Effect of Temperature on Density

We see that, for a given pressure and temperature, the greater the molar mass of the gas, the greater its density. Equation 10 also shows that, at constant temperature, the density of a gas increases with pressure. When a gas is compressed, its density increases because the same number of molecules are confined in a smaller volume. Similarly, heating a gas that is free to expand at constant pressure increases the volume occupied by the gas and therefore reduces its density. The effect of temperature on density is the principle behind hot-air balloons the hot air inside the envelope of the balloon has a lower density than that of the surrounding cool air. Equation 10 is also the basis for using density measurements to determine the molar mass of a gas or vapor. 

It should be remembered that density refers to the weight per unit volume of product and specific gravity is the ratio of the density of a product to that of water at some specified temperature. The coefficient of thermal expansion is the effect of temperature on density, and each substance has its own coefficient. Thus, when speaking of specific gravity, it is desirable to state both the sample and water temperatures frequently, they are the same. 

The products of the process have a density of about 0.96 g/cm, similar to the Phillips polymers. Another similarity between the processes is the marked effect of temperature on average molecular weight. The process is worked by the Furukawa Company of Japan and the product marketed as Staflen. 

Figure 10.6. Effect of temperature on the tensile stress-strain curve for polyethylene. (Low-density polymer -0.92g/cm . MFI = 2.) Rate of extension 190% per minute ...

Using the results calculated from the density data, the concentration of the individual components of the methanol/water mixture at different temperatures can be computed thus disclosing the effect of temperature on the elution properties of methanol/water mixtures. The results are shown in Figure 30. 

From this relatively simple test, therefore, it is possible to obtain complete flow data on the material as shown in Fig. 5.3. Note that shear rates similar to those experienced in processing equipment can be achieved. Variations in melt temperature and hypostatic pressure also have an effect on the shear and tensile viscosities of the melt. An increase in temperature causes a decrease in viscosity and an increase in hydrostatic pressure causes an increase in viscosity. Topically, for low density polyethlyene an increase in temperature of 40°C causes a vertical shift of the viscosity curve by a factor of about 3. Since the plastic will be subjected to a temperature rise when it is forced through the die, it is usually worthwhile to check (by means of Equation 5.64) whether or not this is signiflcant. Fig. 5.2 shows the effect of temperature on the viscosity of polypropylene. 

Fig. 3 Effects of pH on the particle yield, size. Fig. 4 Effects of temperature on the particle yield, and number density. (30°C isothermal) size, SDod number density.

The van t Hoff equation also has been used to describe the temperature effect on Henry s law constant over a narrow range for volatile chlorinated organic chemicals (Ashworth et al. 1988) and chlorobenzenes, polychlorinated biphenyls, and polynuclear aromatic hydrocarbons (ten Hulscher et al. 1992, Alaee et al. 1996). Henry s law constant can be expressed as the ratio of vapor pressure to solubility, i.e., pic or plx for dilute solutions. Note that since H is expressed using a volumetric concentration, it is also affected by the effect of temperature on liquid density whereas kH using mole fraction is unaffected by liquid density (Tucker and Christian 1979), thus... 

The effect of temperature on the solubility of 5b was investigated in a series of experiments at the same CO2 density (p = 0.75 gcm ). The temperature that generally may affect the solubility of volatile compounds in compressed fluids has only a minor impact on the solubility of the relatively low volatile complex 5b in the investigated range (Fig. 12). At temperatures between 313 and 333 K, approximately the same quantities of 5b are extracted. 

All surface seawater is presently supersaturated with respect to biogenic calcite and aragonite with Cl ranging from 2.5 at high latitudes and 6.0 at low latitudes. The elevated supersaturations at low latitude reflect higher [COj ] due to (1) the effect of temperature on CO2 solubility and the for HCO3, and (2) density stratification. At low latitudes, enhanced stratification prevents the upwelling of C02-rich deep waters. 

Figure 5(a). Effect of temperature on nucleation for seed density of 200 g/1. Number of crystals 1.2 lm) vs crystallization time. 

With the best electrocatalyst, that is, Pt-Sn (90 10)/XC72, the effect of temperature on the cell voltage E and power density P versus current density j characteristics is shovm in Figure 1.14. It appears clearly that increasing the temperature greatly increases the performance of the cell, from a maximum power density close to 5 mWcm at 50 ° C to 25 mW cm at 110 ° C, that is, five times higher. 

Thermal Expansion. Most manufacturers literature (87,119,136—138) quotes a linear expansion coefficient within the 0—300°C range of 5.4 x 10"7 to 5.6 x 10 7 /°C. The effect of thermal history on low temperature expansion of Homosil (Heraeus Schott Quarzschmelze GmbH) and Osram s vitreous silicas is shown in Figure 4. The 1000, 1300, and 1720°C curves are for samples that were held at these temperatures until equilibrium density was achieved and then quenched in water. The effect of temperature on linear expansion of vitreous silica is compared with that of typical soda—lime and borosilicate glasses in Figure 5. The low thermal expansion of vitreous silica is the main reason that it has a high thermal shock resistance compared to other glasses. 

Figure 36-7 shows the effect of temperature on the densities of aqueous hydrazine solutions... 

The purpose of this study was to clarify the change of density with species, heating rate, and temperature under oxygen-deficient conditions. The major constraint was an arbitrary specimen size (10-mm cube), based on the observation that thicknesses equal to or greater than about 6 mm (approximately the half-thickness of the cubes) produce consistent charring rates (5). The effect of thickness on density changes is currently being studied. 

The results of the model simulation are given in Figures 6, 7 and 8. Figure 6 shows the effect of density on the kinetics of coal liquefaction at temperature of 698 K. It is very clear that conversion increases with an increase in density and it is consistent with the hypothesis made earlier on coal liquefaction with a supercritical fluid. Figure 7 shows the effect of temperature on the kinetics of coal liquefaction at density of 0.601 g/cc. It is evident that conversions are higher at higher temperatures and lower reaction times but at longer reaction times due to condensation reactions, a decrease in rate with temperature is observed. 

The study of adsorption kinetics of a surfactant on the mineral surface can help to clarify the adsorption mechanism in a number of cases. In the literature we found few communications of this kind though the adsorption kinetics has an important role in flotation. Somasundaran et al.133,134 found that the adsorption of Na dodecylsulfonate on alumina and of K oleate on hematite at pH 8.0 is relatively fast (the adsorption equilibrium is reached within a few minutes) as expected for physical adsorption of minerals with PDI H+ and OH". However, the system K oleate-hematite exhibits a markedly different type of kinetics at pH 4.8 where the equilibrium is not reached even after several hours of adsorption. Similarly, the effect of temperature on adsorption density varies. The adsorption density of K oleate at pH 8 and 25 °C is greater than at 75 °C whereas the opposite is true at pH 4.8. Evidently the adsorption of oleic acid on hematite involves a mechanism that is different from that of oleate or acid soaps. 

Porter, N.C. and Lammerink, J.P. (1994) Effect of temperature on the relative densities of essential oils and water. Journal of Essential Oil Research 6(3), 269-277. 

The density of the melt is 1.89-1.94 gem-3. During electrolysis, along with sodium metal, small quantities of calcium ( 4 wt%) are deposited at the cathode. Calcium has a melting point (804°C) far higher than sodium and a low solubility in sodium (see Table 13) [302], Because of that at the cathode a solid alloy phase Na-Ca is accumulated and this blocks the circulation of the electrolyte in the electrolysis cell and the removal of sodium from the cell. Also this solid alloy sometimes causes short-circuiting in the electrolysis cell. Sodium obtained by electrolysis is cooled to 110-120°C and filtered for the removal of calcium. The effect of temperature on the solubility of calcium in sodium [302] is shown in Table 13. At 110°C the calcium content in sodium is reduced to <0.04%. 

However, if the solvent is a supercritical fluid (SCF), it is possible to examine the effects of temperature and density on VER independently. The role of other solvent properties, such as viscosity, dielectric constant, and correlation length, can also be studied. A supercritical fluid is a substance that has been heated above its critical temperature (Tc) and, therefore, no longer undergoes the liquid/gas phase transformation. A typical phase diagram for an SCF is shown in Fig. 1. In an SCF, it is possible to fix the temperature and vary the density continuously (by varying the pressure) from gas-like densities to liquid-like densities. It is also possible to vary the temperature at fixed density. 

The PLC-8 fractionation method is shown to be an appropriate procedure for analyzing the effects of temperature, solvent density and addition of cosolvents on the characteristics of the extracts, allowing the maximization of specific chemical fractions. 

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