Lateral growth of a wheat dough disk under various growth conditions

Numerous studies have tried to understand and model bubble growth inside dough. Experimental studies are inconvenienced by the methods’ inability to capture the dynamic phenomena. In this paper, a versatile experimental method was developed to allow for macroscopic expansion of wheat dough. The study evaluates expansion of a dough disk under varying: moisture content (40, 41, 42, 43, and 44% wb), leavening acid concentration (30, 40, and 50% db), pressure schemas, pressurizing gas (compressed air and CO₂), and lubrication (Teflon^® film coating and Pam^® aerosol lubricant). Dough expansion increased 22.6% by increasing moisture content from 40 to 44%. Increased baking powder formulation (40% db) was used to enhance initial growth conditions and CO₂ production. ‘Pressure pulse’ and ‘pressure vacuum methods’ added pressurization alternatively with full vacuum. The former method included a rest period before vacuum application, and increased expansion by 10.8%. Teflon^® and Pam^® reduced friction between the dough and acrylic plate and increased the final expansion by 14.7% compared to no lubricant following the ‘standard pressurization method’. ‘Pressure pulse’ and ‘pressure vacuum’ experiments decreased expansion by 28.4 and 38.2%, respectively compared to ‘standard pressurization’ while using Teflon^® and Pam^®.     

反相高效液相色谱法检测香草兰豆酊、浸膏中香兰素

采用反相高效液相色谱法测定香草兰豆酊、浸膏中香兰素含量,色谱柱为C_(18)柱,甲醇/0.5%冰乙酸水溶液(20/80.v/v)为流动相,等浓度洗脱,测定波长为280 nm,外标法定量.该方法相对标准偏差分别为0.28%和0.24%.加标回收率为97.89%～100.71%.本方法具有操作简便,结果准确等优点,特别适用于香草兰豆酊、浸膏等精深加工产品中香兰素含量的检测分析.     

胶粘剂种类、加压时间对3种常用斜角榫接合性能的影响

斜角榫接合是传统家具的主要结构方式,也是现代中式家具的标志性结构方式.在木家具结构设计中,特别是中式实木家具结构设计中,木框角部斜角榫接合强度是人们担心的问题.实木家具中木框斜角榫接合强度因其榫卵形式、胶粘剂种类、保压时间等影响因子的不同而不同,其中,抗拉强度和抗弯强度是衡量木框斜角榫接合性能的两个重要指针.本文对3种常用的、易于机械加工的斜角榫接合试件的抗拉强度,抗弯强度进行了实验测定,并对其进行比较、分析.研究结果表明:胶粘剂种类,加压时间都不同程度的影响着木框角部接合的整体结构强度.     

超高压处理对鲜切山药片质量的影响

为研究适宜的鲜切山药片的保藏方法,采用超高压处理对鲜切山药片进行保鲜。将鲜切山药片分别采用0MPa、200MPa、400MPa和600MPa加压处理10min后,在4℃条件下贮藏9d,分析超高压处理对贮藏期间鲜切山药片中细菌总数、多酚氧化酶活性、褐变指数、可溶性固形物、总酸和维生素C含量的影响。结果表明：600MPa压力处理10min后,可抑制于褐变相关的多酚氧化酶,抑制微生物生长,产品在4℃条件下贮藏9d后,仍然可具有较好的理化指标,表明该法是一种较好的鲜切山药片的保藏方法。     

两段变曲率叶型离心泵流场数值模拟

采用CFD技术对两段变曲率叶型离心泵内部流动进行定常和非定常三维数值模拟,并和设计参数相同的普通叶型离心泵进行对比,得到内部流场特征及监测点的压力脉动情况。结果表明,两段变曲率叶型离心泵可以很好地防止叶轮内尾流的产生和发展。叶轮与隔舌间的动静干涉是产生泵压力脉动的主要脉动源,且流量越大,隔舌处压力脉动越大。同一流量下,两段变曲率叶型离心泵的压力脉动幅值比普通离心泵小,在一定程度上减小了泵的水力损失。     

主动配气式生物质气化炉流场模拟与试验

对下吸式固定床气化炉采用两层配气口实现气化剂进给量的主动控制,利用Fluent软件对炉内气压分布和速度进行模拟分析,结果表明气化炉主要反应区气压场呈现"梯级分布、层界分明"规律,速度场由上而下逐渐递增,同一截面流场具有较高的均匀性。以玉米秸秆为原料,对本气化炉压力场和温度场进行了试验研究,结果表明采取主动配气有利于促进气化炉的均匀反应,同一反应截面反应温度相对稳定,燃气组分波动较小,热值保持在5 500 kJ/m3以上。     

带小叶片螺旋离心泵压力脉动特性分析

为了研究带小叶片的单叶片螺旋离心泵压力脉动特性,采用Navier-Stokes方程和标准的k-ε湍流模型对带小叶片和单叶片的螺旋离心泵的内部流场进行非定常数值计算。通过模拟分别获得了带小叶片和单叶片的螺旋离心泵蜗壳出口以及蜗壳内部压力脉动特性,并对其进行对比分析。结果表明:各个工况下,带小叶片和单叶片的螺旋离心泵蜗壳出口以及蜗壳内部压力脉动特性呈周期性变化,且主频均为各自叶片通过频率,压力波动的幅度大部分集中在低频区域;采用小叶片后周期变为原模型周期的一半,蜗壳及蜗壳内部出口压力波动的幅度明显减小,脉动幅值也明显减小,且高频脉动有所减少。研究表明单叶片螺旋离心泵叶轮小叶片的添加可以有效改善泵内部压力脉动特性,且对降低蜗壳上的振动噪声有一定积极作用。     

Combining local pressure and temperature measurements during bread baking: insights into crust properties and alveolar structure of crumb

Improvements in both the miniaturisation and heat compensation of pressure transducers made it possible to measure pressures as low as 5 kPa inside bread dough during baking (ΔT = 80 °C). Additional calibration was found to be necessary to decrease it below 0.18 kPa according to the variations in temperature encountered during baking. Two probes with both a thermocouple and a miniature pressure transducer were used to reveal pressure gradients inside bread dough during baking and post-cooling. During baking, increase in pressure (up to 1.1 kPa) was mainly attributed to the mechanical restrictions exerted on the dough by the stiffened surface layers. Pressure build-up due to the stiffening of bubble walls could not be detected. Various effects of the rupture in the bubble walls are reported. Sudden falls in pressure observed up to 70 °C were attributed to the bubble coalescence phenomenon. Evidence of an open porous structure was provided by the balance in pressure through the dough before the end of baking and the almost simultaneous lowering of pressure (−0.15 kPa) throughout the crumb during cooling. The slight lowering of pressure during post-cooling was also evidence of lower permeability of the crust compared to the crumb.     

Measurement of local pressure during proving of bread dough sticks: Contribution of surface tension and dough viscosity to gas pressure in bubbles

Proving of bread dough is a crucial step in bread making. So far researches have succeeded in modelling the bubble growth according to miscellaneous external conditions. These models are based on assumptions that can be discussed at the light of pressure measurements inside dough bubbles during proving. In this study, the use of miniaturised pressure transducers made it possible to assess pressure inside bubbles of diameter larger than a quarter of a millimetre. Pressure results were discussed with the use of a simplified mathematical model in order to give insights onto the forces restricting bubble growth. The relevance of the surface tension versus the viscous resistance of the dough was discussed into two water content conditions.     

滴头压力对玉米生长发育及产量的影响

为研究不同滴头压力对玉米生长发育及其产量的影响。基于大田试验,研究4个滴头压力水平对滴灌玉米生长的影响。结果表明:灌后不同时间滴头压力为0.03 MPa处理的玉米叶绿素SPAD值均为最高;滴灌玉米抽雄期和成熟期整株生物量均随着压力减少而呈现单峰增长趋势,抽雄期各处理整体生物量呈现0.04 MPa处理0.02 MPa处理0.03 MPa处理0.05 MPa处理,成熟期各处理整体生物量呈现0.03MPa处理0.04 MPa处理0.05 MPa处理0.02 MPa处理;滴头压力为0.03 MPa的处理产量最高,显著高于0.05 MPa处理和常规种植,增产幅度分别为20.3%和21.0%。可见,滴头压力0.03~0.04 MPa对于北疆膜下滴灌玉米生长过程较为有利。