Messung des transienten Massenaustrages und der kurzzeitigen thermofluiddynamischen Vorgänge während der Reaktorentlastung

On the basis of a differential measurement of the reactor reaction force change as a function of the relief time and elimination of the inert reactor mass the integral discharged mass can be reproduced with an accuracy of about 2%. In combination with a parallel highly in time solvable measurement of the swelling mixture conductance ahead of the discharge nozzle on the reactor top a relationship between the intensive fluctuations of the reaction force and the corresponding changes of the discharged mass as well as the periodically repeating intermittent swelling of the mixture due to bubble production, resp., evaporation could be established.     

Influence of process variables and formulation composition on sphericity and diameter of Ca-alginate-chitosan liquid core capsule prepared by extrusion dripping method

ABSTRACT

The influence of process variables and formulation composition on the sphericity and diameter of the alginate capsules which contained dual cations (Ca-and-chitosan) are characterized in this study. Capsule sphericty was not influenced by needle diameter but instead, capsule diameter increased proportionally with the needle diameter. The combined effects of the liquid core solution and alginate solution on the sphericity of the capsules are tabulated. Spherical capsules can be produced when the following criteria were fulfilled: stirring speed is in the range of 240–300 rpm; calcium chloride concentration is >5 g/L; viscosity of liquid core solution is >203 mPa.s; as well as viscosity of alginate solution is in between 47 and 386 mPa.s. The capsule diameter was predicted using a modified Tate’s law equation and an error analysis was conducted to evaluate the equation. The predicted diameter was well correlated with the experimental data with an average absolute deviation <3.6%.     

Two-phase cryogenic flow meters: Part I – Realization of the calorimetric method

While operating with multicomponent flows, one needs to determine such characteristics as temperature, pressure, mass flow rate and component composition – mass quality, and void fraction. The main attention is given to measurement of mass flow rate of the two-phase cryogenic flows which can be used for superconducting accelerators, refueling hydrogen system for space and liquid natural gas industry, in particular. On the one hand, a two-phase flow is one of the simplest cases of multi-component flows which can be observed in cryogenics. On the other hand, this is rather sophisticated problem in cryogenics to create two-phase flow meters and estimate their metrological characteristics. This problem is discussed. Two methods are suggested – calorimetric and pressure drop ones. Features of the calorimetric method are discussed in this part.     

Development of a Compact-Sized Falling Needle Rheometer for Measurement of Flow Properties of Fresh Human Blood

A compact-sized falling needle rheometer with rapid operation and automatic flow analysis has been developed for viscometry of fresh human blood without anticoagulant. The volume of a fresh blood sample only needs to be 3 mL, and the measuring time is within 2 min after taking a blood sample from the human body. Measured flow properties of human blood are evaluated as a flow curve, that is, the relationship between the shear stress (τ) and shear rate (γ). Observed flow curves of fresh human blood show three typical fluid regions, that is, the Casson fluid region for a low shear rate range of 0 < γ > 140 s^?1, the transition region for a shear rate near 140 s^?1 < γ < 160 s^?1, and the Newtonian fluid region for a high shear rate range of 160 s^?1 < γ > 400 s^?1. Flow properties of human blood such as the yield stress (τ _y) in the Casson fluid region and the apparent viscosity (μ) in the Newtonian fluid region are measured, and they are compared between male and female blood. It is found that the range of human blood viscosity for males is (5.5 to 6.4) mPa · s, and for females is (4.5 to 5.3) mPa · s. The viscosities of male blood without anticoagulant show higher values than those of female blood. Human blood viscosities with anticoagulant show a lower value than that without anticoagulant. A linear relationship between the hematocrit value, that is, the volume percentage of red corpuscles in the human blood, and the apparent viscosity are observed for both male and female blood. This article is concerned with the flow analysis of fresh human blood viscosity without anticoagulant using a newly developed compact-sized falling needle rheometer.     

LED封装用液体交联剂的制备与表征

报道了一种功率型发光二极管(LED)封装用液体高分子交联剂的制备方法。将甲基氢环硅氧烷与八甲基环四硅氧烷、甲基苯基混合环体等环硅氧烷,在甲苯溶剂中,40℃~80℃,用阳离子交换树脂催化其开环共聚,并以适量四甲基二氢硅氧烷封端。产物为澄清透明的甲基苯基含氢硅油,其苯基含量(Ph/Si,molar ratio)为0.30~0.60,活泼氢(Si-H)含量为0~0.5%,折光指数为1.39~1.51(25℃),动力黏度为100 mPa.s~550 mPa.s(25℃)。     

Experimental investigation of forced flow boiling of nitrogen in a horizontal corrugated stainless steel tube

Experimental investigation is performed on the heat transfer characteristics of forced flow boiling of saturated liquid nitrogen (LN₂) in a horizontal corrugated stainless steel tube with a 17.6 mm maximum inner diameter. The local heat transfer coefficients (HTCs) are measured at two mass flow rates with a wide range of wall heat fluxes. The effects of the heat flux, mass flow flux and vapor quality on the two-phase heat transfer characteristics are discussed. The results reveal that the local HTCs increase with the heat flux and mass flow flux. The measured local HTCs present a strong dependence on the heat flux. The circumferential averages of the HTCs for the present corrugated tube are compared with the empirical correlations proposed for the smooth tubes, and the results show that the heat transfer is enhanced due to the area augmentation.     

Zur Anwendbarkeit des Massenstrom-Modells nach ISO 6358 mit den Kennwerten Leitwert C und kritisches Druckverhältnis b für Gase im Hochdruckbereich bis 300 bar

Mass flow models for gaseous media describe the relationship between gas flow through throttle elements depending on pressure, temperature and type of medium. These models are used to calculate pneumatic components, to simulate pneumatic systems or to plan facilities. Contrary to real gas some mass flow models are known and verified for ideal gases, such as according to ISO 6358 (International Standard ISO 6358: pneumatic fluid power – components using compressible fluids – determination of flow-rate characteristics, 1989). In the development and application of systems with real gases as for example in the calculation of safety valves, it was found that equations without taking into account real gas properties are only of limited use. The same has been found by Schmidt et al. (Forschung im Ingenieurwesen 73:105–117, 2009). The object of this publication is to recommend an easy useable model for mass flow calculation of real gases. For that purpose, the existing mass flow model, based on equations for the ideal gas range according to ISO 6358, is applied and verified for real gases. The parameters critical conductance C and critical pressure ratio b are obtained, applied and verified in the state space of real gas. The mean deviation between measured and calculated mass flow is within the real gas area around 1.0 %. Therefore the mass flow model is proposed to deliver appropriate results, if the parameters C and b are identified in the real gas range. In addition, it was examined that differences in practical application of 10 % are formed when the parameters C and b are obtained with an ideal gas and used in the real gas area. This high level of deviation can be partly compensated by an iterative calculation using the real state data of the used gas, so that the deviation is reduced to 4.3 %.     

Two-phase upward flow 90° bend pressure loss model

Based on experimental pressure loss data during air-water flow in vertical 90° Plexiglass bends with an internal pipe diameter of 30 mm and a curvature radius of 120, 180, 240 and 300 mm a prediction model in the style of a two-phase flow multiplier is proposed. The underlying single-phase liquid flow pressure loss is calculated on the basis of the model by K.H. Beij, resp., D.S. Miller. The scatter of the logarithmic ratios made of the experimental and the predicted values amounts to about 25 % and is substantially lower than that obtained with selected models recommended in the literature. The new model includes physically consistent the usual design parameters and the limits of single-phase gas as well as liquid flow. Reasonable extrapolations with respect to bend dimensions, fluids and (subcritical) flow parameters should be possible.     

Integral methods of calculation of heat transfer and drag under conditions of turbulent pipe flow of liquid of variable properties: Steady-state and quasi-steady-state flows in a round pipe with constant density of heat flux to the wall

Integral relations are derived for the calculation of the Nusselt number and coefficients of hydraulic drag and friction drag under conditions of pipe flow of dropping liquid and gas of temperature-dependent physical properties. In the limiting case of steady-state flow of liquid of constant properties, the expression for the Nusselt number transforms to the well-known Lyon integral. The results of calculation of heat transfer and drag by an integral method are compared with more exact results obtained using the numerical solution of the set of differential equations of convective heat transfer. An inference is made about the conditions under which integral methods may be employed. An algorithm is developed for the calculation by an integral method of heat transfer and drag under conditions of quasi-steady-state pulsating flow. It is demonstrated that the flow rate oscillations superposed on the flow in the pipe enhance the effect of the variability of the properties on heat transfer, and for gas on friction drag. For a dropping liquid under conditions of pulsating flow, the friction drag depends less significantly on the variability of the properties (viscosity) than in the case of steady-state flow. The degree of manifestation of the effects identified above is the higher, the higher the oscillation amplitude and the lower the value of the Reynolds number of averaged flow.     

Single molecule fluorescence under conditions of fast flow

We have experimentally determined the optimal flow velocities to characterize or count single molecules by using a simple microfluidic device to perform two-color coincidence detection (TCCD) and single pair F?rster resonance energy transfer (spFRET) using confocal fluorescence spectroscopy on molecules traveling at speeds of up to 10 cm s(-1). We show that flowing single fluorophores at ≥0.5 cm s(-1) reduces the photophysical processes competing with fluorescence, enabling the use of high excitation irradiances to partially compensate for the short residence time within the confocal volume (10-200 μs). Under these conditions, the data acquisition rate can be increased by a maximum of 38-fold using TCCD at 5 cm s(-1) or 18-fold using spFRET at 2 cm s(-1), when compared with diffusion. While structural characterization requires more photons to be collected per event and so necessitates the use of slower speeds (2 cm s(-1) for TCCD and 1 cm s(-1) for spFRET), a considerable enhancement in the event rate could still be obtained (33-fold for TCCD and 16-fold for spFRET). Using flow under optimized conditions, analytes could be rapidly quantified over a dynamic range of up to 4 orders of magnitude by direct molecule counting; a 50 fM dual-labeled model sample can be detected with 99.5% statistical confidence in around 8 s using TCCD and a flow velocity of 5 cm s(-1).     

Reproductive accuracy of two-phase flow pressure loss correlations for vertical 90° bends

The method proposed by Sookprasong underpredicts, while the Chisholm B-equation still overpredicts the pressure loss in vertical upward air-water flow through a 90^° Plexiglass bend with an internal diameter of 30?mm and a curvature radius of 120, 180, 240 and 300?mm. The scatter of the logarithmic ratios between the experimental and the predicted values exhibited by both models is about 40%. The Chisholm model, on the other hand, is physically consistent and, therefore, recommended for use, resp., suitable for extrapolations.     

A cold box for the forced cooling systems of superconducting magnets

A cold box, which does not have temperature expanders, designed for a forced cooling system is described. The cold box can be used to maintain superconducting magnets at 4.5 ? + 5 K for a long period of time.Tests on the cold box have shown that the mass flow rate of forced cooling flow is 6 + ? 10 kg h^?1. For this flow rate, 1.1 – 1.3 kg h^?1 of liquid He from the transport dewar is required.     

逆流填料式溶液除湿器性能的数值模拟

对溶液除湿器中传热传质过程进行热力学分析,根据除湿塔的结构及溶液与空气的流动方式,建立除湿器的热质交换物理和数学模型,模拟计算除湿器人口空气和溶液参数对除湿器出口空气参数的影响,得到各入口参数对出口空气温度和含湿量的影响曲线。结果表明：空气出口参数与空气人口含湿量、温度和流量、溶液人口温度和浓度几乎呈线性变化;当溶液入口流量达到2．5kg／s后,空气出口参数的变化趋于平缓。     

Experimental investigations on heat transfer characteristics of pulsating single-phase liquid flow and two-phase Taylor bubble flow through a minichannel

Experimental investigations are reported for pulsating Taylor bubble (PTB) flow through a 2.12 mm horizontal circular minichannel. Air and water are used as working fluids. A T-junction is used to generate Taylor bubble flow in a minichannel. The superficial gas velocity (U _SG ) is kept as 0.0472 m/s. The superficial liquid velocity (U _SL ) is kept as 0.0472 and 0.0708 m/s. The pulsating liquid flow is generated by developing a pulse generator circuit. The investigations are carried out for various pulsating flow frequencies of 0 Hz (continuous flow), 0.1, 0.25, 0.5, 1 and 2 Hz, which correspond to Womersley number (W _o ) 0, 0.84, 1.39, 1.88, 2.65 and 3.75, respectively. Heat transfer enhancement is found to be negligible (less than 1%) for pulsating laminar liquid flow through the minichannel. On the contrary, heat transfer is observed to decrease by 35% for PTB flow compared with continuous Taylor bubble (CTB) flow for imposed frequency of pulsation up to 1 Hz.     

The influence of cavitation on the flow characteristics of liquid nitrogen through spray nozzles: A CFD study

Spray cooling with cryogen could achieve lower temperature level than refrigerant spray. The internal flow conditions within spray nozzles have crucial impacts on the mass flow rate, particle size, spray angle and spray penetration, thereby influencing the cooling performance. In this paper, CFD simulations based on mixture model are performed to study the cavitating flow of liquid nitrogen in spray nozzles. The cavitation model is verified using the experimental results of liquid nitrogen flow over hydrofoil. The numerical models of spray nozzle are validated against the experimental data of the mass flow rate of liquid nitrogen flow through different types of nozzles including the pressure swirl nozzle and the simple convergent nozzle. The numerical studies are performed under a wide range of pressure difference and inflow temperature, and the vapor volume fraction distribution, outlet vapor quality, mass flow rate and discharge coefficient are obtained. The results show that the outlet diameter, the pressure difference, and the inflow temperature significantly influence the mass flow rate of spray nozzles. The increase of the inflow temperature leads to higher saturation pressure, higher cavitation intensity, and more vapor at nozzle outlet, which can significantly reduce mass flow rate. While the discharge coefficient is mainly determined by the inflow temperature and has little dependence on the pressure difference and outlet diameter. Based on the numerical results, correlations of discharge coefficient are proposed for pressure swirl nozzle and simple convergent nozzles, respectively, and the deviation is less than 20% for 93% of data.     

Some observations on liquid flow through filters

Experiments were conducted to assess the relevance to filtration of the Poiseuille analysis of liquid flow in straight cylindrical pipes. Trials using glass filters through which water, a citric acid solution and mercury flowed showed that the analysis was qualitatively relevant. As predicted, the flow rates were a simple function of the pressure difference across the filter and were proportional to the density/viscosity ratio of the liquids. However, quantitative predictions were inaccurate because of uncertainty about filter pore dimensions and the lack of flow through narrow pores when the liquid did not wet the filter material. Flow of a suspension was further complicated by the build up on the entry faces of filters of layers of particulates which acted as secondary filters.     

Critical two-phase stratified flow during horizontal condensation

A theoretical investigation is made for two-phase, stratified, condensing flow between two parallel horizontal plates. From this investigation a correlation predicting critical flows during condensation is developed. According to this correlation it is shown that critical flow conditions are strongly dependent on the condensing mass flux, quality, void fraction and fluid properties. It is also shown that the inviscid Kelvin-Helmholtz theory is in error in predicting critical flow conditions because it ignores the effect of viscosity.     

Development of Maximum Bubble Pressure Method for Surface Tension Measurement of High Viscosity Molten Silicate

A surface tension measurement method based on the maximum bubble pressure (MBP) method was developed in order to precisely determine the surface tension of molten silicates in this study. Specifically, the influence of viscosity on surface tension measurements was quantified, and the criteria for accurate measurement were investigated. It was found that the MBP apparently increased with an increase in viscosity. This was because extra pressure was required for the flowing liquid inside the capillary due to viscous resistance. It was also expected that the extra pressure would decrease by decreasing the fluid velocity. For silicone oil with a viscosity of \(1000\,\hbox {mPa}{\cdot }\hbox {s}\), the error on the MBP could be decreased to +1.7 % by increasing the bubble detachment time to \(300\,\hbox {s}\). However, the error was still over 1 % even when the bubble detachment time was increased to \(600\,\hbox {s}\). Therefore, a true value of the MBP was determined by using a curve-fitting technique with a simple relaxation function, and that was succeeded for silicone oil at \(1000\,\hbox {mPa}{\cdot } \hbox {s}\) of viscosity. Furthermore, for silicone oil with a viscosity as high as \(10\,000\,\hbox {mPa}{\cdot }\hbox {s}\), the apparent MBP approached a true value by interrupting the gas introduction during the pressure rising period and by re-introducing the gas at a slow flow rate. Based on the fundamental investigation at room temperature, the surface tension of the \(\hbox {SiO}_{2}\)–40 \(\hbox {mol}\%\hbox {Na}_{2}\hbox {O}\) and \(\hbox {SiO}_{2}\)–50 \(\hbox {mol}\%\hbox {Na}_{2}\hbox {O}\) melts was determined at a high temperature. The obtained value was slightly lower than the literature values, which might be due to the influence of viscosity on surface tension measurements being removed in this study.     

Effects of boundary slip and apparent viscosity on the stability of microchannel flow

The effects of boundary slip, apparent viscosity and their combined modification on the mean velocity and stability of plane microchannel flow are investigated. Two kinds of microchannel are considered in this approach. One is the channel wall made of the same material. The other is the channel wall made of different materials. The boundary slip is determined by Navier slip condition. Apparent viscosity is considered by a model, where the effects of channel wall on liquid viscosity are assumed as a function of the distance from channel wall. Numerical results show that the boundary slip always stabilizes the flow and the apparent viscosity destabilizes the flow. It also shows that the effects of boundary slip are reduced sharply by considering the apparent viscosity modification. It means that the interaction between the close-wall molecules of liquid and solid wall is strong enough to resist boundary slip.     

Analytical Model for Pipe Wall Friction of Pseudo-Homogenous Sand Slurries

In pseudo-homogenous pipeline flow of sand-water mixtures the measured hydraulic resistance is higher than for the flow of water, but is less than for a liquid having the same density as the mixture but a viscosity equal to that of water. A new analytical model is devised for pipe wall friction in which there is a watery viscous sublayer along the pipe wall. It is assumed that the presence of solids does not affect the viscous properties of the mixture, and that grain-stresses are negligible. A satisfying result is obtained in a particle range of 0.1 to 2 mm median grain diameter and volumetric concentrations up to about 30%. It is found that the model describes a lower bound for hydraulic resistance. The theoretical concept can be used as a basis for further developments into the heterogeneous regime, where additional physical processes come into play.