Powder processing and manufacturing operations are rate processes for which the bottleneck is cohesive powder flow. Diversity of material properties, particulate form, and sensitivity to environmental conditions, such as humidity and tribo-electric charging, make its prediction very challenging. However, this is highly desirable particularly when addressing a powder material for which only a small quantity is available. Furthermore, in a number of applications powder flow testing at low stress levels is highly desirable.

Characterisation of bulk powder failure for flow initiation (quasi-static) is well established. However, bulk flow parameters are all sensitive to strain rate with which the powder is sheared, but in contrast to quasi-static test methods, there is no shear cell for characterisation of the bulk parameters in the dynamic regime. There are only a handful of instruments available for powder rheometry, in which the bulk resistance to motion can be quantified as a function of the shear strain rate, but the challenge is relating the bulk behaviour to the physical and mechanical properties of constituting particles. A critique of the current state of the art in characterisation and analysis of cohesive powder flow is presented, addressing the effects of cohesion, strain rate, fluid medium drag and particle shape.

Immunization can be traced back to classical China. Modern immunization reduces the risk of infection by attenuating or killing the pathogen or using non-infectious antigens to elicit the immune response. The challenge of immunization is to raise a robust protective response without infecting the individual or overstimulating the immune response, and this can be achieved by using nanoparticle delivery systems to specifically target the innate immune system with known antigens and where necessary include an adjuvant to enhance the efficacy. These systems can be targeted to mucosal sites that are located throughout the body with the nasal and pulmonary routes of administration allowing ease of access. Macrophages are the first line of defense of the innate immune system and are the host cell for primary intracellular infection by several respiratory pathogens notably mycobacteria and streptococci. The breadth of nanoparticle technology available to deliver vaccines has been explored and consideration of its value in nasal and pulmonary delivery is addressed specifically.

Circulating fluidized beds (CFB)s are important technical equipment to treat gas–solid systems for fluid catalytic cracking, combustion, gasification, and high-temperature heat receiving because their mass and heat transfer rates are large. Cyclones are important devices to control the performance of CFBs and ensure their stable operation; heat-carrying and/or solid catalyst particles being circulated in a CFB should be efficiently separated from gas at a reduced pressure loss during separation. In commercial CFBs, a large amount of solids (> 1 kg-solid (m³-gas)^–1 or > 1 kg-solid (kg-gas)^–1) is circulated and should be treated. Thus, gas–solid cyclones with a high solids loading should be developed. A large number of reports have been published on gas–solid separators, including cyclones. In addition, computational fluid dynamics (CFD) technology has rapidly developed in the past decade. Based on these observations, in this review, we summarize the recent progress in experimental and CFD studies on gas–solid cyclones. The modified pressure drop model, scale-up methodology, and criteria for a single large cyclone vs. multiple cyclones are explained. Future research perspectives are also discussed.

The growing population and economic development globally has led to increasing resource consumption and waste generation. This has generated concern at local, national and international levels on environmental issues including air quality, resource scarcity, waste management (including plastics) and global warming. The resulting antipathy towards fossil fuels and waste landfilling has spurred the demand for alternative bioenergy and biofuels production methods, making use of abundant biomass and waste feedstock. Although not new concepts, there has been renewed impetus recently to develop advanced thermochemical processes such as pyrolysis and gasification to treat biomass and municipal solid waste (including refuse-derived fuel therefrom). This is because these processes have the potential to add value to cheap and abundant materials by converting them into advanced biofuels and chemicals. The work presented in this paper is concerned principally with the technical analysis and review of new-generation, state-of-the-art systems based on fluidised bed reactors operated with biomass and solid waste. A comprehensive assessment of fluidised bed reactor types and operations is considered, with particular attention given to those processes aimed at the production of clean syngas for the subsequent synthesis of high-value products, including bio-hydrogen, synthetic natural gas (SNG), and liquid fuels.

Multiple industrial applications, including pharmaceuticals, rely on the processing of powders. The current powder characterization framework is fragmented into two general areas. One deals with understanding powders from the standpoint of its constituting agents—particles. The other deals with understanding based on the bulk— the collective behavior of particles. While complementary, the two aspects provide distinct pieces of information. Whenever possible, experimental techniques should be used to predict powder behavior. However, it is equally important to recognize that because of the natural complexity of powders, existing predictive approaches will continue to be of limited success for predicting the collective behavior of particles. This article discusses the understanding of powder properties from two perspectives. One is the effect of surface energy at the bulk level (large collections of particles), which controls interactions between powders. This aspect is most useful if studied at the bulk-powder level, not at the single-particle level. Another perspective deals with the physico-mechanical properties of individual particles, responsible for the observed behavior of powders when subjected to mechanical stress from unit operations such as milling. This aspect, which controls the failure mechanism of powders subjected to milling, is most useful if assessed at the single-particle, not at the bulk level. Therefore, in order to fully understand, and eventually predict, or at least effectively model powder behavior, a good-judgement-based combination of microscopic and bulk-level analytical methods is necessary.