Analytical model of a bubble switch

A model is presented for a bubble switch based on the Y-bar propagation element. Good correlation of the predictions of the model with experimental results is found for 8 μ bubbles. The heuristically derived scaling law, which predicts that the switching current must remain constant as the bubble diameter decreases, is confirmed by direct calculation with the model. The model shows that it will be increasingly difficult to design switches as the bubble diameter is reduced below 1 μ.     

Model of heat transfer in bubble boiling

Based on representation of the bubble-boiling process as near-wall turbulence, limiting relations are obtained that describe heat transfer for the low- and high-pressure regions.     

Mass transfer correlation of NH3–H2O bubble absorption

The objectives of this paper are to study the effect of key parameters on absorption performance and to develop an experimental correlation of mass transfer coefficient for ammonia–water bubble absorption. The orifice diameter, liquid concentration and vapor velocity are considered as the key parameters. This study successfully visualized the bubble behavior and measured the volumetric diameter of bubbles during the bubble absorption process. The bubble absorption is grouped into two processes, bubble growth (process I) and bubble disappearance (process II), respectively. The following conclusions were drawn from the present study. A new experimental correlation for the volumetric bubble diameter was proposed with ±15% error band, which could be applied to calculate the mass transfer coefficient. The mass transfer coefficient increased with a decrease of the liquid concentration. In process II, the mass transfer coefficient increased with an increase of the Galileo number. Finally, experimental correlations of mass transfer coefficient were developed for processes I and II with ±18% error bands.     

Mass transfer from a moving bubble during a slow chemical reaction

A previously proposed method for solving inhomogeneous problems in the theory of heat and mass transfer is refined. As an illustration, the stationary mass transfer from a moving bubble during a slow chemical reaction of first or second order is examined.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 4, pp. 595–599, April, 1982.     

Utilization of liquid-gas bubble mixtures for the transfer of shock-wave disturbances

Transfer of the energy of shock-wave disturbances from a gas to a liquid or to a liquid-gas bubble mixture is considered. It is shown that the energy flux from the gas increases when a liquid with gas bubbles is substituted for the pure liquid.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 4, pp. 674–677, October, 1976.     

Visualization of bubble behavior and bubble diameter correlation for NH3–H2O bubble absorption

The objectives of this paper are to visualize the bubble behavior for an ammonia–water absorption process, and to study the effect of key parameters on ammonia–water bubble absorption performance. The orifice diameter, orifice number, liquid concentration and vapor velocity are considered as the key parameters. The departing bubbles tend to be spherical for surface tension dominant flow, and the bubbles tend to be hemispherical for inertial force dominant flow. A transition vapor Reynolds number is observed at a balance condition of internal absorption potential (by the concentration difference) and external absorption potential (by the vapor inlet mass flow rate). As the liquid concentration increases, the transition Reynolds number and the initial bubble diameter increase. The initial bubble diameter increases with an increase of the orifice diameter while it is not significantly affected by the number of orifices. Residence time of bubbles increases with an increase in the initial bubble diameter and the liquid concentration. This study presents a correlation of initial bubble diameter with ±20% error band. The correlation can be used to calculate the interfacial area in the design of ammonia-water bubble absorber.     

Mass transfer of a single bubble in a minimally fluidized granular bed

The transfer of a gas admixture through the boundary of a cloud of closed circulation of gas is examined with a view to both molecular and convective dispersion.Notation a particle radius - c concentration of the admixture - D, D _c tensors of effective diffusion coefficients and of coefficients of convective dispersion, respectively - D parameter in (14) - D₀, D_m coefficients of molecular diffusion, respectively not taking and taking compressibility into account - F, f functions in (17) and (18), respectively - f fraction of the volume of the sphere with radius R_B occupied by the wake of the bubble - g acceleration of gravity - K mass-transfer coefficient determined in (22) - k coefficient in (7) - L coefficient in (22) - p, s functions determined in (13) - Q, q flow of admixture for the entire bubble and local flow, respectively - r_B, R_c radii of bubble and of cloud of closed circulation, respectively - r radial coordinate - U lift velocity of the bubble - u=v-w; u₀=u_*/u_* minimum velocity of fluidization - V volume of bubble - v, w mean gas velocities in the gaps between particles and of the particles, respectively - parameter determined in (8) - , parameters from (14) - porosity of the dense phase and of the cloud - polar angle - independent variable introduced in (12) - p = 1 - flow function Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 2, pp. 323–333, August, 1980.     

Heat and mass transfer characteristics of a constrained thin-film ammonia-water bubble absorber

A study of absorption of ammonia vapour bubbles into a constrained thin-film of ammonia-water solution is presented. A large-aspect-ratio microchannel constrains the thickness of the weak solution film and ammonia vapour bubbles are injected from a porous wall. A counter flowing coolant in a minichannel removes the generated heat of absorption. Experiments and a simple one-dimensional numerical model are used to characterize the absorber performance at a nominal system pressure of 6.2 bar absolute. Effect of varying the mass flow rate of the weak solution, vapour flow rate, solution inlet temperature, and coolant inlet temperature on absorption heat and mass transfer rates and exit subcooling are discussed. Two absorber channel geometries, each of 600 μm nominal depth, are considered: 1) a smooth-wall channel, and 2) a stepped-wall channel that has 2-mm deep trenches across the width of a channel wall. Results indicate that the reduction in coolant inlet temperature significantly enhances the mass transfer rates in both absorber geometries. While the stepped-wall geometry exhibits higher mass transfer rates at lower coolant inlet temperatures of 30 °C and 40 °C, the smooth-wall channel shows higher mass transfer rates at the highest coolant inlet temperature of 58 °C. Both absorption limited and residence time limited conditions are observed with variation of weak solution flow rate at fixed vapour flow rates.     

空间微膨胀型热开关传热性能试验

为了解决空间相机在冷黑环境下由于姿态变化引起的散热问题,基于金属材料的热特性设计了一种机械制冷式热开关,构建实验平台模拟热开关的实际工作环境,研究在不同热负载条件下,热流密度对传热和散热效率的影响。通过调节加热器功率大小和冷源温度水平,得到热开关的传热以及热闭合特性。实验结果表明,随着加热功率的递增,开关整体热阻逐渐减小,当加热负载为30W,热开关热闭合热阻为0.302 2 K/W,当温度降低时,热开关断开热阻达到230.46 K/W,整体开关比为762.60。该热开关能够自动实现闭合、断开特性,且具有较大的开关比,性能稳定可靠。     

A surface-anchored molecular four-level conductance switch based on single proton transfer

The development of a variety of nanoscale applications requires the fabrication and control of atomic or molecular switches that can be reversibly operated by light, a short-range force, electric current or other external stimuli. For such molecules to be used as electronic components, they should be directly coupled to a metallic support and the switching unit should be easily connected to other molecular species without suppressing switching performance. Here, we show that a free-base tetraphenyl-porphyrin molecule, which is anchored to a silver surface, can function as a molecular conductance switch. The saddle-shaped molecule has two hydrogen atoms in its inner cavity that can be flipped between two states with different local conductance levels using the electron current through the tip of a scanning tunnelling microscope. Moreover, by deliberately removing one of the hydrogens, a four-level conductance switch can be created. The resulting device, which could be controllably integrated into the surrounding nanoscale environment, relies on the transfer of a single proton and therefore contains the smallest possible atomistic switching unit.     

Effect of graphene oxide coating on bubble dynamics and nucleate pool boiling heat transfer

Materials coating has been proved to be an effective mean to increase the number of active nucleating sites, and therefore generate more vapor bubbles and lead to better pool boiling heat transfer performance. In this work, graphene oxide (GO) is coated on a boiling surface by self-assembly method, to enhance critical heat flux (CHF). The pool boiling is carried out on a smooth copper surface to study the effect of GO coating using distilled water as the working fluid along with bubble dynamic visualization. GO coating facilitates bubble nucleation by providing numerous microscale cavities. The visualization investigation of bubble dynamic behavior shows that the CO-coated surface exhibits a higher bubble departure frequency, a smaller bubble departure diameter and smaller bubble diameters in the pool, indicating greatly enhanced heat transfer effects. Meanwhile, the GO-coated surface exhibited a smaller contact angle than the copper surface, revealing that surface becomes more hydrophilic after GO coating. Consequently, GO-coated surface with a coating time of 4 h provides a CHF of 224.3 W/cm² and a heat transfer coefficient (HTC) of 8.79 W/(cm²·K), representing an improvement of 94.0% in CHF and 83.5% in HTC compared to smooth copper surface.     

Heat and mass transfer in vertical tubular bubble absorbers for ammonia-water absorption refrigeration systems

A model is developed for calculation of simultaneous heat and mass transfer processes in vertical bubble absorbers as used for ammonia-water absorption refrigeration systems. Some preliminary experiments have been performed in an absorber without heat removal. The results from these experiments are compared with the literature and give a first indication about the methods for prediction of the absorption process. Experiments have also been performed with simultaneous heat removal. The internal diameters of the absorbers tested were 10.0, 15.3, and 20.5 mm. The mass transfer coefficients resulting from these experiments are correlated by a modified Sherwood relation. An interative procedure is presented which allows design of vertical tubular bubble absorbers for ammonia-water absorption refrigeration systems.     

Current controlled high Tc superconducting switch

When a current is applied above the critical current l_c of a superconductor, the material is in its normal state and has a finite resistance. Below l_c the material becomes a superconductor with zero resistance. Switching between these two states can be achieved by modulating a current through the sample. Various high T_c superconducting (HTS) line structures have been made. In the normal state these structures are ordinary resistors with resistances ranging from 10 μ to 100 kμ. The critical currents are in the range 10 μA–100 mA. Switching behaviour has been observed in a simple divider circuit using the HTS lines at 77 K. Applications of the current controlled HTS switch to digital and logic circuits are discussed.     

Single-mask bubble memories: Bit/Chip organization with decoding

Progress in element and chip design of single-mask bubble chips, based on drive-field operation, is reported. Three new elements, which have been successfully operated, are presented. (i) The replicator copies bubble streams for one propagation direction; when used in combination with the sense of rotation of the drive field it can serve as a bit generator. (ii) The λ-creator can selectively shift a bit over one propagation period. It can be applied in a decoder organization which permits rapid access to stored information. (iii) A current-controlled splitter-type generator was designed, which takes current pulses of about 60 mA for creating new bubbles.     

Critical boiling heat transfer: special case of smooth exchange of bubble and film boiling regimes

The author presents results of an unconventional analysis of critical heat transfer interpreted as boundaries of a transition boiling region with a smooth exchange of bubble and film boiling regimes. A stepwise exchange of these boiling regimes, i.e., critical heat transfer in the textbook sense, is examined as a special case. The influence of various parameters on the boundaries and the transition boiling zone is demonstrated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 3, pp. 437–445, September, 1990.     

单泡声致发光现象 - 气泡运动的Mie散射测量

单泡声致发光现象时间和空间的高重复性,为实验研究气泡动力学特性提供了可能。文章利用Dave倒推算法,计算气泡Mie散射光强随散射角和气泡半径的变化,并选择了散射角80°为实验测量位置。利用R P方程理论计算的R(t)曲线与Mie散射实测结果相拟合,定量研究了气泡平衡半径、压缩比及崩溃阶段气泡的能量转换,结果表明,随激励声压的增大,气泡所吸收的声能可能绝大部分转换成激波及热能,使泡内温度上升。     

Tunable all-optical switch/demultiplexer using nonlinear MMI waveguides

In this paper, a tunable optical switch/demultiplexer has been presented based on nonlinear multimode interference waveguides. The proposed structure can be utilized as a multi-wavelength optical switch or dynamic wavelength division demultiplexer. This dual application of the structure has been designed based on the cooperation of self-imaging and self-guiding phenomena of multimode waveguides. Simulation results show the mean value of insertion loss equal to ?1.91 dB for the switching application of structure. Also, the wavelengths with 3 nm channel spacing and almost 3 nm full width at half power of outputs can be received in the multiplexing application. Two-dimensional beam propagation method has been utilized in order to simulate and verify the performance of proposed device.     

CO2 bubble absorption enhancement in methanol-based nanofluids

In this study, the nanoparticles (i.e. SiO₂ and Al₂O₃ nanoparticles) and methanol are combined into SiO₂/methanol and Al₂O₃/methanol nanofluids to enhance the CO₂ absorption rate of the base fluid (methanol). The absorption experiments are performed in the bubble type absorber system equipped with mass flow controller (MFC), mass flow meter (MFM) and silica gel (which can remove the methanol vapor existing in the outlet gases). The parametric analysis on the effects of the particle species and concentrations on CO₂ bubble absorption rate is carried out. The particle concentration ranges from 0.005 to 0.5 vol%. It is found that the CO₂ absorption rate is enhanced up to 4.5% at 0.01 vol% of Al₂O₃/methanol nanofluids at 20 °C, and 5.6% at 0.01 vol% of SiO₂/methanol nanofluids at −20 °C, respectively.     

Magnetic bubble logic

Although the literature on the bubble logic devices is limited, the concepts and device configurations are diverse. In conductor-access devices, logic can be performed by bubble transfer operations. In field-access devices, logic can be performed by providing alternative paths which are selected by interaction between bubbles. Examples include the conjugate logic gates, the resident-bubble cellular logic, and the chevron 3-3 circuits. Logic can also be performed by counting bubbles, such as in the symmetric switching function implementation. The various mechanisms for implementing bubble logic are all described by truth tables. To assess their efficiency, they are compared in terms of space and delay when they are used to implement the same logic element - a full adder. They are all comparable except for the resident-bubble cellular logic which requires excessive space and delay. However, it is important to point out that only the symmetric switching function devices offer rewrite-ability to eliminate the part number problem, and accommodation for a large number of inputs to ease interconnection and delay equalization problems.     

探地雷达收发开关系统的设计

 针对当前探地雷达中双天线存在严重耦合影响了信号检测的问题,开发了一种高速的开关系统.通过ADS电路仿真和参数优化,利用PIN管芯制作了一种串/并联结构的宽带高隔离度微带单刀双掷开关,设计了开关的电源电路和驱动电路.经过实验测量表明该开关系统达到了技术指标要求,能满足探地雷达的要求.