Abstract
This PhD thesis investigates heat generation in granular materials resulting from
mechanical energy dissipation through friction and plastic deformation. The study
uses numerical and experimental approaches to analyse the generated heat for
particle-substrate contacts and granular mixes of various materials.
The numerical study consists of three parts, where theoretical models and finite
element methods (FEM) models analyse heat generation during sliding and
collisional contacts between a particle and a substrate. The first part examines
friction-induced heat generation in particle-substrate sliding contact. The results
show that theoretical models can accurately predict temperature rise due to frictional
heating, and the FEM model indicates that frictional heat is concentrated in the contact
patch vicinity. The second part investigates heat generation associated with plastic
deformation during normal impact between an elastic-perfectly-plastic particle and
a rigid substrate using FEM and theoretical models. The FEM model agrees with the
theoretical model in predicting the generated heat due to plastic deformation. Also,
the highest temperatures are generally observed in the subsurface, indicating that
heat generation associated with plastic deformation is a volumetric phenomenon.
The third part explores heat generation during oblique impacts between a spherical
particle and a rigid substrate. It identifies simple theoretical solutions to decouple
heat generation from friction and plastic deformation.
The experimental studies consist of two setups: an overhead stirrer and a rotating drum.
The overhead stirrer setup uses thermocouples to measure the temperature of the
granular bed during mixing. The results show that metallic particles heat
up faster than plastic and glass particles. Also, a higher temperature is recorded
for higher rotation speed, larger particle size, higher fill ratio and larger blade size.
For the rotating drum, a thermal camera is used to quantify the bed temperature
during the granular mixing. The results reveal that metallic particles lead to a more
significant temperature increase, indicating that they generate more heat than
nonmetallic particles. Also, a higher fill ratio and higher rotational speeds lead to higher
bed temperatures.
Overall, the findings from the FEM simulations, theoretical models, and experimental
studies contribute to a better understanding of the heat generation mechanisms in
granular flows and can inform the development of more accurate predictive
models for industrial applications.