Parallel Channel System Research Articles

Oscillatory Flow Instabilities in Air-Water Two-Phase Flow System : 3rd Report, Pressure Drop Oscillation in Parallel Channel System

水平に設置された2本の毛細管よりなる並列空気-水二相流系において生じる圧力降下振動に関する実験ならびに集中系モデルによる数値シミュレーションを行った.発生した脈動のタイプは,し緩形と擬調和形であり,これらは並列管の脈動パターン,単一チャンネル形,U字管形,多チャンネル形,搬送波形と密接に関係していること,および周期や振幅などの特性が脈動のタイプによって一義的に決まることを明らかにした.

Weak electrolyte permeation in alimentary epithelia

The potential significance of ionized species in weak electrolyte absorption or secretion has been reexamined using a mathematical model that represents the epithelium as a system of parallel ion-permeable and ion-impermeable channels. An important determinant of weak electrolyte movement in this system is the ratio of ionized and nonionized permeabilities (Pi/Pni). This variable, which has been termed the discrimination coefficient, interacts with the degree of ionization in determining the contributions of ionized and nonionized species to the transepithelial movement of a weak electrolyte. Calculations based on the model suggest that ionized species may contribute significantly to the absorption or secretion of many common weak electrolytes. It is concluded that the frequently made assumption that ionized species do not contribute significantly to transepithelial movements of weak electrolytes in the alimentary tract is not generally valid. Further work is required to delineate the quantitative determinants of discrimination in alimentary epithelia, and two methods for evaluation of epithelial discrimination coefficients are described.

Instabilities in Parallel Channel of Forced-Convection Boiling Upflow System, (III)

The instabilities observed in a parallel-channel system carrying boiling fluid in forced upward flow have been studied theoretically and experimentally, using water as test fluid. The system, where the thermo-hydraulic flow conditions in two channels are different from each other, is studied theoretically and experimentally, in order to make clear the effects of the different conditions on the flow instabilities. The different conditions between parallel channels are made artificially by changing the entrance throttlings, the heater lengthes and the heat fluxes. Consequently, the instability in the system where the own characteristic frequencies are approximately equal in two channels almost agree with the one obtained under the uniform condition equivalent to the average operating condition in two channels, such as the different entrance throttlings and the different heater lengthes. On the other hand, the system, where the characteristic frequencies differ from two channels, becomes more stable with inc...

Transient boiling flow instabilities in a multi-channel upflow system

In this study, the transient boiling flow instabilities in a four parallel channel upflow system with and without cross-connections have been experimentally investigated using Freon-11 as the test fluid. Several series of transient experiments have been run using a step increase in power input with a constant flow control valve setting and a step decrease in flow rate with a constant heat input. Two major modes of oscillations, namely density-wave type and pressure-drop type oscillations, have been observed. Total system pressure drop has been plotted as a function of mass flow rate for various heat inputs and flow control valve settings, and the stable and unstable regions for transient density-wave type and pressure-drop type oscillations have been determined and the boundaries of sustained instabilities have also been indicated. Experiments have been conducted with equal and unequal heat inputs and the results have been compared with each other. A comparison of the transient instabilities observed in four parallel channel system with and without cross connections has also been made.

Instabilities in Parallel Channel of Forced-Convection Boiling Upflow System, (II)

The instabilities observed in a parallel-channel system carrying boiling fluid in forced upward flow have been studied theoretically and experimentally, using water as test fluid. The limits of the stable flow in such a parallel-channel system (the stable boundary) are sought, and the nature of inlet flow oscillation in the unstable region has been examined experimentally under various conditions of inlet velocity, heat flux, liquid temperature, cross section of channel and entrance throttling. The results obtained are compared with calculations based on the mathematical model reported in a companion paper, and good agreement is seen between analysis and experiment in respect of the stable boundary. The experimental results are further examined through phase analysis using the same model.

Studies of Thermal-Hydrodynamic Flow Instability : 2nd Report: Effects of Heating Condition of Thermal-Hydrodynamic Flow Instability

For reliable prediction of flow stability in sodium-heated steam generators, a dynamic model was proposed for boiling flow oscillation in parallel channel systems, and an analysis code was developed. The model contains a description of a sodium flow exchanging heat with a water flow in counter-current fashion. the code was applied to three representative flow systems whose heating conditions differed from each other, whereby their flow stabilities were compared with a focus on the effects of heating condition. Eigenvalues and flow impedances of the oscillation determined for each system reveal that: (1) Two fundamental system for the steam generator, parallel tube system in an evaporator and steam generator modules arranged in parallel, have different stabilities under low frequency oscillation. (2) Existing analysis model conditioned on constant heat flux gives different results on stability from those of either steam generator model under low frequency oscillation.

Instabilities in Parallel Channel of Forced-Convection Boiling Upflow System, (I)

The instabilities occurring in forced-convection upflow passing through a parallel-channel system have been studied theoretically and experimentally, using water as test fluid. A non-linear mathematical model is proposed, that explains the results quite satisfactorily. Close agreement is obtained between calculations based on this model and measure-ments of the stable boundary in a system of two channels. The model is further applied to three and four parallel channels, the results of which indicate that the flow instability behavior in such multiple channels are quite similar to that observed in the two-channel system, in such aspects as the stable boundary, as well as the period and the development of flow oscillations in the unstable region.

Instabilities in Parallel Channel of Forced-Convection Boiling Upflow System, (II)

The instabilities observed in a parallel-channel system carrying boiling fluid in forced upward flow have been studied theoretically and experimentally, using water as test fluid. The limits of the stable flow in such a parallel-channel system (the stable boundary) are sought, and the nature of inlet flow oscillation in the unstable region has been examined experimentally under various conditions of inlet velocity, heat flux, liquid temperature, cross section of channel and entrance throttling. The results obtained are compared with calculations based on the mathematical model reported in a companion paper, and good agreement is seen between analysis and experiment in respect of the stable boundary. The experimental results are further examined through phase analysis using the same model.

Method of controlling the growth and formation of a system of parallel sliding spark channels in air at atmospheric pressure

A method of controlling the growth process of a sliding spark along the surface of a film dielectric by introducing emission centers from chemical compounds with a low electron work function into the surface is presented. It is shown that it is possible, by using this method, to produce a spark channel with sharp corners, such as a Z-shaped channel, and an ordered system of parallel channels, as well as a strictly rectilinear channel up to 2 m long. It is established that the rate of growth of the sliding spark is nonuniform. The mean rate is heavily dependent on the overvoltage, which is related to a reduction in the pauses in its growth.

Studies of Thermal-Hydrodynamic Flow Instability : 1st Report: Theoretical Analysis of Parallel Channel Flow Instability

For the purpose of predicting flow instability in sodium heated steam generators, a theoretical model was presented for boiling flow oscillations in parallel channel systems, and a computer code was developed. The propagation of thermal-hydrodynamic disturbances was described with a matrix transfer function, and the modes of proper oscillations were obtained by solving a characteristic equation, in which the boundary conditions were imposed on the transfer function. Eigenvalues and patterns of the properscillations determined for instability revealed that the frequency given by the eigenvalues is in good agreement with that observed in the performance of a small size steam generator.

A turbulent flow theory of electrodialysis

A hydrodynamic theory is presented of desalination by electrodialysis in a parallel channel system with unobstructed fully developed turbulent flow. A set of turbulent transport equations is derived for the mean salt concentration and electric field. Closure of the set is brought about by introducing a turbulent diffusion coefficient whose behavior is assumed known from empirical mass transfer considerations, and by making two different but phenomenologically reasonable assumptions about that part of the average ion flux which is due to the correlation between the concentration and electric field fluctuations. Estimates show both assumptions to lead to sensibly the same final results. From the equations and boundary conditions it is shown that there are five parameters which govern the system performance. Four are the same as for the corresponding laminar case, while the fifth measures the thickness of the concentration diffusion sublayer, the value of which is taken to be given by semi-empirical turbulent mass transfer results for high Schmidt numbers. The thickness of this diffusion layer is found to be the critical factor governing the salt removal rate. An integral method of solution is used to obtain the distributions of salt concentration and current density. A numerical quadrature is required for the complete solution. Analytic solutions are obtained in the unpolarized and fully polarized limits. Because of the very abrupt transition between these two limits, taken together the limiting analytic solutions are adequate to describe the system performance over the entire range of operating variables. For small fractional salt removal a universal correlation for the average current density embodying the five similarity parameters of the system is suggested based on the limiting solutions. Comparison of the theory is made with the experimental results of Cowan and Brown on average limiting current density and the agreement is found to be satisfactory.

Certain hydrodynamic and heat transfer characteristics of a stream through a system of parallel channels with spills

Results are shown of visual observations concerning the distribution of static pressure, of the transverse velocity to longitudinal velocity ratio, of the flow rates, and of the local heat transfer coefficient in a system of channels with spills.

Capillarity and Seepage from an Array of Channels

The problem of seepage losses from a system of parallel triangular channels having a capillary fringe is solved exactly by use of conformail mapping techniques. The theory predicts the discharge per channel and the height of capillary rise as functions of the physical dimensions of the channel-drain system and the maximum depth of free surface between channels. In general, the system is underlain by a drainage layer at a finite depth. The case of an infinitely deep aquifer is solved separately. Numerical examples for channels having unit side slopes axe given with the results presented in the form of a table.

Seepage from an Array of Triangular Channels

The problem of seepage losses from a system of parallel triangular channels is solved exactly by use of conformal mapping. Formulas for the discharge and the shape of the free surface are given. In general, the system is underlain by a drainage layer at a finite depth, and the case of an infinitely deep aquifer is solved separately. Numerical examples are given with the results presented in the form of graphs and tables.

Natural Convection Flows in Parallel-Channel Systems

An analysis was developed for natural circulation flows in vertical multiple-channel systems with nonuniform heat inputs. A three-channel configuration was investigated in detail both analytically and experimentally. The results showed the existence of a metastable regime in which two metastable flow patterns could occur for a given set of heat input rates. A third predicted flow pattern in this regime was shown to be unstable and, therefore, nonexistent in practice.

Seepage from Parallel Trapezoidal Channels

An exact solution is presented for the seepage flow from a system of parallel trapezoidal channels through a layer of homogeneous, isotropic soil. Under this layer there is a drain that might be represented physically by a bed of gravel or coarse sand. The flow is assumed to obey Darcy’s law and hence there is velocity potential which satisfies the Laplace equation. By constructing the complex potential and the complex velocity planes, the solution is obtained through conformal mapping. General expressions are given for the discharge and shape of the free streamline. A numerical example is presented for which the free surface and the velocity distribution on the channel’s profile were drawn. The quantity of seepage from the bottom and sides were also computed.