Liquids flux method

Borides have been prepared as single crystals by making use of gas-phase, liquid-phase and flux methods, depending on the thermal stability of the boride and on the required size and perfection of the single crystals. 

Using the imposed heat flux method, we carried out NEMD simulations for the HMX melt at six temperatures (550 K - 800 K, in 50 K intervals) and atmospheric pressure. The simulation methodology was similar to the one described above for equilibrium MD simulations with a few exceptions. Each system contained 100 HMX molecules. The orthorhombic simulation box, extended in the z direction, was subdivided into 10 equal slabs with width of about 5.0 A and cross-sectional area of about 625.0 A2. The molecular center-of-mass velocities were exchanged every 500 fs (W=0.002 fs 1) for pairs of molecules belonging to the cold and hot slabs. This choice of the W was based on our previous experience with simulations of liquid n-butane and water [52],... 

The second is the rate of penetration, (dh/dt) method. The principle is that from the driving force for the penetration (a < 90°), i.e. the capillary pressure, the liquid flux can be computed, using the Poiseuille equation. For the ideal case of horizontal homogeneous capillaries and a spherical meniscus. 

The technique consists in measuring the B (e.g. water) flow rate (/) through a membrane impregnated with A (e.g. isobutanol or mixtures of alcohols and water) as a function of the pressure difference AP. We have to note that it is possible to modify the method from "pressure controlled" to "flow controlled" in order to reduce the test time and increase its flexibility [126]. At a certain minimum pressure the largest pores become permeable, while the smaller pores still remain impermeable. This minimum pressure depends mainly on the type of membrane material (contact angle), type of permeate (surface tension) and pore size. When all pores are filled with B, the liquid flux / through the membrane becomes directly proportional to the pressure. 

This short duration test method allows the corrosivity of liquid flux residues after wave soldering to be assessed and employed as a screening test prior to employment of the more time-consuming procedures. 

Using scaling analysis and perturbation methods, we have been able to derive approximate expressions for the momentum and energy flux in dilute gases and liquids. These methods physically involve formal expansions about local equilibrium states, and the particular asymptotic restrictions have been formally obtained. The flux expressions now involve the dependent transport variables of mass or number density, velocity, and temperature, and they can be utilized to obtain a closed set of transport equations, which can be solved simultaneously for any particular physical system. The problem at this point becomes a purely mathematical problem of solving a set of coupled nonlinear partial differential equations subject to the particular boundary and initial conditions of the problem at hand. (Still not a simple matter see interlude 6.2.)... 

The Y concentration in the BaO-CuO liquid is very low. Therefore, the self-flux method, which is commonly used to obtain single crystals in incongruent melting systems, might not be helpM in production of large crystals. 

Fig. 22. A brief classification of R123 crystal growth techniques on a basis of different phenomena taking place at various interfaces between solid, liquid and gaseous phases participating in the solidification process (a) possible interface boundaries and phenomena connected with the presence of such interfaces (b) different interfaces present in the self-flux method note that numbers in brackets correspond to the general scheme of classification (a) (c) a number of interfaces and phenomena of some importance for the unidirectional solidification method note that (crystal-high-temperature phase and melt-high-temperature phase) interfaces are close to each other (d) different interfaces and phenomena to be considered in the SRL-CP pulling technique of bulk crystal production note that solute transport and nudeation can be controlled in order to achieve a desired morphology of the crystal.

In the case of Y123, variation of the initial flux composition is advantageous in the preparation of thick crystals by the self-flux method (sect. 5.1) or in the control of crystalline film orientation in the LPE method (sect. 5.4). However, for LRl 23 crystals the control of liquid composition is crucial even for their superconductivity enhancement. 

This standard defines the classification of soldering materials through specifications of test methods and inspection criteria. These materials include liquid flux, paste flux, solderpaste... 

An alternative NEMD method has been developed that is much simpler to implement than is the SLLOD method, particularly for charged systems such as ionic liquids. The method is called reverse nonequilibrium molecular dynamics (RNEMD) and was first developed as a means for computing thermal conductivity but has also been applied to viscosity. It differs from conventional equilibrium and nonequilibrium methods where the cause is an imposed shear rate and the measured effect is a momentum flux/stress. RNEMD does the opposite it imposes the difficult to compute quantity (the momentum flux or stress) and measures the easy to compute property (the shear rate or velocity profile). The method is very simple to implement because it only requires periodic swapping of momenta between atoms at different positions in the box. These swaps set up a velocity profile in the system (i.e., a shear rate). By tracking the frequency and amount of momentum... 

Foam-like MWNT/polymer nanocomposite has also been prepared by a method already described for silica foams (Cam et al., 2004). First, SWNTs were dispersed in water using carboxymethyl cellulose sodium salt and then a liquid foam was obtained via a bubbling process on a column (Leroy et al., 2007). This method allows control of the size and shape of cells by playing with the diameter of the porous filter and the liquid flux. Finally, the liquid foam was eooled down to -80°C and lyophilized. 

The analysis of gas absorption depends on fluid mechanics and on mass transfer. The fluid mechanics determines the acceptable range of gas and liquid fluxes, which are adjusted by changing the cross-sectional area of the tower. The mass transfer eoeffi-cients determine the rate of absorption and hence the height of the paeked tower. This height can be estimated by either algebraic or geometric methods. The algebraic formulation is simple for the common case of a dilute solute, a case detailed in Section 10.3. This case depends on three key relations an overall mole balance, a thermodynamic equilibrium, and a rate equation. This dilute case is the easiest way to learn about absorption. 

Steam-liquid flow. Two-phase flow maps and heat transfer prediction methods which exist for vaporization in macro-channels and are inapplicable in micro-channels. Due to the predominance of surface tension over the gravity forces, the orientation of micro-channel has a negligible influence on the flow pattern. The models of convection boiling should correlate the frequencies, length and velocities of the bubbles and the coalescence processes, which control the flow pattern transitions, with the heat flux and the mass flux. The vapor bubble size distribution must be taken into account. 

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