The main purpose of this work is a numerical study on unsteady natural convection from outer surface of helical coils. Each heat exchanger consisted of a helical coil and a shell. The helical coil was mounted in the shell vertically. The cold water was in the shell and the hot water was flowing through the coil and was cooled by unsteady natural convection. A CFD code has been used for heat exchanger simulation. The analyses have been carried out for 27 helical coils with different geometries. The effect of helical coil geometry on natural convective heat transfer is investigated. All of continuity, momentum, energy, and turbulence equations are solved for both of fluids simultaneously, so there is no need to simplifying assumptions for boundary conditions. Results are compared with previous experimental researches. Statistical analyses have been done on data points of temperature and natural convection Nusselt number. It is revealed that shell-side fluid temperature and the Nusselt number of the outer surface of coils are functions of in-tube fluid mass flow rate, geometrical parameters of helical coils, and time. A new correlation is presented for calculating the temperature changes of bath fluid. Some other fluids are used as coil and bath fluids and results show that the presented correlation for bath temperature computing have an acceptable accuracy for them.
Inter-model comparison of CFD and neural network analysis of natural convection heat transfer in a partitioned enclosure
