Cloud point apparatus

Three different isothermal crystallization experiments were performed in this work classical static (i.e., quiescent) crystallization in the DSC apparatus, dynamic crystallization with the apparatus described above, and dynamic-static crystallization. Dynamic isothermal crystallization consisted in completely solidifying cocoa butter under a shear in the Couette apparatus. Comparison of shear effect with results from literature was done using the average shear rate y. This experiment did not allow direct measurement of the solid content in the sample. However, characteristic times of crystallization were estimated. The corresponded visually to the cloud point and to an increase of the cocoa butter temperature 1 t) due to latent heat release. The finish time, was evaluated from the temperature evolution in cocoa butter. At tp the temperature Tit) suddenly increases sharply because of the apparition of a coherent crystalline structure in cocoa butter. This induces a loss of contact with the outer wall and a sharp decrease in the heat extraction. 

Figure 4.3. Apparatus for the determination of cloud point and pour point...

The ceU, which is provided with sapphire windows and magnetic stirring, is a modification of the one described by Van Hest and Diepen [4]. A detailed description of this apparatus and the experimental techniques used is given by De Loos et al. [5]. The cloud-point pressures of mixtures of known composition have been measured as a function of temperature by visual observation of the onset of phase separation of the homogeneous phase by lowering the pressure (cloud-point isopleths). The cloud-points have been determined with an absolute error of 0.03 K in temperature and 0.1 MPa in pressure. 

Fig. 8.1 Schematic view of the Cailletet apparatus used for the cloud-point measurements, with 1. mercury,...

Kennis et al. [40] reported on the influence the addition of nitrogen exerts on the location of the miscibility gap for linear polyethylene in -hexane at pressures up to 7.5 MPa in the temperature range 393-453 K for small concentrations of nitrogen. Liquid-liquid phase boundaries (cloud points) were determined with the aid of a Cailletet-like apparatus in which the phase separation was observed visually. Experimental cloud-point isopleths (/ vs r at constant composition) for linear polyethylene in -hexane were reported to be nearly parallel values for dpjdT are positive which indicates upper critical solution pressures (at constant T) and lower critical solution temperatures (at constant p) (Fig. 5). The addition of small amounts of nitrogen shifts these isopleths to higher pressures and lower temperatures. 

Determination of Cloud Point. The apparatus used to measure the cloud point includes a high-pressure stainless-steel cell, a Sybron/Brinkmann PC801 Colorimeter, and an x-y recorder. The high-pressure stainless-steel cell... 

Effects of Divalent Ion Concentration and Degree of Hydrolysis. Fig. 4 shows the cloud point of Polyacrylamide A as a function of initial degree of hydrolysis and divalent ion concentration. For hardness levels below 20 ppm, the cloud point exceeds the capability of our apparatus, 204°C [400°F], for all degrees of hydrolysis. At hardness levels above 20 ppm, cloud point decreased progressively as the hardness level and the degree of hydrolysis increased. For example, for a 1,000-ppm hardness level, the cloud point was 141 °C [286°F] at 39%... 

Although the principle of obtaining the spinodal data or cloud points (as described in Sections 4.4 and 4.5 respectively) has not been changed since the simple Mark I PICS instrument was introduced, a new version of the Mark III apparatus containing the most recent advances in software and hardware applications is now developed and commercially available. The description of this modified Mark III instrument is given in Section 4.6. 

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