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FLORIDA STATE UNIVERSITY / FAMU-FSU
COLLEGE OF ENGINEERING
FINAL DESIGN
Unmodified Design
The overall dimensions of
clothes dryers include the height being 3 feet, the width 29 inches and the
depth is about 25.5 inches. The tumbler diameter is 26.25 inches, and door in
the front is 18.75 by 14.75 inches. The intake inside the dryer permitting
entrance of the heated air is 6.5 inches long and at its widest point 4.5
inches. The exhaust being unlike the intake is 9 inches long and 5 inches wide
at the widest point.
When viewed from behind,
the original dryer design has the heater box located on the right. The heater
box is about 6 inches wide and 22.75 inches long. However, the coils that
actually heat up only go up the housing of the heater about 9 inches. The
exhaust is running from top to bottom on the left hand side. It is about 29
inches long and 7 inches wide. This area makes up the portion of the dryer that
has the lint trap in it. This leaves a large area between the two to implement
our heat exchanger. The area that we are left with is about 9.5 inches wide and
21.5 inches long.
The ambient air (22-25°C) is pulled into the heater and is heated. The air
leaves the heater at about 160°C.
The air is then pulled through the tumbler by a fan located at the exhaust
where it pulls moisture from the wet clothes. This air is now humid and comes
out of the exhaust at about 50-60°C.
Our design is intended to pull energy from this hot, humid air to preheat the
room air before it enters the heater. By doing this it is expected that the
heater will be on less, which is the component that uses a majority of the
energy required to run the dryer. The heater turns on intermittently in order
to maintain the proper temperature in the tumbler. When it is on it is on full
power. The energy savings will then be in the amount of time the heater is on.
Modified
Design
The principle of our
design is the inclusion of a counter-flow heat exchange unit, fitting in
between the exhaust and the intake. The heat exchanger is only about 4 inches
in diameter and 20 inches long so there is plenty of room according to the
measurements done. Figure 17 
shows
the unit in place in the back of the clothes dryer. The unit includes six
1-inch pipes that are contained within an outer tube. However, Figure 17 only
shows one tube on the inside. The six inner pipes carry ambient air through to
the heater, receiving energy in the form of heat from the exhaust air flowing
through the outer tube. The pipes converge at either end be pulled through from
the room to the heater. The intake was to be preheated to 43°C from the original 22-25°C. All pieces are completely sealed and insulated so
as to maximize heat transfer in the system. The heat exchange unit, in our
prototype, is completely removable for easy testing and adjustments. The pipe
material is not important, as the coefficient of thermal conductivity is not a
factor with such thin-walled pipes, so aluminum was used.
FAMU-FSU