Nowadays, applications of turbulent fluid flow in removing high heat flux in rib-roughened narrow channels are drawing much interest. In this work, an improved version of the κ-ε turbulence model is proposed for better prediction of thermal–hydraulic characteristics of flow inside rib-roughened (pitch-to-rib height (p/k) ratio = 10 and 20) narrow channels (channel height, H = 1.2 mm and 3.2 mm). For this, the four turbulence model parameters, C_μ, C_ε1, C_ε2, and σ_k, are calibrated. These parameters are adjustable empirical constants provided for controlling the accuracy of the turbulence model results when needed. The simulated data are used to develop correlations between the relative errors in predicting the friction factor (f), Nusselt number (Nu), and the model parameters using a multivariate nonlinear regression method. These correlations are used to optimize the errors using genetic algorithm. Results reveal that the calibrated parameters are not the same for all the narrow channel configurations. After calibration, the overall predictive improvements are up to 35.83% and 27.30% for p/k = 10 and p/k = 20 respectively when H = 1.2 mm. Also, up to 15.48% and 18.05% improvements are obtained for p/k = 10 and p/k = 20 respectively when H = 3.2 mm. The role of the two parameters C_ε1 and C_ε2 are found to be of primary importance. Furthermore, three types of nanofluids i.e. Al₂O₃-water, CuO-water, and TiO₂-water are studied using the calibrated model to check the potentiality of heat transfer enhancement. Among them, CuO-water nanofluid is predicted to have around 1.32 times higher value of Nu than pure water for the same narrow channel configuration. Article Highlights: κ-ε turbulence model is calibrated for rib-roughened narrow rectangular channels using genetic algorithm. Cε1 and Cε2 are the most influential parameters on the performance of the model inside rib-roughened narrow channel. Suggested calibration process is more effective for channel height of 1.2 mm than 3.2 mm.

Sawmill workers in Bangladesh are increasingly at risk of emerging work-related musculoskeletal disorders (WRMSDs). Their jobs involve awkward manual handling tasks such as lifting, carrying, pushing and pulling. These are identified as risk factors for musculoskeletal disorders. The aims of this study are to find out the prevalence of musculoskeletal disorders and assessing the postural risk level among sawmills workers. This cross-sectional study was conducted with 254 workers from 60 sawmills at the southern part of Bangladesh. The overall 70.1% of sawmills workers were suffering musculoskeletal disorders in at least one body part for the last one year. The average Rapid Entire Body Assessment (REBA) score of four main tasks (Pushing, Pulling, Lifting, and Carrying the timber) was 9.25, which is high risk for MSDs symptoms. The main reasons behind these MSDs are lack of knowledge about workplace safety, working postures and the settings of the workplace. We have recommended to the management to apply the NIOSH (National Institute for Occupational Safety and Health) lifting and Manual Material handling techniques; arrange OSHA (Occupational Safety and Health Administration) ergonomic training to the workers. Also, suggested designing the working table and workplaces in ergonomically to mitigate the musculoskeletal disorders.

Three-dimensional numerical investigations of a novel passive micromixer were carried out to analyze the hydrodynamic and thermal behaviors of Nano-Non-Newtonian fluids. Mass and heat transfer characteristics of two heated fluids have been investigated to understand the quantitative and qualitative fluid faction distributions with temperature homogenization. The effect of fluid behavior and different Al₂O₃ nanoparticles concentrations on the pressure drop and thermal mixing performances were studied for different Reynolds number (from 0.1 to 25). The performance improvement simulation was conducted in intervals of various Nanoparticles concentrations (φ = 0 to 5%) with Power-law index (n) using CFD. The proposed micromixer displayed a mixing energy cost of 50–60 comparable to that achieved for a recent micromixer (2021y) in terms of fluid homogenization. The analysis exhibited that for high nanofluid concentrations, having a strong chaotic flow enhances significantly the hydrodynamic and thermal performances for all Reynolds numbers. The visualization of vortex core region of mass fraction and path lines presents that the proposed design exhibits a rapid thermal mixing rate that tends to 0.99%, and a mass fraction mixing rate of more than 0.93% with very low pressure losses, thus the proposed micromixer can be utilized to enhance homogenization in different Nano-Non-Newtonian mechanism with minimum energy.