Heat transfer, tribology and performance of graphene nanolubricants in an IC engine

Improving the thermo-physical and tribological properties of lubricants has been a challenging subject of research. Over the last few years, nanolubricants, which are oils containing nanoparticle have been reported to possess exceptionally higher thermal and tribological properties than the traditional lubricants. However, nanolubricants complying with the American Petroleum Institute (API) and Society of Automotive Engineers (SAE) standards remain largely unexplored. In this dissertation, graphene based automotive lubricants meeting 20W50 API SN/CF and 20W50 API SJ/CF specifications have been investigated using a wide range of analytical methods. Thermal-physical and tribological properties have been thoroughly studied. A four-stroke IC engine test rig has been fabricated to investigate the performance of the formulated nanolubricant. By adding 0.01 wt% of 60 nm graphene and 1% lubricity additive to 20W50 API SN/CF oil, 21% and 23% enhancement in the coefficient of friction (µ) and thermal conductivity (k) at 80°C respectively was observed. Viscosity of SNCF with 0.01 wt% of 60 nm graphene and 1% lubricity increases by ~6% at 25°C, and ~9% at 105°C. Scanning electron microscopy and Energy-dispersive X-ray spectroscopy suggest that many nano-tribo mechanisms occurring simultaneously or subsequently could be the reason for enhanced anti-wear and antifriction behaviour of the nanolubricant. Graphene found in the used engine oil indicates that the multilayer graphene exfoliates, rolls up to become helical coils or tube like structure and subsequently entangles with other flakes. As a result, gradually augmenting the thermal performance of the oil. Thermogravimetric analysis revealed that the onset temperature of oxidation for the SN/CF oil could be delayed by 13-17 °C in the presence of graphene. Moreover, the rate of oxidation when the weight loss of oil in the presence of graphene reaches 40% to 20% could be delayed by more than 30 °C. Resistance to oil degradation depends strongly on the graphene nanoparticle size and concentration. TGA kinetics studies show that the base oils have higher activation energy (Ea) and the addition of graphene significantly reduces Ea. Furthermore, 70% enhancement in heat transfer rate is also achieved in the presence of graphene. SEM images of the piston rings collected after 100 hours of engine operation show that the oil containing graphene (12 nm) decreases the piston wear compared to base oil without graphene. Elemental analysis indicates that the addition of a natural polymeric ester based lubricity additive helps even the graphene of highest thickness to perform better in boundary lubrication conditions. Essentially, this research has put forth a comprehensive understanding of a novel graphene based nanolubricant. The consolidated approach to understand tribological mechanism proposed in this research is expected to result in de novo strategies for engineering advanced nanolubricants in future

Heat transfer, tribology and performance of graphene nanolubricants in an IC engine

Improving the thermo-physical and tribological properties of lubricants has been a challenging subject of research. Over the last few years, nanolubricants, which are oils containing nanoparticle have been reported to possess exceptionally higher thermal and tribological properties than the traditional lubricants. However, nanolubricants complying with the American Petroleum Institute (API) and Society of Automotive Engineers (SAE) standards remain largely unexplored. In this dissertation, graphene based automotive lubricants meeting 20W50 API SN/CF and 20W50 API SJ/CF specifications have been investigated using a wide range of analytical methods. Thermal-physical and tribological properties have been thoroughly studied. A four-stroke IC engine test rig has been fabricated to investigate the performance of the formulated nanolubricant. By adding 0.01 wt% of 60 nm graphene and 1% lubricity additive to 20W50 API SN/CF oil, 21% and 23% enhancement in the coefficient of friction (µ) and thermal conductivity (k) at 80°C respectively was observed. Viscosity of SNCF with 0.01 wt% of 60 nm graphene and 1% lubricity increases by ~6% at 25°C, and ~9% at 105°C. Scanning electron microscopy and Energy-dispersive X-ray spectroscopy suggest that many nano-tribo mechanisms occurring simultaneously or subsequently could be the reason for enhanced anti-wear and antifriction behaviour of the nanolubricant. Graphene found in the used engine oil indicates that the multilayer graphene exfoliates, rolls up to become helical coils or tube like structure and subsequently entangles with other flakes. As a result, gradually augmenting the thermal performance of the oil. Thermogravimetric analysis revealed that the onset temperature of oxidation for the SN/CF oil could be delayed by 13-17 °C in the presence of graphene. Moreover, the rate of oxidation when the weight loss of oil in the presence of graphene reaches 40% to 20% could be delayed by more than 30 °C. Resistance to oil degradation depends strongly on the graphene nanoparticle size and concentration. TGA kinetics studies show that the base oils have higher activation energy (Ea) and the addition of graphene significantly reduces Ea. Furthermore, 70% enhancement in heat transfer rate is also achieved in the presence of graphene. SEM images of the piston rings collected after 100 hours of engine operation show that the oil containing graphene (12 nm) decreases the piston wear compared to base oil without graphene. Elemental analysis indicates that the addition of a natural polymeric ester based lubricity additive helps even the graphene of highest thickness to perform better in boundary lubrication conditions. Essentially, this research has put forth a comprehensive understanding of a novel graphene based nanolubricant. The consolidated approach to understand tribological mechanism proposed in this research is expected to result in de novo strategies for engineering advanced nanolubricants in future

Enhancement of polymerase chain reaction using graphene nano-flakes

The excellent heat transfer properties of nanoparticles have potential applications in various fields including biology during the last two decades. Recently, the use of various nanoparticles in polymerase chain reaction (PCR) resulted in significant enhancement of its efficiency and specificity. In this research we have demonstrated the effects of a novel material, graphene nano-flakes on PCR. The rationale behind the use of graphene flakes is its unique physical and heat transfer properties. A number of experimental results including the effect of graphene flakes on denaturation of DNA and annealing step will also be discussed. The preliminary results clearly show that enhanced heat transfer effect of nano-flakes augment PCR yield and ultimately overall enhancement in reaction efficiency

Investigation on rheological properties of water-based novel ternary hybrid nanofluids using experimental and Taguchi method

This study presents the rheological behavior of water-based GO-TiO2 -Ag and rGO-TiO2 -Ag ternary-hybrid nanofluids. The impact of nanoparticles’ volumetric concentration and temperature on the rheological properties were studied. All experiments were performed under temperatures ranging from 25 to 50 ◦C in the solid volume concentration range of 0.5–0.00005%. The data optimization technique was adopted using the Taguchi method. The types of nanomaterials, concentration, temperature, and shear rate were chosen to optimize the viscosity and shear stress. The effect of shear stress, angular sweep, frequency sweep, and damping factor ratio is plotted. The experimental results demonstrated that the rheological properties of the ternary hybrid nanofluid depend on the ternary hybrid nanofluid’s temperature. The viscosity of ternary hybrid nanofluids (THNf) change by 40% for GO-TiO2 -Ag and 33% for rGO-TiO2 -Ag when temperature and shear rates are increased. All the ternary hybrid nanofluids demonstrated non-Newtonian behavior at lower concentrations and higher shear stress, suggesting a potential influence of nanoparticle aggregation on the viscosity. The dynamic viscosity of ternary hybrid nanofluid increased with enhancing solid particles’ volume concentration and temperature

Earlier denaturation of DNA by using novel ternary hybrid nanoparticles

Two novel ternary hybrid nanoparticles (THNp) consisting of graphene oxide (GO) and reduced graphene oxides (rGO) were added to samples of DNA. The effect of the addition of nanoparticles on the thermal denaturation of DNA samples was studied by measuring the absorbance using a temperature-controlled Perkin Elmer UV spectrophotometer. Adding GO-TiO 2-Ag and rGO-TiO 2-Ag nanoparticles lowered the denaturation temperature of template DNA significantly. The nanoparticles affect the denaturation rate. The optimal GO-TiO 2-Ag and rGO-TiO 2-Ag concentrations were found to be 5× 10-2, which resulted in 86-and 180-folds augmentation of DNA denaturation (6.5 µg/mL), respectively, while it resulted in 2-and 7-folds augmentation of DNA denaturation (11.5 µg/mL), respectively, at temperature as low as 80 C. The results indicated that rGO-TiO 2-Ag nanoparticles exhibited significantly higher DNA denaturation enhancement than rGO-TiO 2-Ag nanoparticles, owing to their enhanced thermal conductivity effect. Therefore, these nanoparticles could help to get improved PCR yield, hence enable amplification to be performed for longer cycles by lowering the denaturation temperatur

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Experimental Investigation on Rheological Properties of Water Based Novel Ternary Hybrid Nanofluids

This study presents the rheological characterization of deionised water dispersed with two different ternary-hybrid nanoparticles namely, GO-TiO2-Ag and rGO-TiO2-Ag. The stability of 0.05 wt% nanofluid samples are serially diluted by 10 fold in 5 levels is determined using zeta potential measurements. The non-linear viscoelastic measurements at temperatures ranging from 25oC to 50oC reveal that the graphene based ternary hybrid nanoparticle nanofluids exhibit Newtonian behaviour at higher concentrations. However, it displays shear thinning or pseudo-plastic fluid characteristics at lower concentration, suggesting a potential influence of nanoparticle aggregation on the viscosity. The experimental results are found to be in good agreement with the existing water based viscosity models. In addition, the effect due to shear stress, angular sweep, frequency sweep and damping factor ratio is also plotted

Synthesis and Characterization of Novel Ternary-Hybrid Nanoparticles as Thermal Additives

The performance of water as a heat transfer medium in numerous applications is limited by its effective thermal conductivity. To improve the thermal conductivity of water, herein, we report the development and thermophysical characterization of novel metal-metal-oxide-carbon-based ternary-hybrid nanoparticles (THNp) GO-TiO2-Ag and rGO-TiO2-Ag. The results indicate that the graphene oxide- and reduced graphene oxide-based ternary-hybrid nanoparticles dispersed in water enhance the base fluid (H2O) thermal conductivity by 66% and 83%, respectively, even at very low concentrations. Mechanisms contributing to this significant enhancement are discussed. The experimental thermal conductivity is plotted against the existing empirical hybrid thermal conductivity correlations. We found that those correlations are not suitable for the metal-metal-oxide-carbon combinations, calling for new thermal conductivity models. Furthermore, the rheological measurements of the nanofluids display non-Newtonian behavior, and the viscosity reduces with the increase in temperature. Such behavior is possibly due to the non-uniform shapes of the ternary-hybrid nanoparticles

Synthesis and Characterization of Novel Ternary Hybrid Nanoparticles as Thermal Additives in H2O

The performance of water as a heat transfer medium in numerous applications is limited by its effective thermal conductivity. In order to improve the thermal conductivity of water, herein we report the development and thermophysical characterization of a novel metal-metaloxide-carbon based ternary hybrid nanoparticles (THNp), GO-TiO2-Ag and the rGO-TiO2-Ag. The results indicate that the graphene oxide and reduced graphene oxide based ternary hybrid nanoparticles dispersed in water enhance its thermal conductivity by 66% and 83%, respectively, even at very low concentrations. Mechanisms contributing to this significant enhancement are discussed. The experimental thermal conductivity is plotted against the existing empirical hybrid thermal conductivity correlations. We found that those correlations are not suitable for the metal-metaloxide-carbon combinations, calling for the developing a new thermal conductivity models. The rheological measurements of the nanofluids display non-Newtonian behavior, and the viscosity reduces with the increase in temperature. Such behavior is possibly due to the non-uniform shapes of the ternary hybrid nanoparticles

Potent Anti-Platelet Constituents from Centaurea iberica

New naturally occurring nitrogenous compounds 1 and 2, along with a new dimeric lignan glucoside 3, have been isolated from the ethyl acetate soluble fraction of Centaurea iberica. Their structures have been elucidated through spectroscopic techniques. All the isolated compounds showed significant platelet aggregation inhibition