U.S. patent application number 12/805196 was filed with the patent office on 2011-02-24 for clothes dryer.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Phil Soo Chang, Yong Woon Han, Dae Yeong Hong, Myung Sun Kang, Sung Jin Kim, Won Tae Kim, Hyung Woo Lee.
Application Number | 20110041352 12/805196 |
Document ID | / |
Family ID | 43604121 |
Filed Date | 2011-02-24 |
United States Patent
Application |
20110041352 |
Kind Code |
A1 |
Hong; Dae Yeong ; et
al. |
February 24, 2011 |
Clothes dryer
Abstract
A clothes dryer having a preheating unit preheating drawn air is
provided. The clothes dryer includes a main body, a drying tub
rotatably mounted to receive an object to be dried, and a hot air
duct supplying hot air into the drying tub. The hot air duct
includes a heating unit heating drawn air, and a hot air supply
unit connecting the heating unit with the drying tub, thereby
forming a path for heated air. The heating unit includes a first
heating unit having a heater part generating heat, and a second
heating unit surrounding an entrance and outer walls of the first
heating unit, thereby forming a path for the air flowing to the
first heating unit. The second heating unit includes one or more
preheating fins formed on the first heating unit to contact the air
flowing in the second heating unit.
Inventors: |
Hong; Dae Yeong; (Suwon-si,
KR) ; Han; Yong Woon; (Gunpo-si, KR) ; Kim;
Sung Jin; (Seongnam-si, KR) ; Chang; Phil Soo;
(Seongnam-si, KR) ; Kim; Won Tae; (Suwon-si,
KR) ; Lee; Hyung Woo; (Suwon-si, KR) ; Kang;
Myung Sun; (Suwon-si, KR) |
Correspondence
Address: |
STAAS & HALSEY LLP
SUITE 700, 1201 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
43604121 |
Appl. No.: |
12/805196 |
Filed: |
July 16, 2010 |
Current U.S.
Class: |
34/134 ;
165/185 |
Current CPC
Class: |
D06F 58/04 20130101;
D06F 58/26 20130101; F24H 3/0405 20130101 |
Class at
Publication: |
34/134 ;
165/185 |
International
Class: |
D06F 58/04 20060101
D06F058/04; F28F 7/00 20060101 F28F007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2009 |
KR |
10-2009-78037 |
Claims
1. A clothes dryer comprising: a main body; a drying tub rotatably
mounted to receive an object to be dried; and a hot air duct
supplying hot air into the drying tub, wherein the hot air duct
includes a heating unit heating drawn air, and a hot air supply
unit connecting the heating unit with the drying tub, thereby
forming a path for heated air, and the heating unit includes a
first heating unit having a heater part disposed therein to
generate heat, and a second heating unit surrounding an entrance
and outer walls of the first heating unit, thereby forming a path
for the air flowing to the first heating unit.
2. The clothes dryer according to claim 1, wherein the second
heating unit comprises a preheating fin formed on one of the outer
walls of the first heating unit to contact the air flowing in the
second heating unit.
3. The clothes dryer according to claim 2, further comprising a
plurality of the preheating fins, wherein the preheating fins are
arranged parallel with one another in a length direction of the
first heating unit.
4. The clothes dryer according to claim 2, further comprising a
plurality of the preheating fins, wherein the preheating fins are
slanted with respect to a length direction of the first heating
unit.
5. The clothes dryer according to claim 4, wherein the preheating
fins are slanted by about 3.degree..about.7.degree. with respect to
the length direction of the first heating unit.
6. The clothes dryer according to claim 1, wherein the second
heating unit comprises a main body and a flow loss reduction part
to reduce loss of flow during air suction, and the flow loss
reduction part comprises an air suction part having a diameter
larger than a diameter of the main body of the second heating
unit.
7. The clothes dryer according to claim 1, wherein the heating unit
further comprises a galvanized steel sheet.
8. The clothes dryer according to claim 2, wherein the preheating
fins comprise at least one of a galvanized steel sheet, aluminum,
and copper.
9. The clothes dryer according to claim 2, wherein the preheating
fins are arranged at constant intervals.
10. The clothes dryer according to claim 1, wherein the heating
unit comprises a heater plate formed across an inside of the first
heating unit, a nichrome wire emitting heat by supplied
electricity, and a ceramic member fixing the nichrome wire to the
heater plate.
11. A clothes dryer comprising: a main body; a drying tub rotatably
mounted to receive an object to be dried; and a hot air duct
supplying hot air into the drying tub, wherein the hot air duct
includes a heating unit having a heater part to heat air drawn
thereinto to provide the hot air, and the heating unit includes a
main heating unit that heats the drawn air using the heat of the
heater part, and a preheating unit that forms a path for the air
flowing to the main heating unit and heats the air using the heat
of the main heating unit.
12. The clothes dryer according to claim 11, wherein the preheating
unit is disposed on the air path that guides the air flowing to the
main heating unit.
13. The clothes dryer according to claim 11, wherein the air path
is configured so that the air guided to the preheating unit is
reversed and guided to the main heating unit.
14. The clothes dryer according to claim 13, wherein the air path
includes a body of the main heating unit having a pipe form, and
the preheating unit having a pipe form surrounding the main heating
unit.
15. The clothes dryer according to claim 14, wherein ends of the
body of the main heating unit are opened, one end of the preheating
unit being closed while another end of the preheating unit being
opened to form an entrance for an airflow, and the air is guided in
through the entrance of the preheating unit, reversed by the
blocked end, and then guided into the main heating unit.
16. The clothes dryer according to claim 11, wherein the preheating
unit comprises a preheating fin formed on an outside of the main
heating unit so that the heat of the main heating unit is
transmitted to the preheating unit.
17. A clothes dryer including a hot air duct that supplies hot air,
wherein the hot air duct comprises a heating unit to heat air drawn
therein, and the heating unit comprises a first heating unit
directly heating the air flowing therein, and a second heating unit
disposed adjacent to the first heating unit, thereby forming an air
path guiding air in the opposite direction to the air flowing in
the first heating unit, the second heating unit indirectly heating
the air flowing into the first heating unit using the heat of the
first heating unit.
18. The clothes dryer according to claim 17, wherein the first
heating unit comprises one or more preheating fins formed on outer
walls thereof to contact the air flowing in the second heating
unit.
19. A clothes dryer comprising: a main body; a heating unit heating
drawn air; a hot air supply unit connected to an end of the heating
unit, thereby forming a path for the heated air; a drying tub
connected to the hot air supply unit and structured to receive an
object to be dried; a ventilation device circulating the air; and
an exhaust duct guiding the air exhausted from the drying tub to
the outside of the main body, wherein the heating unit comprises a
first heating unit connected to the hot air supply unit and
equipped with a heater part that generates heat therein, and a
second heating unit forming an air path in which air flows in
contact with outer walls of the first heating unit and guiding the
air to the first heating unit.
20. The clothes dryer according to claim 19, wherein the second
heating unit comprises a preheating fin formed on the outer walls
of the first heating unit to enhance heating of the air flowing in
the second heating unit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Korean Patent
Application No. 2009-0078037, filed on Aug. 24, 2009 in the Korean
Intellectual Property Office, the disclosure of which is
incorporated herein by reference.
BACKGROUND
[0002] 1. Field
[0003] Embodiments relate to a clothes dryer having a preheat
function.
[0004] 2. Description of the Related Art
[0005] A clothes dryer is an apparatus that sends hot air into a
drying tub and thereby dries an object to be dried, which is
received in the drying tub.
[0006] Clothes dryers are mainly divided into an exhausting-type
dryer that exhausts hot and humid air passed through the drying tub
to the outside of the clothes dryer, and a condensing-type dryer
that dehumidifies the hot and humid air and recirculates the
dehumidified air into the drying tub.
[0007] Generally, a clothes dryer has a heating device in a hot air
duct which is an air flow path, so as to produce the hot air by
heating air inside the hot air duct.
[0008] According to the clothes dryer with this structure, the hot
air flowing through the hot air duct is produced as air is brought
into contact with or passed by the heating device emitting heat.
The hot air is supplied into the drying tub to dry the object to be
dried.
[0009] However, since the air is heated only when flowing near the
heating device, most of the heat emitted by the heating device is
wasted. Furthermore, in order to produce hot air having a desired
temperature, the heating device needs to be maintained at a
considerably high temperature. Therefore, the energy efficiency is
poor.
SUMMARY
[0010] Therefore, it is an aspect to provide a clothes dryer having
a preheat unit to improve energy efficiency.
[0011] Additional aspects will be set forth in part in the
description which follows and, in part, will be apparent from the
description, or may be learned by practice of the invention.
[0012] The foregoing and/or other aspects are achieved by
providing, a clothes dryer including a main body, a drying tub
rotatably mounted to receive an object to be dried, and a hot air
duct supplying hot air into the drying tub, wherein the hot air
duct includes a heating unit heating air supplied thereto, and a
hot air supply unit connecting the heating unit with the drying
tub, thereby forming a path for heated air, and the heating unit
includes a first heating unit having a heater part disposed therein
to generate heat, and a second heating unit surrounding an entrance
and outer walls of the first heating unit, thereby forming a path
for the air flowing to the first heating unit.
[0013] The second heating unit may include one or more preheating
fins formed on the outer walls of the first heating unit to contact
the air flowing in the second heating unit. The one or more
preheating fins may be arranged parallel with one another in a
length direction of the first heating unit. The one or more
preheating fins may be slanted with respect to the length direction
of the first heating unit. The one or more preheating fins may be
slanted by about 3.degree..about.7.degree. with respect to the
length direction of the first heating unit.
[0014] The second heating unit may include a flow loss reduction
part to reduce loss of flow during air suction, and the flow loss
reduction part may be formed by increasing a diameter of an air
suction part of the second heating unit to be larger than a
diameter of a main body of the second heating unit.
[0015] The heating unit may include a galvanized steel sheet.
[0016] The preheating fins may include at least one of a galvanized
steel sheet, aluminum, and copper.
[0017] The one or more preheating fins may be arranged at constant
intervals.
[0018] The heating unit may include a heater plate formed across
the inside of the first heating unit, a nichrome wire emitting heat
by supplied electricity, and a ceramic member fixing the nichrome
wire to the heater plate.
[0019] The foregoing and/or other aspects may be achieved by
providing a clothes dryer including a main body, a drying tub
rotatably mounted to receive an object to be dried, and a hot air
duct supplying hot air into the drying tub, wherein the hot air
duct includes a heating unit having a heater part to heat air drawn
thereinto to provide hot air and a hot air supply unit guiding the
heated air into the drying tub, and the heating unit includes a
main heating unit that heats the drawn air using the heat of the
heater part, and a preheating unit that forms a path for the air
flowing to the main heating unit and heats the air using the heat
of the main heating unit.
[0020] The preheating unit may include a preheating fin formed on
the outside of the main heating unit so that the heat of the main
heating unit is efficiently transmitted to the preheating unit.
[0021] The foregoing and/or other aspects are achieved by providing
a clothes dryer having a hot air duct that supplies hot air,
wherein the hot air duct may include a heating unit to heat air
supplied thereto, and the heating unit may include a first heating
unit directly heating the air flowing therein, and a second heating
unit disposed adjacent to the first heating unit, thereby forming
an air path guiding air in the opposite direction to the air
flowing in the first heating unit, the second heating unit
indirectly heating the air flowing into the first heating unit
using the heat of the first heating unit.
[0022] The first heating unit may include one or more preheating
fins formed on outer walls thereof to contact the air flowing in
the second heating unit.
[0023] The foregoing and/or other aspects are also achieved by
providing a clothes dryer including a main body, a heating unit
heating drawn air, a hot air supply unit connected to an end of the
heating unit, thereby forming a path for the heated air, a drying
tub connected to the hot air supply unit and structured to receive
an object to be dried, a ventilation device circulating the air,
and an exhaust duct guiding the air exhausted from the drying tub
to the outside of the main body, wherein the heating unit includes
a first heating unit connected to the hot air supply unit and
equipped with a heater part that generates heat therein, and a
second heating unit forming an air path in which air flows in
contact with outer walls of the first heating unit and guiding the
air to the first heating unit.
[0024] The second heating unit may include a preheating fin formed
on the outer walls of the first heating unit to enhance heating of
the air flowing in the second heating unit.
[0025] As described above, the clothes dryer according to the
embodiments is capable of improving the efficiency of hot air
production, by employing a preheat unit which preheats drawn
air.
[0026] Also, the hot air production efficiency may be further
improved by adopting a preheating fin.
[0027] In addition, since an air circulation structure of a heating
unit of the clothes dryer is improved, energy may be conserved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] These and/or other aspects of the invention will become
apparent and more readily appreciated from the following
description of the embodiments, taken in conjunction with the
accompanying drawings of which:
[0029] FIG. 1 is a perspective view of a clothes dryer according to
one embodiment;
[0030] FIG. 2 is a longitudinal-sectional view of the clothes dryer
of FIG. 1;
[0031] FIG. 3 is a perspective view showing a heating unit of the
clothes dryer of FIG. 1 in detail;
[0032] FIG. 4 is a sectional view cut along line I-I' shown in FIG.
3;
[0033] FIG. 5 is a sectional view cut along line II-II' shown in
FIG. 3;
[0034] FIG. 6 is a sectional view cut along line shown in FIG.
3;
[0035] FIG. 7 is a conceptual view showing the operational
processes of the clothes dryer according to the embodiment;
[0036] FIG. 8 is a longitudinal-sectional view showing a heating
unit of a clothes dryer according to another embodiment; and
[0037] FIG. 9 is an upper-sectional view showing a heating unit of
a clothes dryer according to still another embodiment.
DETAILED DESCRIPTION
[0038] Reference will now be made in detail to the embodiments,
examples of which are illustrated in the accompanying drawings,
wherein like reference numerals refer to like elements
throughout.
[0039] FIG. 1 is a perspective view of a clothes dryer according to
one embodiment. FIG. 2 is a longitudinal-sectional view of the
clothes dryer shown in FIG. 1.
[0040] Referring to FIGS. 1 and 2, the clothes dryer 1 according to
one embodiment includes a main body 10, a drying tub 20 rotatably
mounted in the main body 10, a driving device 30 rotating the
drying tub 20, and a hot air duct 100 supplying hot air into the
drying tub 20.
[0041] The main body 10 includes a cabinet 11, a top cover 12
covering a top side of the cabinet 11, a front panel 13 disposed on
a front of the cabinet 11, and a control panel 14 equipped with
various operation buttons for control of the clothes dryer 1 and a
display screen.
[0042] The drying tub 20 has a cylindrical form opened at front and
rear sides, and includes a plurality of lifters 21 protruded from
an inner surface thereof in the form of a ridge having a triangular
sectional shape and adapted to lift and drop objects to be dried.
In addition, a front supporting board 22 and a rear supporting
board 24 are fixed to an inner front part and an inner rear part of
the main body 10, respectively, to cover the front and the rear
opened sides of the drying tub 20 while rotatably supporting the
front and the rear opened sides.
[0043] An input opening 19a is formed through the front side of the
main body 10 and the front supporting board 22. The object to be
dried is put in and out of the drying tub 20 through the input
opening 19a. A door 19 to open and close the input opening 19a is
connected to the front of the main body 10.
[0044] The driving device 30 includes a drive motor 31 mounted at
an inner lower part of the cabinet 10, and a pulley 32 and a
rotation belt 33 transmitting power of the drive motor 31 to the
drying tub 20. The rotation belt 33 is wound on an outer surface of
the drying tub 20 and the pulley 32 connected to a shaft of the
drive motor 31.
[0045] The hot air duct 100 includes a heating unit 200 heating air
supplied thereto, and a hot air supply unit 40 connecting the
heating unit 200 to the drying tub 20.
[0046] The heating unit 200 is disposed below the drying tub 20 to
guide entry of external air and heat the air. To this end, the
heating unit 200 includes a heater part 280 emitting heat in the
heating unit 200. The heating unit 200 will be more specifically
described later.
[0047] The hot air supply unit 40 connects the heating unit 200
with a drying tub suction port 24a formed at an upper part of the
rear supporting board 24, thereby forming an air path. Also, the
hot air supply unit 40 guides the heated air toward the drying tub
20.
[0048] An exhaust duct 50 is connected to a front lower part of the
drying tub 20 to guide discharge of the air guided into the drying
tub 20. The exhaust duct 50 is divided into a front exhaust duct 51
connecting an exhaust port 22b disposed at a lower part of the
front supporting board 22 with an entrance of a ventilation device
60 disposed below the drying tub 20, and a rear exhaust duct 53
formed at a lower part of the cabinet 11 so that an exit of the
ventilation device 60 is fluidly communicated with a rear outside
of the cabinet 11.
[0049] A filter member 55 is mounted to the front exhaust duct 51
to filter out foreign substances such as dust and lint contained in
the hot air discharged from the drying tub 20.
[0050] The ventilation device 60 circulates the air, and includes a
ventilation fan 61 and a ventilation case 63. The ventilation fan
61 is mounted at the lower front part of the drying tub 20. The
ventilation case 63 is formed to surround the ventilation fan 61
and connected to the first and the second exhaust ducts 51 and
53.
[0051] FIG. 3 is a detailed perspective view of the heating unit of
the clothes dryer. FIG. 4 is a sectional view cut along line I-I'
shown in FIG. 3, FIG. 5 is a sectional view cut along line II-II'
of FIG. 3, and FIG. 6 is a sectional view cut along line of FIG.
3.
[0052] As shown in FIGS. 3 to 6, the heating unit 200 includes a
first heating unit 210 in which the heater part 280 is disposed,
and a second heating unit 230 surrounding an entrance 212a and
upper and lower outer walls 211a and 211b of the first heating unit
210.
[0053] The first heating unit 210 substantially has a rectangular
sectional shape and is structured so that air flows therein.
[0054] The first heating unit 210 includes the heater part 280
therein to emit heat, and one or more preheating fins 250 formed at
the upper and lower outer walls 211a and 211b to transmit heat by
contacting the air flowing in the second heating unit 230.
[0055] The heater part 280 includes a heater plate 282 formed
across the inside of the first heating unit 210, a nichrome wire
284 emitting heat by being supplied with electric power, and a
ceramic member 286 fixing the nichrome wire 284 to the heater plate
282.
[0056] The nichrome wire 284 is fixed to the heater plate 282
through the medium of the ceramic member 286, which is capable of
enduring high temperatures. In this case, the heater plate 282 may
be prevented from being damaged by the high temperature of the
nichrome wire 284.
[0057] According to an exemplary embodiment, the heater plate 282
is made of the same material as the first heating unit 210.
[0058] The preheating fin 250 transmits heat of the first heating
unit 210 to the air flowing in the second heating unit 230. For
this purpose, a plurality of the preheating fins 250 may be formed
on the upper and the lower outer walls 211a and 211b of the first
heating unit 210.
[0059] The preheating fins 250 are arranged at constant intervals
to be parallel with one another in a length direction of the first
heating unit 210. Such a structure is intended to improve the
efficiency of thermal transmission into the second heating unit 230
while reducing the resistance of the airflow. Additionally, a
preheating fin 250a disposed near the drying tub 20 may be formed
and is smaller than the other preheating fins 250 due to positional
relationship with the drying tub 20.
[0060] The second heating unit 230 has a larger appearance than the
first preheating unit 210 so as to surround the entrance 212a and
the outer walls 211a and 211b of the first heating unit 210.
Therefore, a space S is formed as an air path between the first and
the second heating units 210 and 230.
[0061] That is, the second heating unit 230 is disposed adjacent to
the first heating unit 210, thereby forming the air path wherein
air flows in the opposite direction to the air flowing through the
first heating unit 210.
[0062] According to the above structure, the air drawn from the
outside of the main body 10 is guided in through an entrance 231a
of the second heating unit 230, passed through the inner space S of
the second heating unit 230, guided to the entrance 212a of the
first heating unit 210, and then passed through the first heating
unit 210, thereby being heated into hot air.
[0063] The heater part 280 and the first heating unit 210 of the
heating unit 200 function as a main heating unit that directly
heats the air. On the other hand, the preheating fins 250 and the
second heating unit 230 function as a preheating unit that heats
the air not yet heated by the main heating unit.
[0064] The heating unit 200 includes a galvanized steel sheet since
it is inexpensive, easily processed and durable.
[0065] The preheating fins 250 may include at least one of a
galvanized steel sheet, aluminum, and copper.
[0066] Although the galvanized steel sheet is generally used for
the material of the preheating fins 250 due to low cost, aluminum
has a higher thermal conductivity as compared to galvanized steel,
but is more expensive. Copper has higher thermal conductivity than
aluminum but is still more expensive.
[0067] Hereinafter, the operation of the clothes dryer 1 according
to the embodiment of FIG. 1 will be described.
[0068] FIG. 7 is a conceptual view illustrating the operation
processes of the clothes dryer 1.
[0069] Referring to FIG. 7, when a user puts an object to be dried
C in the drying tub 20 and operates the buttons of the control
panel 14, the ventilation fan 61 of the ventilation device 60 is
rotated and the heater part 280 emits heat.
[0070] As the ventilation fan 61 rotates, pressure in the drying
tub 20 is reduced. Accordingly, the external air of the main body
10 is drawn into the second heating unit 230 of the heating unit
200 through via holes 11a formed on a rear surface of the cabinet
11.
[0071] The air passes through the entrance 231a of the second
heating unit 230 and flows in the inner space of the second heating
unit 230. Here, since the first heating unit 210 is already heated
by the heat of the heater part 280, heat of the outer walls 211a
and 211b of the first heating unit 210 heats the air in the second
heating unit 230.
[0072] In addition, the heat of the first heating unit 210 is also
transmitted to the preheating fins 250, thereby heating the air in
the second heating unit 230. The preheating fins 250 may have a
plate form to effectively emit heat, and may be disposed midway
within the airflow so as to effectively heat the air.
[0073] That is, the preheating fins 250 and the second heating unit
230 indirectly heat the air.
[0074] The preheated air passes through the entrance 212a of the
first heating unit 210 and flows into the first heating unit 210.
At this time, the heater part 280 directly heats the air flowing in
the first heating unit 210.
[0075] Since the air is sufficiently preheated, time for the direct
heating by the heater part 280 will be greatly reduced. Therefore,
hot air having a desired temperature may be produced in a short
time.
[0076] Furthermore, consumption of power supplied for the heater
part 280 is reduced, thereby conserving energy.
[0077] The hot air produced through the heating unit 200 is passed
through the hot air supply unit 40 and supplied to the drying tub
20. While the drying tub 20 is being rotated by the drive motor 31,
the object to be dried C in the drying tub 20 is repeatedly raised
and dropped and accordingly dried through contact with the supplied
hot air.
[0078] Wet air in the drying tub 20 is exhausted out of the main
body 10 through the front and the rear exhaust ducts 51 and 53.
Since the ventilation device 60 is continuously operated during
this operation, the external air is newly drawn in and the above
processes are repeated, thereby continuing the drying
operation.
[0079] Hereinafter, another embodiment will be described with
reference to the accompanying drawings. The same structures and
functions as in the previous embodiment will not be described
again.
[0080] FIG. 8 is a longitudinal-sectional view showing a heating
unit of a clothes dryer according to another embodiment.
[0081] As shown in FIG. 8 a heating unit 300 has generally the same
structure as the heating unit 200 of the previous embodiment, but
further includes a flow loss reduction unit 335 adapted to reduce
loss of air drawn into a second heating unit 330.
[0082] The flow loss reduction unit 335 is structured by enlarging
an air suction part of the second heating unit 330 so that flow
loss is reduced during air suction. Specifically, as the air
suction part is enlarged, a predetermined interval is formed
between the air suction part of the second heating unit 330 and a
first heating unit 310, such that the air may be naturally drawn
into the second heating unit 330, without causing loss of flow.
[0083] The other features of this embodiment are the same as in the
previous embodiment.
[0084] Hereinafter, a heating unit according to still another
embodiment will be described, omitting a description about the same
structures and functions as in previous embodiments.
[0085] FIG. 9 is an upper-sectional view showing the heating unit
according to this additional embodiment.
[0086] Referring to FIG. 9, the heating unit 400 has the generally
same structure as the heating unit 200 described above, except for
the configuration of preheating fins 450.
[0087] The preheating fins 450 are slanted by a predetermined angle
X.degree. with respect to a length direction of the first heating
unit 410.
[0088] According to this configuration, an air path of the air
flowing in the second heating unit 430 is elongated, accordingly
increasing a contact time between the preheating fins 450 and the
first heating unit 410. As a result, the preheating efficiency is
improved.
[0089] It is exemplary that the slant angle X.degree. of the
preheating fins 450 is 3.degree..about.7.degree. with respect to
the length of the first heating unit 410 because, when the angle
X.degree. is excessively large, resistance of the airflow is
increased, thereby deteriorating the air flow efficiency.
[0090] Although a few embodiments of the present invention have
been shown and described, it would be appreciated by those skilled
in the art that changes may be made in these embodiments without
departing from the principles and spirit of the embodiments, the
scope of which is defined in the claims and their equivalents.
* * * * *