Experimental study on static flash evaporation of aqueous NaCl solution

Experimental study on static flash of aqueous NaCl solution was present. Initial waterfilm concentration and superheat ranged between 0 and 0.15 (mass fraction), between 1.7 and 53.9 K respectively. Influence of factors, such as initial waterfilm concentration, initial waterfilm height and superheat on thermo-properties during flash, such as waterfilm temperature, non-equilibrium fraction (NEF), and volumetric heat transfer coefficient were analyzed and compared with that on flash of pure water. Results suggested that higher initial waterfilm concentration suppressed liquid–vapor phase change, reduced the rate of flash evaporating and weakened the intensity of boiling heat transfer. But the influences of superheat and initial waterfilm height on flash of aqueous NaCl solution were same as that on pure water. At last, NEF was fitted with relative error between ?49.30% and 55.2%, upon which volumetric heat transfer coefficient could be calculated with relative error varying between ?12.6% and 18.8%.     

Experimental study on static/circulatory flash evaporation

Comparative study on heat and mass transfer properties of static/circulatory flash evaporation, i.e., non-equilibrium fraction (NEF), evaporated mass and heat transfer coefficient, was presented based on two experimental systems. NEF evolution in static flash was newly fitted by error function equation, based on which a unified calculating model for heat and mass transfer properties of both flashes was set up initially. At last, heat transfer coefficient was redefined as average heat flux released from unit volume of waterfilm under unit superheat. Results suggested that this coefficient was a time-depended function and a peak value existed in its evolution versus time.     

Simulation analysis of methanol flash distillation circulation process in biodiesel production with supercritical method

High methanol-to-oil ratio is required to obtain a high conversion of oil for the production of biodiesel with supercritical methanol. Recovering the methanol of a stream issuing from a transesterification supercritical reactor by flash distillation instead of evaporation was analyzed. The one-stage and two-stage flash distillation processes were presented and compared. The difference of the recovery percentage of methanol of the above two flash processes is less than 0.5% and the methanol concentration in the vapor for the one-stage process decreases rapidly when feed temperature increases. The process in which the product of transesterification of soybean oil with supercritical methanol is cooled to an appropriate temperature (about 240°C) first and then flashed was put forward. The effect of cooling temperature, feed pressure and flash pressure on methanol concentration and recovery percentage was investigated. According to this study, when the feed pressure range is 15–30 MPa, the flash pressure equals 0.4 MPa, and cooling temperature range is 240°C–250°C, the recovery percentage of methanol is not less than 85%, and the concentration of the vapor in mass fraction of methanol is approximately 99%. Thus, the vapor leaving the flash tank can be directly circulated to the transesterification reactor.     

Simulation analysis of methanol flash distillation circulation process in biodiesel production with supercritical method

High methanol-to-oil ratio is required to obtain a high conversion of oil for the production of biodiesel with supercritical methanol. Recovering the methanol of a stream issuing from a transesterification supercritical reactor by flash distillation instead of evaporation was analyzed. The one-stage and two-stage flash distillation processes were presented and compared. The difference of the recovery percentage of methanol of the above two flash processes is less than 0.5% and the methanol concentration in the vapor for the one-stage process decreases rapidly when feed temperature increases. The process in which the product of transesterification of soybean oil with supercritical methanol is cooled to an appropriate temperature (about 240°C) first and then flashed was put forward. The effect of cooling temperature, feed pressure and flash pressure on methanol concentration and recovery percentage was investigated. According to this study, when the feed pressure range is 15–30 MPa, the flash pressure equals 0.4 MPa, and cooling temperature range is 240°C–250°C, the recovery percentage of methanol is not less than 85%, and the concentration of the vapor in mass fraction of methanol is approximately 99%. Thus, the vapor leaving the flash tank can be directly circulated to the transesterification reactor.     

循环流化床锅炉排渣分选装置的冷态试验研究

在一个可视化冷态试验台上对新型排渣分选装置的气固流动特性进行了试验研究,试验结果表明：分选室和主床同时运行时,主床和分选室之间存在合理的压力分布以形成“主床-分选室-主床”的颗粒循环运动;初始床料特性对分选室分选效果有一定的影响;分选室分选效果随着流化风速比ξ的增大而变好。     

电站锅炉过热器和再热器T型三通对集箱静压分布影响的试验研究

为了获得过热器和再热器T型三通对集箱静压分布及三通两侧分流比对涡流区和集箱静压分布的影响规律,以空气为工质对纯三通模型进行流动特性试验.研究结果表明:带三通集箱静压分布受一次涡流和二次涡流的共同影响,一次涡流影响范围为-2.5D~2.5D(D为等径三通内径),二次涡流影响范围为-1.5D~1.5D;三通两侧分流比对涡流区范围影响较小;随着三通某侧流量增大,该侧静压降低,但静压分布规律无明显变化.在一次涡流影响范围内,正母线和右下40°线的静压差异受分流比的变化影响较小;侧母线的静压差异随分流比的增大而有所增大.     

Study on gas holdup in a fluidized flotation column from bed pressure drop

This paper investigated the overall gas holdup characteristics in a cocurrent three-phase fluidized flotation column with liquid as the continuous phase. The air, water, and glass beads with a diameter of 3 mm were, respectively, used as the gas, liquid, and solid phases in the flotation column. The gas holdup studies were carried out in a plexiglass column with 0.05 m in internal diameter and 2.2 m in height. Bed pressure drop measurements were used to calculate the fractional gas holdup. During the measurements, the superficial gas and liquid velocities, respectively, varied from 0.42 to 2.55 cm/s and from 6.47 to 10.82 cm/s. Detailed experimental investigations were carried out to study the effects of static liquid height, initial static bed height, gas velocity, liquid velocity, and frother concentration on gas holdup in a cocurrent three-phase fluidized flotation column. It was found that the gas holdup increased with the flow rate of air and decreased with an increase in the water flow rate. Certain effect of the static bed height on gas holdup was observed when the gas velocity varied. But the increase in the static liquid height resulted in the decrease in gas holdup when the gas velocity varied.     

Experimental study of flash evaporation of a water film

This experimental study of the flash evaporation phenomenon of a water film was carried out with an initial water height of 15 mm, superheats ranging from 1 to 35 K and initial temperatures from 30 to 75 °C. During a sudden pressure drop, temperature measurements of the water film allowed us to determine the water mass evaporated by this phenomenon as well as the mass flow rates. A correlation between the water mass evaporated by flashing and the superheat was then obtained. Evolution of the flash evaporation rate coefficient let us estimate the duration of the flash evaporation phenomenon.     

Parameter extraction from spherically expanding flames propagated in hydrogen/air mixtures

The characteristics of hydrogen/air flame were studied by using the spherical expanding flame propagated in a constant volume chamber. The influence of ignition induced blast wave and the flame instability on flame propagation was investigated. The nonlinear evaluation method for laminar flame parameter evaluation was established. By using the nonlinear evaluation method and the experimental results of flame propagation, the laminar flame speed and Markstein length were extracted and the difference between the nonlinearly evaluated laminar flame speed and the linearly evaluated one was analyzed. The influence of initial pressure and equivalence ratio on laminar flame speed and flame thickness was investigated. The laminar flame speed varies with equivalence ratio and initial pressure. There exists an equivalence ratio at which the laminar flame speed gets its maximum value. And there also exists an initial pressure at which the laminar flame speed gets its maximum value. The critical radius, Markstein length and flame instability of hydrogen/air flame with different equivalence ratio at different initial pressure had been studied. In hydrogen/air flame the flame stability decreases with the increase of initial pressure, while it increases with the increase of equivalence ratio. The global stability of flame is determined by the combination of the stabilizing effect of stretch effect, thermodiffusive instability mechanism and hydrodynamic instability mechanism.     

静态闪蒸过程汽泡生长的理论与实验研究

本文针对去离子水静态闪蒸时单汽泡的动态生长过程开展了可视化实验观察及理论分析,研究了过热度和闪蒸腔压力对汽泡生长的影响。理论模型考虑了汽泡成核点附近固体壁面对汽泡生长的影响,通过与实验结果的对比表明,壁面效应对汽泡生长影响显著,尤其是汽泡生长速率较小时,引入壁面效应后的理论模型能更好的与实验结果相吻合。通过分析汽泡生长过程的动力学特征可知,相同闪蒸腔压力但过热度较大时,汽泡生长过程具有较短的表面张力控制阶段,并在过渡阶段和传热控制阶段均具有较大的生长速率;而相同过热度但较小闪蒸腔压力时,汽泡在早期的惯性控制阶段生长速率较小,但在后期的传热控制阶段生长速率较大。     

边坡下涵洞顶部垂直土压力三维数值计算

针对边坡下涵洞顶垂直土压力计算理论尚无系统研究的现状,为得到边坡下涵洞顶垂直土压力的变化规律,采用三维数值模拟计算方法,较为系统地研究了边坡下涵洞顶垂直土压力,以明确坡率、坡高、填土高度对洞顶土体垂直土压力的影响。结果表明,土压力系数均大于1,应力集中现象明显;土压力系数随填土高度的增加呈先增后减的趋势;随着坡高的增加,土压力系数呈非线性增大趋势,但在填土高度大于一定值后土压力系数趋于稳定;在一定填土高度范围内,坡率越大土压力系数越大,超过这个范围土压力系数差异很小。     

The effect of secondary flows on the starting pressure for a second-throat supersonic ejector

The effect of the secondary flow on the starting pressure of a second-throat supersonic ejector has been investigated by adapting the height of the secondary flow inlet. The obtained results show that an optimum value of the secondary inlet height exists, and the starting pressure of the ejector becomes a minimum at that condition. Based on the results of the pressure measurements, a qualitative analysis has been made to clarify the flow behavior and the physical meaning of the performance diagram. It appears that the choking phenomenon of the secondary flow plays an important role in the starting process of the ejector. When the secondary inlet height is relatively small, the choked secondary flow and the supersonic primary flow could be employed to protect the static pressure in the suction chamber from being disturbed by the back pressure effect at a certain primary stagnation pressure, which is lower than the starting pressure for the case of the zero-secondary flow. However, as the secondary inlet height increases and exceeds a critical value, the static pressure in the suction chamber rapidly increases, and the starting pressure of the ejector increases accordingly.     

Experimental study on flash evaporation from superheated water jets: Influencing factors and formulation of correlation

This paper reports on the influencing factors and their effects on the intensity of flash evaporation that occurs in the superheated water jets. A variety of experiments were conducted and four variables were investigated namely velocity of flow, initial temperature, superheat degree and injection nozzle diameter. An exponentially decaying curve model that predicts temperature variation at the centerline of the upward flowing jet was proposed and employed in the demonstration of the nature of influence of each experimented variable. Evaporation end height was estimated and correlated by an empirical equation; this equation is thought to be useful in designing the flash evaporation chamber.     

基于MVR技术的单级双效蒸发浓缩系统性能分析

随着我国工业废水行业市场规模与平均处理成本的逐年上升,先进蒸发浓缩技术得到了广泛关注。本文在机械蒸汽压缩机升压能力不断提高的现状基础上,提出机械蒸汽再压缩（MVR）单级双效蒸发浓缩系统,研究物料浓度、蒸发温度、压比、换热温差等对系统热力性能的影响,并通过对比单级压缩机系统,获得单级双效MVR系统的性能分析曲线和节能优势。结果表明,单级双效MVR系统压缩机压比大于1.9时,系统能效系数（COP）可达25以上;在满足蒸汽温升的条件下,系统COP随压缩机压比、蒸发温度升高而降低,压比升高0.1,COP下降4.4%;第一效蒸发温度升高10℃,COP下降3.1%。     

An optical analysis of a static 3-D solar concentrator

Concentrating technology is long established in the field of solar thermal applications. However, there is still scope for improvement due to innovation in design, materials and manufacturing methods. The optical efficiency of a solar concentrator depends largely on the geometry of the concentrator profile. This paper evaluates the optical performance of a static 3-D Elliptical Hyperboloid Concentrator (EHC) using ray tracing software. Ray tracing has been used extensively to calculate the optical efficiency of the static 3-D EHC. Performance parameters such as effective concentration ratio, optical efficiency and geometric concentration ratio are also evaluated for different aspect ratios of the elliptical profile. Optimization of the concentrator profile and geometry is also carried out to improve the overall performance; this parametric study includes the concentrator height, solar incidence angle and aspect ratio of the ellipse. The overall performance of the concentrator was assessed based on the acceptance angle, effective concentration ratio and optical efficiency. Finally, the flux distribution on the receiver area for different concentrator heights is also presented.     

气固流化床内颗粒的内循环特性的研究

分析了气固流化床内颗粒内循环产生的原因,进而,分析了流化床气体速度,静态床层高度,颗粒粒径以及压力对颗凿内循环的影响。当流化床循环增强;而压力增大将使颗粒的内循环减弱。当颗粒的内循环增强时,流化床的脉冲信号（温度,浓度和灰度等）响应曲线的振荡加剧,流化床内颗粒的横向混合将得到改善。     

熔融盐对高含氮废弃物气流床气化产气调质与污染物脱除特性研究

在生物质气流床（5 kg/h）气化和熔融盐调质净化装置上,进行了熔融盐对高含氮废弃物气流床气化产气的调质与污染物脱除实验,考察了不同熔融盐温度、不同静液高度对出口气体调质和含N、S、Cl污染物脱除特性的影响。结果表明：经过熔融盐调质后,产气中CO与CO2浓度下降,H2浓度明显上升。当温度从380℃升高至580℃时,H2/CO值提高至7.3。随着静液高度的提高,出口气体中CO2与CO浓度下降,H2浓度由30.1%提高至36.8%;熔融盐对高含氮废弃物气流床气化产气中含N、S、Cl污染物有较明显的脱除效果,H2S、SO2、HCl与含氮污染物中的HCN与NOx已完全脱除,当温度为580℃、静液高度为67.5 mm时,NH3脱除率达到96%。     

The addition of hydrogen to a gasoline-fuelled SI engine

The results of an experimental investigation involving the addition of hydrogen to a gasoline-fuelled SI engine are reported. Up to 66% by volume (3.7% by mass) of hydrogen as fuel was added as part of the air with little modification to the engine. Cylinder pressure traces were used to calculate the indicated mean effective pressure and mass fraction burned. Electrochemical analysers were used to measure the concentration of CO, NO and O₂ in the exhaust. The added hydrogen resulted in improved work output and a reduction in burn duration and cycle-to-cycle variation while operating under lean conditions (φ<0.85). When operating closer to stoichiometric conditions (φ>0.85) little difference in engine performance was seen. This dependence of hydrogen addition effect on the fuel/air equivalence ratio was confirmed by analysis of variance tests.     

Heat transfer and pressure drop experimental correlations for air–water bubbly flow

In this paper, a novel air–water bubbly flow heat transfer experiment is performed to investigate the characteristics of pressure drop of airflow and heat transfer between water and tubes for its potential application in evaporative cooling. The attempts to reduce the pressure drop while maintaining higher heat transfer coefficient have been achieved by decreasing the bubble layer thickness through the water pump circulation. Pressure drops of air passing through the sieve plate and the bubbling layer are measured for different height of bubble layer, hole–plate area ratio of the sieve plate and the superficial air velocity. Experimental data show that the increase of bubble layer height and air velocity both increase the pressure drop while the effect of the hole–plate area ratio of the sieve plate on the heat transfer coefficient is relatively sophisticated. A pressure drop correlation including the effects of all the tested parameters is proposed, which has a mean absolute deviation of 14.5% to that of the experimental data. Heat transfer coefficients of the water and the outside tube wall are measured and the effects of superficial air velocity, heat flux and bubble layer height are also examined. Through a dimensional analysis, a heat transfer correlation with a mean absolute deviation of 9.7% is obtained based on experimental data.     

Study of heat transport of an osmotic heat pipe: Part 1. effects of the initial concentration on heat transport limits

This paper presents an experimental study on the effects of initial concentration on the critical heat transport rate of an osmotic heat pipe operated under atmospheric pressure. In this experiment, an aqueous polyethylene glycol 600 solution was used as the working fluid and 18 tubular acetyl cellulose membranes were used as the osmotic membranes. The initial concentration was varied between 0.1 to 1.0 kmol/m³ in 0.1 kmol/m³ steps. Consequently, the existence of an optimum initial concentration for the critical heat transport rate was revealed. In addition, solution concentrations in the solution riser and downcomer were found to be related to the initial concentration and solvent contact height. © 1999 Scripta Technica, Heat Trans Asian Res, 29(1): 59–71, 2000