CN101832625B - Low-resistance square elbow - Google Patents

Abstract

The invention discloses a novel low-resistance square elbow, which comprises a first inner arc surface, a second inner arc surface, an outer arc surface and two side surfaces. Wherein, the first inner arc surface is connected with the second inner arc surface; the first inner arc surface, the second inner arc surface and the outer arc surface are respectively connected with two side surfaces and form a rectangular channel; the radius of the first inner arc surface and The arc length is greater than the radius and arc length of the outer arc surface; the radius and arc length of the outer arc surface are greater than the radius and arc length of the second inner arc surface; the centers of the first inner arc surface and the second inner arc surface are respectively at the entrance section and Extension of the exit section. The unique design of the elbow also eliminates the vortex zone generated when the fluid passes through the inner arc of the elbow; and the vortex zone generated by the fluid at the junction of the elbow and the straight pipe. Thereby, the resistance when the fluid passes through the elbow is finally reduced.

Description

Low resistance square elbow

technical field

The invention relates to a partial component of ventilation and air conditioning, in particular to a low-resistance square elbow.

Background technique

Elbows are pipe fittings that change the direction of fluid flow. In curved pipelines, due to the turning of the fluid, there is a centrifugal force from the center of curvature to the outer arc of the pipe, which makes the fluid transition from the straight section of the pipeline to the curved pipe section (at the turn Before the end), the pressure on the outer arc surface increases and the pressure on the inner arc surface decreases. Therefore, the flow velocity of the fluid at the outer dome will decrease, while the flow velocity of the fluid at the inner dome will correspondingly increase. Therefore, the diffusion effect appears near the outer arc surface, while the contraction effect appears near the inner arc surface. When the fluid transitions from the curved pipe section to the straight pipe section (after turning), the opposite phenomenon occurs, that is, the diffusion effect occurs near the inner arc surface, and the contraction effect occurs near the outer arc surface. The diffusion effect makes the fluid detach from the wall, and at the same time, the movement of the fluid in the curved pipe section to the outer arc surface due to inertia further aggravates the separation from the inner arc surface.

When the fluid flows in the elbow, the centrifugal force is proportional to the square of the flow velocity, so the centrifugal force at the high velocity area is greater than that near the wall. This moment causes the water flow to generate a secondary circulation (vortex pair) on the cross section of the elbow. That is to form the so-called vortex pair. It is attached to the main flow parallel to the pipeline axis, so that the streamline has a spiral shape. The spiral shape of the water flow is not limited to the elbow itself, but also continues on a certain length of straight pipe section behind the elbow. The local resistance of the elbow is due to the two phenomena in the above-mentioned water flow structure of the elbow: (1) the vortex on the inner arc surface of the elbow. (2) The secondary vortex at the junction of the curved pipe and the straight pipe, as shown in Figure 1. The flow in the vortex region formed by the separation of the boundary layer and the axial flow have a strong momentum exchange at the interface, which consumes the energy of the mainstream and forms the local resistance loss of the elbow. Among them, the vortex formed at the inner arc surface plays a major role, which basically determines the resistance of the elbow and the deformation of the flow field on a certain straight pipe section after the elbow. Experiments show that the larger the vortex area, the greater the vortex intensity, and the greater the local resistance loss. The secondary flow plays an important role in the redistribution of the axial velocity of the elbow. The redistribution process consumes the energy of the primary flow and increases the local resistance loss of the elbow. The vortex formed by the inner arc and the secondary flow basically determine the characteristics of the velocity distribution of the pipe after the turn. The energy consumption caused by the flow in the elbow is not limited to the elbow itself, but extends to the upstream and downstream of the elbow. The influence of the elbow on the upstream is as far as 1-2 times the pipe diameter, and the downstream is affected by 5 times the pipe diameter.

In the past, ordinary elbows were mainly used in ventilation and air conditioning systems. As shown in Figure 3, since the entrance and exit surfaces of ordinary elbows are symmetrical, there is no distinction between entrance and exit. At the same time, because the radius of the inner arc surface of the ordinary elbow is too small and the arc surface is small, a vortex area with negative pressure and high flow velocity is generated when the fluid passes through it. This vortex area itself will cause a lot of resistance, and it will also cause a large vortex area after the fluid passes through the elbow. And these two vortex regions directly lead to the increase of the resistance when the fluid passes through. In other words, the inner arc of the common elbow is the main part that causes the resistance to increase when the fluid passes through the elbow.

In recent years, some heat recovery systems for simultaneous cooling and heating have appeared, such as the Chinese patent, the patent No. ZL95102932.0 discloses a elbow with guide vanes, and the Chinese patent, the public No. Kind of flue elbow. They all have guide vanes inside, and the vortex at the inner arc surface of the elbow is eliminated by the guide vanes guiding the fluid, so as to reduce the resistance. However, since guide vanes need to be added to the curved pipe, its manufacture and installation are relatively complicated, and the cost will be relatively high.

Contents of the invention

The purpose of the present invention is to provide a low-resistance square elbow. The unique design of the elbow eliminates the vortex zone generated when the fluid passes through the inner arc of the elbow; the vortex area. Thereby, the resistance when the fluid passes through the elbow is finally reduced.

In order to achieve the above object, the low-resistance square elbow provided by the present invention includes an inlet end and an outlet end of the elbow, and an inner arc surface and an outer arc surface are provided along the connecting section of the inlet end and the outlet end, and is characterized in that: Another inner arc surface is provided in the connecting section between the inner arc surface and the entrance end, forming two sections of transitional connection inner arc surfaces; the two sections of transition connection inner arc surfaces are connected with the outer arc surface and two side surfaces to form a rectangular channel.

The two sections of transitional connecting inner arc surface are a first inner arc surface and a second inner arc surface, and the first inner arc surface extends along the arc surface of the second inner arc surface and is connected to the inlet end.

The radius and arc length of the first inner arc surface are greater than the radius and arc length of the outer arc surface; the radius and arc length of the outer arc surface are greater than the radius and arc length of the second inner arc surface; and the center of the first inner arc surface On the extension surface of the section at the inlet end; the center of the second inner arc surface is on the extension surface of the section at the outlet end.

It can be seen from the above that the present invention first decelerates and slowly changes the direction of the inflow fluid close to the inner arc surface through the first inner arc surface, so that the fluid slowly passes through the first half of the inner arc surface that may generate negative pressure and high-speed vortex area. After the fluid passes through the first half of the inner arc surface, in order to make the fluid turn quickly, the radius and arc length of the second inner arc surface are relatively small. This prevents the fluid from forming a vortex at the part connected to the elbow after passing through the elbow. Therefore, the vortex at the inner arc surface of the elbow and the vortex generated after the fluid passes through the elbow are simultaneously eliminated, as shown in FIG. 2 . So as to achieve the effect of less resistance.

Compared with the prior art, the present invention does not need to add guide vanes in the elbow to guide the fluid to eliminate the vortex at the inner arc surface of the elbow, thereby achieving the purpose of reducing resistance. Its manufacture and installation are relatively simple, its cost is low, and it is convenient for popularization and application.

Description of drawings

Fig. 1 is a schematic diagram of the flow field in an ordinary elbow; Fig. 2 is a schematic diagram of the flow field in a low-resistance square elbow of the present invention; Fig. 3 is a schematic diagram of an existing square elbow; Fig. 4 is a schematic diagram of a low-resistance square elbow in the present invention.

Detailed ways

The specific implementation manners of the present invention will be described in further detail below in conjunction with the accompanying drawings.

As shown in Figure 4, the low-resistance square elbow includes an inlet end and an outlet end of the elbow, and an inner arc surface and an outer arc surface 3 are provided along the connecting section of the inlet end and the outlet end, wherein: on the inner arc surface Another inner arc surface is provided in the connection section with the entrance end, forming two sections of transitional connection inner arc surfaces; the two sections of transition connection inner arc surfaces are connected with the outer arc surface 3 and the two side surfaces 4 to form a rectangular channel.

The above-mentioned two transitional connecting inner arc surfaces are the first inner arc surface 1 and the second inner arc surface 2 , and the first inner arc surface 1 extends along the arc surface of the second inner arc surface 2 and is connected to the inlet end. The present invention includes a first inner arc surface 1 , a second inner arc surface 2 , an outer arc surface 3 and two side surfaces 4 . Wherein, the first inner arc surface 1 is connected with the second inner arc surface 2; the first inner arc surface 1, the second inner arc surface 2 and the outer arc surface 3 are respectively connected with two side surfaces 4 to form a rectangular channel. And the radius and arc length of the first inner arc surface 1 are greater than the radius and arc length of the outer arc surface 3; the radius and arc length of the outer arc surface 3 are greater than the radius and arc length of the second inner arc surface 2; and the first inner arc The center of the surface 1 is on the extension surface of the section at the inlet end; the center of the circle of the second inner arc surface 2 is on the extension surface of the section at the outlet end.

As shown in Figure 2, the present invention first decelerates and slowly changes the direction of the inflow fluid close to the inner arc surface through the first inner arc surface 1, so that the fluid slowly passes through the first half of the high-speed vortex area that may generate negative pressure curved surface. After the fluid passes through the first half of the inner arc surface, in order to make the fluid turn quickly, the radius and arc length of the second inner arc surface 2 are relatively small. This prevents the fluid from forming a vortex at the part connected to the elbow after passing through the elbow. Therefore, the vortex at the inner arc surface of the elbow and the vortex generated after the fluid passes through the elbow are eliminated at the same time. Thereby reducing the resistance when the fluid flows through the elbow.

Claims (1)

1. A low-resistance square elbow, including an inlet end and an outlet end of the elbow, an inner arc surface and an outer arc surface (3) are provided along the connecting section of the inlet end and the outlet end, and it is characterized in that: between the inner arc surface and the outlet end Another inner arc surface is provided in the connection section of the inlet end to form two sections of transitional connection inner arc surface; the two sections of transition connection inner arc surface are connected with the outer arc surface (3) and two side surfaces (4) to form a rectangular channel ; The inner arc surfaces connected by the two sections are the first inner arc surface (1) and the second inner arc surface (2), and the first inner arc surface (1) extends along the arc surface of the second inner arc surface (2) connected to the inlet port; The first inner arc surface (1) decelerates and slowly changes the direction of the inflow fluid close to the inner arc surface, so that the fluid slowly passes through the first half of the inner arc surface that may generate negative pressure and high-speed vortex area; after the fluid passes through the first half After part of the inner arc surface, in order to make the fluid turn quickly, the radius and arc length of the second inner arc surface (2) are both small; The radius and arc length of the first inner arc surface (1) are greater than the radius and arc length of the outer arc surface (3); the radius and arc length of the outer arc surface (3) are greater than the radius of the second inner arc surface (2) and arc length; and the center of the first inner arc surface (1) is on the extension surface of the inlet end section; the circle center of the second inner arc surface (2) is on the extension surface of the outlet end section.

Images