Abstarct: As consumption of electrical energy in the world is increasing, optimization of energy in power plants is inevitable. Ljungstrom air preheater with recycling the energy and preheating the air significantly saves the energy. Rotary regenerative or air preheater (Ljungstrom), is one of the most important exchangers for recovery and improvement of energy. Ljungstrom preheats the input air to the boiler to raise the efficiency of many plants around the world. In this study a numerical investigation of heat transfer in regard to the improvement of the Ljungstrom performance is done. Tridimensional model with regard to the symmetry of the geometry is a part of heat transfer surface. Comparing the results of the numerical solution with real results in steady state, shows that the proposed model is an acceptable model. In transient analysis of this model, time performance of Ljungstrom to achieve the stable conditions has been investigated. The results show the matching time between warm and cold parts in stable dynamic conditions. The investigation of relation between rotational speed and air and flue gas outlet temperature, are showed as curves. Finally to investigate the geometrical profile of heat transfer surface, the same analysis is done in a kind of heat transfer surfaces and by changing the thickness and distance between plates some proposals are presented.