الفهرس 
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Abstract
Mixed convection heat transfer in shell and helical coil heat exchanger was experimentally investigated to study heat transfer characteristics and the effect of different parameters on heat transfer coefficient and Nusselt number. Convection heat transfer from outside surface of helical coiled tube to surrounding water in the shell was investigated under a constant temperature. Experiments were conducted with refrigerant R12 which passes inside coil tube and water passes in the shell around the coil. The effects of different parameters on heat transfer coefficient and Nusselt number such as existence of radial fins on coil surface and shell diameter were studied. Four shells with different diameters were studied in this work with finned and unfinned coils. The experimental set up was designed to enable varying and controlling water inlet temperature and water flow rate around the coil (in the shell). Different instruments were incorporated in the experimental set up to enable measuring different parameters such as temperature, flow rate, volt and ampere of water heater. Experiments were carried out for different value of Reynolds number and Grashof number in the range 5.6×1010Gro 3.5×1011 and 271 Re 674; which covers forced and mixed range. The results showed that heat transfer coefficient and Nusselt number depend mainly on Reynolds and Grashof numbers, shell diameter and coil surface finned conditions. Nusselt number increases as Reynolds number increases for low Grashof number. Nusselt number was observed to increase with the increase of Grashof number at low Reynolds number. It was observed that fins existence enhances heat transfer. The results showed that heat transfer coefficient increases as shell diameter increases. A general correlation of the average Nusselt number as a function of Reo, Gro and D* was proposed. The calculated average Nusselt number (Nucorrelated) from the proposed equation was plotted versus experimental data and good agreement was achieved. A comparison between present experimental results and results of previous work was carried out and a satisfactory agreement was achieved. This study enhances the researcher skills in experimental work in the field of heat transfer and fluid mechanics.