Browsing by Author "Karunathilaka, N. G. A."

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Dynamic of a capillary ridge of free surface flow on an inclined heated plate
(Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Nisansala, K. A. D. S.; Karunathilaka, N. G. A.
Formation of capillary ridge on a gravity-driven thin liquid film flowing over a plate is used in lots of commercial applications. Painting and coating, contact lens manufacturing, microchips and microchips fluidic devises are some examples. Capillary ridge forms due to the surface tension, geometrical structure of the flow and the temperature of the fluid. Capillary ridge height varies with the surface tension coefficient, inclination angle and initial thickness. Its height is increased with higher surface tension, steeper inclination angle and bigger initial thickness. In this work, a mathematical model has been developed for a two-dimensional, laminar, incompressible flow of second grade non-Newtonian fluid with temperature-dependent viscosity on an inclined planar plate. Also the capillary ridge height and corresponding velocities, pressure and temperature of the zeroth order expansion are discussed. The thin plate is heated locally and inclined at an angle with the fixed horizontal axis. Simplified Navier-Stokes equations are solved together evolution equation for the description of the liquid thin film height which is derived by using the long-wave approximation. The solution of the resulting equation for the liquid thin film height is approximated using explicit finite difference method on a uniform grid. The solutions are simulated to identify the flow patterns. Capillary ridge height and velocities, pressure and temperature are obtained using the asymptotic expansion. It can be observed that there is an oscillatory behavior of capillary ridge height along the direction of the plate. Furthermore, the upstream of capillary ridges change slightly with the advancement of time and the downstream of capillary ridges do not change with the time. The results indicate that the temperature varies proportionally with the space variable from left end of the domain to the right end of the domain. Behavior of the velocity and the pressure has been discussed in the different directions of fluid flow domain. The results indicate that the velocity component in x direction decreases when negative x approaches to zero and it increases when x increases from zero to the right end of the domain. Velocity component in z direction decreases linearly when x increases. It is also realized that the pressure decreases to zero when negative x increases to zero and the pressure increases when x increases from zero to the right end of the domain.
Investigation of the mixed cation effect and the irradiance level dependence on the efficiency of dye‑sensitized solar cells
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Wickramasinghe, H. M. N.; Karunathilaka, N. G. A.; Gnanarathne, D. M. T.; DeSilva, L. Ajith; Bandara, K. M. S. P.; Bandara, T. M. W. J.
The development of photoelectrochemical energy conversion devices holds immense significance in addressing the escalating demand for renewable and environmentally benign energy. By harnessing the synergistic effects of salt mixtures that encompass both large and small counter ions, notable advancements in dye-sensitized solar cell (DSSC) performance have been realized. The investigated DSSCs with a novel organic electrolyte complex that contains LiI and (tetrahexylammonium) Hex4NI exhibited significant efficiency enhancement compared to that of their individual salt end components. The ionic conductivity variations and frequency-dependent AC conductivity in the electrolyte and dielectric properties were analyzed using complex impedance data. The conductivity in the electrolyte at room temperature is 11.44 mS cm−1. The investigated DSSCs are comprised of improved TiO2 multilayer photoelectrodes and Pt counter electrodes. Under an irradiance of 1000 W m−2, the energy conversion efficiency of the mixed salt system reached 8.37%, marking an impressive enhancement of 86.83% and 76.21% compared to the Hex4NI and LiI-based single salt counterparts, respectively. Additionally, an impressive efficiency of 10.57% is shown when the light intensity drops to 400 W m−2. The cells exhibited commendable short-term stability, likely attributed to the elimination of volatile solvents in the electrolyte. This study underscores the pivotal role played by mixed counter ions in the electrolyte, as they elicit synergistic effects that amplify DSSC performance enhancements, effectively overshadowing the effects imposed by conductivity variation.
Mass and heat transfer of modified second-grade fluid flow through a porous media over a linearly stretching sheet
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Fernando, L. M. N.; Karunathilaka, N. G. A.
In this research, we have developed a mathematical model to describe a boundary layer approximation of modified second-grade fluid flow over a linearly stretching sheet with mass and heat transfer in a porous medium. The purpose of the model is to study the qualitative impact of buoyancy parameter, second-grade fluid parameter, magnetic parameters, porous parameter, power-law index, and chemical reaction parameter on the flow profiles, the radial and axial velocities, temperature, and concentration. The analysis has been started with the steady state governing equations derived from the conservation of mass, momentum, heat, and concentration of the fluid flow. The boundary layer approximations have been obtained on the fluid flow near the stretching sheet with the no-slip condition. The system of partial differential equations has been transformed into a system of nonlinear ordinary differential equations using similarity transformations. The resulting system of ordinary differential equations has been solved numerically and obtain the radial and velocities, temperature, and concentration profiles. The qualitative influence of the above flow parameters on the flow variables has been simulated and graphically presented for comparison. The study reveals that in the shear-thinning fluids, radial and axial velocities increase with solutal Grashoff number, thermal Grashoff number buoyancy parameters, and second-grade fluid parameters. In contrast, the temperature and concentration decrease with the above flow parameters. The Magnetic, Chemical reaction, and porous parameters suppress both radial and axial velocities but enhance the temperature and concentration. A similar impact on flow variables can also be observed for the shear-thinning fluids.