Mixing, heat transfer and the related issues are of important and basic topics. One of the new methods of achieving favorable mixing and heat transfer enhancemanet in the laminar flow regime is generating chaotic advection flow, which is creating chaotic particle trajectories in the laminar flow regime. In the present study, numerical simulation of chaotic heat transfer in laminar flow in a twisted duct is considered in FLUENT software. Two velocities in the steady and pulsating states, in tow thermal boundary conditions of constant wall temperature and constant heat flux are applied in the square cross section duct with three successive bends in macro dimensions. Each bend is 90° degrees curved duct. The angle between the curvature planes of two successive bends is also 90° degrees. Simulations are performed for the Reynolds numbers range 200?Re?800 , velocity amplitude ratios (the ratio of the peak oscillatory velocity component to the mean flow velocity) 1???3 , Womersley numbers 6???17 , and wall temperatures 310?T w (K)?360 . The appearance of homoclinic and heteroclinic connections in the secondary flow structures are the signs of chaos. The more chaos in the flow represents mixing enhancement, and since investigation of secondary flow structures is a qualitative criterion of chaos, vorticity vector method which describes stretching and engulfment of flow, is used to give a quantitative criterion of chaos. Also secondary flow structures are compared in the absence and presence of heat. Heat transfer quantity is discussed by analysis of secondary flow structures, temperature profiles and contours qualitatively, and by calculation of Nusselt and Richardson numbers, quantitative value of heat transfer and buoyancy forces effects respectively, quantitatively in two thermal boundary condition. Results confirm each other. When the Reynolds number and wall temperature increases in the steady flow homoclinic and heteroclinic connections develop and it improves mixing and heat transfer enhancement. In the pulsating flow, in small and moderate values of Womersly numbers 6???10 , increasing Reynolds number, wall temperature and velocity component ratio ? , create a more favorable condition for mixing and heat transfer enhancement. It is observed that increment of Reynolds number in the steady flow and increment of Reynolds and Womersly numbers in the pulsating flow, decrease heating homogeneity and system efficiency from the energy consumption viewpoint. In both steady and pulsating flow, heating homogeneity improves by increscent wall temperature. Heat transfer and heating homogeneity improves for ??2 , compared to steady state flow. It is also observed that, buoyancy forces have an important role in heating homogeneity occurrence. It is concluded from comparing results of two thermal boundary conditions that, in constant wall temperature condition, more chaos, mixing and consequently heat transfer enhancement and heating homogeneity is achieved compared to constant heat flux condition, with almost the same energy consumption quantity. Pulsation energy consumption is higher than the energy needed for increasing Reynolds number of the steady flow to match the same heat transfer enhancement. However, a better heating homogenization is obtained in the pulsating flow which is not the case in the steady flow Keywords: Mixing, Heat transfer enhancement, Chaotic advection, Secondary flow structure, Vorticity vector, Twisted duct, Homogeneous heat transfer