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 inside the CPU cabinet. However, in the case of supercomputers, mainframe computers, and gaming cards, the requirement of heat
(a)
Mr. Gaurav Hedau || 279
dissipation is high which doesn’t get fulfilled by simple air cooling. One of the solutions to above problem is - heat dissipation through
  Fig. 1: Schematic diagram of (a) microchannel application for electronic chip cooling (b) flow pattern fluctuations during high heat dissipation
flow boiling in a microchannel heat exchanger. A microchannel heat exchanger consists of parallel channels having channel dimensions in microns (as seen in the Fig.
1[a]). The microchannel heat
exchanger provides high
heat dissipation capability
because of high surface area to
volume ratio provide compact,
lightweight heat exchanger.
During flow boiling, with
increase the vapor quantity,
different flow patterns appear
inside microchannels such as
bubbly, slug, annular (vapor
core at the centre with liquid
film at the wall of the channel)
as heat flux increases from low
to high. At high heat flux, the
vapor generation rate inside
the channel is very high such
that vapor moves in the upstream direction and temporarily cover the inlet of all parallel channel (as seen in the Fig. 1[b]). However, as the pump pushes cooling fluid continuously, as a result, the pump pressure overcomes
upstream flow pressure of vapor due to which fresh liquid completely fills the channel. These fluctuations in flow patterns result in fluctuations of temperature, pressure, mass
flux and induce mechanical vibrations which are harmful to an integrated circuit board.
Researchers came up with many techniques which include design modification and fluid property modification to abate these fluctuations at a high heat flux to enhance the efficiency and heat dissipation capacity of microchannel heat exchangers. At high heat flux in microchannel as vapor bubble generates, the vapor size increases and quickly confines between the small microchannel wall (width-wise)
and then it starts expanding in both upstream and downstream direction along the length. So, if we can reduce the upstream flow of vapor and able to flush the vapor out of the microchannel then the new fluid will wet the
(b)
   In the present time, processors accommodate around billions of transistors as compared to ‘Intel 4004’ processor with 2250 transistors back in the year 1971. This increase in transistor densities in the processor increases the speed of computations but on the other hand, it leads to a high rate of heat generation.
  




































































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