Estudio teórico-experimental de la transferencia de calor en el tubo receptor de un colector solar de canal parabólico

The capture of solar energy through parabolic trough collectors is a technological application for the use of clean energy, this allows reducing the use of fossil fuels and reducing the generation of greenhouse gases (GHG). Therefore, this article presents a theoretical-experimental study of the heat transfer in the receiver tube of a parabolic channel collector through which the working fluid flows.The receiver tube is made of copper with a nominal diameter of 1 "and is covered by a borosilicate glass tube with an outer diameter of 2 1/2" x 2.5 m long, to reduce convective losses. The theoretical study is carried out in two-dimensional (2D) Cartesian coordinates and axi-symmetric boundary condition to model and simulate fluid dynamics and analyze the behavior of convective heat transfer between the air of the annular space and the working fluid. The simulated fluid temperatures were from 80 to 180 ° C, this range includes various industrial applications where process heat is required. The simulated direct radiation values were from 600 to 1100 W / m2. The difference between the theoretical and experimental results was less than 8%.

Symmetric Boundary Condition for Laplacian on Net of Regular Hexagons

Hexagonal grid methods are found useful in many research works, including numerical modeling in spherical coordinates, in atmospheric and ocean models, and simulation of electrical wave phenomena in cardiac tissues. Almost all of these used standard Laplacian and mostly on one configuration of regular hexagons. In this work, discrete symmetric boundary condition and energy product for anisotropic Laplacian are investigated firstly on general net of regular hexagons, and then generalized to its most extent in two- or three-dimensional cell-center finite difference applications up to the usage of symmetric stencil in central differences. For analysis of Laplacian related applications, this provides with an approach in addition to the M-matrix theory, series method, functional interpolations and Fourier vectors.

Influence of Model Geometry and Boundary Conditions on the Ultimate Strength of Stiffened Panels Under Uniaxial Compressive Loading

The aim of this paper is to determine an appropriate configuration of the boundary conditions and geometric model to calculate the ultimate strength of a continuous stiffened panel under compressive loading in the finite element (FE) analysis. The 1 + 1 spans model with periodical symmetric boundary conditions is proposed to be used in the FE analysis, whose results are compared with the 1/2 + 1 + 1/2 span model with periodical symmetric and symmetric boundary condition, and the 1/2 + 1 + 1 + 1/2 span model with symmetric boundary conditions. The effects of the continuity of the stiffened panel with different geometric models and boundary conditions on its collapse mode are investigated. A beam tension test has been used to define the true stress-strain relationship in the FE analysis. The two-span model, either 1 + 1 or 1/2 + 1 + 1/2, with periodical symmetric conditions give a reasonable FE modeling, which can consider both odd and even number half waves and, thus, have the smallest model uncertainty.

A Concise Finite Element Model for the Analysis of Simple Wire Strand with a Broken Helical Wire

A concise finite element model for the analysis of simple wire strand with a broken helical wire under axial load is presented in this paper. Due to the implementation of accurate helically symmetric boundary condition, the analysis model can be established based only on a small slice of the wire strand cross-section consisting of all of the remaining intact wires excluding the broken helical wire. Full three-dimensional solid elements were used for structural discretization. The finite element results showed that the sharing of loads among the remaining helical wires is highly non-uniform. The two helical wires adjacent to the broken helical wire bear higher loads. The helical wire opposite to the broken wire bears least load.

Displacement and Blocking Force Modeling for Piezoelectric Uniflex Microactuators

Microactuators provide controlled motion and force for applications ranging from RF switches to rate gyros. Large amplitude response in piezoelectric actuators requires amplification of their small strain. This paper studies a uniflex microactuator that combines the strain amplification mechanisms of a unimorph and flexural motion to produce large displacement and blocking force. An analytical model is developed with three connected beams and a reflective symmetric boundary condition that predicts actuator displacement and blocking force as a function of the applied voltage. The model shows that the uniflex design requires appropriate parameter ranges, especially the clearance between the unimorph and aluminum cap, to ensure that both the unimorph and flexural amplification effects are realized. With a weakened joint at the unimorph/cap interface, the model accurately predicts the displacement and blocking force of four actuators.