粉末干燥机的设计含6张CAD图
粉末干燥机的设计含6张CAD图,粉末,干燥机,设计,cad
附录 附录1外文文献中文翻译 附录2外文译文文献复印件柔性丝状粒子在回转干燥器中传热传质的实验研究摘要对柔性丝状粒子的传热传质进行了实验研究。结果表明,DRM壁的温度对旋转干燥器中颗粒的传热传质有明显的影响,随着干壁温度的升高,切梗颗粒的温度显著升高,而钼含量急剧下降。在预热干燥阶段和恒定干燥速率周期内,转速对颗粒温度的影响较小,颗粒的含水量随转速的增加而减小。随着气流温度的升高,颗粒温度升高,水分蒸发速率增加,最终钼含量降低。在恒定干燥速率期间,随着干燥速度的增加,部分节段的温度降低,而在干涸速率期间增加。随着气流速度的增加,含水率显著降低。关键词:柔性丝状粒子,传热,传质,实验方法。介绍颗粒颗粒松散地堆积在气相或液相中,广泛存在于化工、水泥、石灰、煤、面粉、医药、陶瓷、能源、食品等工业领域。消耗大量的能量使其成为粒状粒子制造过程中最耗能的操作之一。干燥是通过热处理从材料中除去水分的常用方法之一(1)。在3050的储存温度范围内开始发生内部自加热。采用二阶偏微分方程研究容器内瞬态温度分布(2)。它可以被描述为一种重要的工业保存方式,其中食物和农产品的含水量和活性降低,以最小化生化、化学和微生物劣化。此外,在干燥过程中,物料和气流之间总是发生传热传质,在干燥过程中起着极其重要的作用。干燥过程通常受物料颗粒状态、表面蒸发速率和内部水分扩散速率的影响。此外,许多典型的干燥设备,例如固定床干燥器、流化床干燥器、旋转干燥器和微波干燥器已经被用于在许多尝试中处理颗粒。通过实验和数值方法,研究了旋转干燥器中物料与气流、物料和转鼓之间的传热传质问题。MykLeSTAD首先预测整个干燥过程中颗粒的产品水分含量,其基于干燥气流的温度、颗粒的初始含水量和产品进料速率。采用传热传质方程研究了木材颗粒的含水率和温度。用阿伦尼乌斯方程计算了颗粒温度与传质系数的关系然而,干燥器的不同部位的柔性丝状颗粒在不同的温度下被加热,这可以提高工艺的效率和材料的质量。研究了柔性丝状粒子在旋转干燥器内的传热传质过程。并对不同操作条件下的干燥结果进行了预测,并分析了旋转干燥器中颗粒的温度和湿度和气流的变化情况。提出了颗粒间的流动是固定的,气相的传热可以忽略不计的热粒子动力学模型。Sharples建立了一个研究干燥过程的模型,并将旋转式干燥机描述为三个阶段,预热、恒速干燥和还原率12 。对谷子干燥动力学的实验结果表明,随着温度的升高和干燥介质的流速的增加,干燥速率显著增加,而随着固体滞留率的增加而降低。概述了新兴的和创新的热干燥技术,这是商业化工业开发的潜力。虽然已经做了大量的工作在旋转式干燥器,仍然缺乏科学和适当的信息对干燥行为的柔性丝状颗粒。旋转干燥器的传热主要有颗粒-鼓壁、颗粒-气体流、颗粒-颗粒和颗粒与气流之间的传质。因此,在旋转式干燥器中,根据滚筒壁温、转速、气流温度和速度等操作参数,对旋转干燥器中的运动颗粒的水分含量和温度进行了实验研究。材料与实验方法2.1。材料性能利用旋转式干燥机对柔性丝状颗粒进行干燥实验,将本研究所涵盖的实验参数列于表1中。本文采用切割茎作为实验材料,由于其结构具有较大的长宽比而被认为是柔性丝状粒子。这种方法利用了阀杆颗粒物理特性,因此提供了一些优于经验关系的优点和便利性,如图1所示。切梗的长度、宽度和厚度分别为14mm、1mm和0.1mm。切割茎颗粒被储存在气密容器中,以保持在本实验中所有实验中水分含量的均匀性。Table 1: Experimentalparameters presented in this paperPropertiesValueLength of dryer, mm570Diameter, mm330Height of flights, mm40Number of flights4Plot ratio of particles18.60%Initial moisture content of particles , kg/kg21%Drying time, s840Fig.1: Experimental material.2.2。实验方法实验装置包括温度控制系统、气体流量系统和滚筒系统三部分。采用油浴法对转鼓壁进行加热。气流从外部压缩,然后被加热到期望的温度,然后通过空气分配板提供给旋转鼓。旋转干燥器的结构如图2所示。在干燥过程中,切断阀杆颗粒。将约5g的干梗颗粒样品以一定的时间间隔从旋转式干燥机中铲出,同时用红外辐射温度计对温度进行测试。另外,储存在密闭容器中,在对流空气烘箱中干燥前称重2h,在100oC2oC.实验操作条件表2示出了在旋转干燥器中使用的实验参数和操作条件的范围。气体流量由速度调节器控制。Table 2: Experimentaloperating conditions in present studyConditionsValueTemperature of drum wall, oC70, 85, 100, 115, 130Rotational speed, r/min8, 10, 12Temperature of gas flow, oC70, 90, 110Velocity of gas flow, m/s0.1, 0.2, 0.3, 0.4结果与讨论图中讨论了不同操作条件对截梗颗粒传热传质的影响,如鼓壁温度、旋转速度、温度和气流速度。对干燥过程中颗粒的水分和温度进行了分析。旋转式干燥机的工作温度通常低于150C15。在干燥过程中,滚筒壁的温度对干梗颗粒的传热和传质起着重要的作用,在这项研究中测试了70130之间的变化。因此,图3(a)和(b)示出了颗粒在干燥时间方面的含水量和温度。结果表明,干燥初期颗粒的温度明显升高,是由于颗粒与鼓壁之间的直接接触所致。结果表明,随着滚筒壁温的升高,截梗颗粒的温度显著升高,含水率显著降低。在70的鼓壁温度条件下,颗粒在预热阶段的水分含量仅下降1%,而在130oC下下降3.5%。滚筒壁与颗粒之间的导热性几乎可以用来提高颗粒的温度,因此水分含量略有下降。由于接触时间的增加,颗粒和气流之间的对流传热和传质明显发生在恒定的干燥速率阶段。此外,表面水分的蒸发结果表明,干梗颗粒内部和外部产生水分梯度和温度梯度,从而加速了水分从内部向外部的转移,相反,温度在那个时期保持稳定。 图3:滚筒壁不同温度下截梗颗粒的含水率和温度。结果表明,随着滚筒壁温的升高,恒速干燥时间缩短。在70条件下,颗粒停留在680,温度保持在约49。然而,图3(a)和(b)表明,当滚筒壁温度升高到130oC时,恒定干燥速率周期的时间约为90,并且颗粒的温度保持在71oC。随着滚筒壁温的升高,含水率显著降低,干燥速率也显著增加。干燥过程中水分含量缓慢下降,同时由于水分含量低,颗粒温度显著升高。在115oC和130oC条件下,可以明显地观察到各干燥速率的变化特征,最终水分含量分别为1.46%和0.71%。在一定条件下,颗粒在不同干燥条件下可能保持不同的干燥速率周期。旋转速度对旋转干燥器中颗粒的运动有影响。切杆颗粒的均匀圆周运动受飞行的影响。在图三(a)和(b)所示的实验中研究了干杆颗粒上的传热传质,以及旋转干燥器在4种转速下的含水量和温度曲线,其值为8r/min、10r/min和12r/min。结果表明,在预热干燥阶段和恒定干燥速率阶段,转速对颗粒温度影响不大。此外,随着转速的增加,分布和加热面更加均匀。根据颗粒与气流之间较大的接触面积,更多的表面水分被蒸发,因此干燥速率快速增加,并且恒定干燥速率周期的时间短。随着干燥速度的增加,颗粒的干燥速率和含水率均降低,颗粒温度迅速升高。(a) (b)图4:不同转速下梗粒的含水量和温度。图4(a)和(b)表明,当转速为8r/min时,颗粒达到干燥后的下降干燥速率周期,在10r/min的条件下干燥540S,在12r/min的条件下干燥400秒,在滞后干燥速率期,水分含量略有下降,C。颗粒与气流、颗粒和颗粒之间的传质很小,通过对流传热和导热获得的热量用来提高温度。气流对颗粒的对流传热和传质起着关键作用。一方面,可以利用气体系统来补充加热面积,从而增加干燥能量。另一方面,水蒸气可以通过气流从旋转式干燥器中有效地取出。不同的气流温度对水分蒸发速率有显著影响。因此,如图5(a)和(b)所示,在不同的气流温度70、90oC和110下,在干茎颗粒上的传热和传质。温度曲线表明,颗粒的温度随着气流温度的升高而增大。颗粒在旋转式干燥器中连续地输送和滴下。随着气流温度的降低,颗粒与气流之间的对流热流率降低,导致颗粒在预热干燥期间颗粒温度缓慢升高。在70条件下,840干燥后的干茎颗粒仍保持在恒定的干燥速率期,而其它两种条件下的颗粒在干燥700后达到下降干燥速率,而水分蒸发速率增加,最终水分含量下降。随着气流温度的升高,颗粒在三种条件下的最终含水率分别为8.88%、6.86%和4.88%。(a)(b)图5:不同气流温度下截梗颗粒的含水率和温度。图6(a)和(b)示出了在不同气流速度下颗粒的含水量和温度的结果,其值分别为0.1M/s、0.2M/s、0.3M/s和0.4M/s。在预热干燥阶段,气流速度对截梗颗粒的温度和水分含量有一定的影响。在恒定的干燥速率期间,增加气流速度可以加强颗粒间的对流传热和传质和气体流动,水蒸发速率也大大增加。因此,通过热传递得到的热量被蒸发,从而导致颗粒温度略微增加,干燥速率显著增加。这四种条件的最终水分含量分别为10.05%、7.19%、5.16%和4.39%,颗粒的温度从78oC变化到83oC。这四种条件下的干茎颗粒在干燥880后保持在恒定的干燥速率阶段,而且可以清楚地看出气流速度对传热的影响不大,对传质有显著影响。4结论本研究以旋转式干燥机为研究对象,对柔性丝状颗粒的传热传质过程进行了一系列干燥实验。实验研究了在不同条件下,滚筒壁温度、旋转速度、温度和气流速度等参数对截梗颗粒含水率和温度的影响。截梗颗粒的温度随着鼓壁温度的升高而显著增加,而含水率显著降低。在预热干燥阶段和恒定干燥速率周期内,转速对颗粒温度的影响较小,颗粒的含水量随转速的增加而减小。随着气流温度的升高,颗粒温度升高,水分蒸发速率增加,最终含水率降低。在恒定干燥速率期间,颗粒的温度随着气流速度的增加而降低,而在下降干燥速率期间增加。随着气流速度的增加,含水率显著降低。文中提出的结果也可供工业应用。随着干燥长度的增加,还可尝试更多的实验方法来测试温度和水分含量,在不同的温度和水分条件下,柔性丝状粒子的有效导热系数和传质系数仍需进一步提高。(a)(b)致谢从对中国国家烟草公司郑州烟草研究院烟草加工技术重点实验室的财政支持和中国国家自然科学基金重大项目(批准号:51390492)真诚地承认。International Proceedings of Chemical, Biological and Environmental Engineering, V0l. 90 (2015) DOI: 10.7763/IPCBEE. 2015. V90. 2Experimental Study on Heat and Mass Transfer of Flexible Filamentous Particles in a Rotary DryerConghui Gu 1, Bin Li 2, Kaili Liu 2, Zhulin Yuan 1+, Wenqi Zhong 11 Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University,Nanjing 210096, China2 Key Laboratory of Tobacco Processing Technology, Zhengzhou Tobacco Research Institute of ChinaNational Tobacco Corporation, Zhengzhou 450001, ChinaAbstract. The effects of temperature of dru m wall, rotational speed, temperature and velocity of gas flowon heat and mass transfer of flexible filamentous particles are experimentally studied. Results showed that temperature of dru m wall had an apparent influence on the heat and mass transfer of particles in a rotary dryer, and the temperature of cut stem particles significantly increased with increase in temperature of dru m wall, while the mo isture content sharply decreased. The rotational speed has little effect on temperature of particles during preheating drying period and constant drying rate period, and moisture content of particles decrease with the increase of rotational speed. Temperature of particles increased, rate of water evaporation increased and the final mo isture content decreased with the increasing of temp erature of gas flow. Temperature of part icles decreased with the increasing of velocity of gas flow during the constant drying rate period, wh ile increased during falling dry ing rate period. The moisture content significantly decreased with the increasing of velocity of gas flow.Keywords: Flexible filamentous particles, heat transfer, mass transfer, experimental method .1. IntroductionGranular particles are loosely piled in gas or fluid phase, which widely exist in the fields of chemical, cement, lime, coal, flour, pharmaceuticals, ceramics, energy, and food industries. Consumption of a large amount of energy makes it one of the most energy intensive operations in the granular particle manufacturing process. Drying is one of the main methods that generally used to store food by removing the moisture from material through thermal treatment 1. Internal self-heating starts to take place at storage temperature range from 30oC to 50oC. A second order partial differential equation was used to investigate transient temperature distribution within a container 2. It can be described as an important industrial preservation way where water content and activity of food and agricultural products are decreased to minimize biochemical, chemical, and microbiological deterioration 3. Furthermore, heat and mass transfer always occur between material and gas flow while drying, and play an extremely important role on the drying process 4, 5. Drying process is usually effected by the state of material particles, vaporization rate of surface and internal moisture diffusion rate. In addition, much typical drying equipment, for example, fixed bed dryers, fluidized bed dryers, rotary dryers and microwave dryers have been used to deal with particles in many attempts . Several researchers have figured out investigations on heat and mass transfer between material and gas flow, material and rotary drum in a rotary dryer by experimental and numerical methods. Myklestad firstly predicted product moisture content of particles throughout a single pass dryer, which based on temperature of drying gas flow, initial moisture content of particles, and the product feed rate 6. Moisture content and temperature of wood particles were studied by using heat and mass transfer equations 7. Arrhenius equation was used to calculate the relationship between temperature of particles and the efficient coefficient of mass transfer 8, 9.+Corresponding author. Tel.: +86 13851999198; fax: +86-25-83689730. E-mail address: 101004322seu.edu.cn.15However, flexible filamentous particles in different parts of dryer are heated in different temperatures, which can improve the efficiency of the process and quality of materials. Heat and mass transfer of flexible filamentous particles in the rotary dryer within the real-time were researched. And results of drying under different operating conditions could be forcasted, and temperature and humidity of particles and gas flow in the rotary dryer were analysed 10. Thermal Particle Dynamics model was put forward, which assumed that flow between particles was stationary and the heat transfer of gas phase could be negligible 11. Sharples had established a model to research drying process and described the rotary dryer as three periods, preheating, constant rate drying and reduction rate 12. Experimental results on the drying kinetics of millet showed that the drying rate was found to increase significantly with the increase in temperature and marginally with flow rate of the heating medium, while decrease with increase in solids holdup 13. An overview of emerging and innovative thermal drying technologies was taken, which were commercialized the potential for industrial exploitation 14.Although considerable work in a rotary dryer has been done, there is still a lack of scientific and appropriate information on drying behavior of flexible filamentous particles. There are there main processing on heat transfer in a rotary dryer, namely, particle to drum wall, particle to gas flow, particle to particle, and mass transfer between particle and gas flow. Therefore, moisture content and temperature of moving particles in a rotary dryer were experimentally investigated under different conditions, with respect to the operating parameters such as temperature of drum wall, rotational speed, temperature and velocity of gas flow.2. Materials and Experimental Methods2.1. Material propertiesDrying experiments on flexible filamentous particles were conducted using rotary dryer, the experimental parameters covered in the present research are listed in Table 1. In this paper, cut stem was employed as experimental materials, which are considered as flexible filamentous particles due to the structure, which have larger aspect ratio. Such approach utilize cut stem particles physical properties, and hence offer some advantages and convenience over empirical relations, as shown in Fig.1. The length, width and thickness of cut stem were 14mm, 1mm, and 0.1mm, respectively. Cut stem particles were stored in air tight containers to maintain the uniformity in moisture content for all experiments in this study.Table 1: Experimentalparameters presented in this paperPropertiesValueLength of dryer, mm570Diameter, mm330Height of flights, mm40Number of flights4Plot ratio of particles18.60%Initial moisture content of particles , kg/kg21%Drying time, s840Fig.1: Experimental material.2.2. Experimental methodThe experiment equipment included three parts, temperature control system, gas flow system and drum system. The rotary drum wall was heated by oil bath method. Air flow was compressed from outside, and then been heated to a desired temperature before provided to the rotary drum through air distribution plate. The structure of rotary dryer was shown in Fig. 2. Cut stem particles in a close-loop while drying. Approximately 5g sample of cut stem particles were scooped out of the rotary dryer at regular intervals of time, at the same time, the temperature was tested by infrared radiation thermometers. In addition, particles stored in air tight container that were weighed before drying in a convective air oven for 2h at 100oC2oC.Fig. 2: Structure of the experimental set up2.3. Experimental operating conditionsTable 2 shows the range of experimental parameters and operating conditions that used in the rotary dryer. The gas flow rate was controlled by a speed regulator.Table 2: Experimentaloperating conditions in present studyConditionsValueTemperature of drum wall, oC70, 85, 100, 115, 130Rotational speed, r/min8, 10, 12Temperature of gas flow, oC70, 90, 110Velocity of gas flow, m/s0.1, 0.2, 0.3, 0.43. Results and DiscussionThe figures address the effect of different operating conditions on heat and mass transfer of cut stem particles, such as temperature of drum wall, rotational speed, temperature and velocity of gas flow. The moisture content and temperature of particles during drying process were analyzed as follows.The working temperature of rotary dryer is usually less than 150C 15. The temperature of drum wall plays a significant role on the heat and mass transfer of cut stem particles during drying process, which was tested to vary from 70oC to 130oC in this study. Accordingly, the moisture content and temperature of particles in terms of drying time were shown in Fig. 3(a) and (b). Results indicate that the temperature of particles obviously increase during the early period of drying is attributed to the direct contact between particles and drum wall. It is found that the temperature of cut stem particles significantly increases with increase in temperature of drum wall, while the moisture content enormously decreases. The moisture content of particles just decline 1% at the preheating period under the drum wall temperature condition of 70oC, while dropped 3.5% at 130oC. Heat obtained from thermal conductivity between drum wall and particles was almost used to rise the temperature of particles, and hence the moisture content slightly decreased. Convective heat and mass transfer between particles and gas flow apparently took place at the constant drying rate period due to the increase of contact time. Furthermore, evaporation of surface moistureresulted in the generation of moisture gradient and temperature gradient between internal and external of cut stem particles, as a consequence, transfer of moisture from interior to exterior was accelerated, the temperature remained steady at that period by contrast.(a)(b)Fig. 3: Moisture content and temperature of cut stem particles under different temperature of drum wall.It is clearly presented that the time of constant drying rate period reduces with the increase of temperature of drum wall. Particles stayed in that period for 680s at the condition of 70oC, and the temperature remained at approximately 49oC. However, Fig. 3(a) and (b) revealed that the time of constant drying rate period was about 90s when temperature of drum wall grew to 130oC, and the temperature of particles remained at 71oC. The moisture content was found to considerably decrease with increase in temperature of drum wall, drying rate markedly increase as well. Moisture content slowly decreased during falling drying rate period, at the same time, temperature of particles significantly increased because of the low moisture content. It could be apparently observe the characteristics of each drying rate period under the condition of 115oC and 130oC, and the final moisture content were 1.46% and 0.71%, respectively. Particles might stay in different drying rate period under different conditions at a certain time.Rotational speed has an influence on movement of particles in a rotary dryer. Uniform circular motion of cut stem particles is effected by flights. Heat and mass transfer on cut stem particles are experimentally studied, and therefore moisture content and temperature curves in a rotary dryer under three kinds of rotational speed, which value are 8r/min, 10r/min and 12r/min, as shown in Fig. 4(a) and (b). It can be found that the rotational speed has little effect on temperature of particles during preheating drying period and constant drying rate period. Furthermore, the distribution and heating surface are more homogeneous with the increase in rotational speed. More surface moisture is vaporized according to larger contact area between particles and gas flow, and hence drying rate fast increase and the time of constant drying rate period short.Both drying rate and moisture content of particles decrease, and temperature of particles fast increase with the increase of rotational speed during the falling drying rate period.(a)(b)Fig. 4: Moisture content and temperature of cut stem particles under different rotational speed.Fig. 4(a) and (b) show that particles reach to the falling drying rate period after drying for 660s when rotational speed is 8r/min, while drying for 540s under the condition of 10r/min, and for 400s under the condition of 12r/min. At lag drying rate period, moisture content marginally decreases, convective mass transfer between particles and gas flow, particles and particles are small, heat obtained by convective heat transfer and thermal conductivity is used to raising temperature.Gas flow has a key role on convective heat and mass transfer of particles. On one hand, gas system can be used to make up for heating area, which increases the drying energy. On the other hand, water vapor can be effectively taken out of the rotary dryer by gas flow. Rate of water evaporation was significantly effected by different temperature of gas flow. Therefore, heat and mass transfer on cut stem particles under different gas flow temperature 70oC, 90oC and 110oC, respectively, as shown in Fig. 5(a) and (b). Temperature curves indicate that temperature of particles increased with the increase in temperature of gas flow. Particles were brought and dropped continuously in a rotary dryer. Convective heat rate between particles and gas flow decreased with decrease of gas flow temperature, which resulted in temperature of particles slowly increasing during preheating drying period. Cut stem particles still stayed in the constant drying rate period after drying for 840s under the condition of 70oC, however, particles of the other two conditions reached to falling drying rate after drying for 700s. Whereas, rate of water evaporation increased and the final moisture content decreased with the increase in temperature of gas flow, the value of final moisture content of particles under these three conditions were 8.88%, 6.86% and 4.88%, respectively.(a)(b)Fig. 5: Moisture content and temperature of cut stem particles under different temperature of gas flow.Fig. 6(a) and (b) show results on moisture content and temperature of particles under different velocity of gas flow, which value are 0.1m/s, 0.2m/s, 0.3m/s
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