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In the present work, effect of T6 heat treatment on the damping behaviour of aluminum/rice husk ash (RHA) composites fabricated by vortex method was studied using dynamic mechanical analyser (DMA) at frequencies ranging from 1 Hz to 25 Hz at room temperature under three-point bending test mode. The matrix material for the present work was A356•2 and reinforced with different weight % of 4, 6 and 8 rice husk ash particles. It was observed that composite exhibits high damping capacities than unreinforced alloy and increases with increase in weight % and the storage modulus increases with the addition of RHA particles but decreases with the increase in weight %. The heat treated composites exhibit higher damping capacity than the composites without heat treatment and increases with the increase in weight % of the reinforcement and loss in the storage modulus was observed and further decreases with the increase in the weight % of reinforcement. The related mechanisms were also discussed.

The noise reduction (NR) of fans used for cooling electric motors is one of the key parameters in the design of a motor fan. In the authors’ previous paper, aeroacoustic analysis (which is based on unsteady computational fluid dynamics results) was performed for the baseline fan to know its sound level. To further find a better blade shape from an NR point of view, aeroacoustic analysis on various blade profiles from the NACA-63 and NACA-65 series was conducted. In this work, an experimental study on the baseline fan and three redesigned composite material fans for the low-noise fan is performed. The experimental parameters under investigation are better aerofoil-shape blade cross-section, using inlet bell-mouth entry, using composite materials, reducing the number of blades, using uneven blade spacing, making it a mixed flow fan, using backward-skewed blade design and reducing tip clearance. From the noise measurements in a semi-anechoic chamber for Fan-2, it is observed that the overall NR was 12.8 dB(A) compared with the baseline fan. It is observed that a mixed flow fan consisting of seven evenly spaced blades of NACA 65-010 aerofoil cross-section with backward swept shape and fabricated with glass and jute fibre produced the low-noise fan design at the fan operating point.