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docsri December 10, 2002 01:38

can some one explain this to me?

I am physician by profession and I am pursuing Biomedical Informatics Masters. I am totally new to fluid dynamics. Could anyone explain to me about the following problem..

Estimate the power (in watts) required from the heart to drive blood through the circulatory system of a giraffe.

Additional information: a giraffe is a large animal, approxiamtely 19 ft tall and 4,000lb. in weight, inhabitating the plains of Africa, characterized by a long neck which allows the animal to eat leaves growing hig in the trees.

Thanks in advance, Dr.Sri.

Allan Morriison December 10, 2002 19:51

Re: can some one explain this to me?
Power = delta pressure times volume divided by time.

In metric units: Pressure is in Newtons/meter squared and Volume flow rate is in cubic meters per second.

Units - N/m2 times m3/second cancels to Nm/second.

A Nm is a joule(J) and a J/second = a Watt.

An elementary attempt at addressing your question.

1. 19 ft x(1 m/3.28 ft) =5.8m

2. delta pressure =specific weight x vertical height. Assuming specific of weight of blood = specific weight of water delta pressure =9810N/m3 times 5.8m =56898 N/m2

3. Assume (??) volume flow =0.1 liter/sec or

=0.0001 m3/sec

4. Power = delta pressure x volume/second

= 56898N/m2 x 0.0001m3/sec

=5.7 watts

5. Compare - the human body produces about 100 watts of heat when a person is sitting abound --- maybe? 5-10% of this is from the heart muscle ??

Above assumes that this is a "straight pump up the "hill" problem" -ie. static pressure at the base of the neck and static pressure in the head (brain?) will also influence the power required. Also pressure drop in the artery (fluid friction) is assumed to be zero. Also that the velocity of the blood is slow.

Please confirm all numbers with actual situation. They may be considerably different from what is assumed here. Use as a preliminary guideline only.

docsri December 11, 2002 22:43

Re: can some one explain this to me?
Dear Morrison,

Thanks a lot for the explanation.

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