Helicoidal pipes

The most prominent characteristic of flow in curved ducts and helicoidal pipes is the secondary flow induced by centrifugal force due to the curvature of the pipe. Consequently, the friction factor is higher in curved pipes than that in straight pipes for the same Reynolds number. The pitch of the helicoidal pipe also has an effect on the flow. As a result, the heat trans-... 

Spiral coils are curved ducts with varying curvature. The friction factor and heat transfer rate for spiral coils are also included in this section. In addition to the dimensionless parameters used in straight pipes, the following parameters are particularly useful in the case of curved ducts or helicoidal pipes the Dean number De the helical number He, and the effective radius of curvature Rc. These are defined as follows ... 

In this section, emphasis will be given to the correlations used for calculating the friction factors and Nusselt numbers for laminar and turbulent flows in curved ducts, helicoidal pipes, and spiral ducts. These will be presented as the ratio of the friction factor in curved ducts to the friction factor in straight ducts fcJfs and the ratio of the Nusselt number in curved ducts to the Nusselt number in straight ducts Nuf/Nus, in most cases. The subscript c represents curved ducts or helicoidal pipes, while the subscript s denotes straight pipes of the same shape. 

Dean [188,189] first studied the velocity profile of flow in helicoidal pipes using perturbation analysis. His result is valid only for De < 20, where the velocity distribution is almost identical to that found in straight ducts. Mori and Nakayama [190] have obtained the solution for De > 100 for a coil with R > a. Their results are in agreement with the experimental data reported by Mori and Nakayama [190] and Adler [191] and numerical simulations [192]. 

The friction factors for fully developed flow in helicoidal pipe proposed by Srinivasan et al. [193] in the range of 7 < R/a < 104 follow ... 

The critical Reynolds number, which is used to identify the transition from laminar to turbulent flow in curved or helicoidal pipes, has been recommended for design purposes by Srinivasan et al. [193] ... 

The fully developed Nusselt numbers for laminar flow in helicoidal pipes subjected to the uniform wall temperature have been obtained theoretically and experimentally by Mori and Nakayama [196], Tarbell and Samuels [197], Dravid et al. [198], Akiyama and Cheng [199], and Kalb and Seader [200]. A comparison of these results has been made using the Manlapaz-Churchill [201] correlation. 

For helicoidal pipes with the thermal boundary condition, the Nusselt number has been developed by Manlapaz and Churchill [201] ... 

In Table 5.44, it can be seen that the pitch of the helicoidal coil has almost no influence on the Nusselt number. However, the studies by Yang et al. [206, 207] have shown a positive effect of the pitch on the Nusselt number when Pr > 1. In addition, the experiments conducted by Austen and Soliman [208] indicated that the Nusselt number for the laminar flow of water (3 < Pr < 6) in the uniformly heated helicoidal pipe is in good agreement with the prediction from Manlapaz and Churchill [201]. 

An experimental correlation has been obtained by Abul-Hamayel and Bell [209] to account for the density and viscosity variations in helicoidal pipe. Experiments with water, ethylene glycol, and w-butyl alcohol in a helicoidal pipe with the boundary condition were conducted. The following equation was derived from the measurement data ... 

G. Yang, Z. F. Dong, and M. A. Ebadian, Convective Heat Transfer in a Helicoidal Pipe Heat Exchanger, J. Heat Transfer, (115) 796—800,1993. 

C. X. Lin, P. Zhang, and M. A. Ebadian, Laminar Forced Convection in the Entrance Region of Helicoidal Pipes, Int. J. Heat and Mass Transfer. In press. 

S. Liu, and J. H. Masliyah, Developing Convective Heat Transfer in Helicoidal Pipes with Finite Pitch, Int. J. Heat and Fluid Flow, (15/1) 66-74,1994. 

The screw conveyor is one of the oldest and most versatile conveyor types. It consists of a helicoid flight (helix rolled from flat steel bar) or a sectional flight (individual sections blanked and formed into a helix from flat plate), mounted on a pipe or shaft and turning in a trough. Power to convey must be transmitted through the pipe or shaft and is limited by the allowable size of this member. Screw-conveyor capacities are generally limited to around 4.72 mVmin (10,000 ftvh). 

The pitch effect in helicoidal circular pipe has been considered in the investigation conducted by Yang and Ebadian [221]. These researchers have concluded that the effect of pitch is minimum on heat transfer. 

Apparatus belonging, to the first type is shown in Fig. 10-6. It consists of a cylindrical tank, containing a helicoid, or spiral, propeller, driven by a pully. Hydrogen is admitted through a perforated pipe, and internal coils... 

Fig. 84 shows this type of mixers, made of a plastic pipe inside which there are helicoidal partitions. We already discussed the mode of action of these mixers earlier. The choice of the mixers depends on the following parameters ... 

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