For environmental
manufacturing, induction heating holds practical potential for its combination
of cleanliness, speed and control; and thus, there is always a need for this
technique to be applied more in the area. Hence, this paper suggests an additional
application of induction heating in environmental engineering that would be
used in PE/PP plastic (i.e. plastic bags, bottles) recycling. In which, the
waste plastic is melted using induction heating then reformed into more-valued
plastic tiles. To realise the application, an effective design of an induction
furnace should be put into consideration with the coil as the heating element
is the main factor. The optimisation of the geometry of the coil for an
efficient heating was conducted in simulation using the COMSOL® Multiphysics
Software, in which multiple coil configurations with different dimensions,
numbers and placements were tested to heat up a same metal mould to a specific
temperature which makes the plastic material inside melted under uniform setup
parameters (i.e. materials, current density, magnetic field, heat flux density,
etc.). Afterwards, corresponding results of behaviours of magnetic flux density
and temperature patterns of each configuration were analysed and compared. From
the results, the effective coil geometry and configuration for the application
was using multiple of rectangular, multiple-turn, perpendicular-oriented,
short-width coils. Such configuration showed an optimal balance between heat
delivery, area of cover, and power usage and therefore, proved the induction
furnace solution for plastic heating-recycling is feasible, which potentially
expand the applications of induction heating in sustainable manufacturing.

Induction heating – an
advanced manufacturing process and an attractive research topic as well. For
its nature of non-contact heating, by-electricity operating and easy
controlling, induction heating, induction heating has been proven to be an
effective processing method for modern environmental manufacturing, because it
would omit the necessity of heat transfer medium, the possibility of
contaminated processed material and the generation of exhaustion fumes.

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An
efficient induction heating relies on several essential factors, including
profile of the component and design of the coil 1. Thus, many studies have
been carried out to further optimised the process and expand its applications.
From some time ago, it theocratically showed that a combination of tolerable
length-to-diameter ratio of the induction coil, specific high-end cut-off
frequency and available preamplifier resulted in a magnetometer configuration
which exposed to minimum noise 2. In addition, when used for surface heating
(i.e. a plate mould), multi-layered coil would achieve better uniform
temperature distribution across the heated target 3. With the configuration
of multi-coil arrays plus permissible design-parameters of hardware, the
enhancement in the application in Localised Hyperthermia, which used in medical
treatment, was shown 4.

The
experiment-based optimisation of the induction heating process using
simulations has been a solid choice for many researchers. In many cases, the
COMSOL® Multiphysics Software has been widely used for its variable physics
studies, graphical estimation and interaction. In a master thesis dissertation
of 5, through simulation, a conceptual electromagnetic heating model of
multi-coil inductor in railway traction was built with every temperature points
of the inductor were predicted and estimated. In other studies, by successfully
simulating key design parameters in COMSOL, short width and distance of
inductor coil and silicon carbide plate and with high frequency controller
would result in an efficient induction heating process used in home appliance
6; or with reasonable heated target thickness, coil pitch and position, a
single-layered induction coil could achieve combination of high heating rate
and low temperature deviation on rapid mould surface heating 7.

 However, studies which are regarding to
various utilisations of induction heating in plastic manufacturing are found
limited. Most found relevant researches shows the application of induction
heating in rapid mould heating in injection moulding as the highest
energy-efficient and the most environmental-friendly among several methods
7–9. Therefore, the purpose of this study is to present a feasible
application of induction heating in a small-sized furnace, in which the PE/PP
plastic flakes (shredded from plastic bags, bottles, etc.) placed inside a
rectangular mould is melted and reproduce as higher-valued plastic tiles. The
idea was based on Reform project of
Evergreen Lab (EGL) to make use of the vast amount of plastic wastes in Vietnam
and turn into a high-value small-scaled recycling production 10. The next
sections would explain how the COMSOL software was used to run simulations of
the induction furnace using different coil geometries and configurations and
analyse the different distribution of magnetic field and temperature on the
same mould to determine if an induction furnace is feasible and which coil
geometry and configuration is the most feasible.

 

2.                  
Material and Methods

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