FIELD OF INVENTION
The present invention relates to an improved suction chamber for a radial fan.
BACKGROUND OF THE INVENTION
Fan is a Turbo machine designed to deliver a given volume and pressure to meet the system requirement.
Fans are very essential auxiliaries to boiler for steam generation in the field of Power & Process Industries. Fans are used as Forced Draft Fan for providing air for combustion, Primary Air fan for carrying pulverized coal to combustion chamber & Induced Draft Fans for exhausting the flue gases to Chimney as per the system requirement. In radial fan suction chamber is very important and essential for smooth intake and guiding of flow, minimizing entry losses and improving meridonial velocity at inlet with proper stream line flow. Where as in the present design suction chamber of BAB2 fan is large in size for this aerodynamic parameters which occupies more space, consume more material
and non unformity of flow resulting in increased suction chamber losses.,
The present development relates to the design improvement of suction chamber using CFD and establishing aerodynamic performance by Prototype testing iteratively.
The conventional radial fan design consists of Impeller [05] which is plate bladed design. This Impeller consists of Back/Centre Plate, formed Blade, taper shroud, ring and hub. The impeller is placed inside of spiral casing [01] which will act as the diffuser to recover the kinetic energy of the fluid leaving the impeller, a suction chamber [02] is provide for uniformly guiding the flow inside the fan

through an impeller scal [06] to the impcller,However,due to the larger size ofl
the suction chamber (02) the inlet losses are higher and inlet meridonial velocity does not constitute a stream line flow leading to a poor aerodynamic efficiency . Further, the suction chamber (02) occupies more space and consumes more material and therefore not economic for manufacturing.
OBJECT OF THE INVENTION
It is therefore an object of the present invention to propose an improved suction chamber for radial fans with higher aerodynamic performance.
Another object of the present invention is to propose an improved suction chamber for radial fans which reduces the entry losses of suction box, optimize the size of the suction box and establish higher aerodynamic performance.
A further object of the present invention is to propose an improved suction chamber for radial fans which is of reduced weight and economic.
SUMMARY OF THE NIVENTION
In the present development, a CFD analysis was carried out on the existing radial fan with original suction chamber. It has been detected that due to non proportionate size of the suction chamber, a void zone develops resulting recirculation losses. Accordingly, the suction box size has been reduced by 25% without compromising the aerodynamic design. Finite Element Analysis has further been adapted to minimize the material content so that the suction chamber could be configured with optimum size. The new suction chamber has reduced a 10% material cost.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1- shows an assembled radial fan, and further in a dis-assembled condition a prior art radial fan having impeller, spiral casing, blade, and suction chamber.
Figure 2- shows an improved suction chamber and a corresponding fan blade according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
In the present development CFD analysis was carried out on radial fan with original suction chamber. At the free zone there is vortex shedding which causes the flow separation and pressure loss at the inlet. Due to this the inlet meridonial velocity is very less and suction chamber losses were higher. The geometry of the suction chamber has been configured as shown in Fig. 02 to minimize these losses. CFD analysis has revealed that the losses were minimized by the above aerodynamic configuration...
The improved suction chamber was used along with fan and performance test was carried out to establish its aerodynamic performance. A considerable improvement (3%) in efficiency comparing to old suction chamber was achieved and reduction in weight compared with conventional suction chamber has been achieved. (Refer Fig. 02,)
The invented Suction Chamber is of aerodynamically optimized design with specific design parameters like width, breadth, height and inlet incidence angle linked to the features of volume coefficient and pressure coefficient. Hence the whole geometry of suction chamber is specific in nature.

As mentioned earlier the existing suction chamber for Backward "Aerofoil Bladed (BAB2) radial fan with volume co-efficient 0= 0.1 and pressure coefficient φ =' 96, is large in size and because of the larger size of the suction chamber (02) the inlet losses are higher and inlet meridonial velocity does not constitute a stream line flow leading to a poor aerodynamic efficiency. This suction chamber (02) occupies more space and consumes more material and therefore not economic for manufacturing.
The above disadvantages were eliminated using computational fluid dynamics iteratively by modifying the geometry after studying the flow pattern and pressure losses.
As shown in Fig. 2, there is a comparison of the improved suction chamber with the existing one where d2 stands for tip diameter of the impeller which is governing aerodynamic parameter in designing all sub components including suction chamber. The existing width is 2 times 'd2' (aO (3990mm). This width is reduced to 1.5 d2 (a2) (2992 mm) in the improved suction chamber. The breadth vb' of the suction chamber is changed from ld2 to 0.9 d2 (1180mm) V, 'd' and V are reference dimensions with respect to the center line of rotor.
During CFD non uniform flow as well as suction chamber losses were observed. Suction chamber was modeled iteratively for different configurations/sizes and run for CFD analysis and studied the flow, Pressure patterns. The most optimized suction chamber was arrived by repeat CFD 'analysis and optimized suction chamber was manufactured and tested at our Fan Testing Station on a proto type fan of NDV 20 BAB2. The performance test was conducted with original suction chamber and optimized suction chamber in the same fan. It is observed that the achieved aerodynamic performance was same even with optimized reduced suction chamber.
The Fan achieved the following aerodynamic performance.
Volume (mA3/s) ... 42.1
Pressure (Nm/Kg) ... 3939
Maximum Efficiency (%) ... 83

Fig. 3 shows a graph where it is observed that the Isentropic head (Y) is more for an improved modified suction chamber (I) for same quantity of flowrate (Q) than with original suction chamber (0).

WE CLAIM
1. An improved suction chamber for a radial Fan of a boiler comprising and
characterized in that;
a chamber with reduced width (a2) of 1.5d2 and reduced breadth (b) of 0.9d2 when d2 being the tip diameter of the impeller for improving the meridonial velocity at inlet and minimizing entry losses of suction chamber wherein, the isentropic head in NM/kg (Y) for the same quantity of flow rate in m3/sec is same or greater in an improved suction chamber (I) compared to the existing one (0).
2. An improved suction chamber as claimed in claim 1, wherein the reduced width is
2992 mm and reduced breadth is 1180 mm.

ABSTRACT

AN IMPROVED SUCTION CHAMBER FOR A RADIAL FAN OF A BOILER
An improved suction chamber for a radial fan of a boiler comprising a chamber with reduced width of 2992 mm and reduced breadth of 1180 mm where the isentropic head in Nm/Kg (Y) is greater or almost same for same quantity of flow rate in an improved suction chamber (I) compared to the existing one (0). The reduced width of the chamber (I) is 1.5 times the tip diameter d2 of the impeller of a turbine and reduced breadth is 0.9 times the tip diameter d2 of the impeller of the same turbine.