Study on downward flame spread over extruded polystyrene foam in a vertical channel: Influence of opening area

Experimental methods and theoretical analysis are employed to investigate effects of channel opening area on downward flame spread characteristics of extruded polystyrene (XPS) thermal insulation materials on building facade. The average flame height first drops and then rises as dimensionless opening area (the ratio of sidewall opening area to sidewall area, ie, S^*) increases. As S^* rises, both the average and maximum temperature of the curtain wall decrease, and the decreasing of the average temperature is linear. XPS surface temperature history can be divided into four stages, ie, inapparent rising stage (preheating), significant rising stage (melting), dropping stage (pyrolysis), and rerising stage (ignition). The preheating length first rises and then drops as S^* increases. The XPS flame spreads steadily at the early period while acceleration occurs at the later period. For different opening areas, the difference in spread distance history is not apparent in the early stage while this difference is significant in the later stage. The flame spread rate (V_f) first increases and then decreases as S^* rises. A downward flame spread model for XPS in vertical channel with openings is built. The varied trend of V_f predicted using this model corresponds to the experimental result.     

Uplift capacity of horizontal anchor plate in geocell reinforced sand

The paper investigates the uplift performance of horizontal anchor plate in geocell reinforced sand through a series of model tests. It is noted that the unreinforced anchor plate undergoes a clear failure at a displacement of about 3% of its width, whereas with the provision of geocell and a layer of geotextile right below the geocell mattress significantly increases the uplift capacity by about 4.5 times higher than that of unreinforced sand and could sustain anchor displacement of more than 60%. Results indicates that the geocell mattress by virtue of its rigidity distributes the uplift load in the lateral directions to a larger area, thereby reducing the stress in the overlying soil mass and hence increases the performance of anchor plate system. The provision of the additional geotextile layer right below the geocell mattress is found to be very effective in increasing the stiffness as well as load carrying capacity of anchor plate system. The optimum size (i.e., width and length) of geocell mattress giving adequate load carrying capacity of anchor plate is found to be 5.4 times of anchor width (5.4B). The comparison of model tests results with 3D numerical analysis shows good agreement, indicating that the proposed model is able to capture the uplift load-displacement behaviour of geocell reinforced anchor plate system.     

Diversity of Biogas Plant Realizations

A techno‐economic analysis for four different types of biogas plant realizations was performed, including one biogas biorefinery concept. For each concept detail, a process flow diagram was created. Mass and energy balances were estimated. The net present value and payback were calculated for each concept for a better feasibility understanding. The results showed that with the used expensive substrate, namely, wheat straw, the obtained paybacks appeared to be more than 100 years. Sensitivity analysis was done for the price range of a substrate. Critical factors were defined to improve feasibility.     

Mathematical model for coal conversion in supercritical water: reacting multiphase flow with conjugate heat transfer

Providing heat for supercritical water gasification (SCWG) of coal by coupling subsequent products oxidation in integrated supercritical water reactor (ISWR) provides an effective method for directional control of temperature field and avoids excessive hot spots caused by uniform heating. An exploratory numerical model incorporating particle-fluid flow dynamics, multispecies transport and thermal coupling between endothermic coal gasification and exothermic product oxidation was established to simulate the reacting multiphase flow process of coal conversion in a novel lab-scale ISWR. An eleven-lump kinetic model was proposed for the prediction of chemical reactions. And the thermal coupling relationship was described by conjugate heat transfer boundary conditions (BC). Detailed physical and chemical field distribution in ISWR were analyzed and influence factors were discussed. The results showed that oxidation of gas products as inner heat source could promote the gasification reaction with only slight or even little maximum temperature increase of the pressure-bearing wall. Coal feeding rate and oxygen supply method significantly affected the field distribution. The multi-injection compressed-air supply method provided a more uniform temperature field but would reduce heat transfer temperature difference. The carbon gasification efficiency (CGE) in the gasification zone could easily reach up to 97% under mild conditions (less than 650 °C).     

气瓶内部淬火过程的流动换热特性

 大直径厚壁气瓶内部淬火时的流动换热过程极其复杂，受到多种因素的影响，而研究气瓶内部压强和温度的变化规律对改善流动换热效果、提高产品组织性能具有重要的理论指导意义。以914 mm厚壁气瓶和瓶内流体为研究对象，建立了二维等效流 固耦合模型；采用多喷嘴系统对气瓶内外进行喷水淬火，研究了气瓶总长、喷水流速及淬火时间对瓶内压强及内壁温度的影响，通过间歇淬火试验验证了数学模型的正确性。结果发现，气瓶长度对瓶内压强和瓶壁温度的影响显著，喷水流速次之，当喷水流速大于8 m/s后，水量对瓶壁的冷却效果大大降低；气瓶内壁长度方向的温度梯度分别随气瓶总长的增加和淬火时间的延长而减小，但基本不受喷水量的影响。     

高温深井通风降温技术的适用条件研究

随着矿山开采深度的不断增加，“三高一扰动”恶劣开采环境问题日益突出，给矿井通风降温工作带来极大困难。对于深井矿山，仅采用通风降温难以满足深部开采的需要，系统研究高温深井矿山通风降温技术的适用性问题，对矿山深部开采具有重要的理论意义和工程适用价值。首先从热力学角度，揭示风流在通风线路中的热交换规律；其次利用差分法原理计算深井筒风流温度，并依此推导出巷道和回采工作面风流温度变化趋势；然后结合采场安全生产允许温度进行反推，最终获取通风降温条件下的可采极限深度计算公式，并选取广西铜坑矿锌多金属矿体作为工程应用试验区进行论证分析。结果表明：基于风流的热交换模型可以推导出风流在井筒、巷道及工作面的温度计算公式，该公式与低温梯度、风流流经路径长度有关；假定工作面温度达到安全开采允许最高温度，可反推出该条件下矿山可采极限深度和巷道通风极限长度（仅采用通风降温措施时）；基于铜坑矿区锌多金属矿的实际条件，代入相关数据，验证计算所得极限开采深度符合实际，即所推导公式是可行的。     

高熵合金制备及热处理工艺研究进展

与传统合金相比,高熵合金表现出了高强韧、良好的软磁性、高温稳定性、耐腐蚀性等突出特点,在许多的领域应用潜力巨大。本文主要介绍真空熔炼、粉末冶金、激光熔覆和磁控溅射等制备高熵合金方法的研究进展及优缺点,分析了不同热处理工艺对组织结构和力学性能的影响,并对高熵合金制备和模拟计算等方面提出了展望。     

MW级空间核反应堆系统热管式辐射散热器分析及优化

空间核反应堆是空间核电源和核推进的研究基础，大功率核反应堆的体积和质量一直是限制航空航天设计的重要因素。针对这一问题，本文对MW级空间核反应堆系统热管式辐射散热器进行建模和分析，建立热管式辐射散热器的热阻模型，利用穷举法和遗传算法在给定工况下探讨裸碳纤维翅片长度L_f和厚度δ_f、冷却剂质量流量m、辐射散热器入口温度T_f1对散热器质量M的影响。结果表明，当T_f1＝800 K、L_f＝5 cm、δ_f＝0.16 mm、m＝9 kg/s时，M达到最优，为906.593 kg，优化了0.63%的系统质量。     

地埋管换热器分区运行对土壤热堆积特性影响的研究

为了缓解埋管区域土壤的热量堆积问题,提出了埋管换热器按内中外、块状、间隔三种分区运行的策略,利用CFD软件建立了10×10的井群换热模型,对地源热泵系统在三种分区与不分区运行策略下运行十年进行数值模拟,分析不同分区运行策略对土壤温度分布和土壤热堆积特性的影响。模拟结果可知:不分区、内中外分区、块状分区、间隔分区四种运行策略下埋管区域的平均温度分别为25.23、23.31、23.06、23.28℃,最高温度分别为40.62、32.77、40.65、38.93℃;分区运行较不分区运行可以有效缓解热堆积作用,埋管区域整体温度较不分区运行时降低了2.00℃左右,内中外分区策略可以显著缓解埋管区域热堆积。