Open-Channel Capillary Trees and Capillary Pumping.

Flow rate limitation in curved open capillary groove channels

In the laminar regimes typical of microfluidic systems’, mixing is governed by molecular diffusion; however this process is slow in nature. Consequently, passive or active methods are usually sought for effective mixing. In this work, open fluidic channels will be investigated; these channels are bounded on all but one face by an air/fluid interface. Firstly, it will be shown that flow in open channels can merge at a Y-junction in a stable manner; hence two fluids can be brought into contact with each other. Secondly, the mixing of these two fluids will be studied. At high flow rates (>300 μl/min) mixing occurs at the junction without need for additional intervention, this mixing is far swifter than can be expected from molecular diffusion. At lower flow rates, intervention is required. A major motivation for open fluidic channels is the ability to interact with the surrounding air environment; this feature is used to effect the desired mixing. It is shown that by blowing an air jet across the junction, shear stresses at the air/fluid interface causes a flow profile within the fluid inductive to rapid mixing of the fluids.

A capillary suction pump giving constant flow rates

Open microfluidics is an emerging field of bio/medical applications that need direct energy/matter exchange between microfluids and environment. This paper presents the design, simulation, fabrication, and test of a microfluidic chip for a water-in-oil (WiO) two-phase flow in closed-open-closed microchannels. The chip, fabricated from PDMS using soft lithography, consists of a flow-focusing structure for WiO droplet generation and a long closed-open-closed channel for droplet flow. A negative pressure applied to the end of the channel is used as the driving force for WiO droplets to flow through the open channel. It is found that the negative pressure that is capable of driving a steady flow for a given flow rate, without overflow and air suction, falls into a pressure range instead of being an exact value. The mechanism for the pressure range is investigated theoretically and experimentally and is attributed to the surface tension. Yeast cells have been incorporated in the droplets, and the successful flow through the open channels verifies the function of the chips.

A numerical investigation on the utilization of a depleted natural gas field for seasonal hydrogen storage: A case study for Değirmenköy gas field

A rectangular broad crested weir is the one mostly used in hydraulic structures for measuring flow rates in open channels and rivers. This study is focused on finding the suitable position of the depth above the weir as control section for estimating the flow rate while avoiding the troubles of approach velocity. It was predicted that the end edge of the weir, as a control section, relates to the critical depth (Yc) as a function of the end depth (Ye). To determine the relationship between these, experimental tests were achieved with ten different values of the longitudinal slope. Statistical regression analysis indicated the relationship between Yc and Ye as about 1.522. Consequently, a new flow rate formula was derived to estimate the flow over the weir and provided a good agreement with the experimental tests. A 3D ANSYS FLUENT Ver. V.16.1 CFD model was also applied to simulate the problem and verify the equation. The water volume fraction and the stream flow pattern were taken into the consideration. The model was able to simulate the problem with a good accuracy for all cases with a percentage error less than 10% when compared to experimental results. Thus indicating that CFD models could be relied upon for describing complex flows.

Brink as a device for measurement discharge for partially filled circular channel

Using the Ansys Fluent 2020 R2 computational fluid dynamics suite, a method for calculating the three-dimensional velocity field in helicoid-type turbine flowmeters has been developed, based on the torque balance equation, i.e. the equality of the driving and retarding torques on the turbine, which is achieved at an equilibrium rotation speed for a given constant volumetric flow rate (which is fulfilled when the angular acceleration is equal to zero). At constant flow rate, when the rotor speed changes, the moment on the rotor blade is determined. The value of the speed is found at which the moment changes sign. The dependence of the torque on the number of revolutions is plotted on a graph and the true number of revolutions is determined at which the torque is zero for a given flow rate. The basis for the mathematical description of turbulent three-dimensional flow in flow meters is a system of differential equations of conservation of mass (continuity equation), momentum and the standard k-ω turbulence model (based on the Wilcox model) with partial derivatives in cylindrical coordinates in a three-dimensional problem setting. The multiple reference frame method incorporated into the Ansys Fluent computing suite allows reducing a problem involving stationary and rotating elements to a stationary one. The numerical calculation was performed at various flow rates (from 354 to 1982 m3/h) and kinematic viscosity (from 0.2 to 140 cSt). The main characteristics of turbine flowmeters are determined: the specific meter factor (or K-factor), Strouhal and Roschko numbers. The greatest discrepancy between the numerical calculation and the experimental data on the K-factor value is obtained at low flow rates and at the highest viscosity of 140 cSt (which is beyond the scope of application of the researched flowmeter) and is no more than 5%.

With the use of theoretical models of filtration liquid flows in fractures of finite and infinite lengths, formed in an oil stratum, the problem on the production of oil from a well, operating in the regimes of constant differential pressure or constant flow rate in this stratum, was solved. On the basis of approximate solution of the problem on the flow of oil from a stratum into a fracture formed in it by the method of successive changing stationary states, fairly simple analytical formulas have been obtained. A comparison of the results of numerical calculations of the practically important parameters of an oil stratum and a hydraulic fracture in it by the approximate formulas constructed and the corresponding exact formulas, which are much more complex than the approximate formulas, has shown that these results are almost identical. In particular, the errors in determining the evolution of the pressure field in a well and its flow rate by the approximate formulas did not exceed several percent. On the basis of numerical analysis of the approximate solutions obtained, the influence of the porosity and permeability of the stratum, the length of a fracture in it, and the rheological properties of the liquid saturating the stratum on the evolution of the pressure in the fracture, the flow rate of a well operating in the regime of constant differential pressure in the stratum, and the changes in the pressures in the fracture and in the well at a constant well flow rate was investigated.

Vincristine has been proven promising regarding its safety and efficacy for the renal artery denervation both in experimental models and in humans. The aim of the study was to compare in an experimental model the efficacy of constant versus random flow rate delivery of vincristine on renal sympathetic denervation. We used 10 juvenile Landrace swine. After the introduction of a 7F sheath into the femoral artery, a guide wire was advanced into the distal part of the renal artery. Then the first delivery balloon catheter, which delivers vincristine in random flow rate, was advanced at the proximal part of the artery, and the balloon was inflated in order to locally deliver vincristine to the media of the renal artery. The process was repeated in the contralateral renal artery, with the use of the double balloon catheter that delivers vincristine with a constant flow rate. Euthanasia of the animals was performed at 28 days. All sections were processed for histological and immunohistochemical analysis. The delivery of vincristine with both catheters was successful and uncomplicated. Immunohistochemistry showed that the mean number of intact nerves in all sections was significantly lower in the group of vincristine delivered with constant flow catheter compared to the group that the delivery was performed in a random fashion. (1.48 ± 0.37 vs. 1.70 ± 0.41, p = 0.04). Chemical renal denervation with vincristine by a constant flow rate catheter is more effective compared to the denervation performed by a catheter that delivers vincristine in a random fashion.

The stability problem of a system of conservation laws perturbed by non-homogeneous terms is investigated. These non-homogeneous terms are assumed to have a small C1-norm. By a Riemann coordinates approach a sufficient stability criterion is established in terms of the boundary conditions. This criterion can be interpreted as a robust stabilization condition by means of a boundary control, for systems of conservation laws subject to external disturbances. This stability result is then applied to the problem of the regulation of the water level and the flow rate in an open channel. The flow in the channel is described by the Saint-Venant equations perturbed by small non-homogeneous terms that account for the friction effects as well as external water supplies or withdrawals.

Determination of formation permeability and well skin factor is important for forecasting flow rates of oil and gas wells. A new technique for analysing test data for stimulated oil wells produced at a constant bottomhole pressure (BHP) has been developed. The method presented in this paper allows one to calculate the skin factor and estimate the formation permeability. It is assumed that the instantaneous flow rate and time data are available from a well produced against a constant bottomhole pressure. Only records of the flowing time and flow rate data are required to compute the values of the skin factor and formation permeability. A semi-theoretical equation is used to approximate the dimensionless flow rate. Our objective is to validate the new suggested method (prior to conducting a field test) by using a simulated example, where a numerical solution is used as an ‘exact’ solution.‘Bottomhole pressure’ means the pressure determined at the face of the producing horizon by means of a pressure-recording instrument. In the case of gas wells or wells having no liquid in the well bore, it means the pressure as calculated by adding the pressure at the surface of the ground to the calculated weight of the column of gas from the surface to the bottom of the hole. Determination of bottomhole pressure (BHP) is an important problem in the oil and gas industry (Akhter and Kreitler, 1990; Schechter, 1992; Yang et al., 2003). At present the majority of well tests are conducted at constant flow rates, where simple solutions of the diffusivity equation can be applied. However, many investigators (Ehlig-Economides and Ramey, 1981; Sengul, 1983; Uraiet and Raghavan, 1980 a.o.) hold to the idea that in practice it is easier to conduct well tests at a constant bottomhole pressure (BHP). It is very difficult to maintain a constant flow rate during long flowing times (especially when testing low permeability formations). The advantages of the constant BHP test are: (1) the fluid production can be easily controlled (at constant flow rate tests the BHP is changing with time); and (2) wellbore storage effects on the test data are short-lived. One of the reasons that constant BHP tests have not been utilized in reservoir engineering is that only numerical solutions of the diffusivity equation for a cylindrical source with a constant BHP have been available. Due to the similarity in Darcy’s and Fourier’s laws, the same differential diffusivity equation describes the transient flow of incompressible fluid in a porous medium and heat conduction in solids. As a result, a correspondence exists between the following parameters: volumetric flow rate, pressure gradient, mobility (formation permeability and viscosity ratio), hydraulic diffusivity coefficient and heat flow rate, temperature gradient, thermal conductivity and thermal diffusivity. Thus, the same analytical solutions of the diffusivity equation (at corresponding initial and boundary conditions) can be utilized for determination of the above-mentioned parameters. Earlier we suggested a semi-theoretical equation to approximate the dimensionless heat flow rate from an infinite cylindrical source with a constant bore-face temperature (Kutasov, 1987). This equation (in terms of pressure and flow rate) was used to process data of step pressure tests when fluid is produced at two successive bottomhole pressures (Kutasov, 1998). The same equation was used to estimate the efficiency of stimulating operations (Kutasov and Kagan, 2003). In both cases a technique for determining the formation permeability and skin factor from flow tests in stimulated wells was developed. The objective of this paper is to suggest a similar technique for determination of the values of formation permeability and skin factor from drawdown constant BHP tests in stimulated wells. We should also like to mention that for damaged wells, when the dimensionless time based on the apparent well radius is very large, a simple equation can be used to process field data (Sengul, 1983; Earlougher, 1977).

The performance of two popular hydraulic models (HEC-RAS and WSPG) for modeling hydraulic jump in an open channel is investigated. The numerical solutions are compared with a new experimental data set obtained for varying channel bottom slopes and flow rates. Both the models satisfactorily predict the flow depths and location of the jump. The end results indicate that the numerical models output is sensitive to the value of chosen roughness coefficient. For this application, WSPG model is easier to implement with few input variables.

This Paper introduces a feedback-type fluidic oscillator design with adjustable frequency at a constant flow rate. Details of the internal and external flowfields were revealed by numerical simulations with the help of frequency measurements and visualizations. Fluidic oscillator’s internal flowfield was manipulated by fluid injection from the islands of the oscillator into the interaction chamber. The interaction between the oscillator’s main jet and the control jets was observed to generate vortices in the mixing shear layers of the jets due to the Kelvin–Helmholtz instabilities. These vortices started to govern the separation bubble characteristics as the control flow rate was increased. After a certain control flow rate threshold was exceeded, the oscillations were no longer controlled by the feedback flow. Instead they were controlled by the vortices generated by the instabilities, resulting in much higher frequencies. These high-frequency oscillations in the supermode control flow rates were determined to be as high as five times the regular frequency of the oscillator. However, a reverse relationship between frequency and sweep angle was also identified. Depending on the amount of control flow at a constant total flow rate, three regions and five cases distributed in these regions are reported.

An inexpensive and simple pumping principle is described that is capable of delivering both small and constant flow rates (10–1,000 nl/min) over a longer period of time (days to weeks). The concept is based on controlled evaporation of a liquid through a membrane into a gas space containing a sorption agent. As long as the sorption agent keeps the vapor pressure in the gas phase below saturation, fluid evaporated from the membrane is replaced by capillary forces inducing flow from a reservoir. In a feasibility study, a total volume of 300 μl of Ringer's solution has been continuously pumped over a period of six days, resulting in an constant average flow rate of 35 nl/min (590 pl/s). The maximum liquid volume transported is limited by sorption capacity and amount of the sorption agent. Low fabrication costs, high reliability (no moving parts), the suitability for integration into planar system architectures and the lack of a special external energy source besides an environment of regulated temperature are important features of the concept, in particular with regard to its potential application in continuous patient monitoring. Truly continuous flow can be achieved in contrast to many other pump mechanisms leading to discontinuous, pulse-type flow. A challenge for a broader range of applications is the inherent temperature dependence of the flow rate. In its current version, the pump can only be used in a suction-mode.