The principles of heat transfer enhancement in the core flow of tube have been proposed to improve the temperature uniformity and reduce flow resistance, which is different from that of heat transfer enhancement in the boundary flow of tube. Helical twisted tape inserts with four different widths (w = 7.5mm, 12mm, 15mm and 20mm) have been investigated for different inlet volume-flow rates ranging from 200L/h to 500L/h. A three-dimensional turbulence analysis of heat transfer and fluid flow is performed by numerical simulation. The simulation results show that the average overall heat transfer coefficients in circular plain tubes are enhanced with helical twisted tape of different widths by as much as 220∼390% at a constant tube-side temperature and the friction factor are enhanced by as much as 50% to 790%. The PEC value of the helical twisted tape inserts of different width varies between 1.60 and 3.15. Physical quantity synergy analysis is also performed. The synergy angles α, β, γ and θ are calculated, and the numerical results verify the synergy regulation among physical quantities of fluid particle in the flow field of convective heat transfer, which can guide the optimum design for better heat transfer units and high-efficiency heat exchangers.
Radiative heat transfer enhancement to a water tube by combustion gases in porous media.