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Abstract
The heat transfer, the fluid flow and the pressure drop characteristics of ongitudinal rectangular-fin arrays are investigated experimentally. The xperiments are preformed to detennine the optimal position for the fin array in e flow field. Then determine the response of the heat transfer from a ongitudinal fin array to the presence of clearance between the fin tips and an .. djacent shroud (plain or equipped with wire coil (modified shroud». Also xperiments are done to determine the effect of the fin array geometries on the ow and heat transfer characteristics. Twelve empirical equations are derived to
orrelate the mean Nusselt number as a function of Reynolds number, fin ickness, fin height, inter-fin space and shroud clearance to fin height ratio. inally, the flow patterns around the tested finned models were visualized.
The following conclusions can be derived from the fluid flow and heat ansfer results as:
The velocity profiles in the inter-fin region showed that at the entrance region of the inter-fin region, the velocity has the greatest value where the flow strongly escape with traveling deeply in the stream-wise direction to outside that region leading to a decrease of the flow pressure, the flow friction and so the flow velocity. This makes the values of temperature increases in the stream-wise direction.
The test section friction factor for the parallel flow case is lower than that for the impinging flow case which is slightly lower than that for the reverse impinging flow case.
The test section friction factor for the parallel flow case decreases with increasing the Reynolds number but the opposite is true for the impinging flow and the reverse impinging flow cases.
The axial pressure drop is increased with increasing the Reynolds number and fin height and with decreasing the inter-fin space and fin thickness.
It was found that decreasing the fin height increases escaping of the flow from the inter-fin region to outside region. Increasing the inter-fin space increases the mass flow rate in the inter-fin region. Increasing the fin thickness increases the wakes at downstream of the leading edge (entrance region of the inter-fin region).
It was found that the parallel flow case yielded the highest heat transfer and the lowest pressure drop followed by the impinging flow case and then the reverse impinging flow case.
Increasing the clearance between the fin tips and an adjacent plain shroud decreases the heat transfer coefficient and tested model-mean Nusselt number up to certain clearance to fin height ratio, C/H =1.25, the effect of the fin tips shroud goes off
The tested model with the modified shroud gives higher mean Nusselt number than that for the tested model with plain shroud up to CIH =1.
. The effect ofthe wire coil of the modified shroud on the fluid flow and heat transfer characteristics goes off when the clearance to fin height ratio equals 1.0.
The values of temperature in the temperature distributions over the fins located in the fully developed region are lower than that for the fins located in the terminal region and the opposite is true for both the local heat transfer coefficient and the local Nusselt number for high height fins. But for 10”, height fins the opposite is true.
The fin-mean Nusselt number (Nur) increases with increasing the Reynolds number (Red, the fin height (H), the fin thickness (t), and the inter-fin space (W).
The tested model-mean Nusselt number (Num) increases with increasing the Reynolds number (Red, the fin thickness (t) and the inter-fin space (W) and with decreasing the fin height (H).
The fin performance (r.) and efficiency (ll) increase with decreasing the Reynolds number (Red, the fin height (H), the fin thickness (t), and the inter-fin space (W).
Eleven empirical correlation were derived to correlate the mean Nusselt number (Num) as a function of (Red, (C/H), (H/W), (t/W) and (W/L). The general empirical formula obtained from the present study is given in the form:
WJO.214171 (H J-o.36263 ( JO.15250885
Nu =5.734146 (Re )0.42422