秸秆-粉煤灰混凝土砌块试验研究

为了减少秸秆、粉煤灰的堆积处理污染，选用秸秆-粉煤灰混凝土砌块作为研究对象，比较分析不同组分的混凝土砌块的物理抗压属性及导热性能。砌块的强度要求为C20。结果表明：将油菜秸秆掺入混凝土时，掺入秸秆的质量比例为1%、2%、3%的情况下，与普通硅酸盐混凝土相比，秸秆混凝土砌块的导热系数分别降低41.7%、47.8%、57.2%。对秸秆混凝土正交试验结果进行综合分析，得到满足C20强度的节能最优组合为秸秆材料为芝麻、秸秆掺量为2%、粉煤灰掺量为10%、水胶比为0.45，测试其抗压强度为20.12 MPa，导热系数为0.466 W/(m·K)。     

600 MW超超临界循环流化床锅炉水冷壁传热特性研究

为获得超超临界压力下CFB锅炉水冷壁内、外传热特性,建立了水冷壁总传热系数计算模型,并通过高温高压条件下的实验数据拟合得到了工质侧传热系数关联式,将此关联式代入水冷壁总传热系数计算模型,使其预测精度大为提高。研究结果表明:水冷壁传热性能是工质侧传热系数、烟气侧传热系数以及水冷壁管导热性能耦合作用的结果;工质侧传热系数沿着炉膛高度的增加而增加,在30 m时出现第一次峰值,后墙、中隔墙和侧墙水冷壁传热系数分别为24.7,25.9和27.3 kW/(m~2·K),而且在此区间内波动剧烈,并在52 m附近达到最大值,后墙、中隔墙和侧墙水冷壁传热系数分别为33.8,35.1和36.2 kW/(m~2·K),超过50 m以上区域则迅速下降;在100%BMCR负荷下,水冷壁总传热系数沿着炉膛高度方向减小,在30 m以下区域,中隔墙、后墙、侧墙水冷壁总传热系数分别从220,215.2和213 W/(m~2·K)下降到了178,174和170 W/(m~2·K),而在30 m～50 m区间仅下降了4～5 W/(m~2·K),在炉膛顶部区域总传热系数几乎不变。     

螺旋管传热系数的研究

螺旋管传热器优越的结构和传热特性,使其在传热领域得到了广泛应用.采用实验方法对其对流传热系数进行了测定,并利用Fluent软件对螺旋管传热情况进行了模拟.结果表明,在设定的实验条件下,水-水螺旋管传热系数,自然对流情况下为350~550 W/(m2·K),强制对流(搅拌状态)下为400~650 W/(m2·K),所建立的Fluent软件模型能基本反映流场的实际情况,其计算结果与实验情况基本吻合.     

夏热冬冷地区商场建筑围护结构的节能研究

采用DeST建筑环境模拟工具,以南京市某百货大楼为原型,进行模拟计算。探讨研究围护结构传热系数K值的改变对商场冷热负荷、空调运行时间的影响。模拟结果表明:夏热冬冷地区商场建筑围护结构传热系数K值并不是越小越节能,而是冬夏季存在一个平衡点,即围护结构K值选取范围为屋面:0.8~0.6W/(m2·K);墙体:1.0~0.7W/(m2·K);窗户:3.0~2.5W/(m2·K)。     

壁挂式平板轧凸真空玻璃太阳能热水开水器

玻璃是现代生活中重要的建筑材料和生产材料.第一代单层玻璃热阻很小,而且对远红外热辐射几乎完全吸收,传热系数高达6.4W/(m2·K)左右,是240厚砖墙的4倍左右,第二代粘接密封中空玻璃,由于不产生空气对流的中间层,虽具有一时的隔声、隔热、防结露、降低冷辐射的功能,但其传热系数也偏高达3.24W/(m2·K);     

办公楼地面及天花铺设隔热材料供暖的节能分析

提出了楼板上、下面(地面、天花)铺设隔热岩棉,可使夜间室温大幅下降的结论。计算了在供暖期平均室外温度及1月份平均室外温度下(北京地区分别为-1.6℃、-4.3℃),围护结构传热系数为3W/(m2.K)的耗热情况。该方法估算节能率达31%~43%。     

热电联供系统中烟气冷凝传热性能试验研究

针对烟气余热不能充分回收的问题,对能够充分回收烟气余热的新型热电联供系统中的烟气冷凝热回收设备进行试验研究,重点研究该工况下光滑管烟气冷凝设备的传热性能.研究结果表明,在该试验工况下,干式、冷凝段传热系数可达60 W/(m~2·K),冷凝段传热系数为90～100 W/(m~2·K),冷凝段传热系数约为干式段传热系数的1.5～1.7倍,并整理了该工况下的传热准则关系式,为该系统型式的推广应用提供设计与运行依据.     

超声波除垢与强化传热实验研究

通过实验研究了流体在管内雷诺数达5.11×104时,超声波功率对抑垢、除垢的匹配关系及声空化强度对传热系数的影响。研究表明,超声波功率在200 W以下时具有抑垢效应;当功率超过200 W以上时具有除垢效果,并且除垢效果与波声功率成正比。超声波功率还对强化传热有明显影响。当超声波功率为300 W时,传热系数达765 W/(m2.K),达到最佳传热效果。本文还初步研究了超声波传播方向改变时对除垢效果的影响。     

干煤粉加压气化炉对流废热锅炉内多相流场和温度场的数值模拟

采用数值模拟方法对干煤粉加压气流床对流废热锅炉3段受热面和3圈环隙内合成气的流动和温度分布进行了模拟和分析,其中连续相采用组分输运方程并结合Realizable k-ε湍流模型进行求解,颗粒相采用DPM模型,两相间的相互作用采用双向耦合模型求解,温度场基于离散坐标法及灰气体加权和模型进行求解,高压气体的基本参数采用对比态方法、压力组分修正法和Hottel图表法进行确定.结果表明:由上段受热面至下段受热面,由外圈环隙至内圈环隙,合成气的速度逐渐减小,由于堵板的作用,沿废热锅炉高度方向上速度波峰出现偏移;颗粒质量浓度在合成气入口、上段堵板挡住区域和各段受热面底部较大,需要布置吹灰装置;上段受热面、中段受热面、下段受热面和外侧水冷壁的总传热系数分别为274 W/(m2.K)、243 W/(m2.K)、198 W/(m2.K)和223W/(m2.K).     

德国节能标准演变

欧洲门窗节能的典型代表是德国。德国门窗节能标准变化是中国门窗节能未来的发展方向。德国的传热系数在1995年以前用K值(同中国现在一致),之后改为U值。1977年德国要求型材Kf值不超过3.5 W/m2.k,到1995年降低为1.8 W/m2.k,降低了接近50%;到2002年则要求整窗Uw值不超过1.7 W/m2.k,2009年降低为1.3 W/m2.k。在32年的时间里,德国门窗传热系数减低了     

350 MW余热锅炉变工况运行特性分析

  目的  整体煤气化联合循环（IGCC）发电技术是高效、低碳的发电技术,余热锅炉是IGCC的组件之一。文章旨在研究余热锅炉变工况运行特性以提高整体煤气化联合循环发电技术的效率。  方法  通过分析余热锅炉的工作原理及传热传质原理,使用MATLAB软件展开编程计算,探究给水温度、给水压力、液相换热系数以及气相换热系数与余热锅炉内吸热量的关系。  结果  结果发现,当液相换热系数在200～1 000 W/(m2·K)和气相换热系数在20～100 W/(m2·K)范围内时,如果给水温度从30 ℃增加到100 ℃或给水压力增加,余热锅炉的吸热量将不断减少。反之,假设给水温度在30～100 ℃范围内,当液相换热系数从200 W/(m2·K)增加到1 000 W/(m2·K)或气相换热系数从20 W/(m2·K)增加到100 W/(m2·K)时,余热锅炉的吸热量不断增加。  结论  在液相换热系数与气相换热系数不变的情况下,给水温度或给水压力增加,余热锅炉的吸热量会减少;在给水温度与给水压力不变时,液相换热系数或气相换热系数增加,余热锅炉的吸热量会增加。     

Numerical investigation on side heat transfer enhancement in 300 kA aluminum reduction cell

Industrial test and numerical simulation were synchronously applied to analyze the side heat transfer process and enhance heat transfer in aluminum reduction cell. The 3D slice finite element model of aluminum reduction cell was developed, with which the sidewall temperature field of the cell was computed by using software ANSYS. The main influencing factors on heat dissipation were analyzed and some effective measures were proposed to enhance sidewall heat transfer. The results show that the shell temperature of the test cell and the common cell is respectively 312°C and 318°C and the ledge thickness is 16 cm and 15 cm when side coefficient of heat transfer between the shell and the surroundings is 70 W/(m²·K). With the increase of the side coefficient of heat transfer between the shell and the surroundings, the temperature of the shell decreases but the thickness of the side ledge increases when the electrolytic temperature, the ambient temperature, the coefficient of heat transfer between molten bath and ledge, the eutectic temperature and the thermo-resistance of the side lining are constant.     

Filtration Gas Combustion in a Porous Ceramic Annular Burner for Thermoelectric Power Conversion

A numerical study of the combustion of lean methane/air mixtures in a porous media burner is performed using novelty geometry, cylindrical annular space. The combustion process takes place in the porous space located between two pipes, which are filled with alumina beads of 5.6 mm diameter forming a porosity of 0.4. The outer tube diameter of 3.82 cm is isolated; meanwhile the inner tube of 2 cm in diameter is covered by a continuous set of thermoelectric elements (TE) for transforming heat energy into electricity. To achieve and maintain the proper temperature gradient on TE, convective heat losses are considered from the TE. Computer simulations focus on the two-dimensional (2D) temperature analysis and displacement dynamics of the combustion front inside the reactor, depending on the values of the filtration velocity (0.1 to 1.0 m/s), the heat loss coefficient from the internal cylinder (400–1500 W/m²/K), and the fuel equivalence ratio (0.06– 0.5). The conditions that maximized the overall performance of the process of energy conversion are: 0.7 m/s of the filtration velocity, 0.363 of the fuel equivalence ratio and 1500 W/(m^2·K) of the heat transfer coefficient from the internal cylinder, to obtain 2.05 V electrical potential, 21 W of electrical power, and 5.64% of the overall process efficiency. The study shows that the cylindrical annular geometry can be used for converting the energy of combustion from lean gas mixtures into electricity, with a performance similar to the specified by manufacturers of thermoelectric elements (TE).     

一种现场测定土壤源热泵岩土热物性的新方法

利用现有土壤源热泵实验台测定了岩土热物性参数,采用传热学反问题的方法对实验数据进行分析。测试过程中从岩土取热,U型地埋管换热器形成一个线热汇,使其在测试过程中与热泵实际运行时的工作状态相接近,测试更准确,节省测量过程的耗电量。以每个采样时刻作为计算节点,取平均值作为计算结果。测定结果显示岩土导热系数为3.2W/(m·K),回填材料导热系数为2.0W/(m·K),岩土热扩散率为0.85×10~(-6)m~2/s。可靠性分析表明:其标准误差分别为0.08W/(m·K),0.04W/(m·K)和0.039×10~(-6) m~2/s。     

Local entropy generation and exergy analysis of the condenser in a direct methanol fuel cell system

This paper aims to identify the irreversibilities in the condenser of a direct methanol fuel cell (DMFC) system and present possible enhancements in its design through local entropy generation analysis (L-EGA). For this purpose, the local entropy generation terms originating from heat and mass calculated from results of a pseudo two-phase computational fluid dynamic (CFD) model of the condenser. Through this analysis, the total irreversibilities due to heat and mass transfer are calculated locally (e.g., film boundary layer, vapour-gas boundary layer) under the variable operating conditions of a DMFC (undersaturated, saturated, and supersaturated conditions of the cathode exhaust gas). Moreover, the exergy destruction ratio of condenser is found to estimate the exergy performance of the condenser. The results show that in the case of supersaturated cathode exhaust gas (CEG) flow, the entropy generation rate due to mass transfer in the film region is found as 0.032 W/(m·K) which is 18 times higher than that for the undersaturated CEG flow. However, entropy generation rate due to mass transfer decreases significantly when the hot flow is just over the film region. In the film region, the entropy generation rates originating from heat transfer are found as 0.0055 W/(m·K) (for the undersaturated case), 0.0032 W/(m·K) (for the saturated case), and 0.0015 W/(m·K) (for the supersaturated case). Moreover, the maximum exergy destruction ratio is found as 0.72 when the CEG is undersaturated and the CEG velocity is 0.18 m/s, while the lowest exergy destruction ratio is calculated as 0.28 when the CEG is saturated.     

A study of heat transfer in a circulating fluidized bed

An experimental investigation was carried out to study the effects of operating parameters on the local bed-to-wall heat transfer coefficient in a 4.5 m tall, 0.150 m diameter circulating fluidized bed with a bed temperature in the range of 65°C to 80°C, riser flow rate varying from 1400 litres/min to 2000 litres/min, bed inventory in the range of 15 kg to 25 kg of sand, and average sand sizes of 200 μm, 400 μm and 500 μm. A heat flux probe was attached to the riser wall at five different vertical locations for measuring the heat flux from the bed to the wall surface. From the present work, the heat transfer coefficient in the dilute phase was found to be in the range of 62 to 83 W/m²K, 51 to 74 W/m²K, and 50 to 59 W/m² K for sand sizes of 200 μm, 400 μm and 500 μm, respectively. Relevant mathematical correlations were developed to predict local heat transfer coefficient based on the results of the practical work.     

Heat transfer to a horizontal tube bundle located in the freeboard of a bubbling fluidized bed combustor

The characteristics of heat transfer from bubbling gas-fired fluidized bed to a horizontal staggered water-tube bundle located in the freeboard region is experimentally investigated. The purpose is to demonstrate the effect of bed temperature on the coefficients of heat transfer by the different modes to each of the four rows of the bundle, which experiences heat transfer by convection from flue gases, luminous radiation from bed material and non-luminous radiation from gases. The bed temperature itself is varied and controlled through the fuel–air mass ratio. Sixteen runs have been conducted with bed temperature ranging from 1114 to 1429 K, resulting in an overall heat transfer coefficient in the range 74·0–105·0 W m⁻² K⁻¹ for the first row and 58·0–65·0 W m⁻² K⁻¹ for the last. An overall convective heat transfer coefficient from gases, and possible carried over sand particles, to the bundle is formulated. © 1997 by John Wiley & Sons, Ltd.     

基于三维CFD技术的发动机冷却水套流动分析

利用计算流体力学软件对发动机冷却水套流动进行了三维数值模拟研究.研究结果表明:平均流速大于0.5m/s时,气缸体水套内表面的上部平均流速和换热系数均比下部高;缸盖火力面冷却效果较好,换热系数高于10kW/(m~2·K),流速大于1.0m/s,但冷却效果欠均匀;总压力降为38.2kPa;上水孔的布置和尺寸使缸盖下层的各火力面有较好的冷却效果.     

深层埋管式能源桩换热性能影响因素分析

提出一种新型的能源桩换热管型式,即深层埋管式能源桩。利用Comsol Multiphysics建立三维方法模拟桩体-土体传热,一维方法模拟管内水动态传热传质的数值模型,考虑了土体温度随深度的变化,模拟出口水温随时间的变化规律并计算换热量,比较深层埋管式与传统的1-U型、1-W型能源桩的换热量,分析了桩径、桩体导热系数、桩体密度、桩体比热容等不同参数对新型深层埋管式能源桩换热量的影响。模拟结果表明：以运行50 h为例,深层埋管式的总体换热量比1-U型、1-W型分别高122%、54%;而对于单位管长换热量,深层埋管式比1-U型、1-W型分别高9%、50%,桩径从0.5 m增加到1 m,换热量增加14.3%;桩体导热系数从1.2 W/(m∙K) 增大至2.5 W/(m∙K),换热量增加9.6%;桩体密度从1 800 kg/m³增大到2 600 kg/m³,换热量增大0.8%;桩体比热容从637 J/(kg∙K) 增大到1 037 J/(kg∙K),换热量增大1.1%。因此深层埋管式的热性能优于传统1-U型和1-W型,在满足能源桩力学性能的前提下,为了提高深层埋管式能源桩换热性能,可以适当增大桩径。对于桩体材料的选择,应该选择导热系数较高的材料。密度和比热容对换热量的提升影响不大。