Pumps for Human Blood Pressure Simulation - Microsurgery: Advances, Simulations, and Applications - page 208

Deep coating yielded a model wall with a 250 μ m-thick urethane
elastomer layer and two 60 μ m-thick silicone layers shielding the
urethane, as shown in Fig. 6.3(a). Water was circulated inside the
model and no plastic deformation occurred at pressure below 200
mmHg. Different models built with this technique and showing the
photoelastic properties of the material are shown in Fig. 6.3(b).

6.2 Lobe Pump Design

Simulating blood pressure requires a capacity pump to provide a
constant low and a variable volume accumulator to introduce low
pulsation. When the piston travels along the pump cylinder, water
volume inside the cylinder changes; the inlet valve opens when the
volume increases and the exhaust valve opens when this volume
decreases. The piston pump cylinder has suficient volume to install
inside a piston-lobe pump. Removing both piston pump check
valves and sealing the inlet results in a hybrid pump suitable for our
simulation purpose. Lobe pumps are rotary positive-displacement
pumps, which force luid between two rotary elements and a static
casing. The pump low is a function of rotational lobes speed, and is
independent from the pressure differential.

6.2.1 Lobe Profiles and Mechanism

Lobe proiles were modeled with parametric equations following
the lobe proile synthesis proposed by Tong et al. [5]. We considered
a required low of 1 lpm, and the cross-sectional diameter is limited
to 42 mm by the piston pump cylinder diameter, and the maximum
desired motor speed is 400 rpm. The low function is sinusoidal, the
low range is between 0.847 and 1.059 lpm, the frequency is 3.2 kHz,
and the two-rotor lobe coniguration has a rotation speed of 800
rpm.
Using nomenclature of [5] for the parameters selected above,
corresponding non-circularity h is 0.75, cavity volume V is 2352 mm 3
and w = 20 mm, yielding the following lobe proile generation
parametric equations are shown in Fig. 6.4.
Inner proile:

G 1 x = 6cos( R ) + 3cos(2 R ) cos( Q - R (6.1)