3D Numerical Simulation of the Heat Transfer in a Horizontal Tube Bundle in a Vertical Channel

In fluidized bed technology, one of the most common processes is the heat transfer between gas and horizontal tube bundle. Hence, immersed surfaces into the fluidized bed are useful to extract heat from it for several industrial processes. To study the influence of the tube bundle distribution is needed to show hydrodynamic analysis, mainly focused on the bubble size and velocity, as well as particle mixture rates.

In the present study, a 3-D numerical simulation is implemented in Barracuda Virtual Reactor (v. 22.1) to perform a hydrodynamic and heat transfer analysis of a fluidized bed heat exchanger. It is based on the experimental study carried out by Moawed et al. (International Journal of Chemical Reactor Engineering, 2010), who used a bundle of tubes in a vertical channel. In line and staggered tubes arrangement have been implemented.

Local behavior of the heat transfer coefficient and particle volume fraction have been studied at different angular positions of a central tube, to properly analyze the relationship between hydrodynamics and heat transfer phenomena. In both tube bundle distribution, the lowest heat transfer coefficients values were obtained at the top region of the tube, which is related to the fact that particles are at stagnant and hot particles close to the surface are not being replaced by new cold particles. This behavior is different at the bottom and sides, where particles are continuously being removed, obtaining low particle volume fraction values and high heat transfer coefficients.

In both cases, the tube bundle limits the bubble coalescence and maintain a low bubble size along the bed. About in line tube bundle, the stagnation region size located at the top is slightly higher than at the staggered tube arrangement, mainly related to the zigzag shape of the air flow circulating around the tube.