0504

0.319/0.33 i

0.319/0.331

Height above pump push plate (cm)"

3.73/3.98

3.05/3.56

3.05/3.56

* With no low temperature foam insulation/with insulation t For 2W daily average power to blood pump push plate.

their pressure must give rise to concern about the feasibility of achieving the desired 10-year life with no maintainance. The peak operating frequency was 25 Hz and was projected to increase to 35 Hz (Johnston ef a!. 1977). An average frequency of say 25 Hz for 10 years corresponds to 3.28xl0M cycles. Trouble-free operation of flexing elements for such extended periods poses a formidable challenge indeed.

A good deal of effort has gone into fatigue testing of components and systems. The best achieved so far (Johnston et al. 1977) was a laboratory

Displacer down Displacer up

Picxure 1

Flexure 2

Cylinder Cylinder

Cylinder Cylinder

Displacer Displacer pistón up pistón down

FtG. 17.5. Principies ot" flexura! hút-cnd displacer guide (after iohnston at. 1975).

bench operation of an engine module lor 3 years with continuous maintenance-free operation using a bellows operating with a pressure difference of 30 lb per sq in.

In a decade of development, remarkable reduction in system weight and volume has been achieved with concomitant improvements in efficiency. A heart-assist unit prepared for animal implant experiments was

Displacer down Displacer up

Fia. 17.6(a). Flexural guide oí spiral coniiguration (aíter Johnston et ai 1975).

Picxure 1

Flexure 2

Fig. 17.6(b).

described as having an overall efficiency of 15 per cent with a 33 watt thermal input, a volume of 930 cm5 (57 in3) with additional 400 cm3 (24 in3) foam insulation and a mass of 2.4 kg (5.3 lbm).

The McDonnel-Douglas system had been used in a number of animal experiments (principally with calves) carried out by the implant team at the Washington State University, Pullman. Most experiments briefly reported by Johnston cl al. (1977) had been of the partial system with electric heating of the engine module. Pull system tests were scheduled for 1978 in six calves.

Johnston el al. (1975) included a history of the McDonnel-Douglas artificial heart program and a complete listing of the eight annual reports and ten technical papers contributed to that time.

aerojet-GENERAL ARTIFICIAL HEART ENGINE

Moise and Faeser (1977) summarized the status of development of the Aerojet artificial heart project. The Aerojet system utilized a thermal energy source and a regenerative engine to generate pneumatic power (compressed helium gas) supplied lo a pneumatic actuator driving the blood pump. A block diagram for the unit is shown in Fig. 17.7. A section view of the engine module is given in Fig. 17.8 and some of the engine operating characteristics are given in Table 17.2.

Abdominal thermal load

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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