HEAT TRANSFER ENHANCEMENT BY ARTIFICIAL ROUGHNESS AT REYNOLDS NUMBERS RELATED WITH LAMINAR AND TRANSITIONAL REGIMES FOR HIGH-VISCOUS LIQUIDS

ABSTRACT Artificial roughness (AR) formed by annular rolling or dimpling is one of the most well-known examples of Reynolds analogy (RA) breaking in a favor of heat transfer . Surfaces which can be called ARPD -Artificial Roughness, are manufactured by wall Pressure Deformation. ARPD surfaces have some similar thermal hydraulic properties which permit to unite them in the common group. General characteristics of ARPD surfaces are considered here. But the main attention is paid to such surface performance for coolants with high Prandtl numbers. It is important that Reynolds numbers must be close sufficiently to its critical value for smooth tube. Some experimental data show that extremely high heat transfer enhancement ratio can be obtained under such conditions for substantially less pressure loss ratio increase. Similar qualitative results obtained for several types of ARPDdimpled, annular rolled and spirally corrugated tubes -are demonstrated. These results are related partially with critical Reynolds number decrease and partially with specific character of heat transfer evolution in laminar -turbulent transition range for high-viscous liquids. Such enhancement method can be used effectively for heat exchangers with high-viscous liquids (oils, for example)