The Energy Budget in Tubular and Planar Type Solid Oxide Fuel Cells Studied through Numerical Simulation

ABSTRACT The energy budget in a tubular and a planar type solid oxide fuel cell (SOFC) is studied based on numerical simulation. By solving the discretized governing equations for flow, temperature, and mass fraction of gas species in the fuel cells, the detailed local parameters determining the local electromotive forces are obtained. The energy flows of electrical power, Joule heating, thermal energy from the entropy change of the electrochemical reaction, as well as the chemical reaction heat by reforming and shift reactions are delineated and compared for the two different types of SOFCs

Inverse Bem Method To Identify Surface Temperatures And Heat Transfer Coefficient Distributions At Inaccessible Surfaces

The purpose of the inverse problem considered in this study is to resolve heat transfer coefficient distributions by solving a steady-state inverse problem. Temperature measurements at interior locations supply the additional information that renders the inverse problem solvable. A regularized quadratic functional is defined to measure the deviation of computed temperatures from the values under current estimates of the heat transfer coefficient distribution at the surface exposed to convective heat transfer. The inverse problem is solved by minimizing this functional using a parallelized genetic algorithm (PGA) as the minimization algorithm and a two-dimensional multi-region boundary element method (BEM) heat conduction code as the field variable solver. Results are presented for a regular rectangular geometry and an irregular geometry representative of a blade trailing edge and demonstrate the success of the approach in retrieving accurate heat transfer coefficient distributions. Copyright © 2005 by ASME

Synthesis and Characterization of Nanocomposites Using the Nanoscale Laser Soldering in Liquid Technique

Abstract We have synthesized Au/CuO and Au/ZnO nanocomposites using the laser soldering technique. The process was carried out by irradiating a solution containing Au-CuO and Au-ZnO nanoparticles using 532 nm laser pulses of 0.1 J/cm 2 continuously for 20 minutes. The beam was focused using a 75 mm focal lens and the laser power near the focal region was estimated to be about 2.4 x 10 12 W/m 2 . Their UV-VIS absorption and transmission were observed and the results indicated that the bandgap energies of the Au/CuO and Au/ZnO are significantly lower than those of pure CuO and ZnO. A theoretical model was developed and the calculation showed that the soldering process was due to the laser melting of the gold nanoparticles and the molten gold got soldered to the ZnO as well as CuO nanoparticles nearby

Time-accurate CFD conjugate analysis of transient measurements of the heat-transfer coefficient in a channel with pin fins

Heat-transfer coefficients (HTC) on surfaces exposed to convection environments are often measured by transient techniques such as thermochromic liquid crystal (TLC) or infrared thermography. In these techniques, the surface temperature is measured as a function of time, and that measurement is used with the exact solution for unsteady, zero-dimensional (0-D) or one-dimensional (1-D) heat conduction into a solid to calculate the local HTC. When using the 0-D or 1-D exact solutions, the transient techniques assume the HTC and the free-stream or bulk temperature characterizing the convection environment to be constants in addition to assuming the conduction into the solid to be 0-D or 1-D. In this study, computational fluid dynamics (CFD) conjugate analyses were performed to examine the errors that might be invoked by these assumptions for a problem, where the free-stream/bulk temperature and the heat-transfer coefficient vary appreciably along the surface and where conduction into the solid may not be 0-D or 1-D. The problem selected to assess these errors is flow and heat transfer in a channel lined with a staggered array of pin fins. This conjugate study uses three-dimensional (3-D) unsteady Reynolds-averaged Navier–Stokes (RANS) closed by the shear-stress transport (SST) turbulence model for the gas phase (wall functions not used) and the Fourier law for the solid phase. The errors in the transient techniques are assessed by comparing the HTC predicted by the time-accurate conjugate CFD with those predicted by the 0-D and 1-D exact solutions, where the surface temperatures needed by the exact solutions are taken from the time-accurate conjugate CFD solution. Results obtained show that the use of the 1-D exact solution for the semi-infinite wall to give reasonably accurate “transient” HTC (less than 5% relative error). Transient techniques that use the 0-D exact solution for the pin fins were found to produce large errors (up to 160% relative error) because the HTC varies appreciably about each pin fin. This study also showed that HTC measured by transient techniques could differ considerably from the HTC obtained under steady-state conditions with isothermal walls