Thermo-hydraulic performance investigation of solar air heater duct having staggered D-shaped ribs: Numerical approach

The thermohydraulic performance (THP) of a solar air heater (SAH) duct with staggered D-shaped ribs as roughness geometry is examined in this work using three-dimensional numerical investigation. The investigation is carried out at roughness parameters of radius of rib to transverse pitch (r/P_tv) ratios of 0.1–0.35 and longitudinal pitch to radius of rib (P_lg/r) ratios of 4–10 under varied operating circumstances of Reynolds number (Re) from 10,200 to 20,200. The maximum Nusselt number (Nu) is obtained to be 81.3 at Re of 20,200, r/P_tv as 0.1, and P_lg/r as 4. In contrast, the maximum friction factor (f) is obtained to be 0.0169 at Re of 10,200, r/P_tv as 0.35, and P_lg/r as 4. In the range of parameters examined, the maximum enhancement in Nusselt number (Nu/Nu_s) is observed to be 1.35 at an optimal parameter of r/P_tv as 0.1, P_lg/r as 4, and Re as 10,200. Correspondingly, the enhancement in the friction factor (f/f_s) at this optimum parameter is 1.87. The maximum value of the THP parameter is found to be 1.1 at the same optimum range of parameters. In further analysis, correlations were developed for Nusselt number (Nu) and friction factor (f) in terms of r/P_tv, P_lg/r, and Re with a deviation of ±2% and ±1.5%, respectively.     

Gate Current Modeling and Optimal Design of Nanoscale Non-Overlapped Gate to Source/Drain MOSFET

In this paper, novel nanoscale MOSFET with Source/Drain-to-Gate Non-overlapped and high-k spacer structure has been demonstrated to reduce the gate leakage current for the first time. The gate leakage behaviour of novel MOSFET structure has been investigated with help of compact analytical model and Sentaurus Simulation. Fringing gate electric field through the dielectric spacer induces inversion layer in the non-overlap region to act as extended S/D region. It is found that optimal Source/Drain-to-Gate Non-overlapped and high-k spacer structure has reduced the gate leakage current to great extent as compared to those of an overlapped structure. Further, the proposed structure had improved off current, subthreshold slope and DIBL characteristic. It is concluded that this structure solves the problem of high leakage current without introducing the extra series resistance.     

Assessment of Metal Contamination in the Mine Water of the West Bokaro Coalfield,India

This study was carried out in the West Bokaro coalfield area of the Jharkhand state of India to assess water quality for drinking and domestic purposes. Thirty mine water samples were collected from opencast and underground mines, and concentrations of Al, As, Ba, Cr, Cu, Fe, Mn, Ni, Se, and Zn were determined using ICP-MS. Spatial distribution maps were prepared using GIS software so that the quality of the mine water could be easily understood. Metal concentrations were higher in the pre-monsoon season than in the post-monsoon season, irrespective of location, but there were more significant seasonal variations in the opencast mine water than in the underground mine water. The concentrations of Al, Ba, Fe, Mn, and Ni exceeded the desirable as well as the permissible drinking water limits in both seasons. The quality of the surface water as well as the groundwater in the region may be adversely affected by the high metal concentrations in this mine water.     

Reactive power compensation of an isolated hybrid power system with load interaction using ANFIS tuned STATCOM

This paper presents an adaptive neuro fuzzy interference system (ANFIS) based approach to tune the parameters of the static synchronous compensator (STATCOM) with frequent disturbances in load model and power input of a wind-diesel based isolated hybrid power system (IHPS). In literature, proportional integral (PI) based controller constants are optimized for voltage stability in hybrid systems due to the interaction of load disturbances and input power disturbances. These conventional controlling techniques use the integral square error (ISE) criterion with an open loop load model. An ANFIS tuned constants of a STATCOM controller for controlling the reactive power requirement to stabilize the voltage variation is proposed in the paper. Moreover, the interaction between the load and the isolated power system is developed in terms of closed loop load interaction with the system. Furthermore, a comparison of transient responses of IHPS is also presented when the system has only the STATCOM and the static compensation requirement of the induction generator is fulfilled by the fixed capacitor, dynamic compensation requirement, meanwhile, is ful-filled by STATCOM. The model is tested for a 1% step increase in reactive power load demand at t = 0 s and then a sudden change of 3% from the 1% at t = 0.01 s for a 1% step increase in power input at variable wind speed model.     

Hydrogen and syngas production from sewage sludge via steam gasification

High temperature steam gasification is an attractive alternative technology which can allow one to obtain high percentage of hydrogen in the syngas from low-grade fuels. Gasification is considered a clean technology for energy conversion without environmental impact using biomass and solid wastes as feedstock. Sewage sludge is considered a renewable fuel because it is sustainable and has good potential for energy recovery. In this investigation, sewage sludge samples were gasified at various temperatures to determine the evolutionary behavior of syngas characteristics and other properties of the syngas produced. The syngas characteristics were evaluated in terms of syngas yield, hydrogen production, syngas chemical analysis, and efficiency of energy conversion. In addition to gasification experiments, pyrolysis experiments were conducted for evaluating the performance of gasification over pyrolysis. The increase in reactor temperature resulted in increased generation of hydrogen. Hydrogen yield at 1000 °C was found to be 0.076 g_gas g_sample⁻¹. Steam as the gasifying agent increased the hydrogen yield three times as compared to air gasification. Sewage sludge gasification results were compared with other samples, such as, paper, food wastes and plastics. The time duration for sewage sludge gasification was longer as compared to other samples. On the other hand sewage sludge yielded more hydrogen than that from paper and food wastes.     

Catalytic transformation of H2S for H2 production

Hydrogen sulfide (H₂S) gas is a by-product from natural gas refining, hydrodesulfurization of various fossil fuels, and syngas cleaning from pyrolysis and gasification. Catalytic pyrolysis of H₂S provides an alternative and effective pathway to recover both H₂ and sulfur. Catalysts from hydrotalcite of ZnAl, ZnNiAl, and ZnFeAl were employed for H₂S pyrolysis and compared with TiO₂ and MoS₂ at atmospheric pressure and temperatures in the range of 923–1123 K. Kinetic analysis was carried out in a packed bed reactor which revealed the effect of H₂S partial pressures to be of the order of 0.8–1 with respect to H₂S. The developed novel catalysts showed improved performance with significantly reduced activation energy compared to TiO₂ by 30 kJ/mol as well as higher H₂S conversion during pyrolysis (17% at 1173 K) than with MoS₂ catalyst, even at high H₂S partial pressure which is necessary for viable hydrogen production. The new approach showed an alternate economical and efficient pathway of catalyst design to obtain high activity and stability for simultaneous H₂ energy and pure sulfur recovery from unwanted H₂S resources.     

Growth and secretome analysis of possible synergistic interaction between green algae and cyanobacteria

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Evaluating the development of elastic anisotropy with plastic flow

It has been observed that many initially isotropic materials show the development of anisotropic elastic response after plastic flow. It is desirable to be able to model this change in the elastic properties as a function of the extent of plastic flow. This is particularly important when considering the traveling of waves in some glassy polymers that exhibit large differences in the wave moduli along the different directions resulting from unequal plastic flow in these directions. A thermodynamically based model of plasticity is developed and used to evaluate the elastic moduli associated with infinitesimal elastic deformations around the unloaded configuration. It is shown that for this model there are at least four independent material functions describing the elastic moduli of an initially isotropic material. These moduli are functions of the isotropic invariants of the right plastic Cauchy stretch tensor.