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Aerodynamic drag reduction is considered to be one of the most effective ways to minimize fuel consumption. Hence, this work focuses on reviewing some of the most promising passive flow control techniques for drag and lift reduction in automotive vehicles for enhanced stability and reduced fuel consumption. Firstly, the working physics behind different strategies, like deflectors, diffusers, spoilers, vortex generators, and flaps were elaborately discussed, followed by a detailed comparison among these techniques in terms of resultant drag and lift forces. Among several strategies, the gurney flap showed the huge potential of reducing 67.74% drag force with a slight increase in the lift force. Moreover, straight and concave deflectors can reduce lift force by 118.89% that will improve the aerodynamic stability of the vehicle by a large margin. This study reveals that a combination of a gurney flap, straight-concave deflector, angled fin diffuser, cylindrical vortex generator, and sports wing-lip spoiler is expected to provide the best aerodynamic performance and needs to be further investigated numerically and experimentally. The future scope of the current study is also presented at the end along with the current challenges associated with the implementation of various passive flow control techniques on road vehicles.

Penguins are the utmost specialized wing-propelled divers as their flapping action is accountable for the entire underwater propulsion. However, numerical evidence of how efficient their underwater propulsion is has not been studied to date. Literature sources suggest that propulsive efficiency peaks when the Strouhal number (St) ranges between 0.2 and 0.4. Therefore, in this study, using field data for free-ranging Little penguins, we estimated the range of Strouhal numbers for Little penguins and also investigated how this range varies with the shape and depth of dives to better understand the behavioural adaptations for underwater swimming. Moreover, it was argued by some researchers that the St value is not sufficient to ensure higher propulsive efficiency because St estimates are based on assumptions that might be incorrect; therefore, to evaluate the reliability of the St estimate, we also calculated the Reynolds and Swimming numbers. Those estimated values precisely designate that, as anticipated, penguins employ efficient propulsion mechanisms.

Understanding the drying kinetics within a food dryer is an important step towards its improvement. This study investigates the drying kinetics of potato slices in a recently proposed waste-heat based convective dryer. Statistical analyses are conducted for ten dissimilar mathematical models to choose the best fit model for the experimental data at various drying temperatures (70 °C, 60 °C, and 50 °C). Results show that the Midilli et al. model is the best fit model to describe the drying kinetics of potato in the proposed dryer as it offers root mean square error (RMSE) of 0.0022, a coefficient of determination (R2) of 0.99, reduced chi-square (χ2) of 9.2 ×10−7. Results also demonstrate that the activation energy is 47.19 kJ⁄mol and the effective moisture diffusivity of dried potato sample is 4.22 ×10−10 to 11.67 × 10−10 m2/s at a drying air temperature of 50–70 °C. Moreover, if the proposed waste-heat based convective dryer is used instead of an electric convective dryer at 60 °C, it can reduce the external energy requirement by 29.98 MJ/kg. Exergo-environmental analysis of the proposed dryer shows that the CO2 emission and CO2 mitigation values for 20-year life cycle periods are 184.46 kg/year and 17.24 tons, respectively. Therefore, successful industrial application of the proposed drying system might be a striding stone towards the advancement of energy-efficient sustainable food drying systems.

Energy insufficiency is obstructing the socio-economic and industrial improvement of Bangladesh. Renewable energy contributes about 560 Megawatt (MW) of the total electricity production of 20,430 MW, which can be a sustainable solution to the demand-supply crisis. This paper, summarises the current energy situation of Bangladesh and examines the available renewable energy resources and their future prospect. It has been revealed that Bangladesh is heavily (62%) relying on natural gas although government has already taken steps to generate electricity from renewable energy sources. Current policies and legislations related to generation of renewable energy in Bangladesh have been discussed explicitly. Finally, some suggestions have been made to tackle the ongoing energy crisis in the country, in addition to the renewable energy.Abbreviations: GDP: Gross domestic product; RNPP: Rooppur Nuclear Power Plant; Tcf: Trillion cubic feet; IDCOL: Infrastructure development company limited; BPDB: Bangladesh Power Development Board: GS: Grameen Shakti; BWDB: Bangladesh Water Development Board: USD: United States Dollar; IPP: Independent power producer: BCAS: Bangladesh center for advanced studies; NWPGCL: North West Power Generation Company Limited: BCSIR: Bangladesh Council of Scientific and Industrial Research; EGCB: Electricity Generation Company of Bangladesh: WRA: Wind Resource Assessment; REB: Rural Electrification Board: BRAC: Bangladesh Rural Advancement Committee; kW: Kilowatt: PJ: Petajoules; MW: Megawatt: IFRAD: Institute for fuel research and Development; GWh: Gigawatt hours: ICS: Improved Cooking Stoves; MWh: Megawatt hours: DoE: Department of Environment; TWh: Trillion-watt hour: DLS: Department of Livestock Services; RPCL: Rural Power Company Limited: mmcfd: million cubic feet per day; APSCL: Ashugang Power Station Company Limited: BSCIC: Bangladesh Small & Cottage Industries Corporation (BSCIC); GOB: Government of Bangladesh: BADC: Bangladesh Agricultural Development Corporation; SREDA: Sustainable and Renewable Energy Development Authority: DIDA: Danish International Development Agency; LGED: Local Government Engineering Directorate: BAU: Bangladesh Agricultural University; NGO: Non-Governmental Organization: HBRI: Housing & Building Research Institute; IRENA: International Renewable energy Agency: : BARD: Bangladesh Academy for Rural Development; ETP: Electronic Traffic Pricing: BCCD: Bangladesh Commission for Christian Development; PV: Photovoltaic: BRRI: Bangladesh Rice Research Institute; SHS: Solar Home Systems: NDBMP: National Domestic Biogas and Manure Program; TOE: Tonne of oil equivalent: K/km: Kelvin/kilometer; LEAP: Long range Energy Alternative Planning