Study of adhesion characteristics of different bitumen–aggregate combinations using bitumen bond strength test

The resistance of asphalt pavements to traffic loading and environmental deterioration depends on the mechanical coupling of the selected bitumen–aggregate material, bitumen–aggregate interfacial properties, and cohesion of bitumen. Studies have shown that bitumen–aggregate bond strength strongly depends on the composition of the two components, and the extent of exposure to moisture. For satisfactory performance of bituminous pavements, there is a need to choose suitable combinations of bitumen and aggregate materials. This paper evaluates the adhesion of different bitumen–aggregate combinations in dry and wet conditions in the form of pull-off tensile strength using bitumen bond strength (BBS) test. Tests were carried out after conditioning the selected combinations for 24, 48, and 72 h. The results indicated that the bond strength reduces with the passage of time for the samples exposed to moisture while it increases if samples are left in the dry condition. Results show that the strength values are also affected by the aggregates’ nature. Samples containing basic aggregates showed good results in comparison to the acidic aggregates under moisture conditioning. Significance of aggregates type, bitumen type, curing condition, and curing time on pull-off tensile strength of bitumen–aggregate samples was also studied. Curing condition showed maximum significance on bond strength.     

Lubrication of a narrow porous journal bearing with a couple stress fluid

This paper describes a theoretical investigation of the rheological effects of couple stress fluids on the performance of narrow porous journal bearings. A most general modified Reynolds equation is derived for narrow porous journal bearings using the Stokes constitutive equations for couple stress fluids. The fluid in the film region and in the porous region has been modelled as a couple stress fluid. The analysis takes into account velocity slip at the porous interface using the Beavers‐Joseph criterion. A closed‐form expression for field pressure is obtained for narrow journal bearings. Eigen‐type expressions for field variations are obtained. The dimensionless load‐carrying capacity, attitude angle, and coefficient of friction are presented for different operating parameters. It is observed that narrow porous journal bearings with couple stress fluids as lubricant show a significant increase in load‐carrying capacity with reduced coefficient of friction as compared to the Newtonian case. The present study predicts the effects of the percolation of polar additives (microstructures) into the porous matrix on the bearing performance.     

Metallized siligraphene nanosheets (SiC7) as high capacity hydrogen storage materials

Nano Research - A planar honeycomb monolayer of siligraphene (SiC7) could be a prospective medium for clean energy storage due to its light weight, and its remarkable mechanical and unique...     

Neutronic and thermal hydraulic analysis for production of fission molybdenum-99 at Pakistan Research Reactor-1

Neutronic and thermal hydraulic analysis for the fission molybdenum-99 production at PARR-1 has been performed. Low enriched uranium foil (<20% ²³⁵U) will be used as target material. Annular target designed by ANL (USA) will be irradiated in PARR-1 for the production of 100 Ci of molybdenum-99 at the end of irradiation, which will be sufficient to prepare required ⁹⁹Mo/^99mTc generators at PINSTECH and its supply in the country. Neutronic and thermal hydraulic analysis were performed using various codes. Data shows that annular targets can be safely irradiated in PARR-1 for production of required amount of fission molybdenum-99.     

Flow and energy fields in a resonant channel

The hydro- and thermodynamical processes near and within a two-dimensional resonant channel are simulated by numerical solution of the compressible Navier–Stokes, continuity, energy equations, and the equation of state (for air as the working fluid). The channel wall is maintained at a constant temperature and the effects of gas viscosity, and heat conduction of the gas are investigated concentrating on the time averaged velocity, temperature, energy flux density and energy streamlines in the gas. Energy streamline contours and energy flux density plots qualitatively agree with Merkli and Thomanns' [P. Merkli, H. Thomann, Thermoacoustic effects in a resonance tube. Journal of Fluid Mechanics, 70 (1975) 161–177.] observations. It is observed that energy transfer inside the channel consisted of two factors for the cases considered: one due to conduction term and the other due to enthalpy term. The results are applicable to thermoacoustic devices.     

Influence of fatty acids content in non-edible oil for biodiesel properties

Physical and chemical properties of biodiesel are influenced by the structural features of fatty acid, such as with saturated, monounsaturated and polyunsaturated fatty acids. In this study, seven non-edible oils have been selected, which include waste cooking oil derived palm olein, Calophyllum inophyllum, jatropha oil, castor oil, rubber seed oil, kapok seed oil and karanja oil. The critical parameters, e.g. cetane number (CN), iodine value (IV) and oxidation stability (OS) of biodiesel were correlated with the degree of unsaturated (DU) fatty acid, whereas the cold filter plugging point (CFPP) was correlated with the long chain saturated factor (LCSF). To meet the minimum EU requirement of EN 14214 of the critical parameter, the DU value of the CN was ≤133.5, IV ≤123.2 and OS ≤98.9. The LCSF values satisfied the Spanish regional standard—RD 61/2006 in summer (0 °C) at ≤8.4 and winter (?10 °C) at ≤0.1 of the CFPP. Based on the composition of the saturated, monounsaturated and polyunsaturated fatty acids, a triangular chart for the biodiesel property prediction was developed. This can then be used as a reference for non-edible oils.     

Prediction of gas hold‐up in a bubble column filled with pure and binary liquids

A dimensionless correlation for gas hold‐up in a bubble column filled with pure liquids and binary mixtures has been developed. The criteria of bubble coalescence in pure liquids and foamability of binary mixtures have been included successfully in the proposed correlation. For the first time, comprehensive data of gas hold‐up with respect to concentration in four binary systems are presented. The often‐reported enhancement of gas hold‐up in aqueous alcohol mixtures has been observed experimentally. The proposed correlation is able to predict successfully the trend of gas hold‐up enhancement with respect to concentration. The estimated values are found to be within 7% of the measured values.