Numerical Formulation

The geometry of plain tube consist of a cylindrical tube of diameter 25.54 mm diameter and length of 1800 mm. The geometry for helical screw tape inserts with different twist ratio is made by winding uniformly a strip of 8.5 mm width over an 8 mm rod using twist option in sweeping of faces. The angle of twist is 3600 over a length of 75, 100, and 125 mm for twist ratios of 2.93, 3.91 and 4.89. The physical boundary conditions for the geometry are defined as inlet, outlet, wall of strip and cylindrical wall. The nano particles in the base fluid may be easily fluidized and consequently the effective mixture behaves like a single phase fluid. It is also assumed that the fluid phase and nanoparticles are in thermal equilibrium with zero relative velocity. This may be realistic as nano particles are much smaller than micro particles and the relative velocity decreases as the particle size decreases. The resultant mixture may be considered as a conventional single phase fluid.

Velocity Magnitude Contour

Conclusion

CFD Simulation study on heat transfer characteristics of a circular tube fitted helical tape insert under constant heat flux condition in laminar flow was presented. The heat transfer increases with Reynolds number and decrease in twist ratio with maximum being tape insert of twist ratio 2.93. By comparing heat transfer rate of water with CuO nanofluids of volume concentrations 0.5, 1.0 and 1.5%, enhancement is more for CuO nanofluids rather than water. The Nusselt number increases with Reynolds number and the volume concentration of nano fluids with maximum being 1.5 %. The increase in Nusselt number is 5-34% for tape inserts of different twist ratios and nanofluids of different volume concentrations. The heat transfer enhancement is 34 % for helical tape insert of twist ratio 2.93 and CuO volume concentration of 1.5 % corresponding to Reynolds number of 2039. The data obtained by simulation are matching with the literature value of water with the discrepancy of less than 10% for plain tube and tube fitted with helical tape inserts for Nusselt number.