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This paper presents a numerical study on waste heat recovery from a fluid stream using thermoelectric elements for energy harvesting. Two fluids were tested, air and steam, and the voltage and overall efficiency were computed for different sets of operational conditions. The mathematical description considered turbulent regime and coupled transport phenomena for the description of the main thermoelectric effects. Numerical solution was achieved using ANSYS/FLUENT commercial software with complementary implementations of user-defined scalars and user-defined functions to account for the mathematical model specific needs. The system global efficiency was computed for a pair of heat extraction conditions and different operational variables giving values within [0.11-9.22] (%). It was found that the global efficiency increases with the fluid temperature and the decrease in the external thermal resistance. For all cases studied, the global efficiency was greater when air was used as a heat carrier fluid due to its specific heat values which were about half the steam ones. Keywords Waste heat • Thermoelectricity • Heat recovery • Seebeck effect List of symbols c p Specific heat capacity c 1 Turbulent model parameter c 2 Turbulent model parameter c Turbulent model parameter Mass transport tensor D Square duct side D Mass diffusivity Electric field intensity vector e Height External field acceleration G k Rate of k generation H Specific enthalpy h Heat transfer coefficient Unitary tensor I Current Electric current density vector Effective conductivity tensor k Turbulent kinetic energy

In this work we present flow simulations in laminar and turbulent regime within a representative elementary volume of a simplified porous media by solving the Navier-Stokes equations and a Low-Re turbulence kÀ model. Numerical solution was achieved with an implementation of the SIMPLE algorithm for pressure velocity coupling of variables, and the solution of the tridiagonal systems of algebraic equations was accomplished by a parallelized ADI scheme based on the Thomas algorithm. Implementation of the numerical solution was done with an in-house C code which combined OMP and CUDA technologies for computations based on CPU and GPU, respectively. Exponential structured grids were employed in the wall vicinity to capture the turbulence behavior. Results indicate that similar profiles for velocity, pressure, turbulent kinetic energy and its dissipation were found. Several CUDA grids were tested and their performances measured over two GPUs: GTX 680 and GTX TITAN. Considerable speedup was achieved by the GPUs over the CPU schemes even without the use of the device shared memory which was not explored due to the nature of the algorithm.

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This paper presents a numerical study of waste heat recovery from a fluid stream using thermoelectric devices. The system consisted of a square section duct with spherical porous media placed in its central region. Hot air circulates continuously through the duct and exchanges energy with the solid matrix and subsequently with the thermoelectric modules. The mathematical model of the system was solved using ANSYS/FLUENT software, requiring the implementation of user-defined functions (UDFs) and user-defined scalars (UDS) regarding porous media and thermoelectric generation modelling. From the simulations carried out, global efficiency and electrical power values were obtained in the range of [0.11–4.51] [%] and [0.01–12.77] [W], respectively. Furthermore, for the set of variables analysed, it was observed that the performance of the system is favoured by an increase in the fluid inlet temperature and speed, as well as by a higher external heat transfer coefficient.