Twisted oval tube heat exchanger has been widely used in chemical industry field. In the present study, fluid flow and heat transfer characteristics in the shell side of this type of heat exchanger are studied numerically with Realized k-epsilon model. Influence of the geometrical parameters including twisted pitch length P and aspect ratio A/B on the performance of the shell side are analyzed. Results reflect that Nusselt number and friction factor both increase with the increasing of P and AIB. Their influence on the shell side overall heat transfer performance h/Delta p is also analyzed. It is concluded that the overall heat transfer performance of the shell side increase with the increasing of NB. But on the aspect of the influence of P. it firstly increases with the increasing of P and then decreases with the increasing of P. Velocity and temperature distributions, stream traces and secondary flow distributions are presented to make the fluid flow and heat transfer characteristics in the shell side clear at the end of the present work. The magnitudes of the total velocity at the self-supporting points are found to be lower and the temperatures are found to be higher than their neighborhoods. Spiral flow can be found in the shell side especially for the cases with A = 14 mm, B = 5 mm. The intensity of the spiral flow becomes more and more drastic with the increasing of A/B and the decreasing of P. Analysis of the secondary shows that the magnitude of the secondary flow increases with the increasing of A/B and decreases with the increasing of P. Irregular secondary flow can also be found around the helixes which are formed by the twisting of the oval sections. (C) 2013 Elsevier Ltd. All rights reserved.