Simulação computacional da transferência de calor no escoamento anular de água aquecida por trocador de calor de leito fluidizado borbulhante

Abstract

Fluidized beds are used in huge variety of applications, such as drying of solids, particle coating, catalytical cracking and also for thermal energy recovery. The behavior of a gas-solid system is similar to the fluids and the heat transfer between the bed and an object in contact with it is significantly higher when it comes to the same system in the absence of solid particles. This thesis compares, using real boundary conditions, experimental tests results of annular flow heat transfer in a bubbling fluidized bed heated jacket type heat exchanger with results found on computational simulation using the Ansys AIM Student software. Results of sixteen tests with different combinations of liquid mass flow, bed temperature and bed-to-wall convective coefficient were compared, resulting on gaps from as 0,05% to 1,89% on values for the outlet water temperature which was heated on its way through the heat exchanger annular region. The water temperature field in contact to the annular region external wall was presented. At given boundary conditions, increasing the mass flow ten times decreases 16 °C in outlet water temperature, resulting in a 416% higher global heat transfer rate. Simulations at different mass flows for two different boundary conditions (different bed temperature and bed-to-wall convective coefficient) shows advantages of a copper made than stainless steel-made heat exchanger, specially when the temperature gap between water and bed rise and the bed-to-wall convective heat transfer coefficient increases. To forecast the heat exchanger effectivity in terms of a better homogeneity in the annular flow region water temperature field distribution, two to ten inlets and outlets heat exchanger geometries were added into the analysis. The decrease of temperature gaps in annular flow’s polar direction as the number of inlets and outlets increases means the axis velocity outperforms tangential velocity, resulting in a significantly improvement in heat transfer rates, specially in higher mass flows.