JPS62178890A - Ceramic heat transfer pipe - Google Patents

Abstract

PURPOSE:To provide a ceramic heat transfer pipe excellent in heat transfer performance with a small pressure loss of a fluid within the pipe, and easy in the fabrication, by causing ceramic particles to adhere to the inner surface of a heat transfer pipe made of ceramics. CONSTITUTION:A slurry-like glaze or frit or the like is applied beforehand onto required portions of the inner surface of a heat transfer pipe, and further ceramic particles are scattered in the pipe to be adhered on the ceramic particle applied portions, thereafter burning the particles. Since the inner surface area of the heat transfer pipe 1 is substantially increased by the ceramic particles 3 and the coarseness of the inner surface thereof is increased by the ceramic particles 3, an effect of stirring a material to be heated flowing through the inner part of the pipe 1 increases. Further, even when the flow of the fluid within the pipe is a low Reynolds flow, it is apt to become a turbulent flow, and hence a high heat transfer effect can be obtained. In addition, the ceramic heat transfer pipe according to the invention can be manufactured only by causing the ceramic particles to adhere to the pipe inside, its manufacturing cost is low and the pressure loss of the fluid within the pipe is small because the flowpath area within the pipe is hardly reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvements in ceramic heat transfer tubes used in ceramic shell-and-tube heat exchangers and the like that recover heat from high-temperature exhaust gas.

(Prior Art) A shell-and-tube heat exchanger in which a large number of ceramic heat transfer tubes through which a heated fluid flows are arranged in parallel inside a frame is already known, for example, from Japanese Patent Laid-Open No. 60-62593. Ceramic heat exchanger tubes, which have smooth inner and outer surfaces, are widely used in this type of heat exchanger. However, due to manufacturing limitations, the wall thickness of such ceramic heat exchanger tubes must be considerably thicker than that of metal heat exchanger tubes. For example, if the outer diameter is 30 m, the wall thickness of a metal heat exchanger tube is 1 mm, whereas ceramic heat transfer tubes may have to have a wall thickness of 4M, which results in a 21% reduction in the heat transfer area within the tube, resulting in a decrease in heat transfer performance. was. In addition, with metal heat transfer tubes, it is possible to expand the heat transfer area by forming a large number of protrusions on the inner surface, but in the case of ceramic heat transfer tubes, the thick and thin sections are integrated. It is difficult and expensive to form, and has the drawbacks of lowering quality and being limited in terms of the length that can be formed. Therefore, as shown in the above-mentioned Japanese Patent Application Laid-Open No. 60-62593, a method has been taken to thin the temperature boundary layer and improve heat transfer performance by inserting a dividing fluid into the interior of the ceramic tube. Since the flow area in the pipe is reduced by the fluid division, and the equivalent diameter of the flow in the pipe becomes smaller, it is unavoidable that the pressure loss of the fluid in the pipe increases.

(Problems to be Solved by the Invention) The present invention solves the problems of conventional ceramic heat transfer tubes, and provides a ceramic heat transfer tube that has excellent heat transfer performance, low pressure loss of the fluid inside the tube, and is easy to manufacture. It was completed for the purpose of being a heat tube.

(Means for Solving the Problems) The present invention is characterized in that ceramic particles are attached to the inner surface of a heat exchanger tube made of ceramic.

The materials of the ceramic heat exchanger tube and ceramic particles used in the present invention are not particularly limited, but it is preferable to use ceramic materials such as silicon carbide and alumina, which have excellent heat resistance and corrosion resistance. The average particle size of the ceramic particles is 1/20 of the inner diameter of the heat transfer tube.
It is preferable to set it to about 0 to 175. If it is less than 1/200, the improvement in heat transfer performance by disturbing the temperature boundary layer will not be significant, and if it exceeds 175, the pressure loss of the fluid in the pipe will gradually increase. Show trends. Further, the adhesion area of the ceramic particles is preferably 5% or more of the inner surface area of the heat transfer tube, and if it is less than this, the effect of improving heat transfer performance will be insufficient. Note that a method for attaching ceramic particles to the inner surface of a heat transfer tube made of ceramic is to apply slurry glaze or frit to the required portions of the inner surface of the heat transfer tube in advance, and then apply the ceramic particles inside the tube. A simple method can be used in which the agent is sprayed and adhered to the applied area, and then baked. The pattern on which the ceramic particles are attached can be of various shapes, such as spiral, ring, or linear, as shown in the following examples, or they can be scattered over the entire surface. As shown in Fig. 4, when ceramic particles are attached in a spiral pattern, it is preferable that the angle that the spiral grooves make with respect to the axis of the tube is 20 degrees or more, and 50 degrees to 70 degrees. It is more preferable to do so.

(Function) The ceramic heat exchanger tube of the present invention can be used by being attached to a shell-and-tube heat exchanger, etc., in the same way as conventional ones, but the ceramic heat exchanger tube of the present invention
The inner surface area of the heat exchanger tube (1) is substantially increased by the ceramic particles (3) attached to the inner surface (2) of the heat exchanger tube (1).
Since the inner surface roughness of the tube increases, the effect of stirring the heated object flowing through the tube increases, and since the flow inside the tube tends to become turbulent even in a low Reynolds flow, a high heat transfer effect can be obtained. Such a stirring effect is particularly remarkable when the material has a ring-like or spiral-like adhesion pattern in which adhered portions and non-adhered portions are alternately repeated in the flow direction. Furthermore, the ceramic heat exchanger tube of the present invention can be manufactured simply by attaching the ceramic particles (3), so the manufacturing cost is low, and since the area of the flow passage inside the tube is hardly reduced, there is an advantage that the pressure loss of the fluid inside the tube is small. The superiority of the ceramic heat exchanger tube of the present invention is clear from the following examples.

(Example) The inner surfaces (2) of two types of silicon carbide heat exchanger tubes (11) with inner diameters of 30 mm and 60 mm were coated with various average particle sizes in various patterns as shown in FIGS. 1 to 4. Each of the obtained ceramic heat transfer tubes was evaluated in terms of heat transfer effect, pressure loss, and formability, and the results are shown in the following table as N., 1 to N, 17. .

For comparison, the three types of heat exchanger tubes described in the prior art section: straight tubes, tubes with protrusions, and fluid-dividing insertion tubes were evaluated in the same manner and found to be N. , 18 to No. 20 were entered in the same table.

(Effects of the Invention) As is clear from the above explanation, the ceramic heat transfer tube of the present invention is superior to conventional ones in terms of overall evaluation of heat transfer effect, pressure loss, formability, and cost.
In particular, the average particle size of the ceramic particles should be set to 1/2 of the inner diameter of the heat transfer tube.
00 to 115 and the ratio of the adhesion area to 5
% or more indicates a remarkable effect. Therefore, the present invention is particularly suitable as a heat transfer tube for recovering heat from high-temperature exhaust gas, and will greatly contribute to the development of industry.

[Brief explanation of drawings]

1, 2, and 3 are partially cutaway perspective views showing the first, second, and third embodiments of the present invention, and FIG. 4 is a partially cutaway perspective view showing the fourth embodiment of the present invention. It is a notch front view. (1): heat exchanger tube, (2): inner surface, (3): ceramic particles. jiI l Fig. 1 Inner surface of heat transfer tube 2 ω 3 t ram, 7 v Gi ÷ Fig. 2

Claims (1)

[Scope of Claims] 1. A ceramic heat exchanger tube characterized in that ceramic particles are attached to the inner surface of the heat exchanger tube made of ceramic. 2. Set the average particle size of the ceramic particles to 1/1 of the inner diameter of the heat transfer tube.
200 to 1/5 of the ceramic heat exchanger tube according to claim 1. 3. The ceramic heat exchanger tube according to claim 1 or 2, wherein the adhesion area of the ceramic particles is 5% or more of the inner surface area of the heat exchanger tube.