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In this study, CFD analysis of air-heating vaporizers was conducted. A longitudinally finned vertical pipe was used to represent the air-heating vaporizer in the CFD model. Nitrogen gas was used as the working fluid inside the vertical pipe, and it was made to flow upward. Ambient air, which was the heat source, was assumed to contain no water vapor. To validate the CFD results, the convective heat transfer coefficients inside the pipe, h i-c , derived from the CFD results were first compared with the heat transfer coefficients inside the pipe, h i-p , which were derived from the Perkins correlation. Second, the convection heat transfer coefficients outside the pipe, h o-c , derived from the CFD results were compared with the convection heat transfer coefficients, h o-a , which were derived from an analytical solution of the energy equation. Third, the CFD results of both the ambient-air flow pattern and temperature were observed to determine whether they were their reasonability. It was found that all validations showed good results. Subsequently, the heat transfer coefficients for natural convection outside the pipe, h o-c , were used to determine the Nusselt number outside the pipe, Nu o. . This was then correlated with the Rayleigh number, R a . The results show that R a and Nu o have a proportional relationship in the range of 2.7414x10 12 ≤ Ra ≤ 2.8263x10 13 . Based on this result, a relation for the Nusselt number outside the pipe, Nu o , was proposed.

The article represents an experimental investigation on friction and turbulent flow characteristics of free airflow through a rectangular duct fitted with semicircular ribs of uniform height (e = 3.5 mm) on one principle wall. The aspect ratio of the rectangular duct was AR= 5 where the duct height was 30 mm. Four different rib pitches of 28 mm, 35 mm, 42 mm, and 49 mm were examined with constant rib height to hydraulic diameter ratio (e/Dh = 0.07) and constant rib height to channel height ratio (e/H = 0.116). The experimental results show some significant effects of pressure drop as well as turbulent characteristics at various configurations among different numbers of rib arrangements varying Reynolds number in the range of 15000 to 30000. Experimental results have been compared with numerical analysis and it can be seen a good agreement. The result explains the phenomena elaborately between two periodic ribs and enables to optimize the rib pitch ratio in terms of turbulence kinetic energy for maximum heat transfer.