Radionuclide concentrations in sand samples from riverbanks of Muzaffarabad,Azad Kashmir

This paper presents the results of a radiological risk assessment arising from the presence of naturally occurring radionuclides in sand samples from three riverbanks in Muzaffarabad.The mean values obtained for 232 Th,226 Ra,and 40 K were found to be 44.58 ± 3.34,48.25 ± 1.77,and 239.92 ± 22.73 Bq kg~(-1),respectively.To assess the uniformity of exposure,the radium equivalent activity(Raeq) was calculated and was found to be130.47 ± 8.29 Bqkg~(-1).The current reported value for Raeqis lower than the maximum permissible value,that is,370 Bq kg~(-1),and equivalent to a gamma dose of1.5 m Svy~(-1).To investigate the possible contribution to health risks of alpha particle exposure,the radon exhalation rate(RER) from the sand samples was determined.The mean RER for all the samples was found to be335 m Bq m-~(2) h~(-1).About 43% of the samples were found to have an indoor excess lifetime cancer risk value slightly higher than recommended safety limit of 1,as proposed by the ICRP.A normalized parameter,the equivalent multiplicative factor,was defined and used to compare the current results with the findings of studies performed in other countries.Our findings are relevant to both human health and future environmental radiation monitoring.     

Maximum density effects on buoyancy-driven convection in a porous trapezoidal cavity

A numerical study of the steady buoyancy-induced flow and heat transfer in a trapezoidal cavity filled with a porous medium saturated with cold water at a temperature around 4 °C has been performed. The analysis has been done for a cavity with different aspect ratios ranging from 0.25 to 0.75 and Rayleigh numbers ranging from 100 to 1000 using a finite-difference method. It is found that four cells are formed inside the cavity independent of the Rayleigh number and aspect ratio. The existence of buoyancy force reversal resulting from the maximum density effect, leads to a reduction in the strength of the convective flow and also the average Nusselt number.     

Numerical sensitivity analysis of temperature-dependent reaction rate constants for optimized thermal conversion of high-density plastic waste into combustible fuels

The use of experimental rate constants for producing a high yield of liquid fuels from the pyrolysis of plastic waste is not widely accepted owing to a lack of compatibility between the different kinetic rate constants responsible for successful conversion reactions. In R software, the Arrhenius law can forecast the ideal combination of reaction rate constants and frequency factors and then perform sensitivity analysis on individual rate constants to estimate the selectivity and quantity of primary pyrolysis products. Sensitivity analysis is a way of determining the effectiveness of individual rate constants in the reaction. This research element is currently lacking in the literature for the cost-effective valorization of plastics into combustible fuels. We are the first to use R software to perform sensitivity analysis on specific rate constants by reducing or raising their initial values to a point where maximum oil yield is attainable in the temperature range of 340–370°C. The primary focus was to save time and cost of extracting empirical rate constants from experiments to produce commercial-scale pyrolytic oil. The H-abstraction, chain fission, polymerization, and scission reactions were chosen due to the high availability of free radicals for maximum oil production. The oil recovery rate improved drastically to 90% at the end of processing time, while the number of by-products gradually decreased. The k8 rate constant driven reaction is the best-suited condition for industrial-scale pyrolysis of high-density plastics into liquid fuels, with 74% improvement in oil production and 14% improvement in light wax during sensitivity analysis.