JPS58179765A - Water heater - Google Patents

Abstract

PURPOSE:To make the average temperatures of both of the side surfaces of a heat generating element substantially equal to each other by a method wherein in the water heater provided with the heat generating element comprising a heat generating resistor held between two cermaic members, each of the ceramic members is made to have an optimum thickness. CONSTITUTION:The heat generating element 1 is formed cylindrical by making the heat generating resistor 1 of a linear heat pattern clamped between the heat resistant ceramic plates 2 and 3. A fluid introduced into an inner pipe 5 of the heat generating element 1 from a fluid inlet port 7 provided in an outer casing is passed through a heating passage 9 about the outer periphery of the heat generating element 1 and is discharged from a fluid outlet port 10 to thereby constitute the water heater. In this case, when the temperature (t1) of the ceramic base plate 2 is made to have a predetermined value in consideration of the mechanical strength or thermal distortion, the thickness of the ceramic base plate 3 is made to have an optimum thickness T2c at a point at which the equation of Tso=Tsi is established from the attached graph showing the relationship between the average temperatures Tso and Tsi of the outer and the inner peripheral surface of the heat generating element 1, and the thickness (t2) of the ceramic base plate 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot water heating device used for hot water supply, space heating, etc.

As shown in FIGS. 6 and 7, a conventional hot water heating device includes a cylindrical surface heating element 22 whose one end is an inlet 21 connected to a cold waterway, and an outer periphery of this cylindrical surface heating element 22. and an outer case 24 forming a heating flow path 23 therebetween. The outer case 24 is provided with an outlet passage 26 located on the inlet 21 side of the surface heating element 22. Further, a heating resistor 28 made of a linear heater pattern is sandwiched between the cylindrical portion 2 and the cylindrical portion 2. And the base material A26
requires a predetermined thickness tl in order to minimize distortion during molding and maintain the mechanical strength of the cylindrical surface heating element 22, and the base material B27 is rolled around the outer periphery of the base material A26. Therefore, in order to perform this work well, the thickness t is very small compared to the thickness tl of the base material A26.
It consists of 2.

In the above-mentioned conventional configuration, the cold water flowing in from the inlet 21 reaches the open left end portion while being heated by the inner pipe 22' of the cylindrical surface heating element 22, and then flows into the heating flow path 23 where it is further heated. The hot water flows out from the outflow path 26 as hot water.

In the above heating step, the surface temperature of the cylindrical surface heating element 220 is the same as that of the ceramic base material A26. B2 thickness 11.12
It is determined by the relationship between and the heat transfer coefficient to water on the surface of the cylindrical surface heating element 22.

In the above-mentioned conventional example, the flow velocity in the inner pipe 22' of the cylindrical surface heating element 22 is faster than the flow velocity in the heating channel 23, so that water on the inner peripheral surface of the cylindrical surface heating element 22 is The heat transfer coefficient is higher than that of the outer peripheral surface. On the other hand, the thickness tl of the inner peripheral surface side base material A26 of the cylindrical surface heating element 22 is larger than the thickness t2 of the outer peripheral surface side base material B2. Therefore, the heat transfer resistance from the heating resistor 28 to the inner circumferential surface of the cylindrical surface heating element 22 is greater than the heat transfer resistance to the outer circumferential surface. As a result, the inner circumferential surface of the cylindrical surface heating element 22 has a large heat transfer coefficient to water, while the heat transfer resistance from the heating resistor 28 is large, so that the surface temperature is lower than that shown in FIG. It decreases as shown in .

In addition, the outer circumferential surface of the cylindrical surface heating element 22 has a low heat transfer coefficient to water, and a low resistance to heat transfer from the heating resistor 28, so its surface temperature is indicated by T8° in FIG. Like, getting higher.

As described above, in the conventional hot water heating device, the difference in surface temperature between the inner circumferential surface and the outer circumferential surface of the cylindrical surface heating element 22 is very large, causing an imbalance in the heat exchange state, and as a result, The entire surface of the heating element is not effectively utilized for heat exchange, resulting in a decrease in heat exchange efficiency.

The outer circumferential surface of the surface heating element 22 becomes hot, causing local nucleate boiling, and the temperature exceeds the saturated solubility of calcium bicarbonate and supergnesium bicarbonate, which are the main components of scale, causing the scale to generate surface heat. It precipitates on the surface of the body 22. FIG. 9 shows the relationship between pH, temperature, and solubility of calcium bicarbonate. This scale gradually increases in thickness on the surface of the cylindrical surface heating element 22, worsening the heat transfer from the cylindrical surface heating element 22 to the heated fluid, lowering the heat exchange efficiency, and increasing the thickness of the heating resistor 22. This has the drawback of causing the heat generating resistor 28 to break due to the abnormally high temperature.

In addition, in the conventional hot water heating device, in order to lower the surface temperature of the outer peripheral surface of the cylindrical surface heating element 22, by increasing the surface area, that is, increasing the outer diameter of the surface heating element 22, Adhesion of scale and heating resistor 28
However, in order to satisfy the above conditions, the surface heating element 22 itself has to be extremely large.

In view of the above-mentioned conventional drawbacks, the present invention distributes the amount of heat transferred from the heating resistor constituting the heating element to the two ceramic substrates so that the average temperatures of both side surfaces of the heating element are approximately equal. Of the two ceramic base materials, if the thickness of the ceramic base material on the fluid inlet side is constant, the thickness of the ceramic base material on the fluid outlet side can be set to the optimal thickness. The above-mentioned conventional drawbacks are solved by controlling the average temperature of both side surfaces of the heat generating element to be below the scale formation temperature at the minimum operating flow rate of the hot water heating device or the set flow rate.

Hereinafter, one embodiment of the present invention will be described based on FIGS. 1 to 4. In FIGS. 1 and 2, reference numeral 1 denotes a heating element having a cylindrical shape, and this heating element 1 is a heating resistor made of a linear heater pattern made of a heat-resistant ceramic base material A2 and a ceramic base material B3. It is constructed by holding the body 4 in an optimal position. This heat generating element 1 still has an inner pipe line 5, and at one end is provided in communication with the inner pipe line 6 a fluid inlet lower having a connecting screw 6 to a cold water supply pipe attached thereto. 8 is an outer case, and this outer case 8 forms a heating flow path 9 between it and the outer periphery of the heating element 1;
Then, the other end side of the inner pipe 6 of the heating element 1 is closed, and the appropriate position on the fluid inflow lower side will be described. First, the thickness tl of the ceramic base material A2 is required to be at least a certain thickness due to conditions such as the mechanical strength of the heat generating element 1 and thermal strain during firing, but on the other hand, from the standpoint of heat conduction, thinner is better. Therefore, this thickness tl is limited to a certain range. Therefore, the optimal position of the heating resistor 4 to maintain the average temperature of both side surfaces of the heating element 1 below the scale generation temperature needs to be set to the optimal thickness t2c by changing the thickness t2 of the ceramic base material B3. be.

FIG. 3 shows ceramic base material A2. Ceramic base material B3
FIG. 3 is an explanatory diagram showing how the heat conduction conditions of the ceramic substrate B3 change depending on the change in the thickness t2 of the ceramic base material B3.

Here, the ceramic base material A2 has a required thickness t2 and is constant.

In FIG. 3, the maximum values of the thickness t2 of the ceramic base material B3, the average surface temperature T8° on the outer peripheral side of the heating element 1, and the average surface temperature ``si'' on the inner peripheral side of the heating element 1 are P1
→P2→P3, and at the 22 points, that is, T8゜−”si ...... (1), the surface average temperature of the heating element 1 is the minimum for the same calorific value. These conditions are optimal from the viewpoint of controlling the scale adhesion generation temperature T8p or lower and from the viewpoint of heat exchange efficiency.

Figure 4 shows the relationship between the outer diameter D of the heating element 1 and the thickness t2 of the ceramic base material B3, which is important when maintaining the average surface temperature of the heating element 1 below the scale formation temperature. As is clear from FIG. 4, the minimum value of the outer diameter D1 of the heating element 1 that satisfies the conditions is when the thickness t2 of the ceramic base material B3 is equal to the optimum thickness t2c, and this is This corresponds to the optimum condition for the thickness t2 of the ceramic base material B3 described in FIG. Therefore, the heating element 1 that satisfies the above formula (1) can be made in the smallest size and with the least amount of resources for the same amount of heat generated. and the third
The relationships shown in the figures and FIG. It can be obtained by inputting the calorific value and performing numerical calculations.

In the embodiment of the present invention described above, the distribution of the surface temperature of the heating element 1 becomes more uniform compared to the conventional example, so that there is an effect that the maximum value of the surface temperature can be reduced. In addition, heating of the heating resistor 4 made of linear heater turns is more or less uneven heating conditions,
It is unavoidable that the surface temperature of the heating element 1 is locally high. This unevenness in temperature distribution is caused by the heating resistor 4 being connected to the two ceramic substrates A2 and B.
Regarding the distance to the surface of No. 3, if the thickness of the ceramic base material B3 is quite thin as shown in the conventional example, there will be locally high temperature areas on the surface. In one embodiment, since the thickness of the ceramic base material B3 is relatively thick, a more uniform heating state can be achieved compared to the conventional example. Each thickness tl of the base material B3.

t2 is determined by the procedure described above. Therefore, in one embodiment of the present invention, the heating element 1 substantially satisfies the condition that the average surface temperature is the lowest for the same amount of heat generation, so the average surface temperature is maintained below the scale formation temperature. As a result, a compact and resource-saving hot water heating device has become possible.

FIG. 6 shows another embodiment of the present invention. In this embodiment, the ceramic base material B3 in the above-mentioned embodiment is made up of multiple layers of thin ceramic tape material 11. Still in this example, the optimum thickness t of the ceramic substrate 3
2c becomes large, and it is difficult to wrap ceramic base material B3 with this thickness around ceramic base material A2 at once and fire it, or when it is necessary to delicately control the optimal thickness t2c. Ceramic base material B corresponding to an arbitrary optimum thickness t2c
3 can be manufactured.

As shown in E-L, the hot water heating device of the present invention distributes the amount of heat transferred from the heating resistor constituting the heating element to the two ceramic substrates, so that the average temperatures of the surfaces of both side surfaces of the heating element are approximately equal. If the thickness of the ceramic base material on the fluid inlet side is constant among the two ceramic base materials,
Since the thickness of the ceramic base material on the fluid outlet side is set to the optimal thickness, the average temperature on both side surfaces of the heating element will be the same at the minimum operating flow rate or set flow rate supplied from the fluid inlet. It is possible to reliably maintain the temperature below the scale formation temperature, and as a result, reliability can be significantly improved, and the heating element can be made more compact.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway side view of a hot water heating device showing an embodiment of the present invention, Fig. 2 is a sectional view taken along the line AA' in Fig. 1, and Fig. 3 is a diagram showing a heating element in the hot water heating device. Surface average temperature T8
An explanatory diagram showing the relationship between and the thickness t2 of the ceramic base material B,
Figure 4 shows the outer diameter of the heating element and the thickness t of the ceramic base material B.
5 is a sectional view of a main part of a heating element in a hot water heating device showing another embodiment of the present invention, and FIG. 6 is a partially cutaway side view of a conventional hot water heating device. Figure 7 is a sectional view taken along the line B-B' in Figure 6, Figure 8 is an expanded graph showing the surface temperature of a conventional cylindrical surface heating element, and Figure 9 is a graph showing the relationship between pH, temperature, and solubility of calcium bicarbonate. It is a graph showing a relationship. 1... Heat generating element, 2, 3... Ceramic base material, 4... Heat generating resistor, 7... Fluid inlet, 1o... Fluid outlet, 11...
Ceramic tape material. Name of agent: Patent attorney Toshio Nakao and 1 other person @
1 Figure n Figure 2 Figure 3 Figure 4 Figure 15 Figure 3 ε Figure 7

Claims (2)

[Claims] (1) A heating element configured by sandwiching a heating resistor between two ceramic base materials, and a heating element provided on both sides of the heating element,
One side has a flow path communicating with a fluid inlet, and the other side has a flow passage communicating with a fluid outlet, and when the lowest flow rate in use or the set flow rate supplied from the fluid inlet, two ceramics are removed from the heating resistor. Of the two ceramic base materials, the thickness of the ceramic base material on the fluid inlet side is kept constant so that the amount of heat transfer to the base materials is distributed so that the average temperature on both side surfaces of the heating element is approximately equal. In this case, the thickness of the ceramic base material on the fluid outlet side is set to the optimal thickness. (2) The hot water heating device according to claim 1, wherein the ceramic base material on the fluid outlet side is constructed by winding a ceramic tape material in multiple layers.