Ts became under the conditions of the
given height H. This increase in the surface temperature Ts is considered to be the
origin of increase in the radiant energy.
[0040] On the other hand, the radiant energy from the heater comprises both the radiant
energy emitted from the surface

and that emitted from the surface

of said thin protruded plates ⑦. Temperature of the surface

was higher than that of the surface

. When said radiation detector ⑨ viewed the heater according to:the present invention
along the boundary line of the vertical circle, the viewed area of the surface

by said radiation detector ⑨ decreased rapidly with increase of the vertical angle
8 and, on the contrary, the viewed area of the surface

increased rapidly with increase of the vertical angle 8. This vertical angular dependence
of the viewed area of the surface

, which can emit
[0041] higher radiant energy than the surface

, is considered to be the origin of the vertical angular dependence of the radiant
energy. In the other words, the rapid increase of the viewed area of the surface

with increase of the vertical angle 8 are considered to be the origin of the vertical
angular dependence of the radiant energy.
[0042] When said radiation detector ⑨ viewed the heater according to the present invention
along the boundary line of the horizontal circle, the viewed area of the surface

and

by said radiation detector ⑨ decreased slowly with increase of the horizontal angle
nearly in accordance with the Lembert's cosine law. This horizontal angular dependence
of.the viewed area of the surface

and

is considered to be the origin of the horizontal angular dependence of the radiant
energy, which is similar to that of the conventional heater.
[0043] Considering the facts: (1) the surface

temperature Ts is determined from the relation that the total energy applied to the
heater, which consists of the applied electric power and the incident thermal energy
to the heater from a surrounding, is equivalent to the total thermal energy dissipated
by radiation and convection under the conditions of conduction being neglected, and
(2) the thermal energy dissipated by radiation increased by means of the heater construction
according to the present invention, it is suggested that the thermal energy dissipated
by convection decreased and, as a result, the surface

temperature increased. In addition, there may exist the possibility that the amount
of the decreased radiant energy emitted for the direction larger than 20~30 degree
in the vertical angle 6 in comparison with that of the conventional heater, the decreased
radiant energy being unavailable for heating, contributed also the increase in the
surface

temperature.
[0044] The reason why the convective thermal energy decreased is considered to be due to
the facts that air fulfilled in said spaces ⑧ is difficult to be heated up because
of its low thermal conductivity and is limited to flow upward by said thin protruded
plates ⑦ even if air is heated up. This fact indicates that said thin protruded plates
⑦ are preferably composed of a low thermal conductive material because its low thermal
conductivity does not increase the surface

temperature, whereon air temperature in said spaces ⑧ depends, greatly, and, as a
result, the convective thermal energy decreases. Considering both radiation characteristics
and the size of the heater suitable for practical uses, it is preferable that said
thin protruded plates ⑦ have the form of 0.05~ 1:0 mm in thickness and 5~50 mm in
height H, and are arranged at the interval P of 2.5~50 mm.
[0045] Since said thin protruded plates ⑦ are arranged on the surface

of said heat generator ①, there decreases the possibility that fingers or other human
body touch directly the surface

kept at high temperature. There exists the possibility that fingers or other human
body touch the top of said thin protruded plates ⑦. However, since the top temperature
is very lower than the surface

temperature, hot discomfort does not arise. Accordingly, the heater according to
the invention is safe and can decrease hot discomfort.
[0046] Referring to Fig. 7, there is shown an another embodiment of the heater according
to the invention, wherein said thin protruded plates ⑦ were inclined for the downward
direction to the surface

of said infrared radiative layer ②. This heater construction was characterized in
the vertical angular dependence of the radiant energy, as shown in Fig. 8. Fig. 8
shows the vertical angular dependence B4 of the radiant energy when the angle θ
1 between said thin protruded plates ⑦ and the surface

was selected at 60 degrees in comparison with that A4. of the conventional heater.
Since the viewed area of the surface

by said radiation detector had the maximum value at the vertical angle of (90-θ
1) degrees, the radiant energy had the maximum value at this vertical angle. It is
obvious that the horizontal angular dependence of the radiant energy had also a similar
tendency. Since this angular dependence indicates that the high radiant energy is
emitted for the downward direction determined by the angle θ
1, this heater construction is much available for local heating such as that of one's
feet. It is preferable that the angle θ
1 between said thin protruded plates ⑦ and the surface

is ranged from 45 to 90 degrees because the radiation for the downward direction
of the angle θ
1 less than 45 degree is not available in practical heatings.
[0047] Referring to Fig. 9, there is shown another embodiment of the heater according to
the invention, further comprising infrared reflective films

formed on the surface

of said thin protruded plates ⑦. Metal films such as Al, Ni, Zn, Ag, Sn and the like
are used as said reflective films

. Since said reflective films

have a. very low emissivity, the radiant energy emitted from said reflective films

is negligible small. On the other hand, parts of infrared rays emitted from the surface

of said heat generator ① are incident to said reflective films

and then reflected many times. As a result, nearly all of'infrared rays emitted from
the surface

are radiated outside the heater. These facts indicate that the radiant energy from
the heater comprises nearly only the radiant energy from the surface

. Moreover, the vertical angular dependence of the radiant energy such as those shown
by curve Bl, Cl in Fig. 4 disappears mostly because the viewed area of the surface

by said radiation detector ⑨ does not decrease with increase of the vertical angle
θ. When a comparatively large spot heating is required with the radiant energy, the
heater is available because the heater can emit the radiant energy for a comparative
large area with a high radiation efficiency.
[0048] It is preferable that said reflective films

have a low thermal conductivity owing to the same reason as that described in the
low thermal conductivity of said thin protruded plates ⑦. The low thermal conductivity
can be obtained by means of a very thin metal films in thickness without decreasing
the reflectivity.
[0049] When the radiant energy emitted from the heater is required to be stronger for the
upward or downward direction, it is obvious that said reflective films

are preferably formed on one upward or downward surface of each of said thin protruded
plates ⑦, respectively.
[0050] Radiation characteristics described in detail hereinbefore were obtained when said
planar-resistive film ⑬ shown in Fig. 2 had a very low positive temperature coefficient
of resistance. On the. other hand, when said resistive film ⑬ has a steeply sloped
positive temperature coefficient of resistance at a selected temperature, different
characteristics from those described hereinbefore were obtained.
[0051] When the electric power was initially applied to said resistive film ⑬, a high electric
power was dissipated because the resistance at the temperature range less than the
selected temperature was determined to have a low value. However, as the temperature
of said resistive film ⑬ increased and approached to the selected temperature, the
applied electric power decreased steeply and then the temperature was saturated near
the selected temperature in the stationary state because the resistance increased
steeply near the selected temperature. These facts cause different characteristics
from those described hereinbefore to be obtained.
[0052] When the heater was constructed as shown in Fig. 2 and said resistive film ⑬ had
the steeply sloped PTC, the vertical angular dependence of the radiant energy showed
the similar characteristics as those shown by curves Bl and Cl in Fig. 4 except for
the fact that the radiant energy for the normal direction of 6=0 and φ=0 degree was
nearly equivalent to that of the conventional heater. The horizontal dependence of
the radiant energy showed the similar characteristics as that of the conventional
heater, shown by curvd A2 in Fig. 5. However, the dissipated electric power decreased
to about 70~80% of the dissipated power in the conventional heater. These facts indicate
that the heater according to the invention has the advantage of being possible to
save the dissipated electric power without decreasing the radiant energy available
for heating.
[0053] When a long and slender electric heat generator standing for the vertical direction
was used as said heat .. generator ①, said thin protruded plates ⑦ were arranged around
said long and slender heat generator. This heater showed the similar vertical angular
dependence of the radiant energy as those obtained with the heater comprising said
resistive film ⑬ having the steeply sloped PTC. On the other hand, the dissipated
electric power also decreased to about 90~80% of that in the conventional heater.
These facts indicate that the heater according to the invention has the advantage
of being possible to save the dissipated electric power without decreasing the radiant
energy available for heating.
[0054] While several embodiments of the invention have been illustrated and described in
detail, it is particularly understood that the invention is not limited thereto or
thereby. For example, the invention can be also applied to gas-firing or oil-firing
infrared radiator and the like.