JPS58183899A - Diffuser with blade - Google Patents

Abstract

PURPOSE:To decrease the sectional area of a scroll to reduce the manufacturing cost of a casing by a method wherein the width of an outlet for the diffuser with blades is made larger than the same of an inlet therefor and the circumferential speed element of outlet flow is increased under keeping the reduction ratio of an absolute speed in the same value as before. CONSTITUTION:The diffuser 8, equipped with the blades, is constituted so that the width of the outlet thereof is larger than the same of the inlet thereof. According to this constitution, the angle of the outlet flow of the diffuser 8 is smaller than the angle of the flow in the conventional diffuser, therefore, the component of the circumferential speed at the outlet of the diffuser becomes larger than the same of the conventional diffuser. In case such flow is entered into the scroll 9a, an average speed in the scroll 9a may be made higher because the circumferential speed is high. Accordingly, the sectional area of the scroll 9a may be decreased and, as a result, the scroll 9a may be miniaturized to reduce the manufacturing cost of the scroll casing 9.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vaned diffuser for a centrifugal or mixed flow type fluid machine, and is particularly suitable for application to a centrifugal or mixed flow compressor.

FIG. 1 is a longitudinal sectional view of a conventional centrifugal compressor. In the figure, 1 is an impeller, 2 is a rotating shaft, and 3 is a nut for fixing the impeller 1 to the rotating shaft 2. On the radially outward side of the impeller, there is a flow path formed only by a pair of mutually parallel diffuser plates 4 and 5, that is, a bladeless diffuser s6, and a bladed diffuser section formed by the diffuser plate 4.5 and the blades 7. 8 is provided, and a scroll case 7 9 is further provided on the outside thereof. 10 is a suction pipe for guiding fluid to the suction port of the impeller 1.

Fluid passes through the suction pipe 10 and is sucked into the impeller 1 from the suction port. After the fluid is pressurized by the impeller 1, it passes through the diffuser section 6.
, 8, the flow is decelerated in the diffuser section 6.8 and then enters the scroll 9a formed by the scroll casing 9.

Here, let us look at the state of the flow at the entrance and exit of the diffuser section 6.8 using the velocity triangle shown in FIG. In the figure, C is the absolute velocity, Cm is the circumferential component of the absolute velocity C, and C1
is the meridional velocity component of the absolute velocity C. The subscript 3 represents the inlet of the vaned diffuser section 8, and 4yd represents the outlet of the vaned diffuser section 8. Since the area within the vaned detuser section 8 increases from the inlet to the outlet, the meridional velocity C, decreases from C13 to Cm4va. Further, the blades 7 of the vaned diffuser section 8 are generally designed so that the exit angle (value measured from the direction of the blade) is larger than the entrance angle. Therefore, the flow angle α4v4 at the outlet of the vaned diffuser section 8 is also larger than the flow angle α3 at the inlet thereof, and the circumferential velocity component C, becomes C@3
to Cm4vd.

As a result, the absolute speed C decreases from C3 to C4va. As described above, the deceleration of the flow in the conventional vaned diffuser section 8 is largely due to the decrease in the circumferential velocity component C1.

Next, the examination of the scroll 9a will be carried out with reference to FIGS. 1 to 3. As shown in FIG. 3, when the average velocity of the flow inside the scroll 9a is C1, this average velocity C,
The cross-sectional area of the scroll 9a is determined so that , satisfies the following condition.

In this equation, 014 is the circumferential velocity component of the flow at the outlet of the vaned diffuser section 8, and 014 is the exit radius of the vaned diffuser section 8, and the radius at the center of the cross section of the rB scroll 9a. That is, in equation (1), the fluid discharged from 8, which has a large difference between the values on the left and right sides of the equation, collides with each other, increasing the scrolling loss, so to avoid this, equation (1) is established. The cross-sectional area of the scroll 9a is determined so as to. Conventionally, the circumferential velocity component Co4vl at sunrise of the vaned diffuser portion 8 is small as shown in FIG. 2, so in order to reduce scroll loss, the average velocity Ca a of the scroll 9a must also be small. To achieve this, it was necessary to increase the cross-sectional area of the 9 m scroll. Therefore, there was a drawback that the manufacturing cost of the scroll casing 9 was high.

The present invention has been made based on the above-described matters, and an object of the present invention is to provide a vaned diffuser that can reduce the manufacturing cost of a scroll casing.

The invention! Mold can be detected in a bladed diffuser for a fluid machine, which is composed of a pair of diffuser plates and a large number of blades provided between the diffuser plates, and is configured so that the outlet width of the bladed diffuser part is larger than the population deviation. At the point.

An embodiment of the present invention will be described below with reference to FIGS. 4 and 5. In the figures, parts given the same reference numerals as in FIGS. 1 to 3 are the same parts. This example shows the case where the present invention is applied to a centrifugal compressor. That is, in the vaned diffuser of the present invention, the diffuser plate 5 on the hub side, which is radially the same, and the vaneless diffuser section 6 are oriented in the radial direction so as to widen the flow path width of the diffuser downstream from the inlet of the vaned diffuser s8. a diffuser plate 4 on the shroud side formed to have a sloped metal plate;
It is composed of a large number of blades 7 provided between these diffuser plates 4 and 5.

The vane 7 is configured such that its exit angle is approximately equal to its entrance angle. The exit radius R of the vane diffuser s8 is the same as that of the conventional one shown in FIG. are chosen so that they are approximately equal.

FIG. 5 shows a flow velocity triangle at the inlet and outlet of the vaned diffuser section 8 according to the present invention. The subscript 40 represents the flow at the outlet of the vaned diffuser section 8 according to the present invention. This figure also shows the velocity triangle of the flow in a conventional vaned diffuser. As can be seen from the figure, the outlet width of the vaned diffuser section 8 according to the present invention is larger than the exit width of the conventional vaned diffuser section, so that the flow at the outlet of the vaned diffuser section 8 according to the present invention is larger than the outlet width of the conventional vaned diffuser section 8. The meridional velocity Cm4m is smaller than the meridional velocity C@4v4 in the conventional bladed diffuser section. Further, the outlet flow angle α4 of the vaned diffuser portion 8 of the present invention. is smaller than the conventional outlet flow angle α4yd, the outlet circumferential velocity component C1 according to the present invention is smaller than the conventional outlet flow angle α4yd.
4 is larger than the circumferential velocity component C146 at the outlet of the conventional bladed dizzer 7-1L-za section 8.

When such a flow enters the scroll 98 formed around the scroll casing 9, the circumferential velocity component C1
4, is large, the average speed C62 in the scroll 9a
can also be made larger. Therefore, scroll 9
The cross-sectional area of m can be reduced, and as a result, the scroll 9a can be made smaller than before, and the manufacturing cost of the scroll casing 9 can be reduced. Furthermore, the meridional velocity component of the flow at the outlet of the vaned diffuser section 8 is all lost within the scroll, but the meridional velocity component C14 of the flow at the outlet of the vaned diffuser section 8 according to the present invention is as follows.
Since it is smaller than the meridional velocity component C, 41 in the conventional case, it has the effect of reducing scroll loss and improving the performance of centrifugal or mixed flow type fluid machines.

In the above-mentioned embodiment, the diffuser plate 4 on the shroud side is configured to have a surface inclined with respect to the radial center line of the diffuser portion, but the diffuser plate 4 on the shroud side is not formed with an inclined surface, By forming an inclined surface on the side diffuser plate 5 to widen the flow path width of the diffuser, or by forming an inclined surface on the side diffuser plate 5, or by forming an inclined surface on the side diffuser plate 5.
．． It is also possible to form an inclined surface on the diffuser 5 to widen the width of the diffuser flow path. It is also effective.

According to the present invention, while keeping the absolute speed reduction ratio of the bladed diffuser the same as before, the circumferential velocity component of the diffuser outlet flow can be made larger than before, so the cross-sectional area of the scroll can be reduced. This has the effect of reducing the manufacturing cost of the scroll casing.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view showing a centrifugal fluid machine equipped with a conventional vaned diffuser, Figure 2 is a diagram showing the velocity triangle of the entrance and exit in a conventional vaned diffuser, and Figure 3 is a diagram showing the velocity triangle between the diffuser outlet and the scroll. A diagram explaining the relationship between
FIG. 4 is a longitudinal cross-sectional view showing a centrifugal fluid machine equipped with an embodiment of the vaned diffuser of the present invention, and FIG. 5 is a diagram showing velocity triangles at the entrance and exit of the vaned diffuser of the present invention. 4... Diffuser plate on the shroud side, 5... Diffuser plate on the hub side, 7... Vane, 8... Diffuser part with vane. Agent Patent Attorney Toshiyuki Usuda 1 Figure v 3 Figure 7 'f3 4 Figure

Claims (1)

[Claims] In a vaned diffuser for a fluid machine consisting of a pair of diffuser plates and a large number of vanes provided between the tiff user plates, the outlet width of the vaned diffuser section is configured to be larger than the inlet width. Features a diffuser with blades.