Effect of turbulence on flame propagation in cornstarch dust-air mixtures

Following the quantitative determination of dust cloud parameters, this study investigated the flame propagation through cornstarch dust clouds in a vertical duct of 780 mm height and 160×160 mm square cross section, and gave particular attention to the effect of turbulence on flame characteristics. The turbulence induced by dust dispersion process was measured using a particle image velocimetry (PIV) system. Upward propagating dust flames were visualized with direct light and shadow photography. The results show that a critical value of the turbulence intensity can be specified below which laminar flame propagation would be established. This transition condition is about 10 cm/s. The measured propagation speed of laminar flames appears to be in the range of 0.45–0.56 m/s, consistent with the measurements reported in the literature. For the present experimental conditions, the flame speed is little sensitive to the variations in dust concentration. Some information on the flame structure was revealed from the shadow records, showing the typical heterogeneous feature of dust combustion process.      

醇胺类增塑剂对玉米淀粉与PVA混合浆相分离行为的影响

用初显分离时间和沉降率为量化指标,以甲酰胺和丙三醇为对照,研究了一乙醇胺、二乙醇胺、三乙醇胺3种不同的醇胺类增塑剂对淀粉和PVA混合浆相分离行为的影响,同时研究了一乙醇胺的用量、PVA的聚合度和醇解度对混合浆液相分离行为的影响。研究结果表明,几种醇胺类增塑剂除三乙醇胺外,都能在一定程度上延长玉米淀粉与完全醇解PVA混合浆液的初显分离时间,降低相分离速度,减少相分离程度,提高混合浆液的稳定性。     

Cationic polyacrylamides increase the rate of liquefaction and hydrolysis of cornstarch

Cationic polyacrylamides (c‐PAMs) bind to starch granules and decrease the temperature for the onset of gelatinization by 8^°C. c‐PAM increases the binding of α‐amylase to cornstarch; the rate of cornstarch hydrolysis also increases. By analogy to previous work on the c‐PAM promoted hydrolysis of cellulose, it is proposed that the polymer reduces the charge on the surface of starch through a charge‐patch mechanism. Because both enzyme and substrate are negatively charged, the bound c‐PAM reduces the charge repulsion experienced by the approaching enzyme, which leads to stronger enzyme‐substrate binding and faster hydrolysis. Overall, the c‐PAM reduces enzyme dose by up to 62% under the conditions used. There is a mirror image relationship between the viscosity of the medium and the hydrolysis rate, which allows optimization of these parameters with enzyme and c‐PAM dosage. Low c‐PAM levels increase viscosity by agglomerating the substrate, but the viscosity drops at higher c‐PAM concentration. © 2012 American Institute of Chemical Engineers AIChE J, 59: 79–83, 2013     

生物塑料聚（3HB-co-4HB）／玉米淀粉共混材料的制备与性能

以聚4-羟基丁酸酯摩尔分数为7．3％的聚（3-羟基丁酸酯-co—4-羟基丁酸酯）和玉米淀粉为原料,通过挤出熔融共混和注塑成型制备了P（3HB-co-4HB）／玉米淀粉共混材料．借用差示扫描量热仪（DSC）、热失重分析仪（TGA）和电子拉力机等考察了玉米淀粉含量对共混材料熔点、结晶度、热分解温度、耐水性及力学性能的影响．结果表明：随玉米淀粉含量增加,共混体系的结晶度减小,熔融温度降低,熔限变宽且出现明显的双峰;玉米淀粉含量为30份的共混材料热分解温度较纯P（3HB—co-4HB）-7.3略有降低,缺口冲击强度和断裂伸长率分别在淀粉含量为10份和20份达最佳,其值分别为4．95kJ／m^2和33．15％,较纯P（3HB—co-4HB）-7.3分别提高14.3％和147．76％．拉伸强度和弯曲强度则随玉米淀粉含量增加逐渐下降．     

黍米黄酒除浊方法的研究

通过考察4种澄清剂（壳聚糖、明胶、蛋清、PVPP）及3种助滤剂（水不溶玉米面、硅藻土、皂土）对黍米黄酒的除浊效果和助滤效果,选择了壳聚糖为澄清剂,水不溶玉米面为助滤剂。在此基础上,考察了二者的用量、静置时间等条件对除浊效果的影响,建立了黍米黄酒除浊方法,其壳聚糖用量为0.005 g/L,水不溶玉米面用量为20 g/L,静置时间为1 h,常温条件下过滤。试验结果表明,处理后的黍米黄酒经冷热交替强化试验或放置1年其透光率均＞99%,同时其总糖、非糖固形物、总酸、氨基酸态氮含量及感官指标均符合GB/T 13662-2008规定。     

高效厌氧反应器与生物接触氧化工艺处理玉米淀粉生产中的废水

介绍了采用高效厌氧反应器(UASB)-生物接触氧化为主体工艺来处理高浓度有机废水的工艺,处理后化学需氧量(CODcr)≤80 mg/L,生物需氧量(BOD5)≈20 mg/L,pH值6.8~7.2,基本达到《国家综合污水排放标准》(GB8978-1996)Ⅰ级排放标准。     

氧化玉米淀粉的研制及稳定性的探究

通过研究玉米淀粉的氧化及在不同贮存条件下的物理化学性能,包括羧基含量、粘度、贮存期等,分析其变质机理。结果表明氧气存在下的氧化交联与水分的蒸发协同作用是导致产品产生结皮,稳定性下降的主要原因。以此为依据加入抗氧化剂制备得到高稳定性的产品。     

淀粉接枝丙烯酰胺的合成及其絮凝性能的研究

以玉米淀粉(St)和丙烯酰胺(AM)单体为原料,采用过硫酸钾引发剂合成了淀粉接枝丙烯酰胺共聚物(St-g-AM)。用红外光谱对接枝共聚物进行了结构表征,用粘度法测定了分子量。讨论了聚合反应的各个因素对接枝共聚反应的影响,考察了接枝共聚物的絮凝性能。结果表明,以接枝效率为考察目标,其最佳的合成工艺为:引发剂的浓度为0.07 g/100 mL,淀粉与丙烯酰胺的质量比为1∶2.2,反应温度为65℃,反应时间3 h。淀粉接枝丙烯酰胺共聚物比430万分子量的聚丙烯酰胺(PAM)对高岭土水样的絮凝性能更好,当接枝共聚物的投加量为6 mg/L时,对高岭土水样的浊度去除率达到81.77%。最佳条件所合成出的淀粉接枝丙烯酰胺的分子量为75万。     

重复韧化对普通玉米淀粉消化、理化性质和结构特性的影响

通过体外消化、快速黏度分析、X射线衍射、傅里叶红外光谱、扫描电子显微镜观察等方法,探究重复韧化处理(55℃,24 h)1～3次对普通玉米淀粉消化、糊化性质及淀粉颗粒结构等的影响。结果表明,重复韧化3次可以降低普通玉米淀粉的膨胀力、快速消化淀粉和慢速消化淀粉含量,降低衰减值和回生值,提高抗性淀粉含量和凝胶硬度,相对结晶度增加4.1%,糊化温度升高2.3℃,淀粉颗粒微观表面的孔洞和缝隙增多,但没有破坏结晶结构。重复韧化处理通过促进淀粉分子链间的相互作用,使淀粉易于形成完美晶体结构,提高淀粉颗粒的热稳定性。