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Determine the height of the chimney to produce a static draught of 22mm of water if the mean flue gas temperature in chimney is 290^oC and ambient temperature in boiler house is 20^oC. The gas constant for air is 29.26Kgm/Kgk and for chimney flue gas is 26.2 Kgfm/Kgk. Assume reading as 760mm of mercury?(a) 38.42m(b) 42.55m(c) 45.84m(d) 44.03mThis question was posed to me during a job interview.I need to ask this question from Draught System topic in chapter Steam Generators & Accessories of Energy Engineering

Answer»

Correct answer is (b) 42.55m

For explanation I would SAY: Density of air at 290K ρg = P/RT = [1.033 * 10^4 / 29.26 * 290]

= 1.217Kg/m^3

Density of fuel GAS at 563K, ρg = [1.033 * 10^4 / 26.2 * 563]

= 0.7 Kg/m^3

Static Draught, p = H (ρa– ρg)

22 = H (1.217 – 0.7)

H = 42.55m


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