Axial Flow Pump

Axial flow pumps

Axial flow pumps have a motor-driven rotor that directs flow along a path parallel to the axis of the pump. The fluid thus travels in a relatively straight direction, from the inlet pipe through the pump to the outlet pipe. Axial flow pumps are most often used as compressors in turbo-jet engines. Centrifugal pumps are also used for this purpose but axial flow pumps are more efficient. Axial flow compressors consist of alternating rows of rotors and stationary blades. The blades and rotors produce pressure rise in the air as it moves through the axial flow compressor. Air then leaves the compressor under high pressure.

6.2.5 Axial flow pumps

Axial flow pumps have a motor-driven rotor that directs flow along a path parallel to the axis of the pump. The fluid thus travels in a relatively straight direction, from the inlet pipe through the pump to the outlet pipe. Axial flow pumps are most often used as compressors in turbo-jet engines. Centrifugal pumps are also used for this purpose, but axial flow pumps are more efficient. Axial flow compressors consist of alternating rows of rotors and stationary blades. The blades and rotors produce an increase in the air pressure as it moves through the axial flow compressor. Air then leaves the compressor under high pressure.

19.5 Axial Flow and Mixed Flow Pumps

Axial flow pumps are of the propeller type, in which the rotation of the impeller forces the water forward axially, and do not strictly qualify as centrifugal pumps. Mixed flow pumps act partly by centrifugal action and partly by propeller action, the blades of the impeller being given some degree of ‘twist’. However, in practical terms there are no precise dividing lines between radial flow (centrifugal), mixed flow and axial flow pumps. In general, axial and mixed flow pumps are primarily suited for pumping large quantities of water against low heads, while centrifugal pumps are best for pumping moderate outputs against high heads. Axial flow pumps have poor suction capability and must be submerged for starting. They are most often used for land drainage or irrigation or for transferring large quantities of water from a river to some nearby ground-level storage. The pumps shown in Plates 32(b) and (c) are mixed flow.

2.7 Second generation devices

The Jarvik 2000 Flowmaker (Jarvik Heart, Manhattan, New York, USA) device incorporates a titanium impeller device that weighs just 85 g, compared to a Heartmate II device that weighs 350 g. It is small enough to fit in the left ventricular cavity and secured to the apex by means of a sewing cuff. Therefore, it does not require an inflow cannula. The external driveline is tunneled through the back, shoulder, and neck, with an exit site located behind the ear. The driveline is connected to a single lithium ion battery. As there is no need for a separate pump pocket, infective complications are reduced.

The HeartAssist5 (ReliantHeart, Houston, Texas, USA) is a second-generation device version of the Micromed DeBakey Noon VAD. It weighs 92 g, has an angled inflow cannula, and is implanted above the diaphragm. The outflow cannula contains an ultrasonic flow probe that measures real time flow. This is in contrast to the other commercially available devices, which estimate flows based on rotor speed, power consumption, and blood viscosity. Performance data from the device can be viewed remotely, potentially facilitating earlier intervention if a problem is detected. The device is approved as a bridge to transplantation and destination therapy in Europe, and is limited to investigational use in the United States.

2.6.2 Axial flow/propeller pump

In 1785, John Skeys patented a pump of novel construction, which was the prototype of the axial flow pump. The English physicist and engineer, James Thomson, initiated the idea of using guide vanes to enhance the performance of pumps. The English scientist Osborne Reynolds designed the first pump with adjustable inlet guide vanes in 1875 (Kaya, 2003). The first systematic investigations of rotodynamic pumps on a scientific basis were commenced in the 1890 s at the works of Sulzer Brothers in Switzerland. This lead was followed by other factories that endeavoured to become leading manufacturers of centrifugal pump design and, after this, the design of helicoidal, diagonal and axial flow pumps was developed rapidly.

As a general rule, axial flow pumps are usually selected for pumping large volumes of water against relatively low heads (1–15 m). The total head increase for axial flow pumps is small compared with that of centrifugal pumps.

Jarvik 2000

The first human implantation of the Jarvik 2000 occurred in the year 2000. About the size of a common C-cell battery, it measures only 2.6 cm in diameter by 7.8 cm in length, with a pump body weight of 85 g. Because of its small size, most of the pump is located within the apex of the left ventricle. To the authors’ knowledge, it is still the smallest clinically available, long-term LVAD. The longest period of left-ventricular support has been achieved with the Jarvik 2000 with 9.5 years of uninterrupted support [7].

Instead of contact bearings, the Jarvik 2000 employs cone bearings to maintain a safe, failure-free impeller operation (not shown). One cone bearing is located upstream and one downstream of the impeller. Both axial and radial forces on the impeller are absorbed in this manner. It is claimed that a small hydrodynamic fluid film is formed and thus separates the rotating impeller from the stationary struts forming the second bearing partner. The pump can be operated at 8000–12,000 rpm and can generate an average flow rate of 3–7 L/min at 4–8 W of power consumption under optimal conditions [16].

4.3.4.3.5 Special Pumps

Special ESP pumps designed to produce well fluids with very high free gas content are also available. These are tapered pumps with an intake inducer (axial flow pump) at the bottom, specially developed, low NPSH (net positive suction head) pump stages in the middle, and standard stages at the top of the pump assembly. The intake inducer provides a positive pressure for the gas/liquid mixture to enter the upper stages, the low NPSH stages mix and compress the gassy fluid so that the standard stages at the top can increase the flowing pressure to the level required for lifting the liquid to the surface. Thanks to the special design of the low NPSH stages, surging and gas locking are eliminated, thus ensuring a long operational life of the ESP equipment even in gassy wells.

9 Conclusions

As the field of surgery robots controlled by surgeons expands, the economical cost is expected to reduce, which will allow surgeons to more commonly use teleoperation in situations that warrants professional staff assistance such as wars, epidemics, and space trips. The situation of “no contact” between the medical personnel and the patient will reduce the risk of loss of health because of the infection(s) from the side of the operating staff.

It is most probable that contemporary telemanipulators will be replaced by adaptive robots in the near future. Currently, the trials of shifting from passive to active systems can be seen. To be clear, let’s define the basic concepts: Teleoperators are remotely controlled by operator robot transferring on distance motoric and sensoric functions, whereas adaptive robots have more advanced control system with sensoric and learning abilities. However, creating the next-generation “intelligent” robots is a true challenge. These robots must be able to work unaidedly in various environments, gathering information from their senses. Optimization of their behavior and the effectiveness of given task realization will depend on “self-learning control algorithm”, which will more resemble systems based on “instincts” in relation to living creatures and contact with surroundings by means of “senses”, zoom, touch sensors (inductive, supersonic, optical, pneumatic, and microwave). I am convinced that they will not be similar to contemporary cardiosurgical robots, but they will be able to replace them considerably. Probably, they will be microrobots that are able to reach, e.g., a given human internal diseased organ (e.g., the heart).