Prof. Sameh A. Nada :: Publications:

Convection heat transfer in shell and helical coil heat exchanger was experimentally investigated to study the effect of shell diameter on average heat transfer coefficient and Nusselt number. The convection at outside surface of helical coiled tubes is investigated with a constant wall heat flux. Refrigerant R12 passes inside tubes and water passes through the shell. The effects of different parameters in shell and helical coil heat exchanger such as the effect of fins existence and shell diameter were tested. Four shells with different diameters were tested in this work with finned coil and again with unfinned coil. The experimental set up is designed to enable varying and controlling the water flow rate and the input power to the shell water. Different instruments were incorporated in the experimental set up to enable measuring the different parameters such as temperature, flow rate, volt and ampere of heater. These measurements enable studying the effect of dimensionless flow parameters such as Reynolds number, Grashoff number and diameter ratio D* (Shell diameter to coil diameter) on the heat transfer characteristics. For 271 < Re < 674 and 9×1011 < Gr < 4×1012; it is concluded that the average Nusselt number (Nu ) increases with the increase of D* at constant Re and Gr. Also, Nu increases with the increase of Re at constant Gr and D*. An increase in Nu is observed again with the increase of Gr at constant Re and D*. A general correlation of the average Nusselt number is obtained to describe the mixed convection from the helical coil with radial fins as the following: Nua=0.0544Re0.427Gr0.146D0.318. For the shown range of Re and Gr; a good agreement between the present experimental data and previous work is achieved.