流体力学粘性流体.ppt

06 - * Use Dh to calculate f, Flow through a Concentric Annulus Approximate Solution Similarly, use an effective diameter Deff is used in calculating f, Better Solution x u(r) u(r) r r=a r=b 06 - * K is the loss coefficient (different for each component, and generally provided by manufactures): Minor Losses Minor Loss The minor loss for a component is characterized by the loss coefficient, K, Loss Coefficient In addition to the major loss hf, the following components in the system bring additional losses called minor losses, denoted as hm. Pipe entrance or exit. Sudden expansion or contraction. Bends, elbows, tees, and other fitting. Valves, open or partially closed. Graduate expansion or contraction. (Recall the major loss ) 06 - * Total Loss and Pump/Turbine Selection Total Loss Total system include the major loss and all minor losses. For constant pipe diameter, Pump Selection The steady flow energy equation, including all losses in the system with a pump (a ? 1 for turbulent flow): Pump/ Turbine Power (hp = pump efficiency) (ht = turbine efficiency) 06 - * Typical Commercial Valves White 6th ed. Fig. 6.17 (a) Gate valve; (b) globe valve; (c) angle valve; (d) swing-check valve; (e) disk-type gate valve 06 - * Open Valves, Elbows Tees (White 6th ed Table 6.5) Valves (fully open) Globe 14.00 8.20 6.90 5.70 13.00 8.50 6.00 5.80 5.50 Gate 0.30 0.24 0.16 0.11 0.80 0.35 0.16 0.07 0.03 Swing check 5.10 2.90 2.10 2.00 2.00 2.00 2.00 2.00 2.00 Angle 9.00 4.70 2.00 1.00 4.50 2.40 2.00 2.00 2.00 Elbows: 45o regular 0.39 0.32 0.30 0.29 45o long radius 0.21 0.20 0.19 0.16 0.14 90o regular 2.00 1.50 0.95 0.64 0.50 0.39 0.30 0.26 0.21 90o long radius 1.00 0.72 0.41 0.23 0.40 0.30 0.19 0.15 0.10 180o regular 2.00 1.50 0.95 0.64 0.41 0.35 0.30 .025 0.20 180o long radius 0.40 0.30 0.21 0.15 0.10 Tees Line flow 0.90 0.90 0.90 0.90 0.24 0.19 0.14 0.10 0.07 Branch Flow 2.40 1.80 1.40 1.1