Simulation of Compression Effect on Filling Process in Compression Resin Transfer Molding

Comparative life cycle assessment of low-pressure RTM, compression RTM and high-pressure RTM manufacturing processes to produce CFRP car hoods

11 - Compression resin transfer moulding (CRTM) in polymer matrix composites

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%.

Simulation of Three-dimensional Flow in Compression Resin Transfer Molding by the Control Volume/Finite Element Method

Compression Resin Transfer Molding (CRTM) is a novel variation of traditional Resin Transfer Molding (RTM). It combines features of RTM, with those of traditional compression molding. The resin is ...

In this paper a mathematical model of two-dimensional resin flow through fiber reinforcements in compression resin transfer molding (CRTM) is presented. The preform is partially filled by resin during the injection phase. Then it is compressed by the mobile upper part of the mold. The resin flow in the fiber bed is governed by Darcy's law according to the theory of flows in saturated porous media. The consolidation of the saturated preform is described by the total mass conservation equation. A filling algorithm based on resin conservation on a deformable grid is used to advance the flow front at each time step. Resin pressure and velocity are calculated by the finite element method. The accuracy of the model is verified by evaluation of the resin mass balance, calculation of the resin pressure and progression of the flow front in time. Comparison of predicted results with analytical solutions is also presented.

Due to their light weight and high performance, fiberreinforced composites are being increasingly used in various commercial products in aerospace and automotive industries. Emerging new methods such as liquid composite molding (LCM) and resin transfer molding (RTM) offer an economic, versatile, and efficient means for manufacturing geometrically complex, large composites. RTM process consists of injecting a thermosetting polymer into a mold cavity preloaded with a dry reinforcing preform, which is most often made of E-glass fibers. In RTM, voids and dry spots are reported to originate primarily from mechanical entrapment during mold filling [1, 2]. This entrapment is believed to arise from uneven movement of flow front due to differences in permeability between the fiber tows and the surrounding pore space. Furthermore, several process parameters such as injection pressure, vacuum assistance, fibers surface treatment, and resin viscosity have been shown to influence the overall voidage, as well as the void morphology defined by the size and shape of voids within the composite [3]. Adverse effects of voids in composites have been well documented. For example, a void content as low as 1% is known to result in a decrease in strength up to 30% in bending, 3% in tension, 9% in torsional shear, and 8% in impact [4]. In addition, void presence is shown to affect both the rate and the equilibrium level of moisture absorption [5]. Voids with irregular shapes are also known to induce early crack formation [6]. However, detailed morphology analyses together with spatial variation of voids in resin transfer molded composites are not available. In this work, we present the radial and through-the-thickness variation of void morphology in a resin transfer molded, E-glass/epoxy composite disk. A resin transfer molded composite disk having 152.4 mm diameter is fabricated using a mixture of epoxy resin EPON 815C and curing agent EPICURE 3282 (Shell Chemicals). The molding is achieved by injecting the mixture into a center-gated mold cavity at a constant flow rate of 5.32 cm3/s. The mold cavity is preloaded with 4 layers of E-glass preform (FiberGlast part #250) yielding a fiber volume fraction of 18.1% in a 3.84 mm thick disk. The transient inlet pressure recorded during mold filling is presented in Fig. 1. During filling, inlet pressure

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.

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 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.

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

Cement-based grout has been widely used in various civil engineering applications. The diffusion of cement-based grouts in porous media is an important issue in soil sealing and the estimate of grouting. To better understand the effects of grouting parameters on the viscosity of slurry, the porosity of an injected media and the pressure variations under constant flow rate and constant pressure conditions, a series of laboratory tests were conducted on the fractal characteristics of sand in a column. Additionally, different grouting flow rates and pressures, water/cement ratios and mass fractal dimensions were studied. The experimental results show the following responses: (1) the variation in the diffusion pressure of the slurry under the condition of a constant pressure is clearly different from that under constant pressure. (2) There is a strong correlation between the porosity and water/cement ratio regardless different hydraulic operating conditions, whereby a reduction or increase in the water/cement ratio control the range of the slurry diffusion. (3) Regardless of the hydraulic operating conditions, the grouting pressure presents a nonlinear decreasing law with the increase in distance from the grouting source. (4) An excessive flow rate or pressure is not conducive to the diffusion of slurry.

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 optimum design of a given number of CSTRs in series performing reversible Michaelis-Menten kinetics in the liquid phase assuming constant activity of the enzyme is studied. In this study, the presence of product in the feed stream to the first reactor, as well as the effect of the product intermediate concentrations in the downstream reactors on the reaction rate are investi- gated. For a given number of N CSTRs required to perform a certain degree of substrate conversion and under steady state operation and constant volumetric flow rate, the re- actor optimization problem is posed as a constrained nonlinear programming problem (NLP). The reactor op- timization is based on the minimum overall residence time (volume) of N reactors in series. When all the reactors in series operate isothermally, the constrained NLP is solved as an unconstrained NLP. And an analytical expression for the optimum overall residence time is obtained. Also, the necessary and sufficient conditions for the minimum overall residence time of N CSTRs are derived analytically. In the presence of product in the feed stream, the re- versible Michaelis-Menten kinetics shows competitive product inhibition. And this is, because of the increase in the apparent rate constant K 0 that results in a reduction of the overall reaction rate. The optimum total residence time is found to increase as the ratio (w 0 ) of product to sub- strate concentrations in the feed stream increases. The isomerization of glucose to fructose, which follows a re- versible Michaelis-Menten kinetics, is chosen as a model for the numerical examples. List of symbols CE;0 (mg/l) initial concentration of active enzyme

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