Ceramic rotary heat exchanger

Abstract: A ceramic rotary heat exchanger consists of a plurality of matrix segments (1), made of ceramics and having a honeycomb structure, being connected with each other by an adhesion material into a disk shape, and a plurality of pins (3) arranged at an outer peripheral portion. To avoid thickening at the connecting portions (2), and loss of strength, the pins (3) are not positioned at connecting portions (2) between respective matrix segments.

Description: The present invention relates to a ceramic rotary heat exchanger comprising the features as indicated in the first part of claim 1. Such heat exchangers are used for for high temperature gases for use in the field of for example gas turbine rotors or sterling engines, The invention relates also to a method of manufacturing the same. The known ceramic rotary heat exchanger has a disk shape having a diameter of 20 to 200 cm and a thickness of 2 to 20 cm and having a honeycomb structure. The ceramic rotary heat exchanger having a diameter under 30 cm can be formed unitarily by an extrusion method. However, it is not possible to form the ceramic rotary heat exchanger having a diameter more than 30 cm by one extrusion. Therefore, such a ceramic rotary heat exchanger is formed by extruding ceramic matrix segments having a honeycomb structure and bonding the matrix segments with each other by means of an adhesion member such as ceramic and glass etc., as shown in Japanese Patent Laid-Open Publication No. 55-46338 or Japanese Patent Laid-open Publication No. 63-263394. Moreover, the ceramic rotary heat exchanger mentioned above has a ring gear arranged on its outer portion and is rotated by means of a pinion meshed with the ring gear. One method of securing the ring gear to the outer portion of the ceramic rotary heat exchanger is known in which solid pins are arranged in the outer portion of the ceramic rotary heat exchanger and the ring gear is secured by means of springs arranged between respective solid pins. Another method is also known such that the ring gear is secured to the outer portion of the ceramic rotary heat exchanger having no pins by binding forces caused by an elastic member arranged thereon. In the ceramic rotary heat exchanger mentioned above, outer peripheral portions at both ends of the rotary heat exchanger are sealed, and a high temperature gas is passed through an inner portion thereof and an outer portion thereof is exposed to the air. Therefore, an abrupt temperature gradient occurs in the ceramic rotary heat exchanger and thus thermal stresses are generated in the seal portion including the pin portion. In order to improve thermal shock properties, there is known a method, in Japanese Patent Laid-Open Publication No. 1-147291, such that use is made of a foaming joint member for connecting the ceramic matrix segments. Further, the ceramic rotary heat exchanger using the pins for securing the ring gear is affected by a mechanical stress due to a driving force concentrated on the pin portion as compared with the heat exchanger using no pins. In case that use is made of a matrix segment connecting method such that a through hole direction of each segments are aligned in one direction as shown in Japanese Patent Laid-Open Publication No. 55-46338 or Japanese Patent Laid-Open Publication No. 62-263394, a position of the solid pins each arranging with a constant distance is liable to be located at a connecting portion between the segments, as shown in Fig. 3. In this case, since the pin 3 is arranged at the connecting portion between the segments and a connecting distance near the pin portion utilizing the foaming joint member becomes long, a foaming force generated during a sintering process becomes larger at the connecting portion mentioned above. Further, in this case, since the segment has a soft structure, the foaming force is adsorbed at the connecting portion between the segments only, but since the solid pin has a hard structure, the foaming force is not absorbed at the connecting portion including the pins between the segments. Therefore, in this case, a thickness of the connecting portion becomes thicker and a crack is generated. As a result, there occur drawbacks such that a mechanical strength of the connecting portion 2 is decreased and a heat exchanging efficiency becomes lower due to a decrease of a heat conduction area, etc. An object of the present invention is to eliminate the drawbacks mentioned above and to provide a ceramic rotary heat exchanger having high mechanical strength, thermal shock strength, heat exchanging efficiency, etc, which can permit smaller thickness of the connecting portion thinner even if the pin is present, and the method of manufacturing the ceramic rotary heat exchanger mentioned above. According to the invention, there is provided a ceramic rotary heat exchanger as set out in claim 1. Further, according to the invention, there is provided a method of manufacturing a ceramic rotary regenerator as set out in claim 3. In the ceramic rotary heat exchanger according to the invention, as shown in Fig. 1, since the matrix segments 1 are connected with each other in such a manner that the pins 3 arranged at an outer peripheral portion of the heat exchanger are not positioned at the connecting portion 2 between the segments 3, the connecting portion 2 between the segments 3 does not become thick and a crack is not generated at the connecting portion 2. Therefore, a thickness of the connecting portion 2 can be less, and a decrease of the mechanical strength at the connecting portion 2 can be eliminated. Moreover, the thermal shock strength need not decrease. Further, an area for a heat conduction can not decrease and a high heat exchanging efficiency can be maintained. The ceramic rotary heat exchanger may be secured inside of the ring gear by arranging a spring not shown to a recess portion 5 formed on an outer surface of respective pins 3, and rotated by means of the pinion meshed with the ring gear. Moreover, according to the method of manufacturing the ceramic rotary regenerator, since the sintering process is performed for the heat exchanger in which the pin 3 is embedded in a position more than 10 mm inside of the edge of the matrix segment 1, a foaming force of the foaming joint member 4 generated during the sintering process is absorbed by the matrix segment 1 having the soft structure, and a part of the foaming force functions to make the connecting portion 2 of the matrix segment 1 thinner, preferably not more than 1.2 mm thick. Fig. 1 is a plan view showing an embodiment of a ceramic rotary heat exchanger according to the invention; Fig. 2 is a perspective view for explaining a manufacturing steps of the ceramic rotary heat exchanger according to the invention; and Fig. 3 is a plan view illustrating an embodiment of a known ceramic rotary regenerator. Hereinafter, the present invention will be explained with reference to the drawings. Fig. 1 is a plan view showing an embodiment of a ceramic rotary heat exchanger element of the invention. In Fig. 1, a plurality of ceramic matrix segments 1 each having a honeycomb structure are connected with each other by using an adhesion material and machined into a heat exchanger having a circular disk shape. A plurality of solid pins 3 are arranged at an outer peripheral portion of the heat exchanger with a constant distance therebetween. The matrix segment 1 is made of cordierite. A dimension of the honeycomb cell structure of the matrix segment 1 is a rectangular shape having short side pitch: 0.56 mm and long side pitch: 0.96 mm and a thickness of the cell is 0.11 mm. The matrix segments 1 having a specific cell structure are aligned as shown in the figure in such a manner that a direction to which Young's modulus becomes smallest is a circumferential direction. All the pins 3 are arranged at positions at which no connecting portions 2 exist. However, since a position of the pins 3 on the peripheral portion of the heat exchanger is defined previously, it is necessary to choose a combination of the matrix segment arrangement so that the pin 3 is positioned more than 10 mm apart from the connecting portion 2. In order to obtain the ceramic rotary heat exchanger mentioned above, the matrix segment 1 in which the cylindrical solid pins 3 are embedded in a position more than 10 mm inside from the edge thereof and the matrix segment 1 in which no pins are embedded are prepared, and the thus prepared matrix segments 1 are connected with each other as shown in Fig. 2 into a substantially disk shape. In this case, a foaming joint member 4 is arranged in a space between respective matrix segments 1 and in a space between the pin 3 and the matrix segment 1. The pin 3 is positioned at an outer peripheral portion which is machined and cut-out later. It should be noted that at this time the outer peripheral portion of the connected matrix segments 1 have an uneven shape as shown in Fig. 2 by a one dotted chain line. The thus connected matrix segments are sintered to obtain an integral ceramic rotary regenerator. In this case, since the pin 3 is positioned more than 10 mm apart from the connecting portion 2 of respective matrix segments 1, a foaming force of the foaming joint member 4 during the sintering process can be absorbed by the matrix segment 1 having the soft structure. Therefore, the connecting portion between respective matrix portions 1 does not become thick and does not generate cracks, and thus the matrix segments 1 are connected in a reliable manner. After that, the outer peripheral portion of the matrix segment 1 is machined mechanically into a circular shape as shown in Fig. 2 by a solid line together with the pin 3 to obtain the ceramic rotary heat exchanger in which the pins 3 are arranged at the outer peripheral portion. The outer surface of the pin 3 is further machined to form the recess portion 5. In case that only half of the pin 3 is embedded in the matrix segment 1, the pin 3 is moved outward from the connecting portion between the pin 3 and the matrix segment 1, and a thickness of the connecting portion thereof become larger and a crack is partly generated. As compared with the ceramic rotary heat exchanger according to the invention, the known ceramic rotary heat exchanger in which a part of the pins 3 are positioned at the connecting portion 2 between the matrix segments 1 as shown in Fig. 3 are manufactured in the same manner other than the pin arrangement. With respect to the thus prepared heat exchanger according to the invention and the thus prepared known regenerator, a thickness of the connecting portion 2 between the matrix segments 1 is measured by using a profile projector having a magnification of twenty times. As a result, the connecting portion 2 of the present invention nearest to the pin 3 is 1.2 mm average, and the same portion of the known embodiment is 1.5 mm average. Therefore, the thickness of the connecting portion of the known heat exchanger is 0.3 mm (25%) thicker than that of the present invention. Then, thermal shock strengths of these regenerators are measured. The thermal shock test is performed in such a manner that the heat exchanger of the present invention and the heat exchanger of the comparative example are kept in an electric furnace maintained at a temperature of room temperature + 700°C for one hour, and after that these regenerators are picked out from the furnace to observe whether or not a crack is generated. Then, when no cracks are generated, a temperature of the electric furnace is increased by 25°C and the same thermal shock test is repeated at that temperature. As a result, the heat exchanger according to the invention generates a first crack at a temperature difference of 900°C, and the heat exchanger according to the comparative example generates a first crack at a temperature difference of 825°C. Therefore, it is confirmed that the heat exchanger according to the invention shows a better thermal shock properties than that of the comparative example. Moreover, samples having a dimension of 25.4×12.7×80 mm are cut out from D-I portions shown in Figs. 1 and 2, and four points flexural strength test is performed with respect to the samples in a condition such that an outer span is 60 mm, an inner span is 20 mm, and a load speed is 0.5 mm/min. As a result, both of the D-F portions of the present invention and the I portion of the comparative example shows a flexural strength of 15 to 18 kg/mm², and a break point is at a position in the matrix segment 1 near the connecting portion 2. Contrary to this, the G and F portions of the comparative example shows a flexural strength of 10 to 12 kg/mm², and a break point is at the connecting portion 2. In this result, since, in both of the F portion of the present invention and the I portion of the comparative example, a distance from the connecting portion between the pin 3 and the matrix segment 1 to the connecting portion between respective matrix segments 1 is 10 mm, it is confirmed that the heat exchanger according to the invention shows a better flexural strength than that of the comparative example. As mentioned above in detail, the ceramic rotary heat exchanger according to the invention can be made thicker the thickness of the connecting portion near the pin arranged in the outer peripheral portion thereof, and can be made higher the mechanical strength, thermal shock strength, heat exchanging efficiency as compared with the known regenerator. Moreover, according to the method of manufacturing the ceramic rotary heat exchanger mentioned above, the heat exchanger is manufactured in a reliable manner by eliminating a trouble generated near the pin during the sintering process. Therefore, the ceramic rotary heat exchanger and the method of manufacturing the same according to the invention, can prevent the drawbacks of the known regenerator.

Claims: A ceramic rotary heat exchanger comprising a plurality of matrix segments (1) made of ceramics and having a honeycomb structure, and connected with each other by using adhesion material into a disk shape, and a plurality of pins (3) arranged at an outer peripheral portion of said connected matrix segments, characterized in that said matrix segments are connected with each other in such a manner that said pins (3) are not positioned at connecting portions between respective matrix segments. A ceramic rotary heat exchanger according to claim 1, wherein for each pin (3) the distance from the connecting portion between the pin (3) and the respective matrix segment (1) to a said connecting portion between matrix segments is more than 10 mm. A method of manufacturing a ceramic rotary regenerator, having a plurality of pins (3) arranged at an outer peripheral portion thereof, comprising the steps of, preparing a plurality of matrix segments (1) made of ceramics and having a honeycomb structure; connecting said matrix segments (1) with each other by using a foaming adhesion material; embedding a plurality of pins (3) at an outer peripheral portion of said connected matrix segments (1) in such a manner that each said pin is positioned more than 10 mm from edge portions of said matrix segments; sintering said connected matrix segments including said pins; and machining said sintered connection matrix segments into a disk shape together with said pins.

Inventors: HORIKAWA OSAMU, MAKINO MIKIO, HORIKAWA, OSAMU, MAKINO, MIKIO
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1990
Main classification: F28D19
IPC codes: F28F21, F28D19