Volume 31, Issue 2

A critical review of the available information about heat transfer between a packed bed with cocurrent downflow of gas and liquid and an external medium was undertaken. Several aspects such as experimental set-ups and methods employed to study heat transfer in trickle bed reactors, models used to interpret experimental data, and literature correlations of heat transfer parameters are addressed. From the analysis of the available experimental information, a refined database has been built, which allows comparing the performance of the existing correlations for the parameters of the extensively employed two-dimensional pseudohomogeneous plug flow model (i.e., effective radial thermal conductivity and wall heat transfer coefficient). In addition, new correlations for effective thermal conductivity have been developed. Identification of gaps in the current knowledge and recommendations for future works are summarized.

This review evaluates computational fluid dynamic applications to analyze solid suspension quality in stirred vessels. Most researchers typically employ either Eulerian-Eulerian or Eulerian-Lagrangian approach to investigate multiphase flow in stirred vessels. With sufficient computational resources, the E-L approach simulates flow structures with higher spatial resolution for dispersed multiphase flows. Common turbulence models such as the two-equation eddy-viscosity models ( k - ε ), Reynolds stress model, direct numerical simulation, and large eddy simulation are described and compared for their respective limitations and advantages. Literature confirms that k-ε is the most widely used turbulence model, but it suffers from some inherent shortcomings due to assumption of isotropy of turbulence and homogenous mixing. Subsequently, the importance of different forces concerning solid particle flotation is concluded. Studies on dilute systems take into account only drag and turbulence forces while other forces have always been ignored. The simulations of off-bottom solid suspension, solid drawdown, solid cloud height, solid concentration distribution, and particle collision are considered for studies involving solid suspension. Different models and methods applied to investigate the abovementioned phenomena are also discussed in this review.

Polymer nanocomposite flame retardancy has become a critical parameter in industrial material application. Recent environmental policies have prohibited the incorporation of halogenated flame-retardant compounds into polymers owing to the high level of environmental degradation caused by high levels of toxic gas and smoke emission. The demand for zero-halogen flame-retardant compounds by both researchers and manufacturers is due to the inherent advantages accruable from their incorporation like very minimal toxic emission, minimal smoke release, zero corrosive gas release, reduced corrosion activities and absence of dripping in fire condition. This has necessitated the quest for eco-compliant replacements for halogenated flame suppressants. Recent insight has shown the eco-compliancy of exfoliated graphene nanoplatelets as flame retardants when incorporated into polymer nanocomposites (PNCs). Relative to the propensity to retard flame, increasing quantities of exfoliated graphene nanoplatelets have exhibited the capability to significantly repress critical flammability parameters like heat release rate (HRR), peak HRR (PHRR), rate of carbon monoxide production, smoke production rate and total mass loss rate while simultaneously increasing limiting oxygen index, time of ignition and total PHRR, thereby retarding flammability and creating better chance to reduce loss and casualty in real-life fire situation through the formation of even layers of carbonaceous char in the condensed phase capable of efficiently suppressing the thermal decomposition caused by oxygen and heat to the polymer matrix and cutting off the flaming path. This paper gives an insight into recent developments in flame retardancy of PNCs, with special emphasis on the flame-retardancy propensity of exfoliated graphite nanoplatelets.

This paper analyzes the applications of various ionic liquids (ILs) as metal ion carriers and extractants utilized for the separation of metal cations from aqueous solutions. Subsequently, an up-to-date review of the use of ILs in polymer inclusion membranes is presented. ILs represent a promising group of extractants and ion carriers of metal ions in extraction and membrane separation processes. The removal of heavy metals ions from aqueous solutions using ILs indicates an extensive and promising research area. It is expected that the role of ILs will gradually increase as the worldwide implementation of separation methods in recovery of metal ions from various aqueous solutions is growing quickly.