Avinash Chandra

Momentum and Heat Transfer from a Semi-Circular Cylinder to Power-Law Fluids in the Vortex Shedding Regime

Flow and heat transfer from a semi-circular cylinder to power-law fluids has been studied in the laminar vortex shedding regime for the range of conditions as follows: Reynolds number, 40 ≤ Re ≤ 140; Prandtl number, 0.7 ≤ Pr ≤ 50; and power-law index, 0.2 ≤ n ≤ 1.8. Extensive results are presented in terms of the streamline, vorticity and isotherm profiles, drag and lift coefficients, Strouhal number, and Nusselt number. The influence of Reynolds number, Prandtl number, and power-law index are seen to be more prominent in shear-thinning fluids (n < 1) than that in shear-thickening (n > 1) fluids. The shear-thinning fluid behavior enhances the rate of heat transfer, whereas shear-thickening fluid behavior impedes it.

Measurement of residence time distribution of liquid phase in an industrial-scale continuous pulp digester using radiotracer technique

A series of radiotracer experiments was carried out to measure residence time distribution (RTD) of liquid phase (alkali) in an industrial-scale continuous pulp digester in a paper industry in India. Bromine-82 as ammonium bromide was used as a radiotracer. Experiments were carried out at different biomass and white liquor flow rates. The measured RTD data were treated and mean residence times in individual digester tubes as well in the whole digester were determined. The RTD was also analyzed to identify flow abnormalities and investigate flow dynamics of the liquid phase in the pulp digester. Flow channeling was observed in the first section (tube 1) of the digester. Both axial dispersion and tanks-in-series with backmixing models preceded with a plug flow component were used to simulate the measured RTD and quantify the degree of axial mixing. Based on the study, optimum conditions for operating the digester were proposed.

Residence time distribution studies using radiotracers in chemical industry—A review

ABSTRACT Use of radiotracer in residence time distribution (RTD) studies in industrial as well as lab scale systems has been emphasized in this review. The advantages of radiotracer over conventional tracers are discussed. The injection and detection protocols of the radiotracers are explained. The pretreatment of RTD data obtained and RTD modeling are explained using industrial- and laboratory-scale studies. The detailed RTD studies in (i) oil and gas, (ii) pharmaceuticals and bioprocesses, (iii) fertilizers and pesticides, (iv) polymer, plastic and fiber, (v) mineral processing, organic and inorganic chemicals, (vi) laboratory scale, (vii) pilot plant scale, and (viii) wastewater treatment processes are considered for this review. The case studies are also explained with RTD experiments. The current trend on the application of radiotracer technology in industry is also explained.