Influence of slug flow on flow fields in a gas–liquid cylindrical cyclone separator:A simulation study

A simulation method for slug flow based on the VOF multiphase flow model was implemented in ANSYS? Fluent via a user-defined function(UDF) and applied to the dissipation of liquid slugs in the inlet pipe of a gas–liquid cylindrical cyclone(GLCC) separator while varying the expanding diameter ratio and angle of inclination. The dissipation of liquid slug in inlet pipe is analyzed under different expanding diameter ratios and inclination angles.In the inlet pipe, it is found that increasing expanding diameter ratio and inclination angle can reduce the liquid slug stability and enhancing the effect of gravity, which is beneficial to slug flow dissipation. In the cylinder, increasing the expanding diameter ratio can significantly reduce the liquid carrying depth of the gas phase but result in a slightly increase of the gas content in the liquid phase space. Moreover, increasing the inclination angle results in a decrease in the carrying depth of liquid in the vapor phase, but enhances gas–liquid mixing and increases the gas-carrying depth in the liquid phase. Taking into consideration the dual effects of slug dissipation in the inlet pipe and carrying capacity of gas/liquid spaces in the cylinder, the optimal expanding diameter ratio and inclination angle values can be determined.     

大口径非标管道的仿真优化设计

对大口径非标管道进行优化设计,利用Solidworks Flow Simulation对非标管道分析了气流速度的影响因素,利用SimulationXpress进行静力仿真分析。得出管道长度对气流速度影响的拟合方程。弯头角度的设计时,角度应尽量小,并且尽量在120°以内。对于弯头内的气流,影响其速度的主要因素为管径比,管道气流速度对着管径比增加而增大,即R越大,气流速度越大。形变量随着倾角的增大而减小,且不同的倾角的形变量最大的位置在管道中间处,支架沿重力方向的支撑方式其应力集中现象较小。     

小管径重力热管启动特性

实验研究了小管径重力热管启动过程特性,分析了加热功率、倾角、冷却水流量对热管启动特性的影响。实验用热管为铜水重力热管,外径8 mm,壁厚1 mm,总长1500 mm。结果表明,随加热功率增大,热管启动时间缩短,当量热导率到达稳定的时间缩短。在倾角为60°时热管启动特性要优于在30°和90°时的情况,90°时启动温差最大、启动时间最长。冷却水流量在10 L·h^-1时,热管启动温差最大,启动时间最长,当量热导率稳定得最慢,而在其他流量下时,热管的启动温差和启动时间大小关系均为10 L·h^-1＞40 L·h^-1＞20 L·^h-1＞30 L·h^-1。     

倾斜对管内上升泡状流局部界面参数分布的影响

采用双头光纤探针法研究了倾斜对圆管内(I.D.50 mm)上升泡状流界面参数径向分布的影响。探针测量的局部界面参数包括局部空泡份额、界面面积浓度(IAC)和局部气泡通过频率。实验以空气和水为工质,表观速度分别为0.002~0.037 m·s^-1和0.072~0.569 m·s^-1;倾斜角度为5°、15°和30°。结果表明,竖直条件下界面参数呈核峰型、壁峰型、中间型及过渡型4种典型的分布。倾斜条件下大量气泡向上部聚集,界面参数分布不对称。中间宽峰向通道上部倾斜,且峰值随倾斜角度增加而增大。同时,下壁面附近峰值被削弱,甚至消失,上壁面附近峰值迅速增大。界面参数沿直径从r_i/R=-0.84到上半部分峰值处逐渐增加,且增加速率随倾斜角度增加而增大。倾斜条件下Sauter直径明显比竖直条件下大。     

Fluctuations in dense phase pneumatic conveying of pulverised coal measured using electrical capacitance tomography

A twin-plane electrical capacitance tomography (ECT) system has been employed to monitor the flow rate of fine coal transported by air in a 36.8 mm diameter pipe at mass fluxes of 1680 kg/m² s. The mean mass flow rate was obtained to be within <1% of the value determined from load cells. The ECT output indicated that there were two types of systematic fluctuations in the time series of mass flow rate and concentration. The frequencies of these have been obtained from power spectral density analyses. For the higher frequency fluctuations, the Strouhal number (fD_t/u_gs) was found to depend on the square root of the solids/gas momentum flux ratio. An examination of the cross-sectional distribution of solids showed that the coal was concentrated around the wall of the pipe and that the concentration fluctuated as noted above.     

Influence of slug flow on flow fields in a gas-liquid cylindrical cyclone separator: A simulation study

A simulation method for slug flow based on the VOF multiphase flow model was implemented in ANSYS^® Fluent via a user-defined function (UDF) and applied to the dissipation of liquid slugs in the inlet pipe of a gas-liquid cylindrical cyclone (GLCC) separator while varying the expanding diameter ratio and angle of inclination. The dissipation of liquid slug in inlet pipe is analyzed under different expanding diameter ratios and inclination angles. In the inlet pipe, it is found that increasing expanding diameter ratio and inclination angle can reduce the liquid slug stability and enhancing the effect of gravity, which is beneficial to slug flow dissipation. In the cylinder, increasing the expanding diameter ratio can significantly reduce the liquid carrying depth of the gas phase but result in a slightly increase of the gas content in the liquid phase space. Moreover, increasing the inclination angle results in a decrease in the carrying depth of liquid in the vapor phase, but enhances gas-liquid mixing and increases the gas-carrying depth in the liquid phase. Taking into consideration the dual effects of slug dissipation in the inlet pipe and carrying capacity of gas/liquid spaces in the cylinder, the optimal expanding diameter ratio and inclination angle values can be determined.     

Flow regime boundaries for an interior subchannel of a horizontal 37-element bundle

A needle contact probe system has been constructed and used to determine flow regime transitions for an interior subchannel in the upper half of a 37-element horizontal bundle (to include the effect of gravity separation) for adiabatic air-water flow. For the experimental range considered (up to ?15.5 K^*s^?1, 50% quality), five distinct flow regimes were identified. Using the equivalent hydraulic diameter concept and cross-sectional average superficial velocities, air quality and total mass flux, flow regime maps were constructed. These maps are shown to deviate from pipe flow regime maps. The stratified smooth flow regime was never observed at the lowest flow rate considered due to the periodical disturbance of the flow by the bundle end plates and mid-plane spacers.     

倾角及冷却工况对多通路并联回路板式脉动热管传热性能的影响

针对多通路并联回路板式脉动热管建立实验台,采用铜质模块加热和水浴冷却方式作为热工条件,着重考察脉动热管在不同倾角（90°,75°,60°）及冷却工况（4.5 g·s^-1和9.0 g·s^-1）下的传热性能,通过壁面温度的振荡和传热热阻来评价其传热效果。实验结果表明,重力对多通路并联回路板式脉动热管传热性能的影响较大,随着倾角的减少,工质的回流变弱,传热热阻变大,传热极限变低;脉动热管的加热功率与冷却能力是相互匹配的,匹配度越高,脉动热管越不易干烧,传热极限越高,在有倾角的工况下提高传热极限表现得更为明显;脉动热管运行时存在一个最佳水流量,在最佳冷却工况下,脉动热管的运行热阻最低。     

用于空调能量回收的板式脉动热管换热器

为提高脉动热管换热器在空调系统排风能量回收中的换热效率,提出了一种新型并联槽道板式脉动热管及由其组成的换热器。首先对单片热管在空调排风夏季工况下的能量回收情况进行了传热性能实验研究,影响因素包括槽道当量直径、充液率、工质种类、风速、风温、微倾角;然后对一组由7片热管顺排形成的板式脉动热管换热器的换热效率进行了计算。研究表明：新型板式脉动热管的适用工质为R141b,最佳充液率为25%;传热性能随新风温度及风速的升高而增强,新风、排风温差小于6℃时热管不启动;随风速增加,换热量增加,但换热效率有所降低;给定工况下板式脉动热管散热器的换热效率为44.1%;微倾角可使空调能量回收系统在保证良好换热效率的同时实现换季不换向,热管安装宜采用+2°左右的微倾角。     

硝酸盐重力热管启动特性初步实验研究

熔盐是一种高效传热工质,广泛应用于太阳能热发电传热、核反应堆传热、金属热处理的工业过程中。以配制的一种混合硝酸熔盐作为热管的传热工质,设计制造了管壳为316L不锈钢、外径Φ22 mm、壁厚2 mm、管壳长度980 mm的硝酸熔盐重力热管,并对硝酸熔盐重力热管的启动性能进行了初步实验研究,分析了混合硝酸盐重力热管的启动特性、稳定性以及倾角对热管启动的影响。然后将采用40 g混合硝酸盐工质的重力热管实验结果与采用40 g萘工质的重力热管的实验结果进行了对比。实验结果表明,混合硝酸盐热管的启动时间比萘热管的时间短,且启动后稳定性高于萘热管;分析认为,该混合硝酸盐的沸点在250℃左右,在倾角为50°时热管启动性能优于在30°、70°、90°时的情况。实验结果初步证明了混合硝酸盐作为热管工质的可行性。     

EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER IN AN AIR DUCT WITH AN INCLINED HEATING SURFACE

In this paper some experimental results showing the influence of inclination of a cylindrical heating surface immersed in an air duct on heat transfer coefficient are presented. The experiments were performed in a laboratory-scaled apparatus of square cross section with dimensions 120 ×120 mm and 1400 mm in height. Heat transfer surface was an electrical heater made of brass tube with outer diameter of 19 mm and 110 mm length. In each experiment the temperatures of the front and rear side of the heating surface, inclination angle, air velocity, inlet air temperature, and heater power were measured. It was concluded that heat transfer coefficient depends on flow conditions and angle of inclination. The maximum Nusselt number (Nu) was observed to occur about 45° inclination relative to the horizon, for the range of Reynolds numbers used in experiments. The values of heat transfercoefficients in the vertical position were very nearly the same as they were in the horizontal position. Based on the experimental results, a correlation was proposed for estimation of Nu at the desired flow velocity and inclination angle, relative to Nu at zero inclination.     

Numerical simulation of flow focusing pattern and morphological changes in two-phase flow inside nozzle

The flow focusing nozzle is a new type of nozzle that performs effective atomization of the discrete phase by means of high-speed motion of the continuous phase.The flow pattern and its morphological changes have a significant effect on the atomization, but the influence of different parameters on the morphological change of the flow pattern remains unclear.The flow focusing pattern and morphological changes in the two-phase flow inside the nozzle were simulated numerically, based on the volume of fluid method.The results demonstrate that the ratio of the nozzle-to-capillary distance and capillary diameter, the gas–liquid velocity ratio, and capillary diameter have significant effects on the flow pattern.When the ratio of the nozzle-to-capillary distance H and capillary diameter D increases, or the capillary diameter D increases, the flow pattern tends to transform into a laminar form; however, when the gas–liquid velocity ratio V increases, the flow pattern tends to transform into a turbulence form.Furthermore, we define the cone-shaped expansion rate, cone-shaped focusing rate,and cone angle in order to study the morphological changes in the cone shape inside the nozzle.The results indicate that the morphological change of the cone shape and flow pattern transformation is interrelated.When the cone shape tends to be unstable, the flow pattern changes towards flow blurring, whereas, a stable cone indicates that the flow tends to exhibit a droplet pattern.     

Evolution of hydrodynamic and statistical parameters of gas-liquid slug flow along inclined pipes

The development of slug flow along two long inclined pipes (2-90° from the horizontal) with internal diameters of 0.024 and was measured by three optical fiber probes. The probes were located in a measurement module at axial distances of between the fiber tips. To measure the evolution of slug flow, the module was placed at different positions along the pipe. Instantaneous elongated bubble velocities and corresponding elongated bubble and liquid slug lengths were determined by processing the optical probe signals. The evolution of the liquid slug and elongated bubble length distributions along the pipes is characterized by a gradual growth of the mean and mode values. The growth rate decreases with decreasing inclination. Mean elongated bubble lengths have a minimum at about 60°, while mean liquid slug lengths decrease slowly with decreasing inclination angle. The coalescence rate, defined as the decrease in the ensemble size, becomes almost negligible at x/D>60, independent of pipe diameter, flow rates and inclination angle. The slug frequency has a maximum at about 60° inclination.     

Sugarcane Bagasse Drying in a Cyclone: Influence of Device Geometry and Operational Parameters

Sugarcane bagasse is becoming more and more commonly used in generating electrical energy, steam, and bioethanol. Drying is important in sugarcane and other types of biomass because it can be used to improve the calorific value and overall energetic use. In this work, sugarcane bagasse was treated by drying in a cyclonic dryer. The influence of the geometry of the device (the conical part of the cyclone) and process parameters (bagasse mass flow rate and temperature) were tested. The modification on the conical part was related to two different angles and with two different inferior outlets (B). Experimental design was carried out for each geometry. The independent variables were the drying agent temperature (35 to 275°C) and the bagasse mass flow rate (0.1 × 10^?2 to 2.9 × 10^?2 kg s^?1). The air flow rate was kept constant at 7.5 × 10^?2 kg s^?1. The dependent variables were moisture reduction (MR) and average particle residence time (t_res) in the cyclonic dryer. For both cyclonic geometries, it was observed that MR was directly proportional to the temperature and inversely proportional to the bagasse mass flow rate. t_res was also inversely proportional to the bagasse mass flow rate. Decreasing B tended to increase tres and MR.     

Experimental investigation of heat transfer in an air duct with an inclined heating surface

In this paper some experimental results showing the influence of inclination of a cylindrical heating surface immersed in an air duct on heat transfer coefficient are presented. The experiments were performed in a laboratory-scaled apparatus of square cross section with dimensions 120 ‐ 120 mm and 1400 mm in height. Heat transfer surface was an electrical heater made of brass tube with outer diameter of 19 mm and 110 mm length. In each experiment the temperatures of the front and rear side of the heating surface, inclination angle, air velocity, inlet air temperature, and heater power were measured. It was concluded that heat transfer coefficient depends on flow conditions and angle of inclination. The maximum Nusselt number (Nu) was observed to occur about 45° inclination relative to the horizon, for the range of Reynolds numbers used in experiments. The values of heat transfercoefficients in the vertical position were very nearly the same as they were in the horizontal position. Based on the experimental results, a correlation was proposed for estimation of Nu at the desired flow velocity and inclination angle, relative to Nu at zero inclination.     

Transfer efficiency for airless painting systems

Spray transfer efficiency (TE) is defined as the mass fraction of sprayed paint which is deposited on the intended target, the remainder of the sprayed paint becomes undesirable overspray. The relationship between TE and gun supply pressure (or paint mass flow rate), gun-to-target distance, gun traverse speed, the angle of the spray gun relative to the target (gun-to-target angle), plus spray cone angle is reported herein for a typical fan spray system. Experimental results indicate that spray momentum rate (SMR) and droplet size dictate the TE for the various combinations of parameters considered here. The key finding is that TE correlates with SMR and spray mean drop size (Sauter mean diameter, or D₃₂) via an expression of the form TE=a+b SMR − c (SMR)²+d D₃₂, where a, b, c, and d are coefficients, determined by fitting the experimental data, and SMR is estimated via SMR=m²/ρA, where the paint mass flow rate m, the paint density is ρ, and the gun exit orifice effective tip cross sectional area is A. This expression accounts for physical phenomena that govern sprayed droplet deposition characteristics, such as entrainment, bounce-back, and drop size. Experimental results also show that, for the range of parameters studied, gun traverse speed has no effect on TE, but increasing the angle of the spray gun relative to the target (gun-to-target angle), increasing the spray cone angle, or increasing the gun-to-target distance will decrease TE.     

Pneumatic transport of solids in an inclined geometry

Flow studies were conducted in 0.0266-m and 0.0504-m glass pipes held at various angles of inclination. Measurements in these experimental setups included particle velocities, solid mass flow rates, and pressure drops in both the upper and the lower halves of the pipe. Visual observations of the flow patterns were made through the glass section. Particles used in this system included glass particles of 67-, 450-, and 900-μm diameter, as well as iron oxide of 400-μm diameter. Mass flows from the two halves of the pipe were obtained by splitting the flow with a knife-edged separator. Experiments were also performed in a 0.0095-m transfer line in an inclined loop. The angle of inclination of the test loop was varied from 0 to 90 degrees from the horizontal. The effect of angle of loop inclination, tube diameter, and particle characteristics on basic flow parameters were studied.     

EFFECTS OF GRADIENT MAGNETIC FIELDS ON THE MAGNETO-THERMAL MIXED CONVECTION OF AIR IN A HORIZONTAL PIPE

Effects of gradient magnetic fields on the mixed convection of air in a gravity field are numerically studied with 3-D model equations. The detailed characteristics of the magneto-thermal wind in a pipe are computed for the length ratios L (pipe length divided by pipe diameter) of 20, 30, 62, and 100, with diameter ratios N (diameter of an electric coil versus that of the pipe) from 2 to 200. It is found that there exists a best diameter ratio N to maximize the airflow rate for a channel with a fixed length. Detailed flow and temperature profiles are graphically presented for various values of N.     

EFFECTS OF GRADIENT MAGNETIC FIELDS ON THE MAGNETO-THERMAL MIXED CONVECTION OF AIR IN A HORIZONTAL PIPE

Effects of gradient magnetic fields on the mixed convection of air in a gravity field are numerically studied with 3-D model equations. The detailed characteristics of the magneto-thermal wind in a pipe are computed for the length ratios L (pipe length divided by pipe diameter) of 20, 30, 62, and 100, with diameter ratios N (diameter of an electric coil versus that of the pipe) from 2 to 200. It is found that there exists a best diameter ratio N to maximize the airflow rate for a channel with a fixed length. Detailed flow and temperature profiles are graphically presented for various values of N.