Pressure drop Helical coils

A number of equations have been proposed for use in the calculation of pressure drop in coils of constant curvature [Srinivasan et al (1968)]. The latter are known as helices. For laminar flow, Kubair and Kuloor (1965) gave an equation for the Reynolds number range 170 to the critical value. In terms of the Fanning friction factor, their equation can be written as... 

For upflow in helically coiled tubes, the flow pattern, pressure drop, and holdup can be predicted by the correlations of Baneijee,... 

Related Calculations. Helical Coils. The same procedure can be used to calculate the pressure drop in helical coils. For turbulent flow, a friction factor for curved flow is substituted for the friction factor for straight tubes. For laminar flow, the friction loss for a curved tube is expressed as an equivalent length of straight tube and the friction factor for straight tubes is used. The Reynolds number required for turbulent flow is 2100[1 + 12(Dj/Dc)1/2], where Dt is the inside diameter of the tube and Dc is the coil diameter. 

The axial pressure drop due to friction for a helical coil tube can then be calculated by... 

Number of turns of the coil required = total length/perimeter = 206/12.97 = 16 The pressure drop is higher due to helical flow (Sriifivasan et al., 1968) ... 

B. E. Boyce, J. G. Coiller, and J. Levy, Hold Up and Pressure Drop Measurements in the Two Phase Flow of Air Water Mixtures in Helical Coils, Co-current Gas Liquid Fluid, Plenum Press, London, pp. 203-231,1969. 

V. Kadambi, Heat Transfer and Pressure Drop in a Helically Coiled Rectangular Duct, ASME paper no. 83-WA/HT-l, 1983. 

Pressure drop in helical coils is dependent on whether the flow is laminar or turbulent. Typically flows are laminar at low fluid velocities and turbulent at high fluid velocities. In cuived pipes and coils a secondary circulation takes plac e called the double eddy or Dean Effect. VVliile this circulation increases the friction loss, it also tends to stabilize laminar flow, thus increasing the critical Reynolds number. 

The flow through a helical coil is uniquely different from that through a straight pipe due to the secondary flow pattern induced by the imbalance in the radial direction between the outwards-directed centrifugal force and the inwards-directed pressure force acting on the fluid. Reviews by Berger et al. [34], Nandakumar and Masliyah [36], and Ito [40] summarize recent studies of curve pipe flows. Ali reported the pressure drop performance of different types of coiled tubes [41]. The literature review attempted here is not broad or deep, but focuses mainly on the pressure drop of fluid flow through horizontal conduits and curved pipes. 

Kubair and Kuloor generated experimental data on non-isothermal pressure drop for different aqueous solutions of glycerol flowing in helical coils of different geometries, placed in horizontal position [92]. They proposed the following equation for isothermal condition... 

Srinivasan et al. [96] conducted an experiment to generate the pressure drop data for flow through the helical coils. They suggested the following equation... 

Mishra and Gupta presented pressure drop data for Newtonian liquid flowing through helical coils of different dimensions [102]. The coils were made of thick-walled, flexible, and smooth polythene pressure tubing of uniform circular cross section. They observed that the pitch had a negligible effect on pressure drop if it was less than the diameter of the coil. They modified the Dean number to incorporate the effect of pitch as... 

Mishra and Gupta [102] conducted experiments through different types of helical coils to generate the pressure drop data for turbulent flow condition and proposed the following empirical correlation... 

Initially he conducted the experiment on water flow through horizontal pipe (same PVC pipe for both cases) to find the roughness values (Venkatesan et al. [62], He compared the experimental friction factor for coil with the values obtained from smooth coil equation and observed that the experimental friction factor was higher than that of smooth coil. He found that as coil diameter increased the friction factor decreased (Figure 2). He presented a generalized correlation for predicting the frictional pressure drop across the rough helical coils as... 

Typical experimental setup used by Das [122] is shown in Figure 3. The experimental apparatus consisted of a water storage tank, a centrifugal pump, a test section, control and measuring systems for the flow rate, and pressure drop. The pipes were wound round a wooden cylindrical frame of known diameter to form a helical coil. The coil diameter could be varied by changing the diameter of the... 

Kubair, V. and C. B. S. Varrier, Pressure Drop for Liquid Flow in Helical Coils, Trans. Indian Instn. Chem. Engrs., 14, 93-97 (1961-1962). 

Kubair, V. and N. R. Kuloor, Non-isothermal Pressure Drop Data for Liquid flow in Helical coils, Indian J. Technol., 3, 5-7 (1965). 

Anglesea, W. T., D. J. B. Chambers and R. C. Jeffrey, Measurements of Water/Steam Pressure Drop in Helical Coils at 179 Bars, Proc. Symp. Multiphase Flow Systems, Inst. Chem. Engrs. Symp. Series No. 38 Paper 12 (1974). 

Ruffell, A. E., The Application of Heat Transfer and Pressure Drop Data to Design of Helical Coil Once-through Boilers, Proc. Sym. Multiphase Flow Systems, Instn. Chem. Engg. Sym. Series, No. 38, Paper 15 (1974). 

Guo, L.-J., Feng, Z.-P., Chen, X.-J., 2001. Pressure drop oscillation of steam-water two-phase flow in a helically coiled tube. International Journal of Heat and Mass Transfer 44, 1555—1564. 

It is to be noted that the ratio of the friction factor / to the heat transfer factor J for compact ribbon-packed heat exchangers is approximately equal to the ratio of / to j reported in the present work. F rom this it may be concluded that more compact heat exchangers can be designed with helically finned and coiled tubing, which also represents a Collins type of heat exchanger, without any sacrifice in shell-side pressure drop. 

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