浆板机气垫式热风箱气体流动及传热特性模拟研究

探讨了浆板机气垫式热风箱的入口风速、气体温度、出风板开孔率、喷口形状及布置方式对气垫式热风箱气体流动和传热性能的影响。研究表明,热风箱内静压值沿流动方向呈线性增加,随出风板开孔率增大而减小;喷口为圆形叉排时表面传热系数最高,为7.74 W/(m2.K),三角孔直排时表面传热系数最低,为5.78 W/(m2.K);热风箱最佳参数为入口空气温度75℃、风速12 m/s、圆孔叉排、开孔率为7.42%。     

气垫橡皮布与高速印刷

在胶印中,常用的胶印橡皮布有两类,一类是普通型橡皮布,它由表面胶层、中间布层和底面布层组成,如图1;另一类是气垫橡皮布,它是由表面胶层、中间二层及底面一层涂胶织物和气垫层组成,如图2。随着胶印技术及印刷机械的发展,印刷速度越来越快,橡皮布的特性也发生了巨大的变化,由原来的合成橡胶型向气垫型过渡,且气垫型已成为橡皮布的主流。在高速印刷中,气垫橡皮布主要有以下优点。     

超高静压下食品压致升温的预测及数学模型建立

为了弄清食品在超高静压下的压致升温情况,以便准确控制杀菌的加工工艺条件,本文测定了较小热损失条件下(利用聚四氟乙烯套筒模拟)食品及其成分的压致升温值并提出了预测某一食品压致升温值的方法,与实测值比较可知此方法能较好地预测其压致升温值;由热力学第一定律推导出一定压力和温度范围内某一食品的压致升温值主要取决于其初始温度和压力,并通过经验方程拟合食品的压致升温值,建立了食品压致升温值与压力和初始温度之间的关系。在100~400 MPa下温度25~55℃时较小热损失条件下对水、大豆油和橄榄油的压致升温值进行拟合,结果表明,对这三种物质拟合得到方程的回归系数依次分别为0.976、0.990和0.981,此外,将实测值和用方程拟合得到的预测值进行比较,相对误差均不超过5%,说明此方程的拟合效果较好。     

气垫橡皮布与高速印刷

在胶印中,常用的胶印橡皮布有两类,一类是普通型橡皮布,它由表面胶层、中间布层和底面布层组成,如图1;另一类是气垫橡皮布,它是由表面胶层、中间二层及底面一层涂胶织物和气垫层组成,如图2.随着胶印技术及印刷机械的发展,印刷速度越来越快,橡皮布的特性也发生了巨大的变化,由原来的合成橡胶型向气垫型过渡,且气垫型已成为橡皮布的主流.在高速印刷中,气垫橡皮布主要有以下优点.     

双循环高静压对鱿鱼原肌球蛋白二、三级结构的影响

为研究双循环高静压处理对鱿鱼原肌球蛋白结构的影响,通过圆二色谱、自由巯基含量和表面疏水性分析原肌球蛋白的二级和三级结构变化。与对照组相比,双循环高静压(200,400 MPa和600 MPa,20 min)使α螺旋降低50%,β螺旋增加10%,随机结构增加40%。双循环高静压降低了蛋白自由巯基含量,增加了表面疏水性,在600 MPa下自由巯基含量减少高达35%,表面疏水性增加47%。高静压引起的原肌球蛋白二、三级结构变化与蛋白致敏性降低具有显著的相关性(P0.01)。研究表明,双循环高静压能够有效改变原肌球蛋白结构,进而降低致敏性。     

喷雾干燥入口温度对大目金枪鱼皮明胶乳化特性的影响

研究不同喷雾干燥入口温度（130、160、190 ℃）对大目金枪鱼皮明胶乳化特性的影响。通过乳析指数和乳液微观结构评价乳化效果,通过表面疏水性和凝胶强度评价不同乳液界面与连续相的差异,通过明胶分子质量分布和红外光谱初步分析喷雾干燥入口温度影响明胶乳化特性的机制。结果表明,随着喷雾干燥入口温度的升高,明胶的高分子质量亚基被过度破坏,降低了三螺旋结构的完整性,从而导致更多的亲水性氨基酸被暴露,进而降低了凝胶强度（851.29～676.65 g）和表面疏水性（218.81～82.96）,表面疏水性的降低不利于明胶在油-水界面的吸附及网络结构的形成,明胶凝胶强度的降低表明乳液连续相中网络结构变得松散,最终表现为明胶乳液的液滴粒径和乳析指数增大,乳液稳定性降低。由此可见,当前研究的喷雾干燥入口温度（130、160、190 ℃）与乳液稳定性呈负相关,利用喷雾干燥制备乳化型鱼皮明胶,入口温度不宜过高,130 ℃时效果更佳。     

电热织物系统热传递模拟及其参数设计

为保证电加热服装的舒适性与安全性,并为其优化设计提供参考,通过Comsol软件建立了包含皮肤层的电热织物系统传热模型,考虑了热传导、热对流、热辐射3种传热方式,进行了多物理场耦合模拟。将模拟的瞬态结果与实验数据进行对比发现,二者随时间变化的温度曲线相近,且实时温度和最终温度相对误差均低于4%,说明模拟值与实验值之间具有良好的吻合性。通过该数值模型进行了稳态的参数化研究,拟合了皮肤温度与环境温度、风速、发热片加热温度、服装内外层热阻之间的线性关系,建立了皮肤温度预测模型,并应用模型设计电加热服装的相关参数。本文研究结果可为特定使用环境下电加热片的设计与选择提供理论参考。     

无水胶印输墨系统油墨温度控制方法

油墨温度控制系统是无水胶印设备的重要控制组件之一,对保持油墨黏度稳定和印刷质量的一致性有重要影响。通过建立温控墨辊表面墨层热载荷时变函数模型,计算墨辊表面油墨平均温度发生变化时的热载荷变化量,根据对温控墨辊螺旋管道的传热性能参数进行等效,在采用涡流管作为温度双向控制伺服装置的前提下,确定了温控气体在设定出入温度差的条件下的输入流量,将温控气体的输入参数,包括流量值、入口温度值作为涡流管伺服控制器的输入参数,建立油墨温度PID整定控制模型,并基于Lab VIEW设计了控制系统。仿真结果表明控制模型合理,无水胶印油墨温控系统控制精度达到±1℃。     

适用于高速印刷的气垫橡皮布

1875年,R.Barclay发明了有中间滚筒的金属印刷用石版印刷机,当时在中间滚筒上使用了经过表面处理的厚纸,这就是印刷橡皮布的起源。大约在1950年,以能耐油墨的优质合成橡胶制成了印刷橡皮布。接着,大约在1960年,开发出了加有压缩层(微孔海绵层)的气垫橡皮布,经过近几年的不断改良,气垫橡皮布已成为橡皮布的主流。随着对微孔海绵层内藏位置、压缩应力的不断研究,气垫橡皮布达到了稳定的品质。     

紫玉米花色苷微胶囊化工艺和性能研究

采用响应面分析法优化紫玉米花色苷微胶囊化的配方及工艺,并对其微观特性进行表征。结果显示：喷雾干燥入口温度是影响紫玉米花色苷包埋率最主要因素;紫玉米花色苷最佳工艺为紫玉米花色苷占总固形物质量分数15%、麦芽糊精占总固形物质量分数45%、总固形物质量分数为25%和喷雾干燥入口温度140℃,在最佳工艺条件下,紫玉米花色苷包埋率为95.2%;扫描电镜和激光粒度仪分析进一步验证当喷雾干燥入口温度为140℃时,微胶囊化紫玉米花色苷的表面无明显裂痕和孔洞,粒径分布均比较集中(2～30μm),峰值出现在7.13μm。     

HEAT TRANSFER COEFFICIENT FOR COOKIE SHAPED OBJECTS IN A HOT AIR JET IMPINGEMENT OVEN

Correlations for average heat transfer coefficient for cookie shaped objects in a hot air jet impingement oven were obtained using aluminum cookie models. The study was carried out in a pilot plant scale hot air jet impingement oven. The effects of individual cookie position, presence of surrounding cookies, air velocity, air temperature and rotation of the oven plate on average surface heat transfer coefficient were investigated. The value of the heat transfer coefficient ranged between 100–225 W/m²K and was found to be a strong function of jet air velocity. The impact of surrounding cookies on the heat transfer coefficient was more for smaller cookies, which had larger cookie‐to‐cookie spacing.     

THERMAL TRANSPORT IN A MULTIPLE JET IMPINGEMENT OVEN

Three‐dimensional numerical simulation of flow field and heat transfer in a jet impingement oven with multiple jets was carried out. Distribution of local heat transfer coefficient on a model cookie in the oven cavity was obtained from the predicted flow and temperature fields, and compared with the experimentally measured values. Effects of air temperature (400, 450K) and air velocity (2.5, 5, 10 m/s), on the surface heat transfer coefficient were studied. Numerical predictions showed good agreement with the experimental results. It was found that heat transfer coefficient was a strong function of air velocity while air temperature had no effect on the heat transfer coefficient. Local heat transfer coefficient values ranged between 11 and 66 W/m²K whereas average heat transfer coefficient values ranged between 24 and 42 W/m²K. Results also showed that because of the presence of the suction fan in the oven, flow field near the model cookie surface was quite different from that for a jet impinging on a flat surface.     

Determination of Retortable Pouch Heat Transfer Coefficients by Optimization Method

A computer-based optimization technique was developed for determining the apparent heat transfer coefficient (h) for retortable pouches heated by circulated hot water under overriding air pressure. The technique incorporated actual process data, a finite difference model and an optimization criteria to converge on h values. A water flow channel was constructed to fit inside a vertical retort which allowed direct water exposure on the pouch surface at a quantifiable velocity. Because the optimization technique was not dependent on analytical equations, it could be applied to such areas as future heat transfer studies of new retortable pouch materials, designing new pouch-holding cassettes and improving water flow patterns in retorts.     

Heat transfer during contact cooking of minced meat patties

Experimental results on heat transfer during heating of four types of minced meat patties by contact with hot plates are given. Experimental equipment, method of measurement and experimental values of heat flux from heating plate to heated product surface during 4 min contact cooking are described. Simultaneous measurements of product and heating plate temperatures as a function of time were used to determine the contact heat transfer coefficient between heating plate and product surface. The results show that the heat flux varied during the heating process. The magnitude of the heat flux as a function of time varies with the type of material heated and the heating plate temperature. The heat transfer coefficients measured were in the range 200 to 1200 W m^?2 K^?1, depending on product type, contact plate temperature, contact pressure and stage in the heat treatment.     

空气冷却器开缝翅片传热与流动特性的数值模拟研究

文章采用CFD软件FLUENT对空压机中间冷却器用开缝翅片和平直翅片的流动和传热进行了三维数值模拟。通过建立管翅结构的局部模型,利用标准κ-ε湍流方程,研究了温度、速度等在翅片附近的分布,并对比了平直翅片和开缝翅片的模拟结果。结果显示:开缝翅片对空气流动有较大扰动作用,在开缝结构附近出现了大量涡流,强化了空气和冷却水之间的传热过程。在同样条件下,开缝翅片空气侧换热系数比平直翅片大8%,而开缝翅片的压力降比平直翅片也相应增大。     

Effect of variety on the heat transfer coefficient during drying of fermented ground cassava

The effect of variety on the heat transfer coefficient of four cassava cultivars (TMS 30555, TMS 30572, NR 8082 and one Native type) was investigated. The cultivars were dried at an air temperature of 142 °C, air velocity of 1.397 m/s⁻¹ and relative humidity of 55%. The heat transfer coefficient obtained varied from 0.0622 to 0.0725 kJ kg s °C. The heat transfer coefficient varied for some cultivars, while some cultivars had close heat transfer coefficient. NR 8082 had the lowest heat transfer coefficient while TMS 30555 had the highest heat transfer coefficient. The cultivars with high heat transfer coefficient were found to have low bulk density, smaller particle diameter, high drying rate, low specific heat capacity and high carbohydrate fat and protein contents than other cultivars.     

Non-uniform Heat Transfer During Air-Blast Freezing of a Fruit Pulp Model in Multilayer Boxes

Effective heat transfer coefficients were measured using an aluminum test body and compared with the results obtained from a Gnielinski correlation for air-blast freezing of a fruit pulp model in multilayer boxes, with the internal airflow through rectangular ducts and the hydraulic diameter as characteristic dimensions. The quantities of products inside the boxes were varied, and the inlet air velocities and temperature profiles during freezing were measured. The inlet air velocities were applied in dimensionless Gnielinski correlations to estimate the local heat transfer coefficient values. The experimental and predicted heat transfer coefficient values were used to determine an average convective heat transfer coefficient weighted by the heat transfer area. The results from this methodology were used in an analytically derived procedure for freezing-time estimates and then compared with experimental results. The average effective heat transfer coefficient underestimated freezing times and demonstrated a higher level of accuracy than the Gnielinski correlation when applied to boxes containing smaller product amounts. For experiments with greater quantity of products, the use of average heat transfer coefficients from the Gnielinski correlation yielded errors lower than 20%. Based on boundary layer theory, the Gnielinski correlation can be used to explain the isotherm behaviors observed during freezing. Many of the results satisfy the standards of accuracy used in engineering, and the procedure does not require extra computational effort.     

An inverse lumped capacitance method for determination of heat transfer coefficients for industrial air blast chillers

An inverse model using lump body was developed to calculate heat transfer coefficients as a dynamic function of time. The model used sequential function specification algorithm to calculate surface heat flux from transient temperature measurements inside a lump body system. Transient temperature measurements were collected during cooling inside an industrial chiller at two different positions with different air velocities using four replicates for each position. The calculated surface heat flux was found to be very accurate as the maximum value of the root mean squares error (RMSE) for temperature is 0.045 °C, lower than the expected error form thermocouple measurements. The calculated heat flux was then used to calculate heat transfer coefficients as a dynamic function of cooling time followed by calculation of time average heat transfer coefficient using numerical integration. The approach developed here could be a pragmatic powerful dynamic method to model spatial variation of heat transfer coefficients for industrial chillers and freezers.     

不同温度场响应对西葫芦采后贮藏品质的影响

为了探讨热处理传热过程对果蔬贮藏生理品质的影响规律,建立西葫芦在热激处理过程中的三维数值模型,进行三维非稳态下的数值模拟,研究热处理时西葫芦组织的传热规律及温度动态响应过程,并以40℃的热空气作为热处理介质,对处理时间分别为0.5、1、2、4 h西葫芦的保鲜效果进行了对比实验研究。结果表明,40℃热空气处理1 h可最大限度地延长采后西葫芦冷害的发生时间,减少果实失重率,延缓丙二醛(MDA)含量和相对电导率的升高,维持较高的果实硬度和抗坏血酸含量。所建的传热模型与实际情况吻合较好,温度最大绝对误差为1.66℃。西葫芦传热模型及相关结论可为西葫芦采后热处理操作参数的确定提供参考。     

加料滚筒内不同截面温度场的分布

为检测及分析烟叶加料过程中,不同加热条件下（热风作用、热蒸汽作用及热风热蒸汽作用）滚筒内部不同截面处的温度场分布情况,设计了一套基于红外热像仪、铜片吸热装置的滚筒内部非接触式温度检测装置,并分别测量了滚筒内不同截面处的温度数据。结果显示:（1）利用铜片吸热装置及红外热像仪组成的温度测量装置精度较好,测量误差小于3.84%,能够直观地表示出滚筒内部温度分布情况。（2）热风作用下,滚筒内部升温较快。（3）热蒸汽作用下,滚筒内部局部温度下降速度较快。（4）热蒸汽及热风共同作用下滚筒内部的升温最快,升温速率稳定,加热性能良好。结论:该温度检测装置是方便可行的,能够间接测量出滚筒内部各个截面的温度分布;热蒸汽及热风共同作用下滚筒内部的温度分布更为均匀、升温更快,加热性能更好。