Bio-char has the ability to isolate carbon in soils and concurrently improve plant growth and soil quality, high energy density and also it can be used as an adsorbent for water treatment. In the current work, the characteristics of four different types of bio-chars, obtained from slow pyrolysis at 375 °C, produced from hard-, medium-, thin- and paper-shelled walnut residues have been studied. Bio-char properties such as proximate, ultimate analysis, heating values, surface area, pH values, thermal degradation behavior, morphological and crystalline nature and functional characterization using FTIR were determined. The pyrolytic behavior of bio-char is studied using thermogravimetric analysis (TGA) in an oxidizing atmosphere. SEM analysis confirmed morphological change and showed heterogeneous and rough texture structure. Crystalline nature of the bio-chars is established by X-ray powder diffraction (XRD) analysis. The maximum higher heating values (HHV), high fixed carbon content and surface area obtained for walnut shells (WS) samples are found as ~ 18.4 MJ kg⁻¹, >80% and 58 m²/g, respectively. Improvement in HHV and decrease of O/C and H/C ratios lead the bio-char samples to fall into the category of coal and confirmed their hydrophobic, carbonized and aromatized nature. From the Fourier transform infra-red spectroscopy (FTIR), it is observed that there is alteration in functional groups with increase in temperature, and illustrated higher aromaticity. This showed that bio-chars have high potential to be used as solid fuel either for direct combustion or for thermal conversion processes in boilers, kilns and furnace. Further, from surface area and pH analysis of bio-chars, it is found that WS bio-chars have similar characteristics of adsorbents used for water purifications, retention of essential elements in soil and carbon sequestration.

The forecasting of ionospheric electron density has been of great interest to the research scientists and engineers’ community as it significantly influences satellite-based navigation, positioning, and communication applications under the influence of space weather. Hence, the present paper adopts a long short-term memory (LSTM) deep learning network model to forecast the ionospheric total electron content (TEC) by exploiting global positioning system (GPS) observables, at a low latitude Indian location in Bangalore (IISC; Geographic 13.03° N and 77.57° E), during the 24th solar cycle. The proposed model uses about eight years of GPS-TEC data (from 2009 to 2017) for training and validation, whereas the data for 2018 was used for independent testing and forecasting of TEC. Apart from the input TEC parameters, the model considers sequential data of solar and geophysical indices to realize the effects. The performance of the model is evaluated by comparing the forecasted TEC values with the observed and global empirical ionosphere model (international reference ionosphere; IRI-2016) through a set of validation metrics. The analysis of the results during the test period showed that LSTM output closely followed the observed GPS-TEC data with a relatively minimal root mean square error (RMSE) of 1.6149 and the highest correlation coefficient (CC) of 0.992, as compared to IRI-2016. Furthermore, the day-to-day performance of LSTM was validated during the year 2018, inferring that the proposed model outcomes are significantly better than IRI-2016 at the considered location. Implementation of the model at other latitudinal locations of the region is suggested for an efficient regional forecast of TEC across the Indian region. The present work complements efforts towards establishing an efficient regional forecasting system for indices of ionospheric delays and irregularities, which are responsible for degrading static, as well as dynamic, space-based navigation system performances.

Electronic gadgets have been designed to incorporating very small components such as microcontrollers, electronic chips, transistors, microprocessors, etc. These components are exceptionally heat sensitive and can be wrecked if heat is not released. As a result, the thermal control of such components is critical to their optimum performance and extended life. The use of a microchannel heat sink (MCHS) has shown promising solutions to remove the excess heat. In this paper, we have proposed a novel design of MCHS and investigated it numerically. Four different surface modifications on the sidewall of the passage, namely, extended triangular surface (ETS), extended circular surface (ECS), triangular groove surface (TGS), and the circular groove surface (CGS) in the passage of the microchannel have been exploited in the Reynolds number of 100–900. In the presence of geometrical modification, the cooling capacities have been enhanced. The results show that the Nusselt numbers of ETS-MCHS, ECS-MCHS, TGS-MCHS, and CGS-MCHS are increased by 4.30, 3.61, 1.62, and 1.41 times in comparison to the Nusselt number of MCHS with smooth passage, while the friction factor values are increased by 7.33, 6.03, 2.74, and 1.68 times, respectively. In addition, the thermohydraulic performance parameter (THPP) has been evaluated and discussed. The fact that MCHS have THPP values greater than unity demonstrates that the passage’s geometries are a practical means of achieving effective thermal management.

In this paper, the impact of an extended surface on the passage of a microchannel using cylindrical ribs with variable sector angles on heat transfer rate is presented using computer simulation. Extended surfaces in the form of cylindrical ribs of varying sector angles in the passage of microchannel in a staggered manner have been designed. The sidewalls of a new kind of microchannel incorporating five distinct ribs with sector angles ranging from 45° to 80° have been analyzed. Ansys Fluent workbench software has been exploited to simulate this novel design of a microchannel heat sink. A three-dimensional heat transfer and fluid flow model of the microchannel heat sink (MCHS) was developed, and the fluid and solid regions were discretized in very fine meshes. All CFD simulations were performed for Reynolds numbers between 100 and 900. Nusselt numbers are varied in the following ranges: 6.93 to 13.87, 6.93 to 14.38, 6.93 to 17.80, 7.15 to 27.86, and 7.20 to 37.38 at sector angles of 45°, 50°, 60°, 70°, and 80°, respectively. It is concluded that the Nusselt number is strongly influenced by the Reynolds number. At an angle of 80°, the maximum friction factor and pumping power requirements were observed. Additionally, a 45° angle has been proven to be the minimal friction factor and pumping power requirement. It is revealed that the THPP has all values larger higher than 1. At angles of 80° and 45°, the maximum and minimum values of THPP have been discovered, respectively. In addition, thermo-hydraulic performance parameters have been evaluated, which are greater than one for all sector angles.

In this paper, six different shape obstacles, namely, Isosceles trapezoid (Type 1), Triangular with curve apex (Type 2), Rectangular with chamfered edges (Type 3), Rectangular with curve edges (Type 4), Triangular with curve corner at bottom (Type 5) and Triangular shape (Type 6) have been tested in inline and staggered fashions in solar air heater (SAH) duct. This work aims to investigate the effect of obstacle shape on heat transfer and friction characteristics. All experiments have been carried out at eight different values of Reynolds number ranging from 2000 to 16000 and fixed value of heat flux of 1000 W/m². As results, Nusselt number and friction factor characteristics have been presented and discussed. The maximum enhancement in Nusselt number and friction factor are observed in case isosceles trapezoid obstacles (Type 1) and rectangular with curve edges obstacles (Type 4) when mounted in staggered fashion, respectively and their respective average enhancement factor in Nusselt number and friction factor are observed as 2.95 and 4.37. Also, thermo-hydraulic performance parameter (η) of all obstacles in both arrangement have been evaluated and found to be average maximum values 1.88 in case of isosceles trapezoid obstacles (Type 1) in staggered manner.