Graphene, a two-dimensional (2D) carbon nanomaterial, has attracted worldwide attention owing to its fascinating properties. One of critical bottlenecks on some important classes of applications, such as printed electronics, conductive coatings, and composite fillers, is the lack of industrial-scale methods to produce high-quality graphene in the form of liquid suspensions, inks, or dispersions. Since 2008, when liquid-phase exfoliation (LPE) of graphene via sonication was initiated, huge progress has been made in the past decade. This review highlights the latest progress on the successful preparation of graphene in various media, including organic solvents, ionic liquids, water/polymer or surfactant solutions, and some other green dispersants. The techniques of LPE, namely sonication, high-shear mixing, and microfluidization are reviewed subsequently. Moreover, several typical devices of high-shear mixing and exfoliation mechanisms are introduced in detail. Finally, we give perspectives on future research directions for the development of green exfoliation media and efficient techniques for producing high-quality graphene. This systematic exploratory study of LPE will potentially pave the way for the scalable production of graphene, which can be also applied to produce other 2D layered materials, such as BN, MoS₂, WS₂, etc.

To improve the performance of a high-pressure refueling liquid oxy-kerosene engine, the influence of drag-reducing additive on the heat transfer characteristics in the supercritical flow of kerosene in a microchannel for regenerative cooling is explored. The finite-volume CFD numerical simulation method is applied using the RNG k-ε turbulence model and enhanced wall function. The current work faithfully represents the effect of the drag-reducing additive in kerosene through numerical calculations by combining a 10-component model for the physical properties of the kerosene and the Carreau non-Newtonian fluid constitutive model from rheological measurements. Results suggest that the 10-component kerosene surrogate can describe the supercritical physical properties of kerosene. The inlet temperature, inlet velocity, and the heat flux on the channel wall are driving factors for the supercritical kerosene flow and heat transfer characteristics. The pressure influence on the heat transfer is negligible. With polymer additives, the loss in pressure drop and heat transfer performance of supercritical kerosene flow decrease 46.8% and 37.5% respectively. The enhancement of engine thrust caused by reduction in pressure drop is an attractive improvement of concern.

Passages between buildings comprise the airflow path through the buildings, and the wind passage is often studied in terms of two buildings located parallel or at a certain angle. From the perspective of urban areas, the wind passage can be considered the series connection of all local wind passages between each row of buildings. Whether the central axis of each local wind passage is collinear or not, the wind passages of the building array can be summarized as distorted and streamlined types. Large-eddy simulations (LESs) are employed to assess the impacts of the above two wind passage types on the airflow and drag characteristics. The mean, unsteady flow fields and the drag distributions are discussed to assess the effects of wind passages types. Span-wise airflow was found in the wake region in the case of distorted wind passages (DWP), whereas the recirculating vortices dominated the wake region for the case of streamlined wind passages (SWP). Span-wise airflow enhanced the mean stream-wise velocity U and span-wise velocity U in the wake region, decreased U in the wind passage region, and increased dispersive stress $〈{\tilde{V}}^2〉$ and $〈{\tilde{U}}^2〉$ within the urban canopy and the peak Reynolds stress above the urban canopy. Further, it strengthened the individual drag forces of buildings and the fluctuations of span-wise and stream-wise individual drag forces. The air of DWP penetrated deeper than SWP. These findings provide theory and data support for better design of wind passages between buildings and may serve as a foundation for urban design and planning.