## 6 Discussion  
Treating patients with right ventricular dysfunction is a complex clinical task. These patients are at a constant risk of complications such as systemic venous hypertension, thromboembolism, and congestive heart failure [17], therefore, the hemodynamics restoration of the cardiovascular system (CVS) for patients with a single-ventricular heart is an important scientific and practical task. In order to restore the hemodynamics of CVS, it is necessary (I) to increase the efficiency of passive blood transfer to CVS, and (II) to provide mechanical support for circulation. The combination of these two approaches is designed to relieve the single-ventricular heart and reduce the risk of heart failure. In this work, the first (I) approach is considered. Computer simulation of the flow in various configurations of TCPC allows one to predict the flow behavior with high accuracy from the distribution of the vector velocity field point of view. This is confirmed by the experiment. Due to this fact, it is possible to clearly observe low flow rates and recirculation zones. In TCPC-1 and TCPC-2 configurations, the blood lines intersect at right angles, which leads to a sharp increase in the velocity value in the region where fluid from IVC and SVC flows towards each other. In case of TCPC-2, flows are distributed more smoothly, however the presence  
Figure 13: Comparison of power loss of TCPC systems for experimental setup (dashed line) and computational fluid dynamics simulation (solid line). Yellow, green, and red lines correspond to TCPC 1–3 models, respectively. of a direct connection leads to the appearance of a recirculation flow when passing from the IVC and SVC. The graphs showing the comparison of velocity profiles for TCPC-1 and TCPC-2 models demonstrate that in cross-sections closer to the flow connection zone, differences in the behavior of velocity profiles are observed. We assume that this is due to the more chaotic behavior of the incoming flows. Moreover, at a distance of two diameters from the walls along the pulmonary axis, the profiles acquire a characteristic parabolic shape, indicating the formation of a laminar type of flow. In case of TCPC-3, due to the smoother connections of the blood lines, the flow behavior significantly differs from the other two configurations. A significant decrease in flow rate was noted during the transition of the flow from IVC to LPA and RPA. This is due to an increase in the total cross-sectional area of the channel due to its bifurcation. The coincidence of the experimental graphs of the velocity profiles with the graphs obtained as a result of the simulation confirms that the flow behavior in all sections of the hydraulic system is smoother. As a result, TCPC-3 configuration has higher energy characteristics and lower hydraulic resistance of the system. Considering the hydraulic system of TCPC in terms of hydraulic losses, TCPC-3 also has a significant advantage at a flow rate of 2.5 L/min compared to TCPC-1. As a drawback of TCPC-3 system, one can note the lack of symmetry of the velocity field during flow separation at the center of the joint. As a result of this, a decrease in the flow rate is observed in one channel, which may adversely affect the process of thrombosis, but this requires a more detailed study. Additionally, this separation of the flow leads to the fact that SVC and IVC flows practically do not mix with each other. This observation also requires additional research. The energy efficiency of Fontan circulation was described elsewhere [6]. There were discussions on the limitations of energy loss calculations with various assumptions, e.g., steady flow conditions as performed in this study. CFD analysis method of hemodynamic characteristics is used in the majority of studies. In present work, we used both CFD and studies on physical TCPC models, that allows to compare theoretical and practical models. As opposed to previous studies, velocity distribution in the cross-sections of TCPC models were obtained.