基于风扇强制对流的茯茶烘房数值优化研究

以某茯砖茶企业烘房为研究对象,利用FLUENT软件对不同风扇优化方案下的茯茶发花过程中烘房内空气的速度场和温度场进行了稳态的数值模拟。研究结果表明:在不改变现有供热方式的情况下,采用双风扇强制对流能够显著改善烘房内的空气对流状况,使烘房内空气的温度均匀性得到明显提高;烘房内空气的最高温度差由原来的5℃改善为2℃。     

茯茶烘房的数值模拟

以某企业茯茶烘房为研究对象,借助FLUENT软件平台,采用数值模拟的方法,引入多孔介质模型,建立茯茶烘房发花期内自然对流流动及传热的三维稳态模型。结果表明:烘房内气流循环速度缓慢,在中部形成了4个气流旋涡;温度场分布不均匀,在竖直方向出现上高下低的分层现象,在水平方向是中间高两端低。数值模拟结果与生产测试数据比较,其最大误差为8.46%,模型可靠。     

螺旋型空气分布器射流特性的实验研究

通过实验研究了螺旋型空气分布器的常温射流特性,进行了不同送风角度条件下,空气分布器射流的包络面、主流区速度分布特性的实验。结果表明,送风射程随着送风风量和送风角度的增加而增大,送风风量对送风宽度的影响不是随着风量的增大而增大或者减小,送风宽度随着扇叶角度的增大而整体呈减小的趋势;使得送风均匀性的扇叶角度在0°~10°。     

多联机性能测试室温度场影响因素的实验研究

为了研究多联机性能测试室温度场的影响因素及解决其温度场不均匀性的问题,本文通过数值模拟和实验,研究了不同送风方式、不同送风速度和不同送风温度条件下测试室的温度场的温度变化情况。实验采用孔板顶送风、侧回风和四面风道送风、顶回风的送风形式;循环风机的转速设置30、40和50 Hz 3种;低温工况选取干球温度-20℃、,高温工况选取干球温度60℃,常温工况选取干球温度30℃。数值模拟结果与实验结果表明:相同送风温度和送风速度情况下,四面风道送风、顶回风的送风形式测试室温度场的均匀性较孔板顶送风、侧回风的送风方式温度均匀性差;相同送风方式和相同送风温度情况下,增大送风速度,相同位置处的温度随之降低,流场和温度场的分布趋势几乎不变;相同送风方式和相同送风速度情况下,送风温度越高,温度场越均匀。研究结果为多联机性能测试室的设计以及多联机性能的测试提供一定的理论和试验基础。     

地铁车厢送风参数对气流组织影响的研究现状

介绍了地铁车厢空调系统送风参数的选取原则和依据,综述了前人对地铁车厢空调系统送风参数的实测结果和气流组织的数值模拟结果,总结了送风参数对地铁车厢内气流组织的影响规律。结果表明,辐流风机有助于改善车厢内气流组织的均匀性;B型地铁载人情况下,当送风速度在1.5m/s左右时,车厢内速度场的均匀性较好;对于相同微风速环境下的A型地铁来说,满载车厢的空调送风速度高于空载车厢的送风速度,以上研究结果为提高地铁车厢的舒适性提供了理论基础。     

远红外油漆烘房的改进措施

远红外油漆烘房由于具有升温快、耗电省、烘烤质量好等特点,在油漆行业中巳得到广泛的应用。但我们也看到不少烘房由于结构上考虑不周,产生了种种弊病:烘房内温度不均匀;被烘件漆膜色泽差异老嫩不均;远红外加热元件寿命不长;烘房炉体保温效果不理想;节电效果不明显;烘烤过程中的废气不能及时排出去;反射壁极易污染等几种常见现象。分析这些现象产生的原因主要是由于砖砌炉体不密闭,保温差散热较大;辐射元件本身质量有问题;远红外辐射波长与吸收波长不相匹配;元件布局不合理等。还有,操作者不按工艺规程操作,采取     

褐煤颗粒垂直移动床干燥过程数值模拟研究

褐煤干燥是提高褐煤能源应用系统性能的重要手段。文中以褐煤垂直移动床干燥过程为对象,建立了传热传质模型,分析了影响干燥性能的主要因素。研究结果表明:对于单程气流,移动床形状因子对除湿量、送风功耗和干燥均匀性具有显著影响;颗粒粒径会影响到干燥饱和区的范围;提高气流流量或温度有利于提高干燥性能;采用多程气流结构有利于提高干燥均匀性,不同流程的高度比是影响干燥均匀性的重要参数。该研究可为移动床干燥过程设计提供理论支持。     

大空间两种气流组织夏季热环境及其能耗实验研究

以某大空间实验基地为研究对象,针对喷口送风和柱状下送风两种分层空调的热环境及供冷量进行了实测研究.研究结果表明:因喷口送风空调区较大,在夏季室外气象参数基本相同的两种室外气象条件下,喷口送风空调系统供冷量比柱状下送风空调系统的供冷量分别高出20.8%、24.4%,且喷口送风空调系统抗干扰能力较柱状下送风强;喷口送风时工作区温度均匀性好于柱状下送风,头足温差较小,但其工作区风速超过标准,而柱状下送风时工作区风速则符合环境设计要求;两种不同送风量下喷口送风时吹风感指数分别为15.64%、11.23%,而柱状下送风时吹风感指数分别为4.17%、2.40%,柱状下送风要明显优于喷口送风.故从节能及热舒适性角度综合考虑,单侧回风的大空间建筑应尽可能采用柱状下送风分层空调,而对于干扰比较大,空调场地较小,无法布置柱状下送风口的场合,则选取喷口送风较好.     

不同送风方式对热舒适度的影响

为了研究不同送风方式对空调房间内舒适度的影响,用实验方法测得下送风、侧送风和上送风3种方式下空调房间不同位置的热舒适度。实验结果表明,空调房间侧送风方式下的舒适性最好,此结论可为空调房间的设计提供参考。     

SPF级实验动物房空气幕送风气流组织研究

为了研究SPF级实验动物房空气幕送风的气流组织,建立数值模型,模拟实验动物房内部的空气流动情况。研究送风换气次数对室内气流组织的影响,并对空气幕送风和方形送风形式进行对比分析。结果显示：相同换气次数下,空气幕送风的室内温度比方形送风的室内温度低,空气幕送风能够更有效地控制污染物。     

Numerical study on premixed hydrogen/air combustion characteristics in micro–combustor with slits on both sides of the bluff body

An approach to improve premixed hydrogen/air combustion in micro combustor is numerically studied in this paper. The micro–combustor with slits on both sides of the bluff body shows better combustion efficiency and uniformity of temperature distribution. The effects of the controllable flow ratio (γ) and the angle of bluff body (θ) on combustion characteristics are investigated by using a two–dimensional model with the H₂/O₂ reaction mechanism. The results show that the increase of controllable flow ratio and angle of bluff body can improve combustion efficiency and decrease velocity extinction limit. However, at higher θ, increasing γ do not play an important role in improving combustion efficiency. In addition, at higher inlet velocity, combustion efficiency do not increase dramatically with the increase of θ. Moreover, at high inlet velocity, a special phenomenon of temperature ‘waist’ is observed in the micro–combustor with slits on both sides of the bluff body, which has a huge impact on combustion characteristics. Therefore, controllable flow ratio and angle of bluff body should be reasonably chosen to improve combustion characteristics.     

中压进汽腔的流场数值模拟比较

通过数值模拟计算,对中压对称进汽和切向进汽两种结构的流场进行了分析比较,结果表明,单一切向进汽腔的总压损失更小,出口汽流角的周向分布均匀度更好。更进一步,为整体评估中压进汽腔的流场以及对叶片级的流动影响,对中压进汽腔及第1级叶片的整体流体域流场情况进行了分析比较,结果表明,采用大几何角静叶的切向进汽腔气动性能最优;当采取切向进汽腔时,需合理选择第1级静叶几何角并耦合计算,才能实现进汽腔的气动优化。     

四角切向燃烧锅炉分隔屏过热器结构对水平烟道烟速偏差的影响

对引进型６００ＭＷ四角切向燃烧锅炉进行了冷态模化试验,首次系统地研究了屏区气流流动特性及改变分隔屏结构布置对水平烟道气流速度场偏差的影响。     

不同导流条安放角下管道双车车间断面周向流速分布特性

为了进一步研究管道双车车间断面螺旋流的水力分布,选取5种导流条安放角(5°、10°、15°、20°、25°),利用粒子图像测速仪(PIV)测量试验管段内管道双车车间流场,分析不同导流条安放角下管道双车车间断面中螺旋流周向流速的分布规律.结果 表明,随着导流条安放角的增加,周向流速分布呈旋转对称的分布趋势;导流条安放角为...     

Lattice Boltzmann method simulation of backward-facing step on convective heat transfer with field synergy principle

The lattice Boltzmann method (LBM) is applied to simulate the two-dimensional incompressible steady low Reynolds number backward-facing step flows. In order to restrict the approach to the two-dimensional flow, the largest Reynolds number chosen was Re = 200. To increase the uniformity of the radial temperature profile for fluid flow in channel and consequently to enhance the heat transfer, the inserted square blockage is used and investigated numerically. In addition, the field synergy principle is also applied to demonstrate that an interruption within fluid results in decreased intersection angle between the velocity and temperature gradient. The numerical results of velocity and temperature field agree well with the available experimental and numerical results.     

An Investigation on the performance Improvement of greenhouse-type agricultural dryers

Drying is simply the process of moisture removal from a product. It can be performed by various methods. In these methods, thermal drying is most commonly used for drying agricultural products. These drying systems are usually classified into low and high temperature dryers according to their operating temperature ranges. In low temperature drying systems, natural-circulation greenhouse-type dryers appear the most attractive option for use in rural locations. They are superior operationally and competitive economically to natural open sun drying. Therefore, two different types of natural-circulation greenhouse crop dryers were designed, constructed and tested for their performance in this investigation. Each dryer mainly consisted of a framework constructed from black coated metal bars, corrosion-resistant plastic mesh and a black coated solar radiation absorber surface. The frameworks of the dryers were clad with clear polyethlene sheet on the all sides. The cladding at rear side was arranged to allow put the moist products into the drying chamber or get dried product from there. The clear plastic cladding at the bottom edge of the front side and rear side was also arranged to allow air to flow into the chamber, while the rectangular stream at the top of the end served as the exit for the moist exhaust air. The dryers were tested in the summer conditions. They were aligned lengthwise in the north-south axis during experiments. All dryers were experimented without crops (no product loaded) and with crops (pepper loaded). The dryers were also tested with chimney constructed from a galvanised iron sheet and without chimney in order to determine the effect of the chimney on the air flows. In addition, pepper was dried in the open-sun drying in order to compare the greenhouse dryers with open air drying. During experiments, temperature distribution inside drying chamber, pepper surface temperature, moist exaust air velocity, wind velocity, solar radiation, temperature and relative humidity of the atmosphere air were measured. Pepper samples, collected from open sun dryer and different positions in greenhouse dryers were also weighted to note amount of water evaporated. The results of the study show that the use of natural-circulation greenhouse dryers for drying agricultural products, is 2…5 times more efficient than open air drying and using black coated solar radiation absorber surface and chimney improve the performance of these dryers. Besides, the output of the greenhouse type dryers has also high quality, compared with open air drying.     

三叶膨胀管换热器壳程强化传热的数值研究

三叶膨胀管是一种新型强化传热管,针对纵向流换热器特点,设计了三种不同管束结构参数的三叶膨胀管自支撑纵向流换热器。应用FLUENT软件及Realizable k-ε湍流模型,对三种不同结构参数的三叶膨胀管换热器壳程强化传热特性展开了数值模拟,并通过与实验数据的对比,验证了计算模型的可靠性。计算了不同壳程介质流速下,三叶膨胀管换热器壳程的换热系数与压降值,并获得了壳程流体流线以及相应的温度场、速度场和二次流分布图。结果发现,在壳程水流速一致的情况下,管束横向间距越大的三叶膨胀管换热器,壳程拥有更高的综合换热性能和更低的压降值,但相应地,换热系数也更低。流场分析显示,壳程流体流线呈现出三维纵向旋流形态,二次流的出现改变了速度场和温度场分布,二次流的强度随着管束横向间距的减小而增大。     

柴油机涡流室内空气流动特性的LDA测试及数学模型

本报导了采用激光多普勒测速仪（ＬＤＡ）首次在实机上对柴油机涡流室内空气运动规律测试的研究结果。研究表明：涡流室内涡流在一定的半径范围内是刚体涡流，在涡流室周边区域可近似看作势涡流。     

Incidences of aligned magnetic field on unsteady MHD flow past a parabolic accelerated inclined plate in a porous medium

An exact analysis of a radiative hydromagnetic flow behavior over a tilted parabolic plate through a permeable medium along with variable species concentration and fluid temperature in the presence of a slanted magnetic field parameter, chemical reaction, and heat generation has been carried out in this study. Closed-form analytical benchmark solutions for flow-governing equations are obtained by using the Laplace transform method. Thereafter, the incidences of different important physical entities on the nondimensional velocity field, temperature distribution, and species concentration are presented using graphs, whereas impacts of various physical entities on wall shear stress, heat and mass transfer rates are presented in tables. It is worth noting that an increase in the magnetic field and its inclination angle causes the reduction in the fluid velocity. However, wall shear stress increases with the increase of magnetic field and its inclination angle. The novel results in this article can be used to improve quicker cooling and producing miniaturized heat flow systems with upgraded efficiency and cost-effectiveness.