2001 Fundamentals Part 1 ppsx

[...]... conduit wall surface For smooth conduit walls, empirical correlations give 0. 316 4 f = 0.25 Re for Re < 10 0.2 21 f = 0.0032 + -0.237 Re for 10 < Re < 3 × 10 5 5 (28a) 6 (28b) Generally, f also depends on the wall roughness ε The variation is complex and best expressed in chart form (Moody 19 44) as 1 = 1. 14 + 2 log ( D ⁄ ε ) f (29a) Values of f between the values for smooth tubes and...2.8 20 01 ASHRAE Fundamentals Handbook (SI) flow control devices to avoid flow dependence on downstream conditions D 2 0.250 2 2 A 1 = π  -  = π   = 0.04 91 m  2  2  0.200 V 1 = Q ⁄ A 1 = - = 4.07 m ⁄ s 0.04 91 FLOW ANALYSIS Fluid flow analysis is used to correlate pressure changes with flow rates... is the same The frictional losses HL are evaluated as 7.5 m of air between stations 1 and 2, and 72.3 m between stations 3 and 4 Solution: The following form of the generalized Bernoulli relation is used in place of Equation (25a), which also could be used: 2 ( p 1 ⁄ ρ 1 g ) + α 1 ( V 1 ⁄ 2g ) + z 1 + H M 2 The term 2 V1 ⁄ 2g can be calculated as follows: 2 2 The term V 2 ⁄ 2g can be calculated in a... in the pressure-density relation: ∫ 2 2 2 V1 V2 dp - + α 1 - + E M = α 2 - + E L 2 2 ρ 1 (25a) Example 1 Specify the blower to produce an isothermal airflow of 200 L/s through a ducting system (Figure 12 ) Accounting for intake and fitting losses, the equivalent conduit lengths are 18 and 50 m and the flow is isothermal The pressure at the inlet (station 1) and following the discharge (station 4),... Colebrook’s natural roughness function: 19 .3 = 1. 14 + 2 log ( D ⁄ ε ) – 2 log 1 + f Re ( ε ⁄ D ) f (29b) A transition region appears in Figure 13 for Reynolds numbers between 2000 and 10 000 Below this critical condition, for smooth walls, Equation (27) is used to determine f ; above the critical condition, Equation (28b) is used For rough walls, Figure 13 or Equation (29b) must be used... opposite sides of the blower Because conditions at stations 1 and 4 are known, they are used, and the locationspecifying subscripts on the right side of Equation (25b) are changed to 4 Note that p1 = p4 = p, 1 = ρ4 = ρ, and V1 = V4 = 0 Thus, ( p ⁄ ρg ) + 0 + 0. 61 + H M = ( p ⁄ ρg ) + 0 + 3 + ( 7.5 + 72.3 ) so HM = 82.2 m of air For standard air (ρ = 1. 20 kg/m3), this corresponds to 970 Pa The pressure difference... configurations For gas flows at pressure ratios below the choking critical [Equation (24)], the mass rate of flow is Pd ( k – 1) ⁄ k  Pu  P d · m = Cd Ao C 1  - - 1 –  -  P u  Tu  Pu Fig 14 Valve Action in Pipeline (36) where C1 = k R T u, d = = = = 2k ⁄ R ( k – 1 ) ratio of specific heats at constant pressure and volume gas constant absolute temperature subscripts referring to upstream... Fig 12 Blower and Duct System for Example 1 (26) where L is the length of conduit of diameter D and f is the friction factor Sometimes a numerically different relation is used with the Fanning friction factor (one-quarter of f ) The value of f is nearly constant for turbulent flow, varying only from about 0. 01 to 0.05 Fluid Flow 2.9 Fig 13 Relation Between Friction Factor and Reynolds Number (Moody 19 44)... as the HM It can be obtained by calculating the static pressure at stations 2 and 3 Applying Equation (25b) successively between stations 1 and 2 and between 3 and 4 gives ( p 1 ⁄ ρg ) + 0 + 0. 61 + 0 = ( p 2 ⁄ ρg ) + ( 1. 06 × 0.846 ) + 0 + 7.5 ( p 3 ⁄ ρg ) + ( 1. 03 × 2.07 ) + 0 + 0 = ( p 4 ⁄ ρg ) + 0 + 3 + 72.3 The elevation changes involving z are often negligible and are dropped The pressure form... information on heat transfer to or from buildings or refrigerated spaces can be found in Chapters 25 through 31 of this volume and in Chapter 12 of the 19 98 ASHRAE Handbook—Refrigeration Physical properties of substances can be found in Chapters 18 , 22, 24, and 36 of this volume and in Chapter 8 of the 19 98 ASHRAE Handbook—Refrigeration Heat transfer equipment, including evaporators, condensers, heating and . 1. 14 Ideal Thermal Cycle 1. 14 Working Fluid Phase Change Constraints 1. 14 Working Fluids 1. 15 Absorption Cycle Representations 1. 16 Conceptualizing the Cycle 1. 16 Absorption Cycle Modeling 1. 17 Ammonia-Water. Re.⁄=⁄= f 0. 316 4 Re 0.25 =for Re10 5 < f 0.0032 0.2 21 Re 0.237 += for 10 5 Re 3<< 10 6 × 1 f 1. 14 2 log D ε⁄()+= 1 f 1. 14 2 log D ε⁄()+=2 log 1 9.3 Re ε D⁄() f +– Fluid Flow 2 .11 change. Such. only from about 0. 01 to 0.05. dp ρ 1 2 ∫ α 1 V 1 2 2 E M ++ α 2 V 2 2 2 E L += p 1 ρ 1 g⁄()α 1 V 1 2 2g⁄()z 1 H M +++ p 2 ρ 2 g⁄()α 2 V 2 2 2g⁄()z 2 H L +++= V 1 2 2g⁄ Fig. 12 Blower and Duct