Fuel Conversion in Transport Phenomena An article in the "Newscript" section of Chemical and Engineering Nnus [November 4, 1963, p. 1841 aroused my economic curiosity. The article stated that, "a fat hummingbird can fly 7.7 hours before its reserve of fat (1 g) is consumed." Having been bombarded by friends on how economical their Volkswagens were with fuel I immediately speculated that I might a t long last havea "vehicle" moreeconomical and thus a defense mechanismagainst them. To develop my defense argument the following reasoning and calculations were required: (1) My ornithologist friends estimated 55 mph as B hummingbird's "cruising" speed. This means that it could fly 420 miles/g of fuel. (2) Assuming a mileage of 30 miles/gal. (muchless than claimed by some of my friends) and a density of 7lh/gal. for gasolineit was calculated that aVolkswagen can travel 0.0094 miles/gof fuel. (3) A comparison of 420 miles/g of fuel for a hummingbird to the 0.0094 miles/g of fuel for the Volkswagen was not equitable because the Volkswsgen must move about 1600 lh of car plus a driver whose weight was estimated at 200 ib. The hummingbird must move only 28 g. It was decided to calculate the (miles) (grams) per grams of fuel for each. The calculations yielded a value of 11900 (miles) (g)/gof fuel for the hummingbird and 7680 (miles) (g)/gof fuel for the Volkswagen. (4) A consideration of the energy content of the two fuels is needed for an honest comparison. This was achieved by calculating the (miles) (g)/kcal value for eachfuel. For the hummingbird avaloe of 1250 (miles) (g)/kcal was calculated. The value for the Volkswagen was 6400 (miles)'(g)/kcal. (5) A comparison of the efficiencies of the two "vehicles" was made by forming aratio of the two (miles) (g)/keal values. The compt~risonrevealed that the Volkswagen is 5.2 times as efficient as a hummingbird in conversion of fuel to net displacement of mass. Confronted with this overwhelming superiority of the Volkswagen I have decided to not mention this fact to my Volkswagen driving friends. However, if they mention this to me I still have the reply that a Volkswagen cannot reproduce itself. These cdculations offerinteresting examples for teaching the use of conversion units.
E, R. GERLACH
Volume 46, Number 7, July 1969
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