A Numerical Study on Performance Enhancement of Locally Produced Axial-Flow Fans for Grain Drying

Abstract

Abstract Utilization of a flatbed dryer (FBD) as a postharvest technology particularly in grain drying is continuously thriving in the Philippines. Throughout the years, its drying chamber component has been upgraded continually to improve overall dryer efficiency. However, its mechanical component, the fan, which drives the heated air into the chamber was found to perform poorly compared to international commercial fans. For instance, locally produced tube-axial fans perform at most 30% in efficiency compared to commercial ones that run at least 67%. The design of one of the tested locally produced fans is investigated through numerical methods, specifically using computational fluid dynamics (CFD), for potential development to achieve higher efficiency. In this way, parametric investigations can be performed at a much less cost compared to the cost of conducting physical testing. A general CFD model is developed to replicate the local standard procedure of testing agricultural fans and blowers. Furthermore, the present study uses the model to examine the effects of varying three (3) blade parameters on the aerodynamic performance of a reference fan. These parameters are the blade count, the tip clearance, and the pitch angle. FBD requires a specific static pressure and volume flow rate (PS-Q) depending on its drying chamber’s capacity and type. A methodology is introduced to capture the optimal rotational speed that applies for both individual PS-Q and a range of static pressures. The investigation yields the following results: the current design (CD) with 12 blades appears to be optimal near the static pressure of 250 Pa. The static efficiency of the fan is proportional to the no. of blades until CD where the performance metric started to plateau. Decreasing the tip clearance drastically enhances the performance of the axial fan, with tip clearance ratio, TR, of 2.13% providing the highest improvement. The increase reached as high as 37% change to the CD with a TR of 4.80%. An axial fan with a blade pitch angle of 33° shows to be the superior option for an FBD with 250 Pa static pressure requirement. For FBD with higher PS-Q requirements such as 375 Pa and 500 Pa, the CD with 27° blade pitch angle is appropriate to use. The current study shows a numerical method like CFD can be applied to perform a cost- and time-effective design optimization to turbomachines such as fans attached to the FBD. More importantly, the developed CFD model can be extended to be used to investigate other parameters of the axial fan or to develop the design of centrifugal fans utilized in Philippine agricultural technologies.