Abstract
The use of vane-less diffuser with large diffusion angle has shown a setback in the diffusion process of high temperature working fluids. The hot gas flow was characterized as a jet-like flow. This paper presents problem, encountered practically, using a vane-less diffuser with large diffusion angle and how the problem is solved by CFD simulation. The investigated thermal diffuser has a length of 0.3 m, an inlet to outlet crosssectional area ratio of 1:25 and diffusion angle of 115.44o. To resolve the jet-like flow problem and poor distribution of the flow temperature at the diffuser outlet, the study suggested the use of guide-vanes into the diffuser. The study employed CFD simulation by ANSYS-FLUENT software to analyze the flow and thermal process in the diffuser. Three different shapes of guide vanes; block-shaped, oval-shaped and airfoil-shaped were considered in this study and at different vanes diffusion angles, as well as vane-less case, which was adopted as the bench mark case. The simulation results of the velocity, temperature and pressure at the diffuser outlet were compared for all cases. It was found that the guide vanes with symmetrical airfoil profile provided the best performance with most uniform distribution at the outlet of the diffuser. Also, the airfoil-shaped guide vanes resulted in lower pressure losses compared to the block-shaped and oval-shaped guide vanes. According to the analysis results, the diffuser was redesigned to improve the diffusion and temperature distribution across the diffuser outlet.
Highlights
Diffusers are common sudden or gradual expansion component employed in piping/fluid flow processes to decelerate flow and recover static pressure, converts kinetic energy into pressure energy
A variation in diffuser area ratio and the diffusion angle with respect to the diffuser non-dimensional length determines the flow regime developed within the diffuser
The results of the study inferred that the angle of the diffuser vane has significant influence on the compressor operating range when compared with vane-less designs
Summary
Diffusers are common sudden or gradual expansion component employed in piping/fluid flow processes to decelerate flow and recover static pressure, converts kinetic energy into pressure energy. Anand and Sandeep [5] studied the fluid flow characteristics in Y-shaped diffusing ducts of two inlets and one outlet using three Y-shaped diffusing ducts of same curvilinear length and area ratio but with varying angle of turn at 15o, 22.5o and 30o. Their results showed that the velocity pattern at the exit is more uniform for the diffusing duct with smaller angle of turn which is 15o/15o as a result of reduced wake at the meeting point of the two inlet ducts. This work focuses on solving an experimental problem encountered using a diffuser with large diffusion angle for discharge of high temperature, high velocity flue gas to a flow channel inclined to the outlet of the diffuser at 45o
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