الفهرس 
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Abstract
It is often required to design the condenser to perform a certain heat transfer duty under the restriction of a permissible pressure drop. In some equipment such as refrigeration system condenser and steam power plant condenser, the vapour enters the condenser in the superheated state.
The present study was concerned with numerical and experimental investigation of local heat transfer coefficient and local pressure gradients during the condensation of superheated and saturated vapour inside horizontal tubes.
An analytical model based on conservations of mass, momentum and energy was developed to predict the local pressure gradients and local heat-transfer coefficients.The analytical model was based on separated flow model assumptions.
The progression of flow patterns observed in several pervious experimental investigations showed that when the condensation occurs in horizontal tube, there is a region of stratified flow pattern. This may exist over a large fraction of the tube. So, The analytical model was constructured to analyze the stratified flow pattern. New correlations based on an analytical and was derived for both heat transfer and pressure drop.
The derived correlation of heat transfer showed that the local heat transfer coefficients depend on the inlet Reynolds number Re, ratio of laten to sensible energies H1, ratio of superheat to sensible energies H2, local quality x, liquid Prandtel number PrL, ratio of vapour to liquid desities E, and ratio of vapour to liquid viscosities K. The last three parameters are pressure dependent parameters.
The analytical results showed that the local Nusselt number decreases with the decreasing of the local quality. The local Nusselt number increases by increasing the inlet Reynolds number, ratio of latent to sensible energies, and ratio of superheat to sensible energies. The local Nusselt Number is shown to decrease by increasing the inlet pressure p.
The derived analytical correlation of pressure DROP shows that the local pressure DROP depends on the inlet Reynolds number Re, local quality x, ratio of vapour to liquid densities E, and ratio of vapour to liquid viscosities K. The last two parameters are pressure dependent parameters.
Analytical results showed also, that the local dimensionless pressure DROP decrease by decreasing of local quality. The correlation showed also the local dimensionless pressure DROP increase by increasing the inlet Reynolds number and inlet pressure.
An experimental investigation was concluded for the pressure of testing the validity of the obtained analytical correlation of heat transfer. The test section was divided to six separated condensing units. Heat balance was carried out in each condensing unit to calculate the local heat transfer and in turn the local Nusselt number. The experiments was carried out within a range of inlet. Reynolds number between 10000 to 45000 and ratio of superheat to sensible energies H2 ranging from 0. 085 to 1. 265.
The effect of variation of inlet Re on the ratio Nu/H1was studied. Also the effect of H2 on the ratio Nu-H2—H1+H2 which represents the part of the heat transfer due to superheat was presented. The effect of H2 on the ratio H2 –H1+H2 which represent the ratio of heat transfer due to superheat to total heat transfer was also investigated.
The experimental results showed that the ratio of Nu/H1 increases by increasing the inlet Re. The increase of H2 produce an increase of ratio NuH2-H1+H2 i.e. the heat transfer due to superheat increases by increasing of degree of superheating. As the value of H2 increases the value of ratio H2-H1+H2 increase. At high degree of superheat (H2=1.265 (560C) the ratio of heat transfer due to super heat to total heat transfer not exceed 5%.
Comparison between present analytical results and present experimental results showed good agreement in low of quality (x) (mist flow and annular flow wavy flow). This expected since the present analysis were developed for stratified flow which exists in low range of (x) (for steam x<.4,Rashwan {13}.
Comparison between the present analytical results and other previous experimental correlations was performed . The comparison showed good agreement with correlation of Traviss {4}, fair agreement withcorrelation of Ananview et al {7} especially at low (x). The coparison between the present experimental results and other experimental correlation showed good agreement with correlation of Shah {5} within ≠5%.