Seite - 1538 - in Book of Full Papers - Symposium Hydro Engineering

3.3. ESTIMATION OF FRICTION FACTOR Implicit equation for estimation of friction factor was given by Colbrook in 1939 1 √𝑓 = −2𝑙 𝑜 𝑔 [ 𝑒 𝐷 3.7 + 2.51 𝑅 𝑒 √𝑓 ] (6) This equation needs iterative steps for its solution. Many investigators (some of them are listed in Annexure A) proposed approximate solution in form of explicit equation. Two power explicit equation given by the author (2017) Chavan is very convenient : 𝑓 = 0.0075( (4000) 𝑅 𝑒 0.05 ) 0.25+( 4000 𝑅 𝑒 ) 5 + 20 𝑅 𝑒 (7) Where 𝑓 = Friction factor Re = Reynolds Number given by 𝑅 𝑒 = 𝜌 𝐷 𝑉 𝜇 (8) 𝜇 = Coefficient of Dynamic viscosity Exit head loss is ℎ𝑒 = 𝑘 𝑒 𝑉 2𝑔 2 (9) Discharging capacity- Discharge passing through the tunnel flowing full is computed backwardly, using known head loss, known conditions in which tunnel is being operated i.e. Reynolds number, and friction factor curves for operation characteristics of particular tunnel are prepared. Based on the above losses, the diameter of the tunnel has to be fixed, such that it results in an overall economy. This is because if the diameter of a tunnel is increased, for example, the friction losses reduces The tunnel diameter determined as a result of economic studies should be examined from practical considerations, such as space requirements for the excavating equipment and the section may be modified if necessary, based on the 1538