الفهرس 
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Abstract
The present study was concerned with the effect of cooling system on heat transfer coefficient during condensation of saturated steam inside horizontal tubes. An analytical model based on conservations of mass, momentum, and energy was constructed to predict the local heat transfer coefficient and the local pressure gradients.
Serveral previous experimental investigations showed that there is a region of annular flow regime exists over a fraction of the tube, and so, the analytical treatment was to analyze the annular flow regime. Annular flow was classified as a separated flow model since liquid and gas flow are confined to defined regions of the total flow area.
New correlations, based on separated flow assumptions, were derived for heat transfer coefficient and pressure drop. The derived correlation of heat transfer coefficient showed that the that the local heat transfer coefficient depend on the inlet Reynolds number (Re ),ratio of laten to sensible energies (HI), local quality (x ), liquid prandtl number( PrL ), Ratio of vapour to liquid densities (e), and ratio of vapour to liquid densities (E), and ratio of vapour to liquid viscosities (K). PrL,E, and K are pressure dependent parameters. The analytical results showed that the local Nusselt number increases with increase in Re and HI. On the other hand,it decreases with the decrease in x and with the increase in the inlet pressure which controls PrL,E,and K.
The derived correlation of pressure DROP showed that the local pressure DROP on Re, x, E,and K.
The derived correlation of pressure DROP showed that the local pressure DROP depends on Re, x, E, and K .The analytical results showed that the local pressure gradient decreases with decrease in x and increases with increase in Re and the inlet pressure which controls E and K.
An experimental investigation was conducted for studying the effect of the cooling system on heat transfer coefficient. The test section was divided tosix separated condensing segments, three condensing segments, two condensing segments, and one condensing segment. In each case of the above four cases, heat balance was carried out in each condensing segment to calculate the local heat transfer coefficient and in turn the local Nusselt number.
The experiments were carried out within a range og Re between 14000 and 48000 and range of working pressure between 1.013 and 1.02 bar. from the experimental study, it was observed that, increasing the number of condensing segments results in increase the heat transfer coefficient and decrease in the condensate quality at exit.Comparisons were made between the present experimental results for the case of six separated condensing segments and other analytical and experimental results of previous studies. The analytical studies are for Ananiev and Shah , but the experimental study is for El-Ghnam. The comparisons showed that the present experimental results are similar in trend with the present the previous experimental and analytical results.