Heat generator

A heat generator includes a heat generating member and a temperature compensating member made from different material. The heat generating member includes a heat flow output face for outputing heat flow and five heat flow insulation faces. The temperature compensating member encloses and contacts the heat generating member except the heat flow output face. A heat flow compensating circuit is electrically connected between the temperature compensating member and the heat generating member for maintaining a state of no heat flow flowing between the heat generating member and the temperature compensating member, whereby the heat energy of the heat flow outputing from the heat flow output face is equal to the heat energy of heat generated by the heat generating member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to three copending U.S. patent applications entitled “HEAT GENERATOR”, filed with the same assignee as the instant application and with application Ser. Nos. 10/930,551 filed on Aug. 31, 2004, 10/951,422 filed on Sep. 28, 2004, and 10/951,360 filed on Sep. 28, 2004, respectively. The disclosures of the above identified applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a heat generator, and particularly to a heat generator having heat flow compensation capability.

BACKGROUND

When developing new material, especially heat conduct material, it need to measure the heat conductivity of the material. When designing a heat dissipation device for electronic devices, the designer need to know the heat conduct capability of the material of the heat dissipation device. Precisely measuring heat conductivity of the material is the key of the design.

In early times, the heat conductivity of a material is measured via sandwiching a specimen made from the material between a heat source and an object with a lower temperature. The heat generated by the heat source flows through the specimen to the object with lower temperature. A temperature gradient ΔT exists between two opposite ends of the specimen. The distance between the two opposite ends of the specimen ΔX can be measured. Assuming that all of the heat generated by the heat source flow through the specimen, the heat energy Q of the heat flow flowing through the specimen is equal to the heat energy Q′ generated by the heat source. The heat energy Q′ generated by the heat source is calculated according to the equation as follows:
Q′=αI2R

wherein R is the resistance value of a thermal resistor embedded in the heat source, I represents the electric current flowing through the thermal resistor, and α is a ratio of electrical power converted to heat energy of the thermal resistor. The heat conductivity K of the material of the specimen can be calculated according to the equation as follows:
K=q*ΔX/ΔT
q represents heat flow which is the rate at which heat energy Q flows through the specimen per square meter, in W/m2.

In the above method, the specimen firmly contact with one face of the heat source. The other faces of the heat source are heat insulated by a layer of insulation material covered thereon in order to ensure all of the heat generated by the heat source flow through the specimen. However, the insulation capability of the insulation material, such as alumina, is limited. Some of the heat generated by the heat source is inevitably dissipated through the other faces which do not contact the specimen. That means, the heat energy Q flowing through the specimen is not equal to the heat energy Q′ generated by the heat source. Thus, the value of the heat flow q flowing through the specimen exists an inaccuracy which results in the calculated value of the heat conductivity K of the material of the specimen existing an inaccuracy.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a heat generator which can output a predetermined heat flow precisely.

To achieve the above-mentioned object, a heat generator in accordance with the present invention comprises a heat generating member and a temperature compensating member made from different material. The heat generating member comprises a heat flow output face for outputting heat flow and a plurality of heat flow insulation faces. The temperature compensating member encloses and contacts the heat generating member except the heat flow output face thereof. A heat flow compensating circuit is electrically connected between the temperature compensating member and the heat generating member for maintaining a state of no heat flow flowing between the heat generating member and the temperature compensating member, whereby the heat energy of the heat flow outputting from the heat flow output face is equal to the heat energy of heat generated by the heat generating member.

Other objects, advantages and novel features of the present invention will be drawn from the following detailed description of a preferred embodiment of the present invention with attached drawings, in which:

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring toFIG. 1, a heat generator in accordance with the preferred embodiment of the present invention comprises a beat generating member10and a temperature compensating member20.

The heat generating member10is a polyhedron and made from material with a higher heat conductivity. In the preferred embodiment, we take a cube shape employed as an example of the heat generating member10. The heat generating member10comprises six faces. One face12is used as a heat flow output face and the other five faces are used as heat flow insulation faces that no heat flow flows therethrough. A thermal resistor14is embedded in the heat generating member10for generating a predetermined heat energy. The quantity Q′ of the heat energy generated by the thermal resistor is calculated according to the following equation
Q′=αI2R.

wherein R is the resistance value of the thermal resistor14, I represents the electric current flowing through the thermal resistor14, and α is a ratio of electrical power converted to heat energy. A first thermistor16is installed in the heat generating member10adjacent each heat flow insulation face of the heat generating member10for sensing the temperature of the heat flow insulation face.

The temperature compensating member20is made from material with a lower heat conductivity in comparison with the higher heat conductivity of the heat generating member10. The temperature compensating member20is cube shape and comprises four side walls and a bottom wall cooperatively forming a cavity therebetween. The heat generating member10is accommodated within the cavity with each of the walls of the temperature compensating member20intimately contacting with a corresponding heat flow insulation face of the heat generating member10. An interface18is therefore formed between each heat flow insulation face of the heat generating member10and the corresponding wall of the temperature compensating member20. A thermal resistor22is embedded in each of the walls of the temperature compensating member20. When electrified the thermal resistor22generates heat. A second thermistor26is installed in each of the walls of the temperature compensating member20adjacent the interface18, for sensing the temperature thereof.

FIG. 2shows a heat flow compensating circuit electrically connected between the thermistors16,26and the thermal resistor22. The heat flow compensating circuit comprises two temperature detection circuits electrically connected to the thermistors16,26respectively, and a temperature reactive compensating circuit electrically connected to the thermal resistor22. The two temperature detection circuits are used to sense the temperature of the heat flow insulation face of the heat generating member10and the temperature compensating member20adjacent the interface18and output a pair of corresponding temperature signals T16, T26to the temperature reactive compensating circuit. When the temperature of the temperature compensating member20adjacent the interface18is not equal to that of the heat flow insulation face of the heat generating member10, the temperature reactive compensating circuit outputs an adjusted current to the thermal resistor22of the temperature compensating member20to adjust the temperature of the temperature compensating member20adjacent the interface18to thereby cause it to be equal to the temperature of the heat flow insulation face of the heat generating member10. Thus, no heat flow flows between the heat flow insulation face of the heat generating member10and the temperature compensating member20and all of the heat generated by the heat generating member10is transferred from the heat flow output face12of the heat generating member10to a specimen (not shown). Therefore, the heat energy Q flowing through the specimen is equal to the heat energy Q′ generated by the heat generating member10, and a predetermined heat flow is able to be precisely transferred from the heat generator.

In the present invention, the heat generating member10is accommodated in the cavity of the temperature compensating member20and the walls of the temperature compensating member20surround and contact the heat flow insulation faces of the heat generating member10. Since the heat generating member10and the temperature compensating member20are made from different material, great heat resistance is therefore formed at the interfaces16between the heat flow insulation faces of the heat generating member10and the walls of the temperature compensating member20. Thus, no additional heat insulation member is required to be installed between the heat generating member10and the temperature compensating member20.