MIXED CONVECTION LAMINAR-FLOW AND HEAT-TRANSFER OF LIQUIDS IN HORIZONTAL INTERNALLY FINNED TUBES

Developing mixed convection flow in internally finned tubes with varia ble viscosity was numerically investigated for a fin geometry range of 8 less than or equal to N less than or equal to 24, 0.1 less than or equal to H less than or equal to 0.3 and an operating condition range of 50 less than or equal to Pr-in less than or equal to 1250, 0 less t han or equal to Ra-in less than or equal to 10(7), and 0 less than or equal to q(w)d/k(in) less than or equal to 2000. The numerical model w as validated by comparison with existing numerical and experimental da ta. Internal finning was found to produce a complex two-cell, buoyancy -induced vortex structure. The results show that coring (retarded velo city in the interfin region) leads to poor heat transfer performance o f tubes with huge numbers of fins or with tall fins. The overall resul ts indicated that large enhancement in the heat transfer can be obtain ed in the entrance region. Furthermore, variable viscosity effects are seen to have a pronounced effect on the friction factor and Nusselt n umber predictions.