流体参数与隔板结构对太阳能蓄热水箱性能的综合影响

为了探寻综合性能最优的蓄热水箱结构，以半球形顶圆柱体水箱为研究对象，通过改变内置水平隔板上开孔的面积、数量及位置，得到13种不同的隔板结构，数值分析了不同冷水入口流速对水箱内温度场和流场的影响特征。结果表明：水箱内置隔板上的不同开孔方式对冷热水混合过程的抑制效果存在差异，本文开孔方式2对用户侧用水量变化的适应性较强。隔板开孔面积不变，增大冷水入口流速或增加开孔数量均能有效提高水箱蓄热量；冷水入口流速不变，在较小的总开孔面积条件下减小各小孔定位圆直径可有效提高水箱蓄热量，6^#水箱蓄热量最大。过高、过低的冷水入口流速均不利于形成良好的温度分层，11^#水箱的温度分层效果最佳。     

平板太阳能迎来产业发展的春天

据中国太阳能热利用产业联盟的统计数据显示,我国平板太阳能热水器产业近两年的增长速度均超过43%,在太阳能热利用行业呈现出比真空管太阳能热水器更快的增长势头。     

水平管内甲烷超临界压力加热的数值模拟

以甲烷为研究对象,采用CFD数值模拟二维水平管内超临界压力甲烷加热情况下的传热性能,分析了热流密度、质量流速和进口温度对其传热性能的影响规律,结果表明:当进口温度和质量流速一定时,随着热流密度的增加壁温增大,而表面传热系数减小;当进口温度和壁面热流密度一定时,表面传热系数随质量流速的增大而增大;当质量流速和壁面热流密度一定时,表面传热系数随进口温度的增大而增大。     

煤气化装置黑水沉降槽流场特性的模拟计算

采用CFD软件对煤气化装置竖流式黑水沉降槽进行建模,计算不同工况条件下黑水沉降槽内流场特性,分别讨论了入口流速和排污量对内部流场的影响规律。结果表明：沉降槽内存在射流区、回流区、扩散沉降区,入口流速和出口排污量是影响沉降槽内流场的主要因素,随着入口流速或排污量的增加,射流区和回流区面积增加;不同排污量或入口流速时,不同位置流体的径向流速分布趋势相同。     

进水流量对新型储热水箱分层特性影响的实验研究

储热水箱被广泛使用在太阳能集热系统以及家用电加热热水器中,是决定集热系统和热水器性能的关键因素之一,储热水箱分层效果越好,越能提高集热系统效率及热水器的热水出水量。本文设计了一种新型均流器,安装在圆柱形储热水箱底部,并搭建了一套储热水箱分层特性测试实验台。在初始水温50℃、进水温度20℃的工况下,分析对比了3组不同流量(0.69L/min、2.14L/min、6.17L/min)时储热水箱的分层特性,结果显示,大流量比小流量温度曲线的斜率更大,温度下降速度更快。同时,基于热力学定律,分别计算了3组流量水箱的取出效率、用能效率、出于能量品质的考虑而采用的(火用)效率,在流量为0.69L/min、2.14L/min、6.17L/min时的取出效率分别为91.8%、95.7%、94.3%,用能效率分别为96.6%、98.6%、97.5%、(火用)效率分别为78.5%、83.1%、77.0%。     

ABS熔体在微尺度通道中粘性耗散效应的研究

针对微尺度通道中粘性耗散效应对非牛顿聚合物熔体流动特性的影响,采用毛细管流变仪、高精度温度传感器和微尺度口模等组成的粘性耗散测量装置,对非结晶型ABS(Acrylonitrile Butadiene Styrene,ABS)聚合物材料,在不同入口温度和剪切速率下,流经直径分别为350μm和500μm,长径比不同的微通道时的粘性耗散效应,进行了实验测量和数值模拟。结果表明,微通道入口熔体温度一定时,粘性耗散效应引起的出口熔体温升,均随剪切速率的增大而近似线性增加;而剪切速率一定时,微通道的出口熔体温升则随其长径比的增大和入口熔体温度的降低而明显升高。     

甲烷化反应器催化剂积炭过程的模拟研究

针对固定床甲烷化反应器内催化剂积炭问题,采用离散元方法(DEM)建立小管径比随机堆积球形催化剂床层,计算流体力学(CFD)方法模拟催化剂外层到内层的积炭形成过程,探讨入口氢气占比、温度、流速和催化剂温度对积炭的影响。结果表明:反应初期积碳最严重,0～4 000 s平均孔隙率值下降了0.34,4 000～8 000 s平均孔隙率值下降了0.075;从催化剂外层到内层,积炭程度呈圆环状减小;入口氢气占比从0～40%、催化剂温度从850～770K,催化剂平均孔隙率值增大0.27、0.22;入口流速从0.015～0.005 m·s~(-1)、温度从500～400 K,催化剂中心孔隙率值减小0.01、0.005。结论可为固定床反应器和甲烷化积炭效应研究提供参考。     

板式蒸发式冷凝器热工性能实验

对影响板式蒸发式冷凝器热工性能的主要因素——空气的湿球温度、冷凝温度、相对湿度做了实验研究。结果显示：冷凝温度和冷凝压力均随着入口空气湿球温度的升高而升高;入口空气相对湿度对压缩机功耗的影响与湿球温度对压缩机功耗的影响均比较大;对基于同一压缩系统的实验比较表明,在冷凝温度为38℃时,板式蒸发式冷凝器的热流密度比管式蒸发式冷凝器平均大30.5%;且在相同的冷凝温度下,入口空气湿球温度越低,板式蒸发式冷凝器的热流密度比管式蒸发式冷凝器大得越多。     

热塑性挤出制品表面质量的影响因素

以聚丙烯(PP)为基体,研究了热塑性挤出制品表面质量的影响因素,并用Matlab对实验数据进行了拟合。结果表明:剪切速率、温度、口模长径比以及硅酮母粒对制品表面粗糙度都有影响,随着剪切速率、口模长径比的增加以及温度的降低,表面粗糙度增加;硅酮母粒的添加在一定程度上降低了制品的表面粗糙度。     

高热流条件下过冷沸腾流动阻力特性试验研究

过冷沸腾在高热流冷却场合得到了广泛的应用,如聚变堆偏滤器冷却、压水堆堆芯冷却。其中,过冷沸腾流动阻力是换热系统设计的关键内容之一。试验研究了高热流条件下竖直通道内水的过冷沸腾流动阻力特性,试验段为内径6 mm、长径比44.4的不锈钢圆管。试验参数范围:热通量7.5～12.5 MW/m~2,质量流速6000～10000kg/(m~2·s),系统压力3～5 MPa,进口流体温度80～200℃。分析了质量流速、热通量、压力、沸腾数、Jacob数等参数对阻力的影响。结果显示,过冷沸腾流动阻力随着热流及质量流速的增加而增加,随压力增加而减小。将试验数据与文献中的经验关联式作对比,结果表明各关联式的预测误差较大,主要归结于拟合参数及工作流体的差异。研究发现管径尺寸效应也是影响阻力的一个因素,为此在前期成果的基础上,提出了一个添加管径因素修正项的经验关联式,该关联式的预测误差在±18%范围内。     

电热水器内部结构优化及储能特性研究

将相变储能技术应用于电热水器,并通过添加石墨纳米颗粒改善相变材料的导热特性,对其储能过程进行调节,可以起到“移峰填谷”的作用。建立了四种不同结构的电热水器三维模型,模拟了电热水器内部速度场与温度场分布特性。考察了进出口水管结构、电加热管布置方式、保温层结构等因素对热水器内部流场及传热特性的影响,研究了不同储能层厚度对电热水器储能的影响。结果表明,水平加热管与垂直加热管相比,加热过程中加热效率提高了2.2%;进水管管径增大1.5倍,热水输出率提升了17.9%;加入相变材料可在相同保温时间内(36 h)使水温最大提高10.6%。     

加氢加热炉的关键设计要素

讨论了影响加氢加热炉设计的关键要素,对高压加氢加热炉应选用单排管双面辐射炉型;炉管表面热强度应根据介质的油品性质、许用油膜温度,管壁温度等条件确定;流速应保证合适的流型;炉管材质的选择;辐射管架的热膨胀问题的处理;炉管表面热电偶的设置的原则;燃烧器选择与布置;炉衬的设计原则.     

Applicability of flashing desalination technique for small scale needs using a novel integrated system coupled with nanofluid-based solar collector

The present study introduces an attempt for the application of flash desalination technique for small scale needs. An integrated system uses a flashing desalination technique coupled with nano-fluid-based solar collector as a heat source has been made to investigate both the effect of different operating modes and that of the variation of functioning parameters and weather conditions on the fresh water production. The flashing unit is performed by similar construction design technique of commercial multi-stage flashing (MSF) plant. The thermal properties of working fluid in the solar collector have been improved by using different concentrated nano-particles. Cu nano-particle is used in the modeling to determine the proper nano-fluid volume fraction that gives higher fresh water productivity. An economic analysis was conducted, since it affects the final cost of produced water, to determine the cost of fresh water production. Although a system may be technically very efficient, it may not be economical. The effect of different feed water and inlet cooling water temperatures on the system performance was studied. The mathematical model is developed to calculate the productivity of the system under different operating conditions. The proposed system gives a reasonable production of fresh water up to 7.7 l/m²/day under the operation conditions. Based on the cost of energy in Egypt, the estimated cost of the generated potable water was 11.68 US$/m³. The efficiency of the system is measured by the gained output ratio (GOR) with day time. The gained output ratio (GOR) of the system reaches 1.058. The current study showed that the solar water heater collecting area is considered a significant factor for reducing the water production cost. Also, the produced water costs decrease with increasing the collecting area of the solar water heater. The volume fractions of nano-particle in solar collector working fluid have a significant impact on increasing the fresh water production and decreasing cost.     

Optimization of the Heat Transfer Rate and Pressure Drop of Inside Profiled Tubes – Part 1

Nine inside profiled tubes were developed and investigated for optimization of the heat transfer rate and pressure drop behavior. The results of this work are presented in two parts. This part describes the comparative investigation of five tubes with different inside profiles to simulate the heat transfer and friction loss of fired tubular heaters in petrochemical processes. In part 2, a further four tubes with different inside profiles will be compared. To test the efficiency of the new profiles a test rig was modified. Using the similarity laws by Reynolds, the Reynolds number calculated for the gas flow in the heater tubes was converted into the flow rate, as well as the pressure and temperature of a distilled water system. Axial and peripheral velocities were measured using a Laser‐Doppler‐Velocimeter (LDV). Friction pressure drop and heat transfer were measured to determine the efficiency of each tested tube under the constant conditions of the distilled water system. The results of the investigations on these five inside profiles showed that profiles with eight flat and symmetrically distributed straight fins (tube III) or with a twist angle of 30° to the tube axis (tube IV), produced heat transfer rates higher that that of the bare tube by 120 % and 156 %, respectively, with increases in pressure drop only 46 % and 76 %, respectively.     

Water Desalination Using Solar Thermal Collectors Enhanced by Nanofluids

The absorption efficiency of a solar collector using different types of nanofluids was improved. Experimental work was carried out to investigate the flat-plate and evacuated-tube collectors under outdoor conditions to produce distilled water. A pilot plant was designed and installed. The yield of distilled water at different seawater flow rates and the physical properties of nanofluids were determined. Solar intensity, water mass flow rate, and temperature were measured. The performance of the desalination unit was evaluated in the presence of carbon nanotubes in paraffin wax and ethylene glycol nanofluids. The evaporation efficiency of the flat-plate collector was improved up to 36 % in the presence of ethylene glycol nanofluid at 80–100 °C.     

A solar desalination system using humidification–dehumidification process: experimental study and comparison with the theoretical results

In this study, influence of the different system operating conditions on the performance of a solar desalination system using humidification-dehumidification process have been investigated experimentally under the climatological conditions of Ankara (40°N, 33°E), Turkey. An experimental set-up that consists of a double-pass flat plate solar air heater with two glass covers, pad humidifier, dehumidifying exchanger and water storage tank was designed and manufactured. Working principle of the set-up is based on the idea of closed water and open-air cycles. A series of tests were performed on it in outdoor environment, in order to assess the effect of mass flow rate of the feed water, process air and cooling water, double-pass flat plate solar air heater, initial water temperature and amount of the water inside the storage tank on the productivity of the system. Additionally, an evacuated tubular solar water heater unit was integrated to the existing system and the effect of this integration on the performance of the system was examined. Solar radiation, wind speed, relative humidity, mass flow rate of the feed water, process air and cooling water, mass of condensate water and temperatures at various locations were obtained during the experiments.

The results of the experimental study showed that under certain operating conditions, the system productivity decreases about 15% if double-pass solar air heater is not used and significant improvement on the productivity of the system is achieved by increasing the initial water temperature inside the storage tank. In addition, productivity of the system increases with increasing the feed water mass flow rate and quantity of water inside the storage tank. However, productivity of the system remains approximately the same when the air mass flow rate is increased. Moreover, increasing the cooling water mass flow rate results in the improvement on the productivity of the system investigated. Finally, results obtained from the present investigation were compared with the theoretical study and a good agreement between them is observed.     

延迟焦化加热炉技术现状

焦化加热炉设计和操作是延迟焦化装置的技术关键。本文阐述了国内焦化加热炉的发展历程，汇总了国内三大石油公司各生产企业在役焦化装置规模和对应炉型，阐述了国内主要炉型双面辐射箱式炉和阶梯炉的技术特点。论文分别从焦化炉管结焦机理、原料反应特性表征及工业应用几方面着重介绍了国内近几年在焦化加热炉方面开发的关键技术。国内各炼化企业焦化加热炉目前大部分为双面辐射箱式炉，新建装置多采用阶梯炉炉型。国内基于炉管结焦机理，通过建立焦化原料加工性能评价方法，开发焦化加热炉过程模拟技术，提出了针对炉管结焦的设计和操作新准则，创立了低温长停留时间增加反应给热量的工艺技术。今后焦化装置在设计以及改造中，均需要依据原料性质提前判断结焦特性，采用先进燃烧方式、合理炉管布置和流程设计、改进管内流动状态以及优化关键操作等措施，在控制炉管结焦的前提下尽量提高炉出口裂化反应深度，从而达到改善产品分布、延长装置操作周期的目的。     

二氧化碳热泵热水器微通道气体冷却器的仿真分析

设计了一种用于二氧化碳热泵热水器的新型微通道水冷气体冷却器,用有限单元法建立了换热计算模型并编制程序。对微通道内CO₂和水侧的流动与换热进行了数值仿真;运用该模型分析了各种参数下气体冷却器的换热性能及CO₂侧的压降。可用于指导优化设计。     

基于肋片式集热板的直膨式太阳能热泵

将一种新型肋片式集热器/蒸发器应用于直膨式太阳能热泵热水器,对其进行实验研究,并提出一系列优化方案。由于集热器表面温度通常低于环境温度,集热器除了从太阳辐射中吸收热能,还能从空气中吸收部分热能,集热效率较高。相同外形尺寸条件下,新型集热器较吹胀板集热器有更大的换热面积。实验结果表明,在天气晴朗的秋季,将150L水从20℃左右加热至50℃,热泵的平均供热性能系数（COP）能达到5.37,即使在环境温度为18.6℃的小雨天气,系统平均COP依旧能够达到3.43。对实验样机建立仿真模型,并针对新型集热器提出一系列优化方案,计算机模拟结果表明,经过优化,在晴朗天气将150L水从20℃加热至50℃,系统的平均COP可达到6。     

H型翅片管湿烟气对流冷凝传热的数值模拟研究

通过数值计算对湿工况下的H型和圆型翅片管换热器通道内充分发展段的对流冷凝传热特性进行模拟研究。计算采用压力与速度耦合的SIMPLER算法,湿烟气流速范围为1~5 m/s,水蒸气质量分数范围为5%~13%。讨论了不同入口速度、水蒸气质量分数对H型翅片管和圆型翅片管传热传质系数、传热量、冷凝水流量和翅片效率的影响,并进行定量比较分析。计算结果表明,H型翅片管的传热能力强于圆型翅片管,但冷凝生成量较圆型翅片管小,同时H型翅片管的总翅片效率和潜热翅片效率小于圆型翅片管。