الفهرس 
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Abstract
In the present work the developing region for smooth and ribbed duct was investigated experimentally to enhance the heat transfer coefficient. The mean velocity of the air stream was varied from 1.62 x 104 to 7.2 x 104 , the rib pitch-to-height ratio (P/e) was 10 and 20, the rib height-to-channel hydraulic diameter ratio (e/De) was fixed at 18.75. A rectangular channel with an aspect ratio (W/H) of 4:1 ribbed with square and inverted trapezoidal rib geometries was investigated at different intake shapes (bellmouth, plenum box, and abrupt intakes).
The effects of the different investigated parameters on the local and average static pressure, friction factor, and heat transfer coefficient were studied.
The experimental results showed that the local static pressure coefficient in the developing length has lower value for sharp intakes (Abrupt and plenum box) than that for bellmouth intake. The maximum static pressure coefficient for smooth duct with abrupt and plenum intakes was found at the reattachment point at about X/De=0.95, while it was found at X/De=0.17 for the bellmouth intake. The effectof the intake shape for ribbed duct was more significant at the entrance region (X/De<0.69). It was found that the static pressure coefficient, Cp, for the ribbed duct with the abrupt intake is lower than that pf plenum and bellmouth ribbed ducts. These may be attributed to that the abrupt intakes accelerate the flow in the entrance region more than that for plenum and bellmouth. Also it was found that the average static pressure coefficient, Cpaverage , for abrupt and plenum intakes is lower than that for bellmouth duct with smooth and ribbed wall geometric and it is independent of Reynolds number for Re>40,000.
It was found that the local temperature ratio (T X-Tbx )/Tin for the abrupt and plenum intakes is lower than that for bellenum intake. The Nusselt number ratio was larger for abrupt and plenum box compared with that for bellmouth near the contraction inlet. This is due to the effect of high turbulence at the sudden contraction inlet. The effect of intake shape on heat transfer coefficient and static pressure coefficient for duct was significant for the case of P/e=20 more than in the case of P/e=10. The sudden contraction intakes (abrupt & plenum) gave higher values for the average Nusselt number ratio Nuaverage/Nus compared to that for the bellmouth intake.
It was found that, the intake shape has a significant effects on the heat transfer and fluid characteristics in the developing region of the ribbed duct especially upstream of the first rib. Also, the sudden contraction intakes (abrupt, and plenum) resulted in higher heat transfer coefficients compared to that for bellmouth intake in general. This is due to the high turbulence generated after the sudden contraction intakes.
Correlation were obtained for the average static pressure coefficient Cpaverage and the average Nusselt number ratio Nuaverage/Nus in the developing region of the test duct for different intake shapes.