| dc.description.abstract | This thesis presents a method for producing open-cell metal foams by vibration-assisted
casting (VAC) and its studies for diverse engineering applications. Metal foams have a wide
range of applications due to their several beneficial properties such as high specific strength,
low relative density, high effective thermal conductivity, and permeable porous structure with
a high surface area to volume ratio. However, their applications are currently limited due
to the complexity and high manufacturing cost. Traditional techniques involve a complex
production setup that includes an inert environment and high-pressure compressed gases to
accomplish molten metal infiltration into the preform to process metal foam. As a result, we
have developed a method to simplify and minimize manufacturing costs by eliminating the
usage of inert environments and high pressure compressed gases. The VAC method carefully
controls the pouring temperature and cooling rate with the additional use of a low-frequency
vibrator for infiltration of molten metal into the preform. The VAC method facilitates
the design and manufactures several metal foams with high specific surface area with pore
diameters ranging from 100 μm to 10 mm. Additionally, the VAC method produces various
types of metal foam, homogeneous, heterogeneous, functionally graded, and composite metal
foams for diverse engineering applications. Furthermore, the VAC method also enables the
production of compact integral foam heat exchangers (HXs) or heat sinks in single-step
casting. Controlling the cooling rate (preheating temperature) allows the metal foam to be
fused bonded to a metal substrate. Thus, it eliminates many intermediate processes that are
unavoidable in conventional metal foam HXs, such as machining, use of epoxy glue, brazing,
press-fitting, or welding, making it easily recyclable. Fusion bonding between the metal
foam and substrate reduces thermal contact resistance (RTCR) and improves the thermal
performance of foam HX. The current technology facilities development of various metal
foam heat exchanger designs such as integral foam heat sink (HS), foam-plate-fin HS, and
foam-pin-fin HS. The following major findings are obtained from the contribution chapters
that are enumerated below:
(i) The effect of foam height, pore diameter, number of foam fins, orientation, and bonding
methods on thermal performance are examined. The heat transfer rate per unit mass
of foam-fin heat sink is approximately double that of commercially available fin heat
sinks.
(ii) The thermal contact resistance (RTCR) of fused-bonded foam heat sinks is approximately
19 times lower than an epoxy-glued foam heat sink, resulting in ∼30% higher
Nusselt number (Nu) of the fused-bonded foam-fin heat sink than the epoxy-glued
foam-fin heat sink.
(iii) Two types of foam heat exchangers (HXs): single-sided fused bonded foam tube heat
exchanger (SFMF) and double-sided fused bonded foam tube heat exchanger (DFMF)
with spherical and ovoid shape pores are developed.
(iv) Increment in foam height has a significant influence in reducing the thermal resistance
(Rth). For the same pumping power (W), the DFMF heat exchanger provides up to
∼25% lower Rth than the fin heat exchanger (Fin HX) and SFMF heat exchanger.
(v) Composite metal foam (CMF) is an efficient energy absorber as compared to foam since
it provides a larger stress plateau region while undergoing deformation. Moreover, the
damping capacity of CMF is ∼7.5 times higher than aluminium foam and synthetic
elastomer, and ∼3.5 folds higher than solid metal due to the high loss modulus of
CMF.
This study concludes that the composite metal foams are efficient energy absorbers and
vibration dampers. Furthermore, an integral foam-fin heat sink with minimal thermal contact
resistance is an excellent solution for thermal management in high-powered electronics with
the benefits of being lightweight, compact, and easily recyclable. | en_US |
