Fossil carbon emissions associated with carbon flowsof wood products

Specific fossil carbon (C) emissions and primary energy useassociated with the manufacture of different wood product groups inFinland are estimated and expressed as emissions or energy use per amountof wood-based C in raw material and per amount in end product. Thecalculation includes both emissions from supplied fuels within the forestindustries, and from electricity and district heat purchased from externalsources. The results are compared to fossil C emissions from the wholelifecycle of harvested wood products. The results of the study show, forinstance, that the emission of fossil C per wood-based C in end products(MgC/MgC) is of the order of 0.07 for sawn wood and 0.3–0.6 for paperin the manufacturing stage. The primary energy use per wood-based C inend product is of the order of 2 MWh/MgC for sawn wood, whereas forvirgin paper grades the figure is between 17 and 19 MWh/MgC. Theprimary energy content is highest in papers based on chemical pulping, butaround 60% of the energy used is produced in this case from by-productwood wastes (black liquor, bark etc.). The specific fossil C emission andprimary energy divided by the estimated service life of the wood productare measures for the relative burden of maintaining the corresponding woodproduct pool. These figures should be kept in mind when considering woodproducts as a potential C sink option.     

海洋碳的源与汇

通过对海洋碳源汇最近研究成果的分析,剖析了海洋碳源汇的内涵,提出了“表观碳源汇”与“实际碳源汇”的概念,对海洋碳源汇不确定性的原因进行分析,提出碳参数测定不淮确与其关键生物地球化学过程不清楚是其根本原因,继而提出了海洋碳源汇研究应特别注重陆架边缘海碳循环过程研究,提高碳参数测定的淮确性和应深入研究控制碳循环关键的海洋生物地球化学过程是其研究关键。     

城市热环境及防治措施

随着城市化速度的加快，热环境诸因素的变化也更显著。分析城市区域特征所引起的热环境各因素的变化趋势，采取相应防治措施，改善城市环境质量。     

Modeling of Flow Field and Heat Transfer in a Copper-Base Automotive Radiator Application

This paper describes a methodology used for designing louvered fins. Louvered fins are commonly used in many compact heat exchangers to increase the surface area and initiate new boundary layer growth. Detailed measurements can be accomplished with computational models of these louvered fins to gain a better understanding of the flow field and heat distribution. The particular louver geometry studies for this work have a louver angle of 23° and fin count of 17 fpi.

The flow and heat transfer characteristics for three-dimensional mixed convection flows in a radiator flat tube with louvered fins are analyzed numerically. A three-dimensional model is developed to investigate flow and conjugate heat transfer in the copper-based car radiator. The model was produced with the commercial program FLUENT. The theoretical model has been developed and validated by comparing the predictions of the model with available experimental data. The thermal performance and temperature distribution for the louvered fins were analyzed and a procedure for optimizing the geometrical design parameter is presented.

One fin specification among the various flat tube exchangers is recommended by first considering the heat transfer and pressure drop. The effects of variation of coolant flow conditions and external air conditions on the flow and the thermal characteristics for the selected radiator are investigated also. The results will be used as fundamental data for tube design by suggesting specifications for car radiator tubes.     

Numerical Analysis of Heat Transfer and Gas Flow in PEM Fuel Cell Ducts by a Generalized Extended Darcy Model

Abstract

In this work, gas flow and heat transfer have been numerically investigated and analyzed for both cathode/anode ducts of proton exchange membrane (PEM) fuel cells. The simulation is conducted by solving a set of conservation equations for the whole domain consisting of a porous medium, solid structure, and flow duct. A generalized extended Darcy model is employed to investigate the flow inside the porous layer. This model accounts for the boundary-layer development, shear stress, and microscopic inertial force as well. Effects of inertial coefficient, together with permeability, effective thermal conductivity, and thickness of the porous layer on gas flow and heat transfer are investigated.     

Evaluation of the Use of Artificial Neural Networks for the Simulation of Hybrid Solar Collectors

Abstract

In the last decade, Artificial Neural Networks (ANNs) have been receiving an increasing attention for simulating engineering systems due to some interesting characteristics such as learning capability, fault tolerance, speed and nonlinearity. This article describes an alternative approach to assess two types of hybrid solar collector/heat pipe systems (plate heat pipe type and tube heat pipe type) using ANNs. Multiple Layer Perceptrons (MLPs) and Radial Basis Networks (RBFs) were considered. The networks were trained using results from mathematical models generated by Monte Carlo simulation. The mathematical models were based on energy balances and resulted in a system of nonlinear equations. The solution of the models was very sensitive to initial estimates, and convergence was not obtained under certain conditions. Between the two neural models, MLPs performed slightly better than RBFs. It can be concluded that similar configurations were adequate for both collector systems. It was found that ANNs simulated both collector efficiency and heat output with high accuracy when “unseen” data were presented to the networks. An important advantage of a trained ANN over the mathematical models is that convergence is not an issue and the result is obtained almost instantaneously.     

Net Ecosystem Production of Boreal Larch Ecosystems on the Yenisei Transect

The study was carried out in the Turukhansk Research Station of Yenisei Transect (65^°46^′N, 89^°25^′E). Larch (Larix gmelinii (Rupr.) Rupr.) is the dominant overstory tree species. The research has been conducted on four permanent test plots in same-age mature (110-year old) and overmature (380-year old) post-fire larch stands of green moss and lichen groups of forest type. Carbon cycle parameters were assessed based on a biometric method. Quantitative analysis of carbon pools and fluxes shows that net ecosystem production of north taiga larch stands averages 32% of net primary production. Sink of atmospheric CO₂ makes 1.22 and 0.74 t C ha^{− 1} year^{− 1} for mature and overmature green moss larch stands, and 0.65 and 0.35 t C ha^{− 1} year^{− 1} for lichen type. Net carbon sink in the tree layer make up 9% of net primary production carbon, ground vegetation – 15%, and dead plant residues accumulation – 8% of atmospheric carbon uptake via photosynthesis.     

珠江流域水化学组成的时空变化特征及对岩石风化碳汇估算的意义

基于水-岩-气-生相互作用的碳酸盐风化碳汇模型表明,陆地碳酸盐风化碳汇是大气CO_2汇的重要组成部分;然而,碳酸盐风化碳汇的过程、机制和控制因素仍有待进一步的研究。本文采用野外监测、现场滴定和样品室内测试相结合的方法,对珠江流域支干流分旱季和雨季进行了4次野外监测取样,研究其水化学组成的时空变化特征。结果表明:珠江流域支干流的水化学组成受流域岩石风化、气候和水生光合作用的共同影响,并具有明显的时空变化特征。空间上,南盘江下游双江口段至红水河上游蔗香段,水流较慢,水质清澈,水生光合作用强烈,电导率、[HCO_3~-]和[Ca~(2+)]的空间变化主要受水生光合作用控制;从红水河上游蔗香段至肇庆西江大桥监测点,反映的是流域岩石风化对水化学空间变化的影响。季节变化上,西江的电导率、[HCO_3~-]和[Ca~(2+)]呈现出夏季低、冬春季高的特征,主要反映稀释效应的控制。西江干流河水的溶解氧具有明显的季节变化,在上述南盘江下游双江口段至红水河上游蔗香段,DO是夏季高冬季低,其他监测点是冬季高而夏季低;DO的季节变化受水生光合作用强度的控制。在南盘江下游双江口段至红水河上游蔗香段,温度是光合作用强度的限制因子,而其他监测点的光合作用限制因子为浊度影响的光照。造成上述差异的原因是监测点的水文环境不同。通过对梧州水文站流量和[HCO_3~-]变化的分析发现,[HCO_3~-]的季节变化幅度相对流量小得多,显示在西江流域中,HCO_3~-也存在化学稳定性行为。因此在西江流域中,流量变化是岩溶碳汇通量变化的主控因子。研究还发现,西江流域中具有强烈的生物碳泵效应,由内源有机碳形成的碳汇通量约占传统计算模式碳汇(溶解无机碳-DIC)通量的40%。因此,在估算珠江流域碳酸盐风化碳汇时,必须考虑水生生态系统光合生物对DIC的利用形成的有机碳的贡献。     

基于锥形量热仪的几种防火布燃烧性能研究

生产企业常在电缆或者贵重高危机器处设置防火布来保护生产设备设施的消防安全,选取五种常用的防火布:石棉纤维防火布、陶瓷纤维防火布、硅胶防火布、涂胶防火布、碳素纤维防火布,通过锥形量热仪实验研究不同辐射强度对防火布燃烧性能的影响。结果表明:点燃时间的均方根倒数与辐射强度之间呈现线性关系;在35 kW/m~2辐射强度工况下,碳素纤维防火布的热释放速率最大,达到272.59 kW/m~2,有效燃烧热的峰值也最大,达到529.52 kJ/g;综合比较各样品的燃烧性能,防火能力强弱顺序为:硅胶防火布石棉纤维防火布陶瓷纤维防火布碳素纤维防火布涂胶防火布。     

密度对聚氨酯软泡收缩及燃烧行为的影响

采用锥形量热仪研究不同密度聚氨酯软泡(FPUF)的燃烧行为,并根据摄像、体视显微镜所观察的样品形体及泡孔结构的变化来研究火灾条件下FPUF的收缩特性。研究结果表明,收缩是表层泡孔受热发生热解生成焦油所致的泡孔塌缩现象,焦油层下方泡孔结构基本没有变化;FPUF密度越大着火前的收缩速率越小,同一时刻表层泡孔热解生成的焦油层越薄。FPUF的着火燃烧可分为受热收缩、燃烧收缩和池火燃烧三个阶段。中高密度样品HRR曲线先出现平台后出现峰值,分别对应于燃烧收缩和池火阶段,且密度越大HRR曲线的平台越低、峰值越高,燃烧收缩阶段的FIGRA越小,而池火燃烧阶段的FIGRA越大。着火前的快速收缩导致低密度样品的HRR曲线不出现平台只呈现单峰。