Appendix - A

CURRENT STATUS OF VENTRICULAR ASSIST DEVICES

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Appendix - A

CURRENT STATUS OFVENTRICULAR ASSIST DEVICES

As new technologies gradually allowed for more efficient heart pumps, several

companies started the development of VADs resulting in various VAD designs, while

many of these VADs are being developed and in various stages of clinical testing.

There are many different criteria of how VADs have been categorized. One obvious

distinction is its system of operation. In the beginning, trials to mimic the heart

function, made VAD designers choose pulsatile displacement pump system.

With the introduction of rotary flow pumps in clinical use, the distinction between

pulsatile and non-pulsatile systems has become important. Rotary continuous flow

blood pumps can be further classified into two categories: centrifugal and axial

pumps. Considering pump design theory, centrifugal pumps are capable of producing

higher pressures at lower flows, while axial flow pumps typically generate higher

flows at lower pressure rises. Axial flow pumps, while they are far more compact

than centrifugal pumps, operate at much higher rotational speeds to produce the

desired pressure rise and flow. Based on this classification, the current commercial

and under development VADs (Table 2) are presented in details as follows.

Table A.1 Overview of well known VADs being developed or available on the market

Pulsatile flow pumps(Positive displacement pumps) Continuous flow pumps (rotary pumps)

Pneumatic Electro-mechanical

Axial pumps Centrifugal (radial) pumps

HeartMate IP

Thoratec IVAD

Medos/HIA-VAD

NovaCor

HeartMate VE

Arrow LionHeart

HeartMate II

Jarvik 2000

DeBakey

Incor

HeatMate III

Levacor

VentrAssist

Heartware HVAD

NEDO Gyro PI-710

DuraHeart

CorAide

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A.1 Pulsatile VADNovacor: The Novacor LVAS, shown in Figure A.1, is a unique intracorporeal

partially implantable VAD manufactured by the World Heart Corporation, which is

based in Ottawa 1. The Novacor system makes use of biological valves and a highly

smooth blood contacting sac. Rather than the more common one pusher plate design,

Novacor employs two pusher plates on the front and the back of the flexible smooth

polyurethane sac to push blood out ensuring excellent washout 2. The pusher plates are

coupled to a spring-decoupled pulsed-solenoid energy converter. When an electric

current is supplied to the energy converter, a magnetic field forces the pusher plates to

sandwich the sac, which results in the blood flow into the aorta. After the electric

current has been switched off, two springs force the pusher plates to move away from

the sac, allowing the blood inflow 3.

(a) (b) (c)

Fig. A.1 (a)NovaCor-pump unit: top dual pusher plate and magnetic actuator can be recognized3, (b) schematic illustration of functional principle of Novacor-System,

(c) Anatomic configuration of the native heart and wearable Novacor LVAD system 4.

The Novacor II miniaturized pulsatile pump is an extension of the current Novacor

technology, that substantially reduces pump size. The single pump is replaced by two

small sac-type pumps, each driven by a central pusher plate mechanism. This supports

LV output with multiple pump cycles. The pusher plate is directly driven by

electromagnetic actuation 2.

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HeartMate IP and VE: The Thoratec Corporation currently produces two models of

HeartMate VADs, the IP and VE devices. The difference between the two HeartMate

devices is that the IP device is pneumatically driven, while the VE device is

electrically driven 5. The VE version of the HeartMate VAD is shown in Figure A.2.

The two HeartMate VAD models are intracorporeal partially implantable devices

commercially available as a bridge to transplantation. Based on the results of the

REMATCH, HeartMate VE VAD was recently approved as a destination therapy 6.

The HeartMate devices have a low speed and high torque motor in combination with a

face cam to drive the pusher-plate type blood pump having a stroke volume of 83 cc.

The flexing diaphragm is made of smooth polyurethane and the pump housing is

made of a titanium alloy. In the inflow and outflow ports, porcine valves are used 4.

By the year 2000, in excess of

4000 LVAD’s had been

implanted worldwide, with the

Heartmate accounting for about half

of this number 2. The longest

surviving patient had the device for

1,142 days 4. In a multi-center

evaluation of HeartMate I

VE as a bridge to

transplantation, the most

common adverse event was

bleeding 31/280 (11%),

infection 113/280 (40%), neurologic dysfunction 14/280 (5%), and thromboembolism

17/280 (6%) 4.

Recently, the HeartMate VE LVAS underwent a number of design improvements and

was renamed the HeartMate XVE LVAS. The modifications (Figure A.3) were

designed to improve pump reliability and durability by reducing the risk of device-

related adverse events and treating the causes of mechanical failure 8.

168

Fig. A.2 The HeartMate VE LVAD system 7.

Fig. A.3 HeartMate XVE design modifications 8.

Thoratec VAD: Thoratec Corporation, of Pleasanton, California, currently

manufactures three VADs, the Thoratec VAD, the TCI HeartMate IP, and the TCI

HeartMate VE 5. The Thoratec VAD is an extracorporeal device with a paracorporeal

pump placement. It can be used to support the left or right ventricle or both.

The major advantages of this Thoratec VAD are its smooth polished titanium pump

housing with a relatively small size and weight (339gm) 9, allowing implantation in

patients ranging from 40 to 100 kg. Only the pump is implanted in a pre-peritoneal

position with a small (9 mm diameter) percutaneous pneumatic drive line for each

VAD connected to a more complex control unit externally, where it can be serviced

and replaced 2.

The Thoratec VAD pump is controlled with a small battery powered pneumatic

unit_10. The valves in the Thoratec VAD are tilting disk valves 5. Figure A.4 is an

illustration of the overall shape of the Thoratec VAD and its specific design features.

The smooth external contours are designed to minimize dead space in the pre-

peritoneal pocket and reduce the risk of infection by taking the advantage of potential

bacteria colonization resistance associated with smooth metallic surfaces.

169

(a) (b)

Fig. A.4 (a) Thoratec VAD positive displacement blood-pump 10,(b) Cross sectional view of the main design features of the Thoratec VAD

(The cross section follows the axis of the inflow port, passes through the center of the cap and continues along the axis of the pneumatic line) 10.

Arrow LionHeart: The Arrow LionHeart VAD is a joint project in the development

stages between Arrow International and Pennsylvania State University. This is the

only completely implantable system (Figure 2.5) without a driveline penetrating the

skin having an implanted batteries recharged using transcutaneous energy

transmission system, namely, by the use of two electromagnetic induction coils 2, 5.

Despite lowering the risk of infection, the patient has to continuously wear a battery,

as the support time of the implanted battery only suffices for about 20 minutes, which

is just enough for a shower or bath 11. Besides, the controller is also implanted and

can be externally programmed 3.

The pump is based on a roller screw mechanism, which causes linear motion of an

attached circular pusher plate, which compresses the polyurethane blood sac during

systole. In diastole the brushless direct current motor reverses to withdraw the pusher

plate. In addition, Two tilting disc valves are used to maintain the required

unidirectional flow 2. The external electronics are composed of the energy

transmission source, a power pack, a battery charger and portable power supplies.

The total weight of the system is 1.3 kg 11.

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Fig. A.5 Anatomic configuration of the totally implantable Arrow LionHeart VAD system 12.

Despite several years of clinical availability, only limited experiences with this device

have been reported 11. The Arrow Lionheart left ventricular assist device is designed

for destination therapy. It was implanted in 23 patients in Europe and in 10 patients

in the United States, from October 2000 till April 2004. It received European

conformity certification on November 7, 2003. Unfortunately, corporate financial

decisions have discontinued the ongoing trials of the Lionheart presently 3.

Medos HIA-VAD: The Medos/HIA-VAD (Figure A.6) is an extracorporeal device

with paracorporeal pump placement developed in Germany by the Hemholtz Institute

in Aachen 5. This device has two chambers, separated by a double layered diaphragm 13. It can be used to support the left or right ventricle or both. Because the systems are

available in a variety of pump sizes (10–80 ml), they are suitable for the entire age

range of pediatric patients including neonates 14. Air is pumped in and out of the first

chamber causing the diaphragm to move up and down, which forces blood in and out

of the second chamber. Polyurethane trileaflet valves are used at the entrance and exit

of the blood chamber in this device 5. The housing is transparent allowing visual

control of filling, emptying, and thrombus formation 13. In the United States,

because device availability is restricted to emergency use, only 25 implants have been

performed 14.

171

Fig. A.6 Medos HIA ventricle assist device.

A.2 Non-Pulsatile VADIn the last decade, non-pulsatile blood pumps providing with continous flow have

attracted much attention, because they have several advantages over pulsatile-flow

pumps. Numerous continuous-flow pumps VADs were developed for CHF support.

These VADs are either axial or centrifugal. As follows, the well-known non-pulsatile

VADS will be briefly demonstrated.

Axial VAD The axial flow rotary blood pump consists of a rotor type impeller which is housed in

a small casing. The displacement volume of these pumps varies from 25 to 64 mL.

The pumps generate high flow at very high pump speeds (8000-25,000 rev/min). The

required impeller peripheral velocity is 2-3 times that of other rotary type devices 2.

Heartmate II: The Heartmate II (Figure A.7) is developed through a collaboration

between Nimbus and the University of Pittsburgh 9. It is an axial flow blood pump

featuring a rotor that spins on two cup-socket ruby bearings 2, 9. It has percutaneous

electrical leads, an external power source, and a battery powered or an alternating

current (AC) supplied power driver 15. The spinning rotor has three curved blades

172

and is energized by a rapidly rotating electromagnetic field. A control algorithm

senses the volume status of the ventricle and adjusts impeller speed accordingly.

Fig. A.7 (a) Schematic illustration of the implanted HeartMate-II LVAD system 16,(b) Cross-sectional internal view of HeartMate II left ventricular assist device 17,

(c) HeartMate-II VAD unit: inflow/outflow cannula and percutaneous cable can be recognized 17.

Although, HeartMate pump is small measuring 2.5 cm in diameter and 4 cm in length

and weighing 370 g, its rotor speeds ranges from 6000 to 15,000, providing with flow

rates from 3 to 10 l/min. The inflow cannula is joined at the apex of the left ventricle

and the outflow to the aorta 6, 18.

A transcutaneous energy transmission system was recently animal-tested and thought

to eliminate, in the future, the current need to perforate the skin and thus minimize the

risk of infection 18.

The Heartmate II is currently undergoing Phase II essential trials in the United States

for BTT and DT. The blood-contacting surface of the Heartmate II is a hybrid

173

(a)

(b)

(c)

between the textured surface of the original Heartmate as well as a smooth titanium

surface to minimize thromboembolization 9.

Jarvik 2000: The Jarvik 2000 VAD (Figure A.8) is a compact axial flow impeller

pump under development by the Texas Heart Institute. The device can be used as

either an LVAD or RVAD. The rotor represents the only moving part of the device

and is supported at each end by tiny blood-immersed ceramic bearings 2, 9. The rotor

(impeller) consists of a neodymium–iron–boron permanent magnet and two

hydrodynamic titanium blades on its surface 9. Power is delivered to a brushless DC

motor through an abdominal drive line. The device measures 2.5 cm in diameter, 5.5

cm in length and weighs 85g with a displacement volume of 25 ml. A pediatric model

is under development with an approximate size of 1/5 the original model 2.

A controller determines the fixed rate motor speeds (8,000 – 12,000 rpm) providing

with a flow up to 7 L/min at a energy consumption of 7 to 8W. The Jarvik 2000

plans to incorporate a rate responsive controller. Detecting rotational speed changes of

the pump with varying loads induced by heart rate changes, the rate-responsive

controller is able to alter the pump speed based on the level of activity. The blood-

contacting surface comprises a smooth mirror finish of titanium 2, 9, 11.

The device received the European conformity certification in 2005 both as bridge to

transplantation and destination therapy. Moreover, it is currently undergoing bridge

to transplantation trials in the United States. The destination therapy version used in

Europe is implanted with the driveline connection on a skull-based pedestal to lower

the incidence of infection, while, has not yet been approved in the USA 2, 9, 11.

174

Fig. A.8 The Jarvik axial flow pump 9.

Debakey LVAD: The DeBakey VAD (Figure A.9) is another compact axial flow

pump developed in a joint work among Baylor College of Medicine, MicroMed

Technology, Inc., and NASA Johnson Space Center 7. The implantable titanium

pump connects the left ventricle apex to the ascending. The pump is driven

electromagnetically and the driving line is guided out percutaneuosly in the region of

the lower abdomen exiting the body near the hip, allowing the external controller to

receive diagnostic information to control the device 2, 19.

Like other axial flow pumps, the DeBakey VAD is compact, measures 7.62 cm in

length, 3.05 cm in diameter and weighs 93g with a displacement volume of 15ml 2.

The pump contains an inducer impeller, actuated by an electromagnet, and is the only

moving part of the system. It is supported at both ends by double pivot bearings. The

bearings of this pump have proven to be extremely reliable in bench mock loop tests,

exceeding 2 years of operability. The inducer impeller has three blades with eight

magnets hermetically sealed in each blade. The impeller rotates at 7,500 to 12,500

rpm with a flow of up to 10 L/min. At 10,000 rpm it requires less than 10 W of

power. Blood flowing through the pump first travels through a flow straightener,

followed by the inducer impeller, and finally through a diffuser before exiting the

device. The diffuser slows the high tangential velocity of the blood as produced in the

impeller region by redirecting it axially, resulting in an increase in the pressure of the

fluid 9, 20.

175

Fig. A.9 The MicroMed-DeBakey ventricle assist device 21.

These illustrations shown in figure A.10 represents a visual comparison of the original

ventricular assist device, top, and the unit after modifications by NASA researchers,

center and bottom. Adding an inducer to the MicroMed DeBakey VAD eliminates the

dangerous back flow of blood by increasing pressure and making flow more

continuous 22.

Fig. A.10 NASA MicroMed-DeBakey VAD development using CFD techniques 22.

The DeBakey VAD has been modified from its original design, and recently has

Carmeda CBAS® heparin biocompatible coating to the internal pump housing and

internal components that contact the blood to reduce the incidence of thrombus

formation 11, 20. In 2008, the modern version of the device, the HeartAssist 5, is

manufactured by US company MicroMed Cardiovascular. It is considered to be a

fifth generation VAD because it can be implanted adjacent to the heart and has an

176

exclusive flow probe that provides direct, accurate measurement of blood flow from

the left ventricle to the aorta. The new miniature device is light, easy-to-handle and

can be monitored and controlled externally. The Debakey VAD received the

European conformity certification in 2002 and is currently in US pivotal trials for

bridge to transplantation and destination therapy 9.

Centrifugal VADDespite miniaturization, centrifugal flow VADs are somewhat larger and heavier than

axial flow VADs. The rotational speeds of centrifugal flow VADs is much slower

than that of axial flow VADs (about 2,000 – 4,000 vs. 8,000 – 25,000 rpm). Higher

speeds may lead to high shear stresses and thus higher probability of blood damage.

For this reason, centrifugal pumps provide less hemolysis. The same general

advantages and disadvantages apply to centrifugal VADs as to axial flow VADs 23, 24.

Heartmate III:

The HeartMate III, developed by Thoratec, is currently in pre-clinical trials, but

represents a new design approach for centrifugal pumps. Intensive research for a

miniature, low cost pump design resulted in the third generation Heartmate III

concept, a compact centrifugal type blood pump. The size is 1/3rd that of the original

Heartmate I, and is supported by a combination of active and passive magnetic

bearings and is completely enclosed in titanium housing 2. The Heartmate III, as

shown in Figure A.11, is a totally implantable uni-/biventricular assist system.

Contrary to most current centrifugal pumps, the Heartmate III system is designed for

long term use. The used suspension system has established robust and stable rotor

magnetic levitation in all axes with no mechanical bearing, contributing to improve

mechanical durability of the pump 2. Thoratec claim service life of up to 10- 15 years,

making the Heartmate III an ideal candidate for a destination therapy / alternative to

transplant. The pump also contains the same textured surface as the Heartmate XVE

system, and is designed to produce an outflow of 7 L/min against 135 mm Hg with 8

W of power consumption and to be capable of up to 10 L/min under such a load 25, 26.

Moreover, pulsatile pressures are achievable via impeller rotational speed variation 2.

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Fig. A.11 Heartmate III ventricular assist device 39.

Levacor VAD: The Levacor VAD (WorldHeart Corporation, Oakland, CA, USA) is

an advanced device designed for long term use. For the improvement of Levacor

VAD durability, a full magnetic suspension of the rotor was established, incorporating

active and passive magnetic bearings to completely levitate the impeller. The

Levacor device uses a compact centrifugal pump with magnetically levitated mixed

flow impeller which is designed to have selectable ranges of speeds to be optimized

for individual patients. The Levacor (Figure A.12) dimensions are 35 in height and

75 mm in diameter, with a total

weight of 440 g 27. Levacor is

designed to produce an outflow of 6.5

L/min against 100 mm Hg and to be

capable of up to 10 L/min under

such a load. Animal study results

have been very promising, with

over 30 calf studies completed.

Plasma-free hemoglobin

levels returned to preoperative

levels, and other hematology results were in the normal ranges 28.

In 2006, the first human implant of the Levacor VAD was performed by a surgical

team at St. Luke's Hospital, Thessaloniki, Greece. The successful implant marked the

start of the feasibility clinical trial for an acute bridge-to-recovery indication. The

patient fully recovered his natural heart function, and the Levacor was explanted after

almost three months support and continues to lead a normal life at home. In 2006, a

178

Fig. A.12 Levacor left ventricular assist device.

(World Heart Corp., Oakland, CA.)

second patient has had the same positive experience, which concluded the feasibility

study. On January 2010, the Levacor VAD received the FDA's unconditional

approval for bridge to transplant trial 28.

VentrAssist: The VentrAssist device (Ventracor Ltd.) is a unique third-generation

centrifugal pump, as the impeller is completely suspended by passive hydrodynamic

forces. Rotation is achieved by direct coupling a DC motor to magnets within the

impeller blades 2, 27. The device weighs 298 g, and measures 60 mm in diameter

(Figure A.13). The operating range of the pump is 1,800 to 3,000 revolutions per

minute (rpm) in the normal setting. The impeller is comprised of four small blades

that are embedded with permanent magnets. The impeller blades act as a rotor for the

pump's brushless DC motor and spin when an electrical current is sequentially

switched between three pairs of coils contained within the titanium housing of the

pump 27.

Fig. A.13 (a) VentrAssist left ventricular assist device,

(b) Internal view demonstrating the VentrAssist pump impeller having four

small blades that are embedded with permanent magnets 27.

The suspension system is performed passively and is achieved entirely through the

use of eight hydrodynamic bearings, one on each face of the four blades. No magnetic

levitation is utilized in the levitation of the impeller. Dynamic interplay between the

eight hydrodynamic bearing forces, fluid forces and gravitational forces prevents the

spinning impeller from touching any part of the housing of the pump. The absence of

magnetic levitation and monitoring systems to identify impeller position results in a

less complicated electronics and smaller pump design 27, 29.

179

Clinical trials of the VentrAssist have been completed in Australia and Europe and are

currently being conducted in the United States as part of a FDA-approved pivotal trial

for both bridge to transplant and destination therapy indications. Unfortunately,

further development of the device ceased owing to exhaustion of company funds 27, 28.

Heartware HVAD: The HVAD (Heartware inc.) is a small continuous-flow rotary

third-generation pump with a centrifugal and non-contact bearing design, shown in

Figure A.14. A unique feature of this device, compared with other third-generation

devices, is that it is small enough to be placed completely within the pericardial cavity

at the apex of the left ventricle. The need for an abdominal dissection and creation of

a LVAD pocket is obviated, simplifying the surgical procedure. The impeller is fully

suspended in place by a combination of passive magnetic and hydrodynamic bearing

systems, rotating at 2,000 to 3,000 rpm with a flow of up to 10 L/min 27, 28.

Fig. A.14 Heartware HVAD left ventricular assist device 27.

The device measures 50 mm in diameter and weighs 145g with a displacement

volume of 50 ml. The design integrates two motor stators for single-motor fault

protection, to increase reliability. Physical contact between the housing and the

impeller is prevented by a thin blood film generated by the hydrodynamic bearings.

The first human implant was performed in March, 2006. The HVAD received the

European conformity certification and is currently in US pivotal trials for bridge to

transplantation 27, 28.

180

NEDO Gyro PI-710: The Baylor College of Medicine group with the support of a

Grant-in-Aid from the New Energy and Industrial Technology Development

Organization (NEDO) started to develop the "Gyro" permanently implantable

centrifugal pump as a biventricular assist device 30. A two week lifetime ‘Gyro’ pump

was initially developed for bypass applications. This was miniaturised to a

polycarbonate model before the current titanium model evolved. The current NEDO

PI-710 VAD system includes a miniaturised titanium ‘Gyro’ centrifugal pump with

ceramic pivot bearings, a hydraulically-levitated impeller, an rpm-controlled

miniaturized actuator (all-in-one actuator plus controller) (Figure A.15), an

emergency clamp on the left outflow, and an eccentric inlet port (to washout the

pivot) 2, 30.

An internal battery, a controller, a transcutaneous energy transfer system (TET), and a

transcutaneous information transfer system (TIT) are also implanted. The emergency

clamp is accommodated on the outflow of the left pump to prevent back-flow in the

case of pump stoppage 30.

Fig. A.15 (a) Schematic illustration of the implanted NEDO Gyro PI-710 VAD system 30,

(b) Internal view demonstrating the main parts of NEDO Gyro PI-710 pump 30.

The overall size of the PI-710 pump, actuator, and controller is 155 mL of

displacement volume and 480 g in weight. The PI-710 pump has a hydraulically-

181

levitated impeller. This mechanism (up–down movement and swing motion) is

important for preventing thrombus formation behind the impeller.

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184

Appendix - B

GEOMETRIC SPECIFICATIONS OF THE HEARTQUEST - CF4 VAD

(BASELINE BLOOD PUMP OF THE PRESENT STUDY)

185

Appendix - B

STRUCTURE-OF-THE HEARTQUEST CF4 VAD

The Prototype of the HeartQuest CF4 VAD, which is used as a baseline model in the

present study, consists of five main components: Front housing, Inlet elbow, Rear

housing, Impeller, and stinger head. The detailed drawings of these components are

shown as follows:

186

187

188

189

190

191

192

Appendix - C

VOLUTE CASING DESIGN PROCEDURE

193

Appendix - C

VOLUTE CASING DESIGN PROCEDURE

Two techniques are introduced for calculating the geometry of the centrifugal pump

volute. The first assumes the fluid follows the principle of momentum conservation;

the second designs the volute to produce a constant velocity from tongue to throat.

Single, double and circular volute types were designed for its evaluation in VAD

application.

Volute calculations are be based on the concept of constant velocity within the volute

passage. Volute designs are based on the average fluid velocities within the volute

passages. Since these average velocities change with varying pump capacities, the

final volute is designed at the best efficiency point (BEP) and the performance at

conditions either side of the BEP are estimated

The absolute velocity at impeller discharge is an important design parameter in volute

casing design; however the most important parameter is the throat area.

Fig. C.1 Volute structure and main characterizing dimensions.

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C.1 Throat Velocity (c3) The volute velocity distribution factor (Rc3) is the ratio of volute throat velocity (c3) to

the impeller discharge velocity (c2’) and depends on the value of specific speed (ns).

The ratio is lower for high specific speed pumps, where the actual discharge angle is

larger. Using previously calculated values of impeller absolute velocity discharge

angle (α2’), the volute velocity distribution factor (Rc3) was selected from Figure C.2.

Fig. C.2 Volute Velocity Distribution Factor.

The throat velocity (c3) is determined by multiplying this factor by the magnitude of

the actual absolute velocity (c2.) using equation (C.1)

C3 = RC3 . C2’ (C. 1)

C.2 Throat Area (Ath)With the impeller geometry established for a certain pump capacity, the throat area

must be sized to establish best efficiency at this capacity. Once the value of throat

velocity (c3) is known, it is possible to calculate the area (Av) for any arbitrary angle

(θ) around the volute. At the volute throat ( θ = 360o), the entire rate of flow (Q)

passes, and therefore the area is calculated from Equation (C. 2).

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Ath = Q / C3 (C. 2)

C.3 Base CircleThe base circle diameter determines the distance of the volute tongue or cutwater

from the rotational axis. This diameter, commonly 10% greater than that of the

impeller, is a critical design component of the pump, especially when operating the

pump at off design conditions.

If the pumping capacity is lower than the design point, the tongue deflects some of the

flow approaching the throat resulting in considerable recirculation. With a large base

circle diameter, the level of recirculation increases leading to reduced efficiency,

since the exert energy is consumed in recirculating the fluid within the pump.

Conversely, with a small base circle diameter, strong pressure fluctuations are

encountered at the blade pass frequency causing an increase in noise.

The base circle is sometimes represented by the minimum diametrical gap between

the base circle diameter (Dbc) and the impeller outer diameter (D2), and expressed as a

fraction (k3) of the impeller diameter, which is selected from Figure C. 3.

Fig. C.3 Volute Constants from empirical experience as stated by Stepanoff.The base circle diameter is then calculated from Equation (C. 3) as follows:

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K3 = (Dbc – D2) / D2 (C. 3)

C.4 Volute AngleTo avoid separation at the volute tongue, the volute angle αv corresponds to the

direction of the absolute velocity vector at the impeller discharge α2’. To satisfy

continuity,

(C.4)

Where, Av is the volute throat area.

However considerable deviation from this angle is possible with little effect on the

efficiency of low to medium specific speed pumps, since there is only one vane

(volute tongue). Efficiency deterioration is more pronounced with mismatched angles

in centrifugal pumps employing diffuser vanes surrounding the impellers

circumference. This angle matching is more important in pumps of higher specific

speed, even to the extent that the high angle part of the volute tongue may be removed

to improve efficiency.

C.5 Volute WidthThe width of the volute is important in allowing passage of the fluid from the impeller

to the volute. There will be lowest loss in this transition if the impeller discharges

liquid in to a body of rotating liquid as opposed to a stationary wall.

.

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Fig. C.4 Volute Width

Table C-1 provides a guide to choosing the correct volute width for a given

application.

Table. C.1 Volute Width Guidelines

The volute width should always be larger than that of the impeller outlet. It is also

suggested that the volute width ratio may be reduced to between 1.4 - 1.8, again with

lower numbers corresponding to higher specific speeds.

C.6 Volute WidthThere are a number of design procedures available for calculating the profile of each

volute design. Further information on the following outlined procedures for single,

double and circular volute design is detailed in (Lobanoff and Ross 1985).

Single Volute

Figure C-5 describes a technique used to lay out the single volute and diffuser profile.

The volute is divided into numerous sections and guidelines dictate each dimension.

Double Volute

Figure C-6 displays a similar technique for profile development. In addition, a

standard template is provided for volute cross section development of both inner and

outer passageways. In this procedure, the outer section continues to increase in area

behind the inner section.

Circular Volute

The diameter of the circular type volute (D3) is calculated in relation to the impeller

outlet diameter (D1) using (Equation C-5),

(C. 5)

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Fig. C.5 Typical Single Volute Profile (Lobanoff and Ross 1985)

Fig. C.6 Universal rectangular double volute pump (Lobanoff and Ross 1985)

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Diffuser

Upon completion of the volute profile, the throat area must transition to the outlet

cannula. Care was taken to maintain a diffusion angle of less than 13 degrees while

providing a smooth transition to the circular outlet cannula, in order to reduce the

incidence of fluid separation.

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Appendix - D

PUBLISHED PAPERS

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M. A. Fouad, M. O. El-Samadony, “Numerical Simulation of Three-Dimensional Turbulent Flow in Blood Pumps”, Bulletin of the Faculty of Engineering and Technology, Minia University, Vol. 31, No. 1, Jan. 2012.

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