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The present research explores the dispersion of SiO2 nanoparticles in compressor lubricant, polyolester (POE) oil for performance enhancement of vapour compression refrigeration system (VCRS). The contribution of SiO2 nanoparticles based nanolubricant was examined for eco-friendly hydrocarbon (HC) refrigerant R600a, retrofitted to hydrofluorocarbon (HFC) compressor based VCRS and also in HC compressor, in governing the performance of VCRS. Wear characteristics improved by the nanolubricants were assessed through pin-on-disc wear testing, using the pins extracted from the actual compressor piston used in VCRS. As compared to POE oil, the average specific wear rate (SWR) and coefficient of friction (COF) of nanolubricant were reduced by about 20% and 29%, respectively. Enhanced average viscosity and average thermal conductivity were observed (35–95 °C), with maximum increases of about 13% at 65 °C and 45% at 95 °C, respectively, in comparison to those of POE oil. Field emission scanning electron microscopy (FE-SEM) was utilized to analyze the morphology of SiO2 nanoparticles, while Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyzed their crystal structure. The Zeta potential tests for the prepared nanolubricant were conducted to ensure its long-term stability. An HC compressor based VCRS shows better performance including average refrigeration effect, average power consumption by compressor, and the average coefficient of performance (COP) of 29%, 7%, and 39%, respectively compared to the base lubricant filled retrofitted system. Hence the findings of the present research provide novel perspectives on the potential benefits of incorporating SiO2 nanoparticles and an HC compressor to improve the VCRS performance. [ABSTRACT FROM AUTHOR]

The environment effect of conventional refrigerants can be improved by adopting eco-friendly hydrocarbon (HC) refrigerants in a vapour compression refrigeration (VCR) system. In this work, various factors such as neutral ozone depletion potential (ODP) and low global warming potential (GWP), use of a lesser quantity of refrigerant, power saving, and retrofitting to the existing VCR system, are encouraged by opting for the HC refrigerant R600a. The mono and the hybrid nano-lubricants prepared by dispersing different concentrations of metallic oxide (TiO2) and non-metallic oxide (SiO2) nanoparticles in POE oil were used as the compressor lubricant. The morphology and crystal structure of each nanoparticle were analysed with the FE-SEM and XRD analysis. The performance parameters of the VCR system were analysed to study the effect of different nano-lubricants. In contrast to the better performance of TiO2 in mono form, a combination of 25% TiO2 and 75% SiO2 in hybrid form performed better amongst all the tested lubricant samples. As compared to the base lubricant (POE oil). This hybrid nano-lubricant combination reduced the compressor power consumption by about 8% and enhanced the refrigeration effect by more than 13%. It resulted in the enhancement in COP by more than 23%. The compressor suction and delivery characteristics (such as pressure) and the pull-down temperature were also studied to evaluate the effect of different nano-lubricants. Furthermore, the viscosity and thermal conductivity analysis at various temperatures were also conducted to observe the tribological and thermo-physical property influence of the mono and hybrid forms of nano-lubricants on VCR system performance. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to investigate the high temperature corrosion behaviour of ZrO2-reinforced Cr2O3 matrix-based composite coatings on ASTM-SA213-T-22 steel at 900°C in molten salt environment. The different coatings were deposited by high velocity oxy fuel (HVOF) method. Design/methodology/approach: Hot corrosion studies were conducted in simulated boiler environment in silicon carbide tube furnace at 900°C for 50 cycles on bare and HVOF-coated boiler steel specimens. Each cycle consisted 50 h of heating in the simulated boiler environment followed by 20 min of cooling in air. The weight change measurements were performed after each cycle to establish the kinetics of corrosion using thermogravimetric technique. X-ray diffraction and scanning electron microscopy techniques were used to analyse the corroded specimens. Findings: The addition of 20 Wt.% ZrO2 in Cr2O3 helped reduce corrosion rate by 89.25% as compared to that of uncoated specimen. The phase analysis revealed the presence of Cr2O3 and ZrO2 phases in composite coating matrix, which may have prevented the base metal from interacting with the corrosive elements present in the highly aggressive environment and thus had increased the resistance to hot corrosion. Originality/value: It should be mentioned here that high temperature corrosion behaviour of thermally sprayed ZrO2–Cr2O3 composite coatings has never been studied, and to the best of the authors' knowledge, it is not available in the literature. Hence, present investigation can provide valuable information for application of ZrO2-reinforced coatings in high temperature fuel combustion environments. [ABSTRACT FROM AUTHOR]

The present work discusses the macrostructure, microstructure, and microhardness of dissimilar metal weld joints between AISI 316L SS-DSS 2205 developed by gas tungsten arc welding (GTAW) welding. Post-weld heat treatments (PWHT) were carried out at temperatures of 750°C for 24 h and 850°C for 0.5 h. The macrostructure and microstructure of the welding joints at different welding conditions were observed by scanning electron microscope. The macrostructure study results indicated that all the welded joints were fully penetrated and free from defects. However, the microstructure investigation revealed a solid-state transformation of ferrite into grain boundary austenite, widmanstatten austenite, intergranular austenite, and partially transformed austenite. The post-weld heat treatment processes enhanced the precipitation of the sigma phase in the ferrite matrix. Secondly, the microhardness across and along the weld bead has been evaluated, and the results are compared. It was observed that the microhardness of the heat-affected zone of DSS 2205 is found to be higher as compared to a heat-affected zone of AISI 316L, the weld metal zone, and base metals at all welding currents (i.e. 90 A, 109 A, and 132 A). The microhardness values decrease when transverse from the face of the weld toward the root pass. Microhardness values at the fill (top) pass of the weld zone at 90 A, 109 A, and 132 A were 268.3 HV, 257 HV, and 255 HV respectively. It was found that the microhardness has improved significantly after post-weld heat treatments and was highest for 750°C/24 h. It may be due to higher holding time which led to the involvement of carbides. [ABSTRACT FROM AUTHOR]

The presence of nanoparticles in the conventional coatings improves their strength by increasing the microhardness and reducing the porosity. The nanocomposite coatings play a significant role in increasing the erosion resistance. The purpose of this study is to observe the erosion behavior of nano yttria stabilized zirconia (Y2O3/ZrO2; YSZ) reinforced WC-10Co-4Cr ceramic nanocomposite coatings. The WC-10Co-4Cr conventional coating powder, and 95% and 90% of WC-10Co-4Cr reinforced with 5% and 10% of nano YSZ powders, coated on CA6NM steel using a high-velocity oxygen fuel (HVOF) spraying process. The Taguchi method using an L9 orthogonal array was applied for experimental design. Erosion test rig was used to perform erosion experiments at various levels of selected parameters. The results of erosion experiments and analysis of variance (ANOVA) for the conventional and nanocomposite coatings revealed that impact velocity performs a significant role in the material loss, followed by slurry concentration, average particle size, and impingement angle. Scanning electron microscopy (SEM) analysis of eroded samples revealed that cracks, protuberances, deep craters, spalling, ploughing, micropores, microcutting, lip formation, chip formation and microcracks are mainly responsible for the erosion of substrate material and different types of coatings. Inclusion of nanoparticles of YSZ into the WC-10Co-4Cr microparticles increased the microhardness and decreased the porosity of the nanocomposite coatings. Thus, the silt particles cannot penetrate more deeply into the metal surface and provided high resistance to erosion. It was observed that 95% (WC-10Co-4Cr) + 5% YSZ and 90% (WC-10Co-4Cr) + 10% YSZ ceramic nanocomposite coatings exhibits higher resistance to erosion in comparison with WC-10Co-4Cr coating and substrate material, due to better mechanical properties. [ABSTRACT FROM AUTHOR]