This document discusses fluid flow concepts like laminar and turbulent flow as well as key fluid parameters. It defines laminar flow as fluid particles moving parallel to tube walls without mixing between layers, while turbulent flow has chaotic and irregular particle trajectories. The Reynolds number is used to characterize flow, with values below 2000 indicating laminar flow and above 3000 indicating turbulent flow. A transitional region exists between 2000-3000. The document also provides some details about blood as a fluid in the human body, including its volume and flow rate, as well as definitions related to rheology, the study of fluid properties.

1. Bernoulli’s equation
Let’s discuss ideal fluid stationary flow. Fluid flow is stationary, if velocity of any points of it
is not changed with time. Let’s define ratio between movement velocities of fluid pressure
and its particles in field of earth gravitational force. Let’s assume that fluid flows near Earth,
in any tube bended towards its surface (Figure 73).
If we assume, that there is not heat exchange between fluid and medium, total energy of
ideal fluid with m mass, and V volume, at flowing will be constant (internal friction in ideal
fluid does not exist).

4. Laminar and turbulent flow. Reynolds number
Fluid particles move in parallel of tube walls and do not remove from one layer to another.
Fluid velocity is constant value at any point of fluid and is not changed by time. Such flow of
fluid is called laminar flow.
At this time fluid particles trajectories are not parallel tube walls. At a certain point of fluid,
flow velocity is not constant; it is changed chaotically, without any order. This kind of flow is
called a turbulent flow.
Reynolds number value R < 2000 is characterized for fluid laminar flow. R exceeds critical
value (R>3000), when 2000≤R ≤3000, stream is transitional – sometimes laminar, sometimes
turbulent. In the table 10 there is characteristic of laminar and turbulent flow.

5. Blood is the main fluid of human body. Blood mass is 7% of body mass. In 65-70 kg human
body 4.5-5 kg is blood. Blood density ρb = 1.04 × 103 kg/m3, consequently blood volume
Vblood = 4.4 – 5.0 l. Blood always circulates through the living body (blood circulation
system). Blood circulation velosity in adult’s body is approximately 5 000 ml/min.
Rheology is a part of science (physics) studying fluidity and deformability of a material,
with complex molecular structure. Blood rheology studies properties of blood and its
elements (plasma and formed elements), its fluidity, which is defined by the totality of
functional condition of formed elements (movement, ability of deformability, aggregative
activity) its viscosity and osmolarity.