Many research projects have been developed for evolution of friction loss of pressurized fluids through out the would. During the last decades, plastic pipes (polyethylene and P.V.C types) have been introduced to the market and several researchers have tried to propose relationships or charts for evolution of friction loss in such pipes. In the present study, it has been tried to design and construct a system for laboratory measurement of friction loss of polyethylene pipes produced by four different Iranian manufacturing companies. The measurements were done on the pipes of 16 to 160 mm diameters. The overall results of the experiments showed that, except for some defected samples, friction loss coefficient conforms to the coefficients of smooth pipe for small diameter samples, and the difference between two becomes larger by increasing the pipe diameter.
Based on the test results and their conformity with the standard friction loss curves, the pipes were divided into three groups according to the diameters as follows:
-group I s32 mm.
-group II 50-60 mm.
-group III 90 mm.
Using regression analysis, the following relationships were obtained for determination of friction loss coefficient of each group:
-Group I = log
Valid for 44OO?Re<14oOOO
Where:
Re = Reynolds Number
I = friction loss coefficient
The maximum deviation with respect to Prandtle formula is 0.6%
Group II log
Valid for 4000 Re < 450000
The maximum deviation with respect to Prandtle formula is 7%
Group III = log
Valid for 4000 ?Re <700.000
The maximum deviation with respect to Prandtle formula is 16%. Since, the friction factor for some of small diameter pipes were less than the values for smooth pipes, it was found that using a factor equal to 1.67 (proposed by Orbina) instead of 2.51 (proposed by Colebrook & Prandtle) can eliminate the differences.
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