edited by
ROD OCONNOR Texas A&M University College Station, TX 77843
Backpacking Stoves
Editor's Note: There is a physical answer to the problem, but there is no "solution" to the backpacker's dilemma. The following is the explanation ot the phenomena.
Herbert Petitjean Pendleton Hlgh School Route 5 Falmouth, KY 41040
I n a recent issue of an outdoor magazine,l Ray Smutek compares backpacking stoves and discusses his experiences with the various types available. One very popular type uses hutane cartridges. This type was used by the first successful American expedition to climb Mount Everest. Members of the expedition had the highest praise for the efficiency and ease of operation of the stove. I t proved quite satisfactory, even'at the final camp (27,200 ft). One year later, Mr. Smutek was climbing Mount Hood with some members of the Everest expedition when a winter storm forced them to their high camp a t 9,600 ft. The stoves had worked beautifully that mornine. but now the climbers had to strueele to maintain a feeble flame. The butane tank was practicaily full, the valve was working.and the orifice was clean. The stove just refused to work. It would seem at first glance that the conditions on Mount Everest would make it harder to operate a stove. On Mount Everest, the temperature might be somewhat lower and it is certain that the air pressure and the amount of oxygen is less. Why should problems develop under seemingly less severe conditions? Should this discourage the fair-weather camper from considering such a stove? 'Smutek. Ray, "The World's Best Backpacker, JuneIJuly 1981, pp. 50-61.
186
Answer
Backpacking Stoves,"
Journal of Chemical Education
The cartridges contain liquified butane. Mast of the butane stoves on the market are vapor fed. In order for them to work, the butane must boil (i.e., the vapor pressure of the hutane must exceed the atmospheric pressure). At sea level the atmospheric pressure is 760 tom and butane will boil a t O°C. At higher elevations, the air pressure is less and the butane will boil at a lower temperature. As long as the temperature of the stove is above the boiling point, the stove will work fine, but if the temperature drops below the boiling point, the stove will refuse to work. The exact temperature a t which this happens depends on the atmospheric pressure, which in turn depends on the elevation.
Approx. atmospheric pressure Elevation above sea level in) (m) (torr)
0 10,000 20,000 27.200
0 3,050 6.100 8.300
760 526 360 250
~ k m p e r ~ t uat r ewhich vapor pressure of butane exceeds atmos. press (boiling pt.) (OF) (OC)
32 15 0 -15
0
-9 -18 -26
Mathematical problems and theoretical questions relating to practical applications will tingle your brains and those of your students in this monthly minifeature. Contrib~tionsto this feature are welcome and should be addressed to the feature editor. Detailed solutions may be requested from the feature editor.
