M. S. Mohan Kumar

Modelling flow through unsaturated zones: Sensitivity to unsaturated soil properties

A numerical model to simulate moisture flow through unsaturated zones is developed using the finite element method, and is validated by comparing the model results with those available in the literature. The sensitivities of different processes such as gravity drainage and infiltration to the variations in the unsaturated soil properties are studied by varying the unsaturated parameters α andn over a wide range. The model is also applied to predict moisture contents during a field internal drainage test.

p53: its alteration and gallbladder cancer.

Gallbladder cancer (GBC) is the most common malignancy of the biliary tract. Despite the recent advancements in the understanding of cancer biology the disease still remains a therapeutic challenge with poor survival, and with early surgical resection as the only powerful treatment. Understanding the molecular events in gallbladder carcinogenesis may provide a novel targeted therapeutic approach. Of these, alterations in the tumour suppressor gene, p53, are commonly observed in most human cancers. However, its impact on the pathogenesis of GBC remains obscure. This study attempts to outline the p53 structure, function and its alterations, with special attention to GBC.

Virus-sized colloid transport in a single pore: Model development and sensitivity analysis

A mathematical model is developed to simulate the transport and deposition of virus-sized colloids in a cylindrical pore throat considering various processes such as advection, diffusion, colloid-collector surface interactions and hydrodynamic wall effects. The pore space is divided into three different regions, namely, bulk, diffusion and potential regions, based on the dominant processes acting in each of these regions. In the bulk region, colloid transport is governed by advection and diffusion whereas in the diffusion region, colloid mobility due to diffusion is retarded by hydrodynamic wall effects. Colloid-collector interaction forces dominate the transport in the potential region where colloid deposition occurs. The governing equations are non-dimensionalized and solved numerically. A sensitivity analysis indicates that the virus-sized colloid transport and deposition is significantly affected by various pore-scale parameters such as the surface potentials on colloid and collector, ionic strength of the solution, flow velocity, pore size and colloid size. The adsorbed concentration and hence, the favorability of the surface for adsorption increases with: (i) decreasing magnitude and ratio of surface potentials on colloid and collector, (ii) increasing ionic strength and (iii) increasing pore radius. The adsorbed concentration increases with increasing Pe, reaching a maximum value at Pe=0.1 and then decreases thereafter. Also, the colloid size significantly affects particle deposition with the adsorbed concentration increasing with increasing particle radius, reaching a maximum value at a particle radius of 100nm and then decreasing with increasing radius. System hydrodynamics is found to have a greater effect on larger particles than on smaller ones. The secondary minimum contribution to particle deposition has been found to increase as the favorability of the surface for adsorption decreases. The sensitivity of the model to a given parameter will be high if the conditions are favorable for adsorption. The results agree qualitatively with the column-scale experimental observations available in the literature. The current model forms the building block in upscaling colloid transport from pore scale to Darcy scale using Pore-Network Modeling.

Analytical solutions for transient temperature distribution in a geothermal reservoir due to cold water injection

An analytical solution to describe the transient temperature distribution in a geothermal reservoir in response to injection of cold water is presented. The reservoir is composed of a confined aquifer, sandwiched between rocks of different thermo-geological properties. The heat transport processes considered are advection, longitudinal conduction in the geothermal aquifer, and the conductive heat transfer to the underlying and overlying rocks of different geological properties. The one-dimensional heat transfer equation has been solved using the Laplace transform with the assumption of constant density and thermal properties of both rock and fluid. Two simple solutions are derived afterwards, first neglecting the longitudinal conductive heat transport and then heat transport to confining rocks. Results show that heat loss to the confining rock layers plays a vital role in slowing down the cooling of the reservoir. The influence of some parameters, e.g. the volumetric injection rate, the longitudinal thermal conductivity and the porosity of the porous media, on the transient heat transport phenomenon is judged by observing the variation of the transient temperature distribution with different values of the parameters. The effects of injection rate and thermal conductivity have been found to be profound on the results.RésuméUne solution analytique pour décrire la distribution transitoire de la température suite à une injection d’eau froide dans un réservoir géothermal est présentée. Le réservoir est composé d’un aquifère captif pris en sandwich entre des roches de propriétés thermo-géologiques différentes Les processus de transport de chaleur considérés sont l’advection, la conduction longitudinale dans l’aquifère géothermal et le transfert conductif de chaleur vers les roches sous et sus-jacentes aux propriétés géologiques différentes. L’équation de transfert de chaleur à une dimension est résolue en utilisant la transformée de Laplace sous l’hypothèse d’une densité constante et des propriétés thermiques à la fois de la roche et du fluide. Deux solutions simples sont ensuite dérivées, en négligeant d’abord la conductivité longitudinale de transport de chaleur et ensuite le transport de chaleur vers les épontes. Les résultats montrent que la perte de chaleur dans les épontes joue un rôle majeur en ralentissant le refroidissement du réservoir. L’influence de certains paramètres, tel que le débit d’injection, la conductivité thermique longitudinale et la porosité du milieu poreux, sur le phénomène transitoire du transport de chaleur est appréhendé en observant la variation de la distribution des températures dans le temps avec différentes valeurs des paramètres. Il apparait que débit d’injection et la conductivité thermique ont un impact important sur les résultats.ResumenSe presenta una solución analítica para describir la distribución transitoria de la temperatura en un reservorio geotérmico en respuesta a una inyección de agua fría. El reservorio está compuesto de un acuífero confinado, intercalado entre rocas de diferentes propiedades termo geológicas. Los procesos de transporte de calor considerados son advección, conducción longitudinal en el acuífero geotérmico, y la transferencia conductiva del calor a rocas subyacentes y suprayacente de diferentes propiedades geológicas. La ecuación de transferencia de calor unidimensional ha sido resuelta usando la transformada de Laplace con la suposición de densidad y propiedades térmicas constantes tanto de rocas como de fluidos. Se extrajeron dos soluciones simples, la primera despreciando la conductividad longitudinal del transporte de calor y por lo tanto del transporte de calor a las rocas confinantes. Los resultados muestran que la pérdida de calor hacia las capas de rocas confinantes juega un rol vital en retardar el enfriamiento del reservorio. La influencia de algunos parámetros, por ejemplo la tasa volumétrica de la inyección, la conductividad térmica longitudinal y la porosidad del medio poroso, sobre el fenómeno de transporte transitorio de calor son juzgados observando la variación de la distribución transitoria de la temperatura con diferentes valores de los parámetros. Se han encontrado los profundos efectos de la velocidad de inyección y de la conductividad térmica en los resultados.摘要研究展示了地热储由于冷水注入造成瞬时温度分布的解析解。热储由一个夹在不同地热特性岩层之间的承压含水层组成。考虑到的热传输过程有对流、地热含水层中的纵向传导、向上覆及下伏的具有不同地质特性的岩石的热传导。假定岩石和液体恒定密度和热特性并采用Laplace变换求解决一维热传导方程。随后推导出两个简单的 解决方法,首先忽略纵向传导的热传输,然后忽略传导到承压岩石的热传输。结果显示对承压岩石层的热损耗在减速热储的冷却上发挥至关重要的作用。有些参数如容积注入率、纵向人传导及多孔介质的孔隙度对瞬时热传输现象的影响根据观测瞬时温度分布的变化的不同参数值来判断。注入速率和热传导对结果有深远影响。ResumoÉ apresentada uma solução analítica para descrever a distribuição da temperatura em regime transitório num reservatório geotérmico em resposta à injeção de água fria. O reservatório é formado por um aquífero confinado, localizado entre rochas de diferentes propriedades térmicas e geológicas. Os processos de transporte de calor são a adveção, a condução longitudinal do aquífero geotérmico e a transferência de calor por condução para as rochas sub- e sobrejacentes de diferentes propriedades geológicas. A equação de transferência de calor unidimensional tem sido resolvida utilizando a transformada de Laplace, com a assunção das hipóteses de densidade e propriedades térmicas constantes das rochas e do fluido. São derivadas duas soluções simples, primeiro negligenciando a condutividade longitudinal do transporte de calor e, em seguida, o transporte de calor para as rochas confinantes. Os resultados mostram que a perda de calor para as camadas de rocha confinantes desempenha um papel vital no abrandamento do arrefecimento do reservatório. A influência de alguns parâmetros, como a taxa de injeção volumétrica, a condutividade térmica longitudinal e a porosidade do meio no fenómeno de transporte de calor em regime transitório, é avaliada observando a variação da distribuição de temperatura em transitório com diferentes valores dos parâmetros. Os efeitos da taxa de injeção e da condutividade térmica mostram ser muito grandes nos resultados obtidos.

Correlation equations for average deposition rate coefficients of nanoparticles in a cylindrical pore

Nanoparticle deposition behavior observed at the Darcy scale represents an average of the processes occurring at the pore scale. Hence, the effect of various pore-scale parameters on nanoparticle deposition can be understood by studying nanoparticle transport at pore scale and upscaling the results to the Darcy scale. In this work, correlation equations for the deposition rate coefficients of nanoparticles in a cylindrical pore are developed as a function of nine pore-scale parameters: the pore radius, nanoparticle radius, mean flow velocity, solution ionic strength, viscosity, temperature, solution dielectric constant, and nanoparticle and collector surface potentials. Based on dominant processes, the pore space is divided into three different regions, namely, bulk, diffusion, and potential regions. Advection-diffusion equations for nanoparticle transport are prescribed for the bulk and diffusion regions, while the interaction between the diffusion and potential regions is included as a boundary condition. This interaction is modeled as a first-order reversible kinetic adsorption. The expressions for the mass transfer rate coefficients between the diffusion and the potential regions are derived in terms of the interaction energy profile. Among other effects, we account for nanoparticle-collector interaction forces on nanoparticle deposition. The resulting equations are solved numerically for a range of values of pore-scale parameters. The nanoparticle concentration profile obtained for the cylindrical pore is averaged over a moving averaging volume within the pore in order to get the 1-D concentration field. The latter is fitted to the 1-D advection-dispersion equation with an equilibrium or kinetic adsorption model to determine the values of the average deposition rate coefficients. In this study, pore-scale simulations are performed for three values of Peclet number, Pe = 0.05, 5, and 50. We find that under unfavorable conditions, the nanoparticle deposition at pore scale is best described by an equilibrium model at low Peclet numbers (Pe = 0.05) and by a kinetic model at high Peclet numbers (Pe = 50). But, at an intermediate Pe (e.g., near Pe = 5), both equilibrium and kinetic models fit the 1-D concentration field. Correlation equations for the pore-averaged nanoparticle deposition rate coefficients under unfavorable conditions are derived by performing a multiple-linear regression analysis between the estimated deposition rate coefficients for a single pore and various pore-scale parameters. The correlation equations, which follow a power law relation with nine pore-scale parameters, are found to be consistent with the column-scale and pore-scale experimental results, and qualitatively agree with the colloid filtration theory. These equations can be incorporated into pore network models to study the effect of pore-scale parameters on nanoparticle deposition at larger length scales such as Darcy scale.

Modeling the co-transport of viruses and colloids in unsaturated porous media

A mathematical model is developed to simulate the co-transport of viruses and colloids in unsaturated porous media under steady-state flow conditions. The virus attachment to the mobile and immobile colloids is described using a linear reversible kinetic model. Colloid transport is assumed to be decoupled from virus transport; that is, we assume that colloids are not affected by the presence of attached viruses on their surface. The governing equations are solved numerically using an alternating three-step operator splitting approach. The model is verified by fitting three sets of experimental data published in the literature: (1) Syngouna and Chrysikopoulos (2013) and (2) Walshe et al. (2010), both on the co-transport of viruses and clay colloids under saturated conditions, and (3) Syngouna and Chrysikopoulos (2015) for the co-transport of viruses and clay colloids under unsaturated conditions. We found a good agreement between observed and fitted breakthrough curves (BTCs) under both saturated and unsaturated conditions. Then, the developed model was used to simulate the co-transport of viruses and colloids in porous media under unsaturated conditions, with the aim of understanding the relative importance of various processes on the co-transport of viruses and colloids in unsaturated porous media. The virus retention in porous media in the presence of colloids is greater during unsaturated conditions as compared to the saturated conditions due to: (1) virus attachment to the air-water interface (AWI), and (2) co-deposition of colloids with attached viruses on its surface to the AWI. A sensitivity analysis of the model to various parameters showed that the virus attachment to AWI is the most sensitive parameter affecting the BTCs of both free viruses and total mobile viruses and has a significant effect on all parts of the BTC. The free and the total mobile viruses BTCs are mainly influenced by parameters describing virus attachment to the AWI, virus interaction with mobile and immobile colloids, virus attachment to solid-water interface (SWI), and colloid interaction with SWI and AWI. The virus BTC is relatively insensitive to parameters describing the maximum adsorption capacity of the AWI for colloids, inlet colloid concentration, virus detachment rate coefficient from the SWI, maximum adsorption capacity of the AWI for viruses and inlet virus concentration.

Modeling Equitable Distribution of Water: Dynamic Inversion-Based Controller Approach

It is a well-known fact that most of the developing countries have intermittent water supply and the quantity of water supplied from the source is also not distributed equitably among the consumers. Aged pipelines, pump failures, and improper management of water resources are some of the main reasons for it. This study presents the application of a nonlinear control technique to overcome this problem in different zones in the city of Bangalore. The water is pumped to the city from a large distance of approximately 100km over a very high elevation of approximately 400m. The city has large undulating terrain among different zones, which leads to unequal distribution of water. The Bangalore, inflow water-distribution system (WDS) has been modeled. A dynamic inversion (DI) nonlinear controller with proportional integral derivative (PID) features (DI-PID) is used for valve throttling to achieve the target flows to different zones of the city. This novel approach of equitable water distribution using DI-PID controllers that can be used as a decision support system is discussed in this paper.

Geothermal Reservoirs - A Brief Review

A brief discussion and review of the geothermal reservoir systems, geothermal energy and modeling and simulation of the geothermal reservoirs has been presented here. Different types of geothermal reservoirs and their governing equations have been discussed first. The conceptual and numerical modeling along with the representation of flow though fractured media, some issues related to non isothermal flow through fractured media, the efficiency of the geothermal reservoir, structure of the numerical models, boundary conditions and calibration procedures have been illustrated. A brief picture of the Indian scenario and some barriers related with geothermal power are discussed and presented thereafter. Finally some gaps of the existing knowledge and recent focuses of research are discussed.

Parameter estimation in an anisotropic leaky aquifer system

Abstract Parameter estimation is made for an anisotropic leaky aquifer system in which the direction of principal axes is unknown. There is a declining water table in the aquitard. The seven governing parameters are the direction of principal axes, the degree of anisotropy, the equivalent transmissivity and storage coefficient of the aquifer, and the leakage coefficient, specific storage and specific yield of the unconfined aquitard. A modified parameter perturbation technique which is computationally efficient is used for the determination of sensitivity coefficients. The parameter estimation procedure is applied to three test problems including one field problem. Situations where the total number of wells is only three are handled with two pump tests by locating the pump in a different well in each test.

Towards an IoT based water management system for a campus

We discuss the design and preliminary results of an IoT based system for management of the water distribution system in a large campus. In particular, we focus on two specific components of the system: a low cost ultrasonic based water level sensor and a sub-GHz based campus scale wireless network to connect the sensors. We describe techniques to achieve a large sensing distance that makes them suitable for installation across overhead tanks (OHT) and ground level reservoirs (GLR). The wireless network, which uses sub-GHz radios, connects to a gateway that can upload the data online for visualisation and analytics.