mAOR: A heuristic-based reactive repair mechanism for job shop schedules

Literature on job shop scheduling has primarily focused on the development of predictive schedules that generate an allocation sequence of jobs on machines. However, in practice, frequent deviations from a predictive schedule occur when the job shop experiences either external (e.g. unexpected arrival of urgent jobs) or internal disturbances (e.g. machine breakdowns) and renders the schedules inefficient. The reactive repair of the original schedule is a better alternative to total rescheduling, as the latter is not only time consuming but also leads to shop floor nervousness. Most of the existing schedule repair heuristics handle singular disruptions only. In this paper, the typical job shop disruptions are studied and their repair processes are decomposed into four generic repair steps, which are achieved using the proposed modified AOR (mAOR) heuristic. An extensive simulation study has also been conducted to evaluate the performance of the mAOR schedule repair heuristic, and the results indicate that the mAOR heuristic is effective in repairing job shop schedules when faced with disruptions.     

Enhancing methane production by anaerobic co-digestion of extruded organic wastes from slaughterhouse and vegetable market in batch and continuous processes

Clean Technologies and Environmental Policy - The organic wastes generated from centralized wholesale markets from urban centres are predominantly disposed in dumpsites/landfills. Although...     

Dynamic simulation of accidental closure of intermediate heat exchanger isolation valve in a pool type LMFBR

In a pool type liquid metal cooled fast breeder reactor (LMFBR), core and other internals such as pumps, heat exchangers are immersed in a pool of sodium. Heat exchange from primary sodium circuit (pool) to secondary sodium circuit (loop) is through four intermediate heat exchangers (IHX) immersed in primary sodium pool. Each IHX is provided with a sleeve valve at its primary sodium inlet window for the purpose of isolating the shell side of IHX from the sodium pool. With such a provision, an inadvertent partial or complete closure of a sleeve valve of one of the IHX during normal operation of the reactor has been considered as a design basis event for the reactor. One dimensional transient thermal hydraulic models of the primary and secondary sodium circuits have been developed to study the thermal hydraulic consequences of such an event. The main areas of concern in the plant and the availability of safety parameters for the detection of the event have been evaluated.     

Computational fluid dynamic investigations and experimental validation of frozen seal sodium valve assembly of a fast reactor

Frozen seal sodium valves are used in fast reactors. To achieve sodium freezing, horizontal fins are attached to the outer surface of valve sheath. Adjacent fins form open-ended cavities and natural convection of air in these cavities is investigated using the PHOENICS code for various values of fin length, spacing and root temperature. It is seen that convective air does not penetrate deep into shallow cavities leading to poor heat transfer coefficient, offsetting the enhancement in surface area. Penetration depth of air is a function of aspect ratio and Rayleigh number based on fin spacing and is independent of fin length. Generalized correlations are derived for Nusselt number in terms of Rayleigh number and aspect ratio. Using these correlations, temperature distribution in entire valve assembly is predicted using the HEATING5 code, to select an optimum design. Experiments have been conducted on a model valve of selected design in the SILVERINA facility available at this centre. Measured stem temperature distribution is found to compare satisfactorily with HEATING5 predictions, validating the correlations derived from computational fluid dynamic studies and integrated thermal analysis methodology.     

Overview of pool hydraulic design of Indian prototype fast breeder reactor

Thermal hydraulics plays an important role in the design of liquid metal cooled fast breeder reactor components, where thermal loads are dominant. Detailed thermal hydraulic investigations of reactor components considering multi-physics heat transfer are essential for choosing optimum designs among the various possibilities. Pool hydraulics is multi-dimensional in nature and simple one-dimensional treatment for the same is often inadequate. Computational Fluid Dynamics (CFD) plays a critical role in the design of pool type reactors and becomes an increasingly popular tool, thanks to the advancements in computing technology. In this paper, thermal hydraulic characteristics of a fast breeder reactor, design limits and challenging thermal hydraulic investigations carried out towards successful design of Indian Prototype Fast Breeder Reactor (PFBR) that is under construction, are highlighted. Special attention is paid to phenomena like thermal stratification, thermal stripping, gas entrainment, inter-wrapper flow in decay heat removal and multi-physics cellular convection. The issues in these phenomena and the design solutions to address them satisfactorily are elaborated. Experiments performed for special phenomena, which are not amenable for CFD treatment and experiments carried out for validation of the computer codes have also been described.     

A fundamental approach to specify thermal and pressure loadings on containment buildings of sodium cooled fast reactors during a core disruptive accident

Reactor Containment Building (RCB) is the ultimate barrier to the environment against activity release in any nuclear power plant. It has to be designed to withstand both positive and negative pressures that are credible. Core Disruptive Accident (CDA) is an important event that specifies the design basis for RCB in sodium cooled fast reactors. In this paper, a fundamental approach towards quantification of thermal and pressure loadings on RCB during a CDA, has been described. Mathematical models have been derived from fundamental conservation principles towards determination of sodium release during a CDA, subsequent sodium fire inside RCB, building up of positive and negative pressures inside RCB, potential of in-vessel sodium fire due to failed seals and temperature evolution in RCB walls during extended period of containment isolation. Various heating sources for RCB air and RCB wall and their potential have been identified. Scaling laws for conducting CDA experiments in small-scale water models by chemical explosives and the rule for extrapolation of water leak to quantify sodium leak in reactor are proposed. Validation of the proposed models and experimental simulation rules has been demonstrated by applying them to Indian prototype fast breeder reactor. Finally, it is demonstrated that in-vessel sodium fire potential is very weak and no special containment cooling system is essential.     

Dynamic model of Fast Breeder Test Reactor

Fast Breeder Test Reactor (FBTR) is a 40 M Wt/13.2 MWe sodium cooled reactor operating since 1985. It is a loop type reactor. As part of the safety analysis the response of the plant to various transients is needed. In this connection a computer code named DYNAM was developed to model the reactor core, the intermediate heat exchanger, steam generator, piping, etc. This paper deals with the mathematical model of the various components of FBTR, the numerical techniques to solve the model, and comparison of the predictions of the code with plant measurements. Also presented is the benign response of the plant to a station blackout condition, which brings out the role of the various reactivity feedback mechanisms combined with a gradual coast down of reactor sodium flow.     

Temperature-aware computer systems: Opportunities and challenges

Temperature-aware design techniques have an important role to play in addition to traditional techniques like power-aware design and package- and board-level thermal engineering. The authors define the role of architecture techniques and describe hotspot, an accurate yet fast thermal model suitable for computer architecture research.     

Quinoxaline-Based X-Shaped Sensitizers as Self-Assembled Monolayer for Tin Perovskite Solar cells

Four X-shaped quinoxaline-based organic dyes, PQx (1), TQx, (2), PQxD (3), and TQxD (4) (D = dye sensitizers) are developed and served as p-type self-assemble monolayer (SAM) for tin perovskite solar cells (TPSC). Thermal, optical, and electrochemical properties of these SAMs are thoroughly investigated and characterized. Tin perovskite layers are successfully deposited on these four SAM surfaces according to a two-step approach and the devices exhibit power conversion efficiency in the order of TQxD (8.3%) > TQx (8.0%) > PQxD (7.1%) > PQx (6.1%). With thiophene π-extended conjugation unit in SAM structure, TQxD (4) exhibits the highest hole extraction rates, greatest hole mobilities, and slowest charge recombination to achieve great device performance of 8.3%, which is the current best result for SAM-based TPSC ever reported. Furthermore, all devices except PQx shows great enduring stability for the performance retaining ≈90% of their original values for shelf storage over 1600 h.     

Correction to: CS-CGMP: Clustering Scheme Using Canada Geese Migration Principle for Routing in Wireless Sensor Networks

Wireless Personal Communications - There was a mix-up of Figs. 5-8 in the initial, online publication.