عنوان المقالة:أنتقال الحرارة في الحمل المختلط في الانابيب المائلة ذات الفيض الحراري الثابت Mixed Convection Heat Transfer in Inclined Tubes with Constant Heat Flux
أحمد توفيق السامرائي , رائد رشاد جاسم , ثامر خليل ابراهيم
المؤلفون بالإنجليزي
, Thamir K. Ibrahim,Ahmed Tawfeeq Ahmed Al-Sammarraie, Raaid Rashad Jassem
الملخص العربي
Mixed convection heat transfer in inclined tubes of circular cross section has been
experimentally studied for assisting, thermally developing and thermally fully developed
laminar-to-turbulent air flows, under constant wall heat flux boundary condition, at
Reynolds numbers (Re<2300) for the laminar and (2300<Re<4000) for transition-toturbulent
air flows, and the heat flux is varied from 492 to 1442 W/m2. The mixed
convection regime has been bounded by the convenient selection of Reynolds number
range and the heat flux range so that the obtained Richardson number (Ri) is varied
approximately from 0.146 to 1.058. The experimental rig consists of three copper tubes as
test section with 600 mm heated length and length to diameter ratio (L/D= 11.8, 15.75 and
31.5). This study has investigated the effect of the heat flux, diameters and inclination
angle of the tube on the mixed convection heat transfer process. In this search, the local
Nusselt numbers (Nu) with the dimensionless axial distance (Z) are presented. The results
have clearly shown that an increase in the Nusselt number values as the heat flux increases
and as the tube inclination angle moves from (q = 60°) to (q = 30°), vice versa the Nusselt
number decrease with effect of increase the length to diameter ratio (L/D). For the range of
Reynolds numbers used in experiments, the maximum Nusselt number has occurred at
about 30° inclination relative to the horizon. Present experimental results have a good
agreement with previous results obtained for similarly tubes inclination angles. Based on
the experimental results, the average Nusselt number ( Nu ) has been correlated in an
empirical equation with the effect of the Rayleigh number, Reynolds number, length to
diameter ratio and inclination angle. Good agreement can be seen between the experimental
results and this equation.
الملخص الانجليزي
Mixed convection heat transfer in inclined tubes of circular cross section has been
experimentally studied for assisting, thermally developing and thermally fully developed
laminar-to-turbulent air flows, under constant wall heat flux boundary condition, at
Reynolds numbers (Re<2300) for the laminar and (2300<Re<4000) for transition-toturbulent
air flows, and the heat flux is varied from 492 to 1442 W/m2. The mixed
convection regime has been bounded by the convenient selection of Reynolds number
range and the heat flux range so that the obtained Richardson number (Ri) is varied
approximately from 0.146 to 1.058. The experimental rig consists of three copper tubes as
test section with 600 mm heated length and length to diameter ratio (L/D= 11.8, 15.75 and
31.5). This study has investigated the effect of the heat flux, diameters and inclination
angle of the tube on the mixed convection heat transfer process. In this search, the local
Nusselt numbers (Nu) with the dimensionless axial distance (Z) are presented. The results
have clearly shown that an increase in the Nusselt number values as the heat flux increases
and as the tube inclination angle moves from (q = 60°) to (q = 30°), vice versa the Nusselt
number decrease with effect of increase the length to diameter ratio (L/D). For the range of
Reynolds numbers used in experiments, the maximum Nusselt number has occurred at
about 30° inclination relative to the horizon. Present experimental results have a good
agreement with previous results obtained for similarly tubes inclination angles. Based on
the experimental results, the average Nusselt number ( Nu ) has been correlated in an
empirical equation with the effect of the Rayleigh number, Reynolds number, length to
diameter ratio and inclination angle. Good agreement can be seen between the experimental
results and this equation.
رائد رشاد جاسم | Raaid Rashad Jassem | 4542