Experiment Research And Numerical Simulation Of An Under-low Specific Speed Centrifugal Blower

The existing heat pump system is mainly used in the drying circle system of the industries such as food processing, chemical fiber manufacturing and wood processing and the under-low specific speed centrifugal blower is one of the most important equipment in the circle system. The blower has the characteristic of low flow rate and high pressure rising, and this aerodynamic characteristic has determined its under-low specific speed. So this blower can only design to use narrow impeller structure. This makes the obvious of wall viscous effect and flow separation phenomenon, so flow loss will be larger than the normal width impeller of the blower. Therefore it leads to the actual application efficiency often lower than the traditional blower. The blower is widely used and long uninterrupted operation, and the actual application efficiency is very low. So the tremendous energy is wasted, and the improvement of the performance is very important practical significance in energy-saving and environmental protection.To centrifugal blower, the performance factors are blade profile and width of the impeller. When install angle of the blade is certain, blade shape affects pressure and velocity distribution of the whole passage, and pressure and velocity distribution certainly will affect the performance of blower. So studying the flow in different blade profile of impeller and width of impeller flow condition and exploring of impeller flow mechanism play an important role in improve its performance. The study focus of this paper is mainly located in the influence of blade profile and impeller width on under-low specific speed centrifugal blower. This paper takes an industrial under-low specific speed centrifugal blower as a reference case and designs a blower model with the same parameters of flow coefficient and pressure coefficient. Three different curve blades which contain forward-curve blade, backward-curve blade and variable-thickness blade in certain parameters have been designed to research.Firstly performance experimental with 3 kinds of impeller has been introduced in the paper, and performance data of 4 rotational speeds under 10 flow conditions has been measured. Then through curve fitting under the similarity principle, blade performance curve is obtained. Based on this result, performance difference of the blower with 3 different blade profiles has been analyzed. The result shows that the wedge blade among 3 blades has a relatively good performance, while the performance of backward-curved blade that common used in the traditional blower is not dominant. In order to further analysis the reason of performance difference among blade profiles on under-low specific speed centrifugal blower, flow visualization experiment is taken on the 3 different impellers. In the flow channel 7 group tracing distribution cable has been installed, the local direction of the airflow is determined by the tracing distribution cables. The influence by blade profile to airflow in the impeller channel is analyzed with the aid of visual observation to the flow passage of impeller, in order to explain the reason of performance difference.Due to the limitation of the experimental condition on flow visualization experiment, the whole information of flow field cannot be obtained. So full 3D-CFD calculation has been held on the centrifugal blower model, mechanism of performance difference among different blade profiles has been analyzed deeply by the simulation. The result shows that the wall viscous effect and separation phenomenon is obvious on the impeller of backward-curved blade, and the backflow phenomenon is also obvious. Wedge shaped blade is produced on the basis of the optimization of the forward-curved blade, and the flow separation effect caused by the narrow channel of the passage has been improved to some extent so the blower has good efficiency.According to the study on the different blade profiles of impeller, it finds that changing the profile of blade is only in certain extent improved the enhancement of viscosity effect and flow separation phenomenon that because of narrow impeller. Thus the impeller width has great influence to the performance of this impeller. Numerical calculation has been taken to further study the different width of the impeller.Different impeller width may lead to the change of outlet flow and pressure rising, and it will off the design condition. So a suitable impeller width will be found which can obtain the best overall performance of the blower in a certain off-value of design condition.