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This study investigates heat transmission and thermal performance factor characteristics in a tube with coil wire and twisted tape inserts using air as the working fluid. This study investigates heat transmission and thermal performance factor characteristics in a tube with coil wire and twisted tape inserts using air as the working fluid. The goal of this research is to improve forced convection heat transfer in tubes with and without swirl inserts and coil wire inserts for air Reynolds numbers ranging from 10.328×103 to 11.769×103. The impacts of different parameters of heat transfer are considered in this work with heat flux are constant conditions of 600 W/m2 and 800 W/m2 with using the coil wire and twisted tapes with three ratios (y/w = 3, 4 and 5). The test section is a horizontal annular passage with outer diameter 10 cm. The results showed that using coil wire inserts to improve heat transfer coefficient factors in tubes resulted in local heat transfer coefficient percentages of (5.1%) to (7.8%) with heat flux are constant conditions of 600 W/m2 and 800 W/m2, respectively. While tube with swirl inserts provide local heat transfer coefficient percentages of (3.6% to 6.1%) for heat fluxes (600) W/m2 and (800) W/m2, respectively. The obtained results demonstrate that as the twisted ratio (y/w) decreases, the mean Nusselt number and heat transfer coefficient in the tube with twisted tape and coil wire rise. Experimental results is shown, heat transfer coefficient for the coil wire when compared with that of swirl inserts tube were ranged between (10.6%) to (16.5%) and (11.5%) to (17.3%) for the heat flux (600) W/m2. [ABSTRACT FROM AUTHOR]

The paper dealt with an experimental investigation for mini vertical tube through study the transfer of CO2 heat convection at supercritical pressures. The dimensions of tube were 4mm and 10mm for diameter and length respectively. Many parameters have been measured to investigate the heat transfer convection which are; coefficients of heat transfer, temperatures of fluid bulk, temperatures of wall, rate of mass flow, temperature of inlet and flux of heat. The collected results showed that the heat transfer by convection has been affected by CO2 heat buoyancy and thermos-physical characteristic. On the other hand, the proportional relationship between heat transfer by convection and mass flow rate not fixed sometimes when the mini tube being empty. Moreover, the main influences on the heat transfer by convection were due to temperature of the inlet, flux of the heat and rate of the mass flow. [ABSTRACT FROM AUTHOR]