Wan Ahmad Kamil Wan Abdullah

Impacts of Cooling Rates on Voids in Waxy Crude Oil under Quiescent Cooling Mode

When waxy crude oil becomes a gel, predicting a restart pressure in pipelines has been a challenge. The formation of gas voids within the gel following sufficient cooling has an impact on the restarting pressure. This study is aimed at analyzing the effects of cooling rates on voids in waxy crude oil gel using Magnetic Resonace Imaging (MRI) technique. The flow loop rig simulating offshore oil production was designed. Waxy crude oil underwent cooling through the same temperature range to observe the effects of cooling rates on voids formed. Cooling rates were found to have different influence on the formation of voids. A maximum total voids volume of 6.96% was formed at cooling rate of 1.00°C/min. Cooling rate of 0.55°C/min produced a minimum voids volume of 5.74% near pipe wall. Higher cooling rates generally produced higher voids volume near pipe wall and in entire pipe. However, there was no definite trend observed for the voids around pipe core at which slower cooling rates were also observed forming higher voids volume.

Effect of anastomosis angle on hemodynamic of side-to-end radiocephalic arteriovenous fistula (RCAVF)

Radiocephalic arteriovenous fistula (RCAVF) at wrist is the chosen access for hemodialysis. Most studies describe access complications without considering the effect of the anastomosis angle. In the present investigation, eighteen three-dimensional, simplified models of RCAVF were used to analyze the hemodynamic effect of anastomosis angle under fixed flow rate of 900 ml/min, corresponding to Reynolds number 950. EFD. Lab software was used in the flow simulation with steady flow conditions. The results show that high pressure drop was observed for RCAVF with smaller anastomosis angle. However, for cases with anastomosis angle larger than 45°, pressure drop became relatively constant. The results also show that large vortices appeared in cases with angle smaller than 30°. For cases with angle larger than 60°, low flow zone appeared at the inner wall that may lead to promotion of intimal thickening and formation of stenosis. Overall, for average flowrate, it is recommended that anastomosis angle should be maintained between 45° and 60° to minimize adverse effects.

Diffusion tensor imaging and tractography for the assessment of leukoaraiosis

Feasibility of acquiring DTI data and constructing fiber tracts for leukoaraiosis study was evaluated. Two healthy male volunteers with either occipital leukoaraiosis or without white matter lesions participated in the study. All data were obtained using GE 1.5 Tesla MRI System, single-shot echo-planar imaging sequence and the following protocols: TR/TE = 17 000/ 101.1 ms, b-value = 0 and 1000 s/mm2, 30 diffusion encoding directions with 3 sets of unweighted images and 2.0 mm isotropic voxel resolution. The total scan time for each subject was 9.38 minutes. Results obtained showed capability of DTI to distinguish leukoaraiosis from normal white matter. Fiber tractography exhibited a good structural differentiation of nerve fibers in the white matter region. The results were further strengthened by quantitative parameters demonstrating significant differences (p <; 0.01) between pathological tissues and normal tissues in the occipital white matter. In conclusion, acquiring DTI data and constructing fiber tractography for assessment of leukoaraiosis was found to be feasible. However, several technical aspects need to be taken into considerations in order to ensure accuracy of the results.