Somnath C. Roy

Bio: Somnath C. Roy is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Materials science & Thin film. The author has an hindex of 30, co-authored 143 publications receiving 3992 citations. Previous affiliations of Somnath C. Roy include Instituto Superior Técnico & Indian Institute of Technology Kharagpur.

An improved strategy for transferring and adhering thin nanoporous alumina membranes onto conducting transparent electrodes for template assisted electrodeposition of high aspect ratio semiconductor nanowires with increased optical absorption.

Abstract: This article presents a new method for transferring and enhancing the adhesion of thin nanoporous alumina (NPA) membranes onto non-atomically flat substrates like Fluorine doped Tin Oxide (FTO) coated glass. The study reports use of Glycerol as an additive to reduce the brittleness of the Polystyrene filler that was used to fill the pores of the NPA membrane. Besides, a new refluxing based method is reported here for complete removal of the Polystryrene filler from the porous channels of Alumina. The adhesion between NPA membrane and an underlying electrode was enhanced by electrodepositing a thin (~ 40 nm) intermediate layer of conducting polymer Polyaniline (PANI). The PANI layer acts as an efficient electrostatic adhesive between the NPA and the conducting glass electrode and ensured ultra-strong adhesion of NPA membrane that survived the harsh conditions of CdTe nanowire electrodeposition (60 °C temperature and acidic electrolyte) without delamination for 30 min. The resulting nanowires clearly templated the structure of NPA and displayed free-standing nanowires over a large area with diameter of around 60 nm and length approximately 2.8 µm (aspect ratio ~ 47) and an areal density of 5.9 × 10 nanowires/cm. Total optical absorption measurement on the free-standing CdTe nanowires exhibited an enhancement by 45% over a wavelength range of 350 nm to 1400 nm as compared to CdTe planar thin film of same thickness.

Numerical Investigation on Heat Transfer Enhancement with Perforated Square Micro-Pin Fin Heat Sink for Electronic Cooling Application

Abstract: In this paper, heat transfer enhancement through perforated square micro-pin fins (edge = 180 microns) has been analyzed through numerical simulation. A three-dimensional model has been developed on computational fluid dynamics (CFD) to study the effect of perforation number (One, Two and three) and shape of perforation (Circular and square) on the solid square micro-pin fin heat sink. The ratio of the perforation edge/diameter to the micro-pin fin edge is taken less than 0.375 that doesn't affect the conduction rate. The staggered array is considered for the arrangement of the perforated micro-pin fin on the heat sink due to non-overlapping wakes. Copper is used as a material of the fins and the heat sink. The flow of air and heat transfer characteristics are studied numerically on ANSYS Fluent for the range of Reynolds number ( $100\leq\text{Re} ). A constant heat flux $(\dot{Q}=50\ \text{kWm}^{-} \ {}^{2})$ is applied at the bottom of the heat sink and an ambient temperature of 300K is considered. The size of the fins, the shape of the perforation and the number of perforation are counted as the prime geometric parameter for the calculation of most efficient heat sink. Thermal performance is calculated for every case and results are compared with the solid square micro-pin fins under the same working condition. Numerical results indicate that micro heat sink with perforation up to three gives better performance than the solid square micro heat sink, which shows that there is great potential to use perforated micro-pin fin heat sink for heat augmentation on electronic devices with high power density.

Application of a High Order Accurate Meshless Method to Solution of Heat Conduction in Complex Geometries.

Abstract: In recent years, a variety of meshless methods have been developed to solve partial differential equations in complex domains. Meshless methods discretize the partial differential equations over scattered points instead of grids. Radial basis functions (RBFs) have been popularly used as high accuracy interpolants of function values at scattered locations. In this paper, we apply the polyharmonic splines (PHS) as the RBF together with appended polynomial and solve the heat conduction equation in several geometries using a collocation procedure. We demonstrate the expected exponential convergence of the numerical solution as the degree of the appended polynomial is increased. The method holds promise to solve several different governing equations in thermal sciences.

Doppler Speckles - A Multi-Purpose Vector field Visualization Technique for Arbitrary Meshes.

Abstract: We present a technique that allows a comprehensive view to volumetric vector fields on arbitrary mesh structures. The technique is inherently independent from the topological structure of the underlying grid by using vertex-based splats that are parameterized in color, shape and transparency by the vector field. It can be easily attached to volumes, surfaces or lines to depict the properties of a vector field, yielding more insight than standard techniques such vector arrows or streamlines. We demonstrate this technique upon datasets from computational fluid dynamics and astrophysics, comprising uniform grids, curvilinear multiblocks and particle systems.

Effect of Impeller Speed Perturbation in a Rushton Impeller Stirred Tank

Abstract: Flow inside an unbaffled Rushton-impeller stirred tank reactor (STR) is perturbed using a time dependent impeller rotational speed. Large eddy simulation (LES) revealed that the perturbation increased the width of impeller jet compared to the constant rotational speed cases. The turbulent fluctuations were also observed to be enhanced in the perturbed flow and showed higher values of production and convection of turbulent kinetic energy. Changes in the mean flow-field during the perturbation cycle are investigated. The trailing edge vortices were observed to propagate farther both in the radial and azimuthal direction in the perturbed case. Production of turbulent kinetic energy is observed to be related to the breakup of the impeller jet in the perturbed case. Dissipation of turbulent kinetic energy is augmented due to the perturbation ensuring a better mixing at the molecular scale.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Nano‐photocatalytic Materials: Possibilities and Challenges

Abstract: Semiconductor photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials. We begin with a survey of efforts to explore suitable materials and to optimize their energy band configurations for specific applications. We then examine the design and fabrication of advanced photocatalytic materials in the framework of nanotechnology. Many of the most recent advances in photocatalysis have been realized by selective control of the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, we discuss the current theoretical understanding of key aspects of photocatalytic materials. This review also highlights crucial issues that should be addressed in future research activities.

Photocatalytic reduction of CO2 on TiO2 and other semiconductors.

Abstract: Rising atmospheric levels of carbon dioxide and the depletion of fossil fuel reserves raise serious concerns about the ensuing effects on the global climate and future energy supply. Utilizing the abundant solar energy to convert CO2 into fuels such as methane or methanol could address both problems simultaneously as well as provide a convenient means of energy storage. In this Review, current approaches for the heterogeneous photocatalytic reduction of CO2 on TiO2 and other metal oxide, oxynitride, sulfide, and phosphide semiconductors are presented. Research in this field is focused primarily on the development of novel nanostructured photocatalytic materials and on the investigation of the mechanism of the process, from light absorption through charge separation and transport to CO2 reduction pathways. The measures used to quantify the efficiency of the process are also discussed in detail.

An overview of current status of carbon dioxide capture and storage technologies

Abstract: Global warming and climate change concerns have triggered global efforts to reduce the concentration of atmospheric carbon dioxide (CO2). Carbon dioxide capture and storage (CCS) is considered a crucial strategy for meeting CO2 emission reduction targets. In this paper, various aspects of CCS are reviewed and discussed including the state of the art technologies for CO2 capture, separation, transport, storage, leakage, monitoring, and life cycle analysis. The selection of specific CO2 capture technology heavily depends on the type of CO2 generating plant and fuel used. Among those CO2 separation processes, absorption is the most mature and commonly adopted due to its higher efficiency and lower cost. Pipeline is considered to be the most viable solution for large volume of CO2 transport. Among those geological formations for CO2 storage, enhanced oil recovery is mature and has been practiced for many years but its economical viability for anthropogenic sources needs to be demonstrated. There are growing interests in CO2 storage in saline aquifers due to their enormous potential storage capacity and several projects are in the pipeline for demonstration of its viability. There are multiple hurdles to CCS deployment including the absence of a clear business case for CCS investment and the absence of robust economic incentives to support the additional high capital and operating costs of the whole CCS process.