Designing forest biodiversity experiments : general considerations illustrated by a new large experiment in subtropical China

Funded by German Research Foundation. Grant Number: DFG FOR 891/1 and 2 National Natural Science Foundation of China. Grant Numbers: NSFC 30710103907, 30930005, 31170457 , 31210103910 Swiss National Science Foundation (SNSF) Sino-German Centre for Research Promotion in BeijingPeer reviewedPublisher PD

Designing forest biodiversity experiments: general considerations illustrated by a new large experiment in subtropical China


 Biodiversity-ecosystem functioning (BEF) experiments address ecosystem-level consequences of species loss by comparing communities of high species richness with communities from which species have been gradually eliminated. BEF experiments originally started with microcosms in the laboratory and with grassland ecosystems. A new frontier in experimental BEF research is manipulating tree diversity in forest ecosystems, compelling researchers to think big and comprehensively.
 We present and discuss some of the major issues to be considered in the design of BEF experiments with trees and illustrate these with a new forest biodiversity experiment established in subtropical China (Xingangshan, Jiangxi Province) in 2009/2010. Using a pool of 40 tree species, extinction scenarios were simulated with tree richness levels of 1, 2, 4, 8 and 16 species on a total of 566 plots of 25.8 × 25.8 m each.
 The goal of this experiment is to estimate effects of tree and shrub species richness on carbon storage and soil erosion; therefore, the experiment was established on sloped terrain. The following important design choices were made: (i) establishing many small rather than fewer larger plots, (ii) using high planting density and random mixing of species rather than lower planting density and patchwise mixing of species, (iii) establishing a map of the initial 'ecoscape' to characterize site heterogeneity before the onset of biodiversity effects and (iv) manipulating tree species richness not only in random but also in trait-oriented extinction scenarios.
 Data management and analysis are particularly challenging in BEF experiments with their hierarchical designs nesting individuals within-species populations within plots within-species compositions. Statistical analysis best proceeds by partitioning these random terms into fixed-term contrasts, for example, species composition into contrasts for species richness and the presence of particular functional groups, which can then be tested against the remaining random variation among compositions.
 We conclude that forest BEF experiments provide exciting and timely research options. They especially require careful thinking to allow multiple disciplines to measure and analyse data jointly and effectively. Achieving specific research goals and synergy with previous experiments involves trade-offs between different designs and requires manifold design decisions.&#13

Exploring the dynamic characteristics of thermoelectric generator under fluctuations of exhaust heat

The thermoelectric generator is a potential candidate to recover waste heat from exhaust gas. Regarding the fluctuations of exhaust heat in practical situations, this paper adopts a transient fluid-thermal-electric multiphysics model to investigate the dynamic performance of the thermoelectric generator. Results show that the fluctuation of exhaust temperature has a greater influence on the dynamic characteristics than the fluctuation of exhaust mass flow rate. The dynamic performance of the thermoelectric generator benefits from a decrease in exhaust heat, but suffers when the exhaust heat is in an upward trend. Compared with the constant power and efficiency values of 4.96 W and 2.49 %, the average power and efficiency of the thermoelectric generator show a notable increase of 5.50 % and 70.61 % respectively during a step decrease in exhaust mass flow rate. Similarly, under a linear decrease, the mean power and efficiency experience a rise of 6.04 % and 45.05 % respectively. Besides, periodic exhaust heat can effectively amplify the dynamic output performance, especially for conversion efficiency. When subjected to a sin wave of exhaust mass flow rate, the efficiency experiences a 15.58 % improvement. This work offers a comprehensive understanding of the dynamic characteristics exhibited by the thermoelectric generator employed for waste heat recovery

Innovative design of an annular thermoelectric generator for enhanced automotive waste heat recovery

The annular thermoelectric generator (ATEG) gains significant attention in the automotive waste heat recovery field due to its compatibility with the exhaust pipe's shape. To address the performance deterioration issue due to the temperature drop, a novel annular thermoelectric module (ATEM) structure is proposed, in which the cross-sectional area of the thermoelectric elements continuously increases along the direction of heat flow. To assess the performance and perform parameter optimizations, this work develops a three-dimensional, steady-state, and fluid-thermal-electric multiphysics numerical model of the entire ATEG. The length difference of thermoelectric elements in different columns (ΔL) is comprehensively optimized through numerical simulations, and the effects of exhaust temperature and velocity on the optimal ΔL value are studied. The results indicate that a great temperature drop exists inside the ATEM, suggesting the advantages and effectiveness of the proposed novel structure configuration for modules. The optimal ΔL value is not sensitive to the exhaust gas temperature and velocity, and when ΔL = 0.06 mm, the novel ATEG achieves the highest output performance, with an output power of 76.66 W and an output efficiency of 1.45 % at the exhaust gas temperature of 550 K and the exhaust gas velocity of 30 m/s. The power and efficiency experience an improvement of 8.97 % and 8.93 %, respectively, compared to the traditional structure. Additionally, the lower exhaust gas temperature and velocity contribute to a greater performance improvement for the novel ATEG. This ATEM structural design provides a new approach to enhance performance when encountering temperature drop issues

Performance improvement of the automotive thermoelectric generator by extending the hot side area of the heat exchanger through heat pipes

In pursuit of enhancing the utilization of exhaust heat in the automotive thermoelectric generator (ATEG), this study introduces a novel heat exchanger with integrated heat pipes to extend the effective hot-side surface area. Meanwhile, a numerical model containing multiphysical fields is developed, and the quantity and arrangement of heat pipes are optimized based on this model. Results suggest that (i) The incorporation of heat pipes markedly enhances the recovery of heat energy from the ATEG, leading to a substantial increase in its output power; (ii) With an increasing heat pipe quantity, the ATEG's output power exhibits a continuous upward trend before eventually reaching stability; (iii) The arrangement of heat pipes also influences system performance, and through optimizations, the optimal quantity of heat pipes is determined to be N = 11 and toleration to be d = 1 mm. At an exhaust temperature of 550 K and a mass flow rate of 60 g/s, the ATEG achieves an output power of 213.19 W and a heat absorption of 4318.02 W, which increased by 42.95 % and 55.6 % respectively, compared with the traditional structure without heat pipes. This structural optimization concept for the heat exchanger provides a new approach to performance improvements of ATEGs. This study provides a design basis and guidance for optimizing the design of ATEG systems with integrated heat pipes

Performance investigation and design optimization of a battery thermal management system with thermoelectric coolers and phase change materials

In this work, a novel battery thermal management system (BTMS) integrated with thermoelectric coolers (TECs) and phase change materials (PCMs) is developed to ensure the temperature working environment of batteries, where a fin framework is adopted to enhance the heat transfer. By establishing a transient thermal-electric-fluid multi-physics field numerical model, the thermal performance of the BTMS is thoroughly examined in two cases. The findings demonstrate that increasing the TEC input current, fin length, and thickness is beneficial for reducing the maximum temperature and PCM liquid fraction. Nevertheless, although the increase in fin length can lower the temperature difference, the influence of fin thickness and TEC input current on the temperature difference is tiny. Based on the numerical findings, the optimal fin length and thickness of 7 mm and 3 mm are obtained. In this situation, when the TEC input current is 3 A, the maximum temperature, temperature difference, and PCM liquid fraction in Case 1 are 315.10 K, 2.39 K, and 0.002, respectively, and those are respectively 318.24 K, 3.60 K, and 0.181 in Case 2. The configuration of Case 1 outperforms that of Case 2, due to the fewer TECs and greater distance from the battery pack to the TEC within Case 2. When experiencing a higher battery discharge rate, the TEC input current should also be correspondingly increased to ensure the temperature performance of the battery. The relative findings contribute to new insights into battery thermal management

Transition Metal-Free Direct C–H Functionalization of Quinones and Naphthoquinones with Diaryliodonium Salts: Synthesis of Aryl Naphthoquinones as β‑Secretase Inhibitors

A novel ligand-free, transition metal-free direct C–H functionalization of quinones with diaryliodonium salts has been developed for the first time. The transformation was promoted only through the use of a base and gave aryl quinone derivatives in moderate to good yields. This methodology provided an effective and easy way to synthesize β-secretase inhibitors. The radical trapping experiments showed that this progress was the radical mechanism