Dust Control Handbook for Industrial Minerals Mining and Processing

Other Hood ConsiderationsWhen dust is captured and pulled into a hood from a dust source, the hood converts staticpressure to velocity pressure and hood entry losses. Hood entry loss is calculated according tothe following equation:H e(K)(VP) SP hVP (1.6)where H e = hood entry loss, inches wg;K = loss coefficient;VP = velocity pressure in the duct, inches wg; andSP h = absolute static pressure about 5 duct diameters down the duct from the hood, inches wg.Air flowing through an exhaust hood will cause pressure changes that need to be calculated whenevaluating the impact on each individual hood in a multiple hood system. Figure 1.8 providesthe hood entry loss coefficients for three different types of hoods commonly used in mining andmineral processing facilities. The first case shows three different hood types: circular, square,and rectangular with plain openings. The second case shows loss coefficients with flangedopenings, and the last case shows a bell mouth inlet for just a circular duct. This figuredemonstrates the significant improvement in the design, and thus the lowering of the hood entryloss coefficient, with each improvement in the hood type.Figure 1.8. Hood entry loss coefficients for different hood types [adapted from ACGIH 2010].18 Fundamentals of Dust Collection Systems