الفهرس 
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Abstract
Evaporation heat transfer of refrigerant R134a flowing inside horizontal copper tubes with internal grooves is experimentally investigated. The results are compared with those obtained for evaporation inside plain tube. Three different geometries for the internal grooves include fin height, H = 0.2 mm, number of fins, N = 60, helix angle, α = 18° and apex angle, γ = 30°, 40° and 53° are tested. An experimental test apparatus equipped with the necessary measuring devices is designed and constructed to achieve this purpose. The test section is a double tube heat exchanger where R134a is evaporated inside the inner tube due to the hot water passing through the annulus in a counter-current manner. The experimental measurements include records of temperatures, volume flow rates and pressures.
The measurements are made under wide ranges of heat flux, mass flux and geometry parameter (apex angle of the fin, γ) on the average evaporation heat transfer coefficient. Experiments are carried out for heat flux ranged from 13 to 98 kW/m2, mass flux from 208 to 286 kg/m2 s, apex angle of the fin, γ = 30°, 40° and 53° at an average evaporation pressure of 4.23 bar.
The results based on the experimental measurements show that, the average evaporation heat transfer coefficient increases with increasing heat and mass fluxes. Also, internally grooved tubes give higher values for evaporation heat transfer coefficient than those obtained using plain tube. The results show that at constant heat flux, mass flux and evaporation pressure as the apex angle of the fin, γ, increases the average evaporation heat transfer coefficient decreases. The enhancement factor (EF) for the three tested tubes is also indicated.
The present experimental results for plain and internally grooved tubes are compared with the corresponding available published data. Favorable agreement is noticed between the present results and the published data.
An empirical correlation (equation (5.14)) is deduced based on the experimental measurements to calculate the average evaporation heat transfer coefficient as a function of the working parameters and the internal groove geometry (apex angle of the fin, γ).