This research presents a Computational Fluid Dynamic (CFD) study of a tube-in-tube helical heat exchanger evaluating two passive technique: i) ridges and ii) torsion in the internal tube. The effects of the fluid flow rate on the heat transfer were studied in the internal and annular flow. A commercial CFD package was used to predict the flow and thermal development in a tube-in-tube helical heat exchanger. The simulations were carried out in counter-flow mode operation with hot fluid in the internal tube side and cold fluids in the annular flow. The internal tube was modified with a double passive technique to provide high turbulence in the outer region. The numerical results agree with the reported data, the use of one passive technique in the internal tube increases the heat transfer up to 28.8 % without torsion in the tube.