الفهرس 
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Abstract
Enaporation heat transfer of refrigerant R-134a flowing inside horizontal tubes with internal grooves is experimentally investigated. The results are compared with those obtained for evaporation inside plain tube. Three different geometrics for the internal grooves are tested plain tube. Three different geometries for the internal grooves are tested. An experimental test rig equipped with the necessary measuring devices is designed and constructed to achieve this purpose. The test section is a double pipe heat exchanger. R134a is evaporated inside the inner tube due to the hot water passing through the counter-current surrounding annulus. The experimental measurements include records for temperatures, volume flow rates and pressures in the test rig.
A verage heat transfer coefficients are obtained for heat flux ranged from 10 to 80kw/m mass flux from 120 to 270kg/m and evaporation pressure from 200 to 275kpa.
The results obtained show that, the evaporation heat transfer coefficient increases with increasing evaporation pressure, mass flux and or heat flux. also, internally grooved sample tubes give higher values for the evaporation heat transfer coefficient than those obtained using plain tube. The average values for the enhancement factor for the three tested samples are 1.44, 1.31 and 1.17, respectively.
An empirical correlation is duduced based on the experimental measurements to predict the average heat transfer coefficient as a function of the working parameters and grooves geometries studied here.
A theoretical model for estimating the heat transfer coefficient and pressure loss inside the plain tube is developed in the cylindrical coordinates using the basic governing equations mainly continuity momentum and energy equations mainly continuity, momentum and energy equations subjected to the necessary boundary conditions and the suitable assumptions. The simplified forms of the governing equations are obtained in dimensionless forms. The finite difference method is used to solve the deduced equations. A computer program written in FORTRAN is designed and used to solve the finite difference equations. The theoretical model results show that the pressure DROP increases as the mass flux increases and as the evaporation pressure decreases.
The results are presented in this thesis for both the experimental measurements and the theoretical predictions. Favorable agreement is obtained between the present experimental measurements for internally grooved tubes with the published data. also, the experimental measurements obtained using plain tube show reasonable agreement with both the present theoretical model predictions and the published data for the pressure DROP and the local and average evaporation heat transfer coefficients.