Direct Numerical Simulations have been carried out to study the forced convection heat transfer of flow through fixed prolate particles for a variety of aspect ratios

Gas-solid flows are defined by the flow of gases through suspended particles of solids. These flows are present in many industrial processes and arise in several natural phenomena as well. These flows are encountered in processes such as drying of food items, particulate pollution control, pneumatic transport, combustion of coal, solid waste ignition, sand blasting, plasma-arc coating, rocket propellant combustion and fluidized bed mixing [

Computational fluid dynamics (CFD) plays an essential role in the analysis of the performance of the reactor hardware. To enhance the role of CFD for the estimation of the performance and safe operation of these reactors, various models are used to explore such physical processes. Direct numerical simulations (DNSs) are an important CFD technique that can be used for the prediction of heat transfer between gas and solid phases. Generally, researchers use Nusselt number correlations developed by Gunn [

Heat transfer of non-spherical particles not only depends on the solid volume fraction and Reynolds number but their orientation may play a significant role in forced convection. In practical applications ellipsoidal particles of different sizes are available. However, most of the particles encountered in practical applications are not spherical in shape, and the particle orientation and shape considerably affect the heat transfer in gas-solid flows. There is a great need to investigate the effect of particle orientation and shape on the heat transfer performance. Ke et al. [

The solid volume fraction and Reynolds numbers are also very important in the non-spherical particles system. He et al. [

Hence, in the present work, DNSs are performed to investigate the heat transfer in gas-solid flows with prolate particles. Flows with particles of three aspect ratios, i.e.,

The adopted three dimensional immersed boundary thermal lattice Boltzmann method is implemented with

_{i}

Nusselt number represents the dimensionless temperature gradient at the surface and it provides a measure of the convective heat transfer occurring at the surface. It is defined as:

In ^{2})^{1/3}, where

More details of this method can be found in [_{slice}^{2}_{slice}_{p}

Random assemblies of prolate particles with different

Domain size of 1.4

In [

After performing the validation of the computer code, the effects of various parameters on Nusselt number are studied. Based on the simulation data, a correlation for Nusselt number is formulated. Further details on the simulation results and the proposed correlation are presented in the following sub-sections.

A series of DNSs are performed for prolate particles with aspect ratio of 5/4. Three solid volume fractions are considered for four different values of

Particles, placed with their major axes normal to the flow direction (

To further explore the effects of the orientations on Nusselt number, assemblies with

Similarly, DNSs of flow past arrays of prolate particles with

The Nusselt number for the single particle depends only on the two parameters which are the Reynolds number and Prandtl numbers. However, in the case of many particles the effects of

The Herman orientation factor is an important factor in forced convection heat transfer of prolate particle. Therefore, for a clearer illustration of the varying trend of Nusselt number with

The impact of Herman’s orientation factor is pronounced for a range of aspect ratios for different values of solid volume fraction and Reynolds number. All these effects have been incorporated in

The correlation presented in

From the correlation presented in

Heat transfer from prolate particles for three different aspect ratios, i.e., 5/4, 5/3 and 5/1 has been simulated using the immersed boundary thermal lattice Boltzmann method. Arrays of particles have been created using the Monte Carlo method for three different solid volume fractions i.e., {0.1, 0.2, 0.3} and four different values of Hermans orientation factors, i.e., {−0.5, 0, 0.5, 1}. It is found that the Nusselt number increases with the rise of the solid volume fraction and Reynolds number. A more important finding is that, even for smaller aspect ratios, changes in

solid volume fraction

particle equivalent diameter

superficial gas velocities

Reynolds number

Hermans orientation factors

distribution functions

relaxation factors

source term in momentum equation

source term in heat equation

fluid thermal conductivity

convective heat transfer coefficient

Nusselt number

average temperature of slice

volume of slice

number of slices

specific surface area

heat flux from particles to the fluid phase

signed level set function

gas velocity in flow direction

angle

particle semi major and minor axis

aspect ratio

number of solid particles

length of cubic computational domain

kinematic viscosity

thermal viscosity

Prandtl number

This computation was supported by the

The authors declare that they have no known conflicts of interest or personal relationships that could have appeared to influence the work reported in this paper.

_{V}≤ 100