JPH0369151B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a PTC immersion heater that is easily used for heating liquids such as water.
In addition to having an automatic temperature control function and a dry firing prevention function for the set Curie temperature,
A water-resistant PTC whose heat source is a heat-sensitive resistance element (hereinafter abbreviated as a positive resistance porcelain element) with positive resistance temperature characteristics, which has advantages such as superior heating rise temperature characteristics due to high surface power density.
This relates to an immersion heater.

Conventional technology This type of immersion heater uses a metal resistor such as iron, chrome, nickel, or aluminum heating wire as the heat source, and the tube is filled with magnesium oxide, fused magnesium, etc. as an insulating agent, and the outside is In recent years, various types of heaters have been proposed, including so-called sheathed heaters in which heat transfer characteristics are obtained by improving the packing density through reduction, and PTC heater type heaters in which a positive characteristic ceramic element is used as a heat source.

The former type of sheathed heater requires a temperature regulator such as a thermostat or zero-volt switch to cut off the power when the temperature of the controlled object such as water rises to a predetermined temperature, and turn the power on again when the temperature drops below the predetermined temperature. There is. The problem with this type of heater is that the power consumption and surface power density are constant throughout, so in order to improve the rise temperature characteristics, the surface area must be increased by considering the surface power density and the power consumption can also be reduced. Since the upper limit of the allowable range is set, pulsations occur at a given temperature, and power consumption also increases or decreases widely due to voltage fluctuations.As a result, the external shape becomes large and complex, which increases manufacturing costs. is expensive.

The problem with the latter PTC heater type heater is that
The cut-off resistance value at the Curie temperature, at which the heat-sensitive resistance value of the PTC ceramic element sharply increases with respect to the set temperature, changes to a certain extent as the energization time passes.
It has been reported that this tendency becomes especially severe when the PTC heater is used in a closed state, and that the heater becomes unusable. In addition, problems have been pointed out in the shape and material of the heat transfer body, which should be placed in a temperature transfer relationship between the electric heat generating part using the positive characteristic porcelain element as the heat source and the water-resistant box, to absorb thermal expansion and contraction. was.

Problems to be Solved by the Invention The present invention provides a dry-firing prevention function that does not cause any danger such as fire even if it is accidentally used in a dry-firing state;
Compared to conventional bimetal control, it has an automatic temperature control function that provides a flat heating temperature without pulsations, quick response characteristics to rapid changes in heat load, and even lower power consumption to large changes in input voltage. The electric heat generating section uses a positive characteristic ceramic element as the heat source, which has various features such as minimal fluctuation, and the elastic heat transfer body, which is an adsorbent that is an occluding medium that adsorbs and desorbs gas, is housed in a water-resistant box. The elastic heat transfer body is connected to the box and the electric heat generating part in a heat transfer relationship to prevent thermal expansion and contraction, and trace gases generated from the electric heat generating part and other parts are transferred to the heating element. The purpose of this project is to provide a PTC immersion heater that can easily heat heat loads such as water by solving the material composition of the heat transfer body in order to completely eliminate any effect on the deterioration of the characteristics of the heat transfer element.

Means for Solving the Problems The PTC immersion heater of the present invention has an electric heat generation section in which a positive characteristic ceramic element having electrodes is insulated and coated, and a heat transfer body formed with an adsorbent, which are arranged inside a water-resistant box. and a power cord connected to the electrode is pulled out to the outside of the water-resistant box, and the heat transfer body is joined to the electric heat generating part and the water-resistant box in a heat transfer relationship. be.

EXAMPLE An example of the present invention will be described in detail based on the drawings, but the present invention is not limited to the following example unless it exceeds the gist thereof.

FIG. 1 is a partially sectional assembly view showing an embodiment of the present invention. Reference numeral 1 denotes a tubular box with a sealed bottom, 2 a positive characteristic ceramic element, and 3 an electrode for supplying power to the positive characteristic ceramic element 2. Reference numeral 4 forms an electric heat generating portion A in which the positive characteristic ceramic element 2 is electrically insulated and covered with an insulating material, and the positive characteristic ceramic element 2 having an electrode 3 is insulated and covered with an insulating material 4. 5 is a heat transfer part and electric heat generation part A
and the tubular case 1 in close contact with each other in a heat transfer relationship. Reference numeral 6 is connected to the electrode 3 by a power cord and drawn out to the outside. 7 is a lid body and a tubular case 1
It is a bulkhead that maintains airtightness.

The positive characteristic ceramic element 2 of the electric heat generating section A is a valence-controlled semiconductor obtained by adding a small amount of rare earth to a barium titanate-based semiconductor, and is a heat-sensitive resistance element with positive resistance temperature characteristics, and has a remarkable resistance at the Curie temperature. There is an automatic temperature control function that rapidly increases the value and controls its own power. The electric heat generating section A, which includes this element and the BSP of the electrode 3 and is covered with a polyimide film (trademark) of the insulating material 4, is well known, so the details thereof will be omitted. In this example, PTH492 (manufactured by Murata Manufacturing Co., Ltd.) was used, but any known element of the same type can be used.

Figures 2 to 4 are sectional views taken along the line B-B in Figure 1, and Figures 2 and 3 show the shape of the heat transfer body 5 being a solid type that utilizes bulk elasticity and a molded type that utilizes shape elasticity, respectively. It is a space type with a 4th
The figure uses a cylindrical positive characteristic ceramic element 2 and a heat transfer body 5.
is a ring type and utilizes shape elasticity.

The heat transfer body 5 is a solid type made by compression molding activated alumina powder of about 100 μm, cut below 340 μm, and has a surface area of 150 m ² /g, but it may also be silica, which has good adsorption ability in the exothermic temperature range. If so, it does not matter what the material is. In addition, the adsorption ability of porosity is important for the heat transfer body 5 which is formed into shape elasticity, and it is necessary to design and manufacture a porous nickel plate, a porous aluminum plate, etc. with particular emphasis on the size of the pores.
The inventor has obtained good results using porous nickel plates. In another example, an aluminum plate was formed into a space type (FIG. 3) and the voids were filled with activated alumina to form the heat transfer body 5, and a considerable adsorption/desorption ability was also obtained.

In order to absorb thermal expansion and contraction and satisfy the heat transfer relationship, which is the key point of the present invention, it is necessary to determine the inner diameter of the tubular box 1 and the outer diameter of the heat transfer body 5 that sandwiches the electric heat generating part A. Although this is important, it is necessary to make the heat transfer body 5 slightly larger than the inner diameter of the box 1 and push it in with pressure when inserting it.

The material of the box 1 may be metal, porcelain, glass, or plastic with good thermal conductivity. If it is beryllia porcelain or boronite porcelain, which is an electrical insulator and has good heat conduction and heat resistance, the insulating material 4 can be omitted. This is even more suitable.

The shape of the box 1 may be flat or spherical instead of tubular, and the shape does not interfere with the spirit of the present invention.

Effects of the Invention In one embodiment of the present invention described above, the heat transfer relationship in which the thermal resistance between the electric heat generating part and the box is summarized by the elastic shape of the heat transfer body is as follows: On the other hand, the surface temperature of the finished product was 257°C in air, the initial heating power when placed in water at 1.25°C was 230W, and the power consumption at water temperature of 100°C was 47W. This PTC immersion heater has excellent response characteristics to rapid changes in heat load, and does not require pulsation because it does not require bimetal control, compared to the temperature rise characteristics of a 300W sheathed heater that uses conventional heating wires. It has an automatic temperature control function that allows you to obtain a flat heating temperature, and a dry-firing prevention effect that prevents unexpected disasters such as water leakage because the temperature does not rise above the Curie temperature. Incidentally, when the heat transfer body was placed with a gap of 0.1 mm between the electric heat generating part and the box, the surface temperature was 143°C.

Next, due to the gas adsorption and occlusion effect of the heat transfer body made of an adsorbent, a positive characteristic ceramic element in a sealed state without contact with air deteriorates rapidly after 600 to 1500 hours of energization, but the active alumina filling of the present invention The one is 2500
No deterioration is observed over time.

[Brief explanation of drawings]

FIG. 1 is a partially sectional assembled view of the present invention, and FIGS. 2 to 4 are sectional views of FIG. 1. A... Electric heat generation part, 1... Box, 2... Positive characteristic ceramic element, 3... Electrode, 4... Insulating material, 5... Heat transfer part, 6... Electric heating cord, 7... Lid body.

Claims (1)

[Scope of Claims] 1. An electric heat generating section in which a positive characteristic ceramic element having electrodes is insulated and coated, and a heat transfer body formed of an adsorbent are arranged inside a water-resistant box, and a power cord connected to the electrodes is arranged. A PTC immersion heater, characterized in that the heat transfer body is drawn out of the water-resistant box and joined to the electric heat generating section and the water-resistant box in a heat transfer relationship. 2. The PTC immersion heater according to claim 1, wherein the heat transfer body has a structure that provides shape elasticity and/or bulk elasticity. 3. The adsorbent according to claim 1 or 2, wherein the adsorbent is a gas storage medium made of a transition metal and/or an active adsorbent having gas adsorption ability.
PTC immersion heater. 4. The PTC immersion heater according to claim 1, wherein the water-resistant box is a hollow heat-resistant tube with one end sealed and a power cord insertion port at the other end of a watertight structure.