148
P. Sarkar et al.
mentioned in Sect. 2.2 that the wormhole defect is nothing but voids inside the weld
line that staggeringly deteriorates the weld quality, as well as strength. However,
utility of the said defect is discussed further.
In 2005, researcher showed that by reversing the material flow generally occurring
in FSW and by purposefully creating and utilizing the wormhole defect, an integral
and continuous tunnel or channel can be created inside a monolithic plate in a single
step [42]. This can be possible by selecting the process parameters and tool designs
that promote the generation of wormhole defect during FSW. The process was named
Friction Stir Channeling (FSC). It was identified that the channels created by FSC
have huge potential to be used in the heat exchanger applications.
4.4.1 Importance of Compact Heat Exchanger
The problem of heat generation and removal is present in a myriad of applications
and processes across the world necessitating the design and development of novel
heat dissipation and exchange devices. From aerospace to power plants, automotive
to space, power systems to consumer electronics, the importance of thermal management calls for innovative designs of heat sinks and heat exchangers and processes to
manufacture them. Heat Exchanger is a device that promotes heat flow between two
or more fluids having a difference in temperature, thus maintaining the temperature
in the desired range. Heat exchangers can be classified based on their geometry (tube,
plate, extended surfaces), based on transfer phenomenon (direct contact type or indirect contact type), flow arrangement types (parallel, counterflow, cross-flow, etc.),
heat transfer mechanisms (single-phase or two-phase), and also surface compactness
(micro, mini, macro, etc.) [43].
In this era, a very serious issue like energy depletion must be addressed sincerely.
Therefore, researchers are continuously thriving to produce energy-efficient systems.
The two most common ways of producing such a system are the integration of
lightweight materials and miniaturization or compactness. It was stated that miniaturization in manufacturing and electromechanical systems would be the economic
drivers shortly [44]. It was observed that heat exchangers with a high aspect ratio
significantly increase the heat transfer efficiency [45]. So, studies on the miniaturization of heat exchangers also gained a considerable thrust. In this regard, two groups
of researchers classified the heat exchangers according to the size. According to
Mehendale’s classification [46] the conventional channels have D h > 6 mm, compact
passages have 1 mm < D h ≤ 6 mm, meso-channels have 100 μm < D h ≤ 1 mm, and
the microchannels have 1 μm < D h ≤ 100 μm. Again as per the classification by
Kandlikar and Grande [47], the cooling channels can be identified as conventional
channel with D h > 3 mm, mini channel having 200 μm < D h ≤ 3 mm, micro-channel
having 10 μm < D h ≤ 200 μm, transitional-channel having 0.1 μm < D h ≤ 10 μm,
and molecular nanochannel D h ≤ 0.1 μm. The former classification was based merely
on the dimension of the heat exchanger channels, whereas the latter and the most
commonly used classification was done by taking the flow into consideration.
P. Sarkar et al.
mentioned in Sect. 2.2 that the wormhole defect is nothing but voids inside the weld
line that staggeringly deteriorates the weld quality, as well as strength. However,
utility of the said defect is discussed further.
In 2005, researcher showed that by reversing the material flow generally occurring
in FSW and by purposefully creating and utilizing the wormhole defect, an integral
and continuous tunnel or channel can be created inside a monolithic plate in a single
step [42]. This can be possible by selecting the process parameters and tool designs
that promote the generation of wormhole defect during FSW. The process was named
Friction Stir Channeling (FSC). It was identified that the channels created by FSC
have huge potential to be used in the heat exchanger applications.
4.4.1 Importance of Compact Heat Exchanger
The problem of heat generation and removal is present in a myriad of applications
and processes across the world necessitating the design and development of novel
heat dissipation and exchange devices. From aerospace to power plants, automotive
to space, power systems to consumer electronics, the importance of thermal management calls for innovative designs of heat sinks and heat exchangers and processes to
manufacture them. Heat Exchanger is a device that promotes heat flow between two
or more fluids having a difference in temperature, thus maintaining the temperature
in the desired range. Heat exchangers can be classified based on their geometry (tube,
plate, extended surfaces), based on transfer phenomenon (direct contact type or indirect contact type), flow arrangement types (parallel, counterflow, cross-flow, etc.),
heat transfer mechanisms (single-phase or two-phase), and also surface compactness
(micro, mini, macro, etc.) [43].
In this era, a very serious issue like energy depletion must be addressed sincerely.
Therefore, researchers are continuously thriving to produce energy-efficient systems.
The two most common ways of producing such a system are the integration of
lightweight materials and miniaturization or compactness. It was stated that miniaturization in manufacturing and electromechanical systems would be the economic
drivers shortly [44]. It was observed that heat exchangers with a high aspect ratio
significantly increase the heat transfer efficiency [45]. So, studies on the miniaturization of heat exchangers also gained a considerable thrust. In this regard, two groups
of researchers classified the heat exchangers according to the size. According to
Mehendale’s classification [46] the conventional channels have D h > 6 mm, compact
passages have 1 mm < D h ≤ 6 mm, meso-channels have 100 μm < D h ≤ 1 mm, and
the microchannels have 1 μm < D h ≤ 100 μm. Again as per the classification by
Kandlikar and Grande [47], the cooling channels can be identified as conventional
channel with D h > 3 mm, mini channel having 200 μm < D h ≤ 3 mm, micro-channel
having 10 μm < D h ≤ 200 μm, transitional-channel having 0.1 μm < D h ≤ 10 μm,
and molecular nanochannel D h ≤ 0.1 μm. The former classification was based merely
on the dimension of the heat exchanger channels, whereas the latter and the most
commonly used classification was done by taking the flow into consideration.