JPS58184498A - Heat exchanger - Google Patents

Abstract

PURPOSE:To control the variation of the heat conduction efficiency due to the flow rate of a fluid and to reduce the resistance against the passage of the fluid due to an increase in the flow rate of the fluid by a method wherein a helical wire is fitted about a tubular fluid passage in such a manner that one end of the wire is held stationary while the other end is made slidable so that the wire is made flexible. CONSTITUTION:The helical wire 8 is fitted about the outer periphery of the tubular fluid passage 1 so as to induce the generation of scales and a turbulent flow of the fluid. In this case, the end 8a of the helical wire 8 on the side of a fluid inlet port 5 is fixed to the fluid passage 1 with a projection 9 of the passage 1 and the other end 8b is held slidable with the heat generating surface of a heat generating element 3 so as to move into a clearance 10 formed between the top end 3a of the heat generating element 3 and an outer cylinder 2 covering the fluid passage 1. In operation, when the flow rate of the fluid passing through the heat exchanger increases, the flexible helical wire 8 is subjected to a force in the flow direction of the fluid due to the resistance of the fluid. However, since the wire 8 is held stationary at its one end adjacent to the fluid inlet port 5, it projects into the clearance 10 by deforming itself in the flow direction of the fluid as it enlarges the pitch among the helical sections thereof so that scales adhered to the heat transfer surface 4 are removed. Further, the pitch among the helical sections of the wire 8 is large on the side of the fluid inlet port 5 and becomes a smaller toward the flow direction of the fluid so that a desirable heat transfer efficiency distribution is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat exchanger in which a heat transfer surface is provided in an annular flow path, and is particularly effective when the heat transfer surface is constituted by a ceramic heating element.

Conventional heat exchanger whose heat transfer surface is an annular flow path, Example 2...-
For heat exchangers used in electric instantaneous water heaters, the usable source pressure of the water supply is limited, so the width of the annular channel is relatively wide to reduce water flow resistance. .

This type of heat exchanger has a low heat transfer coefficient, and a large heat transfer area is required to prevent scale adhesion due to an increase in heat transfer surface temperature, resulting in a large heat exchanger. was there.

Furthermore, when using a ceramic heating element that has been put into practical use recently, this element has a heat transfer surface and a heating part close to each other (for example,
Although it has the characteristics of being able to heat up quickly and have a high heating density, it is sensitive to scale adhesion, and in order to prevent the destruction of the ceramic heating element due to scale adhesion, it is necessary to It was necessary to prevent scale adhesion at a high level.In general, lowering the temperature of the heat transfer surface is effective in preventing scale adhesion, and for this purpose, increasing the heat transfer coefficient, It is possible to increase the area. In a conventional heat exchanger using only an annular flow path, in order to increase the heat transfer coefficient, it is necessary to make the width of the three vanes of the annular flow path as narrow as possible, which not only increases the flow resistance but also increases the Dimensional accuracy was required and it was not practical.

In order to overcome these drawbacks, this type of heat exchanger inserts a spiral cotton body into the annular flow path to make the annular flow turbulent and increase the heat transfer coefficient by generating scale. Compared to conventional heat exchange using only annular flow, a high heat transfer coefficient can be obtained with low pressure loss, but the following problem occurs when the flow rate through the heat exchanger changes significantly.

The heat transfer coefficient of the heat exchanger is designed so that a predetermined value is obtained at the minimum flow rate. Therefore, if the flow rate increases more than the minimum flow rate, not only will the heat transfer coefficient increase more than necessary, but also the pressure loss will increase, and if the flow rate increases further, the pressure loss will become too high to be practical. To solve this problem, the heat exchanger can be made larger, but this does not make it possible to take full advantage of the advantages of making the heat exchanger more compact due to the improved heat transfer mechanism of ceramics, polyurethane heating elements, and the heat transfer mechanism.

The present invention eliminates these drawbacks of conventional heat exchangers, and while making use of the mechanism that increases heat transfer coefficient, it also prevents the heat transfer coefficient from becoming higher than necessary depending on the mass flow rate of the heat exchanger. It is an object of the present invention to provide a heat exchanger that can handle a wide range of flow rate changes without significantly increasing flow path resistance even when a large flow rate flows, and that is also compact in size.

In order to achieve this objective, the present invention inserts a spiral cotton body into an annular channel, fixes one end of the spiral cotton body,
By making the other end slidable and giving flexibility to the spiral cotton body, changes in heat transfer coefficient due to flow rate can be controlled, and the value of the resistance coefficient of the flow path can be changed to increase the flow rate. This reduces the increase in flow path resistance.

With this configuration, a fluid resistance force depending on the flow rate acts on the spiral cotton body provided in the annular flow path, and as a result, the spiral cotton body expands the flow rate and reduces the drag coefficient. 8 Also, because the heat transfer coefficient is improved by increasing the flow rate, it compensates for the decrease in the heat transfer coefficient due to the decrease in the resistance coefficient.
A sufficiently high value is obtained and 5.-a is obtained.

An embodiment of the present invention will be described below. FIG. 1 is a schematic sectional view showing a heat exchanger according to this embodiment. , 1 is an annular flow path, and 5 is an inlet, which is composed of an outer cylinder 2 and a heat transfer surface 4 mainly composed of the outer circumferential surface of the heating element 3, through which the fluid to be heated is introduced. The introduced non-heated fluid is supplied to the annular flow path 1. Reference numeral 6 denotes an outlet, and a flow path 7 constituted by the annular flow path 1 and the inner circumferential surface of the heating element 3
The non-heated fluid flowing out is led out. 8 is a spiral cotton body, which is inserted into the annular channel 1 along the outer peripheral surface 4,
An end 8a of the spiral cotton body 8 on the inlet 6 side, which induces scale and turbulence, is fixed by a protrusion 9 provided in the annular flow path 1, and an end 8b on the other side is fixed to a heating element. The tip 3a of the heating element 3 is slidably installed on the heating surface 4 of the heating element 3.
and the space 10 formed by the outer cylinder 2.

In this embodiment, the heat exchanger 11 is constructed as described above, and the heating element 3 is a ceramic heating element formed by integrally molding the ceramic base material 12 and the ceramic sheet 146 holding the heating resistor 13. .

In this heating element 3, the heating resistor 13, which is the heating part, and the heating surface 4 are thermally coupled via the thin ceramic sheet 14, so that most of the heat generated in the heating part is transferred to the outer peripheral surface. Therefore, the outer peripheral surface becomes the heat transfer surface 4.

Next, the functions and effects of this embodiment will be explained.

FIG. 2 is an explanatory diagram showing the operation of the heat exchanger according to this embodiment when the flow rate increases. When the flow rate passing through the heat exchanger increases, the flexible spiral cotton body 8 receives a force in the flow direction due to fluid resistance force. Since the spiral cotton body 8 has one end on the inflow port 5 side fixed, the spiral cotton body 8 deforms in the flow direction and protrudes into the space 10 while increasing the pinch interval.

FIG. 3 shows changes in the heat transfer coefficient α and the resistance coefficient Of depending on the flow rate Q of the heat exchanger according to this embodiment.

It is shown that as the flow rate increases and the pitch interval of the spiral cotton body 8 widens, the resistance coefficient Cf decreases and the heat transfer coefficient α gradually increases.

7, -7 In the present embodiment, the spiral cover body 8 is inserted along the heat transfer surface 4, so if the amount of heat exchange changes and the spiral cover body 8 begins to move in the flow direction. , the effect of removing scale adhering to the heat transfer surface 4 can be expected.

Furthermore, in this embodiment, the change in the pitch interval of the spiral foreground body 8 due to fluid resistance force is greater on the side of the inlet 5 of the fluid to be heated. It is desirable that the distribution of the heat transfer coefficient on the heat transfer surface be higher as the temperature of the non-heated fluid increases, but in this example, the pitch on the inlet 5 side is wide and the pitch is narrow in the flow direction, so the above desirable distribution is achieved. This has the effect of providing a distribution of heat transfer coefficients.

Therefore, the heat exchanger according to this embodiment has a high heat transfer coefficient without significantly increasing pressure loss by configuring the spiral bending body provided in the annular flow path so that it can be deformed by fluid resistance force. , Wide: Can be put to practical use over a wide flow rate range.

Next, other embodiments of the present invention will be described.

As explained in the previous example, the temperature of the heated fluid increases as it passes over the heat transfer surface, so in order to prevent the temperature of the downstream heat transfer surface from increasing, it is necessary to It is necessary to increase the heat transfer coefficient of In this embodiment, as shown in FIG. 4, the pitch of the spiral contour body 20 becomes narrower toward the downstream side, which is effective in making the heat transfer surface 4 uniform.

A spiral foreground body 21 according to yet another embodiment is shown in FIG. In this embodiment, a spiral foreground body 21 is provided with concavities and convexities 22. When the flow rate of the heat exchanger 11 changes and the spiral cover body moves in the axial direction, foreign matter such as scale attached to the outer circumferential surface 4, which is a heat transfer surface, is removed by the unevenness 21 provided on the spiral cover body 21. I can do it. Furthermore, the unevenness 21 is effective in making the flow near the heat transfer surface 4 turbulent.

As described above, the heat exchanger of the present invention has a high heat transfer coefficient and exhibits an excellent effect in that the change in pressure loss due to the change in flow rate is relatively small.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view of a 9-bay heat exchanger showing the first embodiment of the present invention, Fig. 2 is a schematic sectional view showing the operation of the heat exchanger, and Fig. 3 is a flow rate diagram of the heat exchanger. and heat transfer coefficient. A characteristic diagram showing the relationship between the resistance coefficients, FIG. 4 is a schematic cross-sectional view of a heat exchanger according to the second embodiment, and FIG. 6 is a partial cross-sectional view of a spiral profile body according to the third embodiment. 1... Annular flow path, 4... Heat transfer surface, 5...
...Inflow port, 6...Outflow port, 8, 20.
21...Spiral foreshadowing body, sa, sb...
·edge. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 3
figure

Claims (3)

[Claims] (1) a heat transfer surface formed on at least one side of the annular flow path;
It has an inlet and an outlet communicating with the annular flow path, and a spiral wrap-around body inserted into the annular flow path, and further, an end of the spiral wrap-around body on the inlet side is fixed, and the spiral A heat exchanger in which the other end of the foreground body is slidable and the spiral foreclosure body is flexible. (2) The heat exchanger according to claim 1, wherein the spiral contour body has pinches arranged at unequal intervals. (3) The heat exchanger according to claim 1, wherein the spiral contour body has a roughened surface.