Investigation of pressure drop, acoustics and heat transfer in corrugated pipes

Frictional loss and acoustics of air flow in stainless-steel corrugated pipes have been experimentally investigated. The diameters of corrugated pipes were 20.4, 24.5, 34.5 and 40.1 mm. Flowrates were obtained by measuring pressure drop across orifices. Based on the behavior of the Darcy friction factor, the critical Reynolds numbers of the corrugated pipes at which flow changes from laminar to transition region are found to be 1500 to 1700, depending on the pipe diameters and corrugation sizes. Turbulent region begins at around Re = 2000 to 3000 for all corrugated pipes tested. For turbulent flow, in general, higher friction factors are observed for the larger ratio of the crest width to the pipe diameter. On the other hand, in laminar region the friction factor depends on only Reynolds number. The onset velocity is found to be independent of the pipe length. It transpires that the onset velocity corresponds to the Reynolds numbers at which turbulent region begins. The Strouhal number is observed to be almost constant over the wide range of Reynolds number, and appears to be influenced, not by the pipe length, but by corrugation sizes. The peak-whistling Strouhal number is found to be decreasing as the ratio of the diameter to the crest width increases. Another test setup is built to investigate convection in corrugated pipes which are 20.4 and 34.5 mm in diameter. The pipe is insulated and calibrated by measuring heat loss while no air is in and out from the pipe. Energy conservation is applied to derive the local mean temperature in the corrugated pipe. The local Nusselt number values for crest and hollow surface seem to be almost same. Average Nusselt number values for two pipes with diameters of 20.4 and 34.5 mm are observed to be close to each other in regard to Reynolds number.