Electric resistance heating devices – Heating devices – Radiant heater
Patent
1993-04-08
1997-01-07
Jeffery, John A.
Electric resistance heating devices
Heating devices
Radiant heater
219505, 219553, 501137, 338 22R, H01C 702, H05B 314, H05B 320, F24D 1302
Patent
active
055926479
DESCRIPTION:
BRIEF SUMMARY
FIELD OF ART
The present invention relates to a PTC (positive temperature coefficient) thermistor device using a PTC thermistor element; more particularly, it relates to a panel heater.
BACKGROUND OF THE INVENTION
Panel heaters are now applied to various uses. In particular, panel heaters using PTC thermistors as heating elements are free from overheating, and hence enjoy advantages such as automatic self control of calorific value even under change of surrounding temperature. Accordingly, they are used as components for general use heaters, such as food warmers for hospitals, and for numerous other purposes. Technology of this type is disclosed as panel heaters in Japanese Unexamined Patent Publication No. 61-256123 and Japanese Unexamined Patent Publication No. 62-16994.
The panel heaters as disclosed in the aforementioned unexamined published Japanese patent applications, however, suffer problems. Those problems include the fluctuation of temperature due to local heat just above the heater; insufficient heat conduction from the heater element to the panel due to the presence of thermal resistance at the joint; the necessity of additional process steps, such as bolting, for the joints; and the need for a complicated structure of reinforcing materials which are incorporated into the heater to support the heavy load being applied from the upper side of the heating element.
Furthermore, on installing a panel heater comprising a combination of a PTC thermistor and a metallic heat radiation sheet to materials for walls and floors, a PTC thermistor sintered element capable of covering a large area is a requisite. In practice, however, large area panels are unfeasible, because such a large sintered element for a PTC thermistor will require great difficulties in manufacturing. Even if an alternative process for realizing a large area panel heater were to be taken, i.e., integrating smaller PTC thermistor sintered elements into a larger one, the process would be uneconomical and energy-insufficient. Moreover, such a sintered element obtained by integrating smaller pieces of PTC thermistor sintered elements is not practical, because a large heat emission occurs preferentially at the joint portions of the PTC thermistors with a metallic sheet.
An advantage of a PTC thermistor is a quick temperature rise which is realized as a consequence of the rush current (a large initial surge of current which is generated immediately after applying the current). However, the rush current from a plurality of PTC thermistors will accumulate into a large current that has unwanted effects such as activation of the breaker.
An object of the present invention is to overcome the prior art problems as mentioned hereinbefore, and to provide a simply structured panel heater resistant to heavy loads, and free from local overheating.
Because panel heaters are characterized by their thin sheet-like structure, they have been utilized as general use heaters, floor heating, etc. Accordingly, the PTC thermistor heaters tend to be used more frequently because they have a self control function for temperature, which provides enhanced safety.
Conventional PTC thermistor heaters for use in floor heating were planar heaters comprising a heat-resistant insulating organic material having conductive materials such as carbon particles dispersed therein.
Those conventional planar heaters, however, suffered the following drawbacks: (1) Lack of stability in heat emission--the contact state of the conductive material particles changes along with the changing temperature, providing no assurance that the initial contact state will recover upon return to the initial temperature; (2) Non-uniform heater temperature--as mentioned above, because the contact state of the conductive particles is non-uniform, the electric resistance differs from one place to another; and (3) Difficulty in placing the panel heater--because virtually the entire front panel is covered with a heating element, the positions for safely nailing up the panel are highly restricted.
Accord
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Furukawa Mitsuhiko
Kaimoto Takashi
Rikihisa Katsutoshi
Watanabe Kenji
Yamauchi Masahiro
Jeffery John A.
Kyushu Electric Power Co., Inc.
Nippon Tungsten Co. Ltd.
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