## 1 Introduction  
Process industries often employ fine and ultrafine powders to enhance surface-based rate processes such as gas-solid-catalyzed reactions and various separation processes [1; 2]. An intimate contact between the solid and the fluid phase is an important prerequisite for their efficient utilization. Ultrafine nanopowders, whose size typically ranges from 1 to 100 nm, have a wide range of applications, from in research laboratories to large-scale industrial applications. Their extremely high surface area-to-volume ratio can significantly enhance the processes that depend upon the availability of the surface area. However, the efficacy of nanopowders is often compromised due to their agglomeration behavior, which occurs as a result of strong interparticle van der Waals forces [3; 4; 5; 6; 7]. Fluidized beds enhance the interphase mixing, and impart high mass and heat transfer rates while limiting the pressure drop to effective bed weight, even at high fluid velocities. Their hydrodynamics, however, strongly depend on the physical characteristics of the solid particles such as particle diameter and density [1; 8; 9]. Classified as Geldart group C particles (\(D_{p}<30\) um), nanopowders usually show strong agglomeration behavior, which induces non-homogeneities in the bed during their fluidization. This leads to poor interphase mixing, thereby affecting the effectiveness of the fluidized bed [10; 11; 12; 13]. Assisted fluidization techniques are often used to improve the fluidization behavior by providing additional energy to overcome the interparticle forces and promote deagglomeration [14]. Such techniques sometimes involve internal or external vibrations of the fluidized beds using various devices and configurations, such as ultrasonic communication devices [15], high-shear mixers [16], mechanical vibrations [17], acoustic vibrations [18; 19; 20], and oscillating magnetic particles under a magnetic field [21; 22]. In addition to being energy intensive, these techniques are also difficult to implement on an industrial scale. Some assisted fluidization techniques, which do not require a direct supply of energy, include tapered and inclined fluidized beds [23; 24], fluid flow pulsation [8; 25; 26; 27; 28; 29], and inert particle mixing [3; 4; 30; 31; 32; 33; 34]. In some cases, a combination of two assisted fluidization techniques has also been used to further enhance the performance of fluidized beds [35; 36; 37; 38]. [PERSON] and [PERSON] [6] studied the hydrodynamics of fine powders with sizes ranging from 12 nm to 15 \(\upmu\)m in bubbling fluidized beds. They used the combined assisted techniques of horizontal mechanical vibrations and acoustic vibrations to enhance the fluidization behavior. The combined technique was found to be more effective than mechanical vibrations alone. Both the agglomerate diameter and the minimum fluidization velocities were substantially reduced by the application of combined assisted fluidization techniques. [PERSON] and [PERSON] [39] studied the effect of acoustic and magnetic vibrations on the hydrodynamics of fluidized beds containing fine powders ranging from 5 nm to 45 \(\upmu\)m. The combination of assisted techniques helped to reduce the minimum fluidization velocity to a greater extent as compared to the case when these techniques were used separately. In the present study, a combination of two assisted fluidization techniques, namely, particle mixing and flow pulsation, is used to improve the fluidization behavior of a bed of nanopowder. In the assisted fluidization technique of particle mixing, the premixing of external particles with nanoparticles improves the bed homogeneity and promotes deagglomeration, and thus enhances the fluidization quality. [PERSON] and [PERSON] [30] reported a significant improvement in the fluidized bed hydrodynamics by the addition of even a small proportion of inert Geldart group A particles.