Laltu Chandra

Bio: Laltu Chandra is an academic researcher from Indian Institute of Technology (BHU) Varanasi. The author has contributed to research in topics: Heat transfer & Heliostat. The author has an hindex of 11, co-authored 54 publications receiving 346 citations. Previous affiliations of Laltu Chandra include Indian Institutes of Technology & Government College.

Quantifying differences between computational results and measurements in the case of a large-scale well-confined fire scenario

Abstract: The objective of this work was to quantify comparisons between several computational results and measurements performed during a pool fire scenario in a well-confined compartment. This collaborative work was initiated under the framework of the OECD fire research program and involves the most frequently used fire models in the fire community, including field and zone models. The experimental scenario was conducted at the French Institut de Radioprotection et de Surete Nucleaire (IRSN) and deals with a full-scale liquid pool fire in a confined and mechanically ventilated compartment representative for nuclear plants. The practical use of different metric operators and their ability to report the capabilities of fire models are presented. The quantitative comparisons between measurements and numerical results obtained from "open" calculations concern six important quantities from a safety viewpoint: gas temperature, oxygen concentration, wall temperature, total heat flux, compartment pressure and ventilation flow rate during the whole fire duration. The results indicate that it is important to use more than one metric for the validation process in order to get information on the uncertainties associated with different aspects of fire safety. (C) 2010 Elsevier B.V. All rights reserved. (Less)

A stepwise development and validation of a RANS based CFD modelling approach for the hydraulic and thermal-hydraulic analyses of liquid metal flow in a fuel assembly

Abstract: The demand of reliable and clean energy at affordable prices poses a formidable challenge to the world. The initiatives from various international organizations reserve an important role for liquid metal cooled reactor systems. Assessment of such reactors usually involves unconventional thermal-hydraulics. Consequently, Reynolds Averaged Navier Stokes (RANS) based Computational Fluid Dynamics (CFD) approaches are expected to play a vital role along with various ongoing experiments for the design and the safe operation of these nuclear reactors. One of the major issues is the heat transport in the fuel assembly by the liquid metal. The known difficulties in heat transfer experiments, especially with liquid metals, necessitate the application of RANS in computing details of flow and temperature distribution. Considering these aspects, a four step approach is described in the current paper. As a first step, the heat transfer in a liquid metal flow inside a heated tube is analyzed using a RANS approach and then compared with some of the empirical correlations. The computed Nusselt number reveals the required development length of the thermal boundary layer in liquid metal. Furthermore, these simulations reveal the need of further assessment of this approach and all the existing correlations, and the care that should be taken while applying one of these correlations. In the second step, numerical simulations of the flow of heavy liquid metal around a heated rod in an annular cavity confirm that a RANS strategy can be employed in liquid metal flows. Furthermore, a comparison between computed and experimental non-dimensional axial temperature at the heated rod surface shows that among the considered turbulence models the use of a Baseline-Reynolds Stress Model (BSL-RSM) with automatic wall treatment (AWT) can be preferred for complex geometries. This is also demonstrated in the third step by computing the flow distribution in a triangular arrangement of a fuel assembly and by comparing with an existing hydraulics experiment in rod-bundle. These analyses reveal that the use of the BSL-RSM turbulence model with AWT allows prediction of the cross-flow in this rod-bundle. As the forth and last step, the integral TEGENA (TEmperatur- und GEschwindigkeitsverteilungen in Stabbundel mit turbulenter NAtriumstromung) experiment has been selected for further assessment of RANS based CFD approach in computing both the flow and temperature field. A comparison with literature demonstrates that the use of symmetric boundary condition in such a tightly packed parallel rod-bundle leads to a distorted flow field. The experimentally and the computationally obtained temperature field at a plane in the outlet reveal its acceptable predictive capability. Furthermore, application of two different Reynolds Stress Models yields almost the same temperature distribution as a result of the use of simple first-order gradient model for the turbulent heat fluxes. Consequently, these four steps support the use of this modelling approach for investigating the heat transport in (heavy) liquid metals. Finally, the preferred RANS approach has been applied for thermal-hydraulic evaluation in the square arrangement of a bare rod-bundle as is to be employed in the European Lead-cooled reactor System (ELSY). Also, the influence of rod pitch-to-diameter ratio has been analyzed by numerically re-arranging these rods in the different square lattice. Moreover, arranging the bare rods in triangular lattice at the different rod pitch-to-diameter ratios shows the effect of the square and triangular lattice in thermal-hydraulics. Lastly, comparisons with some of the existing heat transfer correlations for the triangular and the rectangular lattice allows us to identify preferred correlations for these lattice arrangements of bare and liquid metal cooled rod-bundles.

Solar tower based aluminum heat treatment system: Part I. Design and evaluation of an open volumetric air receiver

Abstract: Electrical energy is employed for processing operations of material, such as, smelting, soaking and heat treatment. During this process, fossil, coal, and nuclear as a fuel is employed. Extraction and use of these fuel sources have serious environmental implications. Moreover, the employed process involves conversion of fuel to heat and then to electricity. Double conversion process can be avoided by directly introducing hot air provided by a solar tower equipped with a volumetric air receiver into a retrofitted furnace. This is a clean, green alternative for generating high temperatures required for metals processing operations. Initially a system would be developed for the heat treatment of aluminum, which requires temperature between 290 and 400 °C. A survey of the literature shows that quantitative design basis of individual volumetric air receiver components is conspicuous by its absence. Hence the objective of this investigation has been to use principles of fluid flow and heat transfer to design individual components of an Open Volumetric Air Receiver (OVAR) system. Experiments on a 2 kW th Solar Air Tower Simulator system (SATS) validate the process used in designing individual components of the OVAR. The ultimate aim of this research is to develop a system that can be used for heat treatment of steels and other possible extractive metallurgy operations such as the smelting of metals from its ores.

Simulating fuel assemblies with low resolution CFD approaches

Abstract: In addition to the traditional fuel assembly simulations using system codes, subchannel codes or porous medium approaches, as well as detailed CFD simulations to analyze single sub channels, a Low Resolution Geometry Resolving (LRGR) CFD approach and a Coarse-Grid-CFD (CGCFD) approach are taken. Both methods are based on a low resolution mesh that allows the capture of large and medium scale flow features such as recirculation zones, which are difficult to be reproduced by the system codes, subchannel codes and porous media approaches. The LRGR approach allows for instance fine-tuning the porous parameters which are important input for a porous medium approach. However, it should be noted that the prediction of detailed flow features such as secondary flows (small flows in the direction perpendicular to the main flow) is not feasible. Using this approach, the consequences of flow blockages for detection possibilities and cladding temperatures can be discussed. The goal of the CGCFD approach with SGM is that it can be applied to simulate complete fuel assemblies or even complete cores capturing the unique features of the complex flow induced by the fuel assembly geometry and its spacers. In such a case, grids with a very low grid resolution are employed. Within the CGCFD a subgrid model (SGM) accounts for sub grid volumetric forces which are derived from validated CFD simulations. The volumetric forces take account of the non resolved physics due to the coarse mesh. The current paper discusses and presents both, the CGCFD and the LRGR approaches.

On the design and evaluation of open volumetric air receiver for process heat applications

Abstract: India receives abundant radiant energy from the sun on account of being located at the equatorial solar belt. Especially, an annual global solar radiation of about ⩾2400 kW h/m2 is received in Rajasthan and in northern Gujarat. As a part of research initiative at IIT Jodhpur, heliostat based concentrated solar tower using an open volumetric air receiver is being developed for generation of high-temperature process heat, which can be utilized for metal processing operations. This technology includes sub-systems such as thermal energy storage and heat exchangers. In particular, the presented paper describes the design evaluation of an open volumetric air receiver. Experiments and computational fluid dynamics tool, ANSYS-FLUENT are used for this purpose. The obtained hot air (heat transfer fluid) can be employed, for instance, in heat treatment of metal such as Aluminum. The considered design aspects of the open volumetric air receiver are as follows: a. Influence of material thermal conductivity on the heat transfer modelling and thermally induced flow instability; b. Thermal–hydraulic analysis of recirculating air injection system; c. Influence of absorber porosity on the heat transfer using the performed experiments; d. Design and evaluation of the designed mixer-assembly for uniform and non-uniform heating of porous absorber. In this paper, the first section presents order-of-magnitude analysis to quantify the effect of thermal conductivity of the solid on heat transfer process with porous absorbers. The second section deals with analysis of thermally induced flow instability in porous absorbers with the validated and numerically adopted computational fluid dynamics tool, namely, FLUENT using the reported experiment by Fend et al. (2004a). In addition, the effect of thermal conductivity on thermally induced flow instability is presented. The next section presents three-dimensional analysis of the designed mixer-assembly for receiver using the validated CFD tool FLUENT. For this purpose, analyses are performed with different designs of mixer-plate and for different receiver geometries. Further, based on the detailed analysis, the injection mechanisms of recirculating air for circular and square absorber based receivers are proposed. Finally, a 4kWth experimental facility, which is being commissioned at IIT Jodhpur to test solar thermal sub-systems such as receiver, heat exchanger, thermal energy storage and experimental evaluation of receiver components are described. These experiments demonstrate the effect of absorber-porosity, uniform and non-uniform concentrated solar irradiance level on heat transfer with porous absorbers and effectiveness of the selected mixer-assembly design in such a condition.

Dust and soiling issues and impacts relating to solar energy systems: Literature review update for 2012-2015

Abstract: The purpose of this review survey is to provide a literature compilation, updating materials reported in several review papers on solar-device soiling and mitigation approaches published over the past 5 years. The focus is on the period 2013–2015, but an updated listing is also provided for the year 2012 for completeness. This literature review also provides the first update for a periodic, single collation report on such publications proposed in this journal two years ago. This review presents a listing of the publications, their publication source, and some brief tabulated information to help guide the reader into the focus of each of the works.

Solar and wind energy: Challenges and solutions in desert regions

Abstract: In desert regions, several environmental challenges have the potential to reduce solar energy production. These are the formation of thinly crusted mud and/or carbonates coatings caused from deposited dust aerosols during humid conditions and other weather conditions. These challenges that profoundly affect photovoltaic panel surfaces as well as wind turbines were delineated to conclude the potential feasibility to establish solar and/or wind energy systems in Kuwait. The study concluded that photovoltaic (PV) cells are not the most suitable energy source for Kuwait due to the above mentioned environmental challenges; therefore, alternative renewable energy sources are considered more feasible. After one year of operation at solar units and wind farms in Kuwait, the results clearly show that wind energy records energy production numbers that exceed the industry average. This was associated with high capacity factors throughout the year, resulting in an annual power production that is 2.3 times higher than that of PV; powering 450 homes compared to 199 homes for PV. West of the state of Kuwait and the Bubiyan Island are the recommended potential sites for wind farm establishment.

Small and Medium sized Reactors (SMR): A review of technology

Abstract: In this paper the authors review 25 original Small and Medium sized Reactor designs currently under development, licensing procedure or in operation. Technology overview, safety features and ability to mitigate proliferation are considered. In order to show common research trends and highlight the features of particular designs the authors choose to classify the reactors according to used technology and cooling medium. The main requirement for a new reactor design is to secure inherent and passive safety features, thus different ways to achieve it are shown. The Pressurized Water Reactor (PWR) is the most advanced and most commonly used technology. In PWR, passiveness and inherency of safety features are ensured by integrating steam generators inside the Reactor Pressure Vessel (RPV). It eliminates possibility of Loss of Cooling Accident (LOCA); moreover the technology allows swift removal of heat produced during normal or accidental conditions. Heavy Water Reactors (HWRs) are also in operation, however, the design process of improving emergency cooling system is ongoing. The design of Supercritical Water Reactor (SCWR) based on Canadian HWR is reviewed including the ongoing development in novel leakage detection method and material improvement. Liquid Metal Cooled Reactors (LMCR) are in advanced stage of research and development focusing on lead and sodium as the coolants. LMCR are secured from LOCA accidents due to low operating pressure and integration of the most elements in RPV. In case of Advanced Gas-Cooled Reactors (AGCR) the literature indicates several possible system integrations related to high operating temperature under development. AGCRs are able to use fully passive systems during all events due to their low power density. Furthermore, it is noted that the use of innovative reactor designs can mitigate proliferation concerns to an acceptable level. The authors identify the common research trend among all designs as the fuel cycle evaluation and optimization.