Natural convection heat transfer in heat exchangers with vertical helical coils

Natural convection heat transfer was studied in shell-and-coil heat exchangers. One or more helical coils were installed in a cylindrical shell to form a natural convection shell-and-coil heat exchanger. A heated aqueous solution of 40% propylene glycol was pumped through the coils. Water from a storage tank circulated naturally on the shell side of the heat exchanger. The helical coils were made of copper tubes of 4.76, 6.35, 7.94 and 9.52 mm outer diameter. Coil outer diameter was varied from 35.7 to 74.5 mm and coil pitch from 1.00 to 5.96 tube diameters. Two shell diameters of 51 and 77 mm were tested and the shell height was either 382 or 762 mm. Experiments were conducted for glycol mass flow rates from 0.00185 to 0.0343 kg/s and heat transfer rates from 160 to 2300 W.The effects of tube diameter, coil diameter, coil pitch, shell diameter and shell height on the shell-side heat transfer coefficient were studied. Axial temperature profiles in the heat exchangers were analyzed. The shell-side heat transfer coefficient decreased with increasing coil surface area. The optimum dimensionless pitch for the coils was found to be in the range, 1.25...