Helically coiled tubing service is one of the fastest growing technology in chemical, petrochemical, food and pharmaceutical industries. The helical coils also improve the performance of equipment like heat exchangers, coil steam generators, boilers, evaporators, reverse osmosis units, nuclear reactors, etc. due to its inherent secondary flow generation capability. This book reports the following topics: (i) Flow pattern and its map in helical coil. Model to predict the flow pattern transitions. (ii) Two-phase frictional pressure drop in helical coil based on flow pattern. (iii) The flow pattern-based dispersion characteristic of two-phase flow in vertical helical coil. (iv) The convective heat transfer of two-phase gas-non-Newtonian flow in vertical helical coil. (v) The flow pattern-based confined liquid-wall mass transfer in gas-non-Newtonian liquid flow condition in helical coil. The book may be useful for further understanding the flow phenomena in helical coil systems in different transport processes for industrial applications.