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.