## 3 Results and Discussion  
Firstly, the measurement system was validated with survey \(\Delta p\) as a function of flow rate for a high viscosity Newtonian liquid: glycerol [18]. The results are presented as dependence of viscosity Equation (3) on the experiment time and shear rate Equation (2) and on the Blasius plot (Figure 3). The range of shear rate planned in the experiment provided the maintenance of laminar flow conditions and the viscosity determined from the results of measurements for glycerol, was not dependent on flow conditions. Linearly decreasing dependence of the flow resistance coefficient is characteristic for a laminar flow area. Results comparision of rheological measurements carried out with the use of a capillary tube rheometer with data from a rotational rheometer requires laminar flow conditions in the capillary. The diagram (Figure 4) shows the Darcy friction coefficient relationship Equation (7) from Reynolds number Equation (6).To analyze the obtained capillary tube rheometer data a recalculation was made. The measurement results of the static pressure drop as a function of the flow rate were transform to values of the tangential stress \(\tau_{w}\) Equation (1), shear rate \(\dot{\gamma}\) Equation (2) and apparent viscosity \(\eta_{app}\) Equation (3). The first step of the analysis to determine the correctness of the of the received measurement data was to make a Blasius plot (Figure 4). This graph allowed for checking of the postulate about the laminarity of the flow. For this, in the coordinate system \(f_{D}(Re)\) on the double logarithmic scale shows all obtained measurement points. As can be seen from Figure 5 points are arranged along a straight line, which proves that the analyzed ranges of shear rate (flow rate) were in the area of laminar flow. For all tested xanthan gum solutions within the analyzed Reynolds numbers \(Re\), the obtained data met the assumptions of the correct rheological measurement. Laminarity Flow Assumption confirmation enabled further analysis and modeling of rheological parameters of the tested fluids. It should also be noted that the knowledge of the Blasius diagram allows to determine the value of the flow resistance coefficient \(f_{D}\) in the laminar flow range for the analyzed fluids. This knowledge is very helpful when designing pipeline installations and the selection of process pumps for non-Newtonian fluids. Additionaly the presented diagram (Figure 4) has a general nature due to the use of dimensional analysis, what allows to be used for all non-Newtonian fluids in the analyzed Reynolds number range. The results presented above are in full accordance with the theory of laminar flow and with data obtained for non-Newtonian fluids [19]. For laminar and a fully developed pipe flow the Darcy friction coefficient is given with the relation: \(f_{D}=\frac{16}{Re_{HBE}}\). In the double logarithmic coordinate system, the change in drag coefficient from Reynolds number in the laminar range is given by a linear relationship. From the rheological point of view, aqueous solutions of xanthan gum are classified as rheounstable shear thinning systems. Their apparent viscosity changes with time and the results of the qualitative hysteresis loop test show energy dissipation during flow. This phenomenon is especially visible during the Kemblowski and Petera experiment. The results of such an experiment carried out on a 0.5% solution using a rotational rheometer are presented in Figure 5.  
As expected, the apparent viscosity measured under constant shear rate conditions decreases with time, and the increase in the shear rate implies a behavior characteristic of shear thinning fluids. The range of apparent viscosity values is consistent with the literature data [10; 11; 14]. The curves showing the increase in apparent viscosity, corresponding to the second part of the experiment, indicate irreversible changes in the structure of the shear fluid [11].