РАСЧЕТ ГЕЛИКОИДНЫХ РАСХОДОМЕРОВ МЕТОДАМИ ВЫЧИСЛИТЕЛЬНОЙ ГИДРОДИНАМИКИ

The compression resin transfer molding (CRTM) filling process involves two stages: the injection phase and the compression phase. Two injection modes are considered — constant volumetric flow rate and constant pressure — while the constant compression velocity is utilized in this study. Three typical cases are used to investigate the compression initiation effects on the filling process. When the inlet condition is a constant flow rate, the numerical results show that the compression has both increase and decrease effects on the inlet pressure. Thus, a discontinuity in the inlet pressure is present at the onset or the end of compression. Among three CRTM cases, the process with a simultaneous injection and compression end maximally reduces the inlet pressure by 80% but increases the mold filling time by 65% compared with the resin transfer molding (RTM). For the inlet condition being a constant pressure, the resin may flow out of the mold cavity through the inlet when an excessively low injection pressure and high compression speed are applied concurrently. Compared with RTM, the CRTM processes reduce the mold filling time by 68–76% but cannot ensure a reduction in inlet pressure.

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

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.

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.

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).

Hydrodynamic effects on flow accelerated corrosion at 120 °C and neutral pH conditions

Accurate measurement of relative permeability curve is the basis for evaluating gas reservoir performance. The unsteady-state method could bring significant measurement error for low-permeability cores. However, it is difficult to control the constant gas flow rate in the traditional steady-state method, which obstacles the experimental operation. In this study, an improved steady-state method was proposed. First, the pressure value obtained from the experiment, when the gas permeability no longer changed with the average pressure on the rock core, was set as the testing pressure. Then, the gas was injected under constant pressure, and the water was injected with a constant flow rate. Finally, the relative permeability values of gas and water phases were calculated based on Darcy’s law. Comparative analysis of the results of the relative permeability curves under formation pressure and pressure with negligible slip effect indicates that the relative permeability curves are the same in gas and water phases, proving the feasibility of the new method. Further, the results were compared with those of the test method at normal pressure, the water-phase relative permeability showed no significant change, the relative permeability of gas phase was larger, the two-phase flow area became wider, and the irreducible water saturation was lower than that at the normal pressure. This result reflects that pressure does not significantly affect the flow of wetting phase but tremendously influences the nonwetted phase under low pressure. The relationship between relative permeability and water saturation is linear in the semilogarithmic coordinate diagram and can be described by using the following relationship: ln k rg / k rw = a S w + ln b . With the decrease in the core permeability, relative permeability curve, and isotonic point moved to the right, irreducible water saturation gradually increased, and residual gas saturation decreased, indicating that the smaller permeability induced a lower gas-phase flow capacity.

A capillary suction pump giving constant flow rates

Dehydrogenation performance of metal hydride container utilising MgH2-based composite

Hydrodynamics of a slot-rectangular spouted bed of biomass particles with simultaneous injection of spouting and pulsating air streams

The cavitating venturi is using to provide constant mass flow rate of liquid which is passing through a passage, independent of downstream pressure changes. A cavitating venturi is a converging-diverging nozzle with a suitable throat area for passing flow. The flow rate is a function of the upstream pressure, the throat area, the density and saturated pressure of the liquid. An experimental setup with the capability of supplying constant water flow rate, upstream pressure and temperature was designed and manufactured. Three cavitating venturies were designed and built to investigate the effect of cavitating venturi size on its mass flow rate and capability of performance venturi in wide ranges of flow rates. Three different sets of experiments were conducted to ensure the performance of the venturi to keep constant mass flow rate independent of downstream pressure. In the experiments, under different downstream and upstream pressure conditions, the mass flow rates were examined. The results show that if the ratio of downstream pressure to upstream pressure is less than 0.8, the mass flow rate is constant and independent of the downstream pressure. Whenever pressure ratio exceeds from 0.8, the venturi acts like an orifice.

A systematic presentation of the analytic relations of grout spread to the time period is established. They are divided following the nature of the flow, the property of the mix and the driving process. This includes channel flow between parallel plates and radial flow between parallel discs, nonlinear Newtonian fluids like silica solution, polyurethane and epoxy, and Bingham material like cement-based grout, and three grouting processes at a constant flow rate, constant pressure and constant energy. The analytic relations for the constant energy process are new and complete the relations of the constant flow rate and constant pressure processes. The well-known statement that refusal cannot be obtained during finite time for any injected material at a constant flow rate or constant injection pressure is extended to include the energy process. The term refusal pressure or energy cannot be supported for stop criteria. Stop criteria have to be defined considering confirmed relation of the spread to the time period and of the flow rate to the pressure and spread. It is shown that it is always possible to select a grouting process along which the work will exceed any predefined energy, the consequence of which is that jacking is related to the applied forces and not to the injected energy. Furthermore, a clarification is undertaken concerning the radial flow rate of a Bingham material since there are two different formulations. Their difference is explained and quantified. Finally, it is shown that the applied Lugeon theory is not supported by the analytic relations and needs to be substantially modified.

This paper presents a microfluidic control device that regulates nearly constant flow rates under variable driving pressures. This flow regulator is fabricated from PDMS and exploits the large compliance of PDMS to achieve passive flow regulation without consuming power or requiring active control circuitry. The device features a compliant flap and a rigid block that form a flow constriction in a microchannel within which they are embedded. Under driving pressure variations, the flow constriction is narrowed due to flap deflections, and flow rate changes that would result from the pressure variations are canceled by constriction narrowing effects. As a result, a nearly constant flow rate can be maintained, as will be demonstrated with prototype devices that regulate water flow rates from 0.15 to 1.2 ml/min under driving pressures varying from 100 to 200 kPa.