Foamlike 3D Graphene Coatings for Cooling Systems Involving Phase Change

Conversion of PET Bottle Waste into a Terephthalic Acid-Based Metal-Organic Framework for Removing Plastic Nanoparticles from Water

Micro- and nanoparticles of plastic waste are considered emerging pollutants with significant environmental and health impacts at high concentrations or prolonged exposure time. Here we report the synthesis and characterization of a known metal-organic framework (MOF) using terephthalic acid (TPA) recovered from the hydrolysis of polyethylene terephthalate (PET) bottle waste. This approach adds value to the existing large amounts of bottle waste in the environment. Fully characterized zinc-TPA MOF (MOF-5) was used for the extraction and removal of engineered polyvinyl chloride (PVC) and polymethylmethacrylate (PMMA) nanoparticles from water with a high efficiency of 97% and 95%, respectively. Kinetic and isotherm models for the adsorption of polymer nanoparticles (PNPs) on the MOF surface were investigated to understand the mechanism. The Qmax for PVC and PMMA NPs were recorded as 56.65 mg/g and 33.32 mg/g, respectively. MOF-5 was characterized before and after adsorption of PNPs on the surface of MOF-5 using a range of techniques. After adsorption, the MOF-5 was successfully regenerated and reused for the adsorption and removal of PNPs, showing consistent results for five adsorption cycles with a removal rate of 83-85%. MOF-5 was characterized before and after adsorption of PNPs on the surface using a range of techniques. The MOF-5 with PNPs on the surface was successfully regenerated and reused for the adsorption and removal of polymer nanoparticles, showing consistent results for five extraction cycles. As a proof of concept, MOF-5 was also used to remove plastic particles from commercially available body scrub gel solutions. Such methods and materials are needed to mitigate the health hazards caused by emerging micro- and nanoplastic pollutants in the environment.

Micro-Nano Scale Surface Coating for Nucleate Boiling Heat Transfer: A Critical Review

Nucleate boiling is a phase change heat transfer process with a wide range of applications i.e., steam power plants, thermal desalination, heat pipes, domestic heating and cooling, refrigeration and air-conditioning, electronic cooling, cooling of turbo-machinery, waste heat recovery and much more. Due to its quite broad range of applications, any improvement in this area leads to significant economic, environmental and energy efficiency outcomes. This paper presents a comprehensive review and critical analysis on the recent developments in the area of micro-nano scale coating technologies, materials, and their applications for modification of surface geometry and chemistry, which play an important role in the enhancement of nucleate boiling heat transfer. In many industrial applications boiling is a surface phenomenon, which depends upon its variables such as surface area, thermal conductivity, wettability, porosity, and roughness. Compared to subtractive methods, the surface coating is more versatile in material selection, simple, quick, robust in implementation and is quite functional to apply to already installed systems. The present status of these techniques for boiling heat transfer enhancement, along with their future challenges, enhancement potentials, limitations, and their possible industrial implementation are also discussed in this paper.

Effect of Surface Functionalization and Physical Properties of Nanoinclusions on Thermal Conductivity Enhancement in an Organic Phase Change Material

We probe the role of surface functionalization and physical properties of nanoinclusions in thermal conductivity enhancement during liquid-solid phase transition in a hexadecane-based phase change material (PCM). Hexadecane-based PCM is loaded with six different nanoinclusions: carbon black nanopowder (CBNP), nickel nanoparticles (NiNPs), copper nanoparticles, silver nanowires (AgNWs), multiwalled carbon nanotubes, and graphene nanoplatelets (GNPs). The nanoinclusions CBNP, NiNP, AgNW, and GNP are surface-functionalized with oleic acid. Nanoinclusion-loaded PCM showed a large enhancement in thermal conductivity, which was more prominent in the solid state. Interestingly, a maximum thermal conductivity enhancement of ∼122% was observed in the solid state for the PCM loaded with 0.01 wt % CBNP. Higher thermal conductivity enhancement in the solid state is attributed to the formation of a nanocrystalline network structure during freezing of the PCM, consisting of a needlelike microstructure, which is confirmed by optical phase contrast microscopy. During solidification, the nanoinclusions are driven toward the grain boundaries, thereby forming a quasi-two-dimensional network of percolating structures with high thermal transport efficiency due to the enhancement of phonon-mediated heat transfer and near-field radiative heat transfer. Thermal conductivity increases with the increased loading of the nanoinclusions due to the formation of more interconnecting aggregates. Among the carbon-based nanoinclusions, the highest thermal conductivity enhancement is obtained for the PCM loaded with CBNP, which is attributed to the low fractal dimensions and volume-filling capability of CBNP aggregates. In the case of metallic nanoinclusions, the highest thermal conductivity enhancement is obtained for the PCM loaded with AgNW, which is due to the large aspect ratio of AgNW. The carboxylic group of oleic acid attached to the nanoinclusions is found to provide better steric stability with insignificant aggregation and improved thermal stability, which are beneficial for practical applications. Our results indicate that the initial thermal conductivity of carbon-based nanoinclusions has an insignificant role in the thermal conductivity enhancement of the PCM but the volume-filling capability of the nanoinclusion has a prominent role. The findings from the present study will be beneficial for tailoring the properties of nanoinclusion-loaded organic PCM for thermal energy storage and reversible thermal switching applications at room temperature.