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In the present work, an attempt was made to experimentally quantify the boiling heat transfer coefficient (BHTC) of graphene oxide-water nano-suspension (NS) inflow boiling heat transfer regime. The NS was prepared at weight fractions of 0.025, 0.05, and 0.1% using the two-step method and further stabilized for 17 days (at wt% = 0.1). Results showed that the presence of graphene oxide nanoplatelets (GNPs) imposed an extreme fouling thermal resistance (FTR) to the surface, which caused a reduction in the BHTC over 1000 min of continuous operation after the CHF point. This was mainly due to the presence of the graphene oxide on the surface, which created a surficial fouling layer and heat accumulation on the surface. Instead, the sedimentation layer promoted the critical heat flux (CHF) point such that the point for water was 1370 kW/m2 reaching 1640 kW/m2 for NS at wt% = 0.1. Likewise, the highest BHTC of 17.4 kW/(m2K) at Re = 10,950 was obtained. Also, with increasing the heat flux and flow rate, the BHTC increased. The same trend was also identified with a mass fraction of GNPs up to CHF point. The increase in the BHTC was attributed to the intensification of the Brownian motion and thermophoresis effect in the boiling micro-layer close to the surface. Unlabelled Image • BHTC of GO/ H 2 O nano-suspension inflow boiling heat transfer regime was studied experimentally. • The NS was prepared at ɸ = 0.025, 0.05, and 0.1% and stabilized for 17 days. • The presence of GNPs imposed an extreme fouling thermal resistance to the surface. • The highest BHTC of 17.4 kW/(m2K) at Re = 10,950 was obtained. • With increasing the heat flux and flow rate, the BHTC increased. [ABSTRACT FROM AUTHOR]

In the present work, the boiling heat transfer coefficient (BHTC) and fluid flow characteristics of graphene oxide nanoplatelets (GONPs) nano-suspensions in an annular heat exchanger (AHEX) were experimentally investigated. The BHTC, pressure drop (PD) and the friction factor (FF) of the heat exchanger was quantified, and effects of various operating conditions including heat flux (HF), flow rate (FR), the temperature of the nano-suspension and the mass concentration (MC) of the GONPs on the HTC and the PD of the system was assessed. Results showed that by increasing the HF, the weight concentration of the GONPs, and the temperature of the working fluid, the BHTC of the system increases. Also, the presence of GONPs can augment the friction forces, viscosity, and, as a result, increase the PD and the FF of the system. For all the experiments, the BHTC of the system was more significant than water. A comparison between water-perfluorohexane and water- n-pentane nano-emulsions revealed that water-n pentane has better thermal performance and lower PD in comparison with perfluorohexane despite the presence of the GONPs within the bulk of the nano-emulsion. [ABSTRACT FROM AUTHOR]

Particle size reduction to sub-micrometer dimensions in stirred media mills is an increasingly common formulation strategy used for improving the bioavailability of poorly aqueous soluble active pharmaceutical ingredients (APIs). Due to their hydrophobic character, the API particles need to be stabilised by a surfactant in order to form a stable nano-suspension. This work is concerned with the understanding of an undesired phenomenon often encountered during the development and scale-up of wet nano-milling processes for hydrophobic APIs – the formation of foams. We investigate the microstructure, rheology and stability of these foams, and find them to be Pickering foams stabilised by solid particles at the gas-liquid interface rather than by a surfactant. By exploring the effect of surfactant concentration on the on-set of foaming in conjunction with the milling kinetics, we find a relationship between the specific surface area of the nano-suspension, the quantity of surfactant present in the formulation and the occurrence of foaming. We propose a mechanistic explanation of foam formation, and find that in order to prevent foaming, a large surfactant excess of approx. 100x above the critical micelle concentration has to be present in the solution in order to ensure a sufficiently rapid coverage of freshly exposed hydrophobic surfaces formed during the wet nano-milling process. [ABSTRACT FROM AUTHOR]

Abstract As a typical cold storage media working at sub-zero temperature, NaCl-water solution as a phase change material (PCM) with -21 oC melting point has been selected in this study. 0.0625 vol.%-0.5 vol.% multi-wall carbon nanotube (MCNT) was dispersed in the NaCl-water basefluid via ultra-sonicating to make nano-suspension. The viscosity of MCNT-NaCl-water was measured and the experimental results fitted well with the modified Krieger-Dougherty (K-D) model. The structure of MCNT cluster was derived from the fitting of viscosity data, showing that the lower the temperature, the larger the cluster size could be. Benefited from the MCNT cluster parameter, the thermal conductivity of MCNT-NaCl-water was predicted by modified Hamilton-Crosser (H-C) model, in which the MCNT cluster was considered as a whole part with its equivalent thermal conductivity. In addition, thermal conductivity experiment was also conducted to compare the measured value with the calculated value. The results indicated that the traditional H-C model underestimates the measured thermal conductivity by a large margin while the approach proposed in this paper shows good accuracy. Moreover, it is also found that MCNT will improve the thermal conductivity more significantly at low temperature than at high temperature. [ABSTRACT FROM AUTHOR]

Abstract EG-water based MCNT nano-suspensions were prepared by two-step method. Both experimental work and theoretical analysis were carried out to investigate the rheological property of prepared samples at different volume fraction and temperatures. The results showed that the experimental viscosity value could be matched well with the modified K-D model considering effective volume fraction of aggregations. In addition, this work exhibited an interesting trend of the behaviour of the viscosity vs shear rate curve when temperature is dropping down. A particle aggregation transformation mechanism were proposed to reveal the relationship between MCNT aggregation conditions and temperature, furthermore to explain the variety of shear behaviour of nano-suspensions. [ABSTRACT FROM AUTHOR]

Abstract In this paper, EG of different concentration was added in water to form PCM with different freezing point. Then, 0.0625%, 0.125%, 0.25% and 0.5% MCNT was dispersed in to each EG-water basefluids respectively. The latent heat are 160.0, 141.0, 102.0 and 85.5 J/g and melting point are -12.2, -15.7, -22.1 and -25.4 oC for 15%~30% EG-water basefluids. We found that adding MCNT has very little influence on the latent heat and melting point because the total amount of MCNT is very small. Also, we noticed that thermal conductivity will increase with increasing amount of MCNT concentration in EG-water basefluids. An interesting observation is that the enhancement of thermal conductivity was much greater in solid state samples than liquid state samples. For example, in 0.5% MCNT sample, the enhancement of thermal conductivity in solid state was observed over twice higher than that in liquid state. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the in vitro dissolution performance of the different sized spray-dried nano-crystalline powders of naproxen. A DoE approach was used to formulate and optimize nano-crystalline suspensions. The critical wet milling operation parameters were i . e ., drug concentration, drug-to-stabilizer ratio, stabilizer type (HPMC E15 or Tween 80) and milling intensity. The nano-crystalline suspensions were optimized for size and physical stability and then spray-dried to obtain nano-crystalline powders. Trehalose and lactose were investigated as spray-drying auxiliary excipients to achieve non-aggregating powders. Particle size, DSC and PXRD were utilized for characterization of powder formulations. A modified USP apparatus II was utilized to determine the in vitro release/dissolution of powder formulations. The size of the nano-crystalline suspensions was dependent on drug concentration and milling intensity. HPMC E15 containing formulations were better in terms of the spray-dried powder yield compared to Tween 80 containing formulations. Trehalose was selected to formulate non-aggregating nano-crystalline powders. No polymorphic changes were observed following the wet milling and spray-drying processes. Size dependent in vitro dissolution profiles, utilizing a dialysis sac method were obtained for the crystalline powders. [ABSTRACT FROM AUTHOR]

Abstract: Quality by Design (QbD) principles were explored to understand spray drying process for the conversion of liquid nanosuspensions into solid nano-crystalline dry powders using indomethacin as a model drug. The effects of critical process variables: inlet temperature, flow and aspiration rates on critical quality attributes (CQAs): particle size, moisture content, percent yield and crystallinity were investigated employing a full factorial design. A central cubic design was employed to generate the response surface for particle size and percent yield. Multiple linear regression analysis and ANOVA were employed to identify and estimate the effect of critical parameters, establish their relationship with CQAs, create design space and model the spray drying process. Inlet temperature was identified as the only significant factor (p value <0.05) to affect dry powder particle size. Higher inlet temperatures caused drug surface melting and hence aggregation of the dried nano-crystalline powders. Aspiration and flow rates were identified as significant factors affecting yield (p value <0.05). Higher yields were obtained at higher aspiration and lower flow rates. All formulations had less than 3% (w/w) moisture content. Formulations dried at higher inlet temperatures had lower moisture compared to those dried at lower inlet temperatures. [Copyright &y& Elsevier]

Abstract: A critical problem associated with poorly soluble drugs is low and variable bioavailability derived from slow dissolution and erratic absorption. The preparation of nano-formulations has been identified as an approach to enhance the rate and extent of drug absorption for compounds demonstrating limited aqueous solubility. A new technology for the production of nano-particles using high speed, high efficiency processes that can rapidly generate nano-particles with rapid dissolution rate has been developed. Size reduction of a low melting ductile model compound was achieved in periods less than 1h. Particle size reduction of ibuprofen using this methodology resulted in production of crystalline particles with average diameter of approximately 270nm. Physical stability studies showed that the nano-suspension remained homogeneous with slight increases in mean particle size, when stored at room temperature and under refrigerated storage conditions 2–8°C for up to 2 days. Powder containing crystalline drug was prepared by spray-drying ibuprofen nano-suspensions with mannitol dissolved in the aqueous phase. Dissolution studies showed similar release rates for the nano-suspension and powder which were markedly improved compared to a commercially available drug product. Ibuprofen nano-particles could be produced rapidly with smaller sizes achieved at higher suspension concentrations. Particles produced in water with stabilisers demonstrated greatest physical stability, whilst rapid dissolution was observed for the nano-particles isolated in powder form. [Copyright &y& Elsevier]

Abstract: The purpose of the present study was to obtain nano-scale particles of styrene butadiene rubber. As SBR particles are elastic in nature, conventional methods of size reductions such as impacting, grinding are unable to achieve the final size. So, attempts have been made here to make the nano-particles of the SBR using cavitation technique. Both acoustic and hydrodynamic cavitation techniques have been employed and studied. Hydrodynamic cavitation has been proved to be more energy efficient than the acoustic cavitation on the basis of various parameters. The maximum production rate equivalent to 2kg/h (solid processing) has been achieved in the newly developed hydrodynamic cavitation set-up (made in house). Similar to transient cavitation, stable cavitation has also been shown to contribute for reduction in the size of the material with very low variation in size. This technique has been proved successful for the size-reduction of the elastic material to nano-scale, thus it may also be used for the size-reduction of the other brittle and hard material by adjusting various cavitational parameters. [Copyright &y& Elsevier]

• Performance of a pulsating heat pipe was assessed using graphene nanofluid. • Response surface model was developed to predict the thermal resistance parameter. • Thermal resistance of the heat pipe was experimentally measured. • Transient temperature profile of the heat pipe was recorded. • Minimum thermal resistance of the heat pipe was obtained with the model. In the present work, a series of tests were designed and conducted aiming at investigating the thermal response and performance of a pulsating heat pipe operating with graphene-water ethylene glycol nano-suspension. The heat pipe was tested at various applied heat values between 10 and 100 W, concentrations of 0.1 g/l to 2 g/l of graphene nanoplatelets dispersed in water-ethylene glycol, different filling ratios, and condenser temperatures. Thermal conductivity and viscosity of the nano-suspensions were experimentally measured at various concentrations. A response surface methodology model was developed to optimize the thermal performance of the heat pipe by minimizing the thermal resistance of the system. Results showed that the thermal resistance value decreases by increasing the concentration of the graphene nanoplatelets and also by increasing the heat load to the evaporator. Likewise, filling ratio and temperature of the condenser were found to have a complementary effect on the optimization of the performance of the heat pipe such that the minimum thermal resistance value of 0.36 K/W was obtained at 85 W and condenser temperature of 23 °C, filling ratio of 0.35 and concentration of 2 g/l. It was identified that the presence of the graphene nanoplatelets contributes to the promotion of heat transfer mechanisms due to the intensification in micro-scale phenomena such as Brownian motion and thermophoresis effect. Using nonlinear regression analysis, a correlation was developed to predict the thermal resistance value of the system with an accuracy of <8.7%. [ABSTRACT FROM AUTHOR]

• This is a study on the potential effect of nanoparticle fouling on surface characteristics. • Nanomaterial samples are characterised by SEM, EDX and nanoparticle sizer. • Effect of surface characteristics on boiling performance of CuO-water is studied. • Bubble formation, surface roughness, contact angle and departure time are measured. • Study was categorised into two domains of steady state and transient measurements. In the present work, we report the results of series of experiments aiming at identifying the key mechanisms affecting the transient boiling heat transfer coefficient. Two categories of experiments were designed and conducted in which the heat transfer coefficient and fouling thermal resistance were quantified at steady state condition and in a transient study over 1000 min of continuous operation of the heater. CuO-water nano-suspension was prepared, stabilised and used with the view to improve the thermal conductivity of water and thereby increasing the heat transfer coefficient. Results showed that at initial times of the experiments, the heat transfer coefficient was improved due to the increase in the thermal conductivity of the nano-suspension, and the emerge of some micro-scale phenomena such as Brownian motion and thermophoresis effect. While over 1000 min of continuous measurement, it was identified that the heat transfer coefficient was suppressed due to the formation of the fouling layer. Thermal resistance induced by the fouling layer together with the heat accumulation on the surface, a decrease in surface roughness value and also the suppression of the rate of the bubble formation were the main contributors that decreased the transient thermal performance of the system. It was also identified that the fouling thermal resistance was lower on the surface with lower surface roughness, which was associated with the thickness of the fouling layer formed on the surface. [ABSTRACT FROM AUTHOR]