BACKGROUND AND FORMULATION OF RESEARCH
1.6 Significance of formulated research work
Now-a-days, helical coil is hence gaining importance as a simple intensified and inexpensive means of achieving gas-liquid or gas-liquid-solid reactor. In literature, significant research has been reported to understand the properties of non-Newtonian fluids like thermodynamics, stability, thermal conductivity, thermal diffusively, viscosity and convective heat transfer
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coefficient. Apart from gas-Newtonian liquid reaction, there are lots of reactions with gas- non-Newtonian liquid which are executed in the chemical and biochemical industries.
Literature shows that there are limited works on air-non-Newtonian liquid two-phase flow through helical coils as compared to air-Newtonian fluids. The behaviour of two phase flow in helical system shows a different behaviour than vertical and horizontal systems.
Hydrodynamics studies help to understand the flow patterns, flow behaviour holdup and pressure drop of fluid in the helical system. The residence time of gas bubbles in helical system is more than vertical system. Reactions requiring high residence time can be well handle in helical system. The studies helps to understand the residence time distribution of liquid and the dispersion characteristics of system. Heat transfer coefficient is key parameter in design of gas-liquid contactor. Heat transfer characteristics help to optimise the rate of heat input and output to the reactor. A detailed study of heat transfer is required in helical system to understand and quantify the heat transfer for optimization of the operation and minimize the capital cost. From the literature review mass transfer coefficient in helical system is more than the straight tube. In order to achieve a high degree of mass transfer efficiency, all the parameters affecting mass transfer characteristics has to be studied in detailed.
Nomenclature
dt Diameter of tube (m) Dc Diameter of coil (m)
De Dean Number
Re dt/Dc
(-) Deq Equivalent diameter (Lc/nπ) (m)He Helical number
Re[(dt /Dc)/{1(p/Dc)2}]0.5
(-) NNU Nusselt number (hd/k) (-)Nub Nusselt number (hd/k) in case where the buoyancy force alone acts (-)
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Background and Formulation of Research Nuc Nusselt number (hd/k) in case where the centrifugal force alone acts (-)
Nuo Nusselt number (hd/k) for Poiseuille flow (an incompressible and Newtonian fluid in laminar flow flowing through a long cylindrical tube of constant cross section) (-)
Nsc Schmidt number (=/Dm) (-)
p Pitch (m)
Re Reynolds Number (=dtUl/) (-)
usl Superficial liquid velocity (=Ql/A) (m/s) usg Superficial gas velocity (=Qg/A) (m/s) Vd Drift flux velocity (m/s)
Greek Letters
Density (kg/m3)
λ Curvature ratio (dt/Dc)
l Viscosity of the liquid (kg/m.s)
g Viscosity of the gas (kg/m.s)
eff Effective viscosity (kg/m.s)
Shear stress (N/m2) τn Torsion number (2τRe)
g Gas holdup (-)
θ Contact angle (degree) Subscripts
c Coil
f Frictional
g Gas
l Liquid
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t Tube
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