Results and Discussion
The results obtained during the experimental studies with their discussions are presented in this section.
WAT and Pour Point. The density meter used in the experiments provided WAT results comparable to those from the CPM. Using the density meter, however, had an added value of providing the density vs. temperature profi les of the samples, which could be used for wax deposition modeling purposes. The samples in the density meter were cooled at a rate of 0.5°C every 3 minutes, and their densities were determined by the meter, which related the oscillation frequency of its U-tube to the test fl uid density. Sample viscosity effects introduce an error in the order of k ≈ 0.05 where k is the error in kg/m and η is the viscosity in mPa•s .Hence, two curves were obtained, namely an uncorrected density curve and a second density curve, corrected for viscosity effects. A typical plot obtained from the density meter is presented in Fig. 4, where the WAT is identifi ed as the point of slope change in the density profi le as the sample cools from its initial temperature.
However, for samples with low wax content, delineating this point may be more difficult (Fig. 5). An additional plot of the slope (ρ1-ρ1)/(T1−T1) vs. temperature (T2) (Fig. 6) was used to determine the WAT where the deviation from Newtonian behavior was captured as distinct peaks in the plot. The WAT corresponds to the temperature (T1) preceding the very first peak. This meth-odology in addition to the CPM has been used and proven to be a good alternative for the WAT measurements. A comparison of WAT values from the density meter and CPM are presented in Table 2, indicating in excellent agreement between the results.
The pour point (PP) was identified on the plots as the point where the corrected and uncorrected density curves crossed over, and this point preceded a peak in the slope vs. temperature plot (Fig. 6). It is interesting to observe that, above the WAT, the uncor-rected density curve generally maintains higher values than the corrected curve. However, at PP, because of viscosity effects, the corrected density values exceeded those of the uncorrected density curve. This effect can be likened to the crossover of the viscous and elastic moduli during oscillatory gelation tests at the gelation temperature. The pour point values obtained from the density meter have compared very closely with results from standard methods.