Cold flow parameters

The cooling scan of the pure compounds (Fig. 13.3) shows a broad exothermal peak corresponding to the crystallization of paraffins (for DF) or FAME (for biodiesels). The first cold flow parameters obtained by this analysis are the onset crystallization temperature (CT) and the slope of crystallization. The CT is determined by the intersection of the tangents to the base line and the exothermal peak. The cooling rate should be as low as possible to get close to the equilibrium temperature solid-liquid. 

As shown in Table 13.2, the unsaturates present lower melting and crystallization points (temperatures and enthalpies) than saturates. Therefore, it can be assumed that the cold flow parameters will be better (i.e. low CPs and PPs) for the rapeseed oil methyl ester as it contains more unsaturated compounds compared to the palm oil methyl ester. This affirmation is also supported by Knothe [29] who stated that... 

Even if the enthalpy of 210 J/g is not the corresponding value for the crystallization enthalpy of MEl and ME2 it has been chosen in order to compare the variation of the crystallized fraction for all studied blends. The ME2 and DF have similar low percentages of crystals at —15 °C. However, ME 1 shows a high percentage of crystals at -15 " C. The cold flow parameters of pure compounds are listed in Table 13.3. The CFPP and PP were determined by DSC at 0.45 and 1 % of crystals, respectively, using the same AHcryst as mentioned above. Claudy et al. [9] realized a study on 40 different diesel fuels and established correlations between CFPP and PP determined by ASTM standards and CFPP and PP obtained by DSC measurements. The best correlations were obtained at 0.45 and 1 % of crystals, respectively. In our study, the same values have been retained in order to compare the samples. 

Table 13.3 Cold flow parameters of pure compounds (AHcryst. = 210 J/g)...

The cold flow properties of diesel fuel and biodiesel blends are given in Table 13.4. As can be seen from these results, there is almost no influence when ME2 is blended with DF. This situation changes when MEl is blended with DF, where the quantity of precipitated crystals and the cold flow parameters are higher than those of neat DF and increase when MEl is increased from 10 to 30%. As was expected after the analyses of the pure compounds, blends of MEl with DF have lower cold flow parameters compared with blends of ME2 with DF. 

For any diesel fuel, the crystal size at low temperature is a critical parameter. Indeed, the standard tests for the determination of cold flow parameters are done on a 45 ftm diameter filter. In reality, the injection pump filter pores can have different sizes depending on the vehicle make, varying from approximately 1 5 p.m. Thus, the size of paraffin or FAME crystals needs to be drastically reduced. 

These highly amorphous elastomers have relatively low Tt values (—73 C) and tend to crystallize when stretched. The cold flow of these thermoplastic polymers is reduced when they are crosslinked (vulcanized) with a small amount (2%) of sulfur. Since these polymers of isoprene have a solubility parameter of 8.0 H, they are resistant to polar solvents but are soluble in many aliphatic and aromatic hydrocarbon solvents. The cross-linked derivatives swell but do not dissolve in these solvents. 

Although general treatments of the flow in fluidized beds of coarse particles, in view of the difficulty of the problem, will only evolve slowly, there have been some promising developments. These include the success achieved in correlating heat transfer data (7, 113., 114) and the development of scaling parameters that permit the use of cold flow models to study many of the characteristics of AFBC s (114%115). 

These plastics represent at least 90wt% of all plastics consumed worldwide. Unlike thermoset plastics, they are in many cases reproccssable without any or serious losses of properties. There are those than can have limitations of heat-distortion temperatures, cold flow and creep, and are more likely to be damaged by chemical solvent attack from paints, adhesives, and cleaners. When injection molded, dimensional integrity and ultimate strength are more dependent on the proper process control molding parameters than is generally the case with TSs. 

Exact analytical solutions to the governing equations which produce the penetration trajectory are extremely difficult to obtain. For this reason, empirical penetration equations based on experimental data correlations are most often presented in the literature. These best-fit equations contain the dominant parameters which have been experimentally determined to significantly affect the penetration. To detail the specific ACR penetration phenomena, a series of cold-flow and hot-test experiments was conducted. 

Entrainment and important fluidised bed parameters were measured for a I l /h and a 5 kg/h fast pyrolysis reactor. In addition, a cold-flow model of the Ikg/h rig was built to study fluidisation aspects that were difficult to obtain from the pyrolysis reactor. The cold-flow model was subsequently modified to validate the model s capability to deal with changes in the reactor geometry. The cold flow rig is illustrated in Figure 1. 

A particular set of cold flow simulations were run with the physical properties and model parameters presented in table 10.5. 

During a model study, wind conditions and stack diameter are appropriately scaled down to ensure dymamic similarity. This suffices only the requirements for cold flow conditions. In a burning environment, however, parameters such as fuel pyrolysis time that depends only on fuel chemistry and temperature [66] are also important to be considered. In addition, buoyancy effects are generally neglected in model flares. For all these reasons, the model results must be compared with field test data to validate the correlations developed and develop scaling laws. Due to the unavailability of such data, quantitative scaling laws are yet to be developed. To date, only a few model test results have been compared with field test data. For instance, Schwartz and White [69] compared predictions of radiative emission from various models with field data. Gook et al. [90,91] conducted field-scale... 

Remarkably, this relation turned out to be valid for the deformation ( cold flow ) of solid amorphous and semi-crystalline polymers, both isotropic and slightly drawn ones, as well as at any temperature below Tg. The values of kinetic parameters. 

For the transfer tests and liquid acquisition systems, COLD-SAT parameters from all four studies are compiled in Table A.2. Wherever parameters were not readily available, assumptions were made to derive those parameters. For example, MEOPs were determined from the anticipated maximum ranges of tank pressures during pressurization/ outflow tests. Flow rates were determined from LAD or no vent fill (NVF) subsystem requirements. Re numbers in the transfer line were determined based on total flow delivery from the LAD subsystem and the internal diameter of the pipe. Line velocities were determined using conservation of mass. 

In particular, the curve for model B exhibits a sharp pulse at the beginning caused by the bubbles which flow directly upwards without exchanging with the dense phase. By studying the dependence of model parameters upon the size of the reactor, upon particle size distribution and upon experimental conditions in cold flow experiments, it is possible to establish correlations for scaling-up the reactor. This method was successfully used in the design of commercial reactors [ ] [sj. The way to use this kind of model for predicting chemical conversion is discussed in Sec. 4. 

In addition to scale-up difficulties, there are a number of problems related to the stable operation of a bubble column associated with hydrodynamics. For example, consider the important commercial application of bubble columns in hydroprocessing of petroleum resids, heavy oils and synthetic crudes. Hydrodynamic cold flow and hot flow studies on the Exxon Donor Solvent coal liquefaction process (Tarmy et al., 1984) showed that much of the literature correlations for the hydrodynamic parameters (holdup, interfacial area and dispersion coefficients) obtained with cold flow units, at ambient conditions, are not applicable for commercial units operating at relatively higher pressures. In addition, the flow pattern in commercial units was considerably different. In the hydroprocessing of petroleum residues by the H-Oil and LC-Fining processes, refinery operations have experienced problems with nonuniform distribution of gas and liquid reactants across the distributor, maintaining stable fluidization and preventing temperature excursions (Beaton et al., 1986, Fan, 1989 and Embaby, 1990). Catalyst addition, withdrawal and elutriation have also been identified as problems in these hydrotreaters. 

Extending the a-olefin to RCH = CH2, where R is a C2—Cg alkyl group, one obtains copolymers with superior processibility and physical properties, including high creep resistance and low cold flow [30c,d]. Many other cyclic and polycyclic dienes have been copolymerized with ethylene, propylene, and various a-olefins using conventional Ziegler-Natta catalysts. Of these, compounds (34-40) yield products displaying attractive physico-mechanical parameters [30e-l]. 

In the literature numerous two-fluid models of different complexity have been proposed to predict the fluidized bed reactor cold flow and reactive flow behaviors. Four decades ago emphasis was placed on the modeling of the velocity fluctuation co-variance terms in the dispersed particle fluid phase momentum equations. The early one-dimensional models were normally closed by an elasticity modulus parameterization for the particle phase collisional pressure and a constant viscosity parameter for the corresponding shear stresses. Later, with the improved computer memory and speed capacities, multi-dimensional flow models and more advanced model closures were developed based on the kinetic theory of granular flow (KTGF). Moreover, the... 

Derived flow parameters In the hot legs and steam generators are presented and compared with the experimental results In Table 1. The hot leg results Include the vapor temperatures and mass flow rates. The hot and cold vapor temperatures are overpredicted, on average, by less than 4% and 5%, respectively. The hot leg temperature differences are overpredicted by 4%, on average, and the mass flow rates are underpredicted by approximately, 4%. 

The oxidative stability of biodiesel has been the subject of considerable research as it is, besides cold flow, one of the major technical issues with biodiesel. Some recent overview articles are (Knothe, 2007 Dunn, 2008 Jain and Sharma, 2010 Xin and Saka, 2010). This issue affects biodiesel primarily during extended storage. The influence of parameters such as the presence of air, heat, traces of metal, antioxidants, and peroxides as well as the nature of the storage container was investigated in the aforementioned studies. Generally, factors such as the presence of air, elevated temperatures, or the presence of metals facilitate oxidation. Studies performed with the automated Oil Stability Index (OSI) method confirmed the catalyzing effect of metals on oxidation, however, the influence of compound structure of the fatty esters, especially unsaturation, as discussed later, was even greater (Knothe and Dunn, 2(X)3). 

Selection of cold-model parameters by means of the above dimensionless groups is very simple. Once the fluidizing gas and convenient conditions (for example, ambient) have been chosen, the particle density is fixed by the density number De, after which its diameter follows from the Galileo number Ga. The length number Le and flow number FI then dictate the size of the scale model and the operating fluid flux respectively ... 

ICP-SFMS (Thermo Finnigan, Flement) with cold vapour generation was developed with a guard electrode and a gold amalgamation device using an Au-sorbent for sample pre-concentration to improve the sensitivity. Instrumental parameters of ICP-SFMS such as take-up time, heating temperature of Au-sorbent, additional gas flow, and sample gas flow were optimized. Detection limit calculated as 3 times the standard deviation of 10 blanks was 0,05 ng/1, RSD = 7-9 %. 

Galvanic corrosion typically involves two or more dissimilar metals. It should be recognized, however, that sufficient variation in environmental and physical parameters such as fluid chemistry, temperature (see Case History 16.3), flow velocity, and even variations in degrees of metal cold work can induce a flow of corrosion current even within the same metal. 

Fully developed nonisothermal flow may also be similar at different Reynolds numbers, Prandtl numbers, and Schmidt numbers. The Archimedes number will, on the other hand, always be an important parameter. Figure 12.30 shows a number of model experiments performed in three geometrically identical models with the heights 0.53 m, 1.60 m, and 4.75 m." Sixteen experiments carried out in the rotxms at different Archimedes numbers and Reynolds numbers show that the general flow pattern (jet trajectory of a cold jet from a circular opening in the wall) is a function of the Archimedes number but independent of the Reynolds number. The characteristic length and velocity in Fig. 12.30 are defined as = 4WH/ 2W + IH) and u = where W is... 

Convection requires a fluid, either liquid or gaseous, which is free to move between the hot and cold bodies. This mode of heat transfer is very complex and depends firstly on whether the flow of fluid is natural , i.e. caused by thermal currents set up in the fluid as it expands, or forced by fans or pumps. Other parameters are the density, specific heat capacity and viscosity of the fluid and the shape of the interacting surface. 

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