Numerical analysis of Thermal, Fluid, and Electrical Performance of a Photovoltaic Thermal Collector at New Microchannels Geometry

In the present paper, different paths (direct, spiral, and curved) for water flow in a photovoltaic /thermal (PV/T) system are studied and they are compared together. The intensity of radiation to the cell surface is taken 800 W/m2, and the fluid flow is considered to be laminar in the microchannels. The PV cell absorbing radiation is of an aluminum type. The numerical solution of the three geometries is carried out using the finite volume method using ANSYS-Fluent software. The pressure decomposition, momentum and energy discretization, and the solution of the pressure-velocity coupling are performed based on the standard method, second-order upwind method, and the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) method, respectively. The convergence factor is considered to be respected and for continuity and energy equations. The results indicate that the cell surface temperature and the outlet fluid temperature decrease by increasing the Reynolds (Re) number. Moreover, electricity efficiency increases with increased Reynolds number. The curved path has the highest electrical efficiency in compersion to the other two paths. The fluid pressure drop of the curved path in Re = 600 is 4% and 1.3% higher than the direct and spiral paths, respectively.

Comparative Review on Computational Performance of Multistep Schemes in Solving One-Dimensional Linear Wave Equation

Among several numerical methods used to solve the hyperbolic model of the linear wave equation, single-step algorithms can be the more popular ones. However, these algorithms are time-consuming while incurring numerical inaccuracy. Thus, multistep methods can be a suitable option as it has a high order of accuracy. This study aims to investigate and compare the computational performance of these multistep schemes in solving hyperbolic model based on one-dimensional linear wave equation. The techniques studied in this paper comprise the two-step Lax-Wendroff method, MacCormack method, second-order upwind method, Rusanov-Burstein-Mirin method, Warming-Kutler-Lomax method, and fourth-order Runge-Kutta method. Finite difference method is applied in discretisation. Our simulation found that although higher-order multistep methods are more stable than single-step algorithm, they suffer numerical diffusion. The two-step Lax-Wendroff method outperforms other schemes, although it is relatively simple compared with the other three and four steps schemes. The second-order upwind method is attractive as well because it is executable even with a high Courant number.

Numerical model of gravity segregation of two-phase fluid in porous media based on hybrid upwinding

The paper discusses the numerical algorithm constructing a three-dimensional model for a flow of two-phase incompressible fluid caused by the mass force of gravity in a porous medium. The algorithm is based on a combination of a hybrid upwind method with an explicit scheme for determination of the saturation. The hybrid upwinding allows us to take into account flows of fluid of various nature (in this case, viscous and gravitational flows) separately, which is extremely important in the case of gravitational flow with opposite directions of phase flows. The explicit scheme being extremely simple in implementation provides a small dispersion of solutions on discontinuities. The proposed algorithm is illustrated by the results of numerical experiments demonstrating the monotonicity of the method considered in this paper.

A robust coupled 2-D model for rapidly varying flows over erodible bed using central-upwind method with wetting and drying

This paper aims to develop a robust two-dimensional coupled numerical model based on an unstructured mesh, which can simulate rapidly varying flows over an erodible bed involving wet–dry fronts that is a complex yet practically important problem. Using a modified spatial reconstruction based on the finite volume method, the well-balanced property is preserved, which is important for accurate and efficient simulation of morphological problems. In the present study, the central-upwind scheme is extended to simulation of bed erosion and sediment transport for the first time. It is demonstrated that the proposed scheme shows good accuracy and high efficiency. A modified shallow water system is adopted to improve the model. The shallow water equations, sediment transport equation and bed evolution equation are coupled in the governing system. Multiple test cases are employed to demonstrate the robustness, accuracy, and efficiency of the current model. Furthermore, with a field scale dam-break test case, the efficiency and accuracy of the central-upwind method is verified in comparison with other popular Riemann solvers. The effects of the additional source terms in the adopted modified shallow water equations are also investigated by comparing the numerical results with a laboratory study available in the literature. The proposed scheme can efficiently track wetting and drying interfaces while preserving stability in simulating the bed erosion near the wet-dry fronts. The added terms in shallow water equations can improve the accuracy of the simulation when intense sediment-exchange exists; the central-upwind method adopted in the current study shows great accuracy and efficiency compared with other popular solvers; the developed model is robust, efficient and accurate to deal with various challenging cases.

UNSTEADY LAMINAR CONVECTION FLOW OVER PERIODIC GROOVES BY USING SIO2-WATER NANOFLUID

Unsteady laminar forced convection flow in a 2-dimensional channel over periodic grooves is numerically investigated. Finite volume method is used and the equations were discretized by second order upwind method. The ribheight to channel-height ratio (B/H) is 2. The downstream wall is heated by a uniform heat flux while the upstream wall is insulated. Quasi steady point was obtained at τ=10. The heat transfer is analyzed with different nanoparticles volume fraction and diameter of 0-4% and 20nm-50nm for SiO2 respectively at Reynolds number of 400 and τ=10. Water is used as a base fluid of nanoparticles. The results revealed 124% heat transfer enhancement compared to the water in a grooved channel by using SiO2 nanoparticle with volume fraction and nanoparticle diameter of 4% and 20nm respectively.