水喷淋作用下小室火灾特性

采用全尺寸实验对水喷淋作用下的小室火灾特性展开研究,揭示了小室内烟气的平均温升、O2体积分数、CO体积分数的变化规律以及溢出烟气在大空间内的充填规律.结果表明,低于临界喷淋压力,水喷淋的作用主要是控火,高于此压力,水喷淋的作用主要是灭火;水喷淋可以有效降低小室内的温度,但是也会产生大量的烟水混合气;CO体积分数在水喷淋作用后会急剧增加,控火时存在两个峰值,灭火时只有一个峰值;喷淋压力低于临界压力,CO生成量随着压力的增加而增加,喷淋压力高于临界压力,CO生成量随着压力的增加而减少,在临界压力时CO生成量达到最大;从小室溢出的烟气能在300 s左右从27m下降到3m的高度,烟气生成量与CO生成量的变化趋势一致.     

逆向气流条件下半椭圆管外水平降膜厚度分布研究

为研究半椭圆管水平降膜厚度的分布规律,搭建逆向气流条件下水平降膜实验平台,并结合数字图像处理技术,研究逆流风速(0～5 m/s)和喷淋流量(0.025～0.221 L/min)对液膜厚度的影响。研究表明:逆向气流会对管外水膜产生影响,并存在临界速度;当逆流风速低于临界速度,液膜厚度沿圆周方向先减小后增大,与无空气流动时相似;当逆流风速超过临界速度时,液膜分布严重不均甚至被吹飞;随着逆流风速增大,平均液膜厚度先增大后减小;随着喷淋流量增大,平均液膜厚度持续增大;当喷淋流量减小、逆流风速增大时,平均液膜厚度减小。     

通风条件下细水雾灭火的临界水流率

临界水流率是细水雾系统的重要设计参数.为了研究通风条件对细水雾灭火临界水流率的影响,开展了一系列细水雾熄灭木垛火的模拟实验.实验结果表明,对于木垛火,细水雾的临界水流率同时受到热释放速率、有效喷嘴直径、高度、风速和雾化锥角的影响.基于Heskestad的临界水流率预测模型,利用量纲分析得到的指数关系式对实验数据进行拟合,对纳入通风风速后的模型各参数指数进行了修正,从而将其拓展至通风条件下.     

海水淡化用空心锥喷嘴喷淋性能理论及实验研究

设计开发一种具有高通量、低流阻特征的空心锥喷嘴,并通过理论与实验方法研究空心锥喷嘴的喷淋性能,基于准自由涡理论建立空心锥喷嘴内部流体流动的数学模型,阐明流量系数、喷淋锥角、喷嘴流量与喷嘴结构参数之间的定量关系,并利用多效蒸馏海水淡化喷淋实验台对理论计算结果进行实验测试和验证。研究结果表明:正常工作状态下喷嘴流量系数、喷淋锥角、喷淋流量等参数理论值与测量值之间的误差小于5%,验证了设计模型的准确性。同时根据实验测试数据,拟合得到该类型空心锥喷嘴喷淋锥角与雷诺数之间的经验公式,可为蒸馏海水淡化用大流量空心锥喷嘴的结构设计、工艺选型提供理论指导和数据支持。     

细水雾耦合机械排烟在公路隧道的数值模拟研究

以某公路隧道为研究对象,采用流体动力学软件Fluent,设置火源在细水雾正下方,分析雾化锥角为60°,粒径为100μm时,不同工况下施加细水雾对隧道内温度、氧气浓度、二氧化碳浓度的影响。结果表明:细水雾对火势的抑制效果明显,在没有排烟的情况下,质量流量较小的细水雾(0.1kg/s)可以起到很好的灭火效果,而加大细水雾质量流量(0.2kg/s)对火势的抑制起到很好的促进作用,灭火效果更为明显;在细水雾和排烟同时开启情况下,质量流量较小的细水雾(0.1kg/s)动量不足以克服排烟造成的对细水雾的夹带和飘移作用,灭火效果不佳,温度明显高于同质量流量细水雾的无排烟情况,当质量流量(0.2kg/s)较大时,细水雾与排烟可以优化耦合,在排除高温烟气的同时发挥细水雾的最佳灭火效果。     

叠置式太阳能加湿除湿海水淡化系统的稳态性能研究

介绍一种基于空气加湿除湿技术的太阳能海水淡化装置,装置中除湿腔叠置在加湿腔的上部,以此缩小装置的占地面积并利用热湿空气自然上升的浮力,形成一种新结构。详细说明装置的结构和运行原理,并研究控制海水运行温度、流量、循环空气流率等参数对装置产水性能的影响。实验结果表明,装置产水量随进水流量和运行温度增加而增加,当温度为90℃时,进水流量为420 kg/h,装置的最大产水量达到10.38 kg/h,装置性能系数GOR最大为1.33。系统在类似条件下的理论产水率达到约15.6 kg/h,性能系数达到1.90。对生化小球和加湿帘2种填料及不同填料厚度的产水性能进行测试,结果表明填料的选择,要结合装置体积和传质效率来综合考虑。     

聚光直热式加湿除湿型太阳能海水淡化装置性能测试与经济性分析

对一种聚光直热式加湿除湿太阳能海水淡化装置进行实验测试,根据其产淡水速率和经济成本,对其长期运行的经济性进行分析。在室内稳定条件下,测试给出海水喷淋温度、加热功率等对产水速率的影响曲线。结果表明,采用双层加湿小球作为加湿层材料的系统产水效果最好,在喷淋温度为73℃时,其产水速率为1.12 kg/h。在实际天气下,也测试给出装置内部的工作温度和产水性能随时间的变化曲线。实验结果表明,在平均太阳直射辐照度为692 W/m~2时,最大产水速率达到0.52 kg/h,装置的平均性能系数达到0.84。     

流量对单排插板透水丁坝促淤效果的影响

为研究流量对单排插板透水丁坝促淤效果的影响,确定插板透水丁坝促淤效果最优的流量条件,采用CCHE2D模型对单排插板透水丁坝坝后淤积区形状、坝后最大淤积长度、坝后最大淤积宽度、坝后最大淤积高度及坝后淤积面积随流量变化的规律进行数值模拟。结果表明,当流量为524~950 m3/s时,插板透水丁坝坝后淤积区平面及纵断面形状特点相似且促淤效果较其他流量条件较好;当流量在120.95~1 750 m3/s范围内,随着流量增大,坝后最大淤积长度、坝后最大淤积宽度、坝后淤积面积先增大后减小且均在流量为737 m3/s时达到最优。     

基于Trnsys的太阳能热泵苜蓿干燥系统优化研究

为了提高太阳能辅助水源热泵苜蓿干燥系统的干燥效率和性能系数,从设计和运行两个方面进行模拟研究。利用Trnsys软件设计并搭建了系统仿真模型,输入室外天气参数,对储热水箱体积、水冷集热器流量和是否带有空气-空气热交换器进行模拟研究。结果显示：在储热水箱最佳体积为0.5 m³、水冷集热器最佳流量为0.3 kg/s条件下,不带热交换器可以有效干燥40 kg新鲜苜蓿,带热交换器可以有效干燥50 kg苜蓿。     

长江中下游同流量下水位变化特征

三峡工程作为全球最大的综合性水利枢纽工程,其运行对坝下游的来水来沙条件、河道形态、河道比降及河床糙率等均产生了一定影响,进而引起同流量下洪水、中水、枯水位的适应性调整。为此,以长江中游宜昌至螺山站河段为例,采用多项式拟合法,探究了长江中下游同流量下水位变化特征。结果表明,三峡水库运行后,同流量中水、枯水位为下降趋势,同流量洪水位为上升态势,且存在一个临界流量,等于该流量时,同流量水位不发生变化,因此同流量对应的水位存在上升、下降转换的"临界转换流量"。宜昌站的临界转换流量的上下限为35 200～46 500m3/s,枝城站为35 600～46 400m3/s;受三口分流关系调整的影响,沙市站和监利站的临界转换流量上下限较低,分别为30 000～31 600、30 000～31 000m3/s;受洞庭湖入汇的影响,螺山站临界转换流量上下限值较高,为30 000～45 800m3/s。     

A numerical simulation of the suppression of hydrogen jet fires on hydrogen fuel cell ships using a fine water mist

In this paper, in order to evaluate the reliability of a fine water mist for the suppression of fires on hydrogen fuel cell ships, the fire dynamics simulator (FDS) software was used to simulate the jet fire process and the action of a fine water mist on a fire caused by a hydrogen leakage in the hydrogen storage tank areas of hydrogen fuel cell ships. The fire scenario was classified into vertical or horizontal jet fires according to the location of the leakage in the hydrogen storage tank area, and the suppression effects of a fine water mist on hydrogen jet fires under a different droplet size, spray velocity, and ambient wind speed were compared and analyzed. The results indicate that a fine water mist is not effective in extinguishing hydrogen jet fires; however, by selecting suitable parameters (a spray velocity of 30 m/s and average droplet size of 30 μm), it can effectively reduce the fire field temperature of hydrogen jet fires and prevent the fire from developing further. Increasing the average droplet size of the fine water mist results in a gradual degradation of the suppression effect, while a higher spray velocity of the mist enhances the suppression effect to a certain extent. The ambient wind speed is an important factor that influences the suppression effect of a fine water mist on hydrogen jet fires, and when this speed is less than 4 m/s, a fine water mist with a higher spray velocity and smaller average droplet size is still a superior way of suppressing fires.     

细水雾扑灭油池火的临界条件

通过模拟灭火实验发现细水雾灭火过程中由于雾特性参数的变化而形成两种相异的灭火过程,进而通过理论分析与计算得到了细水雾通过火焰冷却扑灭油池火所需的临界条件,并通过实验室尺度实验与全尺度实验对计算结果进行了验证．在实验中还发现对于下喷式系统而言,细水雾能否穿透烟气羽流层对于细水雾系统能否灭火具有至关重要的影响,为此引入了烟气羽流与细水雾的推力比这一概念,并通过实验确定了采用下喷方式时,细水雾灭火的临界推力比大致为10．     

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.     

受限空间内细水雾抑制熄灭火焰过程中一氧化碳的生成率

细水雾抑制熄灭火焰过程中一氧化碳的浓度是评价细水雾灭火系统安全可靠性的一个重要参数.本文通过受限空间内细水雾抑制熄灭障碍火的模拟实验研究,发现细水雾抑制熄灭火焰过程中一氧化碳生成率存在两种控制模式,即燃料控制模式和细水雾流量控制模式.实验结果表明,在燃料控制模式下,一氧化碳生成率随着燃料流量的增大而增大;在细水雾控制模式下,一氧化碳生成率随着细水雾流量的增大而增大.为了获得两种控制模式的临界转变条件,对燃料控制模式和细水雾控制模式的临界工况进行水蒸气含量分析.通过理论分析,得到一氧化碳生成率控制模式转变的水蒸气含量临界范围与 Suh and Atryeya 理论基本一致,即空气中水蒸气质量分数达到25%~65.5%时,水蒸气对火焰的作用从化学作用转为物理作用,一氧化碳生成率控制模式开始转变     

Thermal characteristics of air-water spray impingement cooling of hot metallic surface under controlled parametric conditions

Experimental results on the thermal characteristics of air-water spray impingement cooling of hot metallic surface are presented and discussed in this paper.The controlling input parameters investigated were the combined air and water pressures,plate thickness,water flow rate,nozzle height from the target surface and initial temperature of the hot surface.The effects of these input parameters on the important thermal characteristics such as heat transfer rate,heat transfer coefficient and wetting front movement were measured and examined.Hot flat plate samples of mild steel with dimension 120 mm in length,120 mm breadth and thickness of 4 mm,6 mm,and 8mm respectively were tested.The air assisted water spray was found to be an effective cooling media and method to achieve very high heat transfer rate from the surface.Higher heat transfer rate and heat transfer coefficients were obtained for the lesser i.e,4 mm thick plates.Increase in the nozzle height reduced the heat transfer efficiency of spray cooling.At an inlet water pressure of 4 bar and air pressure of 3 bar,maximum cooling rates670℃/s and average cooling rate of 305.23℃/s were achieved for a temperature of 850℃ of the steel plate.     

A Zone Model in Simulating Water Mist Suppression on Obstructed Fire

A zone model is proposed for studying the obstructed fire suppression by a total flooding water mist system in a chamber with different ventilation conditions. This is a one-zone thermal model mainly for simulating scenarios where oxygen consumption and dilution by water evaporation are the main fire extinguishing mechanisms. The water flow rate and volume mean diameter of a droplet has been used to characterize the water mist system. The fire is taken as a heat source, and its heat release rate is related to oxygen consumption. Mass and energy conservation equations for gaseous species in the enclosure under fire have been solved. Fire suppression is predicted by investigating the limit of oxygen concentration. Numerical results are verified by two sets of experiments on water mist fire suppression system reported in the literature. The predicted results agreed qualitatively with the experiments. In addition, the predicted results by this model are also compared with other existing models. Factors affecting the fire extinguishment mechanism are analyzed, and the limitations of the model are discussed.     

气泡喷嘴下游雾化与流场特性的研究

本文用激光粒子动态分析仪（ＰＤＡ）测量了水平喷射的气泡雾化喷嘴下游不同截面上的雾化液滴平均直径和速度分布，用水在常温，常压下进行试验，液体的喷射压力变化范围为１５０～５５０ｋＰａ；气液比的变化范围为０～０．１２。研究了随着喷射距离的增大，气泡喷嘴的雾化与流场特性的变化规律，试验结果表明，沿着喷射方向，与喷孔一定距离内，气泡喷嘴的液雾存在明显的扩散过程，气泡喷嘴的喷雾速度呈典型的抛物状分布，在喷雾轴     

Evaluation and optimization of solar desiccant wheel performance

This paper presents the evaluation and optimization of a solar desiccant wheel performance. A numerical model is developed to study and discuss the effect of the design parameters such as wheel thickness, wheel speed, regeneration to adsorption area ratio, wheel porosity, and the operating parameters such as air flow rate, inlet humidity ratio of the air and regeneration air temperature on the wheel performance. It is also used to draw the performance curves of the desiccant wheel to quantify the optimum design parameters for certain operating conditions.Also, an open test loop for the desiccant wheel is constructed with appropriate control devices and measuring instruments. A perforated plate solar air heater of 2 m² area, together with an electric heater, is used as a source of energy to regenerate the desiccant material. The experimental tests are used to validate the numerical model and to evaluate the performance of the solar system and the desiccant wheel under actual conditions of Cairo climate (30° latitude).Comparison between numerical and experimental results shows good agreement between them, especially at low flow rates of air. Numerical results show that there is a maximum value of each design parameter at each operating condition, and above that no remarkable changes in the wheel performance are noticed. The results also show that there is an effective range of the air flow rate, due to which wheel performance becomes inefficient. This range is found to be between 1 and 5 kg/min. The performance curves of the wheel, which help to determine the humidity reduction ratio, are drawn for wheel speeds between 15 and 120 rev/h, dimensionless wheel thickness between 0.15 and 0.5, air flow rate equal to 1.9 and 4.9 kg/min, and regeneration temperature equal to 60 and 90 °C. These curves show that there is an optimum value of the wheel speed for each wheel thickness to obtain the best wheel performance for certain operating conditions.Experimental results show that the perforated plate solar air heater of 2 m² area can share about 72.8% of the total regeneration energy required at 1.9 kg/min air flow rate and 60 °C the regeneration air temperature. This value decreases to about 13.7% at a flow rate equal to 9.4 kg/min and regeneration temperature equal to 90 °C. The perforated plate solar air heater area required to completely fulfill the regeneration energy during the daytime is also calculated.     

Experimental study of flow regime characteristics in diesel multi-hole nozzles with different structures and enlarged scales

The internal flow of diesel nozzles has a strong influence on the subsequent spray and atomization characteristics. A flow visualization experiment system equipped with enlarged transparent nozzles was set up to investigate the effect of different nozzle structures and different nozzle enlarged scales on cavitating flow and subsequent spray characteristics. Significant parameters of internal flow including critical pressure of cavitation inception, critical pressure of hydraulic flip, discharge coefficient, Reynolds number, flow rate and cavitation distribution were fully investigated during the experiments. Experimental results show that the nozzles with small length/diameter ratios at the same orifice diameter were more inclined to cavitate and had higher discharge coefficient than that of nozzles with large length/diameter ratios. Cavitating flow in nozzles with different sac volume structures may incur different spray characteristics in the near-nozzle field and it is the internal cavitating flow that induces the asymmetry of subsequent spray. The investigations indicate that the critical pressure of hydraulic flip and discharge coefficient of nozzles under different needle lifts were quite different even under the same boundary conditions and the nozzle flow characteristics have been greatly influenced by the hydraulic flip phenomenon. Two types of cavitation were observed in nozzles with different scaled-up times and the string cavitation was found in three times scaled-up nozzle, while the cloud cavitation bubbles were appeared in five and eight times scaled-up nozzles. A kind of hysteretic cavitation phenomenon was also observed in the experiment and then was analyzed in this paper.     

Experimental Study of Condensation in a Shell and Tube Heat Exchanger in the Presence of a Noncondensable Gas

In this paper, an experimental study of the condensation of water vapor from a binary mixture of air and low‐grade steam has been depicted. The study is based upon diffusion heat transfer in the presence of high concentration of noncondensable gas. To simplify the study, experimental analysis is supported by empirical solutions. The experimental setup is custom designed for testing a new shell and tube type heat exchanger supplied by the manufacturer. Air–vapor mixture at 80 °C (max) and 20.2% relative humidity enters the heat exchanger at a mass flow rate of 480 kg/h and condenses 27 kg/h vapor using cooling water at an inlet temperature of 7 °C to 10 °C and mass flow rate of 3500 kg/h. By using the experimental data of constant inlet air mass fraction, mixture gas velocity, and different volumetric flow rate of the cold fluid, the local heat transfer coefficients are obtained. The main objective of this work is to establish an approximate value for surface area and overall heat transfer coefficient of a horizontal shell and tube condenser used in process space. Under designed working conditions, the condenser is found to work efficiently with 90% vapor condensation by mass.