Canadian engineer . sible course of callingto their aid the services of an expert, they more frequentlydraw out what they think ought to do, and place the respon-sibility upon the contractor. The present condition of gen-eral knowledge upon the subject of the stability of tall chim-neys is strikingly shown in connection with the This was designed to withstand a windi pressure of160 lb. per square foot; Prof. Rankine calculated that itwould stand only 70 lb. per square foot, while Mr. R. , a later writer, estimated that a wind pressure of only32 lb. per square foot ove
Canadian engineer . sible course of callingto their aid the services of an expert, they more frequentlydraw out what they think ought to do, and place the respon-sibility upon the contractor. The present condition of gen-eral knowledge upon the subject of the stability of tall chim-neys is strikingly shown in connection with the This was designed to withstand a windi pressure of160 lb. per square foot; Prof. Rankine calculated that itwould stand only 70 lb. per square foot, while Mr. R. , a later writer, estimated that a wind pressure of only32 lb. per square foot over the whole height would be suffic-ient to damage it. Tall chimneys ought to be designed uponscientific principles, so that there is an absolute guaranteefor their stability, and in the following paper the authordesires to elucidate these principles. Height.—In designing a tall chimneyj it is desirablefirst to know what height to make it. Forty-five feet is anordinary height to serve two steam boilers, but in some. -g—sr Tons per neekFig. 1—Height of Chimney According to Consumptionof Coal. towns, as Manchester and Leeds, go ft. is the minimum al-lowed. They are sometimes proportioned for height accorxJ-ing to the coal burnt per week of fifty-six hours, thus :—4 tons per week = 75 ft. high. 13 = 100 26 = 120 50 = 150 100 = 180 150 = 200 This table is checked by the graphic curve shown inFig. I. Another rule is to make the height of the chimneythree times length of boiler + twice distance of furthestboiler to chimney. This allows i ft. of height for every footthe gases travel round the boiler and 2 ft. of height for everyfoot of external flue. And again, a round chimney shouldnot exceed twenty-five times its internal diameter in many modern power stations Babcock & Wilcox boilersand Greens economizers are used; what is saved in obstruc-tion in the boilers is lost in the economizers, so that nomaterial difference arises, but the chimney shafts are, as arule, onl
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