4 The distance required for flow to develop is called the entrance length (Le). For flow entering a circular pipe from a reservoir the Le can be calculated from the following equation:-
5 Summary In summary, flow is classified into four categories:- laminar developing,laminar fully developedturbulent developingturbulent fully developed.The key to classification is to calculate the Reynolds number
6 ExampleConsider fluid flowing in a round tube of length 1 m and diameter 5 mm. Classify the flow as laminar or turbulent and calculate the entrance length for (a) air (50°C) with a speed of 12 m/s and(b) Water (15°C) with a mass flow rate of 8 g/s .
7 Solution 1. Air (50°C), ν = 1.79 × 10-5 m2/s. 2. Water (15°C), μ = 1.14 × 10-3 N*s/m2.𝑅𝑒= 𝑉∗𝐷 𝑣 = 12∗ ∗ 10 −5 =3350The flow is turbulent for air𝐿𝑒=50∗𝐷=50∗0.005=0.25𝑚𝑅𝑒= 4∗𝑚ʹ Π∗𝐷∗µ = 4∗ ∗0.005∗1.14∗ 10 −3 =1787The flow is laminar for water𝐿𝑒=0.05∗Re∗D=0.05∗1787∗0.005=0.447m
9 Pipe Head LossComponent head loss is associated with flow through devices such as valves, bends, and tees. Pipe head loss is associated with fully developed flow, and it is caused by shear stresses that act on the flowing fluid.Note that pipe head loss is sometimes called major head loss, and component head loss is sometimes called minor head loss.
10 Darcy-Weisbach Equation To use Darcy-Weisbach Equation the flow should be fully developed and steady. The Darcy-Weisbach equation is used for either laminar flow or turbulent flow and for either round pipes or nonround conduits such as a rectangular duct.
11 Friction Factor For Laminar flow :- 𝑓= 64 𝑅𝑒 For turbulent flow 𝑓= ( log 10 ( 𝑒 3.7∗𝐷 𝑅𝑒 0.9 ) ) 2Or from Moody Chart