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Effects of using phase change material and non‐Newtonian power law nanofluid on different sides of a double pipe heat exchanger for phase change dynamics and energy performance improvements

AbstractIn this study, the effects of using phase change material (PCM) and non‐Newtonian power law (PL) fluid on the performance features of a double pipe heat exchanger were numerically assessed with finite element technique. PCM and PL fluid were used in different sides of the heat exchanger while impacts of cold side fluid Re number, nanoparticles loading amount, and PL index of fluid on the dynamics characteristics of phase change process, and thermal performance were examined. There is a reduction of 71.5% in the full phase transition time (td) when cases with Re = 100 and Re = 300 are compared while cold fluid exit temperature rises by about 5.8 K with PCM‐installed heat exchanger as compared to non‐PCM configuration at Re = 300. As cases with different PL indices (n) between n = 0.8 and n = 1.2 are compared, the value of td rises by about 34%. For different nanoparticle loading, variation of td depends upon the PL index and its value rises with higher n at the highest solid volume fraction. The particle size has also impacts on the variation of td and exit temperatures which is more pronounced for power n values. A polynomial regression model is used for the estimation of td.

Correlation between structure and responsivity in PNIPAM based nanocomposites: A combined nano- and macroscale view

Thermosensitive hydrogels have enormous potential, e.g. in sensors, actuators, microfluidics or drug delivery systems. In these applications the tuneability of their response rate is a key parameter and is therefore of great interest. However, the applicability of these systems is subject to limitations, which may be overcome by enhanced nanocomposite materials. This paper presents a systematic study of the thermal response of graphene oxide (GO) – and carbon nanotube (CNT) – poly(N-isopropylacrylamide) composite systems, and investigates the effect of the nanoparticle filler content, both on the nanoscale and the macroscopic level. While the equilibrium swelling properties of the different nanocomposites are only slightly influenced, the kinetics of the response of the swelling medium following an abrupt temperature increase from 20 to 40 or 50 °C can vary within wide limits depending on the type or the amount of nanoparticle loading, as well as on the temperature difference.

Binary metal oxide nanoparticle incorporated composite multilayer thin films for sono-photocatalytic degradation of organic pollutants

We report reduced graphene oxide (rGO) supported binary metal oxide (CuO–TiO2/rGO) nanoparticle (NP) incorporated multilayer thin films based on Layer-by-Layer (LbL) assembly for enhanced sono-photocatalytic degradation of methyl orange under exposure to UV radiation. Multilayer thin films were fabricated on glass and quartz slides, and investigated using scanning electron microscopy and UV–vis spectroscopy. The loading of catalyst NPs on the film resulted in the change of morphology of the film from smooth to rough with uniformly distributed NPs on the surface. The growth of the control and NP incorporated films followed a linear regime as a function of number of layers. The%degradation of methyl orange as a function of time was investigated by UV–vis spectroscopy and total organic carbon (TOC) measurements. Complete degradation of methyl orange was achieved within 13h. The amount of NP loading in the film significantly influenced the%degradation of methyl orange. Catalyst reusability studies revealed that the catalyst thin films could be repeatedly used for up to five times without any change in photocatalytic activity of the films. The findings of the present study support that the binary metal oxide catalyst films reported here are very useful for continuous systems, and thus, making it an option for scale up.

Thermal sensitivity of carbon nanotube and graphene oxide containing responsive hydrogels

Comparative investigations are reported on poly(N-isopropylacrylamide) (PNIPA) gels of various carbon nanotube (CNT) and graphene oxide (GO) contents synthesized under identical conditions. The kind and concentration of the incor- porated carbon nanoparticles (CNPs) influence the swelling and stress-strain behaviour of the composites. Practically inde- pendently of the filler content, incorporation of CNPs appreciably improves the fracture stress properties of the gels. The time constant and the swelling ratio of the shrinkage following an abrupt increase in temperature of the swelling medium from 20 to 50 °C can be adjusted by selecting both the type and the amount of nanoparticle loading. This offers a means of accurately controlling the deswelling kinetics of drug release with PNIPA systems, and could be employed in sensor appli- cations where fast and excessive shrinkage are a significant drawback. Both CNTs and GO enhance the infrared sensitivity of the PNIPA gel, thus opening a route for the design of novel drug transport and actuator systems. It is proposed that the in- fluence of the CNPs depends more on their surface reactivity during the gel synthesis rather than on their morphology. One of the important findings of this study is the existence of a thermally conducting network in the GO filled gels.

Fabrication and magnetic properties of FePt nanoparticle assemblies embedded in MgO-matrix systems

Hydrophilic FePt nanoparticles (NPs) have been embedded into the MgO-matrix systems via a sol–gel process to prevent FePt NPs from aggregating and sintering during the heat-treatment process required for the L10 ordering. The chemically ordered L10-phase FePt can be obtained after annealing at 700 °C for 60 min in atmosphere containing H2. The effect of the pH value of MgO collosol and FePt nanocrystal loading amount on the structure, morphology, and magnetic properties of FePt/MgO nanocomposites has been investigated. The neutral pH value of 7 in MgO sol is beneficial to stabilize FePt NPs and obtain higher chemical ordering parameter S for the face-centered tetragonal -FePt/MgO nanocomposites with larger coercivity. The FePt NPs loading amount also plays a key role in tuning the microstructure and magnetic properties of the nanocomposites. The relatively higher FePt NPs loading with FePt/MgO molar ratio (RFM) of 1:2 leads to relatively perfect hexagonal assembly and pure L10 phase. When the RFM is 1:5 and 1:10, the MgO-matrix in nanocomposites causes the Fe element loss in FePt NPs along with formation of secondary phases such as magnesioferrite or Pt3Fe during the annealing process. Under optimal processing of neutral pH value of 7 and RFM of 1:2, the presence of MgO matrix produces more homogeneous microstructures and better magnetic properties with higher room-temperature coercivity (H C = 4.65 kOe).

Effect of electrodeposition conditions and reinforcement content on microstructure and tribological properties of nickel composite coatings

In this work, pure nickel and nickel composite coatings (Ni–Al 2O 3, Ni–SiC, and Ni–ZrO 2) were deposited from Watts bath using direct current (DC), pulsed current (PC), and pulsed reverse current (PRC) electrodeposition conditions. Detailed investigations on the effect of deposition conditions on the evolution of surface microstructure, crystallographic micro-texture, microhardness, and sliding wear behavior of pure nickel and nickel composite coatings are presented. For all the coatings, the PC and PRC deposition conditions resulted in more random/weak crystallographic texture compared to DC deposition. The composite coatings deposited using PC and PRC deposition also exhibited significant improvement in microhardness and wear resistance due to enhanced reinforcement of nanoparticles in the coatings. Also, the effect of nanoparticle content of the electrolyte bath on the surface microstructure, tribological properties, and level of reinforcement in the Ni–Al 2O 3 composite coating is investigated. The reinforcement of nanoparticles in the Ni–Al 2O 3 composite coatings increased linearly with the amount of nanoparticle loading in the electrolyte bath. The microhardness and wear resistance of the Ni–Al 2O 3 composite coatings also improved with increasing Al 2O 3 content in the coatings.

Facile encapsulation of nanoparticles in nanoorganized bio-polyelectrolyte microshells

We present a facile method for the encapsulation of nanoparticles' (NPs) systems within the interior space of bio-polyelectrolyte microshells. The microshells, constructed by alternate adsorption of alginate sodium (ALG) and chitosan (CHI) onto the surface of colloidal templates and subsequent removal of cores, allow the polystyrene (PS) or SiO2 nanoparticles (NPs) adsorbed into the internal shells through a simple mix process, as confirmed by confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM) analysis. The NPs-filled microshells form the rigid spherical shape in contrast to the flat and folded structure of microshells at the dry state prior to filling. The interior of NPs-encapsulated microshells was directly visualized by transmission electron microscopy (TEM) image of microtomed slices and cross-section SEM image. The loading amount of NPs in a shell composed of (ALG/CHI)5 was determined in two media i.e. H2O and 0.1M NaCl, and the results showed that the loading amount of the former is greater than that of the latter. The possible encapsulation mechanism is also discussed. The hybrid materials with NPs core and bio-polyelectrolyte shells have potential application for controlled-release drug delivery and catalysis.