Can computer chips be air-conditioned?

During the hot months of summer, many people stay indoors in
order to avoid sweat and sunburns, enjoying the cool comforts
of an air-conditioned apartment or house instead. While
a room without any cooling system would feel stuffy and
uncomfortable, air conditioners provide us with comfortable,
70-degree temperatures.

The air conditioner in your living space works just like the
refrigerator in your kitchen -- it uses similar liquids,
gases and cooling systems to create cooler temperatures.
Instead of simply circulating air around like a fan, both
technologies work by actually removing heat from a specified
area. A compressor compresses the cool gas known as
a refrigerant, causing it to become hot. The hot gas runs
through a set of hot coils and condenses into a liquid until
it reaches an expansion valve. The valve turns the liquid
back into a cool gas by evaporating it; the gas then runs
through another set of coils. This second set of cooled
coils, facing the area that needs to be air-conditioned,
absorbs any warm air to cool down an apartment -- or
refrigerator.

The big difference, of course, is that the cooling system in
your refrigerator is a small, enclosed box. Once closed, the
door traps cool air inside to keep food and drinks fresh for
long periods of time. An apartment's air conditioner, on the
other hand, is responsible for cooling a much larger space.
The walls and doors of the apartment act like the refrigerator
door, keeping the cool air from escaping.

But what if engineers took the technology used in air
conditioners and applied it to a much smaller scale --
a micro scale, for instance? Scientists working at the Purdue
University of Mechanical Engineering, led by Professor Issam
Mudawar, are developing an experimental system that takes
cooling techniques from air-conditioning systems to cool down
small, hard-working computer chips.

How does an air-conditioned computer chip work, especially on
such a small scale? Will you soon find air-conditioning
systems in personal computers, or do computers even get hot
enough to require such an efficient technology? If not, what
kinds of computer chips actually need to be air-conditioned?

CPU Cooling: Microchannels and Microjets

Will we all carry air-conditioned laptops around with us in
the near future? It's highly unlikely; not only would it make
computers several times more expensive, but it would be
an entirely unnecessary addition. Microprocessors in our
personal computers generate a good amount of heat -- if you've
ever worked with a laptop poised on your thighs for a long
period of time, chances are after a while you noticed the
bottom of the machine is warm to the touch.

Personal computers never generate more than 100 watts of heat
for every half-inch square of microprocessor. That's why
internal fans (the whirring sound you hear while your
computer's on) and clever uses of space and materials are
sufficient enough to keep a desktop or a laptop from
suffering a meltdown.

The devices the team at Purdue University hopes to cool down
aren't our measly personal computers. Instead, the
air-conditioning research is directed at high-flux thermal
management, the heating problems associated with more complex
computing systems used for weapons systems and defense
devices such as radar, directed-energy laser and microwave
weapons and aviation electronics.

As the microprocessors for these systems become significantly
smaller and more powerful, the heat generated also increases
dramatically -- experts expect heat fluxes from future
defense systems to reach more than 1,000 watts per half inch,
or 10 times the amount of heat produced from a powerful home
computer [source: Callahan]. Not only is this a big waste of
electricity, but a meltdown from such a system could damage
expensive equipment and potentially cause a great deal of
harm to the people operating it.

The new air-conditioned chip cooling system would attempt to
reduce temperatures to no greater than 257 degrees Fahrenheit
by combining two prominent cooling technologies:
Microchannels and microjets (or jet impingement). The
surfaces of computer chips would be cut with microchannels,
which are simply very small grooves about three millimeters
deep, and covered with metal plates punched with microjets,
or tiny holes. The system would pump hydrofluorocarbons
(HFCs), the same liquid used in conventional air
conditioners, through the microjets and into the
microchannels. The HFCs would vaporize inside the grooves,
cooling the chips, and cycle around via a small loop.

The school has received $500,000 from the Office of Naval
Research, and although the concept is still in the
experimental stages, the Purdue scientists hope to team up
with defense contractors in the near future to further
develop the technology.