粉末干燥機(jī)的設(shè)計(jì)【含6張CAD圖紙】

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附錄 附錄1外文文獻(xiàn)中文翻譯 附錄2外文譯文文獻(xiàn)復(fù)印件 柔性絲狀粒子在回轉(zhuǎn)干燥器中傳熱傳質(zhì)的實(shí)驗(yàn)研究 摘要 對(duì)柔性絲狀粒子的傳熱傳質(zhì)進(jìn)行了實(shí)驗(yàn)研究。結(jié)果表明，DRM壁的溫度對(duì)旋轉(zhuǎn)干燥器中顆粒的傳熱傳質(zhì)有明顯的影響，隨著干壁溫度的升高，切梗顆粒的溫度顯著升高，而鉬含量急劇下降。在預(yù)熱干燥階段和恒定干燥速率周期內(nèi)，轉(zhuǎn)速對(duì)顆粒溫度的影響較小，顆粒的含水量隨轉(zhuǎn)速的增加而減小。隨著氣流溫度的升高，顆粒溫度升高，水分蒸發(fā)速率增加，最終鉬含量降低。在恒定干燥速率期間，隨著干燥速度的增加，部分節(jié)段的溫度降低，而在干涸速率期間增加。隨著氣流速度的增加，含水率顯著降低。 關(guān)鍵詞：柔性絲狀粒子，傳熱，傳質(zhì)，實(shí)驗(yàn)方法。 介紹 顆粒顆粒松散地堆積在氣相或液相中，廣泛存在于化工、水泥、石灰、煤、面粉、醫(yī)藥、陶瓷、能源、食品等工業(yè)領(lǐng)域。消耗大量的能量使其成為粒狀粒子制造過(guò)程中最耗能的操作之一。干燥是通過(guò)熱處理從材料中除去水分的常用方法之一（1）。在30~50℃的儲(chǔ)存溫度范圍內(nèi)開始發(fā)生內(nèi)部自加熱。采用二階偏微分方程研究容器內(nèi)瞬態(tài)溫度分布（2）。它可以被描述為一種重要的工業(yè)保存方式，其中食物和農(nóng)產(chǎn)品的含水量和活性降低，以最小化生化、化學(xué)和微生物劣化。此外，在干燥過(guò)程中，物料和氣流之間總是發(fā)生傳熱傳質(zhì)，在干燥過(guò)程中起著極其重要的作用。干燥過(guò)程通常受物料顆粒狀態(tài)、表面蒸發(fā)速率和內(nèi)部水分?jǐn)U散速率的影響。此外，許多典型的干燥設(shè)備，例如固定床干燥器、流化床干燥器、旋轉(zhuǎn)干燥器和微波干燥器已經(jīng)被用于在許多嘗試中處理顆粒。通過(guò)實(shí)驗(yàn)和數(shù)值方法，研究了旋轉(zhuǎn)干燥器中物料與氣流、物料和轉(zhuǎn)鼓之間的傳熱傳質(zhì)問(wèn)題。MykLeSTAD首先預(yù)測(cè)整個(gè)干燥過(guò)程中顆粒的產(chǎn)品水分含量，其基于干燥氣流的溫度、顆粒的初始含水量和產(chǎn)品進(jìn)料速率。采用傳熱傳質(zhì)方程研究了木材顆粒的含水率和溫度。用阿倫尼烏斯方程計(jì)算了顆粒溫度與傳質(zhì)系數(shù)的關(guān)系 然而，干燥器的不同部位的柔性絲狀顆粒在不同的溫度下被加熱，這可以提高工藝的效率和材料的質(zhì)量。研究了柔性絲狀粒子在旋轉(zhuǎn)干燥器內(nèi)的傳熱傳質(zhì)過(guò)程。并對(duì)不同操作條件下的干燥結(jié)果進(jìn)行了預(yù)測(cè)，并分析了旋轉(zhuǎn)干燥器中顆粒的溫度和濕度和氣流的變化情況。提出了顆粒間的流動(dòng)是固定的，氣相的傳熱可以忽略不計(jì)的熱粒子動(dòng)力學(xué)模型。Sharples建立了一個(gè)研究干燥過(guò)程的模型，并將旋轉(zhuǎn)式干燥機(jī)描述為三個(gè)階段，預(yù)熱、恒速干燥和還原率[12 ]。對(duì)谷子干燥動(dòng)力學(xué)的實(shí)驗(yàn)結(jié)果表明，隨著溫度的升高和干燥介質(zhì)的流速的增加，干燥速率顯著增加，而隨著固體滯留率的增加而降低。概述了新興的和創(chuàng)新的熱干燥技術(shù)，這是商業(yè)化工業(yè)開發(fā)的潛力。 雖然已經(jīng)做了大量的工作在旋轉(zhuǎn)式干燥器，仍然缺乏科學(xué)和適當(dāng)?shù)男畔?duì)干燥行為的柔性絲狀顆粒。旋轉(zhuǎn)干燥器的傳熱主要有顆粒-鼓壁、顆粒-氣體流、顆粒-顆粒和顆粒與氣流之間的傳質(zhì)。因此，在旋轉(zhuǎn)式干燥器中，根據(jù)滾筒壁溫、轉(zhuǎn)速、氣流溫度和速度等操作參數(shù)，對(duì)旋轉(zhuǎn)干燥器中的運(yùn)動(dòng)顆粒的水分含量和溫度進(jìn)行了實(shí)驗(yàn)研究。 材料與實(shí)驗(yàn)方法 2.1。材料性能 利用旋轉(zhuǎn)式干燥機(jī)對(duì)柔性絲狀顆粒進(jìn)行干燥實(shí)驗(yàn)，將本研究所涵蓋的實(shí)驗(yàn)參數(shù)列于表1中。本文采用切割莖作為實(shí)驗(yàn)材料，由于其結(jié)構(gòu)具有較大的長(zhǎng)寬比而被認(rèn)為是柔性絲狀粒子。這種方法利用了閥桿顆粒物理特性，因此提供了一些優(yōu)于經(jīng)驗(yàn)關(guān)系的優(yōu)點(diǎn)和便利性，如圖1所示。切梗的長(zhǎng)度、寬度和厚度分別為14mm、1mm和0.1mm。切割莖顆粒被儲(chǔ)存在氣密容器中，以保持在本實(shí)驗(yàn)中所有實(shí)驗(yàn)中水分含量的均勻性。 Table 1: Experimental parameters presented in this paper Properties Value Length of dryer, mm 570 Diameter, mm 330 Height of flights, mm 40 Number of flights 4 Plot ratio of particles 18.60% Initial moisture content of particles , kg/kg 21% Drying time, s 840 Fig.1: Experimental material. 2.2。實(shí)驗(yàn)方法 實(shí)驗(yàn)裝置包括溫度控制系統(tǒng)、氣體流量系統(tǒng)和滾筒系統(tǒng)三部分。采用油浴法對(duì)轉(zhuǎn)鼓壁進(jìn)行加熱。氣流從外部壓縮，然后被加熱到期望的溫度，然后通過(guò)空氣分配板提供給旋轉(zhuǎn)鼓。旋轉(zhuǎn)干燥器的結(jié)構(gòu)如圖2所示。在干燥過(guò)程中，切斷閥桿顆粒。將約5g的干梗顆粒樣品以一定的時(shí)間間隔從旋轉(zhuǎn)式干燥機(jī)中鏟出，同時(shí)用紅外輻射溫度計(jì)對(duì)溫度進(jìn)行測(cè)試。另外，儲(chǔ)存在密閉容器中，在對(duì)流空氣烘箱中干燥前稱重2h，在100oC±2oC. 實(shí)驗(yàn)操作條件 表2示出了在旋轉(zhuǎn)干燥器中使用的實(shí)驗(yàn)參數(shù)和操作條件的范圍。氣體流量由速度調(diào)節(jié)器控制。 Table 2: Experimental operating conditions in present study Conditions Value Temperature of drum wall, oC 70, 85, 100, 115, 130 Rotational speed, r/min 8, 10, 12 Temperature of gas flow, oC 70, 90, 110 Velocity of gas flow, m/s 0.1, 0.2, 0.3, 0.4 結(jié)果與討論 圖中討論了不同操作條件對(duì)截梗顆粒傳熱傳質(zhì)的影響，如鼓壁溫度、旋轉(zhuǎn)速度、溫度和氣流速度。對(duì)干燥過(guò)程中顆粒的水分和溫度進(jìn)行了分析。 旋轉(zhuǎn)式干燥機(jī)的工作溫度通常低于150°C〔15〕。在干燥過(guò)程中，滾筒壁的溫度對(duì)干梗顆粒的傳熱和傳質(zhì)起著重要的作用，在這項(xiàng)研究中測(cè)試了70～130℃之間的變化。因此，圖3（a）和（b）示出了顆粒在干燥時(shí)間方面的含水量和溫度。結(jié)果表明，干燥初期顆粒的溫度明顯升高，是由于顆粒與鼓壁之間的直接接觸所致。結(jié)果表明，隨著滾筒壁溫的升高，截梗顆粒的溫度顯著升高，含水率顯著降低。在70℃的鼓壁溫度條件下，顆粒在預(yù)熱階段的水分含量?jī)H下降1%，而在130oC下下降3.5%。滾筒壁與顆粒之間的導(dǎo)熱性幾乎可以用來(lái)提高顆粒的溫度，因此水分含量略有下降。由于接觸時(shí)間的增加，顆粒和氣流之間的對(duì)流傳熱和傳質(zhì)明顯發(fā)生在恒定的干燥速率階段。此外，表面水分的蒸發(fā) 結(jié)果表明，干梗顆粒內(nèi)部和外部產(chǎn)生水分梯度和溫度梯度，從而加速了水分從內(nèi)部向外部的轉(zhuǎn)移，相反，溫度在那個(gè)時(shí)期保持穩(wěn)定。 圖3：滾筒壁不同溫度下截梗顆粒的含水率和溫度。 結(jié)果表明，隨著滾筒壁溫的升高，恒速干燥時(shí)間縮短。在70℃條件下，顆粒停留在680℃，溫度保持在約49℃。然而，圖3（a）和（b）表明，當(dāng)滾筒壁溫度升高到130oC時(shí)，恒定干燥速率周期的時(shí)間約為90℃，并且顆粒的溫度保持在71oC。隨著滾筒壁溫的升高，含水率顯著降低，干燥速率也顯著增加。干燥過(guò)程中水分含量緩慢下降，同時(shí)由于水分含量低，顆粒溫度顯著升高。在115oC和130oC條件下，可以明顯地觀察到各干燥速率的變化特征，最終水分含量分別為1.46%和0.71%。在一定條件下，顆粒在不同干燥條件下可能保持不同的干燥速率周期。 旋轉(zhuǎn)速度對(duì)旋轉(zhuǎn)干燥器中顆粒的運(yùn)動(dòng)有影響。切桿顆粒的均勻圓周運(yùn)動(dòng)受飛行的影響。在圖三（a）和（b）所示的實(shí)驗(yàn)中研究了干桿顆粒上的傳熱傳質(zhì)，以及旋轉(zhuǎn)干燥器在4種轉(zhuǎn)速下的含水量和溫度曲線，其值為8r/min、10r/min和12r/min。結(jié)果表明，在預(yù)熱干燥階段和恒定干燥速率階段，轉(zhuǎn)速對(duì)顆粒溫度影響不大。此外，隨著轉(zhuǎn)速的增加，分布和加熱面更加均勻。根據(jù)顆粒與氣流之間較大的接觸面積，更多的表面水分被蒸發(fā)，因此干燥速率快速增加，并且恒定干燥速率周期的時(shí)間短。隨著干燥速度的增加，顆粒的干燥速率和含水率均降低，顆粒溫度迅速升高。 （a） （b） 圖4：不同轉(zhuǎn)速下梗粒的含水量和溫度。 圖4（a）和（b）表明，當(dāng)轉(zhuǎn)速為8r/min時(shí)，顆粒達(dá)到干燥后的下降干燥速率周期，在10r/min的條件下干燥540S，在12r/min的條件下干燥400秒，在滯后干燥速率期，水分含量略有下降，C。顆粒與氣流、顆粒和顆粒之間的傳質(zhì)很小，通過(guò)對(duì)流傳熱和導(dǎo)熱獲得的熱量用來(lái)提高溫度。氣流對(duì)顆粒的對(duì)流傳熱和傳質(zhì)起著關(guān)鍵作用。一方面，可以利用氣體系統(tǒng)來(lái)補(bǔ)充加熱面積，從而增加干燥能量。另一方面，水蒸氣可以通過(guò)氣流從旋轉(zhuǎn)式干燥器中有效地取出。不同的氣流溫度對(duì)水分蒸發(fā)速率有顯著影響。因此，如圖5（a）和（b）所示，在不同的氣流溫度70℃、90oC和110℃下，在干莖顆粒上的傳熱和傳質(zhì)。溫度曲線表明，顆粒的溫度隨著氣流溫度的升高而增大。顆粒在旋轉(zhuǎn)式干燥器中連續(xù)地輸送和滴下。隨著氣流溫度的降低，顆粒與氣流之間的對(duì)流熱流率降低，導(dǎo)致顆粒在預(yù)熱干燥期間顆粒溫度緩慢升高。在70℃條件下，840℃干燥后的干莖顆粒仍保持在恒定的干燥速率期，而其它兩種條件下的顆粒在干燥700℃后達(dá)到下降干燥速率，而水分蒸發(fā)速率增加，最終水分含量下降。隨著氣流溫度的升高，顆粒在三種條件下的最終含水率分別為8.88%、6.86%和4.88%。 （a） （b） 圖5：不同氣流溫度下截梗顆粒的含水率和溫度。 圖6（a）和（b）示出了在不同氣流速度下顆粒的含水量和溫度的結(jié)果，其值分別為0.1M/s、0.2M/s、0.3M/s和0.4M/s。在預(yù)熱干燥階段，氣流速度對(duì)截梗顆粒的溫度和水分含量有一定的影響。在恒定的干燥速率期間，增加氣流速度可以加強(qiáng)顆粒間的對(duì)流傳熱和傳質(zhì)和氣體流動(dòng)，水蒸發(fā)速率也大大增加。因此，通過(guò)熱傳遞得到的熱量被蒸發(fā)，從而導(dǎo)致顆粒溫度略微增加，干燥速率顯著增加。這四種條件的最終水分含量分別為10.05%、7.19%、5.16%和4.39%，顆粒的溫度從78oC變化到83oC。這四種條件下的干莖顆粒在干燥880℃后保持在恒定的干燥速率階段，而且可以清楚地看出氣流速度對(duì)傳熱的影響不大，對(duì)傳質(zhì)有顯著影響。 4結(jié)論 本研究以旋轉(zhuǎn)式干燥機(jī)為研究對(duì)象，對(duì)柔性絲狀顆粒的傳熱傳質(zhì)過(guò)程進(jìn)行了一系列干燥實(shí)驗(yàn)。實(shí)驗(yàn)研究了在不同條件下，滾筒壁溫度、旋轉(zhuǎn)速度、溫度和氣流速度等參數(shù)對(duì)截梗顆粒含水率和溫度的影響。截梗顆粒的溫度隨著鼓壁溫度的升高而顯著增加，而含水率顯著降低。在預(yù)熱干燥階段和恒定干燥速率周期內(nèi)，轉(zhuǎn)速對(duì)顆粒溫度的影響較小，顆粒的含水量隨轉(zhuǎn)速的增加而減小。隨著氣流溫度的升高，顆粒溫度升高，水分蒸發(fā)速率增加，最終含水率降低。 在恒定干燥速率期間，顆粒的溫度隨著氣流速度的增加而降低，而在下降干燥速率期間增加。隨著氣流速度的增加，含水率顯著降低。文中提出的結(jié)果也可供工業(yè)應(yīng)用。隨著干燥長(zhǎng)度的增加，還可嘗試更多的實(shí)驗(yàn)方法來(lái)測(cè)試溫度和水分含量，在不同的溫度和水分條件下，柔性絲狀粒子的有效導(dǎo)熱系數(shù)和傳質(zhì)系數(shù)仍需進(jìn)一步提高。 (a) (b) 致謝 從對(duì)中國(guó)國(guó)家煙草公司鄭州煙草研究院煙草加工技術(shù)重點(diǎn)實(shí)驗(yàn)室的財(cái)政支持和中國(guó)國(guó)家自然科學(xué)基金重大項(xiàng)目（批準(zhǔn)號(hào)：51390492）真誠(chéng)地承認(rèn)。 International Proceedings of Chemical, Biological and Environmental Engineering, V0l. 90 (2015) DOI: 10.7763/IPCBEE. 2015. V90. 2 Experimental Study on Heat and Mass Transfer of Flexible Filamentous Particles in a Rotary Dryer Conghui Gu 1, Bin Li 2, Kaili Liu 2, Zhulin Yuan 1+, Wenqi Zhong 1 1 Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, Nanjing 210096, China 2 Key Laboratory of Tobacco Processing Technology, Zhengzhou Tobacco Research Institute of China National Tobacco Corporation, Zhengzhou 450001, China Abstract. The effects of temperature of dru m wall, rotational speed, temperature and velocity of gas flow on 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. Introduction Granular 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: 101004322@seu.edu.cn. 15 However, 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 Methods 2.1. Material properties Drying 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: Experimental parameters presented in this paper Properties Value Length of dryer, mm 570 Diameter, mm 330 Height of flights, mm 40 Number of flights 4 Plot ratio of particles 18.60% Initial moisture content of particles , kg/kg 21% Drying time, s 840 Fig.1: Experimental material. 2.2. Experimental method The 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 100oC±2oC. Fig. 2: Structure of the experimental set up 2.3. Experimental operating conditions Table 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: Experimental operating conditions in present study Conditions Value Temperature of drum wall, oC 70, 85, 100, 115, 130 Rotational speed, r/min 8, 10, 12 Temperature of gas flow, oC 70, 90, 110 Velocity of gas flow, m/s 0.1, 0.2, 0.3, 0.4 3. Results and Discussion The 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 150°C [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 moisture resulted 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