Saturation degree

Recently, the effect of the lipid composition on the permeability in PAMPA was investigated [129], By varying the phosphate head group and the saturation degree of the acyl chain, differences in transport were observed for a set of five model compounds, which was due to changes in membrane fluidity and ion pairing [129],... 

However, the intercept of the straightline d/dt (In [CIO]) = f ([DMS]) -, which was found to be (80 5)s indicates a substantial wall reactivity of ClO in the presence of DMS. Some dependence of CIO wall loss with DMS concentration can exist if the reactor wall is not saturated with DMS in the range of DMS concentration used to derive kj from the plots - d In [QO] /dt = f([DMS]). In such a case k2 is an upper limit of the rate constant of the homogeneous reaction. In the absence of any indication of the saturation degree of the reactor wall in this study, k should be considered as an upper limit for the rate constant. Such complications have not been observed for the reaction BrO + DMS —> products (3). For DMS and BrO concentrations ranging from 15 x 1014 to 7.9 x 1014 molecules cm 3 and from 1.33 x 1013 to 1.55 x 1013 molecules cm 3, respectively, die following rate constant was determined at 298 K and 1.4 Tom... 

The filter cakes obtained from mineral and chemistry industrials are mostly wastes and sent to the transportation and storage without any thermal operations. The stability properties of the filter cakes such as tensile, shear and compression strength are very important for the deposit of slimes (5). The shear strength of the mineral filter cakes is influenced by the particle size, shape and surface tension as well as the applied pressure and the saturation degree (6, 7). It was mentioned in the recent studies that particle shape has also a very substantial effect on the shear strength of the cake. The shear strength of the mineral filter cake is defined as follows F... 

Figure 1. Tensile strength of calcite agglomerate as a function of saturation degree, Schubert Diagram(8).

To determine the changes in the shear strength of the filter cakes of dolomite and quartz experiments have been done in the seven different saturation degree under three different pressures. The results are given in Figure 5 and 6 for dolomite and quartz, respectively. 

Table 3 shows the effect of the particle size on the shear strength. For the effect of the particle size on the shear strength in the zero saturation degree (completely dried filter cakes) the following equation has been found. 

As it can be seen from the Table 3 that for the saturation region, S=0%, the shear strength is independent of the shape factor, namely independent of the type of the mineral. In contrast to that, as the saturation degree increases, the shear strength is absolutely dependent on the shape factor of the mineral particles. The reason is probably the change in the adhesion forces and liquid bridges between the particles with different shape factors in the more saturated regions. 

The surfactant treatment, on the other hand decreased the shear strength of the cakes very sharply. Although the surfactant helps the filtration operation giving less residual moisture contents in the cakes, it was not possible to obtain saturation degrees higher than 50 and 60 % for kaolin and calcite when using the surfactant. 

S =1. These cakes were then dried for a definite time in the open atmosphere in the laboratory to obtain partially saturated cakes. The required time to reach a definite saturation degree was determined experimentally. The shear strength measurements of the produced cakes were made then using a Fischer test apparatus (6,7) shawn in Fig. 1. All experiments (production and the shear strength measurements of the cakes) have been done at room temperature. 

The saturation degree, S is defined as the ratio of the liquid volume (V ) to the pore volume (Vp) in the cake and it is calculated as follows ... 

In order to see the effect of the pressure and the particle size on the shear strength for all these minerals for a given saturation degree, the data given in the Tables 2-5 can graphically be represented as in the Fig. 11. 

It is clear from the data given in Table 6 and in Fig. 12 that, calcite, quartz and kaolin are drastically affected with the addition of the surfactant and their saturation degrees decreased down to 60 % maximum. It was not possible to obtain for these three minerals the saturation higher than 65 % and the cakes were dry. Ti02, on the other hand was the exception and it was possible to obtain about 100 % saturation for this... 

Thus, the substitutional carbon is reduced and the same amount of SiC particles is generated in the melt. The formation rate of SiC particles and the destruction rate of substitutional carbon are equal and proportional to the super-saturation degree of substitutional carbon and the speed of the chemical reaction (4.3) ... 

Plasticizers give plastic properties to the pciste. Viscous and wetting polymers are used in this case. They also have the capability of holding water in the paste. The plastic property can be characterized by the saturation degree Sd ... 

The acidity of the soil may conveniently be characterized by the content of metal ions, relative to the total cation exchange capacity of the soil. In the acid types of soil considered here, this base saturation degree is usually below 10%. The degree of base saturation will be reduced when (1) the roots take up exchangeable cations from the soil, and (2) when accumulation of dead plant material increases the amount of humus, and thereby the cation exchange capacity. To a certain degree, both of these processes are reversible, but if plant products are removed from the area without application of fertilizers, manure or lime, this represents an acidification by reducing the available supply of cations. 

Simulations of marine-meteoric mixing (e.g. Plummer, 1975 Wigley Plummer, 1976) predicted calcite oversaturation in waters with 20-70% sea water. However, the saturation degree of the mixed waters varies depending on the initial calcite saturation index, C02 and temperature. Nevertheless, predictive models constructed by Frank Lohmann(1995) for low-Mg calcite precipitation in... 

For stationary flow conditions, D and v are independent parameters describing the transport process. In transient conditions, however, the relationship between D and v must be taken into account. Experimental evidences show that for transport in homogeneous saturated porous media, D is a monotoneous function of v. In unsaturated media, this relation becomes extremely complicated since the transport volume 6<,u changes with the water flux. Therefore, the structure of the water fdled pore-space and, hence, the flow field depends on the saturation degree (Flury, M. et al. (1995)) so that the variance of local velocities and the mixing time cannot be simply related to the mean advection velocity. As a consequence, no validated theoretical models exist to calculate the relationship between D and v for unsaturated soils and the dispersivity X cannot be considered to be a material constant, i.e. independent of 0. 

The main results of the calculations, compared to referential cases, are reported in table 4 and S. No visible heat-pipe effect is present the saturation degree does not decrease much more than 0.05 compared to the reference value. Thus, the desaturation of the EB at the contact with the canister can be neglected in every case. The absence of a heat-pipe effect is related to clay-specific behaviour. 

Figures 3 and 4 present the results of the simulation for the mid plane of the deposition hole 1, regarding temperature and saturation degree. These results correspond to the location of some sensors for which some measurements are already available. Degree of saturation measurements have been obtained from relative humidity transducers by means of the psychrometric law.

Saturation degree evolution has been reproduced reasonably. It should be pointed out that near the heater a wetting-drying cycle is observed, which is typical of coupled processes. Indeed, that point first increases its saturation degree, due to the water vaporisation that moves from the heater to the outer bentonite areas, and after a few days it dries because of this effect takes place eventually on that point. Finally water from the rock saturates the bentonite and the degree of saturation increases in a continuous manner. This coupling between temperature and water flow (in liquid or gas form) gives this cyclic response in the bentonite zone closer to the heater. This effect depends partly on the amount of water available for vaporisation. In this case, it was assumed that the slot between heater and bentonite blocks (1 cm) was filled initially with water, because of the initial emplacement conditions of the hole. 

Boundary conditions are as follows Temperature and hydraulic head are fixed on the top and the bottom boundary and no flow boundaries for water and heat are specified on the other boundaries. And slide boundaries are given to all the boundaries. These boundary conditions satisfy the situation that disposal pits are arrayed at regular intervals. Initial state is assumed the time that the repository is closed as initial conditions, hydraulic head in rock mass is 500 m without the effect of excavation, water content of the buffer is 14 %, water content of the backfill is 23% and temperature is 30 °C in all the domain. Heat flux from the waste canister is given as Figure 3. The points A to C in Figure 2 are the monitoring points for temperature and saturation degree. A is close to the waste canister, B is located at the center of the buffer and C is located at the rock close to the buffer. 

Figure 4 and Figure 5 show the time histories of temperature and saturation degree at the monitoring... 

We present now the extension of the constitutive equation (7) to partially saturated porous media. The material is assumed to be saturated by a liquid phase (noted by index w) and a gas mixture (noted by index g ). The gas mixture is a perfect mixture of dry air (noted by index da) and vapour (noted by index va). Based on most experimental data of unsaturated rocks and soils (Fredlund and Rahardjo 1993), and on the theoretical background of micromechanical analysis (Chateau and Dormieux 1998), the poroelastic behaviour of unsaturated material should be non-linear and depends on the water saturation degree. We consider here the particular case of spherical pores which are dried or wetted under a capillary pressure equal to the superficial tension on the air-solid interface. By adapting the macroscopic non-linear poroelastic model proposed by Coussy al. (1998) to unsaturated damaged porous media, the incremental constitutive equations in isothermal conditions are expressed as follows ... 

The parameter b denotes the Biot s coefficient of porous medium and S the water saturation degree, and < i the porosity occupied by gas... 

Equation(ll), the variable defines the capillary pressure. The parameter is Biot s modulus related to capillary pressure, which is a function of water saturation degree through the water retention curve... 

In most unsaturated rocks and soils, elastic properties and plastic flow depend on the capillary pressure which is related to water saturation degree through water retention curve (Fredlund and Rahardjo 1993). In this work, for simplicity, we neglect the variation of elastic constants with capillary pressure. However, we intend to account for the influence of capillary pressure on plastic behaviour of argillites. Only a small number of triaxial compression tests with different water saturation degrees are available. We can only provide a first approximation of such a influence. We consider that the failure parameter A (see Equation 13) linearly increases with capillary pressure ... 

In this section, we present some numerical simulations of triaxial compression tests performed on argillites in natural saturation condition and in different water saturation degree. 

On Figure 4, we present simulations of triaxial compression tests performed with different water saturation degrees. Even if constant elastic parameters have been used, there is a qualitatively good agreement between simulations and data. Mechanical strength of material increases when saturation degree decreases due to effect of capillary pressure. 

Figure 4 Simulation of triaxial compression tests with different water saturation degrees...

---