High efficiency heat exchanger with ceramic rotor

Abstract

An improved regenerative, high temperature gas, high efficiency heat exchanger has a heat absorbing rotor formed of a plurality of gas flow passages and a housing that includes partition columns for dividing the rotor passages into at least one high temperature and at least one low temperature duct. A two section drive shaft supports the rotor in the housing and pressure plates securely connect the rotor to the drive shaft. The rotor is of a size to provide an annular gas bypass channel between the rotor and the housing, which channel is greater than the hydraulic diameter of the rotor flow passages in order that bypass of gas through the channel provides a continual flushing of contaminants therefrom. To prevent leakage between the high and low temperature ducts through this annular channel, air curtains may be employed at the top and bottom of the partition columns. In addition, air curtains may be employed along the length of the partition columns to prevent leakage of contaminants from occurring through the space between the columns and the rotor. SUBACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates in general to high temperature gas, high efficiency regenerative heat exchangers having heat absorbing rotors, and more specifically relates to such exchangers employing a noncontact seal between the rotors and the housings of the exchangers.2. Description of the Prior ArtRegenerative heat exchangers that employ heat absorbing rotors positioned in a housing are well known in the art. The housings of such exchangers typically are formed to provide two separate ducts that ideally are isolated from one another. These heat exchangers have been found to be highly advantageous for use in applications wherein gas at one temperature inside an enclosure is exhausted and gas at another temperature is brought into the enclosure. Through such intake and exhaustion of gas, the heat absorbing rotor is heated or cooled by the gas being exhausted and likewise heats or cools the air being brought into the enclosure.In providing regenerative heat exchangers that have a high efficiency and are adapted to operate with high temperature gases, one of the major areas of concern is the type of seal employed between the exchanger housing and the circumference of the rotor. Heretofore, a majority of those skilled in the art have believed that high efficiency of rotor type heat exchangers was dependent upon the use of mechanical seals between the rotor circumference and the exchanger housing to prevent leakage through the gap therebetween. However, mechanical seals have a major disadvantage in that they include sealing faces that frictionally contact one another, which results in considerable wear and energy required to overcome the friction.In a U.S. Patent to Meijer, No. 3,372,735 issued Mar. 12, 1968, the frictional problem with mechanical seals is pointed out. As a substitute for mechanical sealing, Meijer discloses a regenerative exchanger employing a narrow gap seal between the circumference of the rotor and the exchanger housing. The Meijer reference points out that the gap seal should at most have a width equal to or not more than one half the hydraulic diameter of the rotor gas conducting passages. Because of the narrow width of the Meijer gap seal, the exchanger housing and rotor are described as formed of glass ceramic materials having coefficients of thermal expansion substantially equal to prevent the rotor from becoming jammed in the housing.The heat exchanger of the Meijer reference avoids the frictional problems presented by mechanical seals, but it has been found that narrow gaps between rotors and housings often produce jamming of the rotors with the housings. Such jamming results because of distortion of the rotor and housing due to thermal expansion, deflection of the rotor drive shaft due to the rotor weight or the pressure exerted by gas streams on the rotor, and the collection of foreign materials such as particulates and contaminants in the gap between the rotor and the housing. The Meijer exchanger may not have jamming problems due to distortions because it is formed of low thermal expansion materials and has a relatively small rotor. But in industrial applications wherein relatively large rotors are required, the narrow gaps taught by Meijer are not satisfactory due to the high risk of jamming that they present. Accordingly, the need for a heat exchanger that avoids both the frictional and wear problems of mechanical seals and the jamming problems of gap seals exists.SUMMARY OF THE INVENTIONThe present invention provides a regenerative heat exchanger having a heat absorbing rotor formed of a plurality of parallel gas flow passages, a housing that directs gas into the gas flow passages of the rotor, a drive shaft on which the rotor is mounted by a pair of pressure plates and an annular channel between the housing and the circumference of the rotor that is in a range of from 1-10 times greater in width than the hydraulic diameter of the rotor passages.Due to the width of the annular channel between the outer circumference of the rotor and the housing a significant amount of gas bypasses the rotor by flowing through the channel. However, we have found that such bypass has an insignificant effect on the efficiency of the exchanger and is highly desirable because the channel between the rotor circumference and the exchanger housing is continuously flushed thereby. Therefore, contaminants do not collect in substantial quantities between the rotor circumference and the housing.The rotor of the exchanger is preferably formed of a material having a low coefficient of expansion such as possessed by various ceramics. To provide a strong and durable support for the rotor the exchanger housing and drive shaft upon which the rotor is mounted are formed of preferably high strength metals. Accordingly, the thermal coefficients of expansion of the rotor, housing and shaft all may significantly differ. The relatively large annular channel between the rotor and the housing, thus, substantially eliminates the risk of the rotor binding in the housing as expansion of the housing occurs. To likewise prevent binding of the rotor on its drive shaft, the rotor is mounted thereon by means of a parallel pair of pressure plates that have flat surfaces for engaging the rotor to securely sandwich the rotor in proper position on the shaft but at the same time permit free expansion of the shaft.In a preferred embodiment the housing includes partition members for dividing the flow passages of the rotor into one high temperature duct and one low temperature duct. To provide most complete isolation of the high and low temperature ducts, the housing may include first means for directing pressurized sealing fluid along the length of the partition members to form air curtains between the rotor and such members. Also, second means may be included for directing pressurized streams of sealing fluid at segments of the circumference of the rotor traversing between the partition members to provide an air curtain seal between the high and low temperature ducts at the rotor circumference. Thus, the first and second means insure that little leakage is permitted between gases of the high and low temperature ducts of the exchanger.

Description

Claims

1. A high efficiency, high temperature gas regenerative heat exchanger having:

a ceramic rotor formed of a plurality of parallel, axial gas flow passages and having a substantially cylindrical circumference;

a housing having front and rear partition members located near the front and back of said rotor for dividing the rotor into at least one high temperature and at least one low temperature duct;

a drive shaft assembly that is journaled in the housing for mounting said rotor, which assembly includes an outer portion and an inner portion that is rotatably disposed in said outer portion;

a pair of pressure plates having parallel surfaces, one of which plates is connected to the outer shaft portion and the other of which is connected to the inner shaft portion;

bias means for exerting oppositely directed forces on said shaft portions to urge said pressure plates toward one another to securely clamp said rotor between said parallel surfaces of said plates;

insulating means disposed on an inner portion of said housing to prevent heat transfer through the housing, said rotor and said housing being of such size that there is an annular channel between said housing and the outer circumference of said rotor, said channel being 1-10 times greater in width than the hydraulic diameter of the passages in said rotor; and wherein said housing further includes means for directing sealing fluid at segments of the circumference of said rotor traversing between said partition members to provide curtain seals at such circumferential segments of said rotor.

2. A heat exchanger as recited in claim 1 wherein said rotor is formed from a material having a low coefficient of thermal expansion and said housing is formed from a high strength material hving a substantially larger coefficient of thermal expansion.

3. A heat exchanger as recited in claim 1 wherein one of said partition members has apertures therethrough and pressurized air is supplied to such member to provide a stream of air that exits from said member to provide an air curtain seal between both of said partition members and the rotor.

4. A high efficiency, heat temperature gas regenerative heat exchanger having:

a ceramic rotor formed of a plurality of parallel, axial gas flow passages and having a substantially cylindrical circumference;

a housing having front and rear partition members located near the front and back of said rotor for dividing the rotor into at least one high temperature and at least one low temperature duct;

a drive shaft assembly that is journaled in the housing for mounting said rotor, which assembly includes an outer portion and an inner portion that is rotatably disposed in said outer portion;

a pair of pressure plates, having parallel surfaces, one of which plates is connected to the outer shaft portion and the other of which is connected to the inner shaft portion;

bias means for exerting oppositely directed forces on said shaft portions to urge said pressure plates toward one another to securely clamp said rotor between said parallel surfaces of said plates;

said rotor and said housing being of such size that there is an annular channel between said housing and the outer circumference of said rotor, said channel being 1-10 times greater in width than the hydraulic diameter of the passages in said rotor; and wherein said housing further includes means for directing sealing fluid at segments of the circumference of said rotor traversing between said partition members to provide curtain seals at such circumferential segments of said rotor.