Multi‐objective genetic algorithm optimization of thermoelectric heat exchanger for waste heat recovery

A model is developed to simulate a cross‐flow heat exchanger, including fins, in the wall of which thermoelectric generators are sandwiched. Such a system could be used for waste heat recovery. The model is used to optimize the device based on several objective functions: total volume, total number of thermoelectric modules, power output, and pumping power. The design variables are the local distribution of modules and of current, the shape of the fins, and the division of the heat exchanger in sub‐channels. Pareto fronts are achieved with a multi‐objective genetic algorithm, and are presented here. The results show that the number of sub‐channels in the heat exchanger has a larger impact on the overall performance than the fin geometry for this particular problem. Also, the net power output is mostly correlated to the number of thermoelectric modules, and less to the heat exchanger volume. Various relations between the different competing objectives are shown and analyzed. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis of Thin Films on Metal Surfaces

External reflection infrared spectroscopy was used in combination with other surface analysis techniques such as ellipsometry, Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS) to determine the structure of organofunctional silanes adsorbed onto 2024 aluminum and titanium-6 Al, 4V mirrors. The results obtained indicated that the adsorption of γ-aminopropyltriethoxysilane (γ-APS) onto aluminum was a strong function of pH and adsorption time. Films formed by adsorption of γ-APS at pH = 8.5 were composed of polysiloxanes containing amine hydrochlorides. The structure of films formed by adsorption of γ-APS at pH-10.4 depended on time. Films obtained after one minute were composed of polysiloxanes that did not interact strongly with the oxide but during 15 minutes adsorption the air-formed oxide was dissolved and copper accumulated near the surface of the mirrors. Films formed by the adsorption of γ-glycidoxypropyltrimethoxysilane (γ-GPS) onto aluminum were composed of polysiloxanes that did not interact strongly with the oxide. The structure of films formed by adsorption of γ-APS onto titanium did not depend on adsorption time. Films formed at pH = 10.4 were composed of low molecular weight oligomers that gradually polymerized to polysiloxanes during atmospheric exposure.     

Energy and exergy inventory in aluminum smelter from a thermal integration point‐of‐view

Primary aluminum production is a very energy‐intensive industry (~13 MWh per ton of aluminum produced), involving several complex processes within a plant. The paper presents a mass, energy and exergy analysis of an entire smelter. This work was motivated by the need to evaluate the potential for waste heat recovery/thermal integration in such a plant. Three of the main sectors of a smelter are studied, namely the carbon anode production, the electrolytic reduction and the casting. The analysis is applied to a typical smelter producing 260 000 MT_Al per year. It was found that the most important waste heat source is the exhaust gases, with an exergy of 0.57 MWh per ton of aluminum produced. The total exergy destroyed in the plant was found to be around 7.7 MWh/MT_Al. The potential for doing useful work associated with heat dissipated at process boundaries is also evaluated. Results highlight sources of thermodynamic inefficiencies and indicate where exergy is mainly destroyed throughout the plant. The results contribute in developing a better understanding of the energy and exergy flow within a smelter. Copyright © 2016 John Wiley & Sons, Ltd.     

Selective hydrogen absorption from gaseous mixtures by BCC Ti-V alloys

Hydrogen absorption behaviour of the BCC Ti-V alloys has been studied as related to their potential application for the selective hydrogen absorption from mixtures with active gases containing CO and steam at high temperatures. Alloys and their hydrides were characterised using Scanning Electron Microscopy (SEM), Thermal Desorption Spectroscopy (TDS), Temperature Programmed Reaction (TPR) and in situ synchrotron X-ray powder diffraction (SR-XRD). BCC Ti_0.8V_0.2 and Ti_0.9V_0.1 were able to absorb 3.95 wt.% H by forming a FCC type hydride γ−(Ti,V)H₂. Nanoparticles of Pd and Pd/Pt were electroless deposited on the surface of the hydrides to catalyse hydrogen absorption. TPR tests showed that such alloys were capable of absorbing hydrogen even when substantial amounts of CO and H₂O were present in the gas stream. Nanoparticles of Pd/Pt provide a better performance as compared to Pd alone. In situ SR-XRD has been used to probe the mechanisms of hydrogenation and dehydrogenation.     

Optimal approach for upstream fish passage design: One-size-fits-all or made-to-order?

Nearly 60,000 large dams (higher than 15 m) occur worldwide in addition to an estimated 16 million smaller impoundments with individual surface areas larger than 100 m². The resulting habitat fragmentation threatens global riverine biodiversity and sustainable fish populations. Two opposing approaches for selecting fish passage designs to mitigate river fragmentation are possible: develop a limited number of standardized (reference) designs from which a design for a candidate dam is selected (one-size-fits-all approach) versus conduct scientific fish passage studies specific to each dam and targeted fish species (made-to-order approach). The two approaches vary in probability of effectiveness, cost of supporting biological studies, and overall project cost and schedule impact. To address this conundrum, we analyzed 73 USA dams to identify two groups that differed markedly in fish passage planning approaches. Snake River dams are similar in design, flow, geological setting, and target fish species. By contrast, Mississippi River dams are relatively dissimilar in design, flow, and geological setting but generally similar in target fish species. We conclude that the more similar a candidate dam for fish passage is to a reference set of similar dams (i.e., the Snake River dams), then the more likely fish passage technology can be successfully extrapolated to a proposed dam in the same or a nearby watershed. As a general strategy, we recommend that dams in a region be clustered using key hydrologic, structural, operational, and biological variables. These variables can be used to assign a new dam or retrofit an existing dam to a cluster to which they are most similar, thereby optimally extending existing knowledge to new applications. In the process, reliance on the less efficient and more expensive made-to-order approach can be reduced.