EP1887227A1

EP1887227A1 - Centrifugal blower and air conditioner using the same

Info

Publication number: EP1887227A1
Application number: EP06746380A
Authority: EP
Inventors: Kaku Okada
Original assignee: Toshiba Carrier Corp
Current assignee: Toshiba Carrier Corp
Priority date: 2005-05-26
Filing date: 2006-05-15
Publication date: 2008-02-13
Also published as: JP4693842B2; WO2006126408A1; CN101184922A; KR20080003444A; KR100917091B1; JPWO2006126408A1

Abstract

A centrifugal air blower includes an impeller having a plurality of blades provided between a shroud and a main plate, the shroud side end portion on a blade front edge is formed into a curved shape, and a relationship of R₁<R₂ is established in a case where the curvature radius of a positive pressure surface side of the curved end portion is R₁ and the curvature radius of a negative pressure surface side is R₂.

Description

Technical Field

The present invention relates to an air blower and an air conditioner, and more particularly, to a centrifugal air blower improved in a shroud side shape of a blade front edge, and an air conditioner using the air blower.

Background Art

Generally, a ceiling cassette type air conditioner is often equipped with a turbo fan. This air conditioner has a casing having an opened bottom end portion, and an electric centrifugal air blower is attached to the central portion in this casing. The centrifugal air blower includes an impeller, and a heat exchanger is provided around the centrifugal air blower.
The impeller includes a main plate having a boss provided with a motor rotation shaft mounting hole, a shroud disposed opposing this main plate, and a plurality of blades provided between the shroud and the main plate. Generally, such a centrifugal air blower has a defect that a noise level of this blower is high and fan efficiency thereof is low.
Then, there has been proposed a centrifugal air blower in which a blade length and arrangement thereof such as a blade pitch are improved so as to achieve low noise generation and high efficiency performance (disclosed, for example, in Japanese Unexamined Patent Application Publication No.2003-279061 ). However, according to the description of this Publication, as shown in Fig. 9 and Fig. 10, as for a rounded portion (curved end portion) of the shroud side end portion on a blade front edge 31a of the blade 31, a curvature radius R₃ of a positive pressure surface side and a curvature radius R₄ of a negative pressure surface side are equal (R₃ = R₄), so that a sucked air is separated at a blade front end portion (R₄ portion) of the negative pressure side surface, and separation (peeling-off) on the negative pressure surface side is thereby increased, resulting in reduction in the fan efficiency.
Furthermore, in order to achieve reduced noise and intensified efficiency, a centrifugal air blower, in which thickness of all or part of the blade of the impeller is increased gradually as it extends from the shroud toward the main plate while an interval between the blades is decreased gradually as it extends from the shroud toward the main plate, has been proposed ( Japanese Unexamined Patent Application Publication No.2001-132687 ). However, in the case of this Publication, the interval between the blades on the main plate which produces main stream of air is shortened and the air inflow area is reduced with respect to the shroud side, thereby lowering the airflow rate.

Disclosure of the Invention

The present invention has been achieved in consideration of the above-described circumstances and an object of the invention is to provide a centrifugal air blower having high fan efficiency.
Another object is to provide a high efficiency air conditioner using the centrifugal air blower having high fan efficiency mentioned above.
To achieve the above-described object, a centrifugal air blower of the present invention includes: a main plate having a boss provided with a motor rotation shaft mounting hole; a shroud disposed so as to oppose to the main plate; and an impeller including a plurality of blades provided between the shroud and the main plate, wherein a shroud side end portion on the blade front edge side is formed into a curved shape and a relationship of R₁<R₂ is established in a case where a curvature radius of a positive pressure surface side of the curved end portion is R₁ and a curvature radius of a negative pressure surface side is R₂.
When it is assumed that the thickness of the blade is t, a relationship of R₁<R₂<t may be satisfied.
In the centrifugal air blower, the thickness of the entire blade may be increased gradually as it extends from the main plate side to the shroud side and a relationship of 1<t₂/t₁≤1.7 may be established in a case where the thickness of the main plate side is t₁ and the thickness of the shroud side is t₂.
Further, the air conditioner of the present invention includes a centrifugal air blower including: a main plate having a boss provided with a motor rotation shaft mounting hole; a shroud disposed so as to oppose to the main plate; and an impeller including a plurality of blades provided between the shroud and the main plate and a heat exchanger disposed on an outer peripheral portion of the centrifugal air blower.
The centrifugal air blow of the present invention can be provided as a centrifugal air blower having high fan efficiency. Further, it is possible to provide a high efficiency air conditioner using the centrifugal air blower having high fan efficiency.

Brief Description of the Drawings

Fig. 1 is a longitudinal sectional view of an air conditioner according to the present invention.
Fig. 2 is a plan view of an impeller for use in a centrifugal air blower according to the present invention.
Fig. 3 is a longitudinal sectional view of the impeller taken along the line III-III of Fig. 2.
Fig. 4 is an illustration showing a shroud side end portion on the front edge portion of a blade for use in the centrifugal air blower of the present invention.
Fig. 5 is an illustrated perspective view of the blade for use in the centrifugal air blower of the present invention.
Fig. 6 is a schematic view showing air flow when the blade of the centrifugal air blower of the present invention is used.
Fig. 7 is a diagram representing results of a static pressure and a fan efficiency measurement test using the centrifugal air blower of the present invention.
Fig. 8 is a diagram representing a result of measurement test on thickness ratio of the blade and static pressure ratio, using the centrifugal air blower of the present invention.
Fig. 9 is a schematic view showing a front end portion of the blade of a conventional centrifugal air blower.
Fig. 10 is a schematic view showing an air flow when the blade of the centrifugal air blower of the present invention is used. Best mode for Carrying Out the Invention

Hereinafter, an air conditioner according to an embodiment of the present invention will be described with reference to the accompanying drawings.
In a following description, terms indicating upper/lower, right/left and the like are used in reference to the accompanying drawings or based on an actual mounting condition.
As shown in Fig. 1, an air conditioner 1 of the present invention is, for example, a ceiling cassette type air conditioner, which includes a casing 2 having an opened bottom end portion, and a centrifugal air blower 20 including a fan motor 3 and an impeller 21 is provided within the casing 2. That is, the fan motor 3 is attached to the central portion of an upper bottom of the casing 2 through a motor base 4 and the impeller 21 is mounted on a rotation shaft of the fan motor 3.
A suction (intake) bell mouth 5 is provided on the bottom of the centrifugal air blower 20, and a drain pan 6 is disposed on the outer peripheral portion of the suction bell mouth 5, and a heat exchanger 7 is disposed so as to surround the centrifugal air blower 20. A bottom open end of the suction bell mouth 5 serves as an air inlet, and a filter 8 is attached thereto. An air passage 10 is formed outside the heat exchanger 7 and its bottom surface serves as an air outlet 11. A frame-like front panel 12 is mounted on the opening portion of a casing of the air conditioner. The air conditioner 1 is fixed by being hung from a beam or the like of a ceiling, for example, by means of mounting bracket 13.
As shown in Fig. 2 and Fig. 3, the impeller 21 includes a boss 22 having a motor rotation shaft mounting hole, a main plate 24 having a hub 23 provided on the outer peripheral portion of the boss 22, a plurality of blades 25 provided in the circumferential direction of the main plate 24, and a shroud 26 disposed so as to oppose to the main plate 24 across the blades 25.
As shown in Fig. 3 and Fig. 4, the shape of a round portion (curved end portion) of a shroud side end portion on a front edge 25a side of the blade 25 is set so that a relationship of R₁ < R₂ < t is established in the entire range of the shroud side end on the front edge 25a side of the blade 25, that is, in the entire suction side, where the curvature radius of a positive pressure surface 25b side is R₁, the curvature radius of a negative pressure surface 25c side is R₂ and the thickness of the blade 25 is t.
With such a structure, as shown in Fig. 4 and Fig. 6, separation of sucked air on a negative pressure surface side end portion (R₂ portion) is reduced, and the separation thereof on the negative pressure surface 25c side is suppressed. Consequently, as shown in Fig. 7, a static pressure is increased to thereby improve the fan efficiency. Particularly, in a large airflow (high revolution number) range, the fan efficiency can be improved to expand a fan operating range.
As shown in Fig. 5, the entire thickness of the blade 25 increases gradually from the main plate 24 side toward the shroud 26 side, so that when the thickness of the main plate side is t1 and the thickness of the shroud side is t2, a relationship of 1<t2/t1≤1.7 is established, and more specifically, it is preferred to be 1<t2/t1≤1.5. Consequently, an interval between the blades on the main plate 24 side, which produces main stream of air flow, that is, an interval between the negative pressure surface of a blade located in front and the positive pressure surface of a blade located in the back is larger than the interval between the blades on the shroud 26 side. As a result, the air inflow area on the main plate 24 side is larger than the air inflow area on the shroud 26 side, so that inflow resistance on the main plate 24 side, which produces main stream of air flow, is reduced, thereby increasing the air flow rate. Furthermore, the flow-in area on the shroud 26 side, in which air is likely to separate, will be reduced, thus the separation thereof on the shroud 26 side being reduced.
Consequently, as shown in Fig. 8, the air inflow is smoothed so that the static pressure increases and the fan efficiency is improved.
The air conditioning operation by the air conditioner of the present invention and the air blowing operation of the centrifugal air blower of the present invention will be described hereunder.
As shown in Fig. 1, when the fan motor 3 is energized, the centrifugal air blower 20 is rotated, so that room air is sucked in the direction of an arrow A. After the heat exchanging operation has been carried out through the operation of the heat exchanger 7, air is blown out in the direction of an arrow B through the air passage 10 and the air outlet 11. In this manner, the air conditioning in the room is carried out by the ceiling cassette type air conditioner.
In this air conditioning process, the air sucked through the suction bell mouth 5 is urged by the blades 25 and the air flow speed is increased, and the air is blown out from the impeller 21. Further, in this air flowing process, as shown in Fig. 4, the configuration of the rounded portion (curved end portion) of the shroud side end portion on the front edge side 25a of the blade 25 is in a relationship of R₁ < R₂ < t over the entire range of the suction side in the assumption that the curvature radius of the positive pressure surface 25b side is R₁, the curvature radius of the negative pressure face 25c side is R₂ and the thickness of the blade 25 is t. Thus, particularly, the static pressure in the large airflow range (high revolution number) is increased and the fan efficiency is improved so as to expand the fan operating range.
As shown in Fig. 5, the thickness of the entire blade 25 increases gradually from the main plate 24 side toward the shroud 26 side, and in the case where the thickness of the main plate side is t1 and the thickness of the shroud side is t2, a relationship of 1<t2/t1≤1.7 is established, so that an inflow resistance on the main plate 24 which produces main stream of air flow is reduced, thereby increasing the air flow rate. Further, as shown in Fig. 6, air separation on the negative pressure surface side of the shroud 26, in which the air is separated easily, can be reduced largely. Consequently, the air stream is smoothly flowed in and the static pressure is increased, thereby improving the fan efficiency.
Accordingly, the air conditioner of the present invention, which provided with the centrifugal air blower having the above-described high fan efficiency, can also attain a high efficiency performance.

[Example]

Test 1: A relationship between the static pressure and air flow rate and a relationship between the air flow rate and efficiency were investigated using a centrifugal air blower (example 1) having a blade of a shape shown in Fig. 4 and a centrifugal air blower (conventional example 1) having a blade of a shape shown in Fig. 9.
Fig. 7 shows a result of the relationships of the Test 1, from which it was found that the example 1 had a larger air flow rate under an identical static pressure than that of the conventional example 1 and that the example 1 had a higher efficiency than the conventional example 1 under the identical flow rate.
Test 2: Using a centrifugal air blower (example 2) in which the thickness of the blade 25 shown in Fig. 5 is increased gradually from the main plate 24 side toward the shroud 26 side and a centrifugal air blower (conventional example 2) in which the thickness of the blade 25 is increased gradually from the shroud 26 side toward the main plate 24 side, a relationship between a ratio t2/t1 between the thickness t1 of the main plate side and the thickness t2 of the shroud side and the static pressure ratio was investigated.
Fig. 8 shows a result of the investigation of the above Test 2. According to the example 2, it was found that the static pressure was improved to almost 101.3% with respect to the static pressure in the conventional example 2 when t2/t1 is in a range of 1 - 1.5 and that the static pressure exceeded 100% in a range of 1 - 1.7.
A centrifugal air blower of the present invention can provide a centrifugal air blower having high fan efficiency. It is possible to provide an air conditioner having a high efficiency using such a high fan efficiency centrifugal air blower.

Claims

A centrifugal air blower comprising:
a main plate having a boss provided with a motor rotation shaft mounting hole;

a shroud disposed so as to oppose to the main plate; and

an impeller including a plurality of blades provided between the shroud and the main plate,
wherein a shroud side end portion on the blade front edge side is formed into a curved shape and a relationship of R₁<R₂ is established in which a curvature radius of a positive pressure surface side of the curved end portion is R₁ and a curvature radius of a negative pressure surface side is R₂.
The centrifugal air blower according to claim 1, wherein a relationship of R₁<R₂<t is established when the blade has a thickness of t.
The centrifugal air blower according to claim 1, wherein the thickness of the entire blade is increased gradually from the main plate side to the shroud side and a relationship of 1<t₂/t₁≤1.7 is established when the thickness of the main plate side is t₁ and the thickness of the shroud side is t₂.
An air conditioner comprising:
a centrifugal air blower comprising a main plate having a boss provided with a motor rotation shaft mounting hole, a shroud disposed so as to oppose to the main plate, and an impeller including a plurality of blades provided between the shroud and the main plate; and

a heat exchanger disposed on an outer peripheral portion of the centrifugal air blower.