Question

QUESTION 2 A 30 Watt brake horsepower centrifugal blower rotates at 1200 rpm and delivers air at 0.4 m3/s. The air enters the impeller radially and exits at an angle ?2-34° from radial. The impeller inlet radius is 40 mm and the outlet radius is 100 mm. Assuming 100% efficiency, determine the net head produced by this blower, the tangential velocity component at the outlet (Ved, the outlet blade width and the exit blade angle (Pa). [Use for air: Pai 1.20 kg/m] (20 marks)

Answer 1

Given, Brake hours power = B . P = 30w n bar = 1200 rpm Volume flow site = V = 0.4 m^3 /s alpha_1 = 0 degree , alpha_2 = 34 degree Impeller inlet radios , r_1 = 40mm = 0.04m outlet radios , r_2 = 100mm = 0.1m = 1.2kglm^3 therefore B . P = 30 = PgVH = 1.2 times 9.81 times 0.4 times H H = 6.371m and we also Know, H = w/g (r_2 v_2 , t - r_1 v_1 , t) here, w = 2 pi r/60 = 1200 times 2 pi /60 = 125.66lad/s \r\n and , v_1 , t = { because alpha_1 = 0} Hence: H = w/g (r_2 v_2 , t - 0) = 6.371 rightdoublearrow 125.66/981 times (0.1 times v_2 , t) = 6.371 v_2 , t = 4.974 m/s But, v_2 , t = v_2 n tan alpha_2 rightdoublearrow v_2 , n = 4.974/tan 34 degree = 7.374 m/s now, v_2n = v/2 pi r_2 b_2