Study of Non-Newtonian viscosity and yield stress of blood in a scanning capillary-tube rheometer (A)

Study of Non-Newtonian viscosity and yield stress of blood in a scanning capillary-tube rheometer (A). Ph.D. dissertation. Mechanical Engineering and Mechanics. 2002.Abstract: The study of hemorheology has been of great interest in the fields of biomedical engineering and medical researches for many years. Although a number of researchers have investigated correlations between whole blood viscosity and arterial diseases, stroke, hypertension, diabetes, smoking, aging, and gender, the medical community has been slow in realizing the significance of the whole blood viscosity, which can be partly attributed to the lack of an uncomplicated and clinically practical rheometer. The objectives of the present study were to investigate the theoretical principles of a scanning capillary-tube rheometer used for measuring both the viscosity and yield stress of blood without any anticoagulant, to experimentally validate the scanning capillary-tube rheometer using disposable tube sets designed for daily clinical use in measuring whole blood viscosity, and to investigate the effect of non-Newtonian constitutive models on the blood rheology and flow patterns in the scanning capillary-tube rheometer. The present study introduced detailed mathematical procedures for data reduction in the scanning capillary-tube rheometer for both viscosity and yield-stress measurements of whole blood. Power-law, Casson, and Herschel-Bulkley models were examined as the constitutive models for blood in the study. Both Casson and Herschel-Bulkley models gave blood viscosity results which were in good agreement with each other as well as with the results obtained by a conventional rotating viscometer, whereas the power-law model seemed to produce inaccurate viscosities at low shear rates. The yield stress values obtained from the Casson and Herschel-Bulkley models for unadulterated human blood were measured to be 13.8 and 17.5 mPa, respectively. The two models showed some discrepancies in the yield-stress values. In the study, the wall shear stress was found to be almost independent of the constitutive model, whereas the size of the plug flow region in the capillary tube varies substantially with the selected model, altering the values of the wall shear rate at a given mean velocity. The model constants and the method of the shear stress calculation given in the study can be useful in the diagnostics and treatment of cardiovascular diseases.Ph.D., Mechanical Engineering -- Drexel University, 200