Two-stage radial compressor with compensating elements to compensate for length changes occurring due to temperature changes.

Abstract

The invention relates to a two-stage radial compressor (1) with housing (10) and rotor (20), the two impellers (21, 22) of which are arranged on opposite end sections of a shaft (23), wherein the radial compressor (1) has compensating elements (31) arranged in or on the housing (10) to compensate for a difference occurring during a temperature change between the length changes of rotor (20) and housing (10).

Description

The invention relates to a two-stage radial compressor, the two impellers of which are arranged on opposite end sections of a shaft, wherein the radial compressor has compensating elements to compensate for a change in length occurring during a change in temperature. Two-stage radial compressors in a so-called "end-to-end" configuration are known in the prior art. In these, an impeller is provided at each opposite end of a shaft, such that the inlet sides of the compressor stages, each defined by an impeller, face away from each other and the end sections of the compressor stages face each other. In compressors in general, and radial compressors in particular, axial alignment is of special importance, since a predetermined and preferably as small a distance as possible must be set between the respective impeller and the adjacent housing section, which in radial compressors is referred to as the spiral casing or spiral casing section, in order to enable the intended compression. Accordingly, the shaft of radial compressors is axially supported, with the axial support of the shaft usually being located adjacent to one of the impellers, so that a first impeller of the radial compressor is essentially directly adjacent to the axial support and a second impeller of the radial compressor is spaced away from the axial support in the longitudinal direction of the shaft. As with almost all materials, the materials from which such radial compressors are made also expand when the temperature increases according to a material-specific coefficient of thermal expansion, and shrink when the temperature decreases according to the coefficient of thermal expansion. Although a change in dimensions also occurs in a radial direction, a change in dimensions along the shaft, i.e. in the longitudinal direction, plays a special role in the radial compressors described, since this strongly influences the distance between the impellers and the respective adjacent housing or spiral housing sections. This results from the fact that the tolerance chain is small on the first impeller and the adjacent housing section, which are close to the axial bearing, so a change in length has only a minor effect, whereas it is large on the second impeller and the adjacent housing section, since these are farther from the axial bearing, so that a change in length caused by temperature change has a strong effect and can lead to lower efficiency of the compressor or even to physical damage. This problem is known, so the fundamental engineering task is to ensure that the relative thermal deformation of the shaft and the casing is as similar as possible, regardless of the temperature fluctuations of the compressor, so that the relative positioning of the impellers and the respective volute casing or volute casing section is maintained regardless of the thermal ambient and operating conditions. A simple solution would be to manufacture the housing from the same material as the shaft to achieve identical thermal expansion behavior. However, this is disadvantageous and undesirable in practice, as the shaft material is often expensive or fragile, such as high-precision ceramic. Consequently, such materials are unsuitable for a solid housing that may be subject to impacts. However, radial compressors and in particular two-stage radial compressors are known in the prior art, especially from documents DE 10 2009 024 337 A1, DE 10 2016 221 572 A1 and WO 2025 068403 A1. The invention is therefore based on the objective of overcoming the aforementioned disadvantages and providing a two-stage compressor which does not suffer any physical damage during operation at or after temperature changes and can continue to be operated with high efficiency or without loss of efficiency. This problem is solved by the combination of features according to claim 1. According to the invention, a two-stage radial compressor is proposed, comprising a housing and a rotor mounted in the housing. The rotor has a first impeller, a second impeller, and a shaft, to the opposite end sections or faces of which one of the two impellers is fixed, corresponding to an end-to-end configuration. The rotor has a first coefficient of thermal expansion, which is preferably predetermined or known and can also result from several, and possibly different, coefficients of thermal expansion of the various components of the rotor, such as the shaft and the two impellers. Accordingly, the first coefficient of thermal expansion leads to a change in length of the rotor when the temperature changes. For simplicity, it is assumed that the temperature change for the rotor and the housing is essentially identical.Furthermore, it should be clarified that length is understood to mean the extent of the respective component along a rotational axis coaxial with the shaft, around which the shaft or rotor is arranged to rotate, so that the change in length of the rotor corresponds to the change in the dimensions of the rotor along the rotational axis. Likewise, the housing has a second coefficient of thermal expansion, which is predetermined or known, and which in turn can result from several and possibly different coefficients of thermal expansion of the various components of the housing, such as the housing sections mentioned below.The second coefficient of thermal expansion differs from the first, which, when the temperature changes, leads to a change in the length of the housing that differs from the change in length of the rotor, resulting in different and therefore disadvantageous changes in length. According to the invention, at least two compensating elements extending parallel to the shaft or the axis of rotation are arranged in or on the housing. These compensating elements have a third coefficient of thermal expansion and are designed to induce a predetermined change in the length of the housing when the temperature changes and / or when the rotor and housing temperatures differ in predetermined ways. This change in the length of the housing is then adjusted to match the change in length of the rotor, so that when the temperature changes, the change in length of the housing essentially corresponds to the change in length of the rotor.It follows that the features according to the invention result in very similar or nearly identical changes in length of the rotor and housing, and that the respective relative positioning of the impellers to a respective adjacent housing section or a respective associated spiral housing section remains essentially the same or changes only minimally despite the temperature change. In summary, the invention relates to a two-stage radial compressor with housing and rotor, the two impellers of which are arranged on opposite end sections of a shaft, wherein the radial compressor has compensating elements arranged in or on the housing to compensate for a difference occurring during a temperature change between the length changes of the rotor and the housing. These compensating bodies can also be referred to as compensating elements or compensating bars. Regarding the coefficients of thermal expansion, it should be noted that the first coefficient of thermal expansion of the rotor can be greater than the second coefficient of thermal expansion of the housing. However, the opposite is also possible. By appropriately selecting the thermal expansion properties or coefficient of thermal expansion of the compensating elements, taking into account the thermal expansion properties or coefficients of thermal expansion of the rotor and housing, the thermal expansion properties of the radial compressor housing can be controlled in such a way that the axial expansion or change in length of the rotor and housing exhibits the same thermal behavior. This ensures that the housing and the rotor, and in particular the shaft, deform by the same amount when the radial compressor is exposed to temperature fluctuations, whether at rest (e.g., during storage, transport, or non-use) or during operation. Furthermore, during operation, and especially under extreme operating conditions, different temperature changes can occur at the rotor and the housing, resulting in different temperatures or temperature levels for the rotor and housing. Therefore, according to an advantageous embodiment, the first coefficient of thermal expansion and / or the second coefficient of thermal expansion and / or the third coefficient of thermal expansion can be selected to account for these different temperature levels, such that at predetermined temperature levels, the changes in length at the housing and rotor resulting from the different coefficients of thermal expansion are essentially the same. The first coefficient of thermal expansion of the rotor and an equivalent coefficient of thermal expansion derived from the first and second coefficients of thermal expansion can therefore differ, which, at predetermined different temperatures on the rotor and housing, leads to an essentially identical change in length of the rotor and housing. In addition to the advantages already outlined and the cost savings compared to other known variants, the compressor's clearances and tolerances can be smaller, as the different thermal expansion rates no longer need to be considered in the design. This allows for a further increase in the compressor's efficiency. According to the invention, the compensating elements can be made of the same material as the shaft. Alternatively, the compensating elements can also be made of a different material, which has a corresponding coefficient of thermal expansion to bring about the desired change in length at the housing. Preferably, the compensating elements are evenly distributed around the shaft in the circumferential direction. However, a different distribution could also be provided, which would result in a uniform change in length of the housing. Furthermore, the compensating bodies can each have a circular, rectangular or polygonal, in particular hexagonal, cross-section. Additionally or alternatively, a respective longitudinal axis of the compensating bodies can run parallel and eccentrically, i.e., not coaxially, to the shaft or the axis of rotation. To accommodate the compensating elements on the housing, receptacles can be provided in or on the housing, each corresponding to one of the compensating elements. One compensating element is inserted into each of the receptacles. The housing of the radial compressor preferably has a first spiral housing section corresponding to the first impeller, a second spiral housing section corresponding to the second impeller, and a stator housing section arranged between the two spiral housing sections, which preferably completely accommodates a stator of a motor that drives the rotor around the axis of rotation. Based on this, an advantageous further development provides that the recordings are formed at least section by the housing and in particular by the first spiral housing section and / or the second spiral housing section and / or the stator housing section. Independently or additionally, it may also be provided that the receptacles are formed at least partially by a compensating section of the housing, in particular a cylindrical section, which extends coaxially to the shaft inside or outside the stator housing section. If a compensating section is provided, a sealing plane can be formed between this section and the radially adjacent section, for example the stator housing section. Furthermore, the compensating section can be fixed to one of the spiral housing sections on one end side and be designed to abut the other spiral housing section or the stator housing section on the opposite side. The compensating elements can be arranged in or on the stator housing section and, in particular, can be in contact with the stator housing section with at least one end face. Furthermore, the compensating elements can be arranged between the first spiral casing section and the second spiral casing section, so that a change in the length of the compensating elements along the axis of rotation leads to a change in the distance between the two spiral casing sections. Furthermore, the compensating elements can be positioned against the first spiral casing section and / or the second spiral casing section. With regard to their length along the axis of rotation, the compensating elements can have a length that is shorter or longer than the length of the housing or the stator housing section. It is also possible for the compensating elements to have a length equal to the length of the spiral housing section, so that the compensating elements rest against the spiral housing sections on both sides. Starting from a division of the housing into the aforementioned sections, the stator housing section can be formed integrally with the first spiral housing section or with the second spiral housing section as one body. Alternatively, the stator housing section, the first spiral housing section and the second spiral housing section can each be designed separately as a single body. In both variants, it is preferably provided that a connection and / or seal is formed between the stator housing section, the first spiral housing section and the second spiral housing section, to withstand the change in length and in particular the change in length caused by the compensating elements on the housing, i.e. to maintain the intended function. The compensating elements can be either a single piece or divided longitudinally into several sub-bodies. If multiple sub-bodies are provided for each compensating element, each can have its own section in an associated receptacle, allowing the individual length changes of the sub-bodies to be transferred more easily and uniformly to the housing and, in particular, its stator housing section. Furthermore, the compensating elements can be connected to the housing at several points in the longitudinal direction, thereby transferring a change in length to the housing. This can be achieved, for example, by projections or springs engaging in grooves, similar to a tongue-and-groove connection. The features disclosed above can be combined in any way, provided that this is technically possible and they do not contradict each other. Other advantageous embodiments of the invention are characterized in the dependent claims or are described in more detail below with reference to the figures, together with a description of the preferred embodiment of the invention. The figures show: Fig. 1 a longitudinal section along the axis of rotation through a two-stage compressor; Figs. 2a-c various configurations of a compensating section with compensating elements arranged therein. The figures are schematic examples. Identical reference symbols in the figures indicate identical functional and / or structural features. Fig. 1 shows a two-stage radial compressor 1 designed according to the invention. This has a housing 10 and a rotor 20 rotatably mounted therein about an axis of rotation A, wherein the rotor 20 essentially has a shaft 23 with two impellers 21 arranged at its ends or ends. The rotor 20 is supported and fixed in its axial position by an axial bearing 41 in the housing 10, wherein the first impeller 21 is adjacent to the axial bearing 41 or the distance of the first impeller 21 to the axial bearing 41 is significantly less than the distance of the second impeller 22 to the axial bearing 41, which is spaced from the axial bearing 41 at a distance essentially equal to the longitudinal extent of the shaft 23. Since the components of the rotor 20 and the components of the housing 10 have different thermal expansion properties and, specifically, different coefficients of thermal expansion, the rotor 20 and the housing 10 behave differently with respect to their respective changes in length in the longitudinal direction L, i.e., along the axis of rotation A, when temperatures change. As a result, the efficiency of the radial compressor 1 may deteriorate, or damage may occur, particularly because the axial position of the second impeller 22 relative to the housing 10 changes. To ensure consistently high efficiency and prevent damage, the radial compressor is designed to have at least two compensating elements 31 extending parallel to the shaft 23. These elements have a third coefficient of thermal expansion and are designed to match the change in length of the housing 10 to the change in length of the rotor 20, so that, in the event of a temperature change, the change in length of the housing 10 along the longitudinal axis L corresponds to the change in length of the rotor 20. In addition to a first spiral housing section 11 corresponding to the first impeller 21, a second spiral housing section 12 corresponding to the second impeller 22, and a stator housing section 13 of the housing 10 arranged between them, which completely accommodates a stator 42 of a motor for the rotary drive of the rotor 20 around the axis of rotation A, the housing 10 has a compensating section 32 for this purpose, which runs around the axis of rotation A in a ring-shaped or cylindrical shape and, according to the illustrated variant, borders radially outwards on the stator housing section 13. In the compensation section 32, receptacles 33 are provided for receiving the compensation bodies 31, wherein the receptacles 33 completely pass through the compensation section 32 in the longitudinal direction L. The compensating section 32 is fixed to the side of the second impeller 22 on the second spiral housing section 12 and borders on the side of the first impeller 21 on a collar formed by the stator housing section 13. If the compensating elements 31 arranged in the receptacles 33 cause a change in length, they press with their end faces in longitudinal direction L against the second spiral housing section 12 and over the collar of the stator housing section 13 onto the first spiral housing section 11, so that the spiral housing sections 11, 12 are pushed apart in longitudinal direction. The configuration shown compensates for the change in length in the area of ​​the stator housing section 13 by a relative displacement of the stator housing section 13 and the compensating section 32, whereby a cylindrical sealing plane is formed between them in the radial direction. Figures 2a to 2c show cross-sections of compensating sections 32 with receptacles 33 provided in various configurations with compensating bodies 31. It is fundamental to note that according to the invention at least two compensating bodies 31 are provided, wherein the compensating bodies 31 each have different cross-sections and can be arranged in different orientations around the axis of rotation A. Fig. 2a shows a simple first variant in which exactly two compensating bodies 31 are provided, which by way of example have a square cross-section and are arranged opposite each other in the compensating section 32 of the housing 10. In contrast, Fig. 2b shows three compensating bodies 31 which are evenly distributed around the axis of rotation A in the circumferential direction U and have a round cross-section. According to the variant shown in Fig. 2c, six compensating elements 31 are provided, wherein any two opposing compensating elements 31 have identical cross-sections, and compensating elements 31 with round, rectangular, and hexagonal cross-sections are provided. This can also be used for coding purposes, since then only the predetermined compensating elements 31 can be inserted into the corresponding receptacles 33 with respect to their shape.

Claims

A two-stage radial compressor (1) with a housing (10) and a rotor (20) mounted in the housing (10), which has a first impeller (21), a second impeller (22) and a shaft (23), at the opposite end sections of which one of the two impellers (21, 22) is fixed, wherein the rotor (20) has a first coefficient of thermal expansion which leads to a change in length of the rotor (20) when the temperature changes, wherein the housing (10) has a second coefficient of thermal expansion which differs from the first coefficient of thermal expansion and leads to a change in length of the housing (10) when the temperature changes, which differs from the change in length of the rotor (20), characterized in that at least two compensating elements (31) extending parallel to the shaft (23) are arranged in or on the housing (10), which have a third coefficient of thermal expansion and are designed are,to bring about a predetermined change in the length of the housing (10) in response to temperature changes and / or predetermined differences in the temperatures of the rotor (20) and the housing (10), and to adjust the change in length of the housing (10) to the change in length of the rotor (20), so that the change in length of the housing (10) corresponds to the change in length of the rotor (20) in response to the temperature change. Radial compressor according to claim 1, wherein the compensating elements (31) are uniformly distributed in the circumferential direction (U) around the shaft (23). Radial compressor according to claim 1 or 2, wherein the compensating bodies (31) each have a circular, rectangular or polygonal, in particular hexagonal, cross-section and / or a respective longitudinal axis of the compensating bodies (31) runs parallel and eccentrically to the shaft (23). Radial compressor according to one of the preceding claims, wherein receptacles (33) are provided in or on the housing (10), each corresponding to one of the compensating bodies (31), and wherein one compensating body (31) is inserted into each of the receptacles (33). Radial compressor according to one of the preceding claims, wherein the housing (10) has a first spiral housing section (11) corresponding to the first impeller (21), a second spiral housing section (12) corresponding to the second impeller (22), and a stator housing section (13) arranged between the two spiral housing sections (11, 12) which fully accommodates a stator (42) of a motor driving the rotor (20). Radial compressor according to the two preceding claims, wherein the receptacles (33) are formed at least partially by the housing (10) and in particular by the first spiral housing section (11) and / or the second spiral housing section (12) and / or the stator housing section (13) and / or wherein the receptacles (33) are formed at least partially by a compensating section (32) of the housing (10) which extends coaxially to the shaft (23) inside or outside the stator housing section (13). Radial compressor according to one of the two preceding claims, wherein the compensating elements (31) are arranged in or on the stator housing section (13) and in particular bear against the stator housing section (13) with at least one end face, and / or wherein the compensating elements (31) are arranged between the first spiral housing section (11) and the second spiral housing section (12), such that a change in length of the compensating elements (31) leads to a change in the distance between the two spiral housing sections (11, 12), and / or wherein the compensating elements (31) bear against the first spiral housing section (11) and / or the second spiral housing section (12). Radial compressor according to one of claims 5 to 7, wherein the compensating elements (31) have a length which is less or greater than the length of the housing (10) or the stator housing section (13). Radial compressor according to one of claims 5 to 8, wherein the stator housing section (13) is formed integrally with the first spiral housing section (11) or with the second spiral housing section (12) as one body, or wherein the stator housing section (13), the first spiral housing section (11) and the second spiral housing section (12) are each formed as one body, and wherein a connection and / or seal is formed between the stator housing section (13), the first spiral housing section (11) and the second spiral housing section (12) to withstand the change in length. Radial compressor according to one of the preceding claims, wherein the compensating bodies (31) are each integrally formed or divided into several sub-bodies in the longitudinal direction (L) and / or wherein the compensating bodies (31) are each connected to the housing (10) at several points in the longitudinal direction (L) in such a way as to transmit a change in length to the housing (10).

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