In the present work, heat transfer and fluid flow characteristics for both Newtonian and non-Newtonian fluids in tube-in-tube helical coil (TTHC) heat exchangers have been investigated numerically. The various TTHC heat exchanger configurations studied are (1) parallel and (2) counter flow, with and without baffles. The power law index (n) and Dean number (NDe) are varied from 0.5 to 1.25 and 50 to 500, respectively. Further, two different models have been proposed to predict the friction factor (f) and Nusselt number (Nu) in TTHC. It is observed that f and Nu in the TTHC heat exchanger with baffles in the annulus is higher as compared to without baffles. Furthermore, at low Prandtl number the baffles have significant influence on heat transfer, while at high Prandtl number flow configuration has high significance. Copyright © 2020 American Chemical Society.