14
Round [25]
4 × 103 ≤ Re ≤ 108
0 ≤ ε/D ≤ 5 × 10−2
Non-advisable
15
Brkić [26]
where 
Not specified
Less accurate
16
Rao and Kumar [27]
where 
Not specified
Extremely
inaccurate
17
Swamee and Jain [28]
5 × 103 ≤ Re ≤ 108
10−6 ≤ ε/D ≤ 5 × 10−2
Less accurate
18
Vantankhah and Kouchakzadeh [29]
where 
5 × 103 ≤ Re ≤ 108
10−6 ≤ ε/D ≤ 5 × 10−2
Extremely
accurate