This book presents a new technique to enhance heat transfer coefficient of double pipe heat exchanger. Heat transfer enhancement is the practice of modifying a heat transfer surface to increase the heat transfer coefficient between the surface and fluid. An experimental investigation has been conducted to evaluate the heat transfer performance of double pipe heat exchanger. Experiments were carried out under two condition of full-length and half-length twisted tape inserts in double pipe heat exchanger and result are compared with the smooth double pipe heat exchanger. By inserting twisted tape inside the tube, they act as turbulence promoter. It mixes the boundary fluid with bulk fluid and boundary layer thickness is reduced by imparting a rotational motion to a fluid flowing inside the tube of double pipe heat exchanger.The effect of the full-length and half-length twisted tape on the heat transfer coefficient and pressure drop is experimentally investigated in case of different mass flow rate. The performance evaluation of the smooth tube, and tube with full length and half-length tapes were carried out on the basis of equal mass flow rates and unit pressure drop.