Optimization of Gravity-Driven Granular Flow Around the Tube for Heat Transfer Enhancement

Nowadays, moving bed heat exchanger (MBHE) has been gradually adopted in the field of heat recovery from the granular flow. Compared with fluidized bed, the moving bed cost less. However, it usually brings with relatively poor heat transfer performance. The current study aims to optimize the heat transfer in gravity-driven granular flow through tube vibration, which is helpful to the efficient design of MBHE in the future. The vertical granular flow is numerically simulated with discrete element method, where careful discussion about vibration tube effect is developed. The model has been carefully validated. To focus on the mechanism of heat transfer enhancement, the geometry model is simplified as a single tube. The results show that, tube vibration in different directions could improve heat transfer performance, where the effect of horizontal vibrating direction is more remarkable. It’s also found that a slight sinusoidal vibration is able to accelerate particles update above the tube and drive some particles contact the bottom zone of tube. Therefore, it mitigates the negative effect of stagnation zone and void zone in cases of static tube. Then the heat transfer coefficients would increase. What’s more, tube vibration would rebound particles around the wall, where additional mass diffusion is beneficial to heat transfer at sides of tube at some extent. However, it should be noted that vibration would increase wear rate between tube and particles significantly at the same time. The industrial application relies on the development of wear-resistant technology.