Increasing oil contaminants in water is one of the major environmental concerns due to negative impacts on human health and aquatic and terrestrial ecosystems. The objective of this review paper is to highlight recent advances in the application carbon-based polymer nanocomposite membranes for oily wastewater treatment. Carbon-based nanomaterials, including graphene and graphene-oxide (GO), carbon nanotubes (CNTs), and carbon nanofibers (CNFs), have gained tremendous attention due to their unique physicochemical properties, such as excellent chemical and mechanical stability, electrical conductivity, reinforcement capability, and their antifouling properties. This review encompasses innovative carbon-based membranes for effective oil–water separation and provides a critical comparison of these membranes regarding the permeation flux, wettability, and flux recovery. The current challenges for the successful development of carbon-based nanocomposite membranes and opportunities for future research are also discussed.

Most of the developed models for the air-gap membrane distillation (AGMD) process are one-dimensional and rely on experimentally determined parameters. Herein, inspired by the effectiveness-number of transfer units method for the design of heat exchangers, a new approach of theoretical model is developed based on mass and heat transfer mechanisms in the AGMD process by considering the temperature variation in two dimensions. The results of our self-sustained model match well with the AGMD experimental results, with less than 4% deviation. Using the developed model, the AGMD performance is systematically investigated in terms of permeate flux, energy efficiency, and temperature and concentration polarization effects, and the results are compared with direct contact membrane distillation (DCMD). The results showed that the feed temperature had the most significant impact on the permeate flux and energy efficiency. The thickness of the air-gap and the flow rate were found to be the second most effective parameters. In contrast, the membrane thermal conductivity and porosity did not play a determining role. A 60% increase in the feed temperature increased the permeate flux and energy efficiency by 200 and 2%, respectively. By increasing the flow rate from 0.2 to 8 liters per minute, the permeate flux was enhanced by 67.19%. The air-gap thickness increment from 0.6 to 5.6 mm caused a 36.8% reduction in the permeate flux. In our comparative study, the permeate flux and the gained output ratio for DCMD were 56.6 and 27.3% higher as compared to AGMD at the same conditions. However, the thermal efficiency of the AGMD process was 24.7% larger than that of the DCMD process. The developed model provides solutions to minimize the undesirable effects of temperature and concentration polarization and proposes an optimum design map to achieve higher energy efficiency and permeate flux.

This paper presents an experimental study on frost formation on a plate under natural convection conditions. Frost thickness, mass, density, and surface roughness are measured during each test. Frost thickness and roughness are measured using an image processing technique. The effect of operating conditions (temperature of the plate, and temperature and relative humidity of the air) on the properties of frost is investigated. Frost surface roughness is quantified using two parameters: the average roughness and the skewness of the roughness, which can describe the frost layer shape. The surface roughness of the frost layer is considerably higher than the roughness of a flat plate, which should be considered in frosting studies. In this paper, it is shown that frost surface roughness is related to the frost layer shape, porosity and density. It is also found that the plate temperature affects the frost surface roughness significantly; as the plate temperature decreases, the frost layer has a high average roughness and negative skewness, which correspond to a highly porous, low density frost layer. Increasing the air humidity and air temperature affects the average surface roughness slightly but not skewness of the frost surface.

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